Polarographic and redox potential studies on copper(I) and copper(II) and their complexes

Abstract

Detailed polarographic and redox potential studies of copper (I and II)-ethanolamine (mono-, di- and tri-) complexes have been made. The polarograms taken with ethanolamine (mono-, di- and tri-) complexes reduced with copper gauze in potassium nitrate solutions to equilibrium show an anodic current passing smoothly to the cathodic current. The ratio of the cuprous to cupric complex is ca . 0.5, 0.02 and 0.002 in mono- di- and triethanolamine systems, respectively. It has been possible to compute the current-voltage curve of the reduction and oxidation of the cuprous complex in the monoethanolamine system. With all ethanolamines the formula of the cuprous complex is found to be CuA 2 + . The diffusion current constants of these complexes have been determined. The nature of the cupric complexes in potassium nitrate solutions has been studied both by the drop in pH and by the polarographic-redox potential method. The formulae of the cupric complexes have been established by testing the constancy of functions. α = β i c β o u s = [ C u A p 1 ( O H ) p 2 ( 2 − p 2 ) + ] [ C u A 2 + ] × [ C u + ] [ C u 2 + ] × [ A ] ( 2 − p 1 ) [ O H − ] p 2 γ = β i c β o u s 2 × disproportionation constant = [ C u A p 1 ( O H ) p 2 ( 2 − p 2 ) + [ C u A 2 + ] 2 × [ A ] ( 4 − p 1 ) [ O H − ] p 2 The stability constants of the following complexes have been obtained: CuM 3 OH + , CuD 2 (OH) 2 , CuT 2 OH + , CuM 2 + , CuD 2 + and CuT 2 + . Polarograms of cupric complexes taken in the presence of ethanolammonium ion show the presence of two waves of equal height in mono- and diethanolamine systems indicating reduction via the +1 state. In the case of triethanolamine two waves of unequal height are obtained indicating that two species are in sluggish equilibrium both being reduced straight to the metal.