Solvolysis of methyl OS-ethylene phosphorothioate

Abstract

Rate and product studies of the aqueous hydrolysis of methyl OS-ethylene phosphorothioate are reported. The rate dependence is similar to that previously reported for methyl ethylene phosphate but no exocyclic P–O cleavage is observed throughout the pH range 0–14. Solvolysis in neutral or alkaline solution results in almost exclusive P–S cleavage but endocyclic P–O cleavage increases with increasing acidity and predominates below pH 1·5. These results are shown to be consistent with the intervention of pentacovalent intermediates but the interpretation of the alkaline region is different from that proposed for methyl ethylene phosphate. It is suggested that pentacovalent intermediates are not involved in nucleophilic displacements on OS-diester anions of phosphorothioic acid.