THE ELECTRON DONATING PROPERTIES OF NITROGENCONTAINING ORGANIC BASES IN WATER-ETHANOL AND WATER-ACETONE SOLUTIONS

Abstract

In this paper, the dissociation constants (pKa) of some nitrogen-containing organic bases (aniline, pyridine and octylamine) in water-ethanol and water-acetone media at various concentrations of organic solvent in the system has been determined by the potentiometric titration method. It was established that the value of pKa of nitrogen-containing organic bases in aqueous-organic media naturally decreases with increasing content of organic solvent in the system. It was shown that their nature (aliphatic, aromatic, heterocyclic) and the physicochemical properties of the medium are significantly influenced by the nature and degree of change in the electron donor ability of the nitrogen-containing organic bases studied. It was noted that for aniline in water-ethanol solutions in the transition from water to an organic solvent, the value of pKa does not change much (ΔpKa = 0,9), while for pyridine and octylamine these changes are significant, and the values of ΔpKa are 2,9 and 1,7, respectively, which can be explained by the specific solvation of the aniline amino group with ethanol. In the case of water-acetone solutions, the behavior of the nitrogen-containing organic bases was studied generally similar, and the values of ΔpKa are within the range of 1,7-2,6. It was established that the dependence of the values of pKa of nitrogen-containing organic bases on the inverse of the dielectric constant of water-ethanol and water-acetone solutions tends to be linear, consistent with Izmailov’s theory. Thus, we can conclude that the change in the ratio of the mixed solvent components and, as a result, in general, dielectric permeability of the medium does not lead to a significant change in the solvation characteristics of the nitrogencontaining organic bases studied.

Keywords

• анілін
• піридин
• октиламін
• потенціометричне титрування
• електроно-донорні властивості