Water Molecules in Organic Solvents Involved in the Synergistic Extraction of Europium(III) with β -Diketones and Lewis Bases

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Abstract To explain the difference in the magnitude of synergistic extraction among organic solvents, the water solubility in hexane, carbon tetrachloride, benzene, and chloroform was measured, and then the residual hydration number of europium(III) in the β-diketonato chelate and in their adducts with 1,10-phenanthroline as well as the adduct formation constants were determined. Using the data, the formation constants of the adduct according to a novel definition, in which the water concentration in the organic phase is treated as one variable, were determined. The constants are approximately constant irrespective of the organic solvents, although those according to the conventional definition are different among the solvents. It has been concluded that one of the most important factors controlling the magnitude of synergistic effects is the presence of water, such as the water content dissolved in organic solvents, and the hydration and dehydration of the relevant species, because water molecules compete with a Lewis base in complexation to the metal(III) chelates in the organic solvents.