Stabilities and Transfer Activity Coefficients of Benzo-15-crown-5-Alkali Metal Ion Complexes in Various Solvents

Abstract

Abstract Stability constants in acetonitrile and methanol of 1:1 benzo-15-crown-5 (B15C5)–alkali metal ion complexes and the solubility of B15C5 in acetonitrile, propylene carbonate, methanol, and water were determined at 25 °C by conductometry and spectrophotometry, respectively. In general, selectivity tendency of B15C5 for the alkali metal ions except for Li+ can be interpreted in terms of size-relationship. Stability sequences of the B15C5–alkali metal ion complex among the solvents, except for Rb+ and Cs+ complexes, are the reverse of solvation-ability sequences of the solvents to the corresponding alkali metal ion. By using the stability constants of the B15C5–alkali metal ion complexes, transfer activity coefficients (γ) of the B15C5 complexes were then calculated from γ values of B15C5 (obtained from solubilities of B15C5) and those of alkali metal ions. The γ value of the B15C5 complex from methanol to acetonitrile and propylene carbonate generally varies with a variety of alkali metal ions. From γ values of the B15C5 complexes, it is concluded that there exists a possible specific interaction between the alkali metal ion held in the B15C5 cavity and solvent molecules when the alkali metal ion is much smaller or larger than the B15C5 cavity.