O2-Triggered Electrochemical Generation of Acyl Chloride Promoting Cascade Reaction of Esters Synthesis

Ester compounds as one of the most important organic chemicals are extensively used in chemical industry, medicines, food, plastics, cosmetics and other applications. Traditional ester synthesis is impeded by challenges of slow reaction kinetics, harsh conditions, and environmental concerns. Here, we propose a green and efficient route for synthesis of esters via an electrochemical dechlorination-oxygen insertion cascaded with chemical nucleophilic reaction. A high selectivity of 93.2%, and a yield of 92.5% for methyl 6-chloronicotinate (MCN) generation are obtained by electrochemical reduction of 2-chloro-5-trichloromethyl pyridine over the activated Ag electrode in an O ₂ -saturated alcoholic solution. Electrochemical in-situ characterizations, femtosecond transient absorption spectra, isotope labeling, and theoretical calculations elucidate that the formation of intermediate acyl chloride is a key step, which involves reactive oxygen species of oxygen reduction reaction (ORR) coupling with dechlorination intermediate. The involvement of O₂ alters the electrochemical reaction pathway from conventional hydrodechlorination to oxygenation-dechlorination process, which is attributed to the preferentially occurred ORR than hydrogen evolution reaction. The generated acyl chloride further facilitates the subsequent chemical reaction in an alcoholic solution for MCN synthesis. The broad substrate scope and excellent performance in a flow electrolyzer validate the scalability and potential of this electrocatalysis-cascaded chemistry system for sustainable industrial production.