Analytical Sciences

Thermodynamics of the Distribution of Some Carboxylic Acids between Organic Solvents and a Perchlorate Solution

Isao KOJIMA  and Miho OGAWA

Laboratory of Analytical Chemistry, Department of Applied Chemistry, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan

The distribution of formic, benzoic and 4-methylbenzoic acids between a 0.1 mol dm^-3 (Na⁺, H⁺)ClO₄^- solution and octanol and carbon tetrachloride was studied at five different temperatures of 10 - 30°C. The thermodynamic parameters for the transfer process of monomeric acid between two phases and for the dimerization of monomeric acid in carbon tetrachloride (deltaH and deltaS) were evaluated from the van't Hoff isochore. The free-energy change for the transfer of a methylene group from water to organic solvents was entropically controlled, irrespective of the organic solvents. The distribution constants of formic and benzoic acids were larger than those expected from the distribution constants of acetic and phenylacetic acids, respectively. The free-energy change for all solutes, except for benzoic and 4-methylbenzoic acids, was also entirely entropically controlled in the case of octanol as a solvent. The enthaly-entropy compensation for the dimerization constant of acids in carbon tetrachloride was observed.

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