Benzyl bromide was sulfonated at 298 K in emulsions formed with dioctyldimethylammonium bromide, or chloride. If mixing was sufficient, the emulsion was maintained throughout the reaction period. Lower conversions were obtained whenever benzyl bromide phase separated from the mixture. Chloride as surfactant counterion gave higher reaction rate, but decreased the conversion to C7H7SO3-Na+ due to formation of benzyl chloride. The conversion to C7H7SO3-Na+ displayed a broad maximum as R-2(Me)(2)N+Br- concentration increased. Except at low concentration, the reaction rate increased with the concentration of Na2SO3 in accord with the S(N)2 mechanism. The reaction rate increased with the reactant concentrations until interface saturation was achieved, suggesting that product formation did not interfere with the access of the reactants to the interface.