Nucleophilic substitution sulfonation in emulsions: effect of the surfactant counterion and different decyl halide reactants

The nucleophilic substitution reaction between sodium sulfite and different decyl halides was carried out in emulsions formed by the two-tailed cationic surfactants dioctyldimethylammonium chloride R2(Me)2N+Cl− or bromide R2(Me)2N+Br−. The oil phase of the emulsion consisted of the decyl halide reactant. The effects of R2(Me)2N+Br− concentration and different decyl halide reactants on the conversion were studied. A decyl chloride intermediate formed when decyl iodide or decyl bromide were reacted in R2(Me)2N+Cl− emulsions. The intermediate reacted further to the final product, sodium decyl sulfonate, at a rate which depended on the decyl halide reactant. The conversion to C10H21SO3Na versus R2(Me)2N+Br− concentration displayed a broad maximum. The reactivity of the decyl halides increased in the order: decyl chloride, bromide and iodide. Increasing decyl iodide concentration at a constant R2(Me)2N+Cl− concentration and a constant initial mole ratio of Na2SO3 to C10H21I increased the reaction rate, while the conversion decreased. Plateaus in the conversions to C10H21SO3Na and C10H21Cl were reached for the run at 800 mM equimolar surfactant and reactant concentrations. The pseudophase ion exchange model, with the assumption of trapped amounts of the decyl halides within the emulsion oil core and thus not available for the reaction, described the experimental results.