Polarographic reduction of uranyl-benzenehexacarboxylate complexes in aqueous and dimethyl sulfoxide solution

Abstract

The reduction of the uranyl-mellitate complex at the dropping mercury electrode has been studied in aqueous and dimethyl sulfoxide solution. In aqueous solution, besides the reduction waves of the uranyl-mellitate complex, corresponding to the reduction of U(VI) to U(V), and of U(V) to U(III), an adsorption wave and a catalytic hydrogen wave were obtained; the species formed below pH 4.0 was UO 2(H 3A) - and above pH 4.0 was UO 2(OH)(H 3A) 2-. In dimethyl sulfoxide solution, two well-defined waves were observed; the first wave is due to reduction of a uranyl-mellitate-DMSO complex, and the second to reduction of mellitic acid. The species involved are UO 2(DMSO) 6 2+ below pH 2.2 and UO 2(H 3A)(DMSO) 5 -1 above pH 2.2. The activation energies of the reduction process were determined.