The Polarography of the Cadmium(II)–2-Carboxy-1-pyrrolidinecarbodithioate Chelate

Abstract

Abstract The electrochemical behavior of the cadmium(II) ion in the presence of 2-carboxy-1-pyrrolidinecarbodithioic acid (H2cpcd) as a chelating agent was investigated in an alkaline medium by d.c. polarography, a.c. polarography, cyclic voltammetry, and chronopotentiometry. The cadmium(II) chelate gave a reversible two-electron reduction wave at −0.86 V vs. SCE, with a postwave at −0.95 V. From the dependence of the total wave height on the mercury column height and from the methods of cyclic voltammetry, the electrode reduction of the cadmium(II) chelate was found to be diffusion-controlled. The diffusion current constant was 2.42 μA mol−1 m3 mg−2⁄3 s1⁄2. The postwave was identified as an adsorption wave of the cadmium(II) chelate from the dependence of the postwave height on the mercury column height, the a.c. peak height, the electrocapillary curves, and the results of chronopotentiometry. The surface excess of cadmium(II) chelate adsorbed on the mercury electrode was evaluated by means of three different electrochemical techniques. The composition of the cadmium(II)–cpcd chelate in the presence of excess H2cpcd was Cd(cpcd)22−, and the overall stability constant was estimated to be 8.0×1012 at 25.0 °C and μ=1.5.