Effect of mixed H2O-CH3CN solvent on intramolecular general base-catalyzedcleavage of ionized phenyl salicylate in the presence of DL-proline

Nucleophilic second-order rate constant (kn(ms)) for the reaction of DL-pro line with ionized phenyl salicylate (PS-) shows a nonlinear decrease with t he increase in the content of CH3CN in mixed aqueous solvents at less than or equal to 50 % v/v CH3CN. The values of knms show a mild increase with th e increase in the content of CH3CN at > 50 % v/v CH3CN. The effect of solve nt on k(n)(ms) is explained in terms of solvent effect on the pK(a) of the conjugate acids of leaving group ( i.e. phenolate ion) and DL-proline.