Surfactant structure and micellar rate enhancements: Comparison within a related group of one-tailed, two-tailed and two-headed anionic surfactants

Abstract

Rate enhancements for the reaction between Ni²⁺(_aq) and pyridine-2-azo-p-dimethylaniline (pada) have been investigated by the stopped-flow technique in micellar solutions of a related group of anionic surfactants: the sodium alkoxycarbonylmethanesulfonates, the sodium 1,2-bis(alkoxy- carbonyl)ethanesulfonates, and the disodium 4-alkyl3-sulfonatosuccinates. The second group differs from the first in having an extra identical tail and the third from the first by having an extra polar head. The hexyl, octyl and decyl members of each group were chosen for study except for the second group where the decyl member proved insoluble. The kinetic analysis revealed that adding a second tail did not dramatically increase the binding of pada to the micelles so that rate enhancements were not much increased. Adding a second head decreased the binding of Ni²⁺ ion to the micelles so that the third group appears to have no advantages in rate enhancements.