Joe A. Vinson I organic Qualitative Analysis and William T. Grabowski

University of Scranton Scranton, Pennsylvania 18510 I An improved sodium fusion procedure and a new test

for Nand S

Qualitative organic analysis has traditionally been a structured course for upper division chemistry majors. In many schools, infrared a n d n m r analyses are now taught in the sophomore course and used by students, along with wet chemical tests. for t h e identification of unknown oreanic compounds. 1; t h e interest of greater safety in t h e s i i u m fusion method and in i m ~ t o v i n e and simnlifvine the elemental tests, we have developei a newsodium ?usLon~rocedure and a new single reagent test for nitrogen and sulfur.

Experimental Procedures

Sodium Fusion

In a small test tuhe place about 0.5 g of sodium-lead alloy (dri-Nam from J. T. Baker Chemical Company). Clamp the tube in a vertical position and heat with a flame until the alloy melts and fumes of so- dium are seen up the walls of the tuhe. Do not heat the alloy tored- ness. Add a few drops of liquid sample or 10 mg of solid. During ad- dition be carefulnot to get any sample on thesides of the tuhe. Heat gently, if necessary, until the reaction is initiated; remove the flame until it subsides, then heat to redness fora minute or twoand let cool. Add 3 ml of H20 and heat gently for a few minutes to react the excess sodium with the water. Filter the solution, if necessary. Wash the filter paper or dilute the decanted reaction mixture with about 2 ml of water and proceed with the elemental analysis.

Nitrogen or Sulfur Test

I'ut ahout 10 drops of the fusion solution in a small test tube and saturate it with sohd sodium birarhonaw. Shake toensure saturation and check towe if excess solid is urwnt. Then add 1 or 2 drops of the saturated solution (it is permissible to transfer some of thesolid so- dium bicarbonate) to a test tube containing about 20 droos of a 1% ~~ ~

p-nitrohenzaldrhydesa>lurion mdimethylsulfmide IPNBreagentr. This reagent should he discarded if the initial yellow cdur darkens and should be stored in a brown hottle A purple color indicates ni- trogen is present. A green color indicates sulfur is present. If both sulfur and nitrogen are present, only a purple color will he visible. Therefore, if a positive test for nitrogen is observed with PNB, a test for sulfur hv another method should he emoloved. The lead acetate or sodium &ro-prusside test ( 1 ) are suitadle. i f only a positive test for sulfur is observed by the present method, then nitrogen is defi- nitely absent.

&logen Tests

Transfer about 10 drops of the fusion solution into a test tuhe, ac- idify with dilute nitric acid, and boil to remove any hydrogen cyanide and hvdrozen sulfide. Add 1 droo of aqueous silver nitrate to the so- lutio'. A i h i t e to yellow cloud or precipitate indicates the presence of chloride, bromide, or iodide. Specific tests are then necessary to identify the halogen(s) present.

Presented ar the 169th National Meeting of the American Chemical Society, Chemical Education Dwision. Philadelphia, I'ennrylvania.

Results and Discusion

Fusion Although the Lassaigne procedure (1-3). commonly known as the

sodium fusion test, is easy to perform, there are hazards in the use of metallic sodium: handling difficulties, instability in air, ignition of hydrogen during reaction with water, exothermic reactions with some oreanim. and dismal ~rohlems. The newer calcium oxide-zinc fusion .. . . . ~~

~ ~

procedure ( 4 ) rs less hnmrdous than sodium fusion. Nitrogen corn. puundr are converted to ammonia whrrh ~u deterted hy indicator paper. A blank must be nm ~imultanroualy to distinguish hetween a true and false positive test. False negatives result from eompounda such as 3,5-dinitrobenzoie acid and false positives result from poor technique when the fusion mixture sulatters onto the indicator Paper.

The use of a lead allov with sodium in the ratio 9:l is described bv Lance (5) for the decompmltian of orgames contamlog heteroele- ments. The alloy is m a dry, gmnular f o m and gives no d~ffirulty m handling. It is fairly stable in air and is easily stored in a screw-capped jar. When the material is added to water, i t falls to the bottom of the &ntainer eivina a non-vigorous reaction without any ignition of the hydrogen. l t i skommended that thr residues from sbdium fusion with the alloy be pooled in an open vessel and disposed of properly in order to minimize lead pollution.

Elemental Analysis

Nitrogen is the most difficult element to detect. During sodium fusion. cvanide ion is formed from the nitroeen in the oreanic eom- pound. cyanide ion is usually detected by t<e Pmssian glue test in whieh cyanide is converted to ferroeyanide whieh reacts with ferric ion to farm a precipitate of ferric ferraeyanide or Prussian Blue. The test requires careful control of p H for best results (6). Green or greenish blue solutions after the test indicate poor fusion. The pres- ence of sulfur can obscure the test for nitrogen. When ferrous ion is added, iron sulfide must be removed by centrifugation or filtration before proceeding with the Prussian Blue test.

Many nitrogen compounds, such as polynitro compounds, azo compounds, pyrrole derivatives, and proteins, are difficult to detect because of slow or incomplete reaction with sodium when followed by detection with the relatively insensitive Prussian Blue test. Cheronis ( I ) indicates these compounds should he decomposed hy alternative methods such as magnesium or soda-lime. Greater sen- sitivity can be obtained with henzidine-cupric sulfate. However, sulfide and iodide interfere with this test and henzidine is carcino- genic. A new modification of the pyrazolone color reaction has been developed (5). The cyanide is oxidized by chloramine T and detected by two reagents which are stable for 2 mo in the refrigerator, However, these reagents are dissolved in pyridine which is both obnoxious and

~ ~

tmic. A selective and sensitive cyanide test which ufilizesp-nitroben-

znldehydc (I'NRI and o-dinitrohenzme has been published (7) and used successfullv in the oreanir lahmatorv 16). hrineaninvestieation of this reaction: we founlthat. if the initial reaction of o-nitGhen- . ~~ ~~~~~ ~ ~~ 7 ~~~~~~ ~~

ddehydrand cynnidc werecankl out in dimethylaulfonide,a purple color was formed. This color is the harivuf a simple test fur ryanrde.

April, 1975. This new color test, in combination with the sodium alloy fusion

Volume 54. Number3. March 1977 1 107

Table 1. Diff icult Nitrogen Compounds

Description of Fusion Color and

Type Compound Reaction Rate

p ~ i y n i t r o m-dinitrobenzene moderate purple-rapid picl ic acid violent purple-medium

ALO arobenlene moderate o u r ~ l e - r a ~ i d methyl orange. slow, charred purple-medium

sodium Salt Diazo ~ a s t Blue B moderate pink-slow

Fast Red Salt B fast purple-rapid Amino Acid phenyiaianine fast purple-rapid

arpartic acid fast purple-rapid Protein bovine albumin slow purple-rapid

hemogiobin 11ow.charred purple-rapid Aminonap- 4-amino-l-naptnalen fast pink-slow

thalene ruifonic acid Sulfonic Acid

8-amino-3-napthaiene fast purple-slow s ~ l f o n i c acid

Nitr i te buty l nitr i te fast purple-rapid i~openty l nitr i te fast purple-rapid

Table 2. Sulfur Compounds

Comoound Color w i th PNB

IUI~OI~I~CYI~C w i d green 2-mercatoethanol green dimethyl ruifoxide light green carbon dirulfide dark green thiophenol green p-toluenerulfonic acid green thiophene green tetrahydrothiophene-1.l.dioxide yellow green

method, was used for the analysis of difficult to detect nitrogen compounds. The results are shown in Table 1. Only in the case of picricaeid was thereaction violent with the sodium alloy. A lessvig- orous reaction occurred if small amounts of pierie acid were added intermittently. Heating is necessary for those compounds with slow reactions and should be used routinely with unknowns. Color devel- ooment with P N B reaeent occurred within 15 s for all compounds ekceot the slaw reactin; ones. These took a minute or two f i r color ~~. formation g w n g n pmk i,r pinkish-purple rdur wrth PNR. This is pnnbahly a conrenrmtion cfferi, i r , that rheam~unt ut cyanidrformrd from fusion in these eases is low.

Table 2 lists the sulfur compounds which were tested. All of these compounds reacted rapidly with the sodium alloy. The green color was not stable and disappeared after 5 mi". It could be reformed by the addition of anotherdrooof fusion mixture which had been satu- rated with sodium bicarbonate.

The sensitivity of the method was determined using a standard

Table 3. Representative Compoundr Given As Unknowns

Compound Element(s) Present

~diphenyl th iourea N. S ethyl carbamate N p-bramoaniiine N. X coumarin none carbon tetrabromide benzophenone p-nitrochiorobenzene tribenzyiamine dibenlyl tetraethyl ammonium bromide ~ . t ~ l ~ e n e ~ ~ l f o n i ~ acid b-nitrobenryl bromide 4-amlno-l-napthaiene rulfonic acid dimethyi ruifoxide glycyiglycine iodbform

X none N. X N none N. X s

aqueous solution of sodium cyanide saturated with sodium bicar- bonate. One drop was added to 20 drops of P N B reagent. A brown- purple color was barely evident with 0.25 pg of cyanide. This sensi- tivity is slightly better than the benzidine test (0.5 pg) and much better than Prussian Blue. Hydroxide ion gives a purple color but this in- terference is eliminated by lowering the p H of the fusion mixture by saturating with sadium bicarbonate. No interference was noted with any other anion tested. No problems in either prmedure or identification were encountered

with comoounds in Table 3 eiven as unknowns to a class of 150 stu- dents rf the pnxedureunr tc~~'llou.ed currrrtlv. The two critical steps nerwiary for good r ~ s d t c are first, suffiricnr hraring uf the sodium alhy with the unkncnvn and second, complrtc saturation uf the aqueous filtrate with sodium hiearbonate.

Summary The proposed sodium allay fusion procedure is suitable for use in

organic qualitative analysis and is safer with regards to handling and disoosal than the commonlv used sodium fusion method. The o-ni- trobenzaldehyde color test rs asimple, rapid, and sensitive color test far nitrogen or sulfur.

Literature Cited Ill Cherunii. N. D.. and Entriken, J. B., "SemimicroQualitafive Oqanic Analysis." 2nd Ed.,

Intorscience Publishen. Inc.. New York. 1957. DD. 172-180. 121 Pasto, D. J., and john^^. C. R.. "Orzanic Structure ~eterminstiun: ~rentiee-~sli.

Inc..Eneiewood Cliffs. N.J.. 19R9.p. 916. I91 Shriner, R. L., Funm,R.C.,and Cruiin.D. Y.."TheS*rtematiclndentiflcation nforgmie

Compounda,"Sth Ed.. John Wiiey andLmr. lnc. New York, 1969.p. 62. 141 Snyder, C. H..Sickcin, J. P.. and Del Valie. C. I., J. CHEM. EDUC..SO.72 lL973l. IS1 Lance.R. C..Barnard.A. Land JW,E F..Microrhrm. J.. 20, LO? ll8751. (fiJ Campheli,K. N..sndCemphell. B. K.&CHEM EDIIC..27,2SI 119501. 171 Cuiihaut, G. G..and Kmmer. D. N.,Aooi. Chrm.. 38.894 119661. 18) McCu1iuuph.T.i.. J.CHEM EDUC..50,656 119731.