Analytical Sciences

Solvent Extraction of Alkali Metal (Li - Cs)Picrates with18-Crown-6 into Various Diluents. Elucidation of FundamentalEquilibria which Govern the Extraction-Ability and -Selectivity

Yasuyuki TAKEDA * , Atsuhiro KAWARABAYASHI,Kiyokazu ENDO - , TsuyoshiYAHATA,Yoshihiro KUDO and ShoichiKATSUTA

Department of Chemistry, Faculty of Science, Chiba University, Yayoi-cho -, Inage-ku, Chiba 263, Japan

The actual constants of the overall extractionequilibrium, the distribution for various organic solvents having lowdielectric constants, and the aqueous ion-pair formation(KMLA) of 18-crown-6(18C6)-alkali metal (Li - Cs) picrate 1:1:1complexes were determined at 25°C; the partition constants of 18C6 werealso measured at 25°C. The log KMLAvaluesare 2.53±0.21 for Li, 3.29±0.23 for Na, 4.76±0.27 forK, 4.62±0.36 for Rb, and 4.49±0.36 for Cs. The relativelylargedifference in the log KMLA value between light (Li, Na) and heavy alkali metals (K, Rb, Cs)reflects the difference in thestructure of the 18C6-alkali metal ion 1:1 complex between light and heavyalkali metals. Almost all of the partitionbehavior of 18C6 and its 1:1:1 complexes with alkali metal picrates can beexplained by regular solution theory. Themolar volumes and solubility parameters of 18C6 and the complexes were determined. For every diluent, the extraction-selectivityorder of 18C6 is K > Rb > Cs > Na > Li. The extraction-abilityand -selectivity of 18C6 for the alkali metalion were completely elucidated in terms of the four fundamental equilibria. (Keywords: Solvent extraction, fundamental equilibria, ion-pairformation constant, distribution behavior, solvent effects,regular solution theory, molar volume, solubility parameter, 18-crown-6,alkali metal picrates)

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