Effect of Surfactant Micelles on the Rate of Reaction of Tetranitromethane with Hydroxide Ion

Abstract

Abstract The rates of trinitromethanide anion formation by the reaction of tetranitormethane with hydroxide ion were measured in the presence of anionic, cationic and nonionic surfactant micelles in aqueous solutions. Using the analytical approach which takes into consideration the distribution of hydrophobic reactants among micelles, k1 (a second-order rate constant on micelles associated with one reactant molecule) and K1/N(K1: an association constant of the reactant with micelles having no reactant, N: an aggregation number of surfactant molecule in a micelle) were estimated. The anionic surfactant exhibited no effect on the reaction rate. In the case of cationic surfactants, both k1 and K1 values increased not only with alkyl chain length but also with hydrophobicity of the surfactants. In the case of nonionic surfactants, an increase of alkyl chain length with a given oxyethylene unit resulted in an increase in the k1 values, while an increase of oxyethylene group with the fixed alkyl chain length resulted in an appearance of the maximum k1 value. From temperature dependence of the reaction rate, a stabilization of the activated complex could be explained by an electrostatic interaction of the complex with the charged micellar surface. It was also found from the analytical approach that the distribution of tetranitromethane among micelles used in the present experiment could be approximated by the Poisson distribution.