Pressure mediated reduction with ammonia and hydrazine

Abstract

INTRODUCTION Ammonia and hydrazine both are known for long for their reducing properties. Hydrazine in particular is a powerful reducing agent because it is not only rich in hydrogen content but also its decomposition to hydrogen and nitrogen is an exothermic process (H= -95.459kJ mol-1)1 and thermodynamically highly favourable. Anhydrous hydrazine is a potent explosive2 and therefore, requires careful handling. In contrast, hydrazine hydrate requires no special care in handling, and therefore, it is in this form most commonly used. The reduction with liquid ammonia generally takes place in presence of Na or Li metals. It is used to reduce the C=O bond of aldehydes and ketones, carboxylic acids, internal triple bonds and aromatic rings. In case of hydrazine hydrate, reduction takes place either in presence of an oxidizing agent, an alkali or a catalyst. While the reduction is carried out in an open vessel it is the aerial oxygen that acts as the oxidizing agent3. Potassium periodate4, hydrogen peroxide5 and ferricyanide6 are some of the common oxidizing agents used. Presence of an oxidizing agent presumably facilitate the generation of diimide which is considered responsible for the reducing act7. Reduction of a carbonyl compound with hydrazine hydrate in the presence of a base, for example in Wolff-Kishner reduction, most probably takes place via intermediate formation of a monosubstituted diimide8. Conversion of nitro to amino group is an important methodology both in pure and applied chemistry because amino compounds not only have wide applications but also amino group itself can be converted to a couple of other functional groups such as secondary amine, tertiary amine, quaternary ammonium salts, hydroxy group etc. and many other compounds through coupling, degradation and rearrangement reactions. In industrial chemistry reduction of nitro to amino compounds is a process of immense importance in the production of aniline and aniline derivatives9. In an acidic medium10 nitro group can be converted to an amino...