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 cation ic surfactants dioctyldimethylammonium chloride R-2(Me)(2)N+Cl- or bromide R-2(Me)(2)N+Br-. The oil phase of the emulsion consisted of the decyl halid e reactant. The effects of R-2(Me)(2)N+Br- concentration and different decy l halide reactants on the conversion were studied. A decyl chloride interme diate formed when decyl iodide or decyl bromide were reacted in R-2(Me)(2)N +Cl- emulsions. The intermediate reacted further to the final product, sodi um decyl sulfonate, at a rate which depended on the decyl halide reactant. The conversion to C10H21SO3Na versus R-2(Me)(2)N+Br- concentration displaye d a broad maximum. The reactivity of the decyl halides increased in the ord er: decyl chloride, bromide and iodide. Increasing decyl iodide concentrati on at a constant R-2(Me)(2)N+Cl- concentration and a constant initial mole ratio of Na2SO3 to C10H21I increased the reaction rate, while the conversio n decreased. Plateaus in the conversions to C10H21SO3Na and C10H21Cl were r eached for the run at 800 mM equimolar surfactant and reactant concentratio ns. The pseudophase ion exchange model, with the assumption of trapped amou nts of the decyl halides within the emulsion oil core and thus not availabl e for the reaction, described the experimental results. (C) 2001 Elsevier S cience B.V. All rights reserved.