Selective electro-oxidation of phenol to 1,4-hydroquinone employing carbonaceous electrodes: surface modification is the key

Abstract

The oxidation of phenol leading to 1,4-hydroquinone with high conversion, remarkable selectivity and an excellent yield (87% isolated) has been accomplished under electrolytic conditions in an aqueous medium employing carbon-based electrodes. To achieve this, various factors such as electrode stability, repeatability, and the type of product formed by the electrochemical oxidation of phenol have been investigated using cyclic voltammetry first and then organic transformations under optimized conditions were accomplished by constant current electrolysis. The voltammetric data clearly show that electrochemically generated intermediates passivate the surface of the typically used electrodes, leading to a decrease in their activity, which is a major problem concerning the transformation of phenol electro-oxidation to an industrially adaptable process. In this work, it is established that such difficulties could be circumvented using surface modified carbonaceous electrodes having disordered graphene-like structures and oxygen functional groups. It is also demonstrated that surface modified reticulated vitreous carbon (RVC) based electrodes could be used for electro-oxidation of phenol at a reasonably large scale. The electrolysis conditions have been optimized based on the mechanistic understanding leading to remarkable conversion of phenol with 87% selectivity to 1,4-hydroquinone.