Organic Chemistry

628 CHAPTER 16 Reactions of Substituted Benzenes

If the alkyl group lacks a benzylic hydrogen, the oxidation reaction will not occur

because the first step in the oxidation reaction is removal of a hydrogen from the ben-

zylic carbon.

The same reagents that oxidize alkyl substituents will oxidize benzylic alcohols to

benzoic acid.

If, however, a mild oxidizing agent such as is used, benzylic alcohols are oxi-

dized to aldehydes or ketones.

Reducing a Nitro Substituent

A nitro substituent can be reduced to an amino substituent. Either a metal (tin, iron, or

zinc) plus an acid (HCl) or catalytic hydrogenation can be used to carry out the reduc-

tion. Recall from Section 1.20 that if acidic conditions are employed, the product will

be in its acidic form (anilinium ion). When the reaction is over, base can be added to

convert the product into its basic form (aniline).

MnO 2

OH

CH 2

O

C

H

phenylmethanol

benzyl alcohol

∆

benzaldehyde

MnO 2

OH

CHCH 3

O

C

CH 3

∆

1-phenylethanol acetophenone

MnO 2

Na 2 Cr 2 O 7 , H+

∆

OH

CHCH 3

O

C

OH

1-phenylethanol benzoic acid

CCH 3

tert-butylbenzene

no reaction

CH 3

CH 3

Na 2 Cr 2 O 7 , H+

∆

does not have a

benzylic hydrogen

CHCH 3 COOH

CH 3

CH 2 CH 2 CH 2 CH 3

Na 2 Cr 2 O 7 , H+

∆

COOH

m-butylisopropylbenzene

m-benzenedicarboxylic acid