Metal complexes of 2-(2′-carboxymethylthio-phenylazo)-5-nitrotoluene—II. Complex formation equilibria with copper(II) ion in several dioxane—water solvent mixtures

Abstract

Stability constants of copper(II) complexes formed by 2-(2′-carboxymethyl-thiophenylazo)-5-nitrotoluene in dioxane—water solvent mixtures of several different compositions [50, 60 and 75% dioxane (v/v)] were determined from EMF measurements, at 25°C and 0.1 mol dm −3 NAClO 4 ionic medium. Graphical treatment of experimental data gives for the equilibria nA −+Cu 2+ = Cu A n (2- n)+ ( n = 1 or 2), in a solvent with X% (v/v) dioxane, the following values of log β 1, and log β 2 (given here successively). X = 50:2.41, 6.77; X = 60:3.36, 7.45; X = 75:4.33, 7.64. The relation between solvent composition and the values found for the stability constants is discussed. From EMF measurements made with the copper(II) ion-selective electrode, at constant pH, the nature of the effective donor groups in this potentially terdentate ligand is inferred.