The influence of the changing of P=O to P=S and P-0-R to P-S-R on the reactivity of phosphinate esters under alkaline hydrolysis conditions

Abstract

Alkyl dialkylphosphinates, thionates, thioates, and dithioates have been studied under alkaline hydrolysis conditions in 60% DME - H2O and pure H2O. Substitution of S for O in the phosphoryl group has only a small rate retarding effect, typically less than a factor of 10. The effect of the similar replacement in the leaving group, however, can lead to rate increases greater than a factor of 100. Activation parameters were determined and the ΔS∗ values range from -19 to -49 eu for the bimolecular reactions. The more negative values are for the esters with higher sulfur content and/or sterically large substituents. The results are discussed in terms of a pathway involving a pentacoordinate intermediate.