Arenes : compounds containing both aliphatic and aromatic parts. Alkylbenzenes Alkenylbenzenes...
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Transcript of Arenes : compounds containing both aliphatic and aromatic parts. Alkylbenzenes Alkenylbenzenes...
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- & para-
CH2
CH3
CH2
CH3CH2
CH3
CH2 CH3 CH CH3
Br2, Fe Br
Br
Br2, heat
Br+ HBr
+
Free radical halogenation in the side chain
-C6H5 activates and directs benzyl
Alkylbenzenes, nomenclature:
Special names
CH3 CH3CH3
CH3
CH3
CH3
CH3
toluene o-xylene m-xylene p-xylene
others named as “alkylbenzenes”:
CHH3C CH3 CH2
H2CCH3
H2C
CHCH3
CH3
isopropylbenzene n-propylbenzene isobutylbenzene
CH2
CH2
CH3
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:
CH=CH2
styrene
CH2CH=CH2
3-phenylpropene(allylbenzene)
(Z)-1-phenyl-1-butene
Special name
Rest are named as substituted alkenes
Alkynylbenzenes, nomenclature:
C CH
phenylacetylene5-phenyl-2-hexyne
phenylethyne
Alcohols, etc., nomenclature:
CHH3C OH
1-phenylethanol
phenylethyl alcohol
CH2OH
benzyl alcohol
1-chloro-2-phenylethane
-phenylethyl chloride
CH2CH2-Cl
cyclohexylbenzene
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:
Br
+ H2, Ni
+ Sn, HCl
Br
+ Mg; then H2o
ethylbenzene
Friedel-Crafts:
Ar-H + R-X, AlCl3 Ar-R + HX
Ar-H + R-OH, H+ Ar-R + H2O
Ar-H + alkene, H+ Ar-R
CH3CH3
CCH3
H3C CH3
+ H3C CCH3
BrCH3
AlCl3
+ CH3CH2-OH, H+ CH2CH3
+ CH2=CHCH3, H+CH
CH3
CH3isopropylbenzene
ethylbenzene
p-tert-butyltoluene
H+cyclohexylbenzene
H3C CH2Cl
AlCl3CH2 CH3
ortho-p-benzyltoluene
CH2Cl2, AlCl32 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
CH3CH3Br, AlCl3
+CH3 CH3
CH3
CH3
+
CH3CH3
H3C
+
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
+ CH3CH2CH2-Br, AlCl3
CHCH3H3C
AlCl3+
C CH3H3CCH3
+
H+
isopropylbenzene
tert-butylbenzene
2-methyl-2-phenylbutane
carbocation rearrangements are possible!
CH3CCH2CH3
CH3
CH3CHCH2-BrCH3
CH3CCH2-OHCH3
CH3
n-alkylbenzenes cannot be made by Friedel-Crafts alkylation due to
carbocation rearrangements
R-X cannot be Ar-X
+ R-X, AlCl3
R
+
XAlCl3
NR
The Ar-X bond is strong and does not break like the R-X bond!
NR with rings less reactive than bromobenzene
Br
+ CH3CH2-Br, AlCl3
Br Br
CH2CH3
CH2CH3+
COOH
NO2
+ CH3-Br, AlCl3
+ CH3CH2-OH, H+
NR
NR
-CHO, -COR
-SO3H
-COOH, -COOR
-CN
-NR3+
-NO2
NR with –NH2, -NHR, -NR2
NH2
+ CH3CH2-Cl, AlCl3 NR
NH2
+ AlCl3
NH2 AlCl3
Lewis base 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:
NR NR NR
NR
H2, Ni
H2, Ni
300oC, 100 atm.
CH3CH3
H2C
CH3
H2C
CH3
Alkylbenezenes, oxidation:
NR NR NR
NR NR
KMnO4
KMnO4
heat
CH3CH3
H2C
CH3
COOH
+ KMnO4, heat
+ KMnO4, heat
COOH
COOH
COOH+ 2 CO2
Oxidation of alkylbenzenes.
1) Syn
2) identification
C8H10:
H2C
CH3CH3
CH3
CH3
CH3
CH3
CH3 COOH
COOHCOOH
COOH
COOH
COOH
COOH
bp 136oC
bp 144oC
bp 139oC
bp 138oC
mp 122oC
mp 231oC
mp 348oC
mp 300oC
Alkylbenzenes, EAS
CH2CH3CH2CH3
CH2CH3
CH2CH3 CH2CH3
CH2CH3CH2CH3
CH2CH3CH2CH3
NO2
NO2
SO3H
SO3H
Br
Br
CH3
CH3
+
+
+
+HNO3, H2SO4
H2SO4, SO3
Br2, Fe
CH3Cl, AlCl3
-R is electron releasing. Activates to EAS and directs ortho/para
Alkylbenzenes, free radical halogenation in side chain:
benzyl free radical
CH2CH3
CH2CH3
+ Cl2, heat
+ Br2, heat
CHCH3 CH2CH2-Cl
CHCH3
Cl
+
Br
91% 9%
only
CH2CH3
benzyl free radical > 3o > 2o > 1o > CH3
CHCH3
CHCH3CHCH3 CHCH3.
.
.
.
X2 2 X.
+ X .
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
CHCH3
CHCH3
CHCH2
C
CH=CH2
CH
Br
OH
Cl Cl
styrene
KOH(alc)
H+, heat
Zn
H2, Pd-C
Alkenylbenzenes, synthesis Friedel-Crafts alkylation
not normally used for alkenylbenzenes.
an exception:
+ CH2=CHCH2-Br, AlCl3 CH2CH=CH2
allylbenzene
+ CH2=CH-Br, AlCl3 NR
Br
KOH(alc)conjugated with the ring
+ KOH, heat
Alkenylbenzenes, reactions:
1. Reduction
2. Oxidation
3. EAS
4. Side chain
a) add’n of H2 h) oxymercuration
b) add’n of X2 i) hydroboration
c) add’n of HX j) addition of free rad.
d) add’n of H2SO4 k) add’n of carbenes
e) add’n of H2O l) epoxidation
f) add’n of X2 & H2O m) hydroxylation
g) allylic halogenation n) ozonolysis
o) vigorous oxidation
Alkenylbenzenes, reactions: reduction
CH=CH2
CH=CH2
+ H2, Ni
+ H2, Ni, 250oC, 1,500 psi
CH2CH3
H
CH2CH3
Alkenylbenzenes, reactions oxidation
CH=CH2
CH=CH2
CH=CH2
CHCH2
COOH
CH=O
OHOH
+ CO2
+ O=CH2
KMnO4
heat
1. O3
2. Zn, H2O
KMnO4
Alkenylbenzenes, reactions EAS?
CH=CH2
electrophilic aromatic substitution
electrophilic addition
alkenes are more reactive with electrophiles than aromatic rings!
CH=CH2 + Br2, Fe CHCH2Br Br
In syntheses of alkenylbenzenes, the carbon-carbon double bond must be synthesized after any EAS reactions
CH2CH3 CH2CH3
CH=CH2
Cl
CHCH3
CH2=CH2
HF
Cl2, Fe+ ortho
CH2CH2-ClCl
Cl ClCl
Cl2, hv
KOH(alc)
p-chlorostyrene
Alkenylbenzenes, reactions side chain:
CH=CHCH3 CH2CH2CH3
CHCHCH3
CHCH2CH3
CHCH2CH3
Br
Br
Br
OSO3H
H2, Ni
Br2, CCl4
HBr
H2SO4
Benzyl carbocation
CH=CHCH3 + H+ CHCH2CH3
CHCH2CH3CHCH2CH3 CHCH2CH3
resonance stabilization of benzyl carbocation > 3o > 2o > 1o
CH=CHCH3 CHCH2CH3
CHCHCH3
CHCH2CH3
CH2CHCH3
OH
OH
Br
OH
OH
H2O, H+
Br2, H2O
1. H2O, Hg(OAc)2
2. NaBH4
1. (BH3)2
2. H2O2, NaOH
CH=CHCH3 CH2CHCH3
CH=CHCH3
CH=CHCH3
Br
O
HBr, perox.
CH2N2, hv
PBA
CH=CHCH3 + Br2, heat CH=CHCH2-Br
C CCH3
H
H
(E)-1-phenylpropene
CH3H OH
HO H
CH3HO H
H OH+KMnO4
100 syn-oxidation; make a model!
Alkynylbenzenes, syntheses:
Dehydrohalogenation of vicinal dihalides
CH=CH2 CHCH2Br
BrC CH
Br2 1. KOH
2. NaNH2
HC CH3Br
KOH(alc)
H2C 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 + 2 H2, Ni CH2CH2CH3
+ (xs) H2, Ni heat & pressure
C C CH3 + Li, NH3
+ H2, Pd-C
anti-
syn-
Alkynylbenzenes, reactions: oxidation
C C CH3
KMnO4, heat
O3; then Zn, H2O
COOH + HOOCCH3
KMnO4
Alkynylbenzenes, reactions EAS?
C
electrophilic aromatic substitution
electrophilic addition
alkynes are more reactive with electrophiles than aromatic rings!
C + Br2, Fe C=CH
CH
CH
Br
Br
Alkynylbenzenes, reactions: side chain:
C C H C=CH
C
CCH3
Br
Br
Br
Br
Br
BrCBr
BrH
C=CH2Br
Br2
2 Br2
HBr
2 HBr
C CHH2O, H+
CCH3
O
C CH
C CH
Na
Ag+
C
C
C-Na+
C-Ag+
C CCH3
Ag+
NR, not terminal
Arenes:
alkylbenzenes
alkenylbenzenes
alkynylbenzenes
As expected, but remember that you cannot do EAS on alkenyl- or alkynylbenzenes.