Acid-base equilibria in aqueous micellar solutions. Part 4. - Azo indicators

Abstract

The acid-base equilibria of three azo indicators, viz. dimethyl yellow, methyl orange and methyl red, have been examined in organic solvent-water mixtures, in aqueous non-ionic micellar solutions of Brij-35 and n-octyl β-D-glucoside and in aqueous charged micellar solutions of n-dodecyl-trimethylammonium bromide and/or sodium dodecyl sulphate. The factors primarily responsible for the disparity between the apparent pK value of an azo indicator residing within the interfacial microenvironment of a micelle and its pK value in pure water have been isolated. For the non-ionic micellar systems the disparity can be attributed to the different intrinsic solvent characteristics of the two solvatin..