Reaction of Diphenylphosphinal Formic Acid Hydrazide with Isothiocyanates

A new method has been proposed for the synthesis of diphenylphosphinylformic acid hydrazide based on the reaction of phosphine oxide and trimethylchlorosilane in the presence of a tertiary amine, followed by the reaction with chloroformic acid ester and then hydrazine hydrate. The hydrazide fragment was modified into a thiosemicarbazide fragment by reacting diphenylphosphinylformic acid hydrazide with organic isothiocyanates. It was found that in an aqueous alkaline medium, thiosemicarbasides do not heterocyclize to 1,2,4-triazole-3-thiones, as expected. As a result of the P–C bond rupture, diphenylphosphinic acid and 5-thioxo-1,2,4-triazolidin-3-ones are formed.