Hydrazides, reaction with thionyl chloride

Heating the hydrazides (398) with thionyl chloride in diglyme affords the chlorohy-drazones (399) which yield formazans (400) on reaction with pentaffuorophenylhydrazine. The formazans (400) undergo cyclocondensation with formaldehyde to give the verdazyls (401) which can be hydrogenated to the tetrahydro-l,2,4,5-tetrazines (402 Scheme 22)... 

A parallel synthesis of 1,2,3-thiadiazoles employing a catch-and-release strategy has been reported using the Hurd-Mori reaction. A polymer-bound tosyl hydrazide resin reacted with a-methylene ketones to afford a range of sulfonyl hydrazones. Treatment of these sulfonyl hydrazones with thionyl chloride causes 1,2,3-thiadiazole formation and cleavage of the resin in one step <1999JOC1049>. 

Other possibilities include the reaction of hydrazides with hydrogen chloride in nitromethane or methylene chloride. Also thionyl chloride or sulfiiryl chloride will produce acid chlorides from hydra-zides, although these reactions seem to be of limited scope. 

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