Acid–base equilibria in aqueous micellar solutions. Part 4.—Azo indicators
- 1 January 1989
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 85 (3) , 561-578
- https://doi.org/10.1039/f19898500561
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 pKa value of an azo indicator residing within the interfacial microenvironment of a micelle and its pKa 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 solvating media. For the charged micellar systems the electrostatic micellar surface potential is an additional contributing factor.Keywords
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