Stability of Metal Chelates of 2—Su1phonic-4-Methyl Phenylhydrazono Diethylmalonate in Various mixed Aqueous Solvents

Abstract

Ph-meteric studies have been carried out to determine the dissociation constant of 2-Sulphonic-4-rrethy1 phenyl -hydrazono di-ethylmlonate abb-reviated (2-SPHDEM) ligand, as wel l as, the stability constants of its complexes with trivalent lanthanides and some divalent metal ions in various mixed aqueous solvents, viz: ethanol -water, nethanol -water and dioxane-water at 25' C and 0.1 M ionic strength. The dissociation constant of ligand decreases (increase in acidity) by increasing the dielectric constant of the solvent. The stability constants of 1:1 and 1:2 chelates with trivalent lanthanides have been determined in 50% (v/ v) ethanol -water sol vent. The effect of variation of the dielectric constant of different mixed aqueous solvents on the stability of chelate compounds of divalent metal ions was studied and discussed. The stabil i ty of these chelates follows the order: di oxane-water > ethanol -water > methanol -water. In an ethanol -water mixture, the sequence stability is: 75%>50%>25%.0.0% The stability constants of divalent metal ions in all solvents studied follows the order: cu(ll) >ZN(II)> Ni(ll)>Co(II)>Cd(II).