The COMPLEX FORMATION OF CADMIUM (II) WITH 2-METHYLIMIDAZOLE IN AQUEOUS AND AQUEOS-ALCOHOL SOLUTIONS

Abstract

Using potentiometric titration data, titration curves of the protonated form of 2-methylimidazole [H2-MI]+ in water and water-alcohol solutions were constructed. Forms of formation curves correspond to weak monobasic acids. The value of the formation function () for the studied systems varies between 0.45-0.87, which corresponds to the formation of one protonated form of 2-methylimidazole in aqueous and aqueous - alcoholic solutions. The acid dissociation constant (pKa) of 2-methylimidazole at 298 K was determined by the pH - metric method in aqueous and aqueous - methanol (ethanol) solutions at different contents of the organic solvent. It was revealed that the maximum proportion of molecular form accumulation falls on pH 10-10.5. Below pH 10, the protonated form of 2-methylimidazole begins to accumulate in the solution. Starting from pH = 7.2-methylimidazole exists completely in protonated form in solution. With an increase in the concentration of alcohol in solution, an increase in the acidic properties of the protonated form of 2-methylimidazole is observed. The pKa value of 2-methylimidazole in aqueous ethanol solutions is higher than that of aqueous methanol. The potentiometric method was used to study the complexation of cadmium (II) with 2-methylimidazole (2-MI) at 278-318 K. The effect of the nature and composition of the aqueous-organic solution on the stability of the complexes formed is established. It was revealed that during the interaction of cadmium (II) with 2-methylimidazole in aqueous and aqueous-alcoholic solutions four complex forms are formed. For each complex form, stability constants are found depending on the temperature and the content of non-aqueous solvent. It is shown that when methanol is added to water, an increase in the stability of all complex forms is observed. In contrast to water-methanol solutions in water-ethanol solutions, in addition to the complex particle [CdL4]2+, the stability of other complex forms pass through a minimum. Based on our own and published data, we conclude that the degree of influence that an organic solvent has on the stability of complexes cadmium (II) largely depends on changes in the solvation condition of the ligand molecule and the central atom.