Evaluation of carbon electrodes and electrosynthesis of coumestan and catecholamine derivatives in the FM01-LC electrolyser

This work extends the range of electrodes and conditions under which the FM01-LC reactor has been used in a laboratory environment and evaluates the performance of carbon electrodes. Reticulated vitreous carbon (RVC) has been used to provide a stable, inert, three-dimensional electrode surface for organic electrosynthesis; its performance is compared to that of nickel mesh for the oxidation of catechol to o-quinone. This product was then reacted in situ with (i) 4-hydroxycoumarin and (ii) 1,3-dimethylbarbituric acid to produce, respectively, coumestan and catecholamine, products of synthetic interest. In mass transport experiments using hydroquinone oxidation as a model reaction, performance was similar to nickel electrodes, but Sherwood numbers were reduced by about 5-10% when carbon electrodes were used. The best-performing RVC electrode, however, showed poorer behaviour than its nickel counterpart. Yields for the production of coumestan and catecholamine were approximately 45% and 25%, respectively, although this was mostly due to extraction problems, since current efficiencies were both in the region of 65-70%. The electrode material, rather than the fluid flow behaviour, leads to a reduction in overall cell efficiency; this is confirmed by studies which show a film forming on the surface of the electrode.