Nucleophilicity of halide ions in the micellar pseudophase

The reaction of Br− or Cl− with both n-butyl-4-nitrobenzenesulfonate and n-butyl-4-bromobenzenesulfonate 1a and 1b respectively is catalyzed by cationic micelles of cetyltrimethylammonium chloride or bromide (CTACl or CTABr respectively). The increase of rate constant with [surfactant] can be analyzed in terms of the concentration of substrate (1a - b) and halide ion in the micellar pseudophase, and the second-order rate constants in micellar and aqueous pseudophase are similar.