Lipase‐Mediated Selective Oxidation of Furfural and 5‐Hydroxymethylfurfural

AbstractFurfural and 5‐hydroxymethylfurfural (HMF) are important biomass‐derived platform chemicals that can be obtained from the dehydration of lignocellulosic sugars. A possible route for the derivatization of furanics is their oxidation to afford a broad range of chemicals with promising applications (e.g., diacids, hydroxyl acids, aldehyde acids, monomers for novel polymers). Herein we explore the organic peracid‐assisted oxidation of furanics under mild reaction conditions. Using lipases as biocatalysts, alkyl esters as acyl donors, and aqueous solutions of hydrogen peroxide (30 % v/v) added stepwise, peracids are formed in situ, which subsequently oxidize the aldehyde groups to afford carboxylic acids with high yields and excellent selectivities. Furthermore, the use of an immobilized silica‐based 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) affords the selective oxidation of the hydroxymethyl group of HMF to afford 2,5‐diformylfuran. That product can be subsequently oxidized using again lipases for the in situ peracid formation to yield 2,5‐furandicarboxylic acid, which is considered to be a key building block for biorefineries. These lipase‐mediated reactions proceeded efficiently even with high substrate loadings under still non‐optimized conditions. Overall, a proof‐of‐concept for the oxidation of furanics (based on in situ formed organic peracids as oxidants) is provided.