INTERACTION OF 5,7-DICHLORO-2-METHYL-8-HYDROXYQUINOLINE WITH IONIC MICELLES

The changes in the apparent acid-base equilibria of 5,7-dichloro-2-met hyl-8-hydroxyquinoline (HQ), in solutions of ionic surfactants (sodium lauryl sulphate, SLS; and cetyltrimethylammonium bromide, CTAB) were studied spectrophotometrically in 0.1 M NaCl medium at 25 degrees C. T he partition model, in which the different species involved in the equ ilibria (H(2)Q(+), HQ and Q(-)) can distribute betweeen aqueous and mi cellar pseudophases, was applied to account for the shifts in the appa rent acidity constants. A factor analysis procedure was applied to the spectrophotometric data in order to determine the number of species i n equilibrium. The distribution constants for the different species we re calculated with the SPDIS program. The proposed models for SLS and CTAB solutions were applied to simulate the apparent pK(a) values in t hese media; the satisfactory agreement between experimental and calcul ated values indicates that this model provides a good description of t he effect of ionic surfactants on the acid-base equilibria of HQ.