Interactions Between Orange II and Selected Long Chain Quaternary Ammonium Salts

The interactions between the dye, sodium p-(2-hydroxy-1-naphthylazo)benzenesulfonate (orange II) and four long chain quaternary ammonium salts—1-hexadecylpyri-dinium chloride, dodecylquinolinium bromide, (2-phenoxyethyl)dodecyldimethyl-ammonium bromide, and (diisobutylphenoxyethoxyethyl)dimethylbenzylammonium chloride—have been investiagated. The stoichiometry of these interactions has been deermined to be 1:1 at pH values ranging from 0.73 to 12.91, except for the reaction involving the hexadecylpyridinium ion above pH 12.34, where the stoichiometry of dye to quaternary ammonium ion is 1:2. The solubility of the various solid compounds has been determined at 25, 30, 35, and 40°. From these data, the thermodynamic functions, ΔH°, ΔS°, and ΔF° have been calculated. Marked solubilization of these compounds has been observed in the presence of excess common quaternary ammonium ion at or near the critical micelle concentration of the particular long chain ion. The significance of these results is discussed.