ELECTROCHEMICAL REDUCTION OF BENZYL CHLORIDE ON SILVER, GRAPHITE AND SILVER/GRAPHITE POWDER MACROELECTRODES

• Voltammetry performed at very low scan rate shows that benzyl chloride occurs at ∼−0.7 V/Ag/AgCl for high silver percentages in cathodic materials, i.e. at potentials much higher than in usual voltammetry conditions.
• Even using an aqueous electrolyte, benzyl chloride was totally reduced on cathodic powders made of silver-graphite mixtures and a high estimated yield of dimer was obtained (89%).
• Without DMF, the higher yield of dimer (89%) was obtained on 25% silver −75% graphite mixture with a 62% faradaic yield.
• With DMF, the higher yield of dimer (85%) was obtained on 100% silver with a 100% faradaic yield.

Benzyl chloride reduction was studied in a powder macroelectrode (PME) made of silver, graphite or silver/graphite mixtures (1:3, 1:1 and 3:1) in absence of solvent, or using a very low amount of DMF as solvent (PhCH2Cl/DMF 3:1). A 0.1 mol L−1 KCl aqueous solution was used as anolyte. A competitive hydrogenation and dimerization process was observed, affording the respective toluene and bibenzyl products. The well-known electrocatalytic effect of silver on reduction of the CCl bond was confirmed by a significant positive shift of the benzyl chloride reduction potential in comparison with pure graphite powder. The products distribution was analysed after linear sweep voltammetries at low scan rate (0.1 mV s−1), indicating high yields of bibenzyl produced on Ag/graphite-PME. Pure graphite-PME was not selective towards dimer formation. The best results for bibenzyl production occurred at more positive potentials, in the presence of silver. A small amount of solvent (DMF) play an important role on the electrode surface desorption and diffusion of intermediary species.