Acid hydrolyses of hydrophobic dioxolanes in cationic micelles: A quantitative treatment based on the Poisson-Boltzmann equation

Acid hydrolyses of hydrophobic dioxolanes, 1a and 1b, are inhibited by cationic micelles of myristyl- and cetyltrimethylammonium halides, MTAX and CTAX, respectively (X = Cl, Br), but at surfactant concentrations sufficient to bind all the substrate, first-order rate constants, k_ψ, at constant [HX], increase with increasing [surfactant] and on addition of NaX. In the absence of added NaX k_ψ increases linearly with [MTAX] and [CTACl], but at constant [surfactant] there are breaks in plots of k_ψ against [NaX]. These results can be explained quantitatively in terms of a pseudophase model in which hydrogen ion concentrations at micellar surfaces are calculated by solution of the Poisson-Boltzmann equation.