COMPLEXATIONOF SILVER(I) WITH 1-METHYL-2-MERCAPTOIMIDAZOLEIN WATER-ETHANOL SOLUTION

Abstract

The interfacial distribution method was used to calculate the distribution coefficients and changes in the energy Gibbs of 1-methyl-2-mercaptoimidazole (1MI) at transfer from water to aqueous ethanol solvents. It is shown that the values of ∆trG1MIare positive in the entire range of the investigated compositions of the water-ethanol solvent. In a solvent containing 0.10 mol. frac-tion of ethanol, a significant weakening ofsolvation is observed. With a further increase in the ethanol content, the values of ∆trG1MIdecrease and indicate an increase in solvation of 1MI. It has been found that 1MI in water and in aqueous ethanol solvent is protonated as a very weak base. The dependence pKa=f(χEtOH) have a minimum in the concentration range of 0.1 mol. fraction of EtOH. The transition from water to its mixtures with ethanol practically does not affect the acid-base properties of 1MI. The values of the energy Gibbs of desolvationof H1MI+and H+depending on the composition of the aqueous ethanol solvent and change symbately. The differences in these values almost completely compensated by the change in the solvation contribution of the proton. Small changes in the energy Gibbs oftransfer of the 1MI protonation reaction are due to the com-pensation effect between the solvation contributions of the ions {∆trGH1МИ+–∆trGH+} and the mo-lecular form of 1МИ (∆trG1МИ). The effect of a water-ethanol solvent on the equilibria of silver(I) complexations with 1MI was studied. For 1-methyl-2-mercaptoimidazole silver complexes in aque-ous-ethanol solvents, the dependence lgβi0=f(χEtOH) has a minimum at 0.10 mol. fraction of ethanol. In general, for all complexes, the stability increases from water to a water-ethanol solvent. An analysis of the influence of a water-ethanol solvent on the change in the energy Gibbs of transfer of the reaction of formation of a monocomplex of silver(I) ion with 1MI, and on the change in the energy Gibbs of solvationof the participants in the complex formation, showed that in the entire range of compositions of the water-ethanol solvent. There is a compensation effect of the solvation contributions of the central ion and ligand to change complex stability. As a result, the changes in the solvation state of the [Ag(1MI)]+complex particle determine the complex stability.