Structure-reactivity correlations in the dissociative hydrolysis of 2',4'-dinitrophenyl 4-hydroxy-X-benzenesulfonates

The hydrolysis reactions of several title esters in water at 60 degrees C follow the rate law k(obs) = (k(a) + k(b)[OH-])/(1 + alpha a(H)/K-a), where K-a is the ionization constant of the hydroxy group of the ester and kb is the second-order rate constant for the S(N)2(S) attack of hydroxide ion on the ionized ester. Hammett and Bronsted correlations are consistent with a previous proposal that the mechanism related to k(a) is dissociative. An unusual relationship between k(a) values and redox equilibrium constants for substituted quinones is found to hold: this finding further supports the dissociative nature of the pathway related to k(a).