Table 12.1: Halogenation of Benzene
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H H Table 12.1: Halogenation of Benzene Table 12.1: Halogenation of Benzene + + + + H H Br Br FeBr FeBr 3 Br Br 2 Br Br Bromobenzene Bromobenzene (65-75%) (65-75%)
description
H. Br. Table 12.1: Halogenation of Benzene. FeBr 3. +. Br 2. +. H Br. Bromobenzene (65-75%). H. C(CH 3 ) 3. Table 12.1: Friedel-Crafts Alkylation of Benzene. AlCl 3. +. (CH 3 ) 3 C Cl. +. H Cl. tert -Butylbenzene (60%). O. O. H. CCH 2 CH 3. CH 3 CH 2 C Cl. - PowerPoint PPT Presentation
Transcript of Table 12.1: Halogenation of Benzene
HH
Table 12.1: Halogenation of BenzeneTable 12.1: Halogenation of Benzene
++ ++ HHBrBr
FeBrFeBr33
BrBr22
BrBr
BromobenzeneBromobenzene(65-75%)(65-75%)
HH
Table 12.1: Friedel-Crafts Alkylation of BenzeneTable 12.1: Friedel-Crafts Alkylation of Benzene
++ ++ HHClCl
AlClAlCl33
C(CHC(CH33))33
terttert-Butylbenzene-Butylbenzene(60%)(60%)
(CH(CH33))33CCClCl
HH
Table 12.1: Friedel-Crafts Acylation of BenzeneTable 12.1: Friedel-Crafts Acylation of Benzene
++ ++ HHClCl
AlClAlCl33
1-Phenyl-1-propanone1-Phenyl-1-propanone(88%)(88%)
OO
CHCH33CHCH22CCClCl
CCHCCH22CHCH33
OO
HH
Halogenation of BenzeneHalogenation of Benzene
++ ++ HHBrBr
FeBrFeBr33
BrBr22
BrBr
Electrophile is a Lewis acid-Lewis baseElectrophile is a Lewis acid-Lewis basecomplex between FeBrcomplex between FeBr33 and Br and Br22..
The BrThe Br22-FeBr-FeBr33 Complex Complex
++••••BrBr BrBr•••••••• ••••
•••• ••••
Lewis baseLewis base Lewis acidLewis acid
FeBrFeBr33
BrBr BrBr•••••••• ••••
•••• ••••FeBrFeBr33
––++
ComplexComplex
The BrThe Br22-FeBr-FeBr33 complex is more electrophilic complex is more electrophilic
than Brthan Br22 alone. alone.
Step 1: attack of BrStep 1: attack of Br22-FeBr-FeBr33 complex complex
on on -electron system of aromatic ring-electron system of aromatic ring HH HH
HH HHHH HH
HH HH
HHHH
HH HH BrBr
++
BrBr BrBr FeBrFeBr33
––++
+ FeBr+ FeBr44––
Step 2: loss of a proton from the carbocationStep 2: loss of a proton from the carbocationintermediateintermediate
HH HH
HH BrBrHH HH
HH++ HH HH
HHHH
HH HH BrBr
++
12.6Friedel-Crafts Alkylation of Benzene
HH
Friedel-Crafts Alkylation of BenzeneFriedel-Crafts Alkylation of Benzene
++ ++ HHClCl
AlClAlCl33
C(CHC(CH33))33
Electrophile is Electrophile is terttert-butyl cation-butyl cation
(CH(CH33))33CClCCl
CC CHCH33
HH33CC
HH33CC++
acts as a Lewis acid to promote ionizationacts as a Lewis acid to promote ionizationof the alkyl halideof the alkyl halide
Role of AlClRole of AlCl33
(CH(CH33))33CC ClCl ••••••••
••••++ AlClAlCl33
++
(CH(CH33))33CC ClCl••••
••••AlClAlCl33––
acts as a Lewis acid to promote ionizationacts as a Lewis acid to promote ionizationof the alkyl halideof the alkyl halide
Role of AlClRole of AlCl33
(CH(CH33))33CC ClCl ••••••••
••••++ AlClAlCl33
++
(CH(CH33))33CC ClCl••••
••••AlClAlCl33––
++(CH(CH33))33CC ClCl
••••
••••AlClAlCl33––
••••++
Step 1: attack of tert-butyl cationStep 1: attack of tert-butyl cationon on -electron system of aromatic ring-electron system of aromatic ring
HH HH
HH HHHH HH
HH HH
HHHH
HH HH C(CHC(CH33))33
++
C(CHC(CH33))33++
Step 2: loss of a proton from the carbocationStep 2: loss of a proton from the carbocationintermediateintermediate
HH HH
HH C(CHC(CH33))33
HH HH
HH++ HH HH
HHHH
HH HH C(CHC(CH33))33
++
HH
Reactions Related to Friedel-Crafts AlkylationReactions Related to Friedel-Crafts Alkylation
HH22SOSO44
++
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
12.7Friedel-Crafts Acylation of Benzene
HH
Friedel-Crafts Acylation of BenzeneFriedel-Crafts Acylation of Benzene
++ ++ HHClCl
AlClAlCl33OO
CHCH33CHCH22CClCCl
CCHCCH22CHCH33
OO
Electrophile is an acyl cationElectrophile is an acyl cation
••••CHCH33CHCH22CC OO ••••
++CHCH33CHCH22CC OO ••••
++
Step 1: attack of the acyl cationStep 1: attack of the acyl cationon on -electron system of aromatic ring-electron system of aromatic ring
HH HH
HH HHHH HH
HH HH
HHHH
HH HH
++
OO
CCHCCH22CHCH33++
OO
CCHCCH22CHCH33
Step 2: loss of a proton from the carbocationStep 2: loss of a proton from the carbocationintermediateintermediate
HH HH
HHHH HH
HH++ HH HH
HHHH
HH HH
++
OO
CCHCCH22CHCH33
OO
CCHCCH22CHCH33
can be used instead of acyl chloridescan be used instead of acyl chlorides HH
Acid AnhydridesAcid Anhydrides
AcetophenoneAcetophenone(76-83%)(76-83%)
AlClAlCl33 OO
CCHCCH33
OO
CHCH33COCCHCOCCH33
OO
++
OO
CHCH33COHCOH++
12.8Acylation-Reduction
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), HClAlClAlCl33
RCClRCCl
OO CHCH22RR
permits primary alkyl groups to be attachedpermits primary alkyl groups to be attachedto an aromatic ringto an aromatic ring
Reduction of aldehyde and ketoneReduction of aldehyde and ketonecarbonyl groups by heating with Hcarbonyl groups by heating with H22NNHNNH22
and KOH is called theand KOH is called the
Wolff-Kishner reductionWolff-Kishner reduction..
Acylation-ReductionAcylation-Reduction HH OO
CRCRHH22NNHNNH22, KOH,, KOH,
triethylene glycol,triethylene glycol,
heatheat
AlClAlCl33
RCClRCCl
OO CHCH22RR
permits primary alkyl groups to be attachedpermits primary alkyl groups to be attachedto an aromatic ringto an aromatic ring
HH
Rearrangements in Friedel-Crafts AlkylationRearrangements in Friedel-Crafts Alkylation
Carbocations are intermediates.Carbocations are intermediates.
Therefore, rearrangements can occurTherefore, rearrangements can occur
(CH(CH33))22CHCHCHCH22ClClAlClAlCl33
Isobutyl chlorideIsobutyl chloride terttert-Butylbenzene-Butylbenzene(66%)(66%)
C(CHC(CH33))33
++
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(CH33))22CHCHCHCH22ClClAlClAlCl33
Isobutyl chlorideIsobutyl chloride terttert-Butylbenzene-Butylbenzene(66%)(66%)
C(CHC(CH33))33
++
Rearrangements in Friedel-Crafts AlkylationRearrangements in Friedel-Crafts Alkylation
CC CHCH22HH33CC
CHCH33
HH
ClCl••••
••••AlClAlCl33
++ ––
CC CHCH22HH33CC
CHCH33
HH++
++ ClCl••••
••••AlClAlCl33––
••••
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(CH33))22CHCHCHCH22ClCl
AlClAlCl33
CHCH22CH(CHCH(CH33))22
RecallRecall
(CH(CH33))22CHCHCHCH22ClClAlClAlCl33
Isobutyl chlorideIsobutyl chloride terttert-Butylbenzene-Butylbenzene(66%)(66%)
C(CHC(CH33))33
++
Use Acylation-Reduction InsteadUse Acylation-Reduction Instead
++
(CH(CH33))22CHCClCHCCl
OO
AlClAlCl33 OO
CCH(CHCCH(CH33))22
Zn(Hg)Zn(Hg)HClHCl
CHCH22CH(CHCH(CH33))22
