Hydrazides from acyl halides

Carboxylic acid hydiazides are prepared from aqueous hydrazine and tfie carboxylic acid, ester, amide, anhydride, or halide. The reaction usually goes poody with the free acid. Esters are generally satisfactory. Acyl halides are particularly reactive, even at room temperature, and form the diacyl derivatives (22), which easily undergo thermal dehydration to 1,3,4-oxadiazoles (23). Diesters give dihydtazides (24) and polyesters such as polyacrylates yield a polyhydrazide (25). The chemistry of carboxyhc hydrazides has been reviewed (83,84). 

The iV-acylated derivatives of maleic hydrazide, prepared from open-chain compounds, have been found to differ from acylated products obtained from maleic hydrazide acylations. Acylation of 4- or 5-substituted maleic hydrazides should permit the existence of two 0-acylated isomers. So far, only one isomer of unknown structure has been isolated from benzoylation of the 4-methyl analog. Maleic hydrazide and its 2-substituted analogs are 0-acylated with acetic anhydride, acyl halides, and 0,0-dialkylphosphorochlor-... 

Acid Halides from Acyl Amides and Hydrazides... 

In general, hydrazides may be prepared by many of the methods analogous to those used in the preparation of amides. For example, hydrazine salts of carboxylic acids and reactions of hydrazine with esters, acyl halides, acyl anhydrides, and amides may be used to produce hydrazides. A reaction analogous to the Hofmann degradation is the formation of hydrazides from ureides (acylureas) [54] (Eq. 4). 

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