polynuclear aromatic hydrocarbons

Polynuclear Aromatic Hydrocarbons

07/05/2017 Dr.Mohanad Mousa Kareem.....Polynuclear Aromatic Compounds...3rd stage 1

Polynuclear Hydrocarbons

Benzenoid Non- Benzenoid

AzuleneIsolated Fused rings

Biphenyl

Linear Angular

NaphthalenePhenanthrene

07/05/2017Dr.Mohanad Mousa Kareem.....Polynuclear Aromatic Compounds...3rd stage

I. Isolated Ring Polynuclear Hydrocarbons

Biphenyl (diphenyl):

a) Fittig reaction

b) From benzene diazonium sulphate

c) From benzidine

2Ph-Br + 2Naethersoln

Ph-Ph + 2NaBr

N=N HSO4

Biphenyl

+ N2 + CuHSO4

Preparation of Biphenyl

H2N NH2

HClN=N N=N ClCl

Benzidine

Biphenyl

2 Ph-I2 Cu

Ph-Ph + 2CuI

2 CuI2

sealed tube

4,4'- Dimethyl-biphenyl

H3C CH3H3C

2 CuI2

sealed tube

2,2'- Dinitro-biphenyl

NO2NO2

d) Ulmann diaryl synthesis

e) By using Arylmagnesium halide

PhMgBr + PhBr Ph-Ph + MgBr2

C OC l2

Reactions of biphenylBiphenyl undergoes substitution reactions,

In biphenyl one ring act as electron donating group and the other act as electron withdrawing group

Resonance shows that O- and P- are the most reactive positions towards electrophilic substitution.

The electrophilic substitution occurs in 4- position (major) and 2- position (minor) due to steric effect of other benzene ring.

The 2nd substitution occurs in the empty ring in 2 or 4- position.e.g.

NO2NO2O2N + +

conc HNO3

conc H2SO4

conc HNO3

conc H2SO4

2-Nitro-biphenyl 4-Nitro-biphenyl

4,4'-Dinitro-biphenyl 2,4'-Dinitro-biphenyl 2,2'-Dinitro-biphenyl

Biphenyl derivatives

NH2H2N

COOH COOH

(1) Benzidine (4, 4`-diaminobiphenyl)

(2) Diphenic acid

(3) Diphenyl methane

07/05/2017Dr.Mohanad Mousa Kareem.....Polynuclear Aromatic Compounds...3rd stage

Q. Show how could you prepare benzidine from benzene?

• Answer

conc. HNO3

conc. H2SO4

O2N NO2Zn/HCl

H2N NH2

Benzidine07/05/2017Dr.Mohanad Mousa Kareem.....Polynuclear Aromatic Compounds...3rd stage

Ulmann diaryl synthesis

COOEt COOEt

COOH COOH

biphenyl- 2,2'- dicarboxylic acid(Diphenic acid)

oxidation of Phenanthrene or phenanthraquinone

50% H2O2

Diphenic acid

K2Cr2O7

phenanthrene phenanthraquinone

Oxidation of KMnO4

Diphenic acid

KMnO4COOH

pthalic acid

with sodalime

Diphenic acid

Sodalime

biphenyl

CO2HNO2

Mirror

Optically activeB

MirrorCl H

Optically active

07/05/2017 14Dr.Mohanad Mousa Kareem.....Polynuclear Aromatic Compounds...3rd stage

• When o- position contains two similar groups, the moleculeis optically inactive due to presence of plane of symmetry ..for example

CO2HNO2

CO2HH3OC

Optically inactive due to presence of plane of symmetry

Plane of symmetry

Optically activefree rotation is possible

HO2C NO2

Optically activeF is a small atom so permit

by free rotation

07/05/2017 15Dr.Mohanad Mousa Kareem.....Polynuclear Aromatic Compounds...3rd stage

Friedel- Crafte

+AlCl3

Diphenyl methaneBenzyl chloride

AlCl3CH2

Diphenyl methane

2 + CH2Cl2

1. Nitration

Diphenyl methane

conc. HNO2

conc. H2SO4CH2 NO2

conc. HNO2

conc. H2SO4CH2 NO2O2N

bis(4- nitrophenyl)methane

1-benzyl-4-nitrobenzene

07/05/2017Dr.Mohanad Mousa Kareem.....Polynuclear Aromatic

Compounds...3rd stage17

2. Halogenation

Diphenyl methane

Diphenylmethylbromide

3. Oxidation

Diphenyl methane

K2Cr2O7

benzophenone

II. Fused System

a) Naphthalene18

1-Naphthol or -Naphthol

2-Naphthol or -Naphthol

1,8- Dibromo-naphthalene

SO3HHO3S

Naphthalene-2,7- disulfonic acid07/05/2017

Dr.Mohanad Mousa Kareem.....Polynuclear Aromatic Compounds...3rd stage

Structure elucidation of naphthalene

Phthalic acid

Naphthalene

1- Molecular Formula: C6H8

So naphthalene contain the skeleton

C07/05/2017

So nitro group is present in benzene ring

Nitrophthalic acid

Naphthalene nitrationNitronaphthalene

Phthalic acid

Naphthalene nitrationNitronaphthalene

aminonaphthaleneredn.

The benzene ring in phthalic acid produced by

oxidation of aminonaphthalene is not the same

ring is that obtained by oxidation of

nitronaphthalene.07/05/2017

i.e. Naphthalene contains two benzene rings and

we can explain this by this equation

NO2NH2

A A AB BB

O redn. O

The structure of naphthalene is confirmed by method of its analysis

1- Howarth method

Zn-Hg/HCl

conc.H2SO4

-H2OZn-Hg/HCl

Succinic anhydride

Other way of cyclization

intramoluclar

Zn-Hg/HCl

Succinic anhydride

Friedel Craft

• The reaction occurs if R is o- or p- directing groupsuch as NH2, NHR, OH, OR, R, halogen.

• If R is m- directing group (e.g. NO2, CN, COOH,COCH3, SO3H) no reaction occur.

• The above reaction gives -substitutednaphthalene.

Synthesis of 1-alkyl naphthalene

Zn-Hg/HCl

Succinic anhydride

COOH COOH

benzene 4-oxo-4-phenylbutanic acid 4-phenylbutanoic acid

conc. H2SO4

1) RMgX

2) HOH

1-tetralone 1- Alkyl naphthalene

2- From -benzylidene – propenoic acid

conc. H2SO4

Zn-ZnO

-Benzylidene-3-propenpoic acid

naphthalene

Chemical Reactions of naphthalene

1. Reduction

Naphthalene

1,4- dihydronaphthalene

1,2,3,4-tetrahydronaphthalene

Tetralene

decahydronaphthalene

Decalene

isoamyl alc.

2. Oxidation

Naphthalene

1,4- naphthoquinone

Phthaldehyde

Phthalic anhydride

2) H2O/Zn

Phthalic acid

3. Addition of Cl2

Naphthalene

1,4- dichloro- 1,4- dihydronaphthalene

excess

Cl1,2,3,4- tetrachloro- 1,2,3,4-tetrahydronaphthalene

4. Electrophilic substitution reaction

Naphthalene

one resonance structure

At position 1; carbocation intermediate stabilize by two resonance

So carbocation is more stable position 1 than 2

Q: Naphthalene udergoes

electrophilic substitution atposition 1 not 2. Explain

Examples of electrophilic substitution

Naphthalene

naphthalene-1- sulfonic acid

1- chloronaphthalene

conc. HNO3

conc. H2SO4

1- nitronaphthalene

conc. H2SO4

180°C

naphthalene-2- sulfonic acid

CH3COCl

AlCl3CS2

1- Acetylnaphthalene

CH3COCl

AlCl3PhNO2

2- Acetylnaphthalene

Substituted naphthalene

• Activating groups direct the electrophile to the same ring, while deactivating groups direct it to the other ring.

Elctrodonating group

(EDG):

NH2, OH, OR, alkyl Electrowithdrawing group

(EWG):

NO2, CO, COOH, CN, SO3H

Homonuclear attack

Heteronuclear attack

Major E Major

Examples:

conc. HNO3

conc. H2SO4

conc. HNO3

conc. H2SO4

conc. HNO3

conc. H2SO4

NO2 NO2NO2

Major Minor

conc. HNO3

conc. H2SO4

NO2 NO2

Naphthalene derivatives

1. Nitronaphthalene

• 1. naphthalene is prepared by direct nitration

Naphthalene

conc. HNO3

conc. H2SO4

1- nitronaphthalene

2. naphthalene is prepared by indirect method

2- Aminonaphthalene

N=N BF4

2. Naphthols

• Preparation:

Naphthalene

conc. H2SO4

180°C

Naphthalene-1- sulfonic acid

Naphthalene-2- sulfonic acid

300°C

1- Naphthol

2- Naphthol

• Properties:

Ph-N=N-Cl

2- phenylazo-1- NaphtholAzo form

hydrazo form stable by intermol. H.B

1- Reaction of and - naphthols with aryl diazonium salt

Ph-N=N-Cl

2- phenylazo-2- Naphthol

2- Reaction of and - naphthols with nitrous acid

2- nitroso-1- naphthol

[1,2]naphthoquinone-2-oxime

2- nitroso-2- naphthol

[1,2]naphthoquinone-1-oxime

1- Naphthol

2- Naphthol

3- Conversion of and - naphthols to naphthyl ether

1- Naphthol

conc. H2SO4

1- Naphthol

conc. H2SO4

3. Naphthylamine

•Preparation:1- Naphthylamine

conc. HNO3

conc. H2SO4

Zn/HCl

1- Nitronaphthalene 1- aminonaphthalene

Preparation:2- Naphthylamine

Bucherer reaction

- Naphthol

NH4HSO3

- naphthylamine

Mechanism

- Naphthol

NH4HSO3

- naphthylamine

SO3NH4

-NH4HSO3

4. Halogenated naphthalene

• A) Preparation of 1- halogented naphthalene

1- bromonaphthalene

• B) Preparation of 2- halogenated naphthalene via Sandemeyer

2- Naphthylamine

Questions:

Convert 2- naphthol to:

• A) 2- bromonaphthol

• b) Naphthalene -2- carboxylic acid

• C) 1,2- naphthaquinone-1- oxime

• D) Ethyl –naphthyl ether

5. Alkyl naphthalene

• Synthesis of 1- alkyl naphthalene

Zn-Hg/ HCl

Benzene

Succinic anhydride

4- oxo-4-phenylbutanoic acid

4-phenylbutanoic acid07/05/2017

• Synthesis of 2- alkyl naphthalene

Succinic anhydride

H3C H3CHO

H3C H3C

Toluene

Zn-Hg/HCl

Zn-Hg/HClconc. H2SO4

2- methyl naphthalene07/05/2017

6. Naphthaquinones

• There are six possible naphthaquinones, but only common are 1,2; 1,4; 2,6- naphthaquinones

1,2- Naphthaquinone

1,4- Naphthaquinone

2,6- Naphthaquinone07/05/2017

Preparation of naphthaquinones

1,4- Naphthaquinone:

1,4- Naphthaquinone

Naphthalene

1,2- Naphthaquinone

K2Cr2O7

H2SO4 or PbO2

1- Amino- 2-naphthol

2,6- Naphthaquinone

benzene

2,6- dihydroxynaphthalenel

7. Naphthoic acid

1- Naphthoic acidor

- Naphthoic acid

COOHCOOH

2- Naphthoic acidor

- Naphthoic acid

Preparation of 1-naphthoic acid

From bromonaphthalene

1- Naphthoic acid

COOHBr

Mgdry ether

1) CO2

1- bromonaphthalene 1- naphthyl magnesium bromide

From 1- naphthylamine

HClCuCN

1- Naphthylamine

NH2 N N

1- Naphthoic acid

COOH 1- naphthonitrile

From 1- acetylacetophenone

I2/NaOH

1- Naphthoic acid

1- Acetylacetophenone

2- Naphthoic acid can be prepared by the same above methods

Anthracene

• Anthracene has 4 isomers:

Resonance I, II are more stable, contain 2 benzene rings.07/05/2017Dr.Mohanad Mousa Kareem.....Polynuclear Aromatic

Synthesis of anthracene

• 1. Friedl Crafts

-2HBenzyl chloride

Anthracene07/05/2017

• 2. Elbe reaction

Anthracene

Pyrolysis

o- Methyl- benzenophenone or o- Benzoyl- toluene

• 3. From 1,4- Naphthoquinone

1,3- Butadiene

1,4- Naphthaquinone

9,10- anthraquinone

Anthracene

The above method shows presence of naphthalene in anthracene07/05/2017Dr.Mohanad Mousa Kareem.....Polynuclear Aromatic

• 4. From benzene and phthalic anhydride

AlCl3+ O

Anthracene

O anthraquinone

Phthalic anhydride

Chemical reactions

• 1) Diels Alder

OAnthracene Maleic anhydride

Endo- anthracene- maleic anhydride adduct

• 2) Addition of one molecule of O2

Anthracene

Anthracene epoxide

• 3) Halogenation of anthracene

Anthracene

X= Cl or Br

• 4) Oxidation of anthracene

Anthracene 9, 10- Anthraquinone

Dil HNO3

In using dil. HNO3 only to obtain 9,10- anthraquinone

• 4) Reduction of anthracene

Anthracene 9, 10- Dihydroanthracene

isopropanol

Anthraquinone

Preparation

Anthracene 9, 10- Anthraquinone

Dil HNO3

K2Cr2O7

AlCl3+ O

O anthraquinone

Phthalic anhydride

Chemical Reactions

Distillation or

Zn/H/150°C

Anthracene

9- Anthrone

Sn/HCl/AcOH

Zn/ NaOH

Anthraquinol07/05/2017

• Nitration

NO2NO2

1,5- dinitroanthraquinone

1,8- dinitroanthraquinone

1- nitro-9,10- anthraquinone

• SulphonationO

160°C

Anthraquinone-2-sulfonic acid

Anthraquinone does not undergo Friedl Craft reaction

Anthraquinone-2-sulfonic acid

2- amino-anthraquinone

•Preparation of 2-amino-anthraquinone

Alizarin

1,2-dihydroxyanthraquinone Alizarine

PreparationO

160°C

Oleum, H2SO4

Alizarine

1)NaOH,

2) [O]

9,10- anthraquinone-2- sulfonic acidAnthraquinone

Preparation of Alizarine Blue

Alizarine

1) conc. HNO3 conc. H2SO4

2) [H]

1) Glycerol/ H2SO4

2) PhNO2

Alizarine Blue

Alizarine blue is used for dyeing wool by blue color07/05/2017

Phenanthrene

Position of double bond

The most stable 3 benzenoid rings

Preparation of phenanthrene

• 1) Howrth method

Zn-Hg/HCl

COOHconc.H2SO4

O Zn-Hg/HCl

Naphthalene Succinic anhydride

• Preparation of 2- alkyl phenanthrene:

O 1) RMgX2) HOH

Preparation of 1- alkyl phenanthrene:

Zn-Hg/HCl

COOHconc.H2SO4 O Zn-Hg/HCl

Naphthalene

• 2) Posher synthesis

CH2COONa

Zn-Hg/HCl

NaNO2/H2SO4

N2HSO4

Phenanthrene07/05/2017

Chemical Reactions

Na/EtOH

9,10-dihydro-phenanthrene

1) O2 2) H2O

Biphenyl-2,2'-dicarbaldehyde

9,10-dibromo-9,10-dihydro-phenanthrene

9-bromo-9,10-dihydro-phenanthrene

H2O2 AcOH

Diphenic acid

Benzil-Benzilic rearrangement

NaOH CPh

Benzil Benzilic acid salt

HO CPh O

C OHPh

Proton transfer

Mechanism

Phenanthraquinone 9-hydroxy-9H-flourene-9-carboxylic acid

Proton transfer OH

Mechanism

Phenanthraquinone

• Preparation

K2Cr2O7 H2SO4

PhenanthraquinonePhenanthrene

Condition necessary for aromaticity

Any compound to be aromatic, it must be;

• 1. Cyclic

• 2. Planner

• 3. All atoms must be SP2

• 4. All double bonds must be conjugated

• 5. Obey Huckle rule which state that any aromatic compound must contain 4n+2 pi electrons where n 0,1,2,3,…

Examples

n=1 electron

n=2 electron

n=3 electron

Examples of non- benzenoid aromatic cmpound

All are aromatic( cyclic, planner,1, and agree with Huckle rule: 4n+2= 6 (n=1)

Examples of non- aromatic

Not aromatic; both contain Sp3

Not aromatic

Does not obey Huckel rule

4n+2=8; n=1.5

Not aromatic

Does not obey Huckel rule

4n+2=4; n=0.5

Aromatic; cyclic, planner,

obey Huckel rule

4n+2=2; n=0

Aromatic

4n+2=10; n=2Aromatic

4n+2=14; n=3

Not Aromatic

8 pi electrons

Aromatic

4n+2=10; n=2

Aromatic

4n+2=10; n=207/05/2017

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