Correlation analysis of solubilization data in aqueous cationic and anionic micellar solutions: Case of the halocarbons

Abstract

The partition coefficients P of benzene, toluene, chlorobenzene, halothane, dichloromethane, carbon tetrachloride, butyl bromide, butoxyethanol, 3-phenoxy-1-propanol, and 2-phenoxyethanol have been determined in aqueous micellar solutions of dodecyltrimethylammonium bromide (nDOTMABr) and for some of these molecules they have also been determined in aqueous sodium dodecyl sulfate (SDS) solutions. Previously published P values in the same surfactant solutions have been corrected in order to take into account the degree of dissociation of the micelles. By using available partition data, a discussion is presented using a correlation analysis approach of log P values in cationic and anionic aqueous micellar systems and in the octanol + water system. The linear correlation found previously for both micellar systems with the two-phase octanol + water binary for alcohols, amines, amides, esters, ketones, and nitriles does not hold for halocarbon and nonpolar hydrocarbon molecules. However an excellent log P linear correlation is found for all neutral molecules studied when the two micellar systems are considered. It is suggested that the lack of hydrogen-bonding contributions to the free energy of solubilization in the case of hydrocarbons and halocarbons is responsible for the specificity observed with these two classes of molecules when micellar solutions and the octanol + water system are compared. Also, considerations of data concerning about 40 neutral polar molecules with various polar moieties show that the cationic trimethylammonium group or the anionic sulfate group does not introduce any specificity effect to the overall solubilization process with the molecules (polar and apolar) studied.