Hammett Equation and Micellar Effects upon Deacylation

Substituent effects upon second order rate constants of reaction of OH - with phenyl p-substituted benzoates at surfaces of micelles of cetyltrialkylammonium bromide (alkyl = Me, Et, Pr and Bu) and tetradecylquinuclidinium bromide fit the Hammett equation. Values of p increase with increasing bulk of the surfactant head group and are considerably larger than in water, corresponding to decreases in micellar surface polarity. The effects of substitution of the propyl group into the phenyl and benzoyl groups show that substrate orientation at micellar surfaces plays no significant kinetic role.