Direct Anodic Conversion of 4-Hydroxybenzaldehydes into Benzoquinones

A novel electrosynthetic protocol for the direct conversion of easily accessible 4-hydroxybenzaldehydes into valuable benzoquinones is reported. The transformation is enabled through anodic oxidation and is performed in a reagent-free manner devoid of terminal oxidants and redox mediators to effectively minimize waste. Environmentally benign and inexpensive graphite serves as a metal-free anode material. A broad range of substituents, including halogens, are tolerated in this electrochemical protocol, and the quinones are selectively accessible in yields up to 99%. Furthermore, the compatibility with electrochemical flow synthesis is demonstrated. Moreover, the flow protocol is successfully applied to the biopolymer lignosulfonate and provides quinones in yields up to 7.6 wt%. A mechanistic proposal for this Dakin-type reaction is offered. The sustainability and synthetic utility are evaluated quantitatively and compared to established protocols by application of different green chemistry metrics.

Automated summary

A novel electrosynthetic protocol is reported for the direct conversion of 4-hydroxybenzaldehydes to valuable benzoquinones. The transformation is conducted through anodic oxidation, minimizing waste by eliminating terminal oxidants and redox mediators. Graphite serves as a metal-free anode material. A wide range of substituents, including halogens, are tolerated in this electrochemical protocol, with quinones selectively obtained in up to 99% yield. The compatibility of the protocol with electrochemical flow synthesis is demonstrated, and its application to lignosulfonate yields quinones in up to 7.6 wt%.