One-pot synthesis of an emerging bio-based platform chemical: 5,5′-[oxybis(methylene)]bis-2-furfural

Bio-based platform chemicals are compounds obtainable from biomass that can be employed as starting materials to produce chemical intermediates, building blocks and polymers. Among them, 5-hydroxymethyl furfural (HMF) is a key molecule, from which various other value-added compounds can be derived via suitable chemical transformations. In particular, 5,5′-[oxybis(methylene)]bis-2-furfural (OBMF) can be easily obtained from HMF self-etherification. OBMF finds applications mainly in the synthesis of macrocycles and as a precursor of polyurethanes, polyamides and polyamines. Previous works have reported that it is possible to obtain OBMF from HMF in high yields by its dehydration in acidic conditions, i.e., using a heterogeneous sulfonic resin and dimethyl carbonate (DMC) as green solvent. However, this approach requires a high-purity HMF that has to be prepared from D-fructose and thus purified via cold precipitation leading to its typical yellow crystals. In fact, reactions performed with raw HMF (up to 90% pure) did not yield comparable results. From these premises, the present work aims to design a one-pot green synthetic approach for the synthesis of OBMF from D-fructose via in-situ formation of HMF. This approach will therefore avoid the isolation of HMF, with consequent savings in term of solvents and work-up materials. According to the best-found reaction conditions, OBMF could be obtained by dissolving D-fructose in a mixture of DMC and tetraethylammonium bromide (TEAB) as solvent system, in the presence of an acid heterogeneous sulfonic resin as a catalyst. A Dean-Stark apparatus was necessary to remove water molecules forming both from the triple dehydration of D-fructose and after the self-etherification of HMF, thus promoting the thermodynamics of the process. These reaction conditions allowed the isolation of OBMF for the first time directly from D-fructose in ca 30 % yield. The latter result is an encouraging starting point to further optimize this synthesis procedure that avoids time-consuming and waste-producing purification procedures following the indication of the green principles.