c© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim10.1002/14356007.a03 245

Azo Dyes 1

Azo Dyes

Klaus Hunger, Hoechst Aktiengesellschaft, Frankfurt/Main, Federal Republic of Germany (Chaps. 1 – 4,6 – 10)

Peter Mischke, Hoechst Aktiengesellschaft, Frankfurt/Main, Federal Republic of Germany (Chaps. 1 – 4,6 – 10)

Wolfgang Rieper, Hoechst Aktiengesellschaft, Frankfurt/Main, Federal Republic of Germany (Chaps. 1 – 4,6 – 10)

Roderich Raue, Bayer AG, Leverkusen, Federal Republic of Germany (Chap. 5)

Klaus Kunde, Bayer AG, Leverkusen, Federal Republic of Germany (Chap. 5)

Aloys Engel, DyStar Textilfarben GmbH & Co. Deutschland KG, Leverkusen, Federal Republic of Germany(Chap. 5)

1. Introduction . . . . . . . . . . . . . . 22. Production . . . . . . . . . . . . . . . 32.1. Diazotization and Coupling . . . . 42.1.1. Diazotization . . . . . . . . . . . . . . 42.1.2. Coupling . . . . . . . . . . . . . . . . . 72.2. Other Azo Group Syntheses . . . . 112.2.1. Condensation of Nitro Compounds

with Amines . . . . . . . . . . . . . . 112.2.2. Reduction of Nitro Compounds . . 122.2.3. Oxidation of Amino Compounds . . 132.3. Synthesis from Azo Compounds . 132.3.1. Exposure of Concealed or Protected

Amino Groups . . . . . . . . . . . . . 132.3.2. Acylation of Amino Azo Com-

pounds . . . . . . . . . . . . . . . . . . 142.3.3. Alkylation and Acylation of Pheno-

lic Hydroxyl Groups . . . . . . . . . 142.3.4. Metal-Complex Formation . . . . . . 152.4. Processes without Industrial Im-

portance . . . . . . . . . . . . . . . . . 152.4.1. Reduction of

Diazonium Compounds . . . . . . . 162.4.2. Oxidative Coupling . . . . . . . . . . 162.4.3. Dehydrogenation

of Diarylhydrazines . . . . . . . . . . 172.4.4. Reaction of Arylhydrazines with

Quinones . . . . . . . . . . . . . . . . 172.4.5. Condensation of Nitroso

Compounds with Amines . . . . . . 182.4.6. Azo Compounds from Azido Com-

pounds . . . . . . . . . . . . . . . . . . 182.5. Equipment for Industrial Produc-

tion of Azo Dyes . . . . . . . . . . . . 193. Anionic Azo Dyes . . . . . . . . . . . 203.1. Introduction . . . . . . . . . . . . . . 203.2. Acid Azo Dyes . . . . . . . . . . . . . 203.2.1. Wool Dyes . . . . . . . . . . . . . . . . 21

3.2.1.1. Monoazo Dyes . . . . . . . . . . . . . 223.2.1.2. Disazo Dyes . . . . . . . . . . . . . . . 253.2.1.3. Chrome Dyes . . . . . . . . . . . . . . 283.2.1.4. Metal-Complex Dyes . . . . . . . . . 303.2.2. Polyamide Dyes . . . . . . . . . . . . 313.2.3. Silk Dyes . . . . . . . . . . . . . . . . 333.2.4. Leather Dyes . . . . . . . . . . . . . . 343.2.5. Azo Food Dyes . . . . . . . . . . . . . 354. Direct (Substantive) Dyes . . . . . 374.1. Conventional Direct Dyes . . . . . 384.1.1. Monoazo Dyes . . . . . . . . . . . . . 384.1.2. Disazo Dyes . . . . . . . . . . . . . . . 404.1.2.1. Primary Disazo Dyes . . . . . . . . . 404.1.2.2. Secondary Disazo Dyes . . . . . . . 434.1.3. Trisazo Dyes . . . . . . . . . . . . . . 434.1.4. Tetrakisazo Dyes . . . . . . . . . . . . 444.1.5. Condensation Dyes . . . . . . . . . . 454.1.6. Direct Dyes with a Urea Bridge . . 464.1.7. Triazinyl Dyes . . . . . . . . . . . . . 464.1.8. Copper Complexes of Substantive

Azo Dyes . . . . . . . . . . . . . . . . 484.2. Direct Dyes with Aftertreatment . 484.2.1. Aftertreatment with Cationic Auxil-

iaries . . . . . . . . . . . . . . . . . . . 494.2.2. Aftertreatment with Formaldehyde 504.2.3. Diazotization Dyes . . . . . . . . . . 504.2.4. Aftertreatment with Metal Salts . . 505. Cationic Azo Dyes . . . . . . . . . . 515.1. Cationic Charge at the Coupling

Component . . . . . . . . . . . . . . . 525.1.1. Polyamines as Coupling Compo-

nents . . . . . . . . . . . . . . . . . . . 525.1.2. Heterocycles as Coupling Compo-

nents . . . . . . . . . . . . . . . . . . . 535.1.3. Coupling Components with

Alkylammonium Groups . . . . . . . 54

2 Azo Dyes

5.1.3.1. Coupling Components withDialkylaminoalkyl Groups . . . . . . 54

5.1.3.2. Aromatically LinkedTrialkylammo-nium Groups . . . . . . . . . . . . . . 54

5.1.3.3. Trialkylammoniumalkyl-SubstitutedAnilines . . . . . . . . . . . . . . . . . 55

5.1.3.4. Other Trialkylammoniumalkyl-Substituted Coupling Components . 56

5.1.4. Coupling Components with Dialkyl-hydrazinium Groups . . . . . . . . . 57

5.1.5. Coupling Components with CyclicAmmonium Groups . . . . . . . . . . 57

5.1.5.1. Heterocyclically Linked Cyclic Am-monium Groups . . . . . . . . . . . . 57

5.1.5.2. Aliphatically Linked Cyclic Ammo-nium Groups . . . . . . . . . . . . . . 58

5.1.6. Coupling Components with Con-densed Cyclic Ammonium Residues 59

5.1.7. Cyclic Ammonium Residues at theAzo Group . . . . . . . . . . . . . . . 59

5.1.8. Coupling Components with twoDif-ferent Cationic Residues . . . . . . . 59

5.2. Cationic Charge in the DiazoComponent . . . . . . . . . . . . . . . 61

5.2.1. DiazoComponentswithAminoalkylMoieties . . . . . . . . . . . . . . . . . 61

5.2.2. DiazoComponentswith Trialkylam-monium Residues . . . . . . . . . . . 61

5.2.2.1. Aromatically LinkedTrialkylammo-nium Residues . . . . . . . . . . . . . 62

5.2.2.2. Aliphatically Linked Trialkylammo-nium Residues . . . . . . . . . . . . . 62

5.2.3. Diazo Components with Cyclic Am-monium Residues . . . . . . . . . . . 64

5.2.3.1. Aromatically Linked Cyclic Ammo-nium Residues . . . . . . . . . . . . . 64

5.2.3.2. Aliphatically Linked Cyclic Ammo-nium Residues . . . . . . . . . . . . . 64

5.2.4. Diazo Components with two Differ-ent Cationic Residues . . . . . . . . . 64

5.2.5. Diazo Components with AromaticCondensed Cyclic AmmoniumResidues . . . . . . . . . . . . . . . . . 65

5.2.6. Cyclic Ammonium CompoundsLinked in Meta Position to the AzoGroup . . . . . . . . . . . . . . . . . . . 66

5.3. Different Cationic Charges inBoth the Coupling and the DiazoComponent . . . . . . . . . . . . . . . 66

5.4. Introduction of Cationic Sub-stituents into Preformed Azo Dyes 66

5.5. Cationic Dyes with Sulfur orPhosphorus as Charge-CarryingAtoms . . . . . . . . . . . . . . . . . . 68

5.6. Dyes with Releasable CationicGroups . . . . . . . . . . . . . . . . . 68

6. Developing Dyes . . . . . . . . . . . 696.1. Developing Dyes for Cotton . . . . 706.1.1. Developing Dyes for Dyeing . . . . 706.1.1.1. β-Naphthol Dyes . . . . . . . . . . . 706.1.1.2. Naphtol AS Dyes . . . . . . . . . . . 706.1.2. Developing Dyes for Printing . . . . 776.2. Developing Dyes for Animal

Fibers . . . . . . . . . . . . . . . . . . 856.3. Developing Dyes for Hydrophobic

Fibers . . . . . . . . . . . . . . . . . . 857. Disperse Azo Dyes . . . . . . . . . . 868. Azo Pigments . . . . . . . . . . . . . 869. Alcohol- and Ester-Soluble Dyes . 8610. Fat- and Oil-Soluble Dyes . . . . . 8711. References . . . . . . . . . . . . . . . 89

1. Introduction [1–6]

Azo dyes are characterized by a chromophoricazo group −N=N−, whose nitrogen atoms arelinked respectively to sp2-hybridized carbonatoms. At least one of these carbon atoms be-longs to an aromatic carbocycle (usually a ben-zene or naphthalene derivative) or heterocycle(e.g., pyrazolone, thiazole), whereas the secondcarbon atom adjoining the azo group may alsobe part of an enolizable aliphatic derivative (e.g.,acetoacetic acid). The most common types ofazo dyes can thus be summarized as follows:aryl−N=N−R, where R can be an aryl, het-eroaryl, or −CH=C(OH)−alkyl.

Due to the simple nature of the synthesis, usu-ally in aqueous medium, and the almost unlim-ited choice of starting products, an extremelywide variety of azo dyes is possible. The num-ber of combinations is further increased by thefact that a dye molecule can contain several azogroups.

This diversity of inexpensively produced azodyes permits a wide spectrum of shades and fast-ness properties suitable for use on a variety ofsubstrates.

Naturally occurring azo dyes are unknown(some containing azoxy groups are known), butthe azo dyes represent the most numerous andwidely manufactured synthetic dyes.

Azo Dyes 3

Nomenclature. Depending on the number ofazo groups, the azo dyes are called monoazo,disazo, trisazo, tetrakisazo, etc., dyes, and thosewith three or more azo groups, polyazo dyes.

The structure of an azo dye can be describedby means of a structural formula (a), IUPACnomenclature (b), or practical nomenclature (c),e.g.:

a)

b) 1-hydroxy-2-phenylazo-7-(4′-nitrophenylazo)-8-aminonaphthalene-3,6-disulfonic acid

c) general formulation: D –1 → K ←2– D, inwords: p-nitroaniline –1 →H acid←2– ani-line and in reaction equations:

Designation (b) is less commonly used be-cause of its complexity. The practical nomen-clature (c) makes use of a genetic scheme ofthe technically most common synthesis, i.e., itcharacterizes the azo dye by the starting com-pounds (D= diazo component and K= couplingcomponent) and the direction of coupling. Thisnomenclature is shorter and is commonly usedin industry and technical literature. In the case ofdisazo and polyazo dyes, the coupling directionis specified by arrows, the sequence of opera-tions by appropriate numbers above the arrows,and the coupling conditions by the abbrevia-tions a (acid) and alk (alkaline). Additional ar-rows at the coupling components show the link-age points of both components across the azogroups. All industrially important dyes are alsoclassified according to theColour Index [7]. Thiscatalog of dyes gives information about tradenames, coloristic properties, and, if published,the chemical constitution. The dyes are classi-fied according to color and chemical properties.Aside from its trade names, the azo dye in for-mula 1, for example, can be found as C. I. AcidBlack 1 or C. I. 20470.

Dyes listed as examples in the following sec-tions are cited according to the internationallyused designations in the Colour Index. Tradenames are compiled in tabular form only forthe individual dye classes; historical commonnames are for the most part included in the text.

Classification. Azo dyes can be classified ei-ther according to chemical guidelines (charac-teristic chemical groups) or by color aspects (ap-plication in dye works). A rigid assignment toone of the two classification systems is possible,but not advisable because of overlapping. Thereis therefore scarcely a chemical class of azo dyesthat belongs to a single color class or vice versa.Moreover,manymaterials can be dyedwith dyesfrom various color groups. In this article, a com-promise between the two classification systemswith emphasis on application in the dye worksseemed to be the most appropriate.

The importance of the azo dyes is due to theirmode of application and to the fact that theyrepresent a clearly defined concept. They arebriefly described here and dealtwithmore exten-sively under special headings:→DisperseDyes;→Metal-ComplexDyes;→Pigments, Organic;→Reactive Dyes.

2. Production

For additional information see [1–6] and [8–12].The processes that are important in the pro-

duction of azo dyes are classified as follows:Processes involving synthesis of the azo

group:

– diazotization and coupling– condensation of nitro compounds withamines

– reduction of nitro compounds– oxidation of amino compounds

Syntheses with compounds already contain-ing the azo group:

– exposure of concealed or protected aminogroups

– acylation of aminoazo compounds– alkylation and acylation of phenolic hy-droxyl groups

– metal-complex formation

4 Azo Dyes

2.1. Diazotization and Coupling

Of all the industrially important processes azocoupling, during which the azo group is synthe-sized, is by far the most important. All other in-dustrially employed processes are advantageousonly where azo coupling cannot be utilized, forexample, because of the unavailability of thestarting compounds.

Azo coupling can be summarized as follows:an aromatic amine is linked to a nucleophilicpartner RH (coupling component) in the pres-ence of a nitrosyl-eliminating compound XNOto form an aromatic azo compound. The reactionequation is as follows:

Equation (1) describes the overall azo cou-pling reaction, which consists of two majorsteps: formation of the diazonium compound bymeans of the so-called diazotization and synthe-sis of the azo dye, the actual azo coupling.

2.1.1. Diazotization

Diazotization is defined as the reaction of pri-mary aromatic amines with nitrites, preferablywith sodium nitrite, in a usually aqueous min-eral acid solution at around 0 ◦C, whereby theamine is converted into the corresponding dia-zonium salt:

Weakly basic amines require a higher acidconcentration, since diazoamino compoundsAr−N=N−HN−Ar may otherwise form. Veryweakly basic amines, i.e., amines with severalnegative (−I/−M) substituents (e.g., tetrahalo-gen anilines, di- and trinitroanilines, halogen-nitroanilines) can only be diazotized after be-ing dissolved in concentrated sulfuric acid andsubsequently reacted with nitrosylsulfuric acid,HSO4NO.

A further reason for using concentrated acids(concentrated sulfuric acid) is the fact that dia-zonium salts of weakly basic amines are readilyhydrolyzable in dilute acids.

Diazotization of aromatic diamines givesbisdiazonium compounds and therefore iscalled bisdiazotization. The incorrect term“ tetrazotization ” is frequently found in the tech-nical literature.

The essential step in diazotization is the elec-trophilic nitrosation of the amino group of theprimary aromatic amine (2).

Formation of the diazonium ion (4) then fol-lows via the diazohydroxide (3):

Reaction sequence (3) is a simplification; infact, the reaction rate during diazotization isdetermined by the formation of the nitrosatingagent (at low acidity) or nitrosation of the amine(at high acidity). In a strongly acid medium, i.e.,in the absence of free amines, the protonatedamine surprisingly becomes the nucleophile:

The equilibrium reactions preceding nitro-sation require excess acid during diazotizationleading to the formation of the nitrosating agent:

N2O3 is the nitrosating agent in a weaklyacid medium (Eq. 5), H2ONO in a more acidmedium (Eq. 6), and the nitrosonium ion NO+

in a strongly acid medium (Eq. 7).An excess of sodium nitrite must be avoided,

since nitrite can react with the coupling agent aswell aswith secondary or tertiary amines to formnitroso compounds during subsequent coupling.Excess nitrite can be detected with potassium

Azo Dyes 5

iodide–starch paper. It is eliminated by addingamidosulfuric acid or urea:

Diazo Components. Diazo components forthe production of azo dyes can be divided intothe following groups of aromatic amines:

Aniline and Substituted Anilines. Methyl,chlorine, nitro, methoxy, ethoxy, phenoxy, hy-droxyl, carboxy, carbalkoxy, carbonamide, andsulfonic acid groups are primarily used as sub-stituents.

Examples: Toluidines, nitroanilines, ami-nobenzoyl amides, and the sulfonic acids ofthese compounds.

Naphthylamines and Naphthylamine Sul-fonic Acids. The following compounds, knownby their common names, are examples of naph-thylamine sulfonic acids:

Many of these compounds can also be usedas coupling components (see Section 2.1.2), asshown by the arrow indicating the coupling po-sition.

Diamines H2N−A−NH2. The diamines canbe divided into four groups:

a) A = phenylene or naphthylene radical, alsosubstituted, e.g., by methyl, chlorine, nitro,methoxy, or sulfonic acid groups. Examplesare:

b) A= diphenyl radical, also substituted,mainly by methyl, chlorine, methoxy, car-boxylic acid, or sulfonic acid groups. Exam-ples are:

c)

whereby the aromatic rings can also besubstituted by methyl, chlorine, methoxy,carboxylic acid, or sulfonic acid groups.B = oxygen, sulfur, −NH−, −SO2−,−N=N−, −CH=CH−, −NHCO−,−NH−CO−HN−. Examples are:

6 Azo Dyes

d) Heterocyclic amines and diamines. Exam-ples are:

Diazotizing Methods. Considering the ba-sicity and solubility of the amines being diazo-tized, the following diazotization methods findindustrial use (for further details→Diazo Com-pounds):

a) Direct Diazotization. The primary aromaticamine is dissolved or suspended in aque-ous hydrochloric or sulfuric acid to whichan aqueous, concentrated sodium nitrite so-lution is added. An excess of 2.5 to 3 equiva-lents of acid per equivalent of amine is used.A temperature of 0 to 5 ◦C is maintained byadding ice.

b) Indirect Diazotization.Amineswith sulfonicor carboxylic acid groups are often diffi-cult to dissolve in diluted acid. Diazotizationtherefore takes place as follows: the amine isdissolved in water or weak alkalis, and thecalculated amount of sodium nitrite solutionis stirred into the ice-cooled acid solutionalready in the vessel. The acid can also beadded to the amine–nitrite mixture alreadyat hand.

c) Diazotization of Weakly Basic Amines.Weakly basic amines are dissolved in con-centrated sulfuric acid and diazotized withnitrosylsulfuric acid, which is easily pre-pared from solid sodium nitrite and concen-trated sulfuric acid.

d) Diazotization in Organic Solvents. Thewater-insoluble or only slightly solubleamine is dissolved in glacial acetic acid orother organic solvents and, where neces-sary, diluted with water. After the additionof acid it is diazotized in the usual mannerwith sodium nitrite solution. Nitrosylsulfu-ric acid, nitrosyl chloride, alkyl nitrites, ornitrous gases can also be used to eliminatethe nitrite. Temperature, pH, and the concen-tration of the diazotizing solution often havea considerable effect on the progress of dia-zotization. Physical properties (distribution,particle size) and the addition of emulsifiersand dispersing agents influence the diazoti-zation of slightly soluble amines.

Certain aromatic amines require special dia-zotizing processes:

1-Aminonaphthols, such as 1-amino-2-naphthol and several 1-aminonaphtholsulfonicacids, such as 1-amino-2-naphthol-4-sulfonicacid, are oxidized to the respective quinone bynitrous acid. Diazotization can however takeplace under normal conditions in the presenceof catalytic quantities of metal salts, such ascopper or zinc salts.

o-Diamines, such as 1,2-phenylenediamineor 1,8-naphthylenediamine, undergo cyclizationduring the normal diazotization process to formtriazoles:

The desired bisdiazotization with o-phenylenediamine, as well as with m- andp-phenylenediamine, is achieved in glacialacetic acid with nitrosylsulfuric acid. 1,8-Naphthylenediamine can be bisdiazotized inexcess acid.

Under normal diazotization conditions, vari-ous ortho-substituted aromatic amines also un-dergo more or less complete cyclization to formbenzoheterocycles that are no longer accessibleto subsequent coupling.

Examples are:

Azo Dyes 7

Diazonium compounds are generally stableonly in aqueous solution at low temperatures.When heated, they frequently decompose byeliminating nitrogen to form the correspondingphenol. Some amines, however, can be diazo-tized at temperatures up to 40 ◦C. Light andheavy-metal ions also accelerate the decompo-sition of diazonium compounds. Diazotization,therefore, is usually carried out in wooden vatsor iron stirring vessels with an acid-proof liningor rubber coating (see Section 2.5).

As solidsmost diazoniumcompounds are sta-ble only to a degree and frequently sensitive toheat, impact, and shock (explosive) (→DiazoCompounds).

2.1.2. Coupling

Coupling Sequence. The actual azo cou-pling reaction consists of an electrophilic sub-stitution reaction of the diazonium compoundwith a nucleophilic partner (coupling compo-nent RH):

Ar−N+ ≡NY− +R−H−→Ar–N=N−R+HY (8)

Coupling components are aromatic systemswith nucleophilic centers at the aromatic nu-cleus, particularly phenols, naphthols, andamines or enolizable compounds with reactivemethylene groups. Phenols react as phenolates,naphthols as napththolates, and amines as freebases. According to Equation (8), free acid is

formed during the coupling reaction. In orderto maintain an optimal reaction sequence, thepH must be kept constant by adding alkalis orbuffers. Coupling under strongly alkaline con-ditions is not possible. According to Equation(3), the diazonium compound undergoes a re-verse reaction to form an anti-diazotate, whichcannot be coupled. Under strongly alkaline con-ditions and with amines as coupling agents,the diazonium component may react with theamine nitrogen to form the diazoamino com-poundR−N=N−HN−Ar. Phenols and enols aretherefore generally coupled in the weakly al-kaline range (pH 7 – 9), amines mainly in theweakly acid range (pH 4 – 7).

In the production of developing dyes for tex-tile printing the formation of diazoamino com-pounds is desired (see Section 6.1.2, →DiazoCompounds).

Substituents with donor effects in the aro-matic nucleus of the coupling components in-crease the reactivity. Conversely, donor sub-stituents on the lower the reactivity,whereas sub-stituents with acceptor effects increase it. Thecoupling energy of substituted anilines as diazocomponents decreases as follows:

polynitroanilines> nitrochloroanilines> ni-troanilines > chloroanilines > anilinesulfonicacids > aniline > anisidines > aminophenols.

The C-atom with the highest electron den-sity is usually the preferred coupling positionof a coupling component. Due to the directinginfluence of hydroxyl or amino groups in aro-matic systems, coupling takes place at the or-tho or para position. If these two positions areoccupied, there is either no coupling or one ofthe substituents is exchanged. Coupling neveroccurs at the meta position in relation to the di-recting substituent. Components of the naphtha-lene groups generally couple more easily thanbenzene derivatives.

Amines, which tend to form diazoaminocompounds, can easily be coupled at the paraposition if they have been reactedwith formalde-hyde and sodium hydrogen sulfite to form N-methylenesulfonate [13]:

8 Azo Dyes

p-Aminoazo dyes are obtained by splittingmethylenesulfonate from the coupling productsunder acid or alkaline conditions.

Other reaction conditions besides pH alsoplay an important role in azo coupling. Increasedtemperature generally has a greater effect on thedecomposition of the diazonium salt accordingto Equation (9)

R−N+ ≡NCl− +H2O−→ROH+N2 +HCl (9)

than on the rate of coupling. The advantages aretherefore limited. Coupling can be acceleratedby raising the pH and the concentration of thereactants. In some cases the yield of azo dye canbe increased by adding sodium chloride prior tothe azo coupling. Some azo dyes can only besatisfactorily manufactured by adding pyridineor pyridine homologues; examples are the cou-pling of diazotized aminoazo compounds andaminodisazo compounds, as well as o-amino-phenols for the production of complex formingdyes (→Metal-Complex Dyes).

Pyridine acts as proton acceptor in the elec-trophilic coupling reaction and is especially ben-eficial when bulky substituents are present at theortho or peri position in relation to the couplingposition of the intermediate product or when thediazonium ion (e.g., in the case of o-diazophe-nols) exhibits a slight electrophilic reactivity.

Coupling Components. The most impor-tant coupling components can be divided into thefollowing groups.Where there are several possi-bilities for coupling, the preferred coupling po-sitions are marked by bold arrows and the otherpossible coupling positions by ordinary arrows.

Anilines, Diaminobenzenes. Examples are:

When reacted with aniline, diazotized ani-line (benzenediazonium chloride) yields, apart

froma small quantity of 4-aminoazobenzene (5),diazoaminobenzene (6) as main product:

4-Aminoazobenzene (5) is obtained by cou-pling in a more strongly acid medium, but betterstill by heating diazoaminobenzene (6) in anilinewith addition of aniline hydrochloride.

Electron donor substituents in the aniline,such as methyl or methoxy groups, especiallyat the meta-position, promote the readiness tocouple; the inclination to couple thus increasesin the sequence aniline < o-toluidine<m-toluidine<m-anisidine< cresidine< 1-amino-2,5-dimethoxybenzene (aminohydroquinone di-methyl ether) to the extent that without forma-tion of the diazoamino compound, the last threebases are attached almost quantitatively in thedesired direction, i.e., at the 4-position in rela-tion to the amino group.

m-Phenylene diamines couple to formmonoazo dyes (chrysoidines, see Section 5.1.1)or disazo dyes.

Naphthylamines, NaphthylaminesulfonicAcids. Some examples are mentioned here;other compounds can be found among the di-azo components (see Section 2.1.1), becausemost naphthylaminesulfonic acids are capableof being employed both for diazotization andfor coupling purposes.

Whereas β-naphthylaminesulfonic acids al-ways couple at the adjacent α-position, withthe α-naphthylaminesulfonic acids, the cou-pling location is influenced by the position ofthe sulfonic acid group: 1,6-, 1,7-, and 1,8-naphthylaminesulfonic acids couple at the 4-

Azo Dyes 9

position; 1,5-naphthylaminesulfonic acid (Lau-rent acid) only couples with very “strong cou-plers” (e.g., 2,4-dinitroaniline), mainly at the4-position. With diazotized aniline, chloroani-line, or diazotized anilinesulfonic acids the 2-aminoazo dyes are obtained, but with diazotizednitroaniline, mixtures of the 2- and 4-couplingproducts form:

Phenols, Naphthols. Examples are:

Phenols mainly couple at the 4-position, orat the 2-position if the 4-position is occupied.p-Hydroxybenzoic acid couples with elimina-tion of CO2; resorcinol couples twice: initiallyat the 4-position, with a second equivalent dia-zonium compound at the 2-position under acidconditions or at the 6-position under alkalineconditions. α-Naphthols mainly couple at the 4-position, in addition to which varying quantitiesof 2- and 2,4-coupling products are obtained,depending on the diazo component. β-Naphtholcouples at the 1-position. Substituents in the1-position, such as −SO3H, −COOH, −Cl,−CH2OH, or −CH2N(alkyl)2, may be elimi-

nated during the coupling process. 1-Methyl-2-naphthol forms no azo dye.

Coupling components in this series that are ofparticular industrial importance are 2-hydroxy-naphthalene-3-carboxylic acid arylamides, inparticular anilides, which likewise couple at the1-position (see Section 6.1.1.2).

Phenols and naphthols generally couplemore easily and rapidly than amines; phenol-3-sulfonic acid can be coupled, but not aniline-3-sulfonic acid.

The readiness of the phenols to couple in-creases as the number of hydroxyl groups rises,as, for example, in the following series:

Naphtholsulfonic Acids. Examples are:

1-Naphtholsulfonic acids mainly couple atthe 2-position. The 4-coupling products ob-tained as byproducts have to be carefully re-moved from the azo dyes, because unlike the2-substitution products, their shade changes asa function of the pH value (shade intensificationwith rising pH due to formation of phenolate or

10 Azo Dyes

naphtholate resonance structures; see also Sec-tion 3.2.1).

Aminophenols, Aminophenolsulfonic Acids,Aminonaphtholsulfonic Acids. Examples are:

In an alkaline medium m-aminophenol cou-ples at the para position in relation to the hy-droxy group, in an acid solution p-hydroxy andp-aminoazo dyes are obtained side by side.

In the case of aminonaphtholsulfonic acids,orientation is greatly influenced by the pH valueof the coupling medium. For instance, in an acidmedium the azogroup enters into the positionor-tho to the amino group, in an alkaline medium,in the position ortho to the hydroxyl group. 1-Amino-8-naphtholsulfonic acids with free or-tho positions can couple with two equivalents ofdiazonium compound, coupling initially takingplace in the acidmediumat the o-aminoposition,followed by coupling in the alkaline range atthe o-hydroxy position. Aminonaphtholsulfonicacids (o-hydroxyazo dyes) initially coupled inan alkaline medium cannot normally undergofurther coupling to form disazo dyes:

However, if this initial coupling is followedby ametal-complexing process, further couplingis possible in the neutral or alkaline range.

Compounds with Reactive MethyleneGroups. In this series the coupling componentswith the greatest industrial importance are theN-acetoacetyl derivatives of aromatic amines(acetoacetic arylides):

CH3CO–CH2CO–NH–Ar

Anilines substituted by halogen, alkyl, alkoxy,nitro, and acylamino groups are the aromaticamines mainly suitable.

Example:

Bis(acetoacetylamino) derivatives, such asNaphtol AS–G, also enjoy practical importance.

The following coupling components are alsolisted:

Heterocyclic Components. The most impor-tant compounds in this range are the 5-pyrazolones substituted at the 3-position.

Further examples are:

Azo Dyes 11

Azo Coupling in Practice. The optimumcoupling conditions depend first of all on thenature of the diazo and coupling componentsused. The acid diazonium salt solution is gener-ally allowed to enter the solution of the couplingcomponent. Because, in addition to acid de-rived from the diazotization process, additionalacid is released during coupling, the optimumpH value must be adhered to by adding bases.Alkali hydroxides, sodium carbonate, sodiumhydrogen carbonate, ammonia, calcium carbon-ate, magnesium oxide etc., are used for thispurpose. Such substances as sodium acetate orformiate (weakly acid) or sodium phosphate(weakly alkaline) can also be added to bufferthe acid. These substances are added to the re-action mixture before, during, or after combin-ing the components. Because at the feed pointof the diazonium salt solution the pH value isalways different than after thorough mixing hasbeen completed, the type of stirrer and speedof stirring are also important in many instances.The sequence in which the two components arecombined can also greatly influence the result.

The coupling reaction may be completed im-mediately after the components are mixed orafter several hours. If the reaction requires alonger time, it is advisable to cool with ice andavoid exposure to dazzling light. In order tocheck whether excess diazonium compound isstill present, a drop of reaction solution is spot-ted onto filter paper together with a component

that couples easily (e.g., weakly alkaline H acidsolution). If no coloration appears, the couplingis completed. The presence of unconsumed cou-pling component can be determined by spottingwith a diazonium salt solution.

Attention must also be paid to the volume ofcoupling solution or suspension. With startingcomponents of low solubility, the physical stateis an important factor. In order to achieve com-plete reaction of diazo or coupling componentswith low solubility, it is often necessary to en-sure that the reactants are distributed as finelyas possible. This is carried out, for example, byadding dispersing agents to the diazo componentor to the coupling mixture or by adding emul-sifiers during acid precipitation of the couplingcomponent prior to azo coupling. In each case,the most favorable reaction conditions must beprecisely established and, because of the variousinfluences that result in undesirable side effects,they must be carefully adhered to during manu-facture.

See Section 2.5 for suitable apparatus.

2.2. Other Azo Group Syntheses (See alsoChap. 2.4)

2.2.1. Condensation of Nitro Compoundswith Amines [2, p. 339]

Aromatic azo and polyazo compounds can beproduced by condensation of nitro compoundswith amines in accordance with the followingequation:

R1–NO2 +H2N–R2 −→R1–N=N–R2 +H2O (+O)

Because part of the amine is oxidized to thesymmetrical azo compound R2−N=N−R2, anexcess of amine is expedient. In some conden-sation processes it has been possible to observethe partial formation of azoxy bridges. Reactiontakes place on heating the reactants for severalhours to 40 – 120 ◦C in aqueous sodium hydrox-ide solution.

Substituents in the aniline component withelectron-donor effects accelerate condensation;electron acceptors retard it. In the nitro compo-nent, the substituents have the opposite effect.

Of interest as regards the industrial manufac-ture of dye intermediates are condensation reac-tions of 4,4′-dinitrostilbene-2,2′-disulfonic acid

12 Azo Dyes

with aromatic amines. If specific sodium hy-droxide solution concentrations, temperatures,and reaction times are precisely observed, itis possible with 1,4-diamines, 4-aminophenols,and their sulfonic and carboxylic acids to pro-duce homogeneous monoazo and disazo dyes:

Of importance as regards the industrial pro-duction of the important direct cotton dyesfor orange, scarlet, and brown shades are con-densation reactions of 4,4′-dinitrostilbene-2,2′-disulfonic acid with aminoazo compounds (seeSection 4.1.5). For example, by heating this acidwith an equivalent of 4-aminoazobenzene-4′-sulfonic acid in aqueous sodium hydroxide so-lution, the disazo dye 8 is obtained:

Condensation with two equivalents of 4-ami-noazobenzene-4′-sulfonic acid at 105 ◦C in 5 %sodium hydroxide solution results in the corre-sponding tetrakisazo dye.

The dye synthesis is often followed by an ox-idative aftertreatment (with chlorine bleachingliquor) or a reductive aftertreatment in alkalinemedium (with sodium sulfide or glucose).

Instead of 4,4′-dinitrostilbene-2,2′disulfonicacid as starting product, use is frequently madeof 4-nitrotoluene-2-sulfonic acid, which on be-

ing heated with sodium hydroxide solution isconverted into dinitrodibenzyldisulfonic acidand dinitrostilbenesulfonic acid. All three nitrocompounds condense in the presence of alkali,bothwith amino compounds andwith eachother.A number of direct cotton dyes (e.g.,C. I. DirectYellow 21, 40045 [1325-46-8]) are the result ofcomplex condensation reactions of this type.

Simple azo compounds free of sulfonic acidgroups can be produced with yields of 40 – 84%by condensation of nitrobenzene with o- andp-anisidine, naphthylamines, and phenylenedi-amines without solvent in the presence of pow-dered sodium hydroxide at temperatures of130 – 190 ◦C [14].

Because these reactions can proceed veryvigorously, suitable precautionary measures arenecessary.

2.2.2. Reduction of Nitro Compounds [2,p. 346]

During the reduction of aromatic nitrocompounds, condensation of the nitro andhydroxylamino derivatives that occur as inter-mediate steps may result in the formation ofazoxy compounds, which in a further reductionstep can be converted into azo compounds:

The method is only suitable for the synthesisof symmetrical azo compounds, for when twodifferent nitro compounds are used, mixtures ofall possible combinations are formed:

Glucose has proved especially suitable as areducing agent for reductive linkage of aromaticnitro compounds, other reducing agents beingalcohols, hydrazine, zinc, iron, and numerousinorganic salts. Only the reduction process withglucose has attained industrial significance in thesynthesis of azo dyes, mainly for the linkage ofnitroazo compounds under mild conditions. The

Azo Dyes 13

process generally takes place in a strongly alka-line, aqueousmedium, less frequently in an alco-holic medium. For example, the red trisazo dyeC. I. Direct Red, 25015 [6391-13-5] is obtainedby coupling 2-methyl-5-nitroaniline to Nevile-Winther acid and subsequently treatingwith glu-cose and alkali:

Reduction by glucose often does not proceedquantitatively up to the azo stage; instead the azoand azoxy compounds aremostly formed side byside.Where necessary, therefore, subsequent re-duction of the azoxy compound to form the azodye must follow.

2.2.3. Oxidation of Amino Compounds [2,p. 371]

Reaction of primary aromatic amines with suit-able oxidizing agents results in symmetrical azocompounds, sometimes, by further oxidation ofthe azo stage, in the mixture with azoxy com-pounds:

Hypochlorites are especially suitable asoxidizing agents, others being peroxy com-pounds (hydrogen peroxide, sodium perbo-rate), oxygen or air in the presence of apyridine –Cu(I)chloride catalyst, and chromicacid.

The main industrial application for the ox-idative linkage of aromatic amines in the syn-thesis of azo dyes can be found in the thiazolerange. The yellow cotton dye C. I. Direct Yel-low 28, 19555 [10114-47-3], for example, is ob-tained by treating an aqueous solution of thesodium salt of the so-called dehydrothiotolui-dinesulfonic acid (9) with sodium hypochloritein an alkaline medium:

2.3. Synthesis from Azo Compounds

For specific technical purposes in the productionof azo dyes, further reactions are carried out onthe azo compound after introduction of the azobridge:

– exposure of concealed or protected aminogroups

– acylation of aminoazo compounds– alkylation and acylation of phenolic hy-droxyl groups

– metal-complex formation

2.3.1. Exposure of Concealed or ProtectedAmino Groups

The formation of an amino group in azo dyes isoften necessary for the reaction with acid chlo-rides, e.g., for the production of reactive dyes,or for further diazotization and coupling. Thisis possible by reduction of nitro groups or bysaponification of acylamino groups.

As the reduction of nitro groups must be car-ried out while maintaining the azo group, thenumber of suitable reducing agents is virtuallyrestricted to sodium sulfide. Processing is car-ried out, depending on the nitro compound, in anaqueous alkaline solution or suspension at tem-peratures between 20 ◦C and 90 ◦C. A 10 – 30%addition of alkali chloride has proved favorable,as a result of which most of the dye remainsundissolved. After reduction the water-solublesulfide oxidation products are separated, the dyeis dissolved, and the sulfur is separated. The ami-no azo dye can be further processed straightawayin this form.

The acylamino groups, such as formyl,acetyl, or oxalylamino groups can be saponifiedin an acid or alkalinemedium. As a rule 2 – 10%

14 Azo Dyes

sulfuric acid or 2 – 6 % sodium hydroxide solu-tion is used at temperatures up to the boilingpoint of the reaction mixtures.

2.3.2. Acylation of Amino Azo Compounds[2, p. 390]; [5, vol. VI, p. 1]

Acylation reactions of aromatic amino com-pounds are important both for the productionof reactive dyes, i.e., dyes that in the dyeingof textiles form a covalent bond with the fiber(→Reactive Dyes), and for the synthesis of di-rect dyes (see Section 4), i.e., dyes that, becauseof their pronounced affinity for cellulosic fibers(substantivity), are adsorbed directly onto thecotton fiber from an aqueous solution.

Acylation agents that contain at least tworeactive centers in the molecule and are capa-ble of selective reactions under certain condi-tions, e.g., cyanuric chloride and cyanuric fluo-ride (10), 2,3-dichloroquinoxaline-6-carboxylicacid chloride (11) and chlorotrifluoropyrimidine(12), are used for the synthesis of a relativelylarge number of reactive dyes.

The reactive dyes most widely used so farare the chlorotriazinyl dyes, which can be pro-duced on an industrial scale from dyes f©–NH2containing amino groups and cyanuric chloride,with cleavage of hydrogen chloride, in an aque-ous organic medium at 0 – 5 ◦C and at a pH-value of 6.5 – 7.0. They can be condensed withan aliphatic or aromatic amine or even with asecond dye f©–NH2 at 40 to 50 ◦C to form theless reactive monochlorotriazinyl dyes:

For the production of substantive dyes twoidentical or different aminoazo dyes are linkedtogether by means of cyanuric chloride. Thethird chlorine atom remains either in themolecule or, preferably, is condensed with am-monia or simple aromatic amines at tempera-tures of 80 – 100 ◦C. The reaction with cyanuricchloride not only enables the inner-molecularblend to be varied at will but also considerablyincreases substantivity.

Phosgene, which is introduced into the so-lution of the amino azo compound at 20 – 35 ◦Cand at a neutral pH, is used as a bifunctional acy-lation agent to link two amino azo compounds(see Section 4.1.6).

Numerous commercial dyes of a substan-tive nature have urea bridges of this kind, e.g.,the direct dye C. I. Direct Yellow 50, 29025[8004-79-3], which is produced from diazotized2-aminonaphthalene-4,8-disulfonic acid and m-toluidine by reaction of the azo dye with phos-gene:

2.3.3. Alkylation and Acylation of PhenolicHydroxyl Groups [2, p. 403]

Alkylation. Toovercome the poor alkali fast-ness of p-hydroxyazo dyes (see Section 3.2.1)the phenolic OH groups can be converted intoalkyl ether with such alkylation agents as dialkylsulfate, alkyl halides, epoxides, etc. Depend-ing on the water solubility of the p-hydroxyazodyes, processing is carried out inweakly alkalineaqueous solution or in organic solvents, such asdimethylformamide or ethylene glycol dimethylether, under alkylation conditions, such as areusual with aromatic hydroxy compounds. Thesynthesis of p-alkoxyazo compounds by heatinghydroxyazo compounds in an alcoholic mediumwith the addition of acid is of interest, e.g.:

Azo Dyes 15

The reaction represents the inversion of theacid-catalyzed hydrolysis of azoaryl ethers.

On a large industrial scale hydroxyazo com-pounds are mainly reacted with ethyl chloridein aqueous alkaline solution (sodium carbonate,sodium hydroxide) by heating for several hoursto temperatures of around 100 ◦C in a closedsystem.

Acylation. Here aryl sulfonation plays a par-ticularly important role. In order to convertthem into arylsulfonic acid esters, hydroxyazodyes are reacted with arylsulfonic acid chlo-rides, mainly p-toluenesulfonic acid chloride orbenzenesulfonic acid chloride in an aqueous al-kaline medium. The formation of arylsulfonicacid esters not only overcomes the poor alkalifastness of p-hydroxyazo dyes but, with wooldyes, also improves the fastness to washing andmilling and the neutral affinity.

2.3.4. Metal-Complex Formation

For more details →Metal-Complex Dyes and[15], [2, p. 434].

Azo dyes with certain structural groupingsare capable of forming metal-complex com-pounds. Here even the coupling component,such as salicylic acid, can form a complex:

Technically far more important than thesemetal complexes, most of which are producedon the fiber (see chrome dyes, Section 3.2.1.3),are those dyes whose metal complexes are pro-duced within the dye itself. Here the complex isalways formed with the participation of the azogroup. These dyes have complex-forming sub-stituents in the o,o′ position relative to the azobridge and are, for instance, capable of forming1 : 1metal complexes of the general formula 13.

The azo dye anion always acts as a divalentligand in threefold coordination. The remainingcoordination positions of themetal ions are filledby addition of further ligands with lone electronpairs (e.g., H2O,NH3, amines) or by another azodye anion (formation of 1 : 2 metal complexes).

Suitable complex-forming metals are in par-ticular the trivalent chrome and trivalent cobalt(coordination number 6) and also the divalentcopper and nickel (coordination number 4),whose complex dyes have great industrial im-portance.

One of the hydroxyl groups in the ortho posi-tion relative to the azo bridge can only be formedduring metallizing by cleavage of an o-methoxygroup. This demethylating metallizing processhas been introduced on an industrial scale be-cause of the wide variety of diazo componentsto choose from [15].

The addition of copper to the molecule in anoxidative process, in which a hydrogen atom inthe ortho position relative to the azo group isconverted into the appropriate hydroxyl groupby means of oxidizing agents, such as hydrogenperoxide, has acquired technical significance[16]:

Chrome-complex dyes are best used as dyesfor wool, polyamide, and leather and for col-oring paints and plastics; copper complexes areused as cotton and leather dyes and also as pig-ments; and chrome and cobalt complexes, asspirit-soluble dyes.

2.4. Processes without IndustrialImportance

Of the processes for producing azo dyes via syn-thesis of the azo group, the following are worthmentioning, although they have attained no in-dustrial importance so far:

– reduction of diazonium compounds– oxidative coupling– dehydrogenation of diarylhydrazines– reaction of arylhydrazines with quinones

16 Azo Dyes

– condensation of nitroso compounds withamines

– azo compounds from azido compounds

2.4.1. Reduction of Diazonium Compounds[2, p. 320, 323]

When aromatic diazonium compounds are re-acted with ammoniacal copper(I) salt solution,diarylazo compounds or diaryls are obtainedwith elimination of nitrogen

The course of the reaction depends on thetype of substitution on the aromatic nucleus:whereas electron-attracting substituents result indiaryl formation, diazonium salts in which thesubstituents on the nucleus are electron donorscan be converted to symmetrical azo compounds(Vorlander reaction) [17], [18]:

The action of sulfurous acid or its salts ondiazonium compounds of the naphthalene se-ries results in the formation of symmetrical azocompounds; the starting compounds may alsocontain electron-attracting substituents (Langereaction) [19], e.g.:

Studies by Suckfull and Dittmer haveshown that in this process the diazonium salt re-acts with the diazosulfonate formed from sulfiteand diazonium ion [20]:

Whereas in the Lange reaction (see Eq. 10)the two aryl radicals are identical, Suckfulland Dittmer were able to expand the reactionof diazonium salt and diazosulfonate for the syn-thesis of asymmetrical azo compounds and, withcertain restrictions, extend it to the azo series.The significance of the reaction lies in the ac-cess to azo compounds that are very difficult tosynthesize by conventional means, e.g.:

2.4.2. Oxidative Coupling

Of interest from the preparative and theoreticalaspects is the oxidative azo coupling process dis-covered by S.Hunig, throughwhichmany hete-rocyclic azo compounds have becomeaccessible[21].

A precondition of the reaction is the presenceof a heterocyclic hydrazone, which couples witharomatic amines, phenols, or compounds withactive methylene groups in the presence of de-hydrogenating agents to form the correspondingazo compounds, e.g.:

As regards the coupling components and thecoupling location, the reaction resembles the azocoupling process. As electrophilic component, adiazonium ion 14 is suggested, which is formedfrom the hydrazone component through the ac-tion of the dehydrogenating agent and reacts byelectrophilic substitutionwith the coupling com-ponent with the loss of two hydrogen atoms toform the azo compound.

Azo Dyes 17

In the case of phenols and α-naphthols, theattack in principle always takes place at the p-position. Only when the p-position is occupieddoes coupling occur at the o-position. The opti-mum phenylazo compound yield (approx. 90%)is attained at pH 9. The dehydrogenating agentsmainly used for this purpose are potassium hex-acyanoferrate(III), copper(II) sulfate, silver ni-trate, sodium hypochlorite, or lead(IV) oxide.

The optimum pH range for oxidative cou-pling with aromatic amines and enamines ispH 1 – 3, diluted hydrochloric acid or glacialacetic acid being preferred as reagents. Well-tried dehydrogenating agents for this purpose areiron(III) chloride, red lead, lead(IV) oxide, andlead(IV) acetate.

In order to obtain an optimum yield, reagentand oxidizing agent should in each case be care-fully matched to the coupling component used.Oxidative coupling has so far rarely been usedfor industrial production of azo dyes.

2.4.3. Dehydrogenation of Diarylhydrazines[2, p. 377]

N,N′-Diarylhydrazines can be dehydrogenatedto form azo compounds:

Oxidizing agents frequently used are sodiumhypochlorite or air in the alkaline, or iron(III)chloride or sodium dichromate in the acidmedium, as well as nitrous acid. The method ac-quires importance when the azo compounds tobe synthesized are not accessible by couplingor condensation reactions, or only with diffi-culty, and the relevant diarylhydrazines can beobtained by simple reactions, e.g.:

2.4.4. Reaction of Arylhydrazines withQuinones [2, p. 355]

Benzo- and naphthoquinones as well asquinones of some polycondensed aromatics re-act in an acid aqueous or aqueous alcoholicmedium or in acetic acid to form hydroxyazocompounds, tautomers of quinone hydrazones,e.g.:

The reaction proceeds along the lines ofthis condensation process only if the oxidizingpower of the quinone and the reduction poten-tial of the hydrazine are not at such a high levelthat formation of hydroquinone takes place via aredox reaction. Quinones with a high oxidationpotential (e.g., p-benzoquinone) can thus onlybe reacted with arylhydrazines (e.g., o- and p-nitrophenylhydrazine) and vice versa.

Of significance is the reaction of the quinoneswith arylhydrazines to form azo compounds,when the latter are difficult to obtain by azo cou-pling, e.g., 1-hydroxy-2-phenylazonaphthalene:

Insteadof quinones, it is possible to react theirmonoximes with arylhydrazines, e.g.:

The hydroxylaminoazo compounds formed(15) react with nitrous acid to form azo diazo-

18 Azo Dyes

niumcompounds (16), preliminary stages for thesynthesis of polyazo dyes.

Arylhydrazines can also be converted intoazo compounds by condensation with otherdioxo compounds, provided this possibility ispermitted by the keto-enolic tautomerism. Aninteresting example of this is the reaction ofdioxosuccinic acid with two equivalents ofphenylhydrazine-4-sulfonic acid, which with si-multaneous formation of the pyrazolone ring re-sults in tartrazine (C. I. Acid Yellow 23, 19140[1934-21-0]), the oldest dye in this class:

2.4.5. Condensation of Nitroso Compoundswith Amines [2, p. 332]

Azo and polyazo compounds can be producedby condensation of amines with nitroso com-pounds, very good yields being frequently ob-tained:

Depending on the substitution of the aro-matic rings, the reactions are carried out at roomtemperature or at temperatures of up to about100 ◦C. The reagent used is almost always aceticacid on its own or in mixtures with other or-ganic solvents. Other reagents, such as water oralcohols, cause a sharp decrease in yield. Theinfluence of substituents on the reaction rate isanalogous to that in nitro – amine condensation(see Section 2.2.1).

Whereas nitroso – amine condensation is notgenerally possible in the naphthalene range, itsuse in the benzene range mainly serves theproduction of asymmetrically substituted azocompounds and the formation of polyazo com-pounds. It has no industrial importance in theproduction of azo dyes.

2.4.6. Azo Compounds from AzidoCompounds

Compounds containing activemethylene groupsreact with organic azido compounds in the pres-ence of a base, with formal substitution of a di-azo group for two hydrogen atoms (diazo grouptransfer) [22]:

The resulting diazo compound (19) can becoupled with a second molecule of the methy-lene compound (18) to form a symmetrical azocompound (20):

p-Toluenesulfonic acid azide (17, R =CH3C6H4SO2−), readily obtainable from p-toluenesulfonic acid chloride, has, in particular,proved to be a suitable azido compound.

The method permits the synthesis of a num-ber of interesting heterocyclic azo compounds,e.g.:

So far, however, it has been of no industrialimportance.

Azo Dyes 19

2.5. Equipment for IndustrialProduction of Azo Dyes

Production of azo dyes on an industrial scale isstill carried out on a batchwise basis.

The main items of equipment for industrialdiazotization and coupling are the diazotizingvessel, the dissolving tank for dissolving thecoupling component, and the central couplingtankwith capacities between 25 and 80m3. Cou-pling batches of up to 8 kmol per batch can thusbe processed.

Figure 1 illustrates the flowdiagramandmainitems of equipment in a simple industrial azo dyesynthesis.

Figure 1. Equipment diagram for the production of an azodyea) Diazotizing tank; b) Dissolving tank; c) Clarifying press;d) Coupling vessel; e) Filter press; f) Drying and milling

In the simplest case, the solution of the cou-pling component is transferred to the couplingvessel after mechanical and adsorptive clarifica-tion by means of a clarifying press or a filter,and the diazonium salt solution, likewise afterclarification, is added slowly above or below thesurface of the coupling component solution. Thesolutions can also be added in the reverse se-quence or both at the same time from the dia-zotizing and dissolving tank. The constancy ofthe reaction temperature and of a narrow pHrange is a decisive factor as regards the cou-pling process and must be continuously moni-tored by means of suitable measuring devices.The coupling reaction can be followed in thecoupling tank or other vessels by other reactions,

such as saponification, esterification, acylation,or metal-complexing processes, which if neces-sary must be carried out under pressure and athigher temperatures.

Following the synthesis and any thermal af-tertreatment process that may be required, azodyes insoluble in water (e.g., pigments, dispersedyes) can be directly isolated by means of filterpresses or suction filters. For large-volume prod-ucts, preference is given to continuously operat-ing rotary filters.

Water-soluble azo dyes (e.g., reactive dyes,acid dyes, or direct dyes) must be precipitatedfrom the coupling solution (coupling liquor) bysalting out or changing the pH. If in addition tothe salt content other impurities in the dye arepermissible, the spray drying process is used forseparating water-soluble azo dyes from the re-action solution.

Depending on the requirements regardingcorrosion resistance and ability to withstandcompressive and thermal stress, the materialsused for industrial equipment are iron, stain-less steel, rubber-coated steel with or withoutan acid-proof lining, enameled steel, glass fiberreinforced synthetic resins, and wood.

In general, diazotizing, dissolving and cou-pling vessels are nowadays made from rubber-coated steel. The hard rubber lining can be ex-posed without damage to temperatures of up to100 ◦C; contact with organic solvents should beavoided. Use has also been made of couplingtanks made from glass fiber reinforced syntheticresins (low weight, low cost, easy to repair),which are resistant to hydrochloric acid and canbe exposed to temperatures of up to 100 ◦C.Wooden vats are still of importance in the in-dustrial manufacture of azo dyes, primarily be-cause of their corrosion resistance in aqueoussystems, combined with low capital expendi-ture and repair costs. For reactions in an alka-line medium and in organic solvents, as wellas for reactions under pressure, stainless steeltanks are employed. Stainless steel tanks andother items of equipment made from this mate-rial are not resistant to corrosion bymineral acidsolutions. Stainless steel must also be avoidedfor reactions of weakly acid or salt-containingsolutions carried out under pressure. Enameledequipment is used for reactions in acid mediaperformed under pressure, but is not resistant toalkalis. Its advantage lies in its easy cleaning.

20 Azo Dyes

For reactions under pressure in an acid medium,rubber-coated and brick-lined steel tanks withagitators, heating coils, and thermometer tubesmade fromHastelloy (nickel alloys with varyingMo,Cr,Mn,Cu, Si, Fe, andCcontents) have alsoproved suitable. Brick-lined vessels are chieflyemployed in large-capacity equipment,when theuse of enameled vessels is dispensed with be-cause of the high capital expenditure and repaircosts involved.

In the industrial production of azo dyes inequipment that cannot be placed under pres-sure (wooden vats, drums made from syntheticresins), pumps are needed in order to convey thetank contents from vessel to vessel or via clarify-ing presses and filter presses. When steel drumsare used, the solutions and suspensions are oftentransferred by air or nitrogen pressure.

3. Anionic Azo Dyes [1], [3], [4], [7], [5,vol. I, p. 480; vol. III, p. 268]

3.1. Introduction

Anionic dyes include many compounds fromthe most varied classes of dyes, which ex-hibit characteristic differences in structure (e.g.,azoic, anthraquinone, triphenylmethane, and ni-tro dyes) but possess as a common featurewater-solubilizing, ionic substituents. The an-ionic azoic dyes, which are discussed here, con-stitute the most widely used group of this classof dyes.

Most often sulfonic acid groups serve as hy-drophilic substituents, because they are read-ily introduced and, as strong electrolytes, arecompletely dissociated in the acidity range usedin the dyeing process. Almost invariably theproducts manufactured and employed are water-soluble sodium salts of the sulfonic acids.

Direct Dyes. In principle the anionic dyesalso include direct dyes, but the latter, becauseof their characteristic structures, are used to dyecellulose-containing materials and go onto thefiber from a neutral dye bath. Because the clas-sification used here is based chiefly on the dyes’application in the dyehouse, direct dyes are dis-cussed in a separate chapter (see Chap. 4).

Reactive Dyes. From the chemical stand-point the group of anionic azo dyes includesa large proportion of the reactive dyes which,in addition to the usual structural characteris-tics, also contain certain reactive groups capa-ble of reaction with functional groups of thefiber during the dyeing process, for example,with the hydroxyl groups of cellulose, the ami-no and mercapto groups of wool and silk, orthe amino and carbonamide groups of syntheticpolyamides. Owing to the covalent dye – fiberbond these dyeings usually exhibit good fastnessto wet processing.

For structures of reactive dyes for wool andpolyamide→Reactive Dyes.

Metal-Complex Dyes. The anionic azo dyesalso including the metal-complex dyes, whichare derived from o,o′-disubstituted azo dyes andwhich can bemetallized not only on the fiber butwhose metal-complex compounds are appliedlargely in the form of a complete dye (cf. Sec-tion 2.3.4). They serve for the dyeing of wool(see Section 3.2.1.4), silk and leather (Section3.2.4) and polyamide (see Section 3.2.2), andalso for cotton (seeSection 4.1.8) and as alcohol-and ester-soluble dyes (see Section 6.1.2). Thisdye class, too, is discussed only briefly here; fordetails→Metal-Complex Dyes.

3.2. Acid Azo Dyes

This group of substances also includes dyesthat are classified under other headings,→Anthraquinone Dyes and Intermediates,→Nitro and Nitroso Dyes; →Triarylmethaneand Diarylmethane Dyes.

Azo dyes with relatively low molecularmasses and one to three sulfonic acid groupsserve as so-called acid azo dyes for dyeingand printing wool, polyamide, silk, and basic-modified acrylics and for dyeing leather, fur, pa-per, and food. The main area of application isthe dyeing of wool and polyamide.

Individual dyes also play a part in the manu-facture of color lakes, which are used to pigmentprinting inks and for coloring plastics.

Disazo and polyazo dyes containing sulfonicacid groups are also frequently used in the aboveapplications. Many of them are also sold as sub-stantive dyes for cotton because of their pro-

Azo Dyes 21

nounced affinity toward cellulosic fibers (seeChap. 4).

The term “acid dye” derives from the dyeingprocess, which is carried out in an acidic aque-ous solution (pH 2 – 6).

Protein fibers contain amino and carboxylgroups, which in the isoelectric range (approx-imately pH 5) are ionized mostly to –NH+

3and −COO−. In the acid dyebath the carboxylions are converted to undissociated carboxylgroups owing to the addition of acid HX (sulfu-ric or formic acid), which causes the positivelychargedwool (H3N+−W−COOH) to take up anequivalent amount of acid anions X− (hydrogensulfate, formate) [23]:

The actual dyeing process consists of a re-placement of the absorbed acid anions X− bythe added dye anions f©−, since the latter ex-hibit a much greater affinity for the substratethan the much smaller acid anions. Thus the dyeis bonded to the wool not only by electrostaticattraction (salt formation) but also by its moreor less strong affinity for the fiber.

Acid dyes are divided into three groups basedon their differences in affinity,which is primarilya function of the molecular size.

1) Leveling dyes are relatively small moleculeswhich form a saltlike bond with the proteinfiber. This not very tight bond imparts goodmigration properties to such dyes on wool.The interplay between the bonded dye andthe dye still in the dyebath results in veryuniform, level dyeings. On the other handthey possess only poor wetfastness, so thatthe use of leveling dyes is severely limited.

2) Milling dyes are large-volume dyemolecules, for which salt formation withthe fiber plays only a secondary role and theadsorption forces between the hydrophobicregions of the dye molecule and those ofthe protein fiber predominate. The resultingtighter bond yields good wetfastness, butthe levelness of the dyeings is not always

satisfactory because of an inadequate migra-tion property. In consequence the range ofapplications of milling dyes is also limited.

3) Dyes with intermediate molecular size notonly form a saltlike bond with the wool fiberbut are also bonded to the fiber by inter-molecular forces and have properties lyingin an intermediate position between those ofthe leveling and the milling dyes. They areused mainly where average requirements areplacedon thewetfastness and levelness of thedyeing.

Concerning the possibility of influencing therate of dyeing and the leveling power during thedyeing process by the addition of acid or colorsalt→Dyes, General Survey.

3.2.1. Wool Dyes

The standard dyes for wool are divided essen-tially into four groups according to their differ-ent dyeing behaviors (cf. Table 1).

Table 1. Names of important ranges of acid wool dyes

Manu- Ranges

facturer Group A Group B Group C Group D

Bayer Acilan Supracen Supranol SupraminCiba-Geigy Erio Eriosin PolarHoechst Amido Lanaperl Alphanol

FastICI Lissamin Coomassie CarbolanSumitomo Suminol Suminol

leveling millingSandoz Sandolan- Sandolan-

E N

Group A contain the low-priced, usuallyolder leveling dyes with moderate light fastness.These dyes are still used in larger quantities forcheap articles.

Group B also includes leveling dyes, whichare applied in a strongly acid bath but which ex-hibit very good light fastness.

Group C contains the milling dyes, which areapplied in a weakly acid to neutral bath.

Group D contains the acid dyes withgood leveling properties, intermediate molecu-lar sizes, and for the most part good light fast-nesses.

The product ranges of the various dye manu-facturers do not completely fulfill the demandsmade on the dyes in respect of the individual

22 Azo Dyes

fastnesses, and within a manufacturer’s rangethe properties of the dyes can be individuallyspecified.

In describing the separate dye types it is use-ful to distinguish between the monoazo and thedisazo dyes, and to further break down the dis-azo dyes into primary and secondary types onthe basis of chemico-structural principles.

In the industrial manufacture of acid azo dyesusually aniline derivatives are used as the di-azo components and for disazo dyes also diami-nodiphenyl derivatives andother bifunctional di-amines. The coupling components for orangeto blue shades are commonly aniline, naphthy-lamine, naphthol, and aminonaphthol deriva-tives,whereas phenylpyrazolones aremuch usedfor preparing dyes in the yellow and orangeshades.

In regard to the stability of the shade tochanges in pH, care must be taken that hydroxylor amino groups lie adjacent to the azo groupin order to form a hydrogen bridge with thelatter. This hydrogen bridge prevents a disso-ciation of the hydroxyl groups or a protonationof the amino groups and hence avoids an un-wanted change in shade in response to moderatepH shifts. Groups that are not in the ortho posi-tion must be alkylated or acylated (see Section2.2.3).

3.2.1.1. Monoazo Dyes

Among the acid monoazo dyes are a numberof much used wool dyes that possess no out-standing coloristic properties but that are distin-guished by brilliance of shade, very good level-ing power, and particularly low cost, while theirwash fastness and light fastnessmeet only low tomedium requirements. Partly influenced by theintroduction of the International Woolmark tolabel high-quality wool articles, the fastness re-quirements have risen considerably in the last 20years, which has necessitated the developmentand manufacture of particularly fast dyes. Forthis reason many, and above all the older, aciddyes have lost all importance for the dyeing ofwool and are used today only for the coloring ofpaper, soaps, food, and cosmetics.

In the following discussion the acid monoazodyes are classified according to the type of cou-pling component.

Aromatic Amines as Coupling Compo-nents. One of the oldest azo dyes is C. I.Acid Yellow 36, 13065 (metanil yellow) (21)[587-98-4].

Because of the basic group suitable for saltformation the dye is not fast to acid, but it is stillused today for dyeing wool and in special areas(leather and paper) primarily for price reasons.

CouplingH acid to 1-(phenylamino)naphtha-lene-8-sulfonic acid (N-phenylperic acid) yieldsC. I. Acid Blue 92,13390 (22) [3861-73-2].

On wool the product turns out a very pureblue of good light fastness and with moderatewet fastness and adequate leveling power.

Naphthols and Naphtholsulfonic Acids asCoupling Components. In this series two im-portant acid dyes with very similar struc-tures are C. I. Acid Red 88, 15620 (23)[1658-56-6], derived from diazotized naph-thionic acid and 2-naphthol, and C. I. AcidRed13, 16045 (24) [2302-96-7], from naph-thionic acid and Schaffer’s acid:

Both are all-purpose dyes which, because oftheir attractive red shades, are still in use today inmany areas of textile dyeing and also for leatherand paper dyes. Wool dyeings produced withthese dyes exhibit moderate fastness levels.

A long-known, inexpensive, but only moder-ately fast dye is C. I. Acid Orange 7, 15510 (Or-ange II) (25) [633-96-5]. As a wool dye it is nowof secondary importance, but is used in specialareas such as leather dyeing, paper coloration,and the manufacture of color lakes.

Azo Dyes 23

A previously much used red wool dye is C. I.Acid Red 14, 14720 (26) [3567-69-9], which isnow used to a limited extent in wool dyeing forinexpensive articles.

The usually very low wetfastness of thesesimple acid azo dyes can be improved at theexpense of leveling power by the introductionof special, large-volume substituents. Example:C. I. Acid Orange 19, 14690 (27) [3058-98-8],is a very important acid dye for wool andpolyamide with good fastness properties and yetwith good leveling power.

Aminonaphtholsulfonic Acid as the Cou-pling Component. Important coupling compo-nents are γ acid (2,8-aminonaphthol-6-sulfonicacid) and H acid (1,8-aminonaphthol-3,6-disulfonic acid), from which many importantwool dyes are derived, some of which exhibitvery good light and wetfastness.

Especially in acid coupling γ acid yields dyeswith very good light fastness, which is presum-ably attributable to the formation of a hydrogenbridge between the azo bridge and the hydroxylgroup peri to the azo bridge.

As examples are cited two outstandinglylightfast dyes of good leveling powerwhose dye-ings on wool exhibit moderate wetfastness: C. I.Acid Red 42, 17070 (28) [6245-60-9], and C. I.Acid Red 37, 17045 (29) [6360-07-2].

Through the choice of suitably substituted di-azo components, bluish red to blue wool dyes

with good light and wetfastnesses can be pro-duced. Example:C. I. Acid Violet 14, 17080 (30)[4404-39-1].

Of interest is the manufacture of 4-ami-no-3-(4′-toluenesulfonyl)acetanilide, whichis used as the diazo component: p-phenylenediamine is oxidized with iron(III)chloride to 1,4-benzoquinonediimine, to whichp-toluenesulfinic acid is added. The final step ispartial acetylation:

Further examples are: C. I. Acid Red 32,17065 (31) [6360-10-7], andC. I. Acid Blue 117,17055 (32) [10169-12-7].

On wool both dyes exhibit quite good wet-fastness and high leveling power.

In order to achieve valuable dyes with alka-line coupling to γ acid, the amino group mustbe acylated or arylated. Example: C. I. Acid Red68, 17920 (33) [6369-40-0].

24 Azo Dyes

On wool it exhibits high leveling power andyields light- and wetfast dyeings.

N-arylation of γ acid results in a strongdeepening of the shade. The usually brown toblack dyes thus obtained are fast to light andmilling and go onto wool and silk from a neu-tral liquor. Example:C. I. Acid Brown 20, 17640(34) [6369-33-1].

An important coupling component is H acid.Realization that acylation of its amino groupsubstantially improves the light fastness and inaddition yields dyes with good leveling powerled to many valuable light- and wetfast prod-ucts that even today occupy a firm position onthe market. A relatively simply structured wooldye, C. I. Acid Red 1, 18050 (35) [3734-67-6]is obtained by the alkali coupling of diazotizedaniline to N-acetyl H acid.

Valuable dyes can also be made with N-benzoyl H acid and N-toluenesulfonyl H acid.

An interesting development is the Carbolansof ICI. Their neutral affinity to wool and verygood wetfastness properties are achieved by in-corporating long hydrophobic hydrocarbon rad-icals [5, vol. III, p. 268]. Example:C. I. Acid Red138, 18073 (36) [15792-43-5].

1-Phenyl-5-pyrazolones asCouplingCom-ponents. Especially lightfast yellow shades areobtained by using 1-phenyl-5-pyrazolones ascoupling components. The first representativeof the class to appear was Tartrazine, C. I. AcidYellow 23, 19140 [1934-21-0], which is formedin a smooth reaction when phenylhydrazine-4-sulfonic acid is heated with dioxosuccinic acid(see Eq. 11, Section 2.4.4). Today the start-ing compound is 1-(phenyl-4′-sulfonic acid)-3-carboxy-5-pyrazolone, which can be obtainedfrom oxaloacetic ester and phenylhydrazine-4-sulfonic acid and can be coupledwith diazotizedsulfanilic acid. Tartrazine is an intense yellow,moderately fast dye that is still important inwooldyeing but is also used in the dyeing of leather,the coloring of paper, soap, and food, and in thelake form as a pigment.

For price reasons the 1-aryl-3-methyl-5-pyrazolones and their derivatives are preferred tothe corresponding 3-carboxypyrazolones. Thereis such a wide range of possible variations thatdyes in this series extend from greenish yellowto reddish orange. Examples: C. I. Acid Yellow17, 18965 (37) [6359-98-4].

On wool the product yields a clear, superblylightfast yellow with good to very good generalfastness properties, but relatively poor millingfastness.

C. I. Acid Yellow 76, 18850 (38) [6359-88-2],is obtained by coupling diazotized 4-aminophe-nol to the pyrazolone component and then es-terifying with p-toluenesulfonic acid chloridein an alkaline medium. The toluenesulfonic es-ter group substantially improves the fastness tomilling and makes the shade obtained largelyindependent of pH; the light fastness is not quiteas good as that of Acid Yellow 17.

Azo Dyes 25

3.2.1.2. Disazo Dyes

Dyes with two azo groups are divided onchemico-structural principles into primary andsecondary disazo dyes. Primary disazo dyes aremanufactured either according to the schemeD1→K←D2 from a bifunctional couplingcomponent K and two identical or different di-azo components D1 and D2, or according to thescheme K1←D→K2 by coupling a bisdiazo-tized diamine D to the coupling components K1andK2, whichmay be the same or different. Sec-ondary disazo dyes are manufactured accordingto the scheme D→M→K (M=middle compo-nent) from a diazotized aminoazo dye (D→M)and a coupling component K (series coupling).

Primary disazo dyes of the typeD1→K←D2 are obtained by twofold cou-pling to, for example, resorcinol. These orangeto brown dyes have poor light and wetfast-ness and are used only for inexpensive leatherdyeings. Among the naphthalene derivatives Hacid is one of the most important; it serves asa bifunctional coupling component K for themanufacture of many wool dyes now in use.

Dye synthesis following the above schemegenerally permits little variation of the shade(black, dull brown, and blue), because com-pletely conjugated chromophoric systems areformed.

One of the most important acid dyes is C. I.Acid Black 1, 20470 (39) [1064-48-8].

It dyes wool in blue-black shades with verygood light fastness but only moderate wetfast-ness. Nevertheless, because of its high affin-ity and good leveling power it has remained

an important product, which through shadingwith yellow, orange, or red forms the basis ofmost black acid dyes. To manufacture this typeof dye, coupling is always first carried out inan acid medium with the more strongly elec-trophilic diazonium salt, here with diazotized4-nitroaniline, then in the alkaline range withdiazotized aniline:

Abbreviated manufacturing instructions forC. I. Acid Black 1, 20470: Stir 260 kg of 4-nitroaniline with 1200 L of water and a 23 %solution of 132 kg sodium nitrite for about 1/2 h.Run this suspension into amixture of 4000 Lwa-ter, 530 L 31 % hydrochloric acid, 500 kg ice,and a 23 % solution of 1.2 kg sodium nitrite atno more than 10 ◦C. Add about 1000 kg of iceand then 2600 Lof an aqueous solution of 485 kgH acid within a period of 1 – 2 h with thoroughstirring. Coupling is complete at the end of 3 h.

Meanwhile diazotize 165 kg of aniline in300 L water, 1500 kg ice, and 440 L 31 % hy-drochloric acid by adding 124 kg of sodium ni-trite as a 23 % solution. This yields a volumeof 3000 L. Then dissolve the monoazo dye byadding 360 Lof 30%sodiumhydroxide solutionand cool with about 3000 kg of ice. To this runin the solution of diazotized aniline and then im-mediately 1800 L of 15 % soda solution within2 – 3min. The volume is 22000 – 23000 L. Af-ter 6 h add common salt (9.5 % calculated onthe volume) to cause salting out and continuestirring overnight. Filter off the precipitated dyeand dry; the yield is about 1900 kg.

Usually the acid coupling of 4-nitroanilineis not continued to completion, because this re-quires too much time. Consequently, the com-mercial product normally contains a small pro-portion of redmonoazo dye,which togetherwiththe greenish black disazo dye yields the desiredneutral black shade.

Primary Disazo Dyes of the TypeK1←D→K2 (K1 =K2 or K1 �= K2). Thisseries includes many milling dyes because ofthe molecular size achieved (cf. Table 1, groupC). Depending on the type of coupling compo-nents K1 and K2, which may be phenols, pyra-zolones, acetoacetic acid arylamides, or naph-

26 Azo Dyes

tholsulfonic acids, clear yellow to red shadesare obtained. The preferred diazo componentsare diaminodiphenyl derivatives and similarlystructured diamines. Once important dyes de-rived from unsubstituted benzidine are now ofno further importance because of the latter’s car-cinogenic activity (→Benzidine and BenzidineDerivatives). Because the coupling of bisdia-zotized diamines to form monoazo and disazodyes proceeds with different rates, asymmetri-cal disazo dyes are readily manufactured. Forexample, the milling and wetfast red wool dyeC. I. Acid Red 114, 23635 (40) [6459-94-5], ismanufactured by coupling bisdiazotized 3,3′-di-methylbenzidine with one equivalent of Gacid;the monoazo compound obtained is further cou-pled with phenol to yield the disazo dye, thep-hydroxyl group of which is subsequently es-terified with toluenesulfonic acid to improve thefastness properties and pH stability.

An important discovery was the realizationthat benzidines substituted in the 2,2′-positionare outstandingly suitable for the manufactureof very wash-fast and milling-fast wool dyes,while the substantivity toward cellulosic fibers isreduced. A number of important acid wool dyeshave been developed on this basis, for example,C. I. Acid Yellow 44, 23900 (41) [2429-76-7].

In the manufacture of this dye bisdia-zotized 5,5′-dimethylbenzidine-2,2′-disulfonicacid is coupled to two equivalents of N-acetoacetylaniline. The clear, intense, greenishyellow dyeing obtained on wool is milling fastand exhibits excellent wetfastness but onlymod-erate light fastness.

Other members of this series are C. I. AcidOrange 56, 22895:

benzidine-2,2′- −→ 1-phenyl-3-methyl-5-pyrazolone

disulfonic acid −→2-naphthol

and C. I. Acid Yellow 42, 22910 [6375-55-9]

benzidine-2,2′- −→ 2 equivalents of

1-phenyl-3-methyl-disulfonic acid −→ 5-pyrazolone

Instructions for manufacturing C. I. Acid Yel-low 42, 22910: Dissolve 250 kg of benzidine-2,2′-disulfonic acid in 2500 L of water at 50 ◦Cthat was made weakly alkaline with about 90 kgof soda. Then add 100 kg of sodium nitrite inthe form of a 30 % solution. Run the entire so-lution into 4000 L of water at 25 ◦C, containing350 L 31 % hydrochloric acid and 675 kg rocksalt. The total volume is 7500 L, the temperature30 ◦C. Stir for about 15min during the diazoti-zation process.

In the coupling vat add 264 kg of 1-phenyl-3-methyl-5-pyrazolone to 2000 L of water con-taining 80 kg of soda and dissolve at 80 ◦C. Thenadd another 80 kg of soda and cool with 2000 kgof ice to 20 ◦C. Run in the diazonium salt solu-tion in about 30min; no diazo reaction shouldoccur during this procedure. Stir overnight, dur-ing which coupling takes place. Then draw offthe dye and dry; the yield is about 720 kg.

In addition to benzidine derivatives anotherclass of substances of interest as bifunctionaldiazo components consists of special diaminesthat can be manufactured through the reactionof aromatic amines with benzaldehyde or cyclo-hexanone, e.g.:

Dyes based on these compounds possess, inaddition to good light fastness, excellent wet-fastness and are usually neutral dyeing on wool.This, although of no importance for dyeing purewool, plays an important role in dyeing blendedspun yarn and blended fabrics ofwool and cottonor wool and viscose staple. The neutral dyeingacid dye can be used in combination with directdyes (union wool recipes). Examples are C. I.Acid Yellow 56, 24825 (42) [6548-24-9],

Azo Dyes 27

and C. I. Acid Red 154, 24800 (43; R =CH3)[6507-79-5].

C. I. Acid Red 134,24810 (43; R =OCH3)[6459-69-4], is another interesting dye for wooland polyamide.

Particularly good milling fastness isachieved by the introduction of 4,4′-diami-nodiphenylthioether as the diazo component,for example in the yellow wool dye C. I. AcidYellow 38, 25135 (44) [13390-47-1].

Secondary Disazo Dyes. The secondarydisazo dyes, which can be manufacturedby series coupling according to the schemeD→M→K (D= diazo component; M=middlecomponent; K = coupling component), offermuch greater possibilities for variation thanthe primary disazo dyes. This group includesred dyes and, above all, important navy bluesand blacks. Some of the red dyes of this type aremanufactured from aminoazobenzene, amino-azotoluene, or the corresponding sulfonic acidsby diazotization and coupling to naphtholsul-fonic acids.

One of the oldest disazo dyes is Sudan IV,C. I. Acid Red 66, 26905 (45) [4196-99-0],which today is scarcely of any importance.

A productwith a similar structure isC. I. AcidRed 73, 27290 (46) [5413-75-2], which is impor-tant today inwool dyeing and in paper colorationand leather dyeing because of its outstandinglyclear shade and good leveling power.

The most important dyes of the type D→M→K are, however, black and navy blue wooldyes, which contain as the middle componentMchiefly 1-naphthylamine or 1-naphthylamine-7-sulfonic acid and as the coupling component KN-phenylperi acid [= (1-phenylamino)naphtha-lene-8-sulfonic acid], N-tolylperi acid, andnaphthol or 1-naphthylamine derivatives.

Examples of these high-yield and very wash-fast and lightfast dyes are C. I. Acid Black 24,26370 (47) [3071-73-6], which is manufac-tured by coupling diazotized 1-naphthylamine-5-sulfonic acid to 1-naphthylamine, further di-azotization of the aminomonoazo dye and cou-pling to N-phenylperi acid; and C. I. Acid Blue113, 26360 (48) [3351-05-1]. This blue dyeis very important in the dyeing of wool andpolyamide.

Manufacturing instructions for C. I. Acid Blue113, 26360: Dissolve 250 kg of 100 % aniline-3-sulfonic acid in about 3000 L of neutral wa-ter, add about 1000 kg of ice and 400 L of 31 %hydrochloric acid, and diazotize at 10 ◦C with a23% solution of 100 kg sodiumnitrite. Then dis-solve 220 kg 100 % 1-naphthylamine in 2000 Lwater with 185 L 31 % hydrochloric acid at theboil. Quickly run the solution into the diazotizedaniline-3-sulfonic acid to which 4000 kg of icehas been added. Then in about 45min partly neu-tralize to about pH 4 with 400 L of 15 % sodium

28 Azo Dyes

hydroxide solution, temperature 10 ◦C, volumeof 15000 L. After adding 25 % by volume rocksalt, stir for 2 h and again add 360 L of 15 %sodium hydroxide solution.

After cooling to 0 ◦C with about 1000 kg ofice, add 120 kg of sodium nitrite as a 23 % so-lution and then quickly 600 L of 48.5 % sulfuricacid. After 4 h separate the diazonium salt of theaminomonoazo dye in a filter press and stir thepress cake into 1500 L of water and 400 kg ofice.

Dissolve 438 kg of 100 % N-phenylperi acidin 2000 L of water at about 80 ◦C and then ad-just to a volume of 8500 L and a temperatureof 10 ◦C with about 1500 kg of ice and water.Finally add 230 L of 15 % sodium acetate solu-tion and adjust to pH 3 – 4 with about 10 L of31 % hydrochloric acid. Then simultaneouslyfeed into this solution 400 L of 15 % sodium ac-etate solution and the suspension of the diazo-nium salt press cake. Stir thoroughly and adjustthis dispersion to the alkaline range by adding250 L of 30 % sodium hydroxide solution andcause to dissolve by heating to 80 ◦C. Add 10 %by volume rock salt and continue stirring for 3 h.Separate the dye in a filter press at 70 ◦C. Thefinal volume is 19000 L; the yield is 800 kg ofdried product.

A very wash-fast black wool dye is C. I. AcidBlack 26, 27070 (49) [6262-07-3].

It contains 4-amino-diphenylamine-2-sulfonic acid as the diazo component, 1-naphthylamine as the middle component, and2-naphthol-6-sulfonic acid as the final couplingcomponent.

3.2.1.3. Chrome Dyes [3, p. 464], [15, p. 680]

Azo dyes with certain groupings can be con-verted on the fiber with chromium salts tochromium complexes that are more or less sol-uble (see Section 2.3.4). This “chroming” oflargely acid monoazo dyes improves the lightfastness of the dyeings and above all their wet-fastness, because the complex formation blocks

the hydrophilic groups in the molecule. It alsoresults in a deepening and dulling of the shade,so that these dyes do not yield brilliant colors.Consequently, for combination dyeing the rangeof chrome dyes has been supplemented withbrilliant acid dyes, which cannot form chromelakes and survive the chroming process withoutchange.

Chrome dyes are applied to the fiber chieflywith the aid of the afterchroming method andspecial products also by the one-bath chromingmethod (metachrome process). For ecologicalreasons chrome dyes are of severely limited im-portance.

Dyes for the Afterchroming Method. Inafterchroming the dye is allowed to go ontothe fiber from an acid bath, and this is followedby treatment with dissolved alkali dichromate,which is reduced by the cystine group of thewool to trivalent chromium compounds. Thechromium complex formed on the wool fibercontains two azo dye radicals for each metalatom (1 : 2 complex compound).

In the reversal of this process with so-calledmordant dyes, first the chromium salt is appliedto the fiber (premordanting) and then the dye.Mordant dyeing is essentially only of historicalinterest.

The afterchromingdyes have lost their formerimportance because of the considerable amountof time required by the dyeing process, but theyare still used in wool dyeing because of their lowprice. For the names of important afterchromingdye ranges see Table 2.

Table 2. Important ranges of afterchroming dyes

Manufacturer Range

Bayer DiamantchromCiba-Geigy EriochromSandoz Omegachrom

Furthermore, dyes of this type are still pro-duced in large amounts in theCOMECONcoun-tries and in the People’s Republic of China.

In the yellow and orange types the salicylicacid grouping dominates. One of the most im-portant chrome-developed yellow dyes is C. I.Mordant Yellow 1, 14025 (50) [584-42-9]. Afterchroming it yields a somewhat dull yellow withgood fastness properties.

Azo Dyes 29

C. I. Mordant Yellow 5, 14130 (51)[6054-98-4], possesses two salicylic acidgroups. After chroming the product is greenishyellow and exhibits very good general fastnessproperties. Because diazotized aminosalicylicacid is not sufficiently electrophilic, the dyeis manufactured by coupling diazotized 5-ami-no-2-chlorobenzoic acid to salicylic acid andsaponifying the activated chlorine atom.

The complex formation on the salicylic acidgroup has little influence on shade and lightfastness, in contrast to o,o′-disubstituted ary-lazo compounds, on which complexing bringsabout a considerable deepening of shade andusually marked increase in light fastness. Ex-amples: C. I. Mordant Red 7, 18760 (52)[3618-63-1], dyes wool a dull orange, whichthrough chroming becomes a clear red with verygood fastness properties.

Red, blue, and primarily black afterchromingdyes contain naphthalene radicals in the diazo orcoupling component.

Ablue dye, for example, isC. I.Mordant Blue13, 16680 (53) [1058-92-0].

One of the most important black dyes is C. I.Mordant Black 9, 16500 (54) [2052-25-7].

Oxidation of the dye during chroming withdichromate creates a naphthoquinone structure

in the molecule (55). Two other important blackdyes are C. I. Mordant Black 3, 14640 (56,R =H) [3564-14-5], andC. I. Mordant Black 11,14645 (56, R =NO2) [1787-61-7].

C. I.Mordant Black 11 is also used as an indi-cator in the complexometric titration of variousbivalent metals with which the dye forms com-plexes [24].

The o,o′-dihydroxyaminoazo and o-hydroxy-o′-aminoazo compounds with phenolsor aniline derivatives as coupling componentsyield largely brown shades on chroming; theyinclude one of the most important brown dyeswith very good fastness properties, C. I. Mor-dant Brown 33, 13250 (57) [3618-62-0].

The rarely used chrome-developed disazodyes mostly contain the salicylic acid grouping,which in the type D→M→K (see page 27) isusually introduced into the molecule in the formof aminosalicylic acid as the diazo component.Dyes of the typeK1←D→K2 (see page 25) aremanufactured by coupling bisdiazotized benzi-dine derivatives (D) to two equivalents of sali-cylic acid (K1 =K2) or to one equivalent eachof salicylic acid (K1) and naphtholsulfonic acid(K2).

Dyes for the One-Bath Chroming Method(Metachrome Process). In this method themetal complex is formed on the fiber by thesimultaneous action of chrome dye and dichro-mate. Compared with the afterchromingmethodmetachromedyeinghas the advantage of simplerapplication, but the number of usable dyes forthis process is more severely limited. Whether adye is suitable for the metachrome process de-pends on its hydrophilic character and its rate ofcomplex formation [15, p. 680].

30 Azo Dyes

Themethod is used at present forwool dyeingprimarily because of price considerations.

Examples of typical one-bath chroming dyesare: C. I. Mordant Yellow 30, 18710 (58)[10482-43-6], C. I. Mordant Red 19, 18735 (59)[1934-24-3], C. I. Mordant Red 30, 19360 (60)[6359-71-3], C. I. Mordant Brown 48, 11300(61) [6232-53-7], and C. I. Mordant Blue 7,17940 (62) [3819-12-3].

3.2.1.4. Metal-Complex Dyes

(cf. Section 2.3.4)Only a short overview of the subject will

be given here (for detailed treatment →Metal-Complex Dyes). Metal-complex dyes are man-ufactured in the complete dye form before thedyeing process and usually contain chromiumor cobalt ions, rarely copper or iron ions, boundin the molecule. A distinction is made between1 : 1 and 1 : 2 metal-complex dyes, dependingon whether there is one metal ion for each dye

molecule or for every two dye molecules. Theseproducts generally yield dyeings of high lightand wetfastness but of somewhat muted shades.

1 : 1 Metal-Complex Dyes. Among thesedyes primarily the 1 : 1 chromium complexescontaining sulfonic acid groups have achievedcommercial importance. They must be appliedfrom a strongly acid bath, which imposes certainlimits on their range of applications. The 1 : 1metal complexes are not suitable for polyamide,which is partially decomposed under the dyeingconditions for these products. Their main areaof application is in the dyeing of wool, but theyare also suitable for leather dyeing. See Table 3for a list of ranges.

Table 3. Important ranges of 1 : 1 metal-complex dyes

Manufacturer Range

BASF Palatin FastCiba-Geigy Neolan

The 1 : 1 metal-complex dyes are also pro-duced in large amounts in theCOMECONcoun-tries and in the People’sRepublic ofChina;man-ufacturers in, for example, India or Greece areof lesser significance.

The manufacture of 1 : 1 chrome complexdyes takes place in two operations: manufac-ture of the azo dye capable of chrome devel-opment and formation of the chromium com-plex. Similarly as for the one-bath chromingdyes, negatively substituted o-aminophenolsbut also o-aminonaphthols and their sul-fonic acids are used as diazo components;2-naphthol, 2-naphtholsulfonic acids, pyra-zolones, acetoacetic acid aryl amides, and 2,4-dihydroxyquinoline serve as the coupling com-ponents.

1 : 2 Metal-Complex Dyes. Because oftheir complexed structure 1 : 2 metal-complexdyes exhibit anionic character. Those whichhave gained commercial importance are primar-ily the ones that are free of sulfonic acid groupsand for which adequate water solubility is pro-vided by nonionic, hydrophilic substituents,such as methylsulfone or sulfonamide groups[15, p. 689], [25].

The introduction of 1 : 2 metal-complexdyes, which are applied from a neutral to weakly

Azo Dyes 31

acid bath, represented a significant technical ad-vance over the strong-acid-dyeing 1 : 1 chromecomplex dyes. It has meant better protection ofthe fiber material, simplification of the dyeingprocess, and improvement of the fastness prop-erties.

Because these dyeings, like all metal-complex dyeings, usually exhibit subduedshades, the 1 : 2 metal-complex dyes are com-binedwith small amounts of acid dyes or suitablereactive dyes to brighten the tint.

Owing to their outstanding wetfastness, highlight fastness, and good fiber levelness, the 1 : 2metal-complex dyes are of major importance indyeing wool and polyamide. Important rangesof these dyes are listed in Table 4.

Table 4. Important ranges of 1 : 2 metal-complex dyes

Manufacturer Range

BASF OrtolanBayer IsolanCiba-Geigy IrgalanSandoz Lanasyn

The extent of variation is extremely large as aresult of the great number of available diazo andcoupling components, the choice of complex-forming metal (primarily chromium or cobalt),and the possibility of synthesizing 1 : 2 metalmixed complexes.

Substituted o-aminophenols and also an-thranilic acid and its derivatives are the mostimportant diazo components. The main cou-pling components are pyrazolones, acetoaceticacid arylamides, naphthols, N-substituted ami-nonaphthols, and naphthylamines.

For subdued shades the 1 : 2 metal-complexdyes with one or two sulfo groups continue toplay an important role.Dyeswith one suchgroupcontain the sulfonic acid group in one of thetwo parts bound to the azo group and com-plexed to chromium or cobalt. They are builtup stepwise via the 1 : 1 metal-complex. Com-pared with the 1 : 2 metal-complex dyes withnonionic hydrophilic groups they exhibit bettersolubility inwater but poorer leveling power, andtherefore they are always used togetherwith spe-cially selected leveling auxiliaries. The ranges ofthese dyes (Table 5) contain primarily navy blue,black, dark brown, and olive shades.

Table 5. Important ranges of 1 : 2 metal-complex dyes containingmonosulfonic and disulfonic acid groups

Manufacturer Range

BASF Acidol MBayer Isolan SCiba-Geigy Lanacron SHoechst AzarinICI-Francolor Neutrichrom SSandoz Lanasyn S

The 1 : 2 metal-complex dyes with two sul-fonic acid groups are a more recent develop-ment.

Contrary to the opinion frequently expressedin the literature that such dyes would exhibit in-adequate levelness when applied in a weaklyacid bath and inadequate stability to acid in astrongly acid dyebath, they are very well suitedfor dyeing wool and polyamide if certain pHconditions are observed. These products are verysoluble in water, have high tinctorial strength,and are very high-yield dyes with a relativelysimple structure (for further details →Metal-Complex Dyes).

3.2.2. Polyamide Dyes [5, vol. III, p. 276]

Synthetic polyamides have a structure similarto those of wool and silk but differ in having alow acid-binding power and in their capacity todissolve nonpolar compounds. In consequencematerials of polyamide can be dyed with dis-perse dyes as well as with selected acid dyes,including metal-complex dyes.

When choosing acid dyes for polyamides itmust be borne in mind that owing to the loweracid-binding power dyes with two andmore sul-fonic acid groups in the molecule go onto thefiber much more slowly and to a much lowersaturation value than dyes with one sulfonicacid group. Consequently, these dyes cannot bemixed or combined with one another, which hasbeen taken into account in composing the prod-uct ranges.

Since acid dyes on polyamide behave as theydo onwool in regard to leveling power, build-up,and fastness properties (see Section 3.2.1), theyfall into two classes (cf. Table 6):

GroupA: acid dyeswith good leveling powerand low substantivity for polyamide; theyyield dyeings with reasonably good wetfast-ness.

32 Azo Dyes

Group B: acid dyes with lower levelingpower, higher substantivity and highwetfast-ness standard on polyamide. Many of theseacid dyes with a lower leveling power ratherclearly reveal differences in fiber structurethat may result from, for example, differ-ences in the degree of drawing (so-calledstreakiness), so that it is usually necessaryto add leveling and retarding auxiliaries(→Textile Dyeing).

Table 6. Important ranges of polyamide dyes

Manufacturer Range

Group A Group B

BASF Acidol AcidolBayer Telon Supra Telon FastCiba-Geigy Erionyl Erionyl

TectilonCrompton & Knowles Nylanthrene NylanthreneICI Nylomine A Nylomine C

Nylomine BSandoz Nylosan E Nylosan F

Nylosan N

The main area of application for the acidpolyamide dyes characterized in group A is incarpet dyeing, but they are also used in otherareas of textile dyeing where the fastness re-quirements are not too stringent. A few struc-tures are presented below to illustrate the typesof azo dyes used: C. I. Acid Yellow 25, 18835(63) [6359-85-9], C. I. Acid Orange 67, (64)[12220-06-3], C. I. Acid Red 42, 17070 (65)[6245-60-9], C. I. Acid Red 32, 17065 (66)[6360-10-7].

Group B dyes are used almost exclusivelyfor clothing textiles for which more stringent re-quirements are placed on wetfastness. Some ofthe typical azo dyes of this type are C. I. AcidYellow 42, 22910 (67) [6375-55-9], C. I. AcidYellow 65, 14170 (68) [6408-90-8], C. I. AcidRed 114,23635 (69) [6459-94-5],C. I. AcidBlue113, 26360 (70) [3351-05-1].

Other acid disazo dyes for polyamide are sec-ondary disazo dyes (D→M→K) with one ortwo sulfonic acid groups bound to aromatic nu-clei or with an external sulfate group, whichis situated mainly in the diazo component D.Aniline, 1-naphthylamine, and their derivativespreferably serve as the middle component M,whereas the coupling components of the phenoland arylamine series common in disperse dyesare used as the final hydrophobic component K[26–30], as illustrated by the general structure71.

Azo Dyes 33

R1 and R2 = alkyl groups, partially substi-tuted

The patent literature indicates that polyamidedyes of this type are generally characterized byhigh tinctorial strength and light fastness and agood capacity to compensate for nonuniformityin the material.

Because of increasing standards of wetfast-ness, lightfast reactive dyes are also being usedin polyamide printing, especially to producepastel shades. However, only selected represen-tatives of the cotton reactive dyes so far offeredon the market are suitable for polyamide. Essen-tially the products recommended for polyamidecontain monosulfonic and disulfonic acidgroups with β-sulfatoethylsulfone, α-bromo-acrylamide, α,β-dibromopropionylamide,monochlorodialkylaminotriazine, and tri-halopyrimidyl groups, particularly 2,4-difluoro-5-chloropyrimidyl groups (→Reactive Dyes).

Because of their high fastness standards the1 : 2 metal-complex dyes have also acquiredsome importance in the dyeing of polyamide.They are used primarily in the clothing sector toachieve deep shades. The first complete range ofthese dyes for polyamide fibers was developedin 1940 – 1943 at the Ludwigshafen works ofthe then I. G. Farbenindustrie, but owing to theevents of the day they never reached the market.The range consisted of dyes with and withoutnonionic, hydrophilic groups.

Later these dye types were further devel-oped by other companies and uniform rangeswere placed on the market. Dyes with nonionic,hydrophilic groups are offered for wool andpolyamide dyeing (see page 30), while the useof water-insoluble 1 : 2 metal-complex dyes isrestricted to polyamide dyeing; Table 7 showsranges of these products. In a process compa-rable to disperse dyeing, these dyes are appliedto polyamide from a finely dispersed aqueoussuspension and yield extremely lightfast andwetfast dyeings (for further details →Metal-Complex Dyes).

Table 7. Important ranges of dispersed 1 : 2 metal-complex dyes

Manufacturer Range

BASF VialonCiba-Geigy AvilonICI-Francolor Amichrom

3.2.3. Silk Dyes

Because natural silk, as a protein fiber of ani-mal origin, resembles wool fiber in its chemi-cal structure, it can be dyed with nearly all theclasses of dyes used forwool. The choice of dyesdepends essentially on the fastness properties re-quired.

Of great importance for the dyeing of naturalsilk are selected members of the class of acidwool dyes (see Section 3.2.1). The occasionallyinadequate wetfastness of these dyeings can besubstantially improved by the proper aftertreat-ment (e.g., with potassium sodium tartrate andtannin).

Selected acid 1 : 1 chrome complex dyes, be-cause of their goodwetfastness and light fastnessand their very good leveling power, and also 1 : 2chrome complex and 1 : 2 cobalt complex dyeswith hydrophilic groups (see page 30) have suc-cessfully come into use as silk dyes.

Furthermore, direct dyes (see Chap. 4) areamong the most important silk dyes. Their fast-ness properties can be improved by aftertreat-ment with metallic salts or formaldehyde.

If suitably selected, cationic dyes (seeChap. 5) can also be used for dyeing weightedsilk, toward which they exhibit special affinity,in addition to having good leveling power andvery good wetfastness. On the other hand, thelight fastness of these dyeings is not always sat-isfactory.

Reactive dyes have also found a place in silkdyeing. These dyeings are characterized by veryfast and bright shades with exceptionally goodwetfastness.

Initially the development of synthetic fibersgreatly reduced the importance of silk dyeing.The processing of silk has undergone a markedincrease owing to thegrowingquality conscious-ness of buyers, who appreciate the outstandingwear properties of silk, and because of the inten-sified activities of China on the world market.

34 Azo Dyes

In addition to China the countries that are stillprominent in silk processing today are Japan andItaly.

3.2.4. Leather Dyes

Leather is produced by tanning skins of differentorigin and the tanning process has a decisive in-fluence on the dyeability of the pretreated prod-ucts. The differences in the dyeing behavior ofleather of various origins that has been tanned indifferent ways are about as marked as those ofthe different textile fibers.

Many of the anionic, cationic, metal-complex, and direct dyes employed in the textilefield are also used for dyeing leather. In addi-tion ranges have been developed that are par-ticularly suitable for dyeing leather. The choiceof dye depends largely on the tanning method,the fastness properties required, and the end use,and a distinction is made, depending on thedepth of penetration of the dyes, between sur-face dyeing, part-penetration dyeing, and full-penetration dyeing (for more details on the dye-ing of leather→Leather).

The main shades used are different brownsand blacks, as well as bordeaux, reds, yellows,blues, and greens. Most of the leather dyes be-long to the azo class. They are marketed bothas individual dyes and in the form of mixtures.The most important ranges are listed in Ta-ble 8. Because of the many different classes ofdyes used, several ranges are available:

Group A includes both anionic and di-rect dyes. They are used mainly for dye-ing chrome leather and alum-tanned gloveleather. The basic difference between acidand direct dyes, which is pronounced in tex-tile dyeing, is less marked in the dyeingof leather. Therefore, the two groups oftentend to be combined under the term “anionicdyes”. The dyeings obtained have good lightfastness and good to very good wetfastness,rub fastness, and fastness to washing.GroupB contains acid 1 : 1 chrome-complexdyes aswell as 1 : 2 chrome- and 1 : 2 cobalt-complex dyes with hydrophilic groups (seeSection 3.2.1.4). Particularly stringent de-mands can be made on these dyes in termsof light, wet, and perspiration fastness andleveling properties. Some of the ranges used

here are already familiar from the textilefield.Group C is composed of acid dyes and directdyes. Unlike group A, they are mainly dyemixtures that give marked coloration of theleather as well as good surface coverage.Group D consists of pigment preparationsthat are important for the treatment of leatherand are applied by different methods (spray-ing, padding, curtain coating). The rangescontain both organic and inorganic pigmentsand mixtures of the two. They are marketedas binder-containing or binder-free, finelydispersed aqueous pigment preparations andhave high covering power and in most casesvery good light fastness.

The large number of cationic dyes suitablefor dyeing leather cannot be grouped under onespecific range. They have very good coveringpower and give a high yield and brilliant shades.Their light fastness is generally only moderate.They are used for vegetable tanned leathers andas a so-called top dyeing for chrome leather.

To obtain the good fastness to buffing thatis particularly important in the dyeing of suede,special dyes are used which, in addition to ade-quately deep and level surface dyeing, also givegood penetration so that no change in shade oc-curs when the leather is subsequently buffed.

Some typical anionic azo dyes for leatherare: C. I. Mordant Brown 33, 13250 (72)[3618-62-0]: strong penetration, poor coverage;

C. I. Acid Brown 105, 33530 (73) [8003-78-9]:poor penetration, good coverage;

C. I. Acid Black 24, 26370 (74) [3071-73-6]: nopenetration, good coverage;

Azo Dyes 35

Table 8. Names of important ranges of leather dyes and pigments

Manufacturer Ranges

Group A Group B Group C Group D

BASF Luganil Luganil C Lurazol LeptonEukesolar liq. Lumin Helizarin

Corial Fast

Bayer Baygenal Baygenal L Aciderm EusinBenzo Leather EukanolChrome Leather Baysin

BaydermIsoderm

Ciba-Geigy Sella Fast Sellacron Sellaflor IrgafinNeolanLanacronIrgalanIrgaderm liq.

FMC/ICI CoriacideInoderm

Hoechst Coranil Coranil Fast Remaderm Melustral(with Cassella) Melustral Coating

Sandoz Derma Derma Light RelcaSandoderm Relcasyn

Relcasol

C. I. Acid Yellow 36, 13065 (75) [587-98-4](metanil yellow): strong penetration, poor cov-erage;

3.2.5. Azo Food Dyes

In terms of quantity and value food dyes playonly a relatively minor role in the dye-makingindustry.

A brief survey is given here of the azo dyesthat have been approved for food coloration.For a detailed treatment of the subject, includ-ing legislation and official regulations,→Foods,3. Food Additives.

From the chemical viewpoint some of themost frequently used synthetic food dyes belongto the azo series.

The dyes approved for food coloration in theEEC are listed in the guidelines for colorantsof 23. Oct. 1962, which are continually updated.The member states of the EEC must convertthese guidelines to national law.

The azo dyes listed below bear, in additionto the L number of the Dye Commission of theDeutsche Forschungsgemeinschaft (DFG, Ger-man Research Association), an EEC number (E)under which they are registered in the EEC:C. I.Food Yellow 4, 19140, L-Yellow 2, E 102, Tar-trazine, (76) [1934-21-0]

C. I. Food Yellow 3, 15985, L-Orange 2, E 110,Yellow Orange S, (77) [2783-94-0]

36 Azo Dyes

C. I. Food Red 9, 16185, L-Red 3, E 123, Ama-ranth S, (78) [915-67-3]

C. I. Food Red 7, 16255, L-Red 4, E 124, Pon-ceau 4 R, (79) [2611-82-7]

C. I. Food Red 3, 14720, L-Red 1, E 122, AzoRubine, (80) [3567-69-9]

C. I. Food Black 1, 28440, L-Black 1, E 151,Brilliant Black BN, (81) [2519-30-4]

The use of dyes for pharmaceutical prepa-rations is regulated in the EEC by guidelinesfrom 1978 and 1981 and the Directive concern-ing Pharmaceuticals Dyes of 1982. Here practi-cally the same dyes are permitted as for food.

For other areas of application different regu-lations apply. These regulations differ from oneanother in respect of the dyes permitted (forexample, in the cosmetics sector the cosmeticsguidelines and the Directive on Cosmetics).

The food dyes permitted in the USA arecompiled in the Code of Federal Regulations,Vol. 21, Food and Drugs, Parts 1 to 99; continualamendments are published in the Federal Reg-ister.

A synthetic dye is permitted for dyeing foodonly if thorough toxicological studies reveal nodanger of toxic effects to the consumer. Fooddyes are among the food additives that have beensubjected to the most thorough toxicological ex-aminations.Purity Requirements: Food dyes that are placedon the market must meet special purity require-ments, which have been fixed by law for theFederal Republic of Germany in the Directiveon Additives of 20. 12. 1977. According to thisregulation the following substances must notbe detectable in food dyes:Barium compoundsthat are soluble in dilute hydrochloric acid; cad-mium, mercury, selenium, tellurium, thallium,uranium and chromates; polycyclic aromatic hy-drocarbons with 3 or more fused nuclei; and2-naphthylamine, benzidine, and 4-aminobiphe-nyl (xenylamine).

Upper limits have been specified for the fol-lowing contaminants:

arsenic max. 5mg/kglead max. 20mg/kgantimony, copper,chromium, zinc,barium sulfate

individually max. 100mg/kg

togethermax. 200mg/kg

aromatic amines max. 100mg/kgportions extractablewith ethyl ether∗

max. 0.2 %

water-insolubleportions∗

max. 0.2 %

∗ Only in the dyes E 102 – 110, E 122 – 132, E 142 and E 154.

Furthermore, special purity requirementshave been placed on individual dyes.

In the Federal Republic of Germany the an-alytical methods for testing the degree of purityhave been published by the Dye Commission ofthe DFG.

In the USA the regulations for the purity offood dyes are specified in the Code of FederalRegulations. The Food andDrugAdministration(FDA) is responsible for the registration and cer-tification of food dyes.

Azo Dyes 37

4. Direct (Substantive) Dyes

Direct or substantive dyes are colored com-pounds that are mainly used to dye materialsmade from natural or regenerated cellulose (e.g.,cotton, jute, viscose, or paper) without employ-ing mordants as auxiliaries. The essential re-quirement for classification of a dye in this groupis its substantivity, i.e., its absorption from anaqueous salt-containing solution onto cellulosicmaterials. Absorption onto cotton takes place ina neutral to soda alkalinemediumand onto paperin a weakly acid to neutral medium.

Substantivity was initially attributed to sec-ondary valence bonding between fiber and dye.The fact that coplanar molecules are alwaysmore substantive than nonplanar ones later ledto the coplanarity theorywith its assumption thatcoplanar dyes are in contact with the cellulosemolecule along their entire length.

The presence of hydrogen bonds has alsobeen expounded as a possible explanation forhigh affinity between fiber and dye [31]; how-ever, such bonds are probably prevented by awater layer between fiber and dye [32].

The nature of substantivity has beenvery con-vincingly explained [33].

According to this explanation, single dyemolecules are adsorbed by the intermicellarycavities of the cellulosic fibers and, unlike non-substantive dyes, they form aggregates in thesecavities.

Because of their size, these aggregates canno longer be directly washed out with water, butonly after further solvation has taken place.

Because direct dyes become aggregated inaqueous solutions at normal temperatures, sub-stantivity often cannot take effect until the tem-perature has risen. Only then diffusion into thefiber is possible.

The tendency toward aggregation is thereforecharacteristic of substantive dyes,which also ex-plains why coplanar dyes possess greater sub-stantivity than nonplanar ones.

There is no exact delineation between sub-stantive and nonsubstantive dyes, the boundariesbetween them are fluid.

Structural Characteristics. Azo dyes com-prise the major proportion of the direct dyes;apart from these, only a few azine, phthalocya-nine, and nonazo metal-complex dyes possessa certain significance. The following structural

characteristics are necessary for high substan-tivity:

a) Coplanarity of the Dye Molecules. Theimportance of coplanarity is shown bythe example of 4,4′-diaminodiphenylderivatives. Whereas 3,3′-disubstituteddiaminodiphenyls (e.g., o-tolidine or o-dianisidine) as diazo components pro-duce high absorptive power in dyes,this substantivity is neutralized in 2,2′-disubstituted derivatives and coplanarity ofthese molecules is no longer possible.

b) Long Chain of Conjugated DoubleBonds.Dye molecules of this kind (see alsoSchirm’s rule [34]) can contain bridges,such as −CH=CH−, in addition to thearomatic rings, thus ensuring the devel-opment of resonance forms across the en-tire molecule. Exceptions to this rule arethe bridges −NHCONH−, −CONH−, and−NH−, which increase substantivity in spiteof the interruption in the conjugated sys-tem. In these groups, the ability to formhydrogen bonds is the decisive factor. Othergroups causing an interruption in the conju-gated system, e.g., −CH2−, −CH2CH2−,−CO−, −S−, −SO2−, and cyclohexylene,decisively lower substantivity. Only the sub-stantivity of the linked segments remains.

On the basis of the structural characteristicsdescribed, direct dyes based on benzidine can becommended for their good substantivity. In factthis group was for a long time a significant con-stituent of all important direct dye ranges in theshade spectrum from red to brown, blue, green,and black.

Because of the carcinogenic properties of un-substituted benzidine in humans about 15 – 20years ago almost all major dye manufacturers inthe most important western industrialized coun-tries stopped production of dyes based on thissubstance.

This development led to an intensive searchfor substitute dyes, the results of which are re-flected in particular in the patent literature. Thesignificance of this development is also dis-cernible in the number of direct dyes newly reg-istered with the Colour Index between 1971 and1982. The research efforts are especially appar-ent in the case of black, with 21 new registra-tions; yellow, brown, and blue, each with 19;

38 Azo Dyes

and red, with 17. However, of a total of 115 di-rect dyes, the constitution has as yet only beenstated in 7 instances. It is therefore not possi-ble to evaluate the patent literature results withregard to the industrial significance of the prod-ucts.

Starting Compounds. Based on the require-ments mentioned, the following starting com-pounds are especially suited for the synthesis ofdirect dyes:

a) 3,3′-Disubstituted 4,4′-diaminodiphenylderivatives, but not 2,2′-disubstituted ones.These are, therefore, diamineswith the struc-ture

where X=CH3, OCH3, Cl, SO3H. 1,4-Diaminophenyl derivatives also belong tothis group.

b) Compounds of the type

where X=NH, SO2, −N=N−,−CONH−, −CSNH−, −SO2NH−,−CH=CH−,−HNCONH−,−HNCSNH−,−O2SNHSO2−.

c) 1,4-Diaminonaphthalene and 1,5-diami-nonaphthalene

d) m-Phenylenediamine and other 1,3-disubstituted diamines, e.g., 2,6-diami-notoluene-4-sulfonic acid or bis(3-ami-nophenyl)urea.

e) Heterocyclic diamines

Because of their ease of application andmod-erate price, direct dyes still represent one of thelargest groups of azo dyes, although their wet-fastness, in particular, often only satisfies mod-erate to average requirements. The only slightdecrease in consumption of direct dyes follow-ing the appearance of the wetfast reactive dyesis due to the markedly higher price of reactivedyes. For product ranges see Table 9.

Direct dyes are classified according to theirmethod of application:

a) Conventional Direct Dyes. They includemonoazo, disazo, trisazo, and tetrakisazodyes. It is advantageous to subdivide themaccording to the nature of their chemicalstructure. Disazo dyes, for example, canbe divided according to chemical synthe-sis principles into primary and secondary.Conventional azo direct dyes further includesymmetric urea derivatives, dyes obtainedby oxidation of amines, and triazinyl andcopper-containing dyes.

b) Direct Dyes with Aftertreatment. This groupincludes direct dyes that after being appliedto the fiber by the usual method undergo oneof the following aftertreatments:Aftertreatment with cationic auxiliariesAftertreatment with formaldehydeDiazotization of the dye on the fiber andcoupling with suitable components (dia-zotization dyes)Aftertreatment with metal salts

4.1. Conventional Direct Dyes

4.1.1. Monoazo Dyes

Only a few monoazo dyes possess the necessarysubstantivity to render them suitable for directdyeing of cellulosic fibers.

Of practical importance as diazo com-ponents are only the derivatives of 2-(4′-aminophenyl)-6-methylbenzthiazole, of the so-called dehydrothio-p-toluidine (82):

Azo Dyes 39

Table 9. Designations of important ranges of direct dyes (The names in brackets are the U.S. products of the relevant Western Europeancompany)

Manufacturer Product range

Western EuropeBASF (FRG) Lusantin, (Phenamine)Bayer (FRG) Benzamin, Benzo, Benzocuprol, Sirius, Sirius SupraCiba-Geigy (Switzerland) Cuprophenyl, Diphenyl, Solophenyl, (Diazophenyl)Croda (United Kingdom) Covazol, DiazinHoechst/Cassella (FRG) Cotonerol, Diamin, Duasyn, (Rayon)ICI (United Kingdom) Chlorazol, DurazolPCUK/ICI (France) Cuprodiazol Light, Diazamine, Diazol, Diazol Fast, Diazol Light, MetadiazolRovira (Spain) Hispadiazo, Hispaluz, HispaminSandoz (Switzerland) Cuprofix, Cuprofix C, Indosol, Solar, (Lumicrease, Pyrazol)

United StatesAmer. Cyanamid CalcomineAtlantic Atlantic, Atlantic Diazo, Atlantic Direct, Atlantic ResinCrompton & Knowles Diazo, Direct-, Intrabond, Intralite, Intramet, Sol-Aqua-Fast, SuperlitefastInternat. Dyestuff Elcofast, ElcomineOrg. Chem. Corp. Orcoform, Orcolitefast, Orcomine

JapanHodogaya Aizen Direct, Aizen Primula, DirectMitsubishi Diacotton, Diacupro, Dialuminous, DirectMitsui Toatsu Direct, SuprazoNippon Kayaku Kayafect, Kayaku Direct, KayarusSumitomo Direct, Japanol, Nippon, Sumilight, Sumilight Supra

The compound 82 is obtained by melting p-toluidinewith sulfur at 130 – 230 ◦C.Thederiva-tives (83) – (86) are used to produce monoazodirect dyes:

Whereas 83 and 84 are obtained by sulfona-tion of dehydrothio-p-toluidine (82) with oleum,compounds 85 and 86 are formed in a mixturewith 82 during the sulfur melting process andare separated by vacuum distillation.

Acetoacetic acid arylides and pyrazolonederivatives are the coupling components mainly

used. Naphtholsulfonic acids are of onlyminor importance here. Dehydrothio-p-tolu-idinesulfonic acid (83) and the sulfonatedprimulin base are also used as diazo componentsfor certain orange disazo direct dyes.

Examples. Diazotization of dehydrothio-p-toluidinesulfonic acid (84) and coupling to ace-toacetic acid o-anisidide results in the light-fast yellow C. I. Direct Yellow 27, 13950 (87)[10190-68-8].

Coupling the diazotized monosulfonic acidof the primulin base to acetoacetic acid anilideproduces the clear, greenish yellow C. I. DirectYellow 22, 13925 (88) [10190-69-9].

Substantive yellow monoazo dyes with verygood light fastness are also obtained by oxida-tion of dehydrothio-p-toluidine and its deriva-

40 Azo Dyes

tives (see Section 2.2.3). Oxidation of thesodium salt of the monosulfonic acid of theprimulin base in the alkaline pH range withsodiumhypochlorite results, for example, inC. I.Direct Yellow 29, 19556 (89) [6537-66-2].

As with the corresponding oxidation ofdehydrothio-p-toluidinesulfonic acid (83),which results in C. I. Direct Yellow 28, 19555(see Section 2.2.3), in addition to the azo dye,diphenazines (90) are obtained as byproducts,e.g., which in some cases have to be separated

when they impair the shade and fastness prop-erties of the dyes.

4.1.2. Disazo Dyes

4.1.2.1. Primary Disazo Dyes

Primary disazo dyes are obtained in accordancewith the pattern K1←D→K2 by bisdiazotiza-tion of a bifunctional diazo component D andcoupling to two equivalents of coupling com-ponent K1 and K2, or according to the patternD1→K←D2 by coupling of two equivalents ofdiazo component (D1 and D2) to one equivalentof a bifunctional coupling component. Depend-ing on whether K1 and K2 or D1 and D2 are thesame or different, symmetrical or asymmetricaldyes are obtained.

Type K1←D→K1 Primary symmetricaldisazo dyes with benzidine as bisdiazo compo-nent were long considered to be the prototypeof direct dyes. Development of this dye classcommenced with congo red,C. I. Direct Red 28,22120 (91) [573-58-0].

Both as regards the number of products onthe market and the consumption in terms of vol-ume, the disazo dyes of the bisdiazotized ben-zidine were for a long time the most importantsubstantive dyes. Today, no individual chemicalgroup enjoys such significance. Instead, besidesthe substituted 4,4′-diaminodiphenylene, sev-eral other groups, including heterocyclicones,have taken the place of benzidine.

o-Dianisidine as bisdiazo component has acertain significance in blue direct dyes of thecongo red type. Coupling with two equivalentsof H acid results in C. I. Direct Blue 15, 24400(92) [2429-74-5].

With chromotropic acid (1,8-dihydroxy-naphthalene-3,6-disulfonic acid) as couplingcomponent, C. I. Direct Blue 10, 24340[4198-19-0], is obtained (see page 41).

A very clear pure blue is obtained through thealkaline coupling of bisdiazotized o-dianisidineto two equivalents of Chicago acid SS (1-ami-no-8-hydroxynaphthalene-2,4-disulfonic acid):C. I. Direct Blue 1, 24410 (93) [2610-05-1].

o-Tolidine is also occasionally encounteredas diazo component, e.g., in C. I. Direct Blue14, 23850 (94) [72-57-1].

Azo Dyes 41

The dye enjoyed major significance and inaddition was one of the first chemotherapeuticsto be used as a remedy for protozoal diseases(Trypan Blue).

Other important diamines used for thesynthesis of symmetrical substantive disazodyes are 4,4′-diaminostilbene-2,2′-disulfonicacid (95) and 4,4′-diaminodiphenylurea-3,3′-dicarboxylic acid or -3,3′-disulfonic acid (96):

The diamine 95 is obtained by heating 4-nitrotoluene-2-sulfonic acid in diluted sodiumhydroxide solution with sodium hypochlorite,4,4′-dinitrostilbene-2,2′-disulfonic acid beingformed in the process, and subsequent reduc-tion with iron and hydrochloric acid. Com-pounds 96 can be produced from 4-nitroaniline-2-carboxylic acid or -2-sulfonic acid by treat-ment with phosgene and subsequent reduc-tion. The sodium salt of 4,4′-dinitrostilbene-2,2′-disulfonic acid itself belongs to the groupof stilbene dyes. It is mainly used as C. I. DirectYellow 11, 40000 [1325-37-7] for the colorationof paper.

Stilbene dyes are different self-condensationproducts of 4-nitrotoluene-2-sulfonic acid pro-duced with of sodium hydroxide solution. Thevarious types are synthesized depending on theconcentration of sodium hydroxide, the reac-tion temperature, and the reaction time. In somecases a subsequent reaction with arylamines iscarried out.

An example of the combination with 95 isC. I. Direct Yellow 12, 24895 (97) [2870-32-8],also known as chrysophenine:

The product is obtained by coupling bis-diazotized 4,4′-diaminostilbene-2,2′-disulfonicacid with two equivalents of phenol and sub-sequent ethylation. It is a very high-strengthreddish yellow with very good leveling powerand average fastness properties, which is excel-lently suited for the dyeing of fabric blends, e.g.,cotton – polyamide. For manufacturing specifi-cations see below.

An example of the use of 96 as diamine isC. I. Direct Red 75, 25380 (98) [2829-43-8].

Other direct dyes with the diphenylureagroup can be produced from aminomonoazodyes by subsequent treatment with phosgene(see Sections 2.3.2 and 4.1.6).

Type K1←D→K2 Primary Asymmetri-cal Disazo Dyes. Since the coupling reac-tions of substituted 4,4′-diaminodiphenylene tomonoazoor disazo dyeproceed at different rates,asymmetrical coupling reactions can be carriedout. The first (acid coupling) proceeds from bis-diazotized o-dianisidinewith one equivalent of acoupling component to a monoazo intermediatecompound, which now together with a second(different) coupling component forms an asym-metrical disazo dye.

Example: C. I. Direct Blue 22, 24280(99) [2586-57-4], is obtained by coupling o-dianisidine to Chicago acid SS and β-naphthol:

Production. The following abridged specifica-tions are intended to illustrate processes for the

42 Azo Dyes

manufacture of symmetrical and asymmetricaldisazo direct dyes.C. I. Direct Yellow 12,

24895, (97) [2870-32-8]: 590 kg of 4,4′-diaminostilbene-2,2′-disulfonic acid are ad-justed with water and ice to a volume of ap-proximately 5500 L and a temperature of 5 ◦Cand bisdiazotized with 220 kg sodium nitrite as23 % solution; volume 6000 – 7000 L, tempera-ture 20 – 22 ◦C.

Next, 312 kg of phenol are dissolved with1500 L of water and 150 L of 30 % sodium hy-droxide solution and 225 kg of soda are added.To this is transferred the above bisdiazotizedsolution. Then, 160 L of 30 % sodium hydrox-ide solution is added over 1 h. On the followingmorning, the solution is heated to 70 ◦C, and af-ter addition of 240 L of 30 % hydrochloric acid,the dye is salted out with 12 % rock salt, calcu-lated on the volume. Yield: 2090 kg.

Approx. 5500 kg of the damp press cake,corresponding to 2940 kg of 100 % product,3500 kg of 94 % ethanol, 520 kg of soda, 870 Lof 30 % sodium hydroxide solution, and 840 kgof ethyl chloride are kept in a closed stirrer ves-sel for 24 h at 100 ◦C (5 – 5.5 bar). Themixture isthen cooled to 70 ◦C and transferred at its ownpressure to a distilling vessel, from which theethanol is distilled with direct steam via a col-umn. After being cooled to 80 ◦C, the mixture issuction filtered and dried at 100 ◦C.

C. I. Direct Blue 15, 24400 (92) [2429-74-5].105 kg of dianisidine dihydrochloride is chargedinto 6000 L of water and 400 L of 31 % hy-drochloric acid. Then 2000 kg of ice is addedand the solution is bisdiazotized at 0 ◦C with200 kg of sodium nitrite and stirred for 4 h.

To 210 kg ofH acid as neutral solution 4000 Lof a 20%sodiumcarbonate solution is added andthen 3000 kg of ice to cool to 0 ◦C. This solu-tion is run in the bisdiazonium salt solution andstirred overnight.

Then the solution is heated to 80 ◦C, 4600 kgof sodium chloride is added, and the dye is fil-tered and dried in vacuo at 95 – 100 ◦C. Yield:7600 kg.

Types D1→K←D1 and D1→K←D2The most important coupling component forthese types is the compound 100, which is pro-duced by phosgene treatment of the I acid.

Dyes with a urea bridge, −HN−CO−NH−,are also obtained by phosgene treatment of ami-noazo compounds (see Section 4.1.6). The so-called I acid imide (101), resorcinol and m-phenylenediamine are also of importance. Ex-amples of dyes are: C. I. Direct Orange 26,29150 (102) [3626-36-6],

C. I. Direct Red 250, 29168 (103),

and C. I. Direct Red 23, 29160 (104)[3441-14-3].

The dye 104 is obtained by simultaneous cou-pling of one equivalent eachof diazotized anilineand 4-aminoacetanilide to I acid urea (100). Al-though it only possesses average fastness prop-erties, it enjoys great importance and because ofits good leveling power is used for dyeing unionfabrics, polyamide, and chrome leather.

By coupling diazotized dehydrothio-p-tolui-dinesulfonic acid to resorcinol and subsequentcoupling of diazotized aniline to the monoazodye formed one obtains C. I. Direct Orange 18,20215 (105) [5915-59-3]. The product likewiserepresents an important substantive dye.

Azo Dyes 43

4.1.2.2. Secondary Disazo Dyes

Type D→M→K. For the manufacture ofsecondary disazo dyes, a diazotized amine D iscoupled to an amine M with free para position,which in turn is diazotized and coupled to a cou-pling component K (series coupling).

Dyes of this typemostly have a straight-chainstructure and often contain groups that increasesubstantivity, such as I acid, I acid derivatives,in particular with acylated amino groups, ureabridges, or benzoylamino groups. The shades inthis range extend from orange through red, vio-let, and blue to black.

Examples: From 4-aminoazobenzene-4′-sulfonic acid and benzoyl I acid C. I. DirectRed 81, 28160 (106) [2610-11-9], is obtained.This dye represents an important red grade.

C. I. Direct Black 51, 27720 (107)[3442-21-5], is produced by coupling a mix-ture of diazotized 3- and 5-aminosalicylic acidto 1-naphthylamine and subsequent alkalinecoupling to γ acid.

4.1.3. Trisazo Dyes

The trisazo dyes include in particular blue,green, and black grades. Benzidine, which here,too, used to be an important bisdiazo compo-nent, has been replaced by other diamines, such

as o-tolidine, 4,4′-diaminobenzanilide (DABA),or 4,4′-diaminodiphenylamine-2-sulfonic acid(DADPS).

Themost important synthesis principle in thisrange is the type K1←D1→K2←D2. The se-quence of the three couplings depends on thenature of the components.

An example is C. I. Direct Green 85, 30387(108).

The reaction commences with stepwise cou-pling of the o-tolidine and then aniline with Hacid, followed by coupling of this aminodisazointermediate with phenol.

With C. I. Direct Black 166, 30026 (109),the first step is the acid coupling of 3,3′-diami-nobenzanilide to H acid, followed by alka-line coupling of aniline to the monoazo dyeand finally coupling of the disazo dye to m-phenylenediamine.

C. I. Direct Black 150, 32010 (110)[6897-38-7], is produced by double (alka-line) coupling of bisdiazotized 4,4′-diaminodi-phenylamine-2-sulfonic acid to γ acid and sub-sequent single coupling tom-phenylenediamine.

Among the trisazo dyes, the synthesis prin-ciple of series coupling of the type D→M1

44 Azo Dyes

→M2→K is also of importance. This groupcontains a number of dyes with good to verygood general fastness properties.

Anilinesulfonic acids are chiefly used asstarting component D, naphthylamine andCleveacids as middle components M1 and M2, and Iacid, its N-phenyl derivatives, H acid, γ acid,and their derivatives as final component K. Thistype mainly possesses blue and green shades.Example: C. I. Direct Blue 78, 34200 (111)[2503-73-3].

2-aminobenzene-1,4-disulfonic acid→Cleve acid-7→1-naphthylamine→N-phenyl I acid

In the manufacture of trisazo dyes, good yieldand purity during final coupling are often ob-tained only in the presence of pyridine or otherbases as coupling accelerators [35]. Intermedi-ate isolation and separation of impurities priorto continuation of coupling are also frequentlynecessary.

The use of pyridine during final coupling(pyridine coupling) is illustrated in the followingabridged manufacturing specification for C. I.Direct Green 33, 34270:

2-aminonaphthalene-8-sulfonic acid→ 3,5-xylidine→2-ethoxy Cleve acid-6→N-acetyl H acid

FinalDiazotization:Thedisazodyeproducedbythe usual method aminocroceic acid→ sym. m-xylidene→ 2-ethoxy-Cleve acid-6 (batch size:81 kg aminocroceic acid 100 %) is stirred in theform of a press cake in 600 L ofwater with 500 Lof 50 % acetic acid. Then 26.5 kg of sodium ni-trite in the form of a 30 % solution is added at25 ◦C. After stirring overnight, a reddish-brownsolution is obtained. Final coupling: To 104 kgof H acid 100 %, dissolved in 500 L of water,are added 32 L of 40 % sodium hydroxide so-lution and 17 kg of soda; the mixture is heatedto 70 ◦C and 50 kg of acetic acid anhydride isadded. After acetylation is completed, the mix-ture is transferred to 1500 L of pure pyridine and

2000 kg of ice. The diazotizing solution is addedat 0 – 12 ◦C over the course of 1/2 h. After a fur-ther hour, 375 kg of sodium hydrogen carbonateis added and after 1 h has expired, the mixtureis heated to 60 ◦C by indirect steam. Followingthe addition of 8 % rock salt, the temperature ismaintained at 60 ◦C for a further hour, and thedye is filtered and dried at 110 ◦C (drum drieror circulating air cabinet). Then yield is approx.360 kg.

Other possible combinations are only of mi-nor importance compared with the trisazo dyesmanufactured according to the synthesis princi-ples mentioned.

4.1.4. Tetrakisazo Dyes

Numerous syntheses are possible for these dyes,which all yield only dark shades. Here, too, onlya few types are of industrial importance.

A further extension to the trisazo dyes on theprinciple of series coupling D→M1→M2→M3→K offers no advantages, because the in-termediate isolation that is frequently necessaryleads to yield losses and a chain extension istherefore ruled out on economic grounds. Thisis also reflected in the number of polyazo dyesgiven in the Colour Index [7, vol. 4, p. 4325]. Al-though 78 tetrakisazo dyes with eleven differentsynthesis principles are listed, only 14 dyes withfive and more azo groups are mentioned, two ofwhich are specified with eight azo groups (seetop of next page).

An example of type D→M1→M2→M3→K is C. I. Direct Dye, 35850 [8002-98-0](brown).

sulfanilic acid→m-toluidine→Cleve acid-6→m-toluidine → 1-nitrophenylene-2,4-diamine

A number of important direct dyes are derivedfrom type K1←M1←D→M1→K 1: C. I. Di-rect Black 22, 35435, (112) [6473-13-8] is pro-duced via the primary disazo dye from 4,4′-diaminodiphenylamine-2-sulfonic acid and twoequivalents of γ acid. This dye is bisdiazo-tized and coupled to two equivalents of m-phenylenediamine.

Azo Dyes 45

Another example is C. I. Direct Black 151,35436 (113)

Here, too, the disazo dye is initially preparedfrombisdiazotized 4,4′-diaminodiphenylamine-2-sulfonic acidwith 2 equivalents ofγ acid.Cou-pling is then again carried out stepwise to γ acidand finally to m-phenylenediamine.

C. I. Direct Black 19, 35255 (114)[6428-31-5], is also an important dye. It isobtained by coupling two equivalents of p-nitraniline to H acid, sulfhydrate reduction ofthe two nitro groups, and coupling of the bis-diazotized intermediate compound with twoequivalents of m-phenylenediamine (see top ofpage 45).

4.1.5. Condensation Dyes

These dyes are produced by condensation of ni-tro compounds (see also Section 2.2.1).

Alkaline condensation of dinitrostil-benedisulfonic acid with aminoazo compounds

produces a number of highly fast substan-tive dyes with industrial importance, espe-cially in the shades orange, scarlet, and brown[36]. Example: C. I. Direct Orange 39, 40215[1325-54-8], is obtained by condensation of4-aminoazobenzene-4′-sulfonic acid with dini-trostilbenedisulfonic acid in aqueous sodiumhy-droxide solution. Themain product formed is thetetrakisazo dye of the stilbene-2,2′-disulfonicacid (115), as well as the corresponding azoxycompounds. No uniform product is obtained,since part of the aminoazo compound is con-sumed as reducing agent. Condensation dyesare often purified by aftertreatment with reduc-ing agents or such as glucose or sodium sulfide.Abridged specification: 468 kg of 100 % 4,4′-dinitrostilbene-2,2′-disulfonic acid as sodiumsalt is stirred with 1000 L of water and adjustedto a weakly alkaline pH value with sodium hy-droxide solution.Then440 Lof 30%sodiumhy-droxide solution is added and 346 kg of 100%4-aminazobenzene-4′-sulfonic acid introduced assodium salt. After the contents of the tank havebeen diluted to 4500 L, the temperature is raisedand maintained for 14 h at 100 ◦C. The conden-sation product is transferred into 10000 L of wa-ter and 39 kg of sodium sulfide is then added.The temperature is raised to 85 ◦C and main-tained there for 1/2 h; then salting-out carriedout with 12 % rock salt, calculated on the totalvolume. Isolation is carried out at 70 ◦C usinga filter press. The dye is given a final washing

46 Azo Dyes

with 9000 L of a 10 % rock salt solution heatedto 50 ◦C. The yield is approx. 780 kg dry.

Table 10 shows further examples of conden-sation dyes obtained from the correspondingaminoazo compounds and 4,4′-dinitrostilbene-2,2′-disulfonic acid.

4.1.6. Direct Dyes with a Urea Bridge

By the end of the 19th century, BASF had dis-covered that the reaction of aminoazo dyes withphosgene in an aqueous solution in the presenceof soda resulted in valuable symmetrical ureaazo dyes [37]:

The urea bridge can also be introducedinto direct dyes with 4,4′-diaminodiphenylureaderivatives by means of bisdiazotization andcoupling (see (98) in page 40). C. I. Direct Yel-low 50, 29025 (116) [3214-47-9]

is obtained, for example, by phosgene treat-ment of two equivalents of aminoazo dye pre-pared from diazotized 2-aminonaphthalene-4,8-disulfonic acid coupled to m-toluidine.

Other examples of symmetrical direct dyeswith a urea bridge are shown in Table 11.

Aminodisazo and aminotrisazo dyes can alsobe treated with phosgene, largely red and brownshades being obtained.

Example: C. I. Direct Red 80, 35780[2610-10-8], is rendered accessible by phosgenetreatment of the aminodisazo dye 117:

By mixing two different aminoazo com-pounds A–NH2 and B–NH2 and subsequentphosgene treatment, the asymmetrical dipheny-lurea direct dye 118 is obtained in addition tothe two symmetrical members.

There are a number of yellow substan-tive dyes synthesized by this principle. Ex-ample: C. I. Direct Yellow 41, 29005 (119)[8005-53-6], is obtained by phosgene treat-ment of an equimolar mixture of basesA (sulfanilic acid→ cresidine) and B (p-nitroaniline→ salicylic acid and reduction of theNO2 group). The mixture additionally containsthe two corresponding symmetrical dyes.

4.1.7. Triazinyl Dyes

The principle of linking two or three azo dyesby means of a triazine ring was established byCiba patents [38]. The triazine bridge increasesthe substantivity of the dyes, in a similar man-ner to the −NH−CO−NH− group. Productionis based on cyanuric chloride, the three chlo-rine atoms of which can be replaced in stages bynucleophilic radicals under different conditions(see Section 2.3.2).

The procedure that can be adopted is for in-termediate products with amino groups (e.g., H

Azo Dyes 47

Table 10. Examples of condensation dyes made from aminoazo compounds and 4,4′-dinitrostilbene-2,2′-disulfonic acid

Table 11. Aminoazo compounds for symmetrical direct dyes with a urea bridge

acid) to be condensedwith cyanuric chloride andthe reaction product subsequently attached to thediazo component, or aminoazo dyes are reacteddirectly with cyanuric chloride. In the relevantcommercial azo dyes, the third chlorine atomin the cyanuric chloride is usually reacted withaniline or ammonia and less frequently left un-changed.

Of interest, here, are dyes that yield greenshades through combination of a blue and yel-low component.

Example: C. I. Direct Green 26, 34045 (120)[6388-26-7]. Theblue component (Hacid→ cresidine→H

acid) is linked with the triazine ring by meansof the amino group of the H acid; after reduc-tion of the nitro group, the yellow component(p-nitroaniline→ salicylic acid) replaces thesecond chlorine atom of cyanuric chloride andaniline the third chlorine atom. The dye consti-

48 Azo Dyes

tutes a very pure, clear, bluish green with verygood fastness properties.

4.1.8. Copper Complexes of Substantive AzoDyes

Under certain structural conditions, azo dyes arecapable of forming metal complexes (see Sec-tion 2.3.4). A process for the complexing of o,o′-dihydroxyazo dyes with copper by reaction ofthese dyes with copper sulfate in a weakly acidsolution was described for the first time in 1915[39].

The introduction of copper into conven-tional substantive dyes often increases theirlight and wetfastness considerably, since com-plexing blocks the hydrophilic groups. Coppercomplexes of o,o′-disubstituted azo dyes arechiefly of interest for direct dyes. Substituentsespecially capable of complexing are hydroxyl,methoxy, carboxy, and carbomethoxy groups.BASF developed the oxidative copper treatmentprocess in which on the basis of o-hydroxyazodyes, copper complexes of the correspondingo,o′-dihydroxyazo dyes are obtained [40].

The possibility of first converting suitable azocompounds into copper complexes, and subse-quently using them as coupling components forthe synthesis of azo direct dyes, was also de-scribed.

As in the case of the metal-free direct dyes,a large diversity of structures is encountered;here, too, there are direct dyes with pyrazolones,substituted 4,4′-diphenylamines, or the 1,3,5-triazine ring, urea and stilbene derivatives, andcondensation dyes.

For each dye it is necessary to establish themost favorable conditions under which copper-containing products with improved propertiesare obtained. Because none of the known com-plexing processes provides optimum results inall instances, the production of certain dyes orcomplexing variations is protected by a largenumber of patents.

Especially for ecological reasons, however,the importance of copper complex dyes is de-creasing. This applies in particular to the copperaftertreatment.

A demethylating copper treatment of dyessynthesized with o-dianisidine results in light-

fast blue grades, such as C. I. Direct Blue 98,23155 [6656-03-7], a copper complex of 121;

and C. I. Direct Blue 84, 23610 [13569-92-1], acopper complex of 122.

The following additional examples of sub-stantive copper complex dyes can bementioned:C. I. Direct Violet 47, 25410 [13011-70-6], acopper complex of 123;

and C. I. Direct Green 23, 31985, a copper com-plex of 124.

4.2. Direct Dyes with Aftertreatment

For supplementary literature see [41] and [42,vol. 2, p. 46]

In spite of the reactive dyes with their out-standing wetfastness, the direct dyes continueto hold a large share of the market for inexpen-sive cellulose and paper dyes. Apart from thenew developments to replace the old establishedbenzidine dyes, considerable efforts are beingmade to improve the fastness properties of directdyes by aftertreatment. The various aftertreat-ment methods are described below in the orderof their present importance.

Azo Dyes 49

4.2.1. Aftertreatment with CationicAuxiliaries

Aftertreatment of substantive dyeings with or-ganic, cationic substances has lately begun togain increasingly in importance. Improvementsare obtained in particular in wetfastness proper-ties, especially fastness to water, washing, andwet pressing, as well as fastness to perspirationand cross-dyeing.

The cationic compounds precipitate the (an-ionic) dyes from their aqueous solutions and onthe fiber form higher molecular mass, scarcelysoluble, saltlike compounds with the dyes. Re-moval of the latter from the fiber is thus mademore difficult. A number of companies havecompiled their own ranges of this type of af-tertreatment agent.

Cationic textile auxiliaries canbedivided intotwo groups: quaternary ammonium compoundsand cationic formaldehyde condensation resins.

Quaternary Ammonium Compounds.These contain aliphatic and/or cycloaliphaticradicals (R1 to R4 in Eq. 12), of which at leastone represents a long-chain alkyl radical (withmore than five C atoms). The compounds reactwith the dyes in accordance with the followingpattern:

Use is made, for example, of cetyldi-methylbenzylammonium chloride and pyri-dinium compounds of the type

In addition, the quaternary ammonium com-pounds mostly possess strong affinity for thecellulosic fiber, whereby the insoluble reactionproduct is anchored even more firmly with thedye on the fiber. This high affinity can, however,also result in nonuniform improvements in fast-ness properties. This behavior also prevents the

use of circulating liquor dyeing machines, be-cause even with addition of aftertreatment agentin portions (e.g., in the case of wound pack-ages) no completely uniform aftertreatment canbe guaranteed.

The action of quaternary ammonium com-pounds on the dyed fiber inmany cases producesa change of shade.

A further disadvantage is the possible elim-ination of aliphatic amines, e.g., in an alkalinemedium in the presence of anionic substances orat excessive drying temperatures. This can causean unpleasant (fishy) odor to arise. In such cases,an acid aftertreatment is necessary.

Cationic Formaldehyde CondensationResins. An appreciable improvement in wet-fastness properties is obtained by aftertreatingthe dyeings with polymeric condensation resinscontaining strongly basic groups. This leads tothe formation of insoluble salts from resin cationand dye anion.

Themost important resins of this type are ob-tained from dicyanodiamide (125) by condensa-tion with formaldehyde and hydrochloric acid:

Suitable blending of ammonium salts offairly strongly basic amines (e.g., melamineor guanidine) and acid condensation withformaldehyde enables favorable conditions tobe obtained with regard to solubility and cross-linking of the cationic condensation resins.

The water-soluble resins are inexpensive,and compared with quaternary ammonium com-pounds relatively small quantities often sufficeto achieve amarked improvement inwet fastnessand fastness to perspiration. A disadvantage isa certain influence on light fastness. This maybe lowered by one to two steps on the eight-step blue scale, when these resins are used onmaterials dyed by substantive dyes. Formalde-hyde condensation resins are therefore used es-pecially for articles in which wet fastness andfastness to perspiration are important, but lightfastness is less crucial, e.g., lining fabrics.

50 Azo Dyes

4.2.2. Aftertreatment with Formaldehyde

The wetfastness properties of substantive azodyes containing free amino or hydroxyl groupsas terminal groups (final component of coupling,e.g., resorcinol or m-phenylenediamine) can beimproved by aftertreating the dyed fibermaterialwith aqueous formaldehyde solution. The con-ditions for the presence of free amino groupscan also be satisfied by subsequent reduction ofnitro groups or hydrolysis of acylamino groups.During reaction with formaldehyde, methylenebridges are formed between two dye molecules;i.e., an enlargement of the molecule occurs andhence an improvement in wetfastness, whereaslight fastness is not influenced.

Because of a lack of storage stability in dye-ings treated by this method, the formaldehydeaftertreatment is mainly confined to dark shades(brown and black).

The first patent on this aftertreatment methodwas granted to Geigy as early as 1899 [43]. Al-though the basic, simple process has remainedvirtually unchanged, its importance has latelydeclined sharply for ecological reasons.

4.2.3. Diazotization Dyes

Direct dyes containing one or more diazotizableamino groups in the dye molecule permit fur-ther diazotization on the fiber and subsequentcoupling with a “developer.” β-Naphthol canbe used as a developer for orange, red, brown,blue, and black shades, 1,3-phenylenediamineand 2,4-diaminotoluene for brown, gray, andblack shades.

The shade of the dye applied to the mate-rial usually changes considerably as a result ofthis aftertreatment. wetfastness and fastness toperspiration are greatly improved, light fastnessremains unchanged. The amino group neededfor diazotization is introduced by final couplingwith an amine, an aminonaphtholsulfonic acid,or an amino-acylaminonaphtholsulfonic acid orby reduction of a nitro or hydrolysis of anacylamino group. “Development” results in en-largement of the dye molecule without furthersolubilizing groups being added.

The time-consuming process necessitatescareful handling. Exposure to sunlight or par-tial drying of the diazotized dyeing should thusbe avoided.

Diazotization dyes now enjoy onlyminor im-portance.

Example: C. I. Direct Red 145, 17805 (126)[6771-94-4], yields a clear yellowish red whendeveloped with β-naphthol.

4.2.4. Aftertreatment with Metal Salts

This method is dealt with briefly, mainly on his-torical grounds, because for reasons connectedwith wastewater pollution and because of cer-tain performance drawbacks it is hardly used anylonger.

Metal complexing (see Section 4.1.8) cannotbe carried out until after the fiber has been dyed.This aftertreatment, mainly with copper salts(sulfate, acetate), takes place under mild condi-tions, so that, for example, no metal complexingwith an o-methoxyazo group occurs. Suitablecomplexing systems, on the other hand, are o,o′-dihydroxy-, o-hydroxy-o′-carboxy-, o-hydroxy-o′-carbomethoxy-, and o-carboxy-o′-aminoazogroups.

4,4′-Diaminodiphenyl-3,3′-dicarboxylicacid (127), 4,4′-diaminodiphenyl-3,3′-bisoxyacetic acid (128), and 4,4′-diami-nodiphenylurea-3,3′-dicarboxylic acid (129)have proved successful as diamino componentsfor the synthesis of disazo copper-aftertreateddyes.

Azo Dyes 51

Metal complexing results in blocking of sol-ubilizing groups; aggregation increases, the dyebecomes less soluble, and an improvement inwet fastness occurs. Although the light fastnessis generally also improvedby this aftertreatment,fastness of the dyeings to perspiration is fre-quently reduced. The shades generally becomeduller and flatter. Catalytic action of traces ofheavy-metal ions that are present can cause fibertendering to occur in the presence of detergentscontaining oxidizing agents (peroxides).

An example of a direct dye suitable for cop-per aftertreatment isC. I. Direct Blue 167, 24560(130), see top of the page.

5. Cationic Azo Dyes

Cationic azo dyes carry a positive charge inthe colored portion of the molecule. The salt-forming counterion is, in most cases, the col-orless anion of a low molecular mass inorganicor organic acid. The positive charge is gener-ally carried by nitrogen, but there are also dyesin which this function is taken on by sulfur orphosphorus (see Section 5.5).

The positive charge may be either localizedat an ammonium group (see, e.g., 131)

131

or delocalized across the dye cation. The transi-tion between the two dye classes is continuous.At one extreme, this leads to the dark blue com-pound 132, which is no longer considered anazo dye but classified as a diazacyanine dye(→Methine Dyes and Pigments).

132At an intermediate position, compound 133has its positive charge much less delocalized be-cause of the high energy of the quinoid reso-nance extreme 133b.

Finally, in compound 134 the structure doesnot permit a charge delocalization from the ben-zimidazolium ion to the back ring azo dye sub-stituent.

134

Both 133 and 134 confer a similar orange-red color to polyacrylonitrile and are classifiedas cationic azo dyes.

History. Basic dyes of the azo class areamong the earliest known synthetic dyes. Theywere used originally for dyeing cotton mor-danted with tannin and potassium antimonyl tar-

52 Azo Dyes

trate and wool from neutral solution. They con-tinue to occupy a place of minor importance fordyeing leather, paper, plastics, and waxes, andas constituents of graphic arts colors.

The preparation of the first cationic azodye, Vesuvin, was described by C. Martiusin 1863. It is obtained by coupling diazo-tized m-phenylenediamine to an excess ofthe same amine. An analogous dye fromtoluylenediamine was reported by P. Gries in1878. Chrysoidines, coupling products of ani-line or toluidines to m-phenylenediamine ortoluylenediamine, were reported by H. Caroin 1875 and O. N. Witt in 1876. Thesewere followed in 1886 by cationic safra-nine azo dyes, obtained by coupling dia-zotized diethylphenosafranine to phenols oraromatic amines (→Azine Dyes), and bydyes produced by coupling diazotized ami-nophenyltrimethylammonium chloride to phe-nols and aromatic amines. Both groups formedthe basis of the Janus dye product line, whichgained great importance for a time in dyeingweighted silk.

When polyacrylonitrile fibers appeared onthe market, an intense research effort in the areaof cationic azo dyes was stimulated worldwideat all the leading dye plants. Thesematerials nowoccupy a place of importance in all significantproduct lines.

Azo dyes with several cationic charges,which are substantive dyes for cellulose, are in-creasingly being used for coloring bleached sul-fite cellulose.

The cationic charge may be introduced intothe dyemolecule via either the diazo componentor the coupling component.

5.1. Cationic Charge at the CouplingComponent

Amino groups, amidine residues, trialkylammo-nium, or cyclic ammonium groups may serve ascarriers of the cationic charge in the couplingcomponents.

5.1.1. Polyamines as Coupling Components

Chrysoidines are obtained by coupling di-azonium salts of aniline, toluidines, or mix-tures thereof to 1,3-phenylenediamine, 2,4- or

2,6-toluylenediamine, or mixtures of these di-amines. These dyes confer muted yellow to or-ange shades to paper, leather, and polyacryloni-trile fibers. When they are mixed with malachitegreen and fuchsin, medium-fast black shadesare obtained on polyacrylonitriles. A mixture ofchrysoidine with Crystal Violet or Victoria PureBlue is used to adjust the color of nigrosine hec-tograph inks [44].

Examples are C. I. Basic Orange 1, 11320(135) [4438-16-8] the azo dye from diazotizedaniline and 2,4-diaminotoluene,

135

and C. I. Basic Orange 2, 11270 (136)[532-82-1] the dye from aniline and m-phenylenediamine.

136

The dye Astrachrysoidine RR is a mixture ofseveral compounds.

A mixture of 13 g aniline, 12.5 g o-toluidine,and 3.0 gp-toluidine is diazotized in aqueous hy-drochloric acid solution at 0 ◦C using 66.5mLof a 30 g/100mL sodium nitrite solution. Excessnitrite is destroyed prior to coupling using sul-famic acid. The diazotized solution is added ina thin stream and at 0 ◦C to a solution of 16.5 gofm-phenylenediamine and 18.5 g of 2,4-diami-notoluene in 1000mLofwater. The coupling so-lution is then adjusted to pH 3 – 3.5 by additionof dilute aqueous sodium acetate. After com-pleted coupling, the pH of the reaction mixtureis adjusted with hydrochloric acid using congored indicator. The precipitated dye is collectedby filtration and dried to yield 75 g of a darkorange powder.

Chrysoidine dye salts of dodecylbenzenesul-fonic acid are soluble in glycols andglycol ethersand are used in the production of inks, printinginks, and varnishes [45].

Azo Dyes 53

Mono- and disazodyes from diazotized ani-lines and 2,4,6-triaminotoluene dye wool andcotton [46].

Vesuvin and Bismarck Brown products areobtained when m-phenylenediamine, 2,4- and2,6-diaminotoluene, or mixtures thereof aretreated with nitrite in acidic solution, or whena mixture of the amines and nitrite is acidi-fied. The final products consist of mixtures ofmonoazo, disazo, and polyazo dyes,with the dis-azo species probably predominating in commer-cial products. In the presence of sodium chlo-ride, the dye is salted out immediately after itsformation and thereby the formation of polyazodyes is prevented.

Astravesuvin R (137), C. I. Basic Brown 4,21010, serves as an example:

137

A mixture of 2,4- and 2,6-diaminotoluene(28.5 g, molar ratio 2 : 3) and 25 g of m-phenylenediamine is dissolved in 1200mL wa-ter at room temperature andmixedwith 67mLof30 g/100mL aqueous sodium nitrite. After ad-dition of 450 g of sodium chloride and 800 gof ice, which results in a temperature of − 10to− 12 ◦C, 86mL of concentrated hydrochloricacid is added rapidly. Finally, the pH is adjustedto 3 – 3.5 by the addition of dilute sodium ac-etate solution. After several hours, the couplingsolution is adjusted to pH 1 and the precipitateddye is collected by vacuum filtration and driedto yield 90 g of a yellow-brown powder.

Liquid Vesuvin dye solutions may be ob-tained by diazotization and coupling of aromaticdiamines [47–49] or, if desired, also in mixturewith aromatic monoamines [50] in carboxylicacid solutions. The dye mixtures can be alky-lated with alkylene oxides [51].

m-Phenylenediamine (105 g) is added to amixture of 360 g glacial acetic acid, 80 g water,and 60 g ethylene glycol followed by stirring andwarming to dissolve. The temperature is low-

ered to 8 – 10 ◦C and, at this temperature, 47 gsodium nitrite is added in portions over a periodof 1.5 h. After addition is completed, themixtureis stirred for 1/2 h, 10 g m-phenylenediamine isadded, and stirring is continued for another 3 hat 8 – 13 ◦C. Finally, the reaction is warmed to35 – 40 ◦C for 1 h followed by chilling of the dyesolution.

Vesuvines are used chiefly for dyeing papercontaining wood pulp.

5.1.2. Heterocycles as Coupling Components

If heterocyclic polyamines, e.g., 2,4-diamino-6-hydroxypyrimidine, are used as coupling com-ponents with aromatic diazonium compounds,dyes are obtained that color polyacrylonitrile inlightfast yellow shades and that are character-ized by excellent leveling properties [52]. Anexample is 138 [6979-64-2].

138

Coupling Components with AmidineMoi-eties. Well-leveling azo dyes are also obtainedwhen pyrazolones substituted in the 1-positionby an amidine residue are used as couplingcomponents. The diazo components are pre-dominantly substituted by methyl and methoxygroups [53]. An example is 139 [68936-08-3].

139

By reaction of these dyes with formaldehydeand acetone, condensation products suitable forwetfast dyeing of cotton are obtained [54].

54 Azo Dyes

5.1.3. Coupling Components withAlkylammonium Groups

Numerous cationic azo dyes contain adialkylaminoalkyl or a trialkylammoniumgroupas the charge carrier in the coupling component.

5.1.3.1. Coupling Components withDialkylaminoalkyl Groups

Dyes bearing one or more dialkylaminoalkylsubstituents have found favor for coloring paperbecause they behave as substantive dyes which,when properly substituted, result in a practicallycolorless waste liquor. A suitable starting mate-rial for the preparation of such dyes is the reac-tion product of 2 mol dialkylaminopropylaminewith 1mol cyanuric chloride. This may be con-verted to an acetoacetarylide, which,

140

when coupled with diazotized 2-(4′-ami-nophenyl)-5-methylbenzothiazole, yields theyellow dye 140 [91458-38-7] with greenish castsuitable for coloring paper [55].

By reaction of a similar triazine componentwith J acid (1-hydroxy-6-aminonaphthalene-3-sulfonic acid), followed by coupling with dia-zotized 4-aminoazobenzene, the cationic sub-stantive azo dye 141 [71032-95-6] is obtained,which colors paper in red hues.

141

Copper complexes of thesematerials or of theanalogous γ acid (1-hydroxy-7-aminonaphtha-lene-3-sulfonic acid) dyes confer gray-violet[56] or blue hues [57], [58] to paper, respectively,or dye particles of glass in navy blue tones [59].A commercial product of this series is CartasolRed K-2B (Clariant).

These kinds of triazine moieties may also bepart of pyrazolone and pyridone coupling com-ponents [60], [61].

The dialkylaminoalkyl residue may also beconnected directly to the phenyl residue of theacetoacetanilide. By coupling with diazotized2-(4-aminophenyl)benzimidazole, a yellow dyesuitable for paper is formed [62].

The dialkylaminoalkyl group may be con-nected to the N-1 atom of 3-methylpyrazolone[63], to the amide nitrogen atom of N-phenylpyrazolone-3-carbonamide [64], to theN-2 atom of 3-cyano-2,4,6-trisaminopyridine[65], or to the amino group of 2-amino-4,6-dihydroxypyridine [66].

3- or 6-hydroxy-2-naphthoic acid amidesbearing dialkylaminoalkyl residues on the ni-trogen atom lead to orange dyes for poly-acrylonitrile or paper when coupled with di-azotized aniline [67], [68], or to red dyes,soluble in glycol ethers and useful forink-jet printing, when coupled with diazo-tized 3-amino-4-methoxybenzenesulfonic acid-N,N-diethylamide [69], or to substantive reddyes when the diazo component is a 2-(4′-aminophenyl)benzotriazole [70]. Dialkylami-noalkyl amides of J acid have been used to pre-pare red dyes for polymericmaterials, especiallypaper, with 4-acetylaminoaniline as diazo com-ponent [71], [72].

5.1.3.2. Aromatically LinkedTrialkylammonium Groups

Exhaustive alkylation of aminonaphthols, suchas 2-amino-7-naphthol, and coupling with dia-zotized aromatic amines generates yellow, or-ange, red, and brown cationic azo dyes [73],[74]. Compound 142 dyes human hair and poly-acrylonitrile in brown shades [75].

Azo Dyes 55

142

Exhaustively alkylated 4-aminodiphenyl-amine is also suitable as a coupling component.Dyes (e.g., 143) [41025-69-8] obtained by re-action with diazotized nitroanilines confer fastyellow, orange, and red shades to polyacryloni-trile [76].

143

By exhaustive alkylation of 3-ami-nophenylpyrazolone compounds, a trimethy-lammonium moiety may be introduced intothis coupling component. The disazo dye 144[86565-98-2] colors paper in orange shades [78](see bottom of page).

The trialkylammoniumphenyl group mayalso be part of acetoacetic acid arylides [77] orbe connected to the coupling component via anether link (see 145) [84041-74-7] [79].

145

5.1.3.3. Trialkylammoniumalkyl-SubstitutedAnilines

Dialkylanilines that carry a cationic substituentat one of the alkyl groups are among the mostimportant coupling components of cationic azodyes.

By reaction of N-ethyl-N-(2-chloro-ethyl)aniline or of N-ethyl-N-(2-chloroethyl)-m-toluidine with trimethylamine, ammoniumsalts are obtained that, upon coupling with dia-zotized aromatic amines, yield a large numberof valuable dyes for coloring polyacrylonitrile.

C. I. Basic Red 18, 11 085 (146) [25198-22-5]is derived from the diazo component 2-chloro-4-nitroaniline [80].

146

It is a component of all major product linesused for dyeing polyacrylonitrile.

Commercial products areAstrazonRedGTL(DyStar), Diacryl Red GTL-N (Mitsubishi),Sumiacryl Red F-GTL (Sumitomo), and Ta-iacryl Red GTL (T&T Ind.).

The corresponding dye from 2,6-dichloro-4-nitroaniline as the diazo component is also ofcommercial importance.

Other suitable diazo components are4-nitroaniline (orange), 2,6-dichloro-4-nitroaniline (yellow-brown) [81], 2-cyano-4-nitroaniline (red) [82], 2,6-dichloro-4-(N,N-dimethylsulfamoyl)aniline (orange),4-aminobenzophenone (yellow), 2,4,6-trichloroaniline (yellow), 2,4,6-tribromoaniline

144

56 Azo Dyes

(yellow), 2,6-dibromo-4-nitroaniline (yellowbrown) [83], and 2-cyano-5-chloroaniline (or-ange).

Heterocyclic diazo components include 2-aminothiazole substituted with ester groups[84], and the coupling product of diazotized4-nitroaniline with 2-amino-3-cyanothiophene[85].An especially favored startingmaterial is 3-phenyl-5-amino-1,2,4-thiadiazole, which is alsoused in the production of disperse dyes. It yieldsvery bright dyes for coloring polyacrylonitrile[80]. An example is 147 [85283-77-8].

147

A commercial product is Astrazon Red BBL(DyStar).

By coupling aminobenzothiazoles to the qua-ternary ammonium bases red cationic dyes (e.g.,148) are obtained [86].

148

This is to be contrasted with the blue di-azacyanines, which derive from the quaternizedbenzothiazole residue.

Dye affinity to polyacrylonitrile and, thereby,the dyeing rate may be enhanced by introducingan aralkyl residue [87] or an aryloxyalkyl residue[88] in place of an alkyl group at the trialkylam-monium group.

The solubility of these dyes is signifi-cantly enhanced by introduction of alkenyl [89],hydroxypropyl [90], or polyetheralkyl [91] moi-eties into the trialkylammonium group. The tri-alkylammoniumgroupmay also be a componentof a heterocyclic ring [92].When the trialkylam-monium residue contains an alkyl chain of morethan 11 carbon atoms, the dyes become solu-ble in aliphatic and alicyclic hydrocarbons andcan be used for the production of printing inks[93]. Also C. I. Basic Black 8 is recommendedas a dye for ink-jet printing [94]. The quater-

nization to the trialkylammonium residue mayalso be carried out using dialkyl phosphites orphosphonates [95].

With aromatic diamines as the diazo compo-nents, such as 4,4′-diaminodiphenylsulfone, ba-sic disazo dyes are obtained which are suitablefor dyeing acid-modified polyamide materials[96].

The diamine of dye 144 leads to cationic dis-azo dyes that color paper in brilliant orange hues[97].

5.1.3.4. OtherTrialkylammoniumalkyl-SubstitutedCoupling Components

Thecoupling component 2,6-dihydroxypyridine,already an acknowledged component of high-intensity chromophores in disperse dyes, hasalso been applied successfully to the synthesis ofcationic azo dyes. The trialkylammoniumalkylgroup may be linked either to the pyridine ni-trogen [98] (149) [71873-54-6] or to C-3 of thepyridine ring [99] (150).

149

150

Dyes with cationically substituted deriva-tives of 2-hydroxy-6-aminopyridine [100], of2,6-diaminopyridine [101], and of 5-hydroxy-3-methyl-1-phenylpyrazolone [102] as thecoupling components have also been de-scribed. Coupling components based on 4-hydroxynaphthalimide, which carry the trialky-lammoniumalkyl substituent at the imide nitro-

Azo Dyes 57

gen, have been used for the synthesis of redcationic azo dyes [103].

Aromatic coupling componentsmay have thetrialkylammoniumalkyl linked via a carboxam-ide group [104], e.g., 151.

151

Also described as linking groups are ether[105], thioether [106], carbonyl [107], car-boxylic ester [108], carbonamide [109–112] andsulfonamide [113] moieties.

Monofluortriazine reactive dyes, in whicha trialkylammoniumalkyl group is bound tothe heterocycle by an amino group are rec-ommended for blends of polyacrylonitrile withwool, synthetic polyamides or cellulosics [114–116].

5.1.4. Coupling Components withDialkylhydrazinium Groups

A number of valuable cationic azo dyes con-tain the dialkylhydraziniumgroup as the chargedmoiety of the coupling component. The aromaticamines used as the diazo components are thesame as those described for the dyes mentionedin Section 5.1.3.3. The red dye 152 [4531-45-7]is formed with 2-chloro-4-nitroaniline:

152

A yellow dye is obtained with 1-amino-2,6-dichloro-4-(N,N-dimethylsulfamoyl)benzene,an orange dye with 1-amino-2,5-dichloro-4-(N,N-dimethylsulfamoyl)benzene, a yellowbrown dye with 1-amino-2,6-dichloro-4-nitro-benzene, a ruby dye with 1-amino-2-cyano-4-nitrobenzene, and a violet species with 1-ami-no-2,4-dinitro-6-bromobenzene [117].

Red dyes are obtained with 3-phenyl-5-ami-no-1,2,4-thiadiazole as the diazo component[118].

5.1.5. Coupling Components with CyclicAmmonium Groups

By reactionof heteroaromatics, such as pyridine,with intermediates that contain anionically dis-placeable groups, coupling components are ob-tained that derive their positive charge from acyclic ammonium group. Alternately, the hete-rocycle may be linked to the coupling compo-nent by other means for later quaternization.

5.1.5.1. Heterocyclically Linked CyclicAmmonium Groups

Reaction of chloroacetamide with pyridine, fol-lowed by condensation with acetoacetic estersin alcoholic sodium hydroxide, leads to a 2,6-dihydroxy-4-methylpyridine that is substitutedin the 3-positionby apyridiniummoiety. If this iscoupledwith diazotized aromatic or heterocyclicamines, yellow to red cationic azo dyes (e.g.,153) [92691-25-3] are obtained [119], [120].

153

With aromatic diamines and triamines as thediazo components, cationic substantive disazoand trisazo dyes (e.g., 154) [62073-65-8] are ob-tained, which are suitable for bulk dyeing of pa-per [121], [122], [123] or ink-jet printing [124].

A commercial product is Cartasol Yellow K-GL (Clariant).

Also known are 2,6-dihydroxypyridine dyesthat carry a quaternized benzothiazole [125],benzimidazole [126], or imidazole [127], [128]moiety in the 3- or 4-position.

58 Azo Dyes

154

5.1.5.2. Aliphatically Linked CyclicAmmonium Groups

By reaction of N-ethyl-N-chloroethylaniline,N,N-bis(chloroethyl)aniline, or N-ethyl-N-chloroethyl-m-toluidine with heteroaromatics,especially pyridine, coupling components areobtained that carry cyclic ammonium groups.

155

The red cationic azo dye 155 [36986-04-6],obtained with 2-chloro-4-nitroaniline [129], isrepresented in numerous cationic dye prod-uct lines: e.g., Maxilon Red 2GL (Ciba), andYoracryl Red 2G (YDC).

Introduction of a second pyridiniumalkylresidue (156) [24447-84-5] leads to a brighten-ing of the hue to orange.

156

Here again, all compounds cited in Sec-tions 5.1.3.3 and 5.1.4 are used as the di-azo components. In addition, the follow-ing have been described as diazo compo-nents: 2,5-dichloro-4-nitroaniline (red) [130], 2-chloro-5-trifluoromethylaniline (yellow) [131],4-nitro-2-trifluoromethylaniline (red) [132],2-amino-5-trifluoromethyl-1,3,4-thiadiazole(red) [133], 3-methylmercapto-5-amino-1,2,4-thiadiazole (red) [134], 3-methyl-4-nitro-5-ami-noisothiazole (blue violet) [135], 2-amino-6-chlorobenzothiazole (red) [136], 3-amino-5-

nitro-7-bromobenzisothiazole (blue with a redcast) [137], and 2-amino-4-chloro-3-cyano-5-formylthiophne (blue) [138].

The solubility of these dyes is enhancedwhenpicolines are used for quaternization in place ofpyridine [139].

Concentrated aqueous solutions of these dyesare obtained by dissolving the bicarbonate saltsof the dyes in aqueous organic acids, e.g., aceticacid [140].

If monoalkylanilines are reacted with vinyl-heterocycles, especially vinylpyridine, and if theheterocyclic nitrogen is then quaternized, cou-pling components are obtained that carry thepyridinium component by way of a carbon link-age [141], e.g., 157.

157

The place of the pyridinium residue mayalso be taken by the 1,2,4-triazolium [142],the benzimidazolium [143], or the imidazolium[144] moieties. An example is the dye 158[47660-05-9].

158

The cyclic ammonium residue may also belinked to the coupling component via a sulfon-amide [145] or an ester [146] group.

A yellow cationic substantive paper dyeis obtained by coupling diazotized 2-(4′-ami-nophenyl)-5-methylbenzothiazole onto an ace-

Azo Dyes 59

toacetic arylide, e.g., N-aryl-acetoacetamide,substituted by a pyridinium residue [147], orby coupling tetraazotized 4,4′-diaminostilbenewith the coupling component of dye 155 [148].

5.1.6. Coupling Components withCondensed Cyclic Ammonium Residues

Heterocyclic compoundswherein the condensedbenzene ring is substituted by a hydroxyl or anamino function may be coupled with diazoniumcompounds and may also be quaternized, ei-ther prior or subsequent to the coupling reac-tion, to yield cationic azo dyes. 1,2-Dialkyl-6-nitroindazolium salts are reduced to the 6-ami-no compounds and then coupledwith diazoniumsalts of aromatic amines. These dyes (e.g., 159)color polyacrylonitrile in bright yellow to orangeshades [149].

159

6-Amino-1,3-dimethylbenzotriazoliumchloride may also be used as the couplingcomponent [150]. By hydrolysis of 6-amino-1,2-dialkylindazolium chloride in dilute sulfu-ric acid at 180 – 190 ◦C, a hydroxyl group isintroduced into the 6-position. The 6-hydroxy-1,2-dialkylindazolium salt formed is suitable forthe generation of mono- [151] (160) and disazodyes [152] (161) [92888-19-2].

160

161

In a similar manner 6-amino-1,3-di-methylbenzotriazolium chloride may be con-verted into the 6-hydroxy compound for use asa coupling component [153].

5.1.7. Cyclic Ammonium Residues at theAzo Group

If azo dyes from aromatic diazonium com-pounds and 1-phenyl-3-methyl-5-pyrazolone or1-phenyl-3-methyl-5-aminopyrazole are quater-nized at the 2-nitrogen of the pyrazole, cationicazo dyes are obtained. A resonance charge ex-change is prevented through lack of a donorfunction at the aromatic moiety [154], [155]. Anexample is dye 162.

162

Azo dyes from aromatic diazonium com-pounds and indolizine derivatives may also beconverted into cationic azo dyes by quaterniza-tion [156].

5.1.8. Coupling Components with twoDifferent Cationic Residues

Mono- and polyazo dyes have been prepared, inwhich the coupling component carries at leasttwo different basic and/or cationic groups. Ofthese, mostly yellow to orange dyes are derivedfrom pyridones with a cyclic ammonium groupand an amino- or trialkylammoniumalkyl group.To obtain a technically sufficient affinity to cel-lulose fibers disdiazo components are preferredeither with the same coupling component [157–161] (e.g., 163) or with different ones [162],[163] (e.g., 164).

A step further is the connection of two suit-able molecules with the help of a dihaloalkane[164], [165] (e.g., 165).

Dyes of this kind can be used to color anodi-cally generated oxide layers on aluminum [166].

60 Azo Dyes

163

164

165

A commercial product is Cartasol Yellow K-3GL liq.

Orange, red and violet dyes can be ob-tainedbyusing as coupling components aminon-aphtholsulfonic acids that are connected viathe N atom to a 1,3,5-triazine with dif-ferent aminoalkylamino, trialkylammonium-alkylamino or cyclic ammonium substituents inpositions 4 and 6 [167] (e.g., 166).

166

For example, 167 dyes paper in a scarletshade [168].

167

Between the N atom of the ami-nonaphtholsulfonic acid and the triazine ring,spacer groups can be introduced, e.g., ami-noaroyl or aminophenylcarbamoyl groups[169], [170].

Adifferentway to synthesize a coupling com-ponent with two different basic groups is to re-act N-dibromopropionylaminonaphtholsulfonicacids with dialkylaminoalkylamines to giveaziridine derivatives; red dyes are obtained bycoupling these with a diazonium salt of p-ami-noazo-benzene [171] (e.g., 168).

Azo Dyes 61

168

5.2. Cationic Charge in the DiazoComponent

Diazo components may contain the cationiccharge at amino, dialkylamino, trialkylammo-nium, or cycloammonium groups.

5.2.1. Diazo Components with AminoalkylMoieties

Yellow dyes are prepared by aminomethylationof 2-(4′-aminophenyl)-5-methylbenzothiazolefollowed by diazotization and coupling withacetoacetarylides. Red cationic dyes are ob-tained with naphthols or hydroxynaphthoic acidarylides. All are suitable for dyeing paper. Thebleachability of these dyes is important forthe recycling of waste paper [172]. The ami-nomethylation of aromatic amines is carriedout by reaction with formaldehyde and phthal-imide, followed by hydrolytic scission of the

phthalic acid residue. By diazotization of 4-methoxy-3,5-bis(aminomethyl)aniline trihydro-chloride and coupling with 3-hydroxynaphthoicacid arylides, red cationic substantive paper dyesare obtained [173]. Of importance in the manu-facture of cationic substantive paper dyes are re-action products of cyanuric chloride with 2moldialkylaminoalkylamine and 1mol 1,3- or 1,4-diaminobenzene.

Yellow paper dyes (e.g., 169) are obtainedby diazotization of these aromatic amines andcoupling with acetoacetarylides [174], [175].

By coupling to derivatives of J acid, sub-stantive dyes (e.g., 170) are obtained whereinthe charge on the sulfonic acid group is morethan compensated for by the multiple cationiccharges. These dye paper in shades of red [176].

Dyes wherein the dialkylaminoalkyl group isconnected to the diazo component via the estergroup of anthranilic acid [177–180], a carbox-amide [181], a sulfonamide [184], [182] or anether [183] residue have also been described.

5.2.2. Diazo Components withTrialkylammonium Residues

The trialkylammonium group may be linked tothe diazo component either via aromatic substi-tution or by way of an aliphatic residue.

169

170

62 Azo Dyes

5.2.2.1. Aromatically LinkedTrialkylammonium Residues

Aminophenyltrimethylammonium chloride wasalready an important diazo component of theJanus line of dyes. The fastness of these dyes,e.g., 171, on polyacrylonitrile is enhanced byintroduction of halogens. Mono- and dialkylan-ilines are suitable coupling components [185].

171

Disazo dyes of this series (e.g., 172) aresuitable for dyeing polyacrylonitrile and paper[186].

172

A commercial product is Anilan Golden Yel-low RL (Ciech).

4-Hydroxynaphthalimide as a coupling com-ponent yields cationic dyes that confer anorange-red shade to polyacrylonitrile [187].

Heterocyclic coupling components thathave been coupled with diazotized ami-nophenyltrimethylammonium chloride are5-hydroxy-1-phenylpyrazole-3-carbonamide[188], 1-alkyl-6-hydroxy-2-pyridone [189], 1-amino-3-hydroxy-isoquinoline [190], and 2,4-diamino-6-hydroxypyrimidine [191]. The tri-alkylammoniumaryl residue may also be con-nected to the aromatic diazo component via asulfone or a sulfonamido function [192]. Dis-azo dyes in this series (e.g., 173) [77901-21-4]may also be generated from monoazo dyes that

still contain a primary amino group by dimer-ization using phosgene [193], [194] or cyanuricchloride [195].

Coupling with β-naphthol results in a yel-lowdye suitable for polyacrylonitrile [196], cou-pling with 2,5-dimethoxyaniline gives an or-ange dye that is recommended for hair coloration[197].

5.2.2.2. Aliphatically LinkedTrialkylammonium Residues

TheFriedel – Crafts acylationof acetanilidewithchloroacetyl chloride yields 1-acetamido-4-chloroacetylbenzene. The trimethylammoniumgroup is introduced by reaction with trimethyl-amine, followed by hydrolysis of the acetamidegroup. This diazo component is a constituentof numerous yellow, orange, and red cationicazo dyes. Using diethyl-m-toluidine as the cou-pling component, the lightfast red dye (174)[67905-12-8] is obtained [198].

174

Introduction of an unsaturated alkyl residueimproves the solubility of the dye [199]. N-Methyl-N-cyanoethylaniline yields an orangedye. The shade is shifted to yellow with a redcast using N-cyanoethyl-2-chloroaniline (175)[72208-25-4].

173

Azo Dyes 63

175

Commercial products are SevronYellow3RL(CKC), and Sumiacryl Yellow E-3RD (Sumit-omo).

Use of 2-methylindole as the heterocycliccoupling component has led to commerciallyimportant dyes (e.g., 176) [25784-16-1] [200].

176

However, dyes have also been gener-ated from 1-phenyl-3-methyl-5-aminopyrazole[200], 2,4-dihydroxyquinoline [201], 2,6-dihydroxypyridine [202], 2,6-diaminopyridine[203], 2,4,6-triaminopyridine [204], and 3-phenyl-5-hydroxyisoxazole [205]. The solubil-ity of such dyes may be enhanced by introduc-tion of polyether moieties [206].

Cationic dyes with reactive functionalgroups, e.g., dichlorotriazine or vinylsulfone,suitable for dyeing wool and silk, have also beengenerated in this series [207]. Bis-cationic dyes,for instance 177, are suitable for dyeing mixed-fiber fabrics containing acid-modified and un-modified polyamide, whereas the latter does nottake up the dye [208].

177

A commercial product is Sevron Red YCN(CKC).

The trialkylammonium alkyl residue mayalso be attached directly to the aryl residue ofthe diazo component [209]. Dyes that derivefromaminomethylated 2-aminonaphthalene andcontain acetoacetarylides, naphthols, or pyra-zolones as the coupling components are suit-able for dyeing paper. An example is the yellowmonoazo dye 178.

178

Disazo dyes are obtained by using couplingcomponents with a primary amino group anddimerization with phosgene [210]. The diazocomponents are prepared by exhaustive alkyl-ation of aminomethylated 2-aminonaphthalene-1-sulfonic acid, followed by scission of the sul-fonic acid group in the presence of mineral acids[211].

The trialkylammonium residue may also beconnected to the diazo component by way of anether [212], a carbonamide [213], [214], a sul-fone [215], or a sulfonamide group [216], [217].

Bis-cationic metal-complex dyes are suit-able for dyeing leather. Cationic monoazo dyeswherein a trialkylammonium group is linked viaa carboxamide group to the diazo component[218] and disazo dyes are known. The latterare prepared from dialkylamino compounds byquaternization using alkylene dibromides. Theyare suitable for dyeing paper [219].

Azo dyes with 2-(4′-aminophenyl)-5-methylbenzothiazole as the diazo componentand carrying trialkylammoniumalkyl residuesare suitable for dyeing paper in the same man-ner as the dyes described in Section 5.2.1 [172],[220]. Also described as carriers of the cationiccharge were dialkylhydrazinium residues linkedto the diazo component via a sulfonamide [221]or a carboxamide group [222].

64 Azo Dyes

5.2.3. Diazo Components with CyclicAmmonium Residues

The cyclic ammonium residue may either belinked directly to the aromatic ring or attachedto the diazo component via an aliphatic residue.

5.2.3.1. Aromatically Linked CyclicAmmonium Residues

For the preparation of a diazo component thatcontains a 1,2,3-triazolium residue in the paraposition, p-nitrophenylazide in acetone solutionis first reacted with acetylene in an autoclave togive 1-(4-nitrophenyl)-1,2,3-triazole. The nitrogroup is then reduced, the resultant amine acety-lated, and the triazolemoiety is quaternizedwithdimethyl sulfate. After hydrolysis of the acetylgroup, the resultant aminemaybe diazotized andtreated with ethylcyanoethylaniline to give dye179 [47553-94-6] [223]. The dye colors poly-acrylonitrile to a lightfast orange.

179

The triazole moiety may also be linked inthe 2-position with respect to the azo link-age [224]. Among cyclic ammonium residueslinked via carbon bonds to the aromatic ringof the diazo component have been cited:1,3-dialkylbenzimidazolium [225], benzothia-zolium [226], methylpyridiniumoxazole [227],and pyridinium [228] moieties, linked via ni-trogen, as well as the benzotriazolium moiety[229].

5.2.3.2. Aliphatically Linked CyclicAmmonium Residues

Upon reaction with pyridine azo dyes that carrya chloroethylsulfonamido group in the diazocomponent form cationic azo dyes, e.g., 180[33869-97-5], which color polyacrylonitrile inbrilliant shades [230].

180

The chloroethylsulfonamide may also be re-acted with 1,2,4-triazole [231].

Dyes containing the pyridinium group linkedto the diazo component via a carboxylic esterfunction (e.g., 181) [32017-47-3] are obtainedby condensation of 4-nitrobenzoyl chloride withchloroethanol, reaction of the ester with pyri-dine, reduction of the nitro to an amino group, di-azotization, and coupling with aromatic amines[232].

181

This dye imparts anorange shade topolyacry-lonitrile. The cyclic ammonium residues mayalso be linked to the diazo component via a car-boxamide [233] or an ether group [234] or di-rectly by means of an alkyl residue [235].

5.2.4. Diazo Components with two DifferentCationic Residues

Mono- and disazo dyes have been prepared inwhich the diazo compound carries at least twodifferent basic and/or cationic groups.

Reaction of 2,4- or 2,5-diaminobenzene-sulfonic acids with 2-chloro-1,3,5-triazines thatare substituted in the 4- and 6-positions byaminoalkylamines and cyclic ammoniumalky-lamines, respectively, leads to diazo compo-nents which, when diazotized and coupled withderivatives of aminonaphtholsulfonic acids, giverise to dyes for cotton, leather, and especiallypaper [236]. An example is 182, which colorspaper in a violet hue.

Azo Dyes 65

182

183

Reaction of chloromethyl derivatives of4′-aminophenyl-2-benzothiazoles with e.g.N ′,N ′′,N ′′′-permethyldiethylene-triamine leadsto compounds with alkylaminoalkylammoniumresidues that can be diazotized and coupledwith, e.g., acetoacetarylides [237]. An exampleis 183, which colors paper in a greenish shadeof yellow.

5.2.5. Diazo Components with AromaticCondensed Cyclic Ammonium Residues

Polynuclear N heterocycles that carry an ami-no group in the carbocyclic aromatic ring maybe diazotized and then joined to azo dyes usingaromatic or heterocyclic coupling components.Quaternization at the heterocyclic nitrogen atommay occur before or after coupling. The azodye 184, from 2-methyl-5-aminobenzimidazoleand 1-phenyl-3-methyl-5-pyrazolone, used inthe form of its hydrochloride, dyes paper andleather in clear yellow shades [238].

184

By exhaustive alkylation, dyes are obtainedthat are suitable for polyacrylonitrile [239].

Introduction of halogen yields dyes with es-pecially valuable properties. A suitable diazocomponent is 4-amino-6-chlorobenzimidazole.The sequence of diazotization, coupling witharomatic amines, and quaternization gives col-orants (e.g., 185) [36116-31-1] that confer fastorange and red shades to polyacrylonitrile [240].

185

66 Azo Dyes

Trifluoromethyl-substituted aminobenzimid-azole compounds have also been described asdiazo components [241].

A bathochromic shift is obtained by us-ing 4-amino-6-chlorobenzotriazole in placeof the benzimidazole. The quaternized cou-pling products with dialkylanilines (e.g., 186)[36116-25-3] dye polyacrylonitrile in red shadeswith a blue cast [242].

186

Red dyes for polyacrylonitrile are obtainedwith 6- or 7-aminoindazole as the diazo compo-nent [243], (e.g., 187).

187

Other heterocyclic diazo components thathave been used to generate cationic dyesare 4-amino-7-nitrobenzisothiazole [244], 2-methyl-6-aminoquinoline [245], and 5-ami-noimidazo[1,2-a]pyridine compounds [246].

5.2.6. Cyclic Ammonium CompoundsLinked in Meta Position to the Azo Group

Coupling of diazotized N-heterocyclic aminocompounds that carry the amino group in the 2-or 4-position to the heterocyclic nitrogen to aro-matic or heterocyclic coupling components andsubsequent quaternization of the heterocyclic ni-trogen leads to diazacyanine dyes (→MethineDyes and Pigments).

If the starting materials are heterocyclic ami-no compounds with the amino group in ameta position, a mesomeric charge exchange isnot possible. Therefore, dyes of this type aregrouped with the cationic azo dyes.

By coupling of diazotized 3-aminopyridineto 2-naphthol, followed by quaternization, dyes(e.g., 188) [41313-61-5] are obtained that color

polyacrylonitrile in fast yellow shades and ex-hibit excellent leveling characteristics [247].

188

This dye is also recommended for dyeing ofhuman hair [248], as well as the dye containing2-methylindole as coupling component [249],[250].

5.3. Different Cationic Charges in Boththe Coupling and the Diazo Component

A further means to introduce different basicand/or cationic residues (cf. Sections 5.1.8 and5.2.4) into a dye has been developed by combin-ing diazo and coupling components that eachcarry different basic or cationic groups. Theyare synthesized according to the procedures thathave been described in Sections 5.1 and 5.2.

Dyes have been prepared that color paper inhues ranging from orange [251] (e.g., 189, seenext page)

to red [252–254] (e.g., 190)

190

to black [255] (e.g., 191)The yellow dye 192can be used in ink-jet systems to flocculate

anionic pigment dispersions, thus improving thebleedfastness [256], [257].

5.4. Introduction of CationicSubstituents into Preformed Azo Dyes

Cationic substituents may also be introducedinto preformed azo dyes. In this manner, mix-tures of isomers are obtained which may carry

Azo Dyes 67

189

191

192

193

one to four cationic groups in various positions.The multiplicity of isomers is a cause for goodwater solubility. These dyes are predominantlyused for coloring paper.

Reaction of chlorosulfonic acid with mono-[258] or disazo dyes [259] yields sulfonylchlorides, which can then be transformed intocationically substituted sulfonamides by reac-tion with dialkylaminoalkylamines. The cou-pling product of diazotized 2-anisidine with 2-hydroxynaphthoic acid arylide upon such treat-ment dyes paper red and the azo dye from tetraa-zotized dianisidine and 1-phenyl-3-methyl-5-pyrazolone gives yellowish orange shades.

Numerous cationic azo dyes are preparedby the action of N-hydroxymethylchloroacet-

amide on azo dyes in sulfuric acid medium, fol-lowed by displacement of the reactive chlorosubstituent by pyridine or trialkylamine. Of spe-cial significance for dyeing paper are dyes thatare prepared by coupling of diazotized 2-(4′-aminophenyl)−5-methylbenzothiazole to ace-toacetarylides, pyrazolones, naphthols [260], orbarbituric acid derivatives [261], followed byreaction with N-hydroxymethylchloroacetam-ide and pyridine or N-methyl-1,3-diaminopro-pane [262] . The azo dye obtained by ox-idative dimerization of 2-(4′-aminophenyl)−5-methylbenzothiazole may also be subjected tothis conversion [263]. Dye 193 colors paper yel-low.

68 Azo Dyes

194

195

Disazo dyes with β-naphthol as the couplingcomponent give red shades [264].

By removal of the chloroacetyl residue ami-nomethylated dyes are obtained which are usedfor coloring paper either as such or upon furtheralkylation [265]. An example is the yellow dye194.

Reaction of azo dyes with formaldehyde and4-methylimidazole, followed by alkylation, pro-duces cationic azo dyes that dye paper with ex-cellent wetfastness [266]. An example is the dis-azo dye 195, which confers a brilliant red shadeto paper.

A commercial product is Cartasol BrilliantYellow K-5GL (Clariant).

5.5. Cationic Dyes with Sulfur orPhosphorus as Charge-Carrying Atoms

When dyes containing anionically displaceablegroups are reacted with thioethers, cationic dyes(e.g., 196) are obtained in which the sulfoniummoiety carries the charge [267]. The sulfoniumgroupmay also be linked directly to the aromaticcoupling component [268].

196

By reacting dyes that contain a chloroethylgroup with thiourea, the cationic charge maybe introduced in the form of an isothiouroniumresidue (e.g., 197) [269].

197

To introduce phosphorus as the charge-carrying moiety, dyes that contain haloalkylgroups are reacted with phosphines, such as di-methylphenylphosphine (e.g., 198) [270].

198

5.6. Dyes with Releasable CationicGroups

Dyes with releasable cationic groups are con-verted to water-insoluble dyes when heated inthe dye bath. They can then enter textile mate-

Azo Dyes 69

rials that are amenable to dyeing with dispersedyes. Using this method, for instance, it is pos-sible to dye polyester materials without havingfirst to generate a finely dispersed form of thecolorant with the aid of surfactants. An exampleof such a releasable group is the isothiouroniummoiety [271]. Dyes with isothiouronium groupsare also suitable for wool [272].

Reaction of dyes containing a primary aminogroupwith dimethylformamide and an inorganicacid chloride, e.g., phosphoryl chloride, permitsintroductionof the formamidiniumgroup,whichis also scissionedoff uponheating in the dye bath(e.g., 199) [273].

199

A similar reaction occurs with the trialkylhy-drazinium moiety obtained by reacting formyl-substituted azo dyes with dialkylhydrazines andsubsequent quaternization [274].

6. Developing Dyes

General Survey. There is no standard defi-nition of the term developing dyes. They caninclude all dyes that are synthesized on the fiberor converted there into their final form. In thisrespect it is possible to distinguish between twomain groups:

Developing dyes whose final chromophoricsystem is synthesized on the fiber with for-mation of an insoluble dye. In the azo dye se-ries, thesemainly include theβ-naphthol andNaphtol AS dyes, which are directly synthe-sized on the fiber; the substrate impregnatedwith the coupling component is “developed”in a suitable diazonium salt solution. Whendyeing or printing the fiber, it is also possiblefor coupling component and diazo compo-nent to be applied simultaneously; not untilan aftertreatment is carried out is the cou-pling process then initiated.The diazotization dyes are also frequentlynumbered among this group (see Section

4.2.3). As a result of the diazotization of di-rect dyes with free amino groups and subse-quent reaction with suitable coupling com-ponents, an azodyeof highermolecularmasswith especially good adhesion is synthesizedon the fiber.Developing dyes from another dyeclass are the phthalocyanine develop-ing dyes (e.g., Phtalogen dyes (Bayer)→Phthalocyanines).Developing dyes whose color-impartingstructure is synthesized before they are ap-plied to the substrate in the form of solublederivatives; they are converted into an insol-uble form by aftertreatment on the fiber.These include the polycondensation dyes,in particular in the azo range, which con-tain thiosulfate groups (–S–SO3–) as water-solubilizing groups. In the presence of con-densing agents (e.g., sodium sulfide), thesecompounds undergo polycondensation onthe fiber to form insoluble dyes, S–S bridgesbeing formed at the same time (e.g., Inthiondyes from Hoechst) [275], [276].A further example is that of esterified Naph-tol AS dyes. If azo dyes formed fromNaphtolAS components and diazotized color basesare reacted with suitable acylation agentscontaining sulfo groups, soluble esters ofazo compounds, which can be applied to thefiber, are obtained.By saponification in an al-kaline medium the esters are then convertedon the fiber into insoluble dyes, e.g., Neoco-ton dyes (Ciba); Tinogenal dyes (Geigy) andNeogenol dyes (Sandoz) [277].

Developing dyes in the second group havenever been able tomaintain theirmarket positionover a lengthy period: they are only mentionedhere because their mode of action is of interestfrom the chemical aspect.

The first group of developing dyes, on theother hand, includes products ofmajor industrialinterest. Among all the developing dyes, by farthe greatest importance attaches to the insolubledyes known as Naphtol AS dyes, which are pro-duced on the fiber from 2-hydroxy-3-naphthoicacid amides and other carboxylic acid amidescapable of coupling (Naphtol AS components)and suitable diazo components. Only membersof this class of compounds are dealtwith in detail

70 Azo Dyes

in this chapter. In accordance with dyeing andperformance aspects they can be divided into

developing dyes for cottondeveloping dyes for animal fibersdeveloping dyes for hydrophobic fibers

The large number of dyeing and printingmethods used will be discussed under the key-words→Textile Dyeing and→Textile Printing.

6.1. Developing Dyes for Cotton [5,vol. III, p. 290], [42, vol. 1, p. 502], [278–280]

The principal fields of application are the dye-ing and printing of textiles made from cellulosicfibers (natural or regenerated), of which cottonis the main material. Cotton dyeing with devel-oping dyes was being practiced by the end ofthe 19th century (ice colors); it received a boostwith the introduction ofNaphtolAS componentsin 1911. Ten years later, the Rapid Fast range(see page 82) made possible an especially sim-ple method of application in the printing of cot-ton. Cotton dyeing and printing on the basis ofdeveloping dyes have now reached such an ad-vanced stage of development, and the dyeingsobtained possess such a high quality level, thatthis class of dye is likely to continue to maintainits market position in the future.

6.1.1. Developing Dyes for Dyeing

6.1.1.1. β-Naphthol Dyes

β-Naphthol dyes are only of historical inter-est. The initial results achieved in the dyeingof cotton by producing an azo dye on the fiberwere patented by Th. and R. Holliday (1880).They impregnated cotton with an alkaline so-lution of β-naphthol and, after drying, “devel-oped” the impregnated material by immersing itin an acetate-buffered solution of diazotized α-or β-naphthylamine. In particular the attractivered (para red) obtained by Gallois and Ull-rich (1889) using 4-nitroaniline as diazo com-ponent was for a long time of importance in thedyeing and textile printing industries. The intro-duction of further suitable diazo components ledto a whole range of shades in these “ice colors”

(so-called because of the ice used during diazo-tization); see Table 12.

Table 12. Amines for the development of cotton impregnated withβ-naphthol and shades obtained

5-Nitro-2-aminotoluene orange5-Nitro-2-aminoanisole pink4-Chloro-2-aminoanisole scarlet4-Nitroaniline red1-Naphthylamine bordeaux3,3′-Dimethoxy-4,4′-diaminodiphenyl(with Cu salts) blue

3,3′-Dimethyl-4,4′-diaminodiphenyl brownMixture of 4,4′-diaminodiphenylamineand 4-dimethylamino-4′-aminoazobenzene black

Numerous disadvantages of β-naphthol dye-ing (difficulty in obtaining uniform fixation ofthe coupling component when drying materialimpregnated with β-naphthol; very limited fast-ness of the dyeings to light, chlorine, washing,and rubbing) pushed subsequent developmentsin the direction of the so-calledNaphtolASdyes.

6.1.1.2. Naphtol AS Dyes

In Offenbach (now Hoechst) in 1911,A. Winther, L. Laska, and A. Zitscher dis-covered that instead of β-naphthol it is moreadvantageous to use the anilide of 2-hydroxy-3-naphthoic acid, listed in the technical literatureunder its trade nameNaphtol AS;AS is short for“Amid einer Saure” (amide of an acid). Com-pared with that of β-naphthol, the sodium saltof this coupling component possesses the greatadvantage of having a certain degree of substan-tivity, i.e., it is absorbed onto the cotton fiber likea direct dye. Uniform fixation on the substrate isthus guaranteed. Moreover, in comparison withβ-naphthol, the alkaline solutions ofNaphtolASpossess higher air resistance, with the result thatthe moist cotton fibers impregnated with it canbe exposed to air for a prolonged period withoutundergoing a change. The dyeings obtained onthe fiber after development with suitable diazocomponents are distinguished by a high fastnesslevel.

With the development of a large number ofsubstituted anilides of 2-hydroxy-3-naphthoicacid (known as “β-oxynaphthoic acid arylides”)and related compounds as Naphtol AS cou-pling components (the various products are de-noted by additional letters following theAS) anda selection of suitable aromatic amines (“Fast

Azo Dyes 71

Color Bases”) and their stabilized diazoniumsalts (“Fast Color Salts”) as diazo components,the Naphtol AS dyeing sector underwent rapidexpansion.

World production of Naphtol AS compo-nents, Fast Color Bases, and Fast Color Salts fordyeing and printing of cellulosic fibers amountsin 1982 to approx. 24000 t (around 6000 t are inaddition used for production of azo pigments).This is equivalent to just under 5 % of colorantconsumption in the textile sector as a whole, al-though as a result of a decrease in the proportionof world fibers demand accounted for by cotton,a declining trend can be observed in the percent-age rate.

The percentage of Naphtol AS developingdyes in the dyestuffs requirement for textilesmade from cellulosic fibers has for years re-mained constant at around 8%, although the useof reactive dyes, particularly since the start of the1970s, has gained increasingly in importance.Around 60 % of Naphtol AS dyes are employedfor dyeing, around 40 % in the printing sector.

Table 13 provides a survey of the most im-portant ranges of coupling and diazo compo-nents for Naphtol AS dyeing (and printing). Themanufacturing countries are combined into threelarge groups: Western Europe and USA, Indiaand Japan, and the state-trading countries. Thefirst group accounts for about 50%of productionvolume, and the other two have approximatelyequal importance.

The trade names indicate that the spellingNaphtol AS is reserved for the Hoechst range.Naphthol AS components belong to otherranges. The Hoechst spelling is the one mainlyused below.

Coupling Components. The following fac-tors were of major importance to the rapid de-velopment of numerous new coupling compo-nents and their use in cotton dyeing: a sim-ple synthesis process for substituted 2-hydroxy-3-naphthoic acid aryl amides, improved dye-ing properties (substantivity, fastness, shades forcombinations), and reduction in the sensitivityof the moist impregnated material to air.

2-Hydroxy-3-naphthoic acid can be pro-duced under pressure by reaction of carbon diox-ide with the sodium salt of β-naphthol (Kolbe-Schmitt synthesis). The aryl amides are obtainedby one-step reaction, 0.4 – 0.5 equivalents of

phosphorus trichloride being added slowly at70 – 80 ◦C to a mixture of one equivalent eachof carboxylic acid and amine in an inert solvent(usually toluene and polychloroalkanes). The re-actionmixture is then boiled for some hours and,after cooling, treated with soda to remove theacid. The Naphtol AS compound is filtered off,the solvent recovered.Theyield is almost quanti-tative. The addition of formaldehyde to alkalinesolutions of 2-hydroxy-3-naphthoic acid amidesimproves the air stability of the damp impregna-tions. The stabilizing action of the formaldehydecan be explained by the reversible formation ofhydroxymethyl compounds, the sodium salts ofwhich possess improved hydrolysis resistance.

By varying the substituents in the aryl amideradical and in the hydroxynaphthoic acidmoiety,a wide range of coupling components was syn-thesized.The substituents naturally influence theshade and fastness properties of the azo dyes ob-tained after development. For example, the in-troduction of alkoxy groups in the aryl amideradical has a favorable influence on light fast-ness.

With the commercial products compiled inTables 14 and 15, the shades obtained with dia-zotized color bases, such as chloro- or nitroani-lines, are almost always orange, red, or bor-deaux. Therefore, these Naphtol AS derivativescan also be referred to as “Red Naphtols.”

The classification principle used in the Ta-bles is largely that adopted in the Colour Index[7], which is based on the chemical constitution.The trade names aremainly those of the Hoechstrange, since as a result of the historical develop-ment, the field of Naphtol AS developing dyesis an undisputed domain of this manufacturer. Anumber of compounds are listed under the dif-ferent designations of other manufacturers (e.g.,Naphthol, Naphtanilid). Only in some cases dothe letter combinations in the trade names of dif-ferent firms agree with regard to one and thesame compound.

Whereas with 2-hydroxy-3-naphthoic acidamides, only red shades (apart from a few red-dish brown shades) can be obtained by varyingthe aryl amide radical in combination with sim-ple diazo compounds, coupling components de-rived from o-hydroxycarboxylic acids of otherring systems yield brown and black shades.Here, derivatives of carbazolecarboxylic acid

72 Azo Dyes

Table 13. Trade names of important coupling components and diazo components for Naphtol AS dyeing and their manufacturers

Country Manufacturer C. I. Azoic Cou- C. I. Azoic Diazo Component

pling Component Bases Stabilized salts

Germany, Hoechst Naphtol AS- Echt-Base Echt-SalzFed. Rep. Azanil-Salz

Variaminblau

Switzerland Rohner Naphtanilid Fast Base Diazo Fast

USA Blackman Uhler Naphtol AS- Fast Base Fast SaltPfister Chem. Naphtol AS- Azoene Fast Base Azoene Fast Salt

India Amar Dye Amarthol AS- Amarthol Fast Base Amarthol Fast SaltAtul Prod. Tulathol AS- Tulabase Fast –

Japan Daito Chem. Ind. Daito Grounder Daito Base Daito SaltSanyo Colour Works Sanatol Sanyo Fast Base Sanyo Fast SaltSumitomo Naphthoide (Fast) Base SaltShowa Chem. Co. Kako Grounder Kako Base Kako Salt

China, P.R. Youhaothol AS- Fast Base Fast SaltYouhaoriamin Blue

Czech Rep. Ultrazol Fast Base Fast Salt

Poland Ciech Naphtoelan Naphtoelan Fast Base Naphtoelan (Fast) Salt

fromer Soviet Union Azotol Azoamin Diazol

and dibenzofurancarboxylic acid are of partic-ular importance (see Table 16).

Yellow dyeings are not obtainable by combi-nation of o-hydroxyarylcarboxylic acid amideswith color bases. The coupling componentsused for yellow shades are derived from acetyl-and benzoylacetic acid amides. Although in thechemical sense they are therefore not naphtholderivatives, they are classified as Naphtol AScomponents and in accordance with their col-oristic properties are often called “YellowNaph-tols” (Table 17).

In contrast to the red Naphtols (Tables 14 and15) and heterocyclic coupling components (Ta-ble 16), the yellowNaphtols are stable in alkalinesolution; therefore, no addition of formaldehydeis necessary, and because of side reactions it iseven inadmissible.

Apart from the coupling components listed inthe tables, mention should also be made of thosethat as a special structural characteristic containazo groups, e.g., Naphthol AS-BN (BlackmanUhler) (C. I. Azoic Coupling Component 43, ex-act constitution not as yet published).

An interesting development during the six-ties was Naphtol AS-FGGR (Bayer) (C. I. AzoicCoupling Component 108): the condensation

product of a blue dye (nickel phthalocyaninesulfochloride) and a coupling component in theyellow range (aminophenyl pyrazolone deriva-tive) yields in combination with suitable diazocomponents brilliant yellowish greens with out-standing light fastness [281]. Since the couplingcomponent possesses virtually no affinity for thecellulosic fiber, the product was mainly used fortextile printing by the Rapidogen process (seepage 83). Green dyeings are now obtained al-most exclusively by combination of phthalocya-nine developing dyes, e.g., Phtalogen (Bayer),with yellow Naphtol AS dyes.

Diazo Components. A large number of dia-zotizable aromatic amines are available for azoiccoupling with the coupling component (see Ta-ble 18). The diazo components are sold eitheras nondiazotizable bases, so-called “Fast ColorBases” (both as free amines, if they are stableand nontoxic, and as hydrochlorides or sulfates),or as stabilized diazonium salts, so-called “FastColor Salts” (for trade names see Table 13).The diazonium compounds are isolated (“pre-cipitated”) in the form of chlorides, sulfates, hy-drogen sulfates, double salts of zinc chloride,fluoroborates, oxalates, and neutral or acid 1,5-

Azo Dyes 73

Table 14. Naphthol AS components: 2-hydroxy-3-naphthoic acid amides

74 Azo Dyes

Table 14. (Continued)

∗ A former Hoechst product, no longer manufactured by any company.

naphthalenedisulfonates and other aromatic sul-fonates, the optimum conditions depending onthe type of base. Final stabilization is achievedby mixing (“adjusting”) with inert salts (usuallyaluminum sulfate). For further details→DiazoCompounds.

With the diazo components, too, the chemi-cal constitution naturally has a great influenceon fastness properties and shade of the dyeingobtained with a coupling component. It has beenfound that negative substituents (halogens, nitro,nitrile, RO2S, and, in particular, CF3 groups) inthe aromatic nucleus exert a favorable influenceon light fastness. In addition to suitable substi-tuted aniline derivatives, which in combinationwith 2-hydroxy-3-naphthoic acid amides almostwithout exception yield red shades (orange, red,bordeaux), color bases have been developed

that can be combined with the same NaphtolAS components to give blue and violet shades.Here, chief mention can be made of: N-aroyl-p-phenylenediamine derivatives, which containno negative substituents, and 4-aminodiphenyl-amine derivatives. With compounds of the lattertype (Variamin Blue bases and salts; Hoechst)attractive blue shades are obtained and in com-bination with Naphtol AS-GR (C. I. Azoic Cou-pling Component 36, 37585; see Table 16) greendyeings as well. 4-Aminoazobenzene deriva-tives produce black dyeings in combinationwithRed Naphtols.

The diazo components compiled in Table 18have been classified first by coloristic aspects(shades) and second by constitutional character-istics (in accordance with the Colour Index [7]).The shades specified in the trade names relate,

Azo Dyes 75

Table 15. Naphthol AS components: derivatives of 2-hydroxy-3-naphthoic acid amides

with only a few exceptions to the dyeings ob-tained with Red Naphtols.

Basically speaking it is possible for the dyerto combine any aromatic base with any Naph-tol AS component. However, only a limited se-lection of all conceivable combinations fulfilthe preconditions for a coloristically high-gradedyeing. The dyeings generally possess high fast-ness to rubbing, washing, chlorine, and light.Many of the Naphtol AS dyes obtained on thefiber attain fastness levels of Indanthren dyes,without being chemically related to these com-pounds, which are usually polycyclic (examplessee Table 19).

Other Developments. A new developmentin Naphtol AS dyeing, which commenced atthe start of the 1960s, utilized the tendency ofcertain azo dyes to form metal complexes. Het-eroaromatic amines that fulfil certain structuralpre-conditions (see Section 2.3.4) are used as di-azo components and the dyeings obtained on thefiber with Naphtol AS components by the usualmethod are converted into especially lightfastmetal complex dyeings by aftertreatment withheavy-metal salts (copper, cobalt):

C. I. Azoic Diazo Components 135 – 137(bases I, II, III fromHoechst, nowwithdrawn bythe manufacturer on price grounds) [282–284],[15, p. 676].

A further development concerns improve-ment in the dyeing methods. The conventionaltwo-bath technique (impregnation of the mate-rial with the alkaline solution of the substantivecoupling component, removal of the excess, andsubsequent treatment with the diazonium saltsolution) can often be considerably simplifiedand shortened by using the so-called one-bathmethod: a highly substantive Naphtol AS im-pregnating component and the developing com-ponent are prepared together in one bath. Notuntil the acid has been added is formation of thedye initiated. Diazo components suitable for thispurpose consist of a diazoamino compound not

76 Azo Dyes

Table 16. Naphthol AS components: o-hydroxy compounds of polycondensed and heterocyclic arylcarboxylic acid amides

capable of coupling in the neutral and alkalinerange, which in the presence of acid is regener-ated into the active diazonium salt (see Section6.1.2). The addition of dispersing agents to thedeveloping component ensures that the insolu-ble dye formed in the liquor remains in colloidaldispersion and can be removed during the subse-quent washing process (Azanil Color Salts fromHoechst) [285–288].

The introduction of liquid brands of azoiccoupling components and azoic diazo compo-nents results in a considerable simplificationof important steps in the dyeing and printingwith Naphtol AS developing dyes. The for-mer are 25 – 45 % solutions of monoalkali saltsof Naphtol AS components in high-boiling al-cohols (usually ethylene or diethylene glycol)miscible with water. These highly concentratedmolecular solutions with good storage stabil-ity permit dust-free handling of the couplingcomponent and enable ready-to-use impregnat-ing baths to be prepared especially quickly by

simply pouring in the relevant liquid brand intoaqueous diluted sodium hydroxide solution. Theliquid brands of the diazo components are ei-ther molecular solutions or dispersions: aro-matic amines with low melting points (downto approx. 80 ◦C) are dissolved as free basesin monoalkyl ethers of diethylene glycol (oc-casionally with the addition of dimethylsulf-oxide or N-methylpyrrolidone); higher meltingamines (mp above 100 ◦C) can in the presenceof suitable surfactants and other auxiliaries (eth-ylene glycol, glycerol, or sorbitol) be processedin more highly concentrated dispersions. Apartfrom dust-free handling, all liquid brands of di-azo components are distinguished by particu-larly rapid and complete diazotizability withouttroublesome side reactions [289] (see also page82).

Azo Dyes 77

Table 17. Naphthol AS components: acylacetic acid amides

6.1.2. Developing Dyes for Printing [5,vol. III, p. 290 – 301], [278–280], [290]

For details of the printing method →TextilePrinting.

Two-Stage Printing Processes. As with thedyeing of cotton fibers, two-stage methods canalso be employed when printing. Depending onwhether the coupling component (as sodiumsalt) or the diazo component (as diazonium salt)is applied during the printing process, a distinc-tion is made between naphtholate printing pro-cesses and base printing processes.

In the naphtholate printing process, thesodium salts of the Naphtol AS compounds inthe form of aqueous, thick pastes (additions ofhigh-swelling, nonionic or anionic polysaccha-rides) are printed on the textile material and thendeveloped as azo dyes on the fiber by treatmentwith the solution of a diazotized base.

Naphtholate printing has always been of onlysecondary importance.

In the so-called base printing process, thecellulosic material is first impregnated with the

solution of a sodium naphtholate and, after dry-ing, the thickened solution of the diazotized FastColor Base is printed onto the material.

In contrast to cotton dyeing, with the wide di-versity of Naphtol AS derivatives that are used,price, coloristic, and substantivity reasons dic-tate that only two components capable of cou-pling are in the main used for impregnation ofthe textile to be printed: Naphtol AS (C. I. Cou-pling Component 2, 37505, see Table 14) as redcomponent and Naphtol AS-G (C. I. CouplingComponent 5, 37610, see Table 17) as yellowcomponent. The cotton impregnated with thesodium salts of these Naphtols by padding andsubsequent drying has good, if only limited, sta-bility when stored in a cool, dark place. Becauseof their low substantivity for the cellulosic fiber,Naphtol AS and Naphtol AS-G additionally sat-isfy the important requirement that after the baseprinting process they can be completely washedoff again from the unprinted parts.

By combining the two Naphtols with numer-ous azoic diazo components, a relatively widerange of printed shades is possible. The addi-tion of Naphtol AS enables shades in the or-

78 Azo Dyes

Table 18. Color bases and color salts

Azo Dyes 79

Table 18. (Continued)

80 Azo Dyes

Table 18. (Continued)

Azo Dyes 81

Table 18. (Continued)

82 Azo Dyes

ange, scarlet, red, bordeaux, violet, navy blue,and black range to be obtained, Naphtol AS-Gis used in the yellow to brown range. If higher re-quirements must bemet with regard to light fast-ness, Naphtol AS-G can be replaced by NaphtolAS-IRG (C. I. Coupling Component 41, 37613,see Table 17).

Right into the 1940s, the base printing pro-cess enjoyed considerable industrial impor-tance, but in comparison with the one-stage pro-cess it then receded into the background. Thedevelopment of reactive dyes resulted in aworld-wide revival of the two-stage base printing pro-cess, because vinyl sulfone dyes, in particular,can in many cases be applied together with colorsalts or diazotized color bases. The possibilityof printing a broader range of shades on cot-ton, which had long been desired, can thus beachieved [291].

The additional combination of the yellow togolden yellow azoic developing dyes with theblue phthalocyanine developing dyes, in par-ticular with a cobalt-phthalocyanine derivativeof clear, dark blue color (C. I. Ingrain Blue 5,Phtalogen Blue IBN [37370-33-5] from Bayer)makes it possible to match deep green shadesand thus close a gap in the color range.

These subsequent developments have re-sulted in the base printingmethod acquiring con-siderable importance, in particular for so-calledAfrican and Java prints.

Other Developments. In the conventionaldiazotizing process, the differences in the re-activity of aromatic amines frequently lead tothe uncontrolled release of nitrous gases and un-desired side reactions, in spite of the fact thatice is used. With the use of liquid brands (seepage 75) instead of the powder of the free base,it was possible to increase the rate of diazo-tization considerably and to eliminate the for-mation of byproducts. A further refinement ofthis technique led to an especially elegant vari-ation of the base printing process, the so-calledDIP process (“Diazotization in the paste”): theaqueous – alcoholic dispersion or molecular so-lution of the base is stirred into a paste of sodiumnitrite which without being cooled is thenmixedwith the aqueous paste of a medium-strong acid(it is best to use phosphoric acid). Diazotationis completed quickly without any formation ofnitrous gases. The diazo salt paste obtained no

longer needs to be buffered; during the subse-quent printing process it couples rapidly andcompletely with the Naphtol in the impregnatedfabric [289], [292].

The possibility of diazotizingmixtures of dif-ferent azoic diazo components at the same timein a single paste has proved to be a particular ad-vantage of the diazotization process described.The use of mixed coupling products thus openedup a further possible method of shade matching.

One-Stage Printing Processes. Especiallysimple methods of printing cotton fibers weredeveloped using the one-stage direct printingprocess. In this technique, the diazo componentin the form of a stabilized diazo compound, i.e.,not initially capable of coupling, is applied atthe same time as the coupling component andcoupling is then initiated by a damp aftertreat-ment in an acidmedium or by acid, or frequentlyalso neutral steaming.

Three different diazo derivatives are em-ployed in textile printing as stabilized diazocompounds (a more appropriate term is con-cealed diazo compounds): antidiazotates, di-azo sulfonates, and diazoamino compounds(for properties and production →Diazo Com-pounds).

Combinations with diazoamino compoundswere of particular industrial importance, butwith the appearance of the reactive dyes, they,too, receded into the background.

Because of its relatively complicated chem-ical background, the one-stage printing processmust be dealt with in somewhat more detail.

Combinations with Antidiazotates. Un-like the unstable syndiazotates, the stable antidi-azotates do not couple with alkaline β-naphtholsolution, or if so only very slowly.

Not until the acid treatment is carried outis the diazonium ion formed with subsequentrapid azo coupling. This fact acquired impor-tance in textile printing, diazotates of weaklybasic, mainly chlorinated amines being used in

Azo Dyes 83

particular, because of their good stability anddevelopment ability.

Antidiazotates are obtained in a simple man-ner by introducing a diazonium salt solution intoconcentrated aqueous alkali and heating to tem-peratures above 100 ◦C, whereby the syndiazo-tate formed initially is rearranged into the anticompound.

Mixtures of sodium salts of 2-hydroxy-3-naphthoic acid amides and other coupling com-ponents in the Naphtol AS range with antidia-zotates in the form of pastes and powder brandshave been marketed since 1921 as Rapid Fastdyes. If the fibers impregnated or printed withthem undergo an acid aftertreatment, regenera-tion of the active diazonium salt and couplingof the azo dye take place on the substrate. Anumber of combinations and the shades obtainedwith them are compiled in Table 20, consider-able importance attaching in particular to RapidFast Blue BN.

Table 19.Combinations for developing dyes in theNaphtolAS rangewith high fastness properties

Naphtol Color base Dyeingobtained

AS-L4G Fast Orange RD yellowAS-OL Fast Orange GGD orangeAS-OL Fast Scarlet GGS scarletAS-LT Fast Scarlet LG redAS-ITR Fast Red ITR redAS-ITR Fast Bordeaux BD bordeauxAS-E Variamin Blue FGC blueAS-FGGR Fast Yellow GC greenAS-BT Fast Scarlet TR brownAS-SG Fast Red B black

Table 20. Examples of printing combinations with antidiazotates

Dye Antidiazotate of Couplingcomponent

Rapid Fast Yellow GH Fast Scarlet GG Base Naphtol AS-GRapid Fast Orange RH Fast Scarlet GG Base Naphtol AS-PHRapid Fast Red RH Fast Red RC Base Naphtol AS-OLRapid Fast BordeauxRH

Fast Red R Base Naphtol AS-BS

Rapid Fast Blue BN Fast Blue B Base Naphtol ASRapid Fast Brown IBH Fast Red R Base Naphtol AS-LB

The generally limited storage stability of themixtures has proved to be a disadvantage of theprocess described, because slow splitting of theantidiazotate takes place in the alkaline printingpaste.

Combinations with Diazosulfonates. Dia-zosulfonates Ar−N=N−SO−

3 , obtained by re-action of diazonium salts with sulfites, do notcouple in their stable anti form with 2-hydroxy-3-naphthoic acid amides, or if so only slowly.The diazonium compound capable of couplingis reformed when exposed to light or when thetemperature increases.

The Rapidazol dye range introduced in 1932utilizes this property: ready-to-use mixtures ofdiazosulfonates, in particular from the 4-ami-nodiphenylamine range (Variamin Blue bases,see Table 18), with coupling components of theNaphtol AS type are printed on the fiber andthen developed into azo dyes in neutral steam,especially in the presence of oxidizing agents.

In spite of its limited color scale, the range,with its high-quality blue and black brands, wasa welcome addition to the diazotate mixtures.It was especially important at a time when nodiazoamino compounds capable of being devel-oped in a neutral medium were available.

Combinations with Diazoamino Com-pounds [6, p. 177]. Among the Naphtol AScombinations for printing, it is the stablediazoamino compounds that are mainly used.Since the release (1930) of the first Rapidogendyes up to the worldwide introduction of the re-active dyes, standardizedmixtures of these com-binations had enjoyed major industrial impor-tance. The most important commercial rangesbased on diazoamino compounds are compiledin Table 21.

Table 21. Designations of important ranges of Naphtol AS printingcombinations with diazoamino compounds

Country Manufacturer Ranges

Germany, Bayer RapidogenFed. Rep.

France ICI-Francolor NeutrogenSwitzerland Rohner Ronagen, SinagenUSA Blackman Uhler Printing

Pfister Chem. Azogen

India Amar Dye StabageneAtul Prod. Tulagene

Japan Kiwa Chem. Ind. PolydogenSanyo Col. Works ThiugenSumitomo Sumika Fast

Poland Pologen

Diazoamino compounds (further details→Diazo Compounds) are obtained by reacting

84 Azo Dyes

a diazonium salt (200) with a primary or sec-ondary aliphatic or aromatic amine:

In the case of aromatic amines, the diazoami-no compound only forms if blocking or deacti-vation of the coupling positions in the aromaticnucleus prevents the formation of an aminoazocompound. The reaction (13) is reversible, i.e.the addition of acid causes the diazoamino com-pounds to be split again into their initial compo-nents. If a primary amine R–NH2 (201) is used,the resulting triazene (202) is in balance with itstautomer (202a):

The splitting process can thus lead to the for-mation of a new diazonium salt (201a) (“redia-zotization”).

The tautomer equilibrium 202� 202a is de-pendent on the nature of the two radicals Arand R: as the basicity of amine Ar−NH2 (200a)increases and that of amine R−NH2 (201) de-creases, the equilibrium shifts in favor of thediazoamino compound (202), which is split inthe desired manner to form the original diazo-nium salt.

For practical usage as a stabilized diazocompound in printing combinations, only thosediazoamino compounds are suitable that satisfythe following conditions:

Well-defined splitting without rediazotiza-tion.No possibility for the diazonium salt ob-tained after splitting to couplewith the aminecomponent.Solubility of the diazoamino compound inwater.

As amine component, the so-called stabilizer,use is thus generally made of non-diazotizablesecondary amines, or the equilibrium is influ-enced by 2nd order substituents in the stabiliz-ing amine (decreasing basicity). When aromaticstabilizers are used, the o- and p-position in re-lation to the amino group is usually blocked bysubstituents, with the result that after splitting ofthe diazoamino compound no coupling to ami-noazo products can occur. If a possible couplingposition is free, the azo coupling is handicappedby the deactivating influence of carboxylic acidor sulfonic acid groups. These substituents ad-ditionally impart the desired water solubility tothe diazoamino compound used in the printingcombinations.

Stabilizers frequently used are sarcosine, N-methyltaurine and anthranilic acid derivatives:

Sarcosine N-Methyltaurine

Anthranilic acid derivatives

The diazoamino compound (for further de-tails→DiazoCompounds) is generally obtainedby adding a diazonium salt solution to the neu-tral or alkaline solution of the stabilizer in theform of its sodium salt. The reactivity of the di-azonium salt determines the speed of the reac-tion. The diazoamino compound precipitated orsalted out is filtered, dried, ground, and adjustedwith the sodium salt of a Naphtol AS compo-nent.

After the textile fabric has been printed withthe printing combination, the dyeing is devel-oped by acid steaming (in the presence of aceticand formic acid vapors). The reaction of the twosoluble components on the fiber to form the in-soluble azo dye is illustrated by the example ofRapidogen Red GS (205).

Azo Dyes 85

203: Diazoamino compound of Fast Red KB base and sar-cosine.204: Naphtol AS-D

The diversity of combinations on the marketmakes it possible to obtain dyeings of any shadefrom greenish yellow through orange, scarlet,red, bordeaux, violet, blue, green to black.

The need for acid development has occasion-ally proved to be a certain disadvantage. Thisstep can be avoided by using a steam-volatileorganic base, such as diethylaminoethanol, in-stead of the alkali employed in the NaphtolAS diazoamino combinations. During neutralsteaming, the alkali component in the printingmixture then escapes and azo coupling takesplace, especially in the presence of salts whichin the steam undergo hydrolysis to form com-pounds with an acid reaction (e.g., ammoniumor pyridinium salts). Selection of suitable modi-fied stabilizers, such as 206 or 207, also enablesthe splitting tendency of the diazoamino com-pounds to be so carefully “counterbalanced” thatthe relevant printing combinations can be devel-oped in neutral steam (Rapidogen N, Neutrogendyes, etc., see Table 21).

206

207

For use of diazoamino compounds for thedyeing of cotton, see page 77, and of syntheticpolyamide fibers, see Section 6.3.

6.2. Developing Dyes for Animal Fibers

Compared with the dyeing and printing of hy-drophilic cellulosic fibers, the dyeing of animalfibers (protein fibers) with products in the Naph-tol AS range has never attained industrial im-portance. In this connection, mention is madehere only of theHoechst ranges ofOfna-Lan andRauna dyes, which are no longer on the marketandwere used for the dyeing ofwool – cellulosicblends and furs. The problem with this dyeingmethod proved to be the alkalinity of the impreg-nating baths (alkaline solutions of the NaphtolAS coupling components), because of the sen-sitivity to hydrolysis of the peptide compoundsof animal fibers [293].

Pure silk can be dyed in the same way as cel-lulosic fibers, since, unlike wool, silk is largelyinsensitive to alkali.

6.3. Developing Dyes for HydrophobicFibers

Naphtol AS dyes have also been used com-mercially for dyeing hydrophobic syntheticfibers, particularly polyester and polyamide.Two methods were developed [294]:

In the modified azo process, the couplingcomponent and the azoic diazo component areapplied to the fiber consecutively or from anaqueous bath at 80 – 130 ◦C, if necessary in thepresence of a carrier, and the fiber impregnatedby this means is then treated with nitrous acid.Development of the dyeing takes place with di-azotization and simultaneous coupling.

Products are being introduced that in the op-timum mixture ratio contain selected combina-tions of coupling and diazo components capa-ble of development (Intramin dyes, Hoechst;Ronasyn dyes,Rohner). The process only gainedimportance in the inexpensive black dyeing ofpolyester fibers (C. I. Azoic Black 16, e.g., In-tramin Black G, Hoechst). Multicolored shadesare more advantageously obtained with dispersedyes.

86 Azo Dyes

When using diazoamino compounds (so-called Ofnaperl process, Hoechst) a suitablediazoamino compound is added to the alkalinebath, in which the Naphtol AS component is dis-solved. After the fiber is impregnated in this bathat 60 – 80 ◦C, the development process is initi-ated in the warm acid bath by liberating the con-cealed diazonium salt. Unlike the components ofthe printing combination, the diazoamino com-pounds used contain no carboxylic acid or sul-fonic acid groups; theyhaveonly limited solubil-ity in water but must be readily dispersible (C. I.Azoic Diazo Components 127, 128, and 130,Of-naperl Salts, Hoechst). The process has provedespecially effective for the dyeing of polyamidefibers (perlon, nylon).

7. Disperse Azo Dyes (→Disperse Dyes)

Disperse dyes are dyes sparingly soluble in wa-ter which are used for dyeing synthetic fibers.The dyes are added to the aqueous dye bath infinely dispersed form and are uptaken out of thisdispersion by the hydrophobic fiber.

Thefiber hereby represents the organic phase,in which the disperse dyes are more soluble thanin the aqueous dyebath.

About half of all disperse dyes belong to theazo range. Originally developed for cellulose ac-etate fibers, disperse dyes are nowadays used inlarge quantities for dyeing polyester fibers.

8. Azo Pigments (→Pigments, Organic)

Pigments are coloring matters that are practi-cally insoluble in the application media (DIN55944). Coloring matters are all color-spendingmaterials according to DIN 55945.

Azo pigments are the most important classwithin the group of organic pigments. Mono-and disazo pigments are the two main ranges.

Whereas in English a strict differentia-tion exists between pigments (insoluble color-ing matters) and dyes (soluble coloring mat-ters) in German some confusing terms arestill occasionally used, e.g., “Pigmentfarb-stoffe”, “Korperfarben”, “Farbkorper”, “Lack-farbstoffe”. These terms should be discontinuedand only “pigments” and “dyes” used.

Azo pigments, like all other organic pig-ments, serve for the coloration of polymericmaterials such as plastics, elastomers, rubber,paints and other coating materials, and for print-ing pastes. The relatively inexpensive azo pig-ments have gained noticeable importance due tothe rapid economic and industrial developmentin the past three decades.

9. Alcohol- and Ester-Soluble Dyes

With the exception of the blue copper phthalo-cyanine derivatives, these products are azo dyessoluble in polar solvents, such as alcohols, gly-cols, esters, glycol ethers, and ketones. Dyessoluble in alcohol and esters are used in protec-tive lacquers for the transparent coating of metal(aluminum) foils and other materials, such aswood (greening lacquers); in flexographic inksfor the printing of metal foils, cellophane andpaper; as well as for the coloration of celluloseesters, celluloid, and poly(vinyl acetates), and,in the office supplies sector, for stamping inksand pastes for pressure recorders. See Table 22for important product ranges.

Table 22. Designation of important alcohol- and ester-soluble dyeranges

Manufacturer Range

BASF Neozapon, Zapon FastBayer Irisol FastCiba-Geigy Grasol Fast, Irgacet, Oracet, OrasolGAF Azosol FastICI MethasolSandoz Savinyl

In modern formulations for foil lacquers,dyes with better solubility in esters are givenpreference over the older products, which aremainly soluble in alcohols. As regards chemicalconstitution, there is no precise delineation bet-ween alcohol- and ester-soluble dyes, nor bet-ween these two groups and the fat- and oil-soluble dyes described in Chapter 10.

In accordance with chemical aspects, themost important alcohol- and ester-soluble azodyes can be divided into three groups:

1 : 2 Metal complexes of (mainly mono-) azo dyes, without sulfonic or carboxylicacid groups, and trivalent metals (→Metal-Complex Dyes).

Azo Dyes 87

The metals chiefly suitable are chromiumand cobalt, as well as nickel, manganese,iron, or aluminum. Diazo components aremainly chloro- and nitroaminophenols oraminophenol sulfonamides, coupling com-ponents are β-naphthol, resorcinol, and 1-phenyl-3-methlylpyrazolone (5). Formationof a complex from an azo dye and a metallicsalt generally takes place in the presence oforganic solvents, such as alcohols, pyridine,or formamide. An example is C. I. SolventRed, 12715 (208) [33270-70-1].

208

1 : 1 Metal-complex azo dyes that containsulfonic acid or carboxylic acid groups andare present in the form of internal salts. Here,azamethin –metal complexes are also of im-portance. An examples is C. I. Solvent Yel-low 32, 48045 (209) [61931-84-8].

209

In the case of C. I. Solvent Orange 56, sim-ilar to 18745 : 1 [13463-42-8], also a metalcomplex, diazotized 2-hydroxy-3-amino-5-nitrobenzene sulfonic acid is coupled to 1-phenyl-3-methylpyrazolone (5).C. I. Solvent Yellow 82, similar to 18690, isa 1 : 1 metal complex of the azo dye ob-tained from anthranilic acid and 1-phenyl-3-methylpyrazolone (5).Reaction products of acid azo dyes, acid 1 : 1metal-complex azo dyes, or 1 : 2 metal com-plex azo dyes without acid groups, with or-ganic bases or cationic dyes.

Cyclohexylamine, dodecylamine, and sul-fonium or phosphonium compounds serveas bases, whereas derivatives of the xan-thene range (rhodamines) are mainly usedas cationic dyes. Example: C. I. Solvent Red109 [53802-03-2] is composed of SolventYellow 19, 13 900 : 1, (210) [10343-55-2]and Solvent Red 49, 45 170 : 1, (211)[81-88-9]:

210

211

These dyes are saltlike compounds of ametal-complex azo dye acid and a base.

10. Fat- and Oil-Soluble Dyes

Fat- and oil-soluble dyes are also soluble inwaxes, resins, lacquers, hydrocarbons, halo-genated hydrocarbons, ethers, and alcohols, butnot in water. It is not possible to differentiateclearly between them and the alcohol- and ester-soluble dyes (see Chap. 9).

Table 23. Designations of important fat- and oil-soluble dye ranges

Manufacturer Range

Amer. Cyanamid CalcoBASF SudanBayer CeresBitterfeld SudanDu Pont OilEthyl Corp. Oil SolubleHoechst FatICI WaxolineSiegle Sico FatWilliams Oil

With the exception of the blue anthraquinonederivatives, all fat- and oil-soluble dyes belong

88 Azo Dyes

to the azo range. These azo dyes are gener-ally based on simple components. According totheir degree of solubility they usually containhydroxy and/or amino groups, but not sulfonicacid and carboxylic acid groups. See Table 23for important product ranges.

As examples, mention can be made of someof the most important fat- and oil-soluble azodyes produced on an industrial scale: C. I. Sol-vent Yellow 56, 11021 (212) [2481-94-9]

212

C. I. Solvent Yellow 14, 12055 (Orange) (213)[842-07-9]

213

C. I. Solvent Yellow 16, 12700 (214) [4314-14-1]

214

C. I. Solvent Red 23, 26100 (215; R =H)[85-86-9]; C. I. Solvent Red 24, 26105 (215;R =CH3) [85-83-6]

215

C. I. Solvent Black 3, 26150 (216)[4197-25-5]

216

The products are sold in powder form, asgranules, or as flakes, and some dyes also as liq-uid brands. The liquid brands are highly concen-trated solutions of fat-soluble dyes in aromatichydrocarbons, in some cases also solvent-free100 % liquid products.

Fat- and oil-soluble dyes are used on a largescale in awide variety of industrial sectors.Mainfields of application are the coloration of prod-ucts in the mineral oil and plastics industries,as well as of wax products (e.g., candles, shoepolish, floor polishes).

Mineral oil products (fuels, fuel oil, lubricat-ing oils, and greases) are colored as a means ofdistinguishing between different grades (super-grade petrol) or for compulsory identification,e.g., of diesel and fuel oils, for duty purposes.The plastics industry values the fat- and oil-soluble dyes for the highly transparent colorings,usually with very good light fastness, that areobtainable with them. Products in this dye classare most frequently used for the coloration ofpolystyrene, as well as for incorporation in poly-methacrylate and unsaturated polyester castingresins.

An interesting factor is the high degree towhich the light fastness of fat- and oil-solubledyes is dependent on the medium colored.Whereas, for example, 0.05% colorations of thedye Solvent Yellow 56, 11021, in candle mate-rials possess only moderate light fastness (step3 on the eight-step Blue Scale), transparent col-orations in polystyrene are distinguished by out-standing light fastness (step 8).

Other fields of application are the pyrotech-nics industry (high sublimation tendency of thedyes), the office supplies industry (inks for felt-tip pens, oil-based stamping inks), the lacquersindustry (especially coloration of transparentlacquers on aluminum foil) and the cosmeticsindustry (approval restricted to a few products).

Azo Dyes 89

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1. P. Rys, H. Zollinger: Farbstoffchemie, 3rd ed.,Verlag Chemie, Weinheim 1982.

2. Houben-Weyl, 10/3, 213 – 465, 467 – 485.3. H. R. Schweizer: Kunstliche organische

Farbstoffe und ihre Zwischenprodukte,Springer Verlag, Berlin 1964.

4. W. Seidenfaden: Kunstliche organischeFarbstoffe und ihre Anwendungen, EnkeVerlag, Stuttgart 1957.

5. K. Venkataraman: The Chemistry of SyntheticDyes, Academic Press, New York, vol. I(1952), vol. II (1952), vol. III (1970), vol. IV(1971), vol. VI (1972), vol. VII (1974).

6. H. Zollinger: Azo and Diazo Chemistry,Interscience, New York – London 1961.

7. Colour Index, Society of Dyers and Colouristsand American Association of Textile Chemistsand Colorists, 3rd ed., Bradford 1971, FirstRevision 1975, Second Revision 1982.

8. K. Holzach: Die aromatischenDiazoverbindungen, Enke Verlag, Stuttgart1947.

9. Houben-Weyl, 10/3, 1 – 212.10. N.N. Woroshzow: Grundlagen der Synthese

von Zwischenprodukten und Farbstoffen, 4thed., Akademie Verlag, Berlin (DDR) 1966.

11. H. E. Fierz-David, L. Blangey: GrundlegendeOperationen der Farbenchemie, 8th ed.,Springer Verlag, Wien 1952.

12. P. F. Gordon, P. Gregory: Organic Chemistry inColour, Springer Verlag, Berlin – Heidelberg– New York 1983.

13. A. Eibner, Justus Liebigs Ann. Chem. 316(1901) 126; H. Bucherer, A. Schwalbe, Ber.Dtsch. Chem. Ges. 39 (1906) 2798.

14. M. Martynoff, Bull. Soc. Chim. Fr. 18 (1951)214.

15. H. Baumann, H. R. Hensel: “NeueMetallkomplexfarbstoffe. Struktur undfarberische Eigenschaften”, Fortschr. Chem.Forsch. 7 (1967) no. 4.

16. H. Pfitzner, H. Baumann, Angew. Chem. 70(1958) 232.

17. D. Vorlander, F. Meyer, Justus Liebigs Ann.Chem. 320 (1902) 122.

18. D. C. Freemann, C. E. White, J. Org. Chem.21 (1956) 379.

19. H.H. Hodgson, F. Leigh, G. Turner, J. Chem.Soc. 1942, 744.

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74 (1962) 818.22. M. Regitz, Angew. Chem. 79 (1967) 786.

23. T. Vickerstaff: The Physical Chemistry ofDyeing, Oliver and Boyd, London –Edinburgh 1954.

24. E.M. Diskant, Anal. Chem. 24 (1952) 1856.25. G. Schetty, J. Soc. Dyers Colour. 71 (1955)

705.26. Sandoz, BE 717458, 1967 (M. Studer).27. Bayer, DE-OS 1923680, 1969 (H. Nickel, F.

Suckfull).28. Toms River Chem. Corp., DE-OS 1931691,

1969 (H.A. Stingl).29. Crompton & Knowles, DE-OS 1957115, 1969

(J. F. Feeman).30. Bayer, DE-OS 1960816, 1969 (K. L. Moritz).31. J. Boulton, J. Soc. Dyers Colour. 67 (1951)

522.32. I. D. Rattee, M.M. Breuer: The Physical

Chemistry of Dye Absorption, AcademicPress, London – New York 1974.

33. H. Bach, E. Pfeil, W. Phillippar, M. Reich,Angew. Chem. 75 (1963) 407.

34. E. Schirm, J. Prakt. Chem. 144 (1935) no. 2,69.

35. H. Zollinger, Helv. Chim. Acta 38 (1955)1597, 1623; R. Putter, Angew. Chem. 63(1951) 186.

36. Cassella, DE 204212, 1907 (A. Greßly).37. BASF, DE 46737, 1888; DE 47902, 1889

(C. L.Muller).38. Ciba, DE 436179, 1923.39. Ciba, DE 335809, 1915.40. BASF, DE 807289, 1948 (H. Pfitzner, H.

Merkel); H. Pfitzner, H. Baumann, Angew.Chem. 70 (1958) 232.

41. J. Offenbach: Deutscher Farbekalender, EderVerlag, Stuttgart 1972, pp. 185 – 194.

42. L. Diserens: Die neuesten Fortschritte in derAnwendung der Farbstoffe, vol. 1, 3rd ed.,1951; vol. 2, 2nd ed., 1949, Birkhauser, Basel.

43. Geigy, DE 114634, 1899.44. GAF, DE 901419, 1950; DE 901540, 1950.45. BASF, DE-OS 2557561, 1975 (H. Kast, G.

Riedel).46. Tekhnolog Constr. Techn. Bur., RU 21 02 415,

1994.47. BASF, DE-OS 3011235, 1980 (K. Schmeidl).48. BASF, DE-OS 37 13 618, 1987 (K. Schmeidl).49. BASF, EP 341 325, 1988 (K. Schmeidl).50. Bayer, DE-OS 3025557, 1980 (K. Linhart, H.

Gleinig, R. Raue, H.-P. Kuhlthau).51. Bayer, DE-OS 33 03 512, 1983 (R. Raue).52. Amer. Cyanamid, DE-AS 1072222, 1958.53. Bayer, DE-AS 1044310, 1956.54. VEB Bitterfeld, DE-OS 2038411, 1970.55. Bayer, DE-OS 3048998, 1980 (K. Kunde).

90 Azo Dyes

56. Sandoz, DE-OS 2915323, 1979; 3030197,1980 (R. Pedrazzi).

57. Sandoz, DE-OS 33 11 091, 1982 (J. Troesch,W. Portmann).

58. Sandoz, DE-OS 33 29 817, 1982 (J. Troesch,W. Portmann).

59. Sandoz, DE-OS 34 12 762, 1983 (J. Troesch).60. Sandoz, DE-OS 35 03 844, 1984 (R. Pedrazzi).61. Sandoz, EP 341 214, 1988 (H.A. Moser, R.

Wald).62. Bayer, DE-OS 3133360, 1981 (K. Kunde).63. Nippon Chem. Works, JA 04 93 365, 1990.64. BASF, EP 281 920, 1987 (J. Dehnert).65. Bayer, EP 632 104, 1993 (K. Hassenrueck, P.

Wild).66. Bayer, EP 312 838, 1987 (A. Engel).67. Intreprenderea “Sintofarm”, RO88 681, 1984.68. BASF, DE-OS 42 02 566, 1992 (E. Hahn, H.

Hengelsberg, U. Mayer).69. Orient Chem. Works, JA 08 048 924, 1994.70. Nippon Chem. Works, JA 04 183 754.71. BASF, DE-OS 42 35 154, 1992 (U. Schloesser,

U. Mayer).72. BASF, EP 666 287, 1994 (U. Schloesser, U.

Mayer).73. Wella, EP 852 942, 1996 (U. Lenz, E. Nowald).74. L’Oreal, WO97/20 545, 1997 (H. Samain).75. Sandoz, DE-OS 1644138, 1966.76. Ciba, FR 1322766, 1961.77. Bayer, DE-OS 32 31 398, 1982 (P. Wild, F.-M.

Stoehr).78. Bayer, DE-OS 3138182, 1981 (K. Kunde, P.

Wild).79. ICI, GB 951667, 1961.80. Bayer, DE-AS 1011396, 1955 (W.

Kruckenberg).81. VEB Chem. Bitterfeld, DDR227 148, 1984

(E. Guhl, G. Knochel, H. Noack, J. Schlykow).82. VEB Chem. Bitterfeld, DDR227 149, 1984

(R. Freitag, E. Guhl, G. Knochel, H. Noack, J.Schlykow).

83. Bayer, DE-OS 2850706, 1978 (K. Leverenz, J.Reppert).

84. Chemie Bitterfeld-Wolfen, DE-OS 41 28 490,1991 (H. Hartenstein et al.).

85. Mitsubishi Chem., JA 59 170 147, 1983.86. Sumitomo, JP 7313753, 1969.87. Bayer, DE-OS 2024184, 1970; DE-OS

2036952, 1970; DE-OS 2036997, 1970;DE-OS 2041690, 1970; DE-OS 2065685,1970 (W. Kruckenberg). ICI, DE-OS 2646967,1975 (P. Gregory).

88. Sandoz, DE-OS 2338729, 1972 (B. Henzi).89. Bayer, DE-OS 2059947, 1970.

90. Bayer, DE-OS 2309528, 1973; DE-OS3030918, 1980 (K. Linhart, H. Gleinig, G.Boehmke, K. Breig); DE-OS 3101140, 1981(K. Linhart, H. Gleinig, G. Boehmke).

91. Bayer, DE-OS 2508884, 1975; DE-OS2631030, 1976 (W. Kruckenberg).

92. Ciba, DE-OS 2011428, 1970 (G. Hegar).Sandoz, CH 546269, 1964; CH 552032, 1964(R. Entschel). Du Pont, US 3890257, 1973;US 3987022, 1973 (D. S. James).

93. Pentel K.K., JP 77101125, 1976.94. Mitsubishi Kasei, JA 01 284 570, 1988.95. Bayer, DE-OS 2533428, 1975 (G. Boehmke,

U. Hendricks).96. Sumitomo, JP 7237675, 1969.97. Ciba-Geigy, EP 696 619, 1994 (A. Kaeser).98. Sandoz, DE-OS 2118536, 1970; DE-OS

2712265, 1976; DE-OS 2741010, 1976;DE-OS 2805264, 1978 (M. Greve); BE756820, 1970; CH 549629, 1971. Montedison,DE-OS 2851373, 1977 (F. Merlo).

99. ICI, DE-OS 2200270, 1971; DE-OS 2364592,1973; DE-OS 2364593, 1972.

100. Sandoz, DE-OS 2313526, 1972 (W.Steinemann).

101. Ciba-Geigy, DE-OS 2429927, 1973 (V.Ramerathan).

102. Sandoz, DE-OS 31 17 127, 1980 (P. Doswald,E. Moriconi, H. Moser, H. Schmid).

103. Mitsubishi, JP 4957169, 1972; JP 4990327,1972; JP 49109422, 1973; JP 5000179, 1973;JP 5003123, 1973; JP 5031181, 1973; JP5246184 1973.

104. Ciba, BE 587048, 1959. GAF, FR 1295862,1960.

105. I. Gmai et al., SU 287217, 1966.106. Inst. f. Org. Ind., PL 64734, 1968.107. Du Pont, DE-OS 2003540, 1969.108. Ciba-Geigy, DE-OS 2509596, 1974.109. Sandoz, DE-OS 20 61 964, 1969 (H. Moser, H.

von Tobel).110. Ciba-Geigy, EP 15 233, 1979 (P. Galafassi,

J.-M. Adam, P. Loew, H. Scheidegger).111. Ciba-Geigy, DE-OS 38 21 627, 1987 (W.

Stingelin).112. Ciba-Geigy, EP 294 330, 1987 (W. Stingelin).113. Ciba, BE 672152, 1964, Amer. Aniline, US

3881866, 1972 (E. E. Renfrew). ACC, US4204994, 1979; US 4211697, 1979 (K.A.Desai).

114. Mitsubishi Chem., JA 59 140 265, 1983.115. Mitsubishi Chem., JA 61 151 269, 1984.116. Mitsubishi Chem., JA 62 263 262, 1986.117. Sandoz, FR 1325176, 1961.118. Sandoz, CH 508709, 1969. Bayer, DE-OS

2042662, 1970.

Azo Dyes 91

119. Sandoz, DE-OS 2054697, 1969 (W.Steinemann); DE-OS 2752282, 1976 (M.Greve). ICI, DE-OS 2638051, 1975; DE-OS2656879, 1975; DE-OS 2657147, 1975;DE-OS 2657149, 1975; DE-OS 2702777,1976; DE-OS 2702778, 1976 (B. Parton).

120. TU Dresden, DDR289 043, 1989 (P.Bellmann, K. Gewald, H. Schafer).

121. Sandoz, DE-OS 2627680, 1975 (M. Greve, H.Moser); CH 601433, 1976; FR 2360632, 1976(H. Moser). Ciba-Geigy, DE-OS 3223436,1981 (V. Ramanathan, W. Stingelin).

122. Hodogaya Chem. Ind., JA 03 192 158, 1989.123. Nippon Kayaku, JA 01 283 269, 1988.124. BASF, DE-OS 38 01 945, 1988 (H. Bruder, R.

Dyllick-Brenzinger, U. Mayer, S. J. Bares).125. ICI, DE-OS 2920487, 1978 (B. Parton).126. ICI, EP 23770, 1979 (B. Parton, P. F. Gordon).

BASF, DE-OS 2500064, 1975 (J. Dehnert, P.Miederer).

127. BASF, EP 482 508, 1990 (M. Ruske, U.Mayer).

128. BASF, DE-OS 19 809 994, 1997 (M. Ruske, P.Erk, H. Hengelsberg).

129. Ciba, BE 698730, 1966; BE 698917, 1966; EP55221, 1980 (P. Loew). Yorckshire DyewareCorp., GB 1047293, 1964; GB 1157867, 1967;GB 1349511, 1970 (J. F. Dawson, J.Schofield). ICI, GB 2009208, 1977 (M.G.Hutchings).

130. ICI, GB 1211078, 1967.131. Yorckshire Dyeware Corp., GB 1233729,

1968.132. GAF, DE-OS 2244459, 1971.133. Yorckshire Dyeware Corp., GB 1380571,

1971.134. ICI, GB 1247683, 1968.135. ICI, DE-OS 2331953, 1972.136. Yorckshire Dyeware Corp., GB 1361542,

1972.137. Ciba-Geigy, DE-OS 2125911, 1970. ICI,

DE-OS 3008899, 1979 (P. Gregory, D. Thorp).138. BASF, DE-OS 36 11 228, 1986 (K.H. Etzbach,

G. Hansen, H. Reichelt, E. Schefczik).139. ICI, DE-OS 2548879, 1974; DE-OS 2703383,

1976; DE-OS 2817638, 1977 (P. Gregory).Sandoz, CH 627487, 1977 (U. Blass).

140. Ciba-Geigy, EP 514 336, 1991 (A. Nicopoulos,H. Birri, G. Hanika).

141. Sandoz, BE 668688, 1964. ICI, DE-OS2817638, 1977; DE-OS 3008899, 1979; GB2074598, 1980 (P. Gregory).

142. ICI, GB 1374801, 1971.143. Ciba-Geigy, DE-OS 2154477, 1970.144. BASF, DE-OS 2046785, 1970.

145. ICI, GB 1282281, 1967; GB 1290321, 1967.146. Ciba-Geigy, CH 745871, 1974; CH 745872,

1974.147. Ciba-Geigy, EP 16726, 1979 (J.M. Adam, P.

Galafassi).148. Ciba-Geigy, EP 306 452, 1987 (W. Stingelin).149. Kuhlmann, BE 626882, 1962; DE-OS

2314406, 1972 (J. P. Stiot, C. Brouard).150. Kuhlmann, FR 1364560, 1962.151. Kuhlmann, FR 1364647, 1963.152. Kuhlmann, FR 1389432, 1963; FR 1414876,

1964; DE-OS 2140511, 1970; DE-OS2314406, 1972 (J. P. Stiot, C. Brouard).

153. Kuhlmann, FR 1467822, 1965.154. Kuhlmann, FR 1403092, 1964. Geigy, FR

1322747, 1961.155. Chemie Bitterfeld-Wolfen, DDR293 604,

1990 (E. Dehmel et al.).156. ICI, GB 1528801, 1975; GB 1531752, 1975

(B. Parton, F. L. Rose).157. Sandoz, DE-OS 36 09 590, 1985 (H.A. Moser,

R. Wald).158. Sandoz, DE-OS 35 16 809, 1984 (J. Dore).159. Sandoz, DE-OS 37 15 066, 1986 (H.A. Moser,

R. Wald).160. Sandoz, DEOS 33 40 483, 1982 (M. Greve, H.

Moser).161. Sandoz, DE-OS 33 11 294, 1983 (H. Moser, W.

Samhaber, H. Schmid).162. Sandoz, DE-OS 35 38 517, 1984 (H.A. Moser,

R. Wald).163. Sandoz, DE-OS 19 629 238, 1995 (J. Geiwiz,

H. Moser, R. Pedrazzi, H. A. Moser).164. Sandoz, DE-OS 39 32 566, 1988 (H.A. Moser,

R. Wald).165. Sandoz, DE-OS 19 500 203, 1994 (H.A.

Moser).166. Sandoz, DE-OS 44 39 004, 1994

(J.-P-Chavannes, G. Schofberger, G. Scheulin).167. Bayer, DE-OS 31 14 088, 1981 (F.-M. Stohr,

H. Nickel).168. Sandoz, DE-OS 36 25 576, 1985 (J. Dore, R.

Pedrazzi).169. Bayer, DE-OS 31 33 568, 1981 (F.-M. Stohr,

H. Nickel).170. Clariant, WO97/35925, 1996 (R. Pedrazzi).171. Ciba-Geigy, EP 122 458, 1983 (J.-M. Adam,

H. Schwander).172. Sandoz, DE-OS 2250676, 1971 (H. Moser).173. Sterling Drug, DE-OS 2604699, 1975 (N. C.

Crounse).174. Bayer, EP 54616, 1980; EP 74589, 1981;

DE-OS 3222965, 1982 (K. Kunde).175. Bayer, DE-OS 35 02 927, 1985 (K. Kunde, N.

Petzeit).

92 Azo Dyes

176. Sandoz, DE-OS 2915323, 1978 (R. Pedrazzi).177. BASF, DE-OS 33 26 812, 1983 (H. Loeffler).178. BASF, DE-OS 34 13 022, 1984 (H. Colberg).179. BASF, DEOS 34 18 672, 1984 (H. Colberg,

H. J. Degen, J. P. Dix).180. BASF, DE-OS 35 02 693, 1985 (H. Colberg, E.

Hahn).181. Sandoz, DE-OS 3030196, 1980 (R. Pedrazzi).182. Nippon Chem. Works, JA 04 183 755, 1985.183. Ciba-Geigy, DE-OS 34 20 777, 1983 (V.

Ramanathan).184. Sterling Drug, US 4376729, 1980 (N. C.

Crounse).185. Hoechst, DE-OS 2028217, 1970; DE-OS

2057977, 1970.186. Mitsubishi, JP 2181/66, 1963. ICI, GB

1516978, 1974 (P. Gregory). Bayer, DE-OS3110223, 1981 (P. Wild, H. Nickel).

187. Mitsubishi, JP 4986424, 1972; JP 49116384,1973.

188. Chemie Bitterfelden-Wolfen, DDR296 501,1990 (E. Forst, E. A. Jauer, R. Muehlberg, W.Mueller, H. Noack).

189. ICI, NL 6918341, 1968; DE-OS 2216206,1971.

190. Hoechst, DE-OS 2347756, 1973.191. Hoechst, FR 1601787, 1967.192. Sandoz, CH 555876, 1971 (R. Entschel).193. Bayer, EP 24322, 1979 (H. Nickel, F.Muller,

P. Mummenhoff).194. BASF, EP 324 415, 1988 (H. Bruder, U.

Mayer).195. Bayer, EP 24321, 1979 (H. Nickel, F.Muller,

P. Mummenhoff).196. Nippon Chem. Works, JA 05 132 629, 1991.197. Warner-Jenkinson, DE-OS 19 752 665, 1996

(R.W. Pengilly, F. C. P. McLoughlin,R. G. J. C. Twigg).

198. Du Pont, DE-AS 1054616, 1954.199. Bayer, DE-OS 2135152, 1971.200. Ciba, DE-AS 1156188, 1959.201. Du Pont, US 2965631, 1958.202. Ciba, DE-OS 1956142, 1968. Sandoz, CH

553241, 1969 (R. Entschel, C.Muller, W.Steinemann).

203. Hoechst, DE-OS 2222099, 1972 (E.Fleckenstein, R. Mohr, E. Heinrich).

204. Ciba-Geigy, DE-OS 2263109, 1971.205. ICI, GB 1414503, 1972 (D. B. Baird, J. L.

Lang, D. F. Newton).206. Bayer, DE-OS 2559736, 1975 (W.

Kruckenberg).207. Hodogaya, JP 7215473, 1969; JP 7215476,

1969.208. Du Pont, DE-OS 2137548, 1970.

209. Sterling Drug, GB 1299080, 1968; JP4702127,1970; US 3935182, 1973; US3996282, 1974. Scott Paper, GB 2020703,1978.

210. Bayer, DE-OS 3114075, 1981; DE-OS3114087, 1981 (H. Nickel, P. Wild, F.M.Stohr).

211. Bayer, DE-OS 3048694, 1980 (H. Nickel, P.Wild).

212. Mitsubishi, JP 49118721, 1973.213. Ciba-Geigy, EP 263 073, 1986 (W. Stingelin).214. Ciba-Geigy, EP 434 623, 1989 (W. Stingelin).215. Eastman Kodak, US 3804823, 1972. Hoechst,

DE-OS 2339713, 1973 (E. Fleckenstein).216. Toyo Ink, JA 05 125 290, 1991.217. Bayer, DE-OS 2315637, 1973 (K. L. Moritz,

K.-H. Schundehutte). Sandoz, DE-OS2120878, 1970; EP 41040, 1980; EP 93828,1980; EP 93829, 1980 (P. Doswald, E.Moriconi, H. Moser, H. Schmid). Kuhlmann,DE-OS 2119745, 1970. Eastman Kodak, US3836518, 1972 (G. T. Clark).

218. Bayer, DE-OS 2101999, 1971 (M. Wiesel, G.Wolfrum). Mitsubishi, JP 5043284, 1973.

219. Sandoz, DE-OS 3313965, 1982.220. Sandoz, DE-OS 2251041, 1971 (H. Moser).221. Sandoz, DE-OS 2120590, 1970; DE-OS

2120878, 1970.222. Sandoz, CH 516622, 1968.223. Bayer, DE-OS 1544529, 1965.224. Hoechst, FR 1484099, 1965.225. Hoechst, FR 1484503, 1965. Amer. Cyanamid,

DE-AS 1155547, 1957; DE-AS 1162014,1957.

226. IG Farbenind., DE 477913, 1927. ICI, DE-OS2319090, 1972.

227. Ciba-Geigy, EP 284 567, 1987 (J.M. Adam).228. ICI, DE-OS 2421822, 1973 (J. L. Leng, D. F.

Newton); GB 2011454, 1977 (M.G.Hutchings). Ciba-Geigy, GB 1257346, 1968.

229. Kuhlmann, FR 1391676, 1963.230. ICI, GB 1246632, 1967; GB 1365625, 1972

(J. S. Hunter, J. L. Leng, C. Morris).231. Bayer, DE-OS 2141987, 1971 (M. Wiesel, G.

Wolfrum).232. GAF, DE-OS 2050246, 1969 (N.A. Doss).233. Sandoz, CH 554917, 1969 (R. Entschel,

C.Muller, W. Steinemann). Hodogaya, JP7130110, 1968.

234. Ciba, DE-OS 1644110, 1966.235. MLB Hoechst, DE 105202, 1898. Bayer, DE

272975, 1911. Geigy, DE 473 526, 1927.236. Sandoz, DE-OS 37 17 869, 1986 (R. Pedrazzi).237. Sandoz, DE-OS 33 40 486, 1982 (M. Greve, H.

Moser).

Azo Dyes 93

238. Bayer, DE 181783, 1906.239. Kuhlmann, FR 1380628, 1963. VEB

Bitterfeld, DE-OS 2031561, 1970.240. Hoechst, DE-AS 1242773, 1963; FR 2019355,

1968; DE-OS 2516687, 1975; DE-OS2522174, 1975 (R. Mohr, E. Mundlos, K.Hohmann).

241. Hoechst, DE-OS 1816985, 1968.242. Hoechst, BE 677795, 1965; DE-OS 2221989,

1972; DE-OS 2222042, 1972 (E. Mundlos, R.Mohr, K. Hohmann); DE-OS 2357448, 1973(K. Hohmann); FR 2016982, 1968.

243. Kuhlmann, DE-OS 2154662, 1970.244. BASF, DE-OS 2020479, 1970.245. Leningrad Lensovet, Tech., RA 595309, 1975.246. Eastman Kodak, US 3928309, 1974; US

3936435, 1974 (G. T. Clark).247. Amer. Cyanamid, FR 1340397, 1961; DE-OS

2741395, 1976 (R. B. Balsley). Hodogaya, JP56134280, 1980.

248. Ciba-Geigy, WO95/15 144, 1993 (P. Moeckli).249. L’Oreal, WO99/20 235, 1997 (Ch. Rondeau).250. L’Oreal, EP 920 856, 1997 (C. Deneulenaere).251. Ciba-Geigy, EP 116 513, 1983 (V.

Ramanathan, P. Moeckli).252. BASF, DE-OS 35 29 968, 1985 (M. Ruske,

H.-J. Degen).253. Sandoz, DE-OS 33 13 965, 1982 (J. Dore, R.

Pedrazzi).254. Sandoz, DE-OS 34 40 777, 1983 (J. Dore, R.

Pedrazzi).255. Sandoz, DE-OS 34 16 117, 1983 (M. Greve, H.

Moser, R. Pedrazzi, R. Wald).256. Lexmark, GB 23 15 493, 1996 (J. F. Feeman,

J. X. Sun).257. Lexmark, GB 23 15 759, 1996 (B. L. Beach,

J. F. Feeman, T. E. Franey, A. P. Holloway,J.M. Mrvos, J. X. Sun, A.K. Zimmer).

258. Sterling Drug, US 4379088, 1980.259. Sterling Drug, US 4379089, 1980.260. Sandoz, DE-OS 2403736, 1973 (H. Moser).261. Ciba-Geigy, EP 84372, 1982 (J.M. Adam).262. Bayer, EP 321 778, 1987 (G. Franke, P. Wild).263. Ciba-Geigy, EP 14677, 1979 (J.M. Adam, V.

Ramanathan, P. Galafassi).264. Ciba-Geigy, EP 57159, 1981 (J.M. Adam).265. Sandoz, DE-OS 1903058, 1969; DE-OS

1965994, 1968. Sterling Drug, DE-OS2810246, 1977.

266. BASF, EP 34725, 1980 (M. Patsch, M. Ruske).

267. ICI, BE 601144, 1960.268. CZ 182 658, 1976 (J. Kroupa, V. Chmatal, J.

Dvorak).269. ICI, BE 601145, 1960; BE 601146, 1960;

DE-OS 2436138, 1973 (C.W. Greenhalgh,D. S. Phillips).

270. ICI, BE 603028, 1960. V.V. Kormachev, G. P.Pavlov, V.A. Kukhtin, R. S. Tsekhawski. Zh.Obshch. Khim. 49 (1979) no. 111, 112479.

271. Bayer, BE 661025, 1964.272. G. B. Guise, I.W. Stapleton, J. Soc. Dyers

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1245.277. Ch. Granacker, H. Brungger, F. Ackermann,

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(1954) 429.280. W. Staab, Melliand Textilber. 42 (1961) 1373.281. F. Gund, J. Soc. Dyers Colour. 76 (1960) 151.282. Hoechst, DE 1086832, 1958 (U. Dreyer, W.

Kirst); DE 1088060, 1959 (R. Mohr, H.Hertel); DE 1126545, 1959 (R. Gross, H.Hertel, W. Kirst, R. Mohr).

283. A. Ruckert, Melliand Textilber. 41 (1960)1541.

284. R. Gross, Text. Prax. 15 (1960) 1046.285. W. Kirst, Z. Gesamte Textilind. 68 (1966) 772.286. P. Heinisch, Text. Prax. 21 (1966) 342.287. R. Lowenfeld, Textilveredlung 2 (1967) 677.288. R. Lowenfeld, Z. Gesamte Textilind. 70 (1968)

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432.291. E. Fees, Melliand Textilber. 47 (1966) 1162,

1300.292. Hoechst, DE 2850901, 1978 (E. Feess, P.

Karacsonyi, H. Curtius).293. Naphtol Chemie Offenbach, DE 848639, 1948

(W. Kirst).294. R. Lowenfeld, Melliand Textilber. 40 (1959)

295.