Alkaline hydrolysis of phosphate triesters in solution: Stepwise or concerted? A theoretical study

We have studied the alkaline hydrolysis mechanism for six different dimethylphosphate triesters. According to our calculations, we can conclude that for esters with poor leaving groups (pKalg>8) the reaction occurs via a stepwise mechanism, whereas for good leaving groups, it occurs via a concerted mechanism. The attack of the hydroxide anion has the same characteristics for the six esters. So the stepwise or the concerted character of the hydrolysis mechanism is only due to the intrinsic characteristics of the leaving group. This point should be kept in mind when predicting the products of the hydrolysis reaction of phosphate triesters such as organophosphates.