Integrated catalytic and electrocatalytic conversion of substituted phenols and diaryl ethers

• Electrocatalytic hydrogenation of phenolic compounds and diaryl ethers on Rh/C.
• The reaction proceeds at room temperature without external H2.
• Hydrogenation of the aromatic rings is the dominant reaction pathway.
• Methoxy and benzyloxy groups undergo C–O bond cleavage at room temperature.
• Increasing cathodic potentials favors the rates of ECH over H2 evolution.

Electrocatalytic hydrogenation and catalytic thermal hydrogenation of substituted phenols and diaryl ethers were studied on carbon-supported Rh. The rates of electrocatalytic hydrogenation increase with increasingly negative potentials, which have been related with the coverage of adsorbed hydrogen. For electrocatalytic and catalytic thermal hydrogen addition reactions, the dominant reaction pathway is hydrogenation to cyclic alcohols and cycloalkyl ethers. The presence of substituting methyl or methoxy groups led to lower rates compared to unsubstituted phenol or diphenyl ether. Methoxy or benzyloxy groups, however, undergo C–O bond cleavage via hydrogenolysis and hydrolysis (minor pathway). The surface chemical potential of hydrogen can be increased also by generating a H2 atmosphere above the reaction media, supporting the conclusion that thermal and electrochemical routes share the same reaction pathways.

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