Study on the speciation of copper(I) in the presence of cyclohexylamine in alkaline solution by differential pulse polarography

Abstract

The strong complexation of Cu with cyclohexylamine in coolant waters of power stations containing this amine as a pH regulating anticorrosion agent may have technically significant consequences affecting the dissolution of copper from the alloy material of the heat exchanger components. The speciation of Cu(I) with cyclohexylamine (CHA) was studied in alkaline solutions in the pH range from 8.6 to 10 by differential pulse polarography. It was proved that the peaks correspond to the reversible reduction of Cu(I) complexes at the DME. The first reduction step Cu(II)/Cu(I) appeared only as a shoulder on the Hg-oxidation peak. The potentials of the Cu(I)-peaks are shifted more negatively with increase of the cyclohexylamine concentration and the pH. A modified DeFord-Hume-treatment was applied for the evaluation of the stoichiometric overall stability constantsβi andβij and ligand numbers of the formed simple complexes (Cu(CHA)2)+, (Cu(CHA)3)+, (Cu(OH)2)− and the mixed uncharged complex (Cu(OH) (CHA)) from the relationships between the peak potential shiftsΔE p and the ligand concentrations. The logarithms of the stability constants logβ between 11 and 17 indicate a strong binding of Cu(I). From the resulting stability constants the distribution of Cu(I) among these complexes was calculated and also presented graphically as three-dimensional plots of the dependence of the formation degree as well on the cyclohexylamine concentration as on pH.