Unusual Rate Enhancement in the Hydroxide-Ion-Catalyzed Cleavage of Acetyl Salicylate Ion (Aspirin Anion) in the Presence of Anionic Micelles

The reaction rate studies on the hydrolytic cleavage of acetyl salicylate ion (AS^-) within the [^-OH] range 0.010-0.025 M reveal AS^- and ^-OH as the reactants. The effects of micelles of sodium dodecyl sulfate (SDS) on observed pseudo-first-order rate constants (k_obs) for the hydrolytic cleavage of AS^- have been studied at different [OH^-]. At a constant [OH^-], the rate constants (k_obs) follow an empirical relationship: k_obs = C + F [SDS]_T where [SDS]_T represents total SDS concentration. The magnitudes of C and F increase with an increase in [OH^-]. These data are explained in terms of the pseudophase model of the micelle.