19.16: Preparation of Amines: Reduction of Oximes and Nitro Compounds
Oximes can be reduced to primary amines using catalytic hydrogenation, hydride reduction, or sodium metal reduction. The reduction of aliphatic and aromatic nitro compounds to primary amines takes place by either catalytic hydrogenation or by using active metals like Fe, Zn, and Sn in the presence of an acid.
Though catalytic hydrogenation can reduce nitrobenzenes, the reduction is nonselective in the presence of other functional groups. For instance, if nitrobenzene contains an aldehyde group, both nitro and aldehyde groups will get reduced.
Conversion of the nitro group to the amino group while retaining the aldehydic group can be achieved through acidic reduction using SnCl2, followed by treatment with base.
The reduction of nitrobenzene and its derivatives are useful in industries that manufacture various aniline dyes. This process also has medicinal importance—for example, the synthesis of topical anesthetic benzocaine.