Solvolysis of some phosphoramidic halides: the question of metaphosphorimidate intermediates

Abstract

The solvolytic studies on methyl N-cyctohexylphosphoramidothioic chloride are extended and compared with some closely related phosphoramidic chlorides. It is shown that the basic hydrolysis of the former in aqueous methanol shows clear borderline behaviour between a solvent assisted displacement on the anion and a true S_N1 (P) reaction. Strong evidence is presented to indicate that the monomeric metaphosphorimidothioate intermediate reacts preferentially with methanol in the mixed system. From a comparison of the rates of solvolysis of the corresponding PO chloride with the above and other related compounds it is deduced that although the base solvolysis of this proceeds via the anion a metaphosphorimidate intermediate is highly improbable. Arguments are advanced to suggest that monomeric metaphosphate esters will not be important reaction intermediates.