On the mechanism of hydrolysis of sulfinate esters: oxygen isotope exchange and theoretical studies

Abstract

A small but detectable amount of ¹⁸O loss at the sulfinyl oxygen was observed during acid hydrolysis of ¹⁸O-labelled methyl benzenesulfinate, while no detectable loss of the label was found during alkaline hydrolysis. The relative rates of the acid-catalysed isotope exchange and hydrolysis were evaluated to be about 1/200. This large difference in the rates seems to be incompatible with the reaction of water with the conjugate acid of the substrate protonated at the sulfinyl oxygen. A mechanism involving an S_N2-like reaction at the sulfur through the protonation at the alkoxy oxygen of the substrate is proposed on the basis of theoretical calculations.