Acid-base equilibria in aqueous micellar solutions. Part 2. - Sulphonephthalein indicators

Abstract

The acid-base equilibria of three sulphonephthalein indictors, viz. bromocresol green, bromothymol blue and phenol red, in 1,4-dioxane-water mixtures and aqueous solutions of both non-ionic and cationic micelles have been studied. The difference between the acid-base equilibrium constant of a sulphonephthalein indicator in pure water, pKaw, and the apparent acid-base equilibrium constant of a sulphonephthalein located entirely within the interfacial microenvironment of a non-ionic micelle has been explained quantitatively in terms of the different intrinsic solvent properties of the two systems. A number of factors are considered to be primarily responsible for the difference between the app..