Collect. Czech. Chem. Commun. 1987, 52, 616-625

Anodic oxidation of mercury in the presence of thioether acids: Methane-1,1-bis-mercaptoacetic acid

E. Casassas, M. Esteban and C. Ariño

Departament de Quimica Analitica, Universitat de Barcelona, 08028 - Barcelona, Spain


The anodic oxidation of mercury in the presence of methane-1,1-bis-mercaptoacetic acid (MBMA) has been studied by DCr, DP, AC1, and AC2 polarography, cyclic voltammetry, and coulometry. The electrode process is controlled by the adsorption of the product formed according to: Hg + 2 H(2-n)Ln- → H(2-n)HgL2n- + (2-n) H+ + 2e with n = 0 at pH < pK1, n = 1 at pK1 < pH < pK2, and n = 2 at pH > pK2. No adsorption of MBMA is observed. The behaviour of MBMA at a hanging mercury drop electrode (HMDE) by cathodic stripping voltammetry (CSV) has been also studied. At MBMA concentrations above 1 10-6 mol l-1, the stripping voltammograms showed two well defined peaks, at c. -0.140 V and at c. -0.300 V. The anodic process occurring during the pre-electrolysis in CSV is described by the formation of a Hg(I) compound: 2 Hg + 2 H(2-n)Ln- → H(2-n)Hg2L2(2-2n)+ + 2e followed by its disproportionation: H(2-n)Hg2L2(2-2n)+ →c H(2-n)HgL2(2-2n)+ + Hg,
where n has the above-mentioned values.