ELECTROLYTE DROPPING ELECTRODE POLAROGRAPHIC STUDIES - SOLVENT EFFECT ON STABILITY OF CROWN ETHER COMPLEXES OF ALKALI-METAL CATIONS

A simple three-electrode polarographic assembly with the electrolyte dropping electrode for the study of the ion transport across a liquid-liquid Interface was presented. Transfer of alkali-metal cations from water to nitrobenzene (NB) or 1, 2-dichloroethane (1, 2-DCE) facilitated by complex formation with dibenzo-18-crown-6, dlbenzo-24-crown-8, or dlbenzo-30-crown-10 was studied. Experimental current vs potential data were used to clarify the mechanism of the ion transport and to evaluate the stability constants of crown ether complexes. The stability constants are 105—107 larger in NB and 1010-1012 larger in 1, 2-DCE than those In water. The selectivity sequence changes with the solvent, comparing water (K+ > Na+ > Rb+ > Cs+) with NB (Na+ > K+ > Rb+ > Cs+, Li+) and 1, 2-DCE (Li+ > Na+ > K+ > Rb+ > Cs+). Solvent effects can be understood in terms of differences in cation solvation, which plays a dominant role in low polar media. © 1990, American Chemical Society. All rights reserved.