Preparation of dialkoxyphosphinothioylthioacetamide insecticides

Abstract

Dialkoxyphosphinothioylthioacetamides may be prepared conveniently in good yields and high purity from the reaction between dialkoxyphosphinothioylthioacetic acetic anhydrides and the appropriate amine. The necessary mixed anhydrides were readily prepared under very mild conditions by allowing keten to react with a dialkoxyphosphinothioylthioacetic acid in acetone. The method was applied to the preparation of both dimethoxy-and diethoxyphosphinothioylthioacetic anhydrides. The former was then interacted with methylamine to yield N-methyl dimethoxyphosphinothioylthioacetamide (dimethoate) or with morpholine to yield N-(dimethoxyphosphinothioylthioacetyl) morpholine. The diethoxy compound was converted to diethoxyphosphinothioylthioacetamide with ammonia. An alternative approach via the acid halides was examined. For this purpose dimethoxyphosphinot hioylthioacetyl chloride and diethoxyphosphinothioylthioacetyl chloride and fluoride were prepared. They could not be obtained pure. The alkaline hydrolysis rates of dimethoxy-and diethoxyphosphinothioylthioacetic acids were determined and the acid dissociation constant of the latter compound was obtained by two methods.