Hydrogenolytic Cleavage Reactions of Phenylhydrazides

Abstract

Although phenylhydrazides have been well known for some time as derivatives of carboxylic acids and esters, not much work has been done on the selective reductive cleavage reactions of the nitrogen-nitrogen single bonds of these compounds.[1],[2] Information about this process would be instrumental in the development of new indirect amidation methods for the facile conversion of acids and esters to the corresponding amides under mild conditions, particularly for those instances where direct methods are not successful.[3] In general, the nitrogen-nitrogen single bond is expected to be subject to cleavage. Hydrazine itself has a bond strength of 70 kcal/mole, and more highly subsittuted hydrazines often have weaker bonds. [4], [10], [11] The preparation of amides from simple acid hydrazides by hydrazides by hydrogenoloysis over Raney nickel in alcoholic solvents has been invesitgated. [5], [6] The raction typically requires supstantial quantities of Raney nickel, on th order of 10 grams of catalyst per gram of hydrazide sustrate, with yields being quite variable. Th effect of further acylation on th rate of hydrogenolysis over Raney nickel has been studied, [7], [8],[9] and results have shown that hydrogenolysis often requires elevated temperatures and pressures. [12]