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 wat er, reacted with vinyl sulfonate anion (VS) to form a water soluble co mplex (concentrations >0.1 M). Acidic CuOTF solutions prepared with re latively large VS/Cu(I) ratios were comparable in stability to solutio ns containing excess chloride ion. Reversible binding of alkenes (ethy lene, 1,3-butadiene and 1-butene) to copper(I) in aqueous CuOTf/VS sol utions 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 che mical shift for VS, The strength of alkene complexation followed the o rder ethylene >1-butene approximate to 1,3-butadiene. The electrochemi stry for the Cu(II/I) couple showed a quasi-reversible reaction that d epended on acidity and the concentration of VS in the solution. Bindin g to copper(I) caused substantial amounts of the alkenes to be absorbe d into CuOTf/VS solutions from the gas phase, especially at low [VS]/[ Cu(I)] ratios. Calculations indicated that CuOTF in aqueous solution c ontaining VS is superior to CuCl in chloride media for electrochemical ly modulated complexation-based separation of alkenes from alkanes.