Determination of the speciation of copper in the presence of morpholine in alkaline solutions by DC and differential pulse polarography

Abstract

The speciation of Cu with morpholine (tetrahydroxo-1,4-oxazine) was studied in alkaline solutions bydc- and differential pulse polarography. In the pH range 8.7–9.8 Cu forms a mixed morpholinehydroxo complex which is reduced reversibly at the dropping mercury electrode by the uptake of 2 electrons. By the evaluation procedure of Fisher and Hall for the half-wave potential shift of a metal ion complexed with two different types of ligands the ligand number for hydroxide and morpholine and the stoichiometric complexity constant have been determined fromdc-polarographic and differential pulse polarographic data. The resulting values indicate the formation of a Cu(II) complex containing one hydroxide and two morpholine groups. From the visible spectra and the ESR-spectra the monomeric [CuL2(OH)(H2O)3]+ with octahedral structure emerges as the only possible structure and the formation of a dimer is clearly excluded. The average value of the stability constant is about 1018 and indicates a stronger binding than that for the Cu-ammonia-complex of the same sterical configuration. The strong complexation of Cu with morpholine in boiler waters of power stations containing morpholine as a pH regulating anticorrosive agent may have significant consequences on the chemical speciation of Cu in effluent waters and consequently on the Cu-uptake by planktonic species in natural waters into which those effluent water is discharged.