The partition constants of a number of carboxylic acids were determined for the partition systems using 1-octanol and benzene as a solvent, and the dimerization constants of carboxylic acids in the benzene phase were also determined. A linear relationship between the partition constants (log KD ,HA) of carboxylic acids and the molar volume of the respective carboxylic acids was found. A new good relationship on the partition equilibrium of carboxylic acids was found between the partition systems using 1-octanol and benzene, that is, a good linear relationship exists between the values of (log K2,HA+21og KD,HA) for benzene/water system and the values of log KD,HA for 1-octanol/water system, irrespective of the kinds of carboxylic acids.
The solvent extraction of copper(II) with 3-phenylpropanoic, 4-phenylbutanoic, and 2-phenylbutanoic acids was carried out using 1-octanol and benzene as solvents at 25˚C and at an aqueous ionic strength of 0.1 mol dm -3 (NaClO4). Each extraction equilibrium for these systems was determined in detail by a slope analysis and curve-fitting method. In the aqueous solution, the formation constants of copper(II) with these phenylcarboxylate anions were potentiometrically determined. The present results have been compared with the previous results for the extraction of copper(II) with phenylacetic acid using 1-octanol and benzene as solvents. Between the partition constants of CuA2 and HA (HA: phenylcarboxylic acid), the following relationship was set up: log KD,CuA2=1.8log KD,HA-1.5 for four kinds of phenylcarboxylic acids in the 1-octanol systems. Although a remarkable difference in the extracted species between the benzene and 1-octanol systems was observed, the extraction constants of dimeric copper(II) species and dimerization constants in these extraction equilibria were found to show a high correlation between the 1-octanol and benzene systems. The dimerization constants of copper(II) carboxylates in the 1-octanol systems increased with the number of carbon atoms in the acids: phenylacetic<3-phenylpropanoic<4-phenylbutanoic 2-phenylbutanoic acids, and the extraction constants of the dimeric species, Cu2A4(HA)2 in the benzene systems decreased in the order: 2-phenylbutanoic>phenylacetic>3-phenylpropanoic>4-phenylbutanoic acids. In the systems using 1-octanol and benzene, 2-phenylbutanoic acid was superior to the other phenylcarboxylic acids as an extractant for copper(II).
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