CH 3
CH 3
NO 2
CH 3
NO 2
Toluene
HNO 3
H 2 SO 4
+
ortho-Nitrotoluene
(61%)
para-Nitrotoluene
(39%)
+
Apart from the usual electrophilic aromatic substitution reactions, other
reactions can be carried out involving the methyl group in toluene, e.g.
oxidation and halogenation of the alkyl group.
Oxidation of toluene
Regardless of the length of the alkyl substituent in any alkylbenzene, it can
be oxidized to a carboxylic acid provided that it has a hydrogen atom,
bonded to the benzylic carbon. So, reaction can occur with 1
and 2
, but not
3
, alkyl side chains. Toluene is oxidized to benzoic acid.
CH 3
CO 2 H
Toluene
KMnO
Benzoic acid
H 2 O
Benzylic bromination of toluene
Bromine selectively substitutes for a benzylic hydrogen in toluene in a
radical substitution reaction to produce bromomethylbenzene or benzylbromide. N-bromosuccinimide is used to carry out benzylic bromination of
toluene.
CH 3
CH 2 Br
N
O
O
Br
Toluene
Bromomethylbenzene
CCl 4
Bromomethylbenzene or benzylbromide can be subjected to further
nucleophilic reactions. Bromine can be replaced by a variety of nucleophiles
by means of an S N 2 and S N 1 reaction, resulting in various monosubstituted
benzenes.
128
CH4 ORGANIC FUNCTIONAL GROUPS