1

Aromatic chemistry and Toluene

For HS(12)

C-32(part-2)

2

Equal moles of aryl halide and alkyl halide

dissolved in dry ether when reacts with Na

produces alkyl benzene

Wurtz-Fittig reaction

Cl

+ 2Na + Cl-CH 3

Dry ether

CH 3

+ 2NaCl

Disadvantage : biaryl and alkanes are side products

Ar-X + 2Na + X-Ardry ether

Ar-Ar + 2NaX

R-X + 2Na + X-R dry ether

R-R + 2NaX

3

• When phenyl magnesium bromide/iodide reacts with methyl bromide/iodide in dry ether produces toluene

Using Grignard reagent

MgBr

+ CH 3BrDry ether

CH 3

+ MgBr2

Benzyl magnesium chloride on hydrolysed by dil HClProduces toluene

CH 2MgCl

dil HCl

CH 3

+ MgCl2

4

• In Friedel-Crafts alkylation, treatment of benzene with an alkyl halide and a Lewis acid (AlCl3) forms an alkyl benzene( when R = -CH3, toluene forms)

Friedel-Crafts Alkylation

+ CH 3Cl Anh AlCl3

CH 3

Polyalkylation is the main disadvantage of this reaction.

5

From tolueic acid & p-toluidine

CH 3

COONa

+ NaOHCaO

Heat

CH 3

Sodium salt of tolueic acid

CH 3

NH 2

p-toluidine

HCl/NaNO 2

00C

CH 3

N=NCl

H 3PO 2

CH 3

6

1.Insoluble in water

2.Soluble in alcohol in ether

3.Lighter than water

4.Used as solvent

Physical properties

7

-CH3 gr is ortho para orienting, so –CH3 directs o/p

position for incoming group.

(a) Ring chlorination (b) side chain chlorination

Chemical properties-chlorination

(a)

CH 3

+ Cl2Fe dust

CH 3 Cl

+

CH 3

Clo-chloro toluene

p-chloro toluene

Ring chlorination should be done at ordinary temperature in pr of halogen carrier I2 or anh AlCl3 or FeCl3 of Fe dust

8

Bromine reacts similar way that of chlorine

Bromination

CH 3

+ Br2

Fe or FeBr3+

CH 3

BrCH 3

Br

9

Condition : boiling toluene or in pr of UV light

Reaction : H atoms in –CH3 gr substituted by –Cl

atom one by one….to form benzyl chloride, benzal

chloride and benzotrichloride.

Sidechain chlorination

CH 3

C l2

1100C

CH 2Cl

Cl2

1100C

CHCl2

Cl21100C

CCl3

10

Benzyl chloride on hydrolysis gives benzylalcohol,

benzalcloride gives benzaldehyde and benzo tri chloride

gives benzoic acid.

Hydrolysis of side chain chlorinated product

CH 2Cl

+ NaO H

CH 2O H

CHCl2

+ Ca(O H)2

C O H

O H

H

-H 2O

CHO

CCl3

+ Ca(O H)2

H 2O

1500C

C O H

O H

HO CO O H

-H2O

11

Side chain bromination

CH 3

NBS(1 m ole)

sunlight

CH 2Br

12

At ordinary condition 1:1 mixture of conc HNO3 and

conc H2SO4 react with toluene to form orto and para

nitro toluene

Nitration of toluene

conc HNO 3

conc H 2SO 4

+

CH 3CH 3 CH 3

NO 2

NO 2

When the above mixture is heated at 60-800C it gives 2,4-dinitro toluene

13

At ordinary condition 1:1 mixture of fuming HNO3

and fuming H2SO4 react with toluene to form 2,4,6

trinitro toluene

Preparation of TNT

Mixture of TNT and ammonium nitrate is known as amatol

fum ing HNO 3

fum ing H 2SO 4

CH 3 CH 3

NO 2

NO 2

O 2N

TNT

14

Toluene when heated with conc sulphuric acid

produces ortho and para toluene sulphonic acid.

Sulphonation

conc H 2SO 4

CH 3 CH 3

SO 3H

+

CH 3

SO 3H

Ortho product predominates at lower temp but para product predominates at higher temperature.

Heat

15

Toluene when reacted with methyl chloride and anh

AlCl3, ortho xylene and para xylene form

Friedel craft reaction

CH 3

CH 3Cl

anh AlCl3+

CH 3CH 3

CH 3

CH 3

16

(i) Etard reaction : Toluene when oxidised by chromyl

chloride in CS2 of CCl4 at room temperature produces a

complex which subsequently hydrolysed to form

benzaldehyde.

Oxidation of toluene

CH 3

(i) CrO 2Cl2

(ii) H 2O

CHO

+ H 2O

17

(ii) chromic acid in acetic anhydride oxidises toluene into

benzaldehyde which immediately conveted to benzylidine

di acetate which hydrolysed by dil H2SO4 produces

benzaldehyde

Oxidation of toluene

CH 3

CrO 3

(CH 3CO)2O

CH

OCOCH 3

OCOCH 3

dil H 2SO 4

CHO

+ 2CH 3COOH

Benzylidine di acetate prevents the oxidation of benzaldehyde to benzoic acid

18

(iii) Toluene when reacted with MnO2 + moderately conc

H2SO4 at 400C produces benzaldehyde

Oxidation of toluene

CH 3CHO

M nO 2

H 2SO 4

+ M nSO 4 + H 2O

If acid is concentrated and temperature is high , the product of the above reaction will be benzoic acid.

19

(iv) Toluene when reacted with alkaline KMnO4 or acidic

K2Cr2O7 produces benzoic acid

Oxidation of toluene

We can also use air passed over V2O5(cat) at 3000C with toluene vapour produces benzoic acid

CH 3

KMnO 4

NaOH

COONa

H +

COOH

K 2Cr2O 7 + H 2SO 4

20

Toluene vapours when reacted with H2 passed over

finely devided Ni ( cat) at 180-2000C forms methyl

cyclohexane.

Hydrogenation of toluene

CH 3

+ 3H 2

Ni

2000C

CH 3

21

Aromatic chemistry and Chlorobenzene

For HS(12)

C-32(part-2)

22

In presence of Fe or FeCl3 at ordinary temperature,

benzene reacts with chlorine gas to form chlorobenzene

preparation of chlorobenzene

Cl2

Fe or FeCl3

Cl

+ HCl

In presence of excess chlorine o- and p- dichloro benzene results

23

In industry, chlorobenzene is prepared by passing a

mixture of benzene vapour, HCl and air over Cu2O as

catalyst at 2500C

Indutrial method(Rasching process)

Cl

HCl

1/2 O 2, Cu2O

2500C

+ H 2O

24

Benzene diazonium chloride disolved in HCl when

heated with cuporus chloride produces chlorobenzene

From benzene diazonium chloride

Second step of the above reaction is known as Sandmeyer reaction.

NH 2

NaNO 3+ HCl

00C

N=N-Cl

CuCl/HCl

Cl

+ N 2 + HCl

25

Other preparations:

O H

+ PCl5

Cl

+ PO Cl3 + HCl

+ HO Cl H +

Cl

+ H 2O

26

The Low Reactivity of Halobenzenes The Low Reactivity of Halobenzenes• The p orbital on the carbon atom of the

benzene ring side-way overlaps with the p orbital of halogen atom

form a delocalized bonding system

27

The Low Reactivity of Halobenzenes The Low Reactivity of Halobenzenes• The CX bond of halobenzenes is stronger

than that of haloalkanes

partial bond character

Breaking of the CX bond requires a larger amount of energy

substitution reactions of halobenzenes are difficult to occur

28

At 3000C and 300 atm pressure chlorobenzene reacts

with NaOH to form sodium phenate which on acidification

produces phenol

Replacement by –OH group

C l

+ 2NaOH 3000C

300 atm

ONa

dil HCl

OH

29

Replacement by –NH2 and –CN gr

Cl

+ 2NH 3Cu2O

2000C, 60 atm

NH 2.HCl

NaO H

NH 2

CuCN

Pyridine, 2000C

CN

+ CuCl

Or KNH2 in liq NH3 at -330C

30

At 1000C chlorobenzene react with a mixture of conc

HNO3 and conc H2SO4 to form a mixture of o-and p-

chloronitrobenzene

Nitration reaction

Cl

conc HNO 3

conc H 2SO 4

1000C

+

Cl Cl

NO 2

NO 2

31

Halogenation and sulphonation

Cl

Cl2

Fe or FeCl3+

ClCl

Cl

Cl

conc H 2SO 4

Cl

SO 3H

+

Cl

SO 3H

O- and p- chlorobenzenesulphonic acid

600C

32

F.C. alkylation & acylation

Cl

+ CH 3Cl anh

A lCl3 +

Cl ClCH 3

CH 3CO Cl

anh AlCl3+

Cl Cl

CO CH 3

CO CH 3

o- and p- chloroactophenone

o- and p- chlorotoluene

CH 3

33

DDT is produced when a mixture of chlorobenzene and

chloral is heated with conc H2SO4

Preparation of DDT

Cl

2 + O =C-CCl3

H

Cl

Cl

C CCl3

H

DDT

34

Preparation of biphenyl

C l

2 + 2Na ether

+ 2NaCl (W urtz reaction)

I

2 + Cu + CuI2 (U llm ann reaction)

35

Equal moles of aryl halide and alkyl halide

dissolved in dry ether when reacts with Na

produces alkyl benzene

Wurtz-Fittig reaction

Cl

+ 2Na + Cl-CH 3

Dry ether

CH 3

+ 2NaCl

Disadvantage : biaryl and alkanes are side products

36

Different conversions from chlorobenzene

Cl

M g in dry ether

M gCl

CH 2 CH 2

O

, H 3O +

C 6H 5CH 2CH 2O H

HCHO

H 3O +

C 6H 5CH 2O H

CH 3CHO

H 3O +

C 6H 5-CH

CH 3

O H

CH 3CN

H 3O +

C 6H 5CO CH 3

CO 2

H 3O +

ether m edium

C 6H 5CO O H

37

Aromatic chemistry and Nitrobenzene

For HS(12)

C-32(part-2)

38

Nitrobenzene is obtained by the action of a mixture of

Conc HNO3 and conc H2SO4 on benzene at 50-600C. At

higher temperature meta dinitrobenzene forms

Lab method

+ HO -NO 2

H 2SO 4

600C

NO 2

+ H 2O

In place of nitrating m ixture,we can use (a) conc HNO 3 of sp gr 1.5

(b)Fum ing nitric acid( containing 6-12% NO 2)

(c) Nitronium tetrafluoroborate ( NO 2+BF 4

-)

(d) Acetyl nitrate ( CH 3CO O NO 2)

39

Other preparation

C 6H 5N=N-ClHNO 2

Cu2OC 6H 5NO 2

HBF 4C 6H 5N 2

+BF 4- NaNO 2

Cu, heatC 6H 5NO 2

C 6H 5NH 2 + 3CF 3COO OH C 6H 5NO 2 + 3CF 3COO HTrifluoro per acetic acid

40

Nitrobenzene is very stable compound not easily

attacked by acids or alkalis but it is easily reduced.

There are two types of reactions of nitrobenzene :

(i) Reaction at nitro group (ii) Recation at benzene

nucleus

Chemical properties

41

Nitrobenzene when heated with Sn or Zn with conc

HCl or Fe dust + conc HCl or SnCl2/HCl, it is reduced to

aniline.

Reduction in acidic medium :

NO 2

Sn /HCl(C)

NH 2

+ 2H 2O

42

Nitrobenzene when warmed with powdered Zn and

NaOH( in methanol) converted to azoxy benzene.

Reduction in alkaline medium

NO 2

+

O 2NZn

m ethanolicNaOH

N=N

O

+

Azoxy benzene is further reduced to azobenzene with conc m ethanolic NaOH solution

N=N

O

+ Zn

m ethanolic NaOH

N=N

43

Nitrobenzene is reduced to hydrazo benzene when

treated with Zn dust and hot aq NaOH solution

Reduction in alkaline medium :

NO 2

+

O 2NZn

aqNaO H

N- N

H H

44

Nitrobenzene is reduced to phenyl hydroxylamine

when it is warmed with Zn dust and an aq solution of

NH4Cl in presence of ethanol

Reduction in neutral medium :

NO 2

Zn

NH 4Cl

NHOH

+ H 2O

45

The presence of NO2 can be confirmed using this

test.The compound is heated with Zn + 50% aq

ethanolic solution of NH4Cl.After cooling it is reacted

with Tollen’s reagent and formation of grey or black

ppt of metallic Ag confirms –NO2 gr.

Mulleken Barker Test

NO 2

Zn

NH 4Cl

NHO H

+ H 2O

C 6H 5NHO H + 2[Ag(NH 3)2]+O H - C 6H 5NO + Ag + NH 3 + H 2O

46

Other reductions :

Catalytic hydrgenation :

NO 2

+ H 2

raney Ni

NH 2

heat + 2H 2O

Electrolysis in weakly acidic m edium :

NO 2

+ 6H + + 6e

NH 2

Electrolysis in strongly acidic m ediumusing Ni electrodes :

NO 2

+ 4H + + 4e

NHOH

intram olecularrearrangem ent

NH 2

OH

p-am inophenol

47

If we want to reduce one nitro gr of m-dinitrobenzene,

the reducing agent to be used : NH4HS or aq Na2S or

methanolic NaHS or SnCl2 in HCl

Selective reduction

NO 2

NO 2

NH 4HS

NO 2

NH 2

m -nitroaniline

48

Substitution reactions

NO 2

Cl2

Fe powder

NO 2

Cl

Br2

Fe

NO 2

Br

conc HNO 3

conc H 2SO 4

900C

NO 2

NO 2

fum ing sulphuric acid

heat

NO 2

SO 3H

49

Nucleophilic substitution

NO 2

KO H

air

NO 2

OH

NO 2

O H

+