Soluble Copper Xanthate Complexes

Abstract

Abstract When solutions of cupric perchlorate (10−6 to 10−2 M) are mixed with solutions containing nonequivalent quantities (concentrations) of xanthate (O-alkyl-dithiocarbonate) ions, clear solutions containing soluble nonionic and ionic complexes are obtained, despite the fact that the solubility product for a given metal xanthate salt may be exceeded by several orders of magnitude. Ultraviolet and visible (UV and VIS) spectroscopy, and dc and ac differential polarography have been employed to study these complex species. The spectral changes taking place on the addition of potassium ethyl xanthate to cupric perchlorate solutions, and also turbidity measurements, indicate that copper xanthate complexes are formed before the precipitation of cuprous ethyl xanthate, Cu(S2 COC 2 H 5). In very dilute solutions containing near equivalent concentrations of the reactants, a spectrum containing three broad maxima (235, 285, and 375 nm) is obtained and is interpreted as due to a nonionic cupric complex, Cu(S2 COC 2 H 5)2, (I). In the presence of excess cupric ions a second complex, an ionized cupric monoxanthate, Cu(S2COC2H5)+, (II), is formed with bands at 256, 283, 325, and 382 nm. The relative concentrations of the reactants determine not only which complex is formed in these dilute solutions, but also whether or not the cuprous xanthate precipitates. The species in solutions giving the spectrum of complex (I) is not stable. It decomposes quickly to cuprous xanthate and dixanthogen. Solutions of the ionic cupric complex (II) are stable for many for many hours. It is suggested that the ionic complex (II) may play a role in activating sphalerite in alkaline solutions.