C12 aromatic triol-furoin and diol-furil from bio-based 5-(hydroxymethyl)furfural: enhanced selective synthesis, scale-up and mechanistic insight into cyclic catalysis†

Abstract

In this study, we investigate the valorization of 5-(hydroxymethyl)furfural (5-HMF), a versatile and pivotal renewable C6 platform chemical, into a C12 heteroaromatic triol, 5,5′-bis(hydroxymethyl)furoin (DHMF), and a C12 heteroaromatic diol, 5,5′-bis(hydroxymethyl)furil (BHMF). The carboligation of 5-HMF to DHMF is catalyzed by an N-heterocyclic carbene, 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene (TPT), generated in situ from its stable methoxy adduct, 5-methoxy-1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazoline (TPA-OMe). This reaction achieves quantitative yield in dimethyl carbonate, a more environmentally friendly solvent. The resulting DHMF precipitate was readily purified via simple filtration and washing. Moreover, an enhanced selective oxidation was conducted at the secondary hydroxyl group of DHMF to generate the ketone group of BHMF in quantitative yield by using organo-catalysts, anionic exchanger, and NaOH. We proposed and subsequently validated a cyclic catalysis mechanism for the oxidation through the colorimetric detection of the by-product, H₂O₂, in the reaction. All synthetic processes to produce these C12 triol-furoin and diol-furil compounds were successfully demonstrated on a scale ranging from 20 to 400 grams. The feasibility of these processes was established with high yields achieved under moderate reaction conditions and ambient pressure, making them suitable for large-scale production. Consequently, these C12 multi-functional chemicals can find applications in the production of bio-based aromatic polymers such as polyesters, polyurethanes, and polycarbonates.