A Conductance Study of Benzo-18-crown-6- and Its Analogs-Alkali Metal Ion Complexes in Various Solvents

Abstract

Abstract Limiting ionic molar conductivities of benzo-18-crown-6 (B18C6)–alkali metal ion complexes in various nonaqueous solvents were determined at 25 °C. The mobilities of the B18C6 complexes were compared with those of 18-crown-6 (18C6)– and dibenzo-18-crown-6 (DB18C6)–alkali metal ion complexes. Regardless of varieties of alkali metal ions held in the crown ether cavity, the larger is the size of the crown ether complex, the less mobile the complex is. For aprotic solvents (acetonitrile, DMF, DMSO, propylene carbonate), the mobility of the B18C6–K+ complex is smaller than that of (n-C4H9)4N+; however, for the protic solvent (methanol), they are almost the same. Walden product value of the B18C6–K+ complex as well as 18C6– and DB18C6–K+ complexes somewhat changes with the variation of solvents. For these three crown ether–K+ complexes, Walden product values of acetonitrile and propylene carbonate are larger than or nearly equal to those of DMF and DMSO. This may indicate that, for the aprotic solvents, donicity is a very important factor in determining the magnitude of mobility of the crown ether–K+ complexes. The B18C6–K+ complex as well as 18C6- and DB18C6–K+ complexes seems to act as a structure breaker in a hydrogen-bonding solvent.