The acid-catalysed dehydration of the four 2-ketohexoses (fructose, sorbose, tagatose and psicose) to furanics was studied in methanol (65 g L(-1) substrate concentration, 17 and 34 mm sulfuric acid, 100 °C) with Avantium high-throughput technology. Significant differences in the reactivities of the hexoses and yields of 5-hydroxymethylfurfural (HMF) and its methyl ether (MMF) were observed. Psicose and tagatose were the most reactive, and psicose also afforded the highest combined yield of MMF and HMF of approximately 55 % at 96 % sugar conversion. Hydroxyacetylfuran and its corresponding methyl ether were formed as byproducts, particularly for sorbose and tagatose, with a maximum combined yield of 8 % for sorbose. The formation of hydroxyacetylfuran was studied through (13) C NMR spectroscopy with labelled sorbose, which provided new insights into the reaction mechanism.
Keywords: biomass; carbohydrates; isotopic labelling; oxygen heterocycles; reaction mechanisms.
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