John Richard Kosak

CATALYTIC HYDROGENATION OF AROMATIC HALONITRO COMPOUNDS

Catalytic hydrogenation is a useful and economical method for the reduction of aromatic nitro compounds to the corresponding amines. However, when an aromatic halogen is also present, hydrogenation of the nitro group without concomitant dehydrohalogenation can sometimes present a formidable problem. This problem is especially difficult when the halogen is activated by orthoor para-orientation to a nitro group as in the case of orthoand parachloronitrobenzene. Prior to about 1958, there appeared to be little, if any, hydrogenation technology available in the literature for the conversion of aromatic halonitro compounds to the corresponding haloaromatic amines. Increased interest and usage of chloroaniline derivatives led to a search for a satisfactory process for large-scale manufacture of these intermediates. The classical method of reduction, iron and acid, presented practical difficulties and was expensive. Catalytic hydrogenation offered practical and economic advantages if a suitable process could be developed.