Monoacylhydrazides

The reaction of monoacylhydrazide with 1,2-allenic phosphine oxide 148 afforded /f iminylphosphine oxide 150. Here the unreacted C=C bond in the aUylic phosphine oxide 149 tautomerized to form a C=N bond during the reaction (Scheme 10.72) [77]. 

This hydrazine is available by catalytic reduction of acetone azine.1 Protection of carboxylic acids.2 The reagent reacts with carboxylic acid derivatives (the acyl chloride or mixed anhydride) to give a monoacylhydrazide, RCON(CHMe2)-NH(CHMe2). The derivatives are stable to both acids and bases. They are reconverted into carboxylic acids by selective oxidation, preferably with lead tetraacetate. The new method of protection has been used for penicillins. 

A mixture of phenylacetic acid, a slight excess of hydrazine hydrate, activated alumina (Alcoa F-1), and 1-butanol heated with vigorous stirring in an oil bath at 140-150°, benzene added gradually to maintain a heavy reflux at 94-95° with water separation in a Dean-Stark apparatus, and the product isolated after 5 hrs. -> phenylacetyl hydrazide. Y 99%. — Alumina shows a remarkable catalytic activity promoting exclusively the formation of monoacylhydrazide. The catalyst permits lowering of the reaction temp, to a point where byproducts are no longer formed. The water produced must be continuously removed. F. e. s. T. Rabini and G. Vita, J. Org. Chem. 30, 2486 (1965). 

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