Solvation of Carboxylic Acids in Nonaqueous Binaries. Solvation Models for Butyric and Trichloroacetic Acids in Nitrobenzene–Toluene Mixtures

Abstract

Abstract The partitions of trichloroacetic and butyric acids between aqueous solutions and various nitrobenzene–toluene mixtures have been carried out at 25.0 and 30.0 °C, respectively. The observed nonlinearities for both acids of the monomer partition constants and the dimerization constants with the nitrobenzene mole fraction are interpreted in terms of the fractionation factors of effective exchangeable solvation sites of the involved species. Butyric acid monomer is concluded to have three sites for the solvation of the carboxylic hydrogen, carboxylate region, and alkyl chain. Desolvation of the former two sites is necessary for the formation of the dimer for which only two sites corresponding to its two alkyl chain are identified. The solvation sites of trichloroacetic acid monomer and dimer are identical and a singly hydrogen-bonded structure for the dimer is deduced. Dimerization of this acid in the organic phase proceeds by desolvation of what is equivalent to the sites of only one monomer.