EFFECTS OF 1-BUTANOL-MODIFIED MICELLES ON SN2 REACTIONS IN MIXED-ION SYSTEMS

The overall rate of reaction of Br- with methyl naphthalene-2-sulfonate (MeONs) in micelles of cetyltrimethyl- and triethylammonium bromide (CTABr and CTEABr) modified by 1-butanol (BuOH) is increased by addition of NaBr. The increase can be treated quantitatively in terms of a pseudophase model in which the rate constant at the micellar surface is proportional to the mole ratio of bound Br- to micellized surfactant and bound BuOH. The distribution of Br- between water and the micelles is described by an equation with the form of a Langmuir isotherm. A similar treatment fits the rate increase on addition of NaBr to CTACl + BuOH, provided that the value of the association constant of Br- to the micelles is affected by Cl-. Second-order rate constants in the micellar pseudophase, k(M), are very similu in aqueous and alcohol-modified micelles.