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-methyl-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. The partition model, in which the different species involved in the equilibria (H(2)Q(+), HQ and Q(-)) can distribute betweeen aqueous and micellar pseudophases, was applied to account for the shifts in the apparent acidity constants. A factor analysis procedure was applied to the spectrophotometric data in order to determine the number of species in equilibrium. The distribution constants for the different species were calculated with the SPDIS program. The proposed models for SLS and CTAB solutions were applied to simulate the apparent pK(a) values in these media; the satisfactory agreement between experimental and calculated values indicates that this model provides a good description of the effect of ionic surfactants on the acid-base equilibria of HQ.