Microemulsions and emulsions can be used to carry out reactions in which the reactants are not soluble in the same phase. In this work, the nucleophilic substitution reaction between an organic soluble compound, decyl bromide, and a water-soluble salt, Na2SO3, to produce sodium decyl sulfonate was carried out in batches in o/w microemulsions and emulsions formed with the two-tailed cationic surfactant dioctyldi-methylammonium chloride, R-2(Me)(2)N+Cl-. The surfactant counterion Cl-, substituted for bromide to give decyl chloride, an intermediate that further reacted to give the final product. The effects of stirring and preconditioning, surfactant concentration, the concentration of decyl bromide, and the initial mole ratio of the reactants on the conversion to sodium decyl sulfonate and decyl chloride were determined. Although phase separation occurred and emulsions formed in most of the samples, stirring and preconditioning did not have a significant effect on the conversion. An optimum surfactant concentration was found at which the maximum conversion to the final product was obtained. Increasing the concentration of decyl bromide increased the molar rate of sodium decyl sulfonate formation, but the conversion dropped. Increasing the mole ratio of Na2SO3 to decyl bromide increased conversion to the final product and reduced conversion to the intermediate. A pseudophase ion-exchange model with the interfacial volume as a fitted parameter, varying only with the surfactant concentration, represented well the experimental results.