Extraction of sodium and potassium picrates with 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (lariat 16C5) into various organic solvents. Elucidation offundamental equilibria which determine the extraction ability for Na+ and K+ and the selectivity

To quantitatively elucidate the effects of the side chains and diluents on the extraction selectivity for sodium and potassium picrates of 15-(2,5-dio xahexyl)- 15-methyl-16-crown-5 (L16C5) from the viewpoint of equilibrium, t he constants for the overall extraction (K-ex). the partition for various d iluents of low dielectric constants: (K-D.MLA), and the aqueous ion-pair fo rmation (K-MLA) of L16C5-sodium and -potassium picrate 1:1:1 complexes were determined at 25 degreesC; the distribution constants of L16C5 were also m easured at 25 degreesC. The log K-MLA values for Na+ and K+ are 2.74 +/- 0. 29 and 1.70 +/- 0.36, respectively. In going from 16-crown-5 (16C5) to L16C 5. the side chains decrease the K-MLA value, but do not increase the differ ence in K-MLA between Na+ and KC. The distribution behavior of L16C5 and it s 1:1:1 complexes with the alkali metal picrates closely obeys regular solu tion theory, except for chloroform. Molar volumes and solubility parameters of L16C5 and the 1:1:1 complexes were determined. The magnitude of K-ex is mainly governed by the K-M(L16C5)A value. For every diluent, L16C5 shows N a (+) extraction selectivity over K+. The Naf extraction selectivity of L16 C5 is determined completely by K-M(L16C5)A. The extraction ability and sele ctivity for sodium and potassium picrates by L16C5 are compared with those of 16C5 on the basis of the fundamental equilibrium constants. (C) 2001 Els evier Science B.V. All rights reserved.