DOI: 10.1002/cssc.201300345 Dehydration of Different Ketoses and Aldoses to 5- Hydroxymethylfurfural Robert-Jan van Putten, [a, b] Jenny N. M. Soetedjo, [b] Evgeny A. Pidko, [c] Jan C. van der Waal, [a] Emiel J. M. Hensen, [c] Ed de Jong,* [a] and Hero J. Heeres* [b] Introduction The replacement of fossil feedstocks with sustainable resources for energy generation, transportation fuels, bulk and fine chemicals, and materials is currently considered as a pivotal challenge, receiving increasing social and scientific interest. To achieve this, alternative sources of organic carbon need to be found. Biomass is an attractive option as it is the most abundant non-fossil source of organic carbon. Biomass mainly comprises carbohydrates, lignin, fatty acids, lipids, and pro- teins. Carbohydrates represent the largest fraction of biomass, predominantly present in polymeric form (cellulose, hemi-cellu- lose, starch, inulin) and are built up from hexoses (glucose, fructose, mannose, galactose) and pentoses (arabinose, xylose). The acid-catalyzed dehydration of pentoses [1, 2] and hexoses [3] leads to the formation of furfural and 5-hydroxymethylfurfural (HMF), respectively, along with many by-products. Both mole- cules, and derivatives thereof, are in Bozell’s ‘Top 10 + 4’ list of bio-based chemicals and are considered to be key components in the development of a bio-based economy. [4] This has led to an enormous increase in research published on acid-catalyzed dehydration of sugars over the last decade. [2, 3] Both furfural and 5-hydroxymethylfurfural (HMF) can be used in different application areas. Furfural has high potential in fuel and solvent applications. HMF is considered a promising platform chemical due to its high derivatization potential. It can be converted to a wide range of interesting bulk and fine chemicals, for instance, as a monomer for new bio-based polymers. Avantium is currently developing a process for the production of polyethylenefurandicarboxylate (PEF) from C 6 sugars as a next-generation replacement material for polyethy- leneterephtalate (PET), having improved barrier properties. [5] Attention to the development of highly efficient routes to HMF has strongly increased in recent years. [3] Glucose or glu- cose-based oligomers and polymers, especially those derived from lignocellulosic sources, are favored feedstocks due to their availability and presence in agricultural side streams and other waste. [6] The vast majority of experimental studies, how- ever, show that fructose, a ketose, is much more efficiently de- hydrated to HMF than glucose, an aldose. Under aqueous acidic conditions, fructose yields a maximum of around 50 % HMF at best because of the formation of polymeric material, known as humins, and hydration of HMF to levulinic and formic acids (Scheme 1). [3, 7, 8] For glucose, the maximum HMF yield is only around 5 %. Higher HMF yields from fructose (> 80 %) have been reported in other solvent systems, especial- ly in ionic liquids and aprotic polar solvents such as DMSO. [3] Work on glucose dehydration with heterogeneous base/acid bi-catalytic systems, [9] chromium-catalyzed glucose dehydration in ionic liquids [10, 11] and organic solvents, [12] and other cata- lysts, [13] indicate that, apart from an acid, an additional catalyst 5-Hydroxymethylfurfural (HMF) is considered an important building block for future bio-based chemicals. Here, we pres- ent an experimental study using different ketoses (fructose, sorbose, tagatose) and aldoses (glucose, mannose, galactose) under aqueous acidic conditions (65 g L 1 substrate, 100– 160 8C, 33–300 mm H 2 SO 4 ) to gain insights into reaction path- ways for hexose dehydration to HMF. Both reaction rates and HMF selectivities were significantly higher for ketoses than for aldoses, which is in line with literature. Screening and kinetic experiments showed that the reactivity of the different ketoses is a function of the hydroxyl group orientation at the C3 and C4 positions. These results, in combination with DFT calcula- tions, point to a dehydration mechanism involving cyclic inter- mediates. For aldoses, no influence of the hydroxyl group ori- entation was observed, indicating a different rate-determining step. The combination of the knowledge from the literature and the findings in this work indicates that aldoses require an isomerization to ketose prior to dehydration to obtain high HMF yields. [a] R.-J. van Putten, Dr. J. C. van der Waal, Dr. E. de Jong Avantium Chemicals Zekeringstraat 29, 1014 BV Amsterdam (The Netherlands) E-mail : ed.dejong@avantium.com [b] R.-J. van Putten, J. N. M. Soetedjo, Prof. Dr. H. J. Heeres Department of Chemical Engineering University of Groningen Nijenborgh 4, 9747 AG Groningen (The Netherlands) E-mail : h.j.heeres@rug.nl [c] Dr. E. A. Pidko, Prof. Dr. E. J. M. Hensen Laboratory of Inorganic Materials Chemistry Schuit Institute of Catalysis Eindhoven University of Technology P.O. Box 513, 5600 MB Eindhoven (The Netherlands) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201300345.  2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemSusChem 2013, 6, 1681 – 1687 1681 CHEMSUSCHEM FULL PAPERS