Distribution of oxalic acid between water and organic solutions of tri-n-octylamine

The extraction of oxalic acid from an aqueous solution into solutions of tri-n-octylamine in single solvents toluene, chloroform, and methyl isobutyl ketone was investigated. In addition to batch extraction experiments and isopiestic measurements in the binary system oxalic acid/water, infrared spectroscopic measurements were performed. These spectroscopic investigations yield information about the stoichiometry of complex formation. All measurements were carried out at 298.15 K. A model for the liquid-liquid equilibrium is presented which was used to correlate the experimental data. The model takes into account chemical reactions as well as physical interactions in both phases. Many of the model parameters could be deduced from information about subsystems using also the new isopiestic measurements. However, as several complexes of oxalic acid and tri-n-octylamine with as well as without water have to be considered, some model parameters had to be adjusted using experimental data from batch extraction experiments. The model reliably describes the partitioning of all components onto the coexisting phases.