Synthesis of monoesters of phosphonic acids

Dialkyl esters of aryl- and alkylphosphonic acids, RP(O)(OR')(2), can be hydrolyzed smoothly, rapidly, and in high yield by refluxing in aqueous or ethanolic alkali. Furthermore O,O-diethyl phenylpbosphonothioate, C5H5P(S)(OC2H5)(2), was found to hydrolyze to the monoester using excess ethanolic or aqueous base. Attempts to prepare the monoester of CCl3P-(O)(OC2H4)(2), using excess aqueous alkali failed. Finally hydrolysis of C5H6P(O)(OC5H6)(2) with excess alkali presumably resulted in phenylphosphonic acid. Mechanistic interpretations for these findings are presented.