Transcript Document

Arenes:
compounds containing both aliphatic and aromatic parts.
Alkylbenzenes
Alkenylbenzenes
Alkynylbenzenes
Etc.
Emphasis on the effect that one part has on the chemistry of the
other half.
Reactivity & orientation
Example: ethylbenzene
EAS in the aromatic part
-CH2CH3 activates and directs ortho- & paraCH3
CH2
CH3
CH2
CH3
CH2
Br
Br2, Fe
+
Br
Free radical halogenation in the side chain
-C6H5 activates and directs benzyl
Br2, heat
CH2 CH3
CH CH3
Br
+
HBr
Alkylbenzenes, nomenclature:
Special names
CH3
CH3
CH3
CH3
CH3
CH3
CH3
toluene
o-xylene
m-xylene
p-xylene
others named as “alkylbenzenes”:
H3C
CH
CH3
isopropylbenzene
CH3
H2C
CH2
H2
CH3
C
CH
CH3
n-propylbenzene
isobutylbenzene
CH2 CH3
CH2 CH3
o-diethylbenzene
n-butylbenzene
Use of phenyl
C6H5- = “phenyl”
CH2CH2
2-methyl-3-phenylheptane
1,2-diphenylethane
do not confuse phenyl (C6H5-) with benzyl (C6H5CH2-)
Alkenylbenzenes, nomenclature:
Special name
CH=CH2
styrene
Rest are named as substituted alkenes
CH2CH=CH2
3-phenylpropene
(allylbenzene)
(Z)-1-phenyl-1-butene
Alkynylbenzenes, nomenclature:
C CH
phenylacetylene
phenylethyne
5-phenyl-2-hexyne
Alcohols, etc., nomenclature:
H3C CH OH
CH2OH
1-phenylethanol
benzyl alcohol
 phenylethyl alcohol
CH2CH2-Cl
1-chloro-2-phenylethane
cyclohexylbenzene
 -phenylethyl chloride
phenylcyclohexane
Alkylbenzenes, syntheses:
1. Friedel-Crafts alkylation
2. Modification of a side chain:
a) addition of hydrogen to an alkene
b) reduction of an alkylhalide
i) hydrolysis of Grignard reagent
ii) active metal and acid
c) Corey-House synthesis
Modification of side chain:
+
H2, Ni
Br
+
Sn, HCl
ethylbenzene
Br
+
Mg; then H2o
Friedel-Crafts:
Ar-H
+ R-X, AlCl3  Ar-R + HX
Ar-H
+ R-OH, H+
 Ar-R + H2O
Ar-H
+ alkene, H+
 Ar-R
+
CH2=CHCH3,
CH3
CH
CH3
H+
+ CH3CH2-OH, H+
CH2
CH3
isopropylbenzene
ethylbenzene
CH3
CH3
+
CH3
H3C C CH3
Br
AlCl3
p-tert-butyltoluene
H3C C CH3
CH3
H+
H3C
cyclohexylbenzene
CH2Cl
AlCl3
CH2
CH3
ortho-
p-benzyltoluene
2
CH2Cl2, AlCl3
CH2
diphenylmethane
Friedel-Crafts limitations:
a) Polyalkylation
b) Possible rearrangement
c) R-X cannot be Ar-X
d) NR when the benzene ring is less reactive
than bromobenzene
e) NR with -NH2, -NHR, -NR2 groups
polyalkylation
CH3
CH3Br, AlCl3
CH3
CH3
+
CH3
CH3
CH3
+
+
H3C
CH3
The alkyl group activates the ring making the products more
reactive that the reactants leading to polyalkylation. Use of
excess aromatic compound minimizes polyalkylation in the lab.
The electrophile in Friedel Crafts alkylation is a
carbocation:
R-X + AlX3

R+
R-OH + H+

R+
| |
— C = C — + H+ 
R+
Carbocations can rearrange! 
rearrangement
H3C
+
CH
CH3
CH3CH2CH2-Br, AlCl3
isopropylbenzene
CH3
H3C C CH3
+
+
CH3
CH3CHCH2-Br
CH3
CH3CCH2-OH
CH3
AlCl3
tert-butylbenzene
H+
carbocation rearrangements are possible!
CH3
CH3CCH2CH3
2-methyl-2-phenylbutane
n-alkylbenzenes cannot be made by Friedel-Crafts alkylation due to
carbocation rearrangements
R-X cannot be Ar-X
R
+
R-X, AlCl3
X
AlCl3
+
NR
The Ar-X bond is strong and does not break like the R-X bond!
NR with rings less reactive than bromobenzene
Br
Br
Br
CH2CH3
+
+
CH3CH2-Br, AlCl3
CH2CH3
COOH
+ CH3-Br, AlCl3
NR
-CHO, -COR
-SO3H
-COOH, -COOR
-CN
NO2
+ CH3CH2-OH, H+
NR
-NR3+
-NO2
NR with –NH2, -NHR, -NR2
NH2
+
NH2 AlCl3
NH2
+
Lewis base
NR
CH3CH2-Cl, AlCl3
AlCl3
Lewis acid
deactivated to EAS
Friedel-Crafts limitations:
a) Polyalkylation
b) Possible rearrangement
c) R-X cannot be Ar-X
d) NR when the benzene ring is less reactive than
bromobenzene
e) NR with -NH2, -NHR, -NR2 groups
In syntheses it is often best to do Friedel-Crafts
alkylation in the first step!
Alkylbenzenes, reactions:
1. Reduction
2. Oxidation
3. EAS
a) nitration
b) sulfonation
c) halogenation
d) Friedel-Crafts alkylation
4. Side chain
free radical halogenation
Alkylbenezenes, reduction:
H2
C
CH3CH3
H2, Ni
NR
NR
H2
C
H2, Ni
300oC, 100 atm.
NR
NR
CH3
CH3
Alkylbenezenes, oxidation:
H2
C
CH3CH3
KMnO4
NR
NR
KMnO4
heat
CH3
NR
COOH
NR
NR
COOH
+
KMnO4, heat
COOH
COOH
+
KMnO4, heat
+
2 CO2
Oxidation of alkylbenzenes.
1) Syn
H2C
CH3
COOH
2) identification
bp 136oC
mp 122oC
C8H10:
CH3
CH3
bp 144oC
CH3
COOH
COOH
mp 231oC
COOH
mp 348oC
bp 139oC
CH3
COOH
CH3
COOH
bp
138oC
mp 300oC
CH3
COOH
Alkylbenzenes, EAS
CH2CH3
HNO3, H2SO4
CH2CH3
NO2
CH2CH3
+
NO2
-R is electron
releasing.
Activates to
EAS and directs
ortho/para
H2SO4, SO3
CH2CH3
SO3H
CH2CH3
+
SO3H
Br2, Fe
CH2CH3
Br
CH2CH3
+
Br
CH3Cl, AlCl3
CH2CH3
CH3
CH2CH3
+
CH3
Alkylbenzenes, free radical halogenation in side chain:
benzyl free radical
CH2CH3
+
Cl2, heat
CHCH3
Cl
91%
CH2CH3
+
only
CH2CH2-Cl
9%
CHCH3
Br
Br2, heat
+
X2
2X
.
CH2CH3 + X
.
.CHCH3
.
.
CHCH3
CHCH3
benzyl free radical > 3o > 2o > 1o > CH3
.
CHCH3
Alkenylbenzenes, syntheses:
1. Modification of side chain:
a) dehydrohalogenation of alkyl halide
b) dehydration of alcohol
c) dehalogenation of vicinal dihalide
d) reduction of alkyne
(2. Friedel-Crafts alkylation)
Alkenylbenzenes, synthesis modification of side chain
KOH(alc)
CHCH3
Br
H+,
CH=CH2
heat
CHCH3
OH
styrene
Zn
CHCH2
Cl Cl
H2, Pd-C
C CH
Alkenylbenzenes, synthesis Friedel-Crafts alkylation
not normally used for alkenylbenzenes.
+
CH2=CH-Br, AlCl3
NR
an exception:
+
CH2=CHCH2-Br, AlCl3
CH2CH=CH2
allylbenzene
KOH(alc)
conjugated with the ring
Br
+
KOH, heat
Alkenylbenzenes, reactions:
1.
Reduction
2.
Oxidation
3.
EAS
4.
Side chain
a) add’n of H2
j) oxymercuration
b) add’n of X2
k) hydroboration
c) add’n of HX
l) addition of free rad.
d) add’n of H2SO4
m) add’n of carbenes
e) add’n of H2O
n) epoxidation
f) add’n of X2 & H2O
o) hydroxylation
g) dimerization
p) allylic halogenation
h) alkylation
q) ozonolysis
i) dimerization
r) vigorous oxidation
Alkenylbenzenes, reactions: reduction
CH=CH2
+
CH=CH2 +
H2, Ni
CH2CH3
o
H2, Ni, 250 C, 1,500 psi
CH2CH3
H
Alkenylbenzenes, reactions oxidation
CH=CH2
KMnO4
CHCH2
OHOH
KMnO4
CH=CH2
COOH
+
CO2
CH=O
+
O=CH2
heat
1. O3
CH=CH2
2. Zn, H2O
Alkenylbenzenes, reactions EAS?
electrophilic addition
CH=CH2
electrophilic aromatic substitution
alkenes are more reactive with electrophiles than aromatic rings!
CH=CH2
+
Br2, Fe
CHCH2
Br Br
In syntheses of alkenylbenzenes, the carbon-carbon
double bond must be synthesized after any EAS reactions
CH2CH3
CH2=CH2
CH2CH3
Cl2, Fe
+ ortho
HF
Cl
Cl2, hv
CH=CH2
Cl
CHCH3
CH2CH2-Cl
Cl
Cl
KOH(alc)
Cl
p-chlorostyrene
Alkenylbenzenes, reactions side chain:
H2, Ni
CH2CH2CH3
CH=CHCH3
Br2, CCl4
Br
CHCHCH3
Br
HBr
CHCH2CH3
Br
H2SO4
CHCH2CH3
OSO3H
Benzyl carbocation
CH=CHCH3
CHCH2CH3
+
H+
CHCH2CH3
CHCH2CH3
resonance stabilization of benzyl carbocation > 3o > 2o > 1o
CHCH2CH3
CH=CHCH3
H2O, H+
CHCH2CH3
OH
Br2, H2O
Br
CHCHCH3
OH
1. H2O, Hg(OAc)2
2. NaBH4
CHCH2CH3
OH
1. (BH3)2
2. H2O2, NaOH
CH2CHCH3
OH
HBr, perox.
CH=CHCH3
CH2CHCH3
Br
polymer.
CHCH2
CH=CH2
n
polystyrene
CH2N2, hv
CH=CHCH3
PBA
CH=CHCH3
O
CH=CHCH3
H
C C
H
CH3
+
CH=CHCH2-Br
Br2, heat
KMnO4
CH3
H
OH
HO
H
+
CH3
HO
H
H
OH
(E)-1-phenylpropene
100 syn-oxidation; make a model!
Alkynylbenzenes, syntheses:
Dehydrohalogenation of vicinal dihalides
Br2
CH=CH2
Br
CHCH2
Br
1. KOH
C CH
2. NaNH2
KOH(alc)
H
C CH3
Br
H2
C CH3
CH2=CH2
HF
Alkynylbenzenes, reactions:
1. Reduction
2. Oxidation
3. EAS
4. Side chain
a) reduction
e) as acids
b) add’n of X2
f) with Ag+
c) add’n of HX
g) oxidation
d) add’n of H2O, H+
Alkynylbenzenes, reactions: reduction
C C CH3
C C CH3
+
2 H2, Ni
+
(xs) H2, Ni
heat & pressure
+
Li, NH3
+
H2, Pd-C
CH2CH2CH3
anti-
syn-
Alkynylbenzenes, reactions: oxidation
O3; then Zn, H2O
KMnO4
COOH
C C CH3
KMnO4, heat
+
HOOCCH3
Alkynylbenzenes, reactions EAS?
electrophilic addition
C CH
electrophilic aromatic substitution
alkynes are more reactive with electrophiles than aromatic rings!
C CH
+
Br2, Fe
Br
C=CH
Br
Alkynylbenzenes, reactions: side chain:
Br2
Br
C=CH
Br
2 Br2
Br Br
C C H
Br Br
C C H
HBr
C=CH2
Br
2 HBr
Br
CCH3
Br
H2O, H+
C CH
O
CCH3
Na
C C-Na+
C CH
Ag+
C C-Ag+
C CH
Ag+
C CCH3
NR, not terminal
Arenes:
alkylbenzenes
alkenylbenzenes
alkynylbenzenes
As expected, but remember that you cannot do EAS on
alkenyl- or alkynylbenzenes.