SOLVENT-EXTRACTION OF ALKALI-METAL (LI-CS) PICRATES WITH 18-CROWN-6 INTO VARIOUS DILUENTS - ELUCIDATION OF FUNDAMENTAL EQUILIBRIA WHICH GOVERN THE EXTRACTION-ABILITY AND EXTRACTION-SELECTIVITY

The actual constants of the overall extraction equilibrium, the distri bution for various organic solvents having low dielectric constants, a nd the aqueous ion-pair formation (K-MLA) Of 18-crown-6 (18C6)-alkali metal (Li-Cs) picrate 1:1:1 complexes were determined at 25 degrees C; the partition constants of 18C6 were also measured at 25 degrees C. T he log K-MLA values are 2.53+/-0.21 for Li, 3.29+/-0.23 for Na, 4.76+/ -0.27 for K, 4.62+/-0.36 for Rb, and 4.49+/-0.36 fur Cs. The relativel y large difference in the log K-MLA value between light (Li, Na) and h eavy alkali metals (K, Rb, Cs) reflects the difference in the structur e of the 18C6-alkali metal ion 1:1 complex between light and heavy alk ali metals. Almost all of the partition behavior of 18C6 and its 1:1:1 complexes with alkali metal picrates can be explained by regular solu tion theory. The molar volumes and solubility parameters of 18C6 and t he complexes were determined. For every diluent, the extraction-select ivity order of 18C6 is K > Rb > Cs > Na > Li. The extraction-ability a nd -selectivity of 18C6 for the alkali metal ion were completely eluci dated in terms of the four fundamental equilibria.