Application of the pseudophase ion-exchange model to reactivity in quaternary water in oil microemulsions

Abstract

The nucleophilic attack of a bromide ion on benzyl chloride (BCl) and the acid denitrosation of N-methyl-N-nitroso-para-toluenesulfonamide (MNTS) in quaternary microemulsions of TTABr and SDS containing 1-hexanol as cosurfactant were studied. The experimental results were examined in the light of a kinetic model which allows the quaternary microemulsion to be reduced to a pseudo-ternary microemulsion, by considering the cosurfactant partition between the continuous medium and the interface of the microemulsion to be determined by Shulman titration. The incorporation of the alcohol into the interface alters the interfacial volume to be used in constructing the kinetic model. The second step of the process involves determining how the reactants partition among the different microenvironments of the pseudo-ternary system, the interface being the sole reactive region in the microemulsion. Accounting for the results obtained in the acid denitrosation of MNTS required using the ion-exchange formalism. Based on the results, the product of the fraction of neutralized charge at the interface and the rate constant is independent of the water content of the system. This suggests that the degree of dissociation of the surfactant at the interface does not depend on the water content of the microemulsion. Under the assumption of a surfactant fraction of neutralized charge of β = 0.8, we calculated the rate constants at the interface for both processes. Such rate constants were smaller than in the aqueous medium and consistent with the effects found in nitroso group transfer reactions in microemulsions.