Electrochemistry, stability, and alkene complexation chemistry of Copper(I) triflate in aqueous solution. Potential for use in electrochemically modulated complexation-based separation processes

Copper(I) trifluoromethanesulfonate (CuOTf), which is insoluble in water, reacted with vinyl sulfonate anion (VS) to form a water soluble complex (concentrations >0.1 M). Acidic CuOTF solutions prepared with relatively large VS/Cu(I) ratios were comparable in stability to solutions containing excess chloride ion. Reversible binding of alkenes (ethylene, 1,3-butadiene and 1-butene) to copper(I) in aqueous CuOTf/VS solutions was observed by H-1-NMR. The copper(I) displayed a competitive reaction with VS and the alkenes. This allowed the binding affinity of the alkenes to the copper(I) to be calculated based on the proton chemical shift for VS, The strength of alkene complexation followed the order ethylene >1-butene approximate to 1,3-butadiene. The electrochemistry for the Cu(II/I) couple showed a quasi-reversible reaction that depended on acidity and the concentration of VS in the solution. Binding to copper(I) caused substantial amounts of the alkenes to be absorbed into CuOTf/VS solutions from the gas phase, especially at low [VS]/[Cu(I)] ratios. Calculations indicated that CuOTF in aqueous solution containing VS is superior to CuCl in chloride media for electrochemically modulated complexation-based separation of alkenes from alkanes.