The paired electrochemical synthesis of sorbitol and gluconic acid in undivided flow cells. I

The strategy of paired electrochemical synthesis for the production of organic chemicals, in which the reactions at both the anode and cathode simultaneously contribute to the formation of the final product(s), could result in as much as a 50% reduction in energy consumption as compared to conventional electro-organic syntheses. In order to evaluate this hypothesis the electrochemical oxidation of glucose to gluconic acid and the reduction of glucose to sorbitol were paired in undivided flow-through parallel plate and packed bed cells. To date, the optimum electrode materials and operating conditions for the paired synthesis are: an amalgamated zinc cathode, a graphite anode, an initial glucose concentration of 0.8 mol dm−3, a 0.8 mol dm−3 NaBr supporting electrolyte, an electrolyte flow rate of 0.81 min−1 and an electrolyte pH of 7. Under these conditions the current efficiencies for sorbitol and gluconic acid were 26% and 68%, respectively at 0.25 F mole−1. Current losses are believed to be due to hydrogen evolution and the reduction ofδ-gluconolactone (an intermediate in the formation of gluconic acid) to glucose.