SOLVENT EFFECTS ON EXTRACTION OF ALKALI-METAL PICRATES WITH 15-CROWN-5 INTO VARIOUS ORGANIC-SOLVENTS - ELUCIDATION OF FUNDAMENTAL EQUILIBRIA WHICH GOVERN EXTRACTION-EFFICIENCY AND EXTRACTION-SELECTIVITY

Extractions of alkali metal (Na-Cs) picrates (MA) with 15-crown-5 (15C 5) into various diluents of low dielectric constant were conducted at 25 degrees C. Using the extraction data, the ion-pair formation consta nts (K-MLA) in water of 15C5-MA 1:1:1 complexes were determined by an equation derived from the regular solution theory (log K-MLA = 4.43 +/ - 0.27 for Na, 3.27 +/- 0.42 for K, 3.58 +/- 0.35 for Rb, and 2.78 +/- 0.41 for Cs). The actual overall extraction equilibrium constants wer e obtained by considering the concentrations of the 1:1:1 15C5 complex es and the ion-pair formation between uncomplexed alkali metal and pic rate ions in the aqueous phase. The distribution constants of the 15C5 complexes were calculated and their partition behavior is explained b y the regular solution theory. Molar volumes and solubility parameters of 15C5 itself and the complexes were determined. Extraction-efficien cy and -selectivity of 15C5 for alkali metal picrates were completely elucidated from the standpoint of equilibrium. (C) 1998 Elsevier Scien ce B.V. All rights reserved.