The hydrolytic reactions of sulfonate esters have previously been considered to occur by concerted mechanisms. We now report the observation of a break in a Brønsted correlation for the alkaline hydrolysis of aryl benzenesulfonates. On either side of a break-point, βleaving group values of− 0.27 (pKa< 8.5) and− 0.97 (pKa> 8.5) are measured. These data are consistent with a two-step mechanism involving a pentavalent intermediate that is also ...