Analysis of Ion Association Reaction between Crown Ether Complexes of Alkali Metal Ions and Hydrophobic Anions by Capillary Zone Electrophoresis

Abstract

Abstract Reaction equilibria in liquid–liquid distributions of alkali metals as crown ether complexes were clarified. The reactions and their equilibria of interest are the complex formation, the ion association of the complexes with the pairing anions in an aqueous solution, and the distribution of the formed ion associates to the organic phase. A capillary-electrophoretic method was proposed for the analysis of the equilibria in an aqueous solution. By using this method, complex formation and ion association in an aqueous solution were studied by electrophoretic mobility measurement, which was done in reactant systems consisted of alkali metal ion, dibenzo-18-crown-6, and picrate or perchlorate ion by capillary zone electrophoresis. Complex formation constants obtained agreed with the reported values obtained by the solubility measurement, and the ion association equilibria between the metal complexes and pairing anions were for the first time analyzed in this study. The reactivity of complex formation in the aqueous solution was in the order of K+ > Na+ > Rb+ > Cs+ > Li+, and the ion associability with picrate ion was in the order of Na+ > K+. By using the ion association constants and the extraction constants, distribution coefficients of the ion associates between an aqueous and a benzene phase were calculated.