MICELLAR EFFECTS UPON THE RATES OF SN2 REACTIONS OF HALIDE-IONS

Observed first-order rate constants for reactions of Cl- or Br- with substituted alkyl benzenesulfonate (1a-c) in micelles of cetyltrimethylammonium surfactants (CTAX, X = Cl, Br, OMes, 0.5SO4) increase monotonically with increasing [CTACl] or [CTABr] or halide ion concentration and tend to limiting values. In CTAOMes or (CTA)2SO4, the rate constants go through maxima. The variation of the rate constants with concentrations of surfactant and halide ion can be fitted to an equation that accounts for the distribution of both reactants between water and micelles, i.e., in terms of ion-exchange and mass-action models. The second-order rate constants in the aqueous and micellar pseudophases are similar. © 1990 American Chemical Society.