Deep eutectic solvents as recyclable solvent-electrolyte systems for electroreductive C-O cleavage of lignin models

Abstract

Deep eutectic solvents (DESs), formed from hydrogen bonding acceptors and donors, are investigated as recyclable solvent-electrolyte systems for the electroreductive cleavage of C-O bonds in lignin model ethers. The widely used DES composed of choline chloride and methyl urea demonstrates a suitable electrochemical window and high cathodic stability enabling efficient cleavage of benzyl phenyl ether, achieving up to 97% selectivity for phenol over three reaction cycles in a simple, undivided cell without catalysts or additives. Optimization studies show that the choice of electrode material significantly affects both conversion and yield.Furthermore, the method is applicable to a selection of lignin model ethers, with observed reactivity trends correlating to substrate structure and solubility. The work highlights the potential of low-cost DESs as novel, dual-function, and recyclable media for green electrosynthesis, providing a foundation for future advances in electrochemical lignin depolymerization. Notably, the approach reduces waste associated with traditional supporting electrolyte salts and solvents in electrosynthesis, and continued improvements in faradaic efficiency and process integration will unlock the full green potential of this novel strategy.