Sulphonation

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1. Chapter 12Chapter 12
Reactions of Arenes:Reactions of Arenes:
Electrophilic Aromatic SubstitutionElectrophilic Aromatic Substitution

HH

EE
++EEYY ++HHYY
dd++dd––

2. 12.1
Representative Electrophilic Aromatic
Substitution Reactions of Benzene

HH

EE
++EEYY ++HHYY
dd++dd––

3. HH

EE
++EEYY ++HHYY
dd++dd––
Electrophilic aromatic substitutions include:Electrophilic aromatic substitutions include:
NitrationNitration
SulfonationSulfonation
HalogenationHalogenation
Friedel-Crafts AlkylationFriedel-Crafts Alkylation
Friedel-Crafts AcylationFriedel-Crafts Acylation

4. HH
Table 12.1: Table 12.1: Nitration of BenzeneNitration of Benzene
++
++HH
22OO
HH
22SOSO
44
HOHONONO
22

NONO
22
NitrobenzeneNitrobenzene
(95%)(95%)

5. HH
Table 12.1: Sulfonation of BenzeneTable 12.1: Sulfonation of Benzene
++
++HH
22OO
heatheat
HOHOSOSO
22OHOH

SOSO
22OHOH
Benzenesulfonic acidBenzenesulfonic acid
(100%)(100%)

6. HH
Table 12.1: Halogenation of BenzeneTable 12.1: Halogenation of Benzene
++
++HHBrBr
FeBrFeBr
33
BrBr
22

BrBr
22
BromobenzeneBromobenzene
(65-75%)(65-75%)

7. HH
Table 12.1: Friedel-Crafts Alkylation of BenzeneTable 12.1: Friedel-Crafts Alkylation of Benzene
++
++HHClCl
AlClAlCl
33

C(CHC(CH
33))
33
terttert-Butylbenzene-Butylbenzene
(60%)(60%)
(CH(CH
33))
33CCClCl

8. HH
Table 12.1: Friedel-Crafts Acylation of BenzeneTable 12.1: Friedel-Crafts Acylation of Benzene
++
++HHClCl
AlClAlCl
33
1-Phenyl-1-propanone1-Phenyl-1-propanone
(88%)(88%)
OO
CHCH
33CHCH
22CCClCl

CCHCCH
22CHCH
33
OO

9. 12.212.2
Mechanistic PrinciplesMechanistic Principles
ofof
Electrophilic Aromatic SubstitutionElectrophilic Aromatic Substitution

10. Step 1: attack of electrophileStep 1: attack of electrophile
on on pp-electron system of aromatic ring-electron system of aromatic ring

HH HH
HH HH
HH HH
EE
++

HH HH
HH
HH
HH HHEE
++
highly endothermichighly endothermic
carbocation is allylic, but not aromaticcarbocation is allylic, but not aromatic

11. Step 2: loss of a proton from the carbocationStep 2: loss of a proton from the carbocation
intermediateintermediate
HH HH
HH EE
HH HH
HH
++ HH HH
HH
HH
HH HHEE
++
highly exothermichighly exothermic
this step restores aromaticity of ringthis step restores aromaticity of ring

12. H
H
H H
H + E
+

H
E
H
H H
H + H
+

H

H H
H
H
H HE
+

13. Based on this general mechanism:Based on this general mechanism:
what remains is to identify the electrophile in what remains is to identify the electrophile in
nitration, sulfonation, halogenation, Friedel-nitration, sulfonation, halogenation, Friedel-
Crafts alkylation, and Friedel-Crafts acylation Crafts alkylation, and Friedel-Crafts acylation
to establish the mechanism of specific to establish the mechanism of specific
electrophilic aromatic substitutionselectrophilic aromatic substitutions

14. 12.3
Nitration of Benzene

15. HH
Nitration of BenzeneNitration of Benzene
++
++HH
22OO
HH
22SOSO
44
HOHONONO
22

NONO
22
Electrophile isElectrophile is
nitronium ion nitronium ion
OONNOO
••••
++
••••
••
••
••
••

16. Step 1: attack of nitronium cationStep 1: attack of nitronium cation
on on pp-electron system of aromatic ring-electron system of aromatic ring

HH HH
HH HH
HH HH
NONO
22
++

HH HH
HH
HH
HH HHNONO
22
++

17. Step 2: loss of a proton from the carbocationStep 2: loss of a proton from the carbocation
intermediateintermediate
HH HH
HH NONO
22
HH HH
HH
++ HH HH
HH
HH
HH HHNONO
22
++

18. Where does nitronium ion come from?Where does nitronium ion come from?
HH
22SOSO
44
OO
NN
HH
OO
OO
++
•••• ••••
••••
••
••
••
••
••
••
••••
––
OO
NN
HH
OO
OO
++
•••• ••••
••••
••
••
••
••
••••
––
HH
++
OONNOO
••••
++
••••
••
••
••
••
++
HH
OO
••••
HH
••••

19. 12.4
Sulfonation of Benzene

20. HH
Sulfonation of BenzeneSulfonation of Benzene
++
++HH
22OO
heatheat
HOHOSOSO
22OHOH

SOSO
22OHOH
Several electrophiles present:Several electrophiles present:
a major one is sulfur trioxidea major one is sulfur trioxide
OO
SS
OO
OO
++
•••• ••••
••••
••
••
••
••
••
••
••••
––

21. Step 1: attack of sulfur trioxideStep 1: attack of sulfur trioxide
on on pp-electron system of aromatic ring-electron system of aromatic ring

HH HH
HH HH
HH HH
SOSO
33
HH HH
HH
HH
HH HHSOSO
33
––
++

22. Step 2: loss of a proton from the carbocationStep 2: loss of a proton from the carbocation
intermediateintermediate
HH HH
HH SOSO
33
––
HH HH
HH
++ HH HH
HH
HH
HH HHSOSO
33
––
++

23. Step 3: protonation of benzenesulfonate ionStep 3: protonation of benzenesulfonate ion
HH HH
HH SOSO
33
––
HH HH

HH
22SOSO
44
HH HH
HH SOSO
33HH
HH HH

24. 12.5
Halogenation of Benzene

25. HH
Halogenation of BenzeneHalogenation of Benzene
++
++HHBrBr
FeBrFeBr
33
BrBr
22

BrBr
22
Electrophile is a Lewis acid-Lewis baseElectrophile is a Lewis acid-Lewis base
complex between FeBrcomplex between FeBr
33 and Br and Br
22..

26. The BrThe Br
22-FeBr-FeBr
33 Complex Complex
++••
••BrBrBrBr••
••
•••• ••••
•••• ••••
Lewis baseLewis base Lewis acidLewis acid
FeBrFeBr
33

BrBrBrBr••
••
•••• ••••
•••• ••••
FeBrFeBr
33
––
++

ComplexComplex
The BrThe Br
22-FeBr-FeBr
33 complex is more electrophilic complex is more electrophilic
than Brthan Br
22 alone. alone.

27. Step 1: attack of BrStep 1: attack of Br
22-FeBr-FeBr
33 complex complex
on on pp-electron system of aromatic ring-electron system of aromatic ring

HH HH
HH HH
HH HH

HH HH
HH
HH
HH HHBrBr
++

BrBrBrBrFeBrFeBr
33
––++
+ FeBr+ FeBr
44
––

28. Step 2: loss of a proton from the carbocationStep 2: loss of a proton from the carbocation
intermediateintermediate
HH HH
HH BrBr
HH HH
HH
++ HH HH
HH
HH
HH HHBrBr
++

29. 12.6
Friedel-Crafts Alkylation of Benzene

30. HH
Friedel-Crafts Alkylation of BenzeneFriedel-Crafts Alkylation of Benzene
++
++HHClCl
AlClAlCl
33

C(CHC(CH
33))
33
Electrophile is Electrophile is
terttert-butyl cation-butyl cation
(CH(CH
33))
33CClCCl
CC CHCH
33
HH
33CC
HH
33CC
++

31. acts as a Lewis acid to promote ionizationacts as a Lewis acid to promote ionization
of the alkyl halideof the alkyl halide
Role of AlClRole of AlCl
33
(CH(CH
33))
33CC
ClCl••
••
••••
••••
++AlClAlCl
33

++
(CH(CH
33))
33CC
ClCl
••••
••••
AlClAlCl
33
––

32. acts as a Lewis acid to promote ionizationacts as a Lewis acid to promote ionization
of the alkyl halideof the alkyl halide
Role of AlClRole of AlCl
33
(CH(CH
33))
33CC
ClCl••
••
••••
••••
++AlClAlCl
33

++
(CH(CH
33))
33CC
ClCl
••••
••••
AlClAlCl
33
––

++
(CH(CH
33))
33CC
ClCl
••••
••••
AlClAlCl
33
––
••
••
++

33. Step 1: attack of tert-butyl cationStep 1: attack of tert-butyl cation
on on pp-electron system of aromatic ring-electron system of aromatic ring

HH HH
HH HH
HH HH

HH HH
HH
HH
HH HHC(CHC(CH
33))
33
++
C(CHC(CH
33))
33
++

34. Step 2: loss of a proton from the carbocationStep 2: loss of a proton from the carbocation
intermediateintermediate
HH HH
HH C(CHC(CH
33))
33
HH HH
HH
++ HH HH
HH
HH
HH HHC(CHC(CH
33))
33
++

35. HH
Rearrangements in Friedel-Crafts AlkylationRearrangements in Friedel-Crafts Alkylation
Carbocations are intermediates.Carbocations are intermediates.
Therefore, rearrangements can occurTherefore, rearrangements can occur
(CH(CH
33))
22CHCHCHCH
22ClCl
AlClAlCl
33
Isobutyl chlorideIsobutyl chlorideterttert-Butylbenzene-Butylbenzene
(66%)(66%)

C(CHC(CH
33))
33
++

36. HH
Rearrangements in Friedel-Crafts AlkylationRearrangements in Friedel-Crafts Alkylation
Isobutyl chloride is the alkyl halide.Isobutyl chloride is the alkyl halide.
But But terttert-butyl cation is the -butyl cation is the
electrophile.electrophile.
(CH(CH
33))
22CHCHCHCH
22ClCl
AlClAlCl
33
Isobutyl chlorideIsobutyl chlorideterttert-Butylbenzene-Butylbenzene
(66%)(66%)

C(CHC(CH
33))
33
++

37. Rearrangements in Friedel-Crafts AlkylationRearrangements in Friedel-Crafts Alkylation
CCCHCH
22
HH
33CC
CHCH
33
HH
ClCl
••••
••••
AlClAlCl
33
++
––

CCCHCH
22
HH
33CC
CHCH
33
HH
++
++ClCl
••••
••••
AlClAlCl
33
––
••
••

38. HH
Reactions Related to Friedel-Crafts AlkylationReactions Related to Friedel-Crafts Alkylation
HH
22SOSO
44
++
CyclohexylbenzeneCyclohexylbenzene
(65-68%)(65-68%)


Cyclohexene is protonated by sulfuric acid, Cyclohexene is protonated by sulfuric acid,
giving cyclohexyl cation which attacks the giving cyclohexyl cation which attacks the
benzene ringbenzene ring

39. 12.7
Friedel-Crafts Acylation of Benzene

40. HH
Friedel-Crafts Acylation of BenzeneFriedel-Crafts Acylation of Benzene
++
++HHClCl
AlClAlCl
33
OO
CHCH
33CHCH
22CClCCl

CCHCCH
22CHCH
33
OO
Electrophile is an acyl cationElectrophile is an acyl cation
••••
CHCH
33CHCH
22CCOO••
••
++
CHCH
33CHCH
22CCOO••
••
++

41. Step 1: attack of the acyl cationStep 1: attack of the acyl cation
on on pp-electron system of aromatic ring-electron system of aromatic ring

HH HH
HH HH
HH HH

HH HH
HH
HH
HH HH
++
OO
CCHCCH
22CHCH
33
++
OO
CCHCCH
22CHCH
33

42. Step 2: loss of a proton from the carbocationStep 2: loss of a proton from the carbocation
intermediateintermediate
HH HH
HH
HH HH
HH
++ HH HH
HH
HH
HH HH
++
OO
CCHCCH
22CHCH
33
OO
CCHCCH
22CHCH
33

43. can be used instead of acyl chloridescan be used instead of acyl chlorides

HH
Acid AnhydridesAcid Anhydrides
AcetophenoneAcetophenone
(76-83%)(76-83%)
AlClAlCl
33

OO
CCHCCH
33
OO
CHCH
33COCCHCOCCH
33
OO
++
OO
CHCH
33COHCOH++

44. 12.8
Acylation-Reduction

45. Reduction of aldehyde and ketoneReduction of aldehyde and ketone
carbonyl groups using Zn(Hg) and HCl is carbonyl groups using Zn(Hg) and HCl is
called the called the Clemmensen reductionClemmensen reduction..
Acylation-ReductionAcylation-Reduction

HH

OO
CRCR
Zn(Hg), HClZn(Hg), HCl
AlClAlCl
33
RCClRCCl
OO

CHCH
22RR
permits primary alkyl groups to be attachedpermits primary alkyl groups to be attached
to an aromatic ringto an aromatic ring

46. Reduction of aldehyde and ketoneReduction of aldehyde and ketone
carbonyl groups by heating with Hcarbonyl groups by heating with H
22NNHNNH
22
and KOH is called theand KOH is called the
Wolff-Kishner reductionWolff-Kishner reduction..
Acylation-ReductionAcylation-Reduction

HH

OO
CRCR
HH
22NNHNNH
22, KOH,, KOH,
triethylene glycol,triethylene glycol,
heatheat
AlClAlCl
33
RCClRCCl
OO

CHCH
22RR
permits primary alkyl groups to be attachedpermits primary alkyl groups to be attached
to an aromatic ringto an aromatic ring

47. Example: Prepare isobutylbenzeneExample: Prepare isobutylbenzene
No! Friedel-Crafts alkylation of benzene No! Friedel-Crafts alkylation of benzene
using isobutyl chloride fails because of using isobutyl chloride fails because of
rearrangement.rearrangement.
(CH(CH
33))
22CHCHCHCH
22ClCl
AlClAlCl
33


CHCH
22CH(CHCH(CH
33))
33

48. RecallRecall
(CH(CH
33))
22CHCHCHCH
22ClCl
AlClAlCl
33
Isobutyl chlorideIsobutyl chlorideterttert-Butylbenzene-Butylbenzene
(66%)(66%)

C(CHC(CH
33))
33
++

49. Use Acylation-Reduction InsteadUse Acylation-Reduction Instead
++

(CH(CH
33))
22CHCClCHCCl
OO
AlClAlCl
33

OO
CCH(CHCCH(CH
33))
22
Zn(Hg)Zn(Hg)
HClHCl

CHCH
22CH(CHCH(CH
33))
33