Indirect Baeyer-Villiger Oxidation of Furfural by In Situ Formed HOBr in an Undivided Electrochemical Cell

Furfural is a promising renewable platform chemical derived from biomass. Its electrochemical conversion offers the opportunity for considerable sustainability gains, i.e., by using a combination of a renewable feedstock and renewable energy. To widen the range of products available by electrochemical conversion/derivatization, indirect electrolysis (using a redox-active mediator), is a viable way. Existing methods for indirect electrolysis of furfural have been developed for divided cells only, requiring specific membranes that increase complexity and costs. Here, we describe a convenient indirect electrochemical method of furfural oxidation in an undivided cell. In this approach, HOBr is produced in situ from bromide salt and subsequently used as an oxidant in Baeyer-Villiger-type oxidation. The initially produced product, 2(3H)-furanone, immediately hydrolyzes into succinic semialdehyde. During extraction with an organic solvent, it converts back and could be isolated from the aqueous reaction mixture in the form of 2(3H)-furanone, an unstable compound. Finally, it is isomerized into the more stable 2(5H)-furanone isomer in 48% yield. The developed method represents a simple and convenient electrochemical tool for the synthesis of a renewable furanone-based building block in an undivided cell with yields comparable to existing thermochemical methods and allows to use (renewable) electricity as a driving force.