COMPLEXATION OF SILVER (I) WITH 1-METHYL-2-MERCAPTOIMIDAZOLE IN WATER-ETHANOL SOLUTION

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 Delta(tr)G(1MI) are positive in the entire range of the investigated compositions of the water-ethanol solvent. In a solvent containing 0.10 mol. fraction of ethanol, a significant weakening of solvation is observed. With a further increase in the ethanol content, the values of Delta(tr)G(1MI) decrease 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 pK(a)=f(chi(EtOH)) 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 desolvation of 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 of transfer of the 1MI protonation reaction are due to the compensation effect between the solvation contributions of the ions {Delta(tr)GH(1M)(+) - Delta(tr)G(H)(+)} and the molecular form of 1M (Delta(tr)G(1M)). 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 aqueous-ethanol solvents, the dependence lg beta(0)(i) = f(chi(EtOH)) 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 solvation of 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.