Direct cyanation reaction from benzoic acid to benzonitrile by paired electrosynthesis in liquid ammonia†

Abstract

Nitriles are essential intermediates in organic synthesis processes and are widely used in various industries. Several nitrile synthesis methods have been reported. Among these, the cyanation of carboxylic acids, which are abundant in nature, has attracted significant attention for the valorisation of biomass-derived components. However, these reactions require expensive catalysts, toxic reagents, and high-temperature/-pressure conditions. Herein, we propose a novel cyanation reaction of benzoic acid to benzonitrile, which is achieved by electrolysis in liquid ammonia at room temperature. In this reaction, benzoic acid is reduced to benzyl alcohol, and the iodide anion derived from the supporting electrolyte is oxidised to iodine. Following the electrochemical reactions, benzyl alcohol and iodine react chemically in liquid ammonia to form benzonitrile. The reaction is a paired electrosynthesis process because the products generated on the cathode (benzyl alcohol) and anode (iodine) react to form the final product (benzonitrile). The current efficiency of the electrochemical reduction of benzoic acid to benzyl alcohol and the conversion rate from benzyl alcohol to benzonitrile were 32% and 6% after 1 h of electrolysis, respectively. We also observed that the Pb cathode becomes porous during electrolysis, which facilitates the electrochemical reduction of benzoic acid. This novel reaction enables direct nitrile synthesis from carboxylic acids at room temperature without the use of toxic reagents or expensive catalysts. These findings confirm that the proposed reaction is a novel green cyanation method for carboxylic acids and provides new insights into electrochemical reactions in liquid ammonia for organic synthesis.