Abstract
Abstract In order to determine the ion-pair formation constant of a crown ether–metal salt complex (1 : 1 : 1) in water, an equation is derived from the regular solution theory. Then, the theoretical predictions are verified experimentally by solvent extraction with 15-crown-5 (15C5), sodium picrate (NaA), and various organic solvents of low dielectric constant. The partition constants of 15C5 and the actual overall extraction constants of NaA with 15C5 were determined at 25 ± 0.2 °C. The partition constants of the Na(15C5)A complex are calculated from these data, the literature value for the complex-formation constant of Na(15C5)+ in water, and the ion-pair formation constant (KNa(15C5)A) in water determined in this study (log KNa(15C5)A = 4.09 ± 0.23 at 25 °C). The distribution behavior of 15C5 and Na(15C5)A is explained by the regular solution theory. The obtained molar volumes V/cm3 mol−1 and solubility parameters δ/cal1/2 cm−3/2 are as follows; V15C5 = 189 ± 34, VNa(15C5)A = 215 ± 46, δ15C5 = 12.0 ± 0.1, and δNa(15C5)A = 12.0 ± 0.1.
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