Characterization of associates in ternary mixtures of amines, diprotic acid dyes and quaternary ammonium compounds in dichloromethane and in dichloromethane/water systems.

Ternary mixtures of Bromocresol Green (BCGH), Benzethonium Chloride (BZ(+)Cl(-)), and Quinine (Q) in dichloromethane (CH(2)Cl(2) for ratios 1:>/=1:>/=1 (BCGH(2):BZ(+)Cl(-):Q) generate species BCGH(-)BZ(+), BZ(+)BCG(-)-H-Q) and BCG(2-) (BZ(+))(2) in chemical equilibrium; whose thermodynamic parameters are determined. A new method to study ternary mixtures in a non-polar solvent has been given and other amines (A) and quaternary ammonium compounds (QAC) instead of Q and BZ(+)Cl(-) have also been researched. Species BCGH(-)BZ(+), and BCG(2-)(BZ(+))(2) are ion associates of 1:1 and 1:2 (dye:BZ(+)Cl(-)) stoichiometry and species BZ(+)BCG(-)-H-Q presents a hydrogen bond, being of 1:1:1 (dye:BZ(+)Cl(-):Q) stoichiometry. The Vis-VU, IR and (1)H-NMR spectra of the associates suggest that they are in nature resonance hybrids. A new and fundamental equation which governs extraction of any 1:1:1 associate is deduced and checked experimentally, showing that its extraction depends on the high capacity of the amine to accept hydrogen bonds and the high extractability of the ammonium ion. Extraction of the 1:1:1 associate using different amines and ammonium ions is studied both, experimentally and by the new equation, checking that the 1:1:1 associate containing Q and BZ(+) is selectively extracted due to the fact that Q has a high hydrophobicity and high capacity to form hydrogen bonds and species BZ(+)Cl(-) has a high ion-associability. Selective extraction of this 1:1:1 associate is useful for quantitative determination in complex mixtures of ammonium ions of high ion associability as BZ(+)Cl(-).