Conductimetric titrations of symmetrical aliphatic dicarboxylic acids in solvents pyridine and pyridine–benzene mixtures

Nine symmetrical aliphatic dicarboxylic acids, namely oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, and sebacic acids, were titrated conductimetrically with tetrabutylammonium hydroxide in pyridine and pyridine–benzene mixtures ((2 + 1), (1 + 1), (1 + 2), (1 + 3), and (1 + 4)). Titration curves of the acids exhibited two distinct and stoichiometric end-points in media of dielectric constants 13.5, 10.0, 8.2, 6.3, 5.3, and 4.7, respectively. The closer investigations of the titration curves revealed that three factors mainly influence the shapes of the titration curves: dielectric constant of the medium, number of the methylene groups in the acid, and formation of hydrogen bonds between several species. As dielectric constant of the medium decreases, conductivity of the medium also decreases at any point in the titration curve. Increase in the number of methylene groups from one to five decreases conductivity of the medium linearly at the first end-points of the acids, from then the conductivity becomes practically constant in acids having five to eight methylene groups in pyridine and pyridine–benzene mixtures of 2 + 1 and 1 + 1 ratios. Keywords: conductimetric titration in pyridine, conductimetric titration in pyridine–benzene mixtures, symmetrical aliphatic dicarboxilic acids.