RESUMO
The reaction of I (-) with methyl naphthalene-2-sulfonate (MeONs) is accelerated by the micellized sulfobetaine surfactants N-decyl, N-dodecyl, N-tetradecyl, and N-hexadecyl- N, N-dimethylammonio-1-propanesulfonate. Concentrations of micellar-bound I (-) were determined by using ion-selective electrodes (ISE), and capillary electrophoresis. At low concentrations, I (-) incorporation fits Langmuir isotherms and is related to changes in micellar surface potentials. Rate effects of dilute KI are fitted quantitatively by a pseudophase model that describes I (-) binding in terms of a sorption isotherm, but at higher [KI], where the simple model predicts saturation, rates increase due to electrolyte invasion. This model considers transfer equilibria of both reactants between water and micelles and second-order rate constants in each pseudophase. Estimated second-order rate constants for reaction of MeONs with I (-) in the micellar pseudophase are 3.2- to 3.5-fold higher than the second-order rate constant, k 2w, in water, depending on surfactant structure and assumptions in the treatment.
RESUMO
The rate of specific hydrogen ion-catalyzed hydrolysis of 2-( p-heptoxyphenyl)-1,3-dioxolane and acid-base equilibrium of 4-carboxy-1-n-dodecylpyridinium in zwitterionic micelles of SB3-14, C14H29NMe2+(CH2)3SO3(-) are controlled by NaClO4, which induces anionic character and uptake of H3O+ in the micelles. Other salts, e.g., NaF, NaCl, NaBr, NaNO3, NaI, NaBF4, have similar, but smaller, effects on the uptake of H3O+. Salt effects upon zeta potentials of SB3-14 micelles, estimated by capillary electrophoresis, are anion specific, and the anion order is similar to that of the rates of acid hydrolysis and of acid-base equilibria. Fluorescence quenching shows that the micellar aggregation number is not very sensitive to added salts, consistent with electrophoretic evidence. These specific anion effects follow the Hofmeister series and are related to anion hydration free energies.
