Ionic Competition in Micellar Reactions: A Quantitative Treatment

摘要

Inert counterions compete with reactive counterions for micellar surfaces, and reduce reaction rates, and an understanding of ion binding is an integral part of any description of reactions in such ionic colloids as micelles and microemulsions. The effectiveness of the competition increases with decreasing charge density of the inert ion, and the variation of rate with concentrations of surfactant or added electrolyte can be treated quantitatively in terms of the pseudophase, ion-exchange, model. This model treats water and micelles as distinct reaction regions so that rates will depend upon distribution of both reagents between these regions. Distribution of reactive and inert hydrophilic ions about a spherical micelle has been estimated taking account of specific and Coulombic interactions by using the Poisson-Boltzmann equation over a range of electrolyte and surfactant. The treatment is applied to dephosphorylation and aromatic nucleophilic substitution by OH- and an S sub N2 reaction of thiosulfate ion in micellized cetyltrimethylammonium chloride and bromide.