Abstract
2,5-Diformylfuran (DFF) is an important biorenewable building block, namely for the manufacture of new polymers that may replace existing materials derived from limited fossil fuel resources. The current reported methods for the preparation of DFF are mainly derived from the oxidation of 5-hydroxymethylfurfural (HMF) and, to a lesser extent, directly from fructose. 5-Chloromethylfurfural (CMF) has been considered an alternative to HMF as an intermediate building block due to its advantages regarding stability, polarity, and availability from glucose and cellulose. The only reported method for the transformation of CMF to DFF is restricted to the use of DMSO as the solvent and oxidant. We envisioned that the transformation could be performed using more attractive conditions. To that end, we explored the oxidation of CMF to DFF by screening several oxidants such as H2O2, oxone, and pyridine N-oxide (PNO); different heating methods, namely thermal and microwave irradiation (MWI); and also flow conditions. The combination of PNO (4 equiv.) and Cu(OTf)2 (0.5 equiv.) in acetonitrile was identified as the best system, which lead to the formation of DFF in 54% yield under MWI for 5 min at 160 °C. Consequently, a range of different heterogeneous copper catalysts were tested, which allowed for catalyst reuse. Similar results were also observed under flow conditions using copper immobilized on silica under thermal heating at 160 °C for a residence time of 2.7 min. Finally, HMF and 5,5′-oxybis(5-methylene-2-furaldehyde) (OBMF) were the only byproducts identified under the reaction conditions studied.
Highlights
The pursuit of new biorenewable building blocks and/or more efficient synthetic routes has intensified during the last few years
The discovery of new polymer monomers that may replace the current well established portfolio derived from fossil fuel resources has been recognized as an important issue. 2,5-Furandicarboxylic acid (FDCA), 2,5-dihydroxymethylfuran (DHMF) and 2,5-diformylfuran (DFF), among others, have been identified as promising monomers [5,6]
microwave irradiation (MWI); yields were determined by analysis the crude reaction mixture min under yields determined by H-Nuclear magnetic resonance (NMR)
Summary
The pursuit of new biorenewable building blocks and/or more efficient synthetic routes has intensified during the last few years. 2,5-Furandicarboxylic acid (FDCA), 2,5-dihydroxymethylfuran (DHMF) and 2,5-diformylfuran (DFF), among others, have been identified as promising monomers [5,6]. These furan derivatives are commonly obtained from HMF, which, Molecules 2017, 22, 329; doi:10.3390/molecules22020329 www.mdpi.com/journal/molecules. Bras and later used by the Mascal preparation of DFF was previously described in 2014 by Estrine and Le Bras and later used by the group. We envisioned the possibility of performing such an oxidation without attractive (Scheme 1) [38,46].
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