SOLVATION NUMBERS AND HYDRATION CONSTANT FOR THORIUM(IV) IN ETHANOL-WATER MEDIUM

The solvation number and hydration constant of Th4+ in ethanol-water m edium were determined at 25 degrees C using UV-spectral and electroche mical measurements. A solvate formation equilibrium is demonstrated an d characterized. Three molecules of ethanol (S) can bond to the metal cation with strengths comparable to that for H2O to form ThS3(H2O)(3)( 4+) Formation of thorium monochelate with lawsone (2-hydroxy-1,4-napht hoquinone) eliminates bonding with alcohol molecules. The dissociation constant of the chelating agent K-s(a) and the formation contant of t he monochelated metal ion K-s(f) that are essentially independent of the solution composition are evaluated Hydration titrations involving thorium-lawsone monochelate are performed and the data obtained from t he changes of pH with solvent composition are analyzed. The solution i ndependent constant, K-s(f) for thorium-lawsone complex formation in mixed aqueous ethanol is given by log K-s(f) = vpK(a) + log(s)K(h) - log [LH] - vpH + 3 log v where vpK(a) is the dissociation constant of the chelating agent LH in the solvent system of v volume fraction of w ater and K-s(h) is the solution-independent hydration constant of thor ium (IV) in the solvent system. Log-values for the constants K-s(h), K -s(f) and K-s(a)* are found to be 7.8 +/- 0.02, 11.38 +/- 0.04 and -0 .753, respectively.