Rapid and selective reduction of nitro compounds is of importance for the preparation of amino derivatives in organic synthesis, particularly when a molecule has other reducible substituents^1-5. Numerous new reagents have been developed for the reduction of aromatic nitro compounds^6-8, however, little attention has been paid to the reduction of aliphatic nitro compounds^9-11, which are traditionally reduced by high pressure^12,13. Most of these methods are unfortunately subject to substantial limitations as concerns the presence of reducible functional groups and lack therefore the desired generality for true synthetic utility. Moreover, poor selectivity was reported in the reduction of aromatic nitro compounds which have carbonyl and halogen substituents. Therefore, we have examined several methods to improve the reduction process, and especially to obtain the selectivity over carbonyl, halogens or other labile substituents. In this context, the use of ammonium formate and 5% platinum on carbon was found to be efficient but expensive¹⁴.

Now we wish to report a selective, rapid and mild method of reduction of aliphatic and aromatic nitro compounds to the corresponding amino derivatives using Raney nickel and formic acid at room temperature. This new system reduced with ease a wide variety of nitro compounds directly to the corresponding amines and many functional groups can be tolerated. When formic acid is replaced by ammonium formate the reduction proceeds effectively and the products were obtained in almost comparable yields.

The reduction of nitro group in presence of Raney nickel and HCOOH or HCOONH₄ was complete within 10-30 min. The course of the reaction was monitored by TLC and IR. The workup and isolation of the products were easy. Thus all the compounds reduced (Table 1) by this system were obtained in good yield (80-90%) . All products were characterised by comparison of their TLC, IR and melting points with authentic samples. A control experiment carried out using nitro compounds with HCOOH or HCOONH₄ without nickel does not yield the desired product.

Thus the reduction of nitro compound can be accomplished with nickel instead of expensive Pt, Pd etc., without affecting the reduction of any reducible substituents including halogen and carbonyl compounds. The yields were virtually quantitative and analytically pure. Further it has been found that ammonium formate was less effective donor than formic acid with raney nickel. The obvious advantages of the proposed method over the previous methods are: (I) selective reduction of nitro compounds in the presence of other reducible groups including carbonyl and halogens, (II) ready availability and easy to operate, (III) rapid reaction, (IV) high yields of substituted anilines, (V) avoidance of strong acidic media, (VI) required no pressure apparatus and (VII) less expensive. This procedure will therefore be of general use especially in cases where rapid, mild and selective reduction is required. Further investigations of other useful applications related to deblocking of protecting groups in peptide synthesis are in progress.