Interpretation by the Solvophobic Theory on the Linear Additive Representation of the Logarithm of Ion-Pair Extraction Constant with Individual Contributions of Cation, Anion, and Organic Solvent

Abstract

A theoretical basis was given for the linear additive representation of the logarithm of ion-pair solvent extraction constant (Kex) in terms of logarithmic values of three individual extraction constants (Kcation, Kanion, and Ksolvent) for cations, anions, and organic solvents constituting ion-pair extraction systems. The differences in extractability between cations and between anions were quantitatively discussed according to the thermodynamic cycle model of 1:1 ion-pair extraction. The increment of log Kcation and log Kanion of hydrophobic ions is explained by taking the increment of the free energy change of the hydration (ΔGhyd) of the ions into account. The order of the extractability of inorganic cations and anions was also interpreted using literature data of ΔGhyd of each inorganic ion. The free energy change of the solvation of a hypothetical ion-pair having a shape of spherical was calculated on the basis of the solvophobic theory. The difference in extracting powers of some extracting organic ...