The influence of surfactants on the electrocatalytic hydrogenation of organic compounds in micellar, emulsified, and hydroorganic solutions at Raney nickel electrodes

Abstract

The electrocatalytic hydrogenation (ECH) of limonene (1) and carvone (4) at a Raney nickel cathode was studied both in hydroorganic medium (methanol–water) and aqueous micellar and emulsified solutions. In methanol–water, the ECH of 1 stopped at p-menthene (2) and proceeded with low current efficiencies (18–24%). In micellar solutions containing a cationic surfactant (CTAB), the ECH of 1 was more efficient, giving p-menthane (3) as the main product with current efficiencies up to 30%. The pH of the solution (hydroorganic and micellar) had little influence. With anionic (SDS) and nonionic (Brij 35) surfactants, some p-menthane (3) was formed but the conversion rate and current efficiency were much lower. The ECH of carvone (4) was slightly less efficient in methanol–water than in micellar and emulsified solutions. The saturated alcohols neocarvomenthol (8), carvomenthol (9), isocarvomenthol (10), and neoisocarvomenthol (11) were the main products with current efficiencies of 75% (hydroorganic medium) to 90% (micellar solutions). The effect of surfactant concentration and pH on the efficiency and stereochemistry of the ECH of carvone (4) was also studied. Keywords: electrocatalytic hydrogenation, limonene, carvone, Raney nickel, micellar medium.