Electrochemical oxidation of phenols in flow: a versatile and scalable access to para-benzoquinones

Abstract

A novel and scalable protocol for the synthesis of para-benzoquinones from inexpensive phenols is reported. In advancement of previous methods, the oxidation is performed free of catalyst, mediator or terminal chemical oxidizer, effectively minimizing waste. Electricity serves as a sustainable, reagent-free oxidant and enables excellent selectivity. The complex effect of protic additives on the oxidation is studied and utilized to optimize the reaction outcome. A basis for continuous production is provided by the development of a flow protocol, which is operable at mild, ambient conditions. Moreover, the versatility of the method was demonstrated for 26 examples in yields up to 99%. The scalability of the reaction was proven on gram-scale without corrosion in yield.