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Innovative processes for converting carbohydrates to materials and fuels form the basis for profitable bio-based economies of the future. For such innovation, approaches that provide detailed structural information would be desirable to detect uncharted chemistries of carbohydrate conversion. Among the most important value-added products accessible though conversion of biomass is 5-hydroxymethylfurfural (HMF), whose market values strongly depends on the quality of the product. Here, we use high-field in situ NMR spectroscopy to shed light on obscure competing reactions of CrCl3-catalyzed carbohydrate conversion to HMF in water. High-field NMR spectroscopy has enormous prowess in distinguishing isomeric and dehydrated products formed from glucose. Previously unidentified compounds were identified with this approach and include anhydrosugars and a variety of branched and linear mono- and disaccharides. Other identified compounds leverage the understanding of the active catalyst species. In addition to providing mechanistic insight, the approaches and findings described herein help to measure and manage carbon balances and product quality in HMF production. [ABSTRACT FROM AUTHOR]

In this work, ionic liquid (IL) modified H-Beta zeolites were prepared and the physicochemical properties of the catalysts were investigated. IL modified zeolites were applied in 5-hydroxymethylfurfural (HMF) etherification to tert-butoxymethylfurfural (tBMF) which is a potential (bio)diesel component. The best catalyst, IL-H-Beta-25, yielded at BMF selectivity of 76 % corresponding to a HMF conversion of 46 %. [ABSTRACT FROM AUTHOR]

A wide range of metal halides and triflates were examined for the conversion of d-glucose to HMF in DMSO. Chromium and aluminium salts were identified as the most promising catalysts. The effect of process variables like initial d-glucose concentration (0.1-1.5 M), reaction time (5-360 min) and reaction temperature (100-140 °C) on the yield of HMF were examined at a fixed Al(OTf) concentration (50 mM). Highest yields of HMF (60 mol%) were obtained using 1 M d-glucose (16 wt%), Al(OTf) (5 mol%) at a temperature of 140 °C. A reaction pathway involving initial isomerisation of d-glucose to d-fructose followed by a number of dehydration steps is proposed. Kinetic analysis reveals that the reaction is second order in d-glucose with an activation energy of 138 kJ mol. [ABSTRACT FROM AUTHOR]

The mechanisms and energetics for Brønsted acid-catalyzed glucose condensation, dehydration and isomerization reactions were discussed based on our earlier CPMD-MTD simulation results. Glucose condensation reaction is initiated by the protonation of C1-OH, whereas both dehydration and isomerization reactions are initiated by the protonation of C2-OH to form a common 5-member ring intermediate. Glucose dehydration to form HMF occurs via the direct cyclic mechanism, rather than via the open chain mechanism converting glucose to fructose then to HMF. Fructose is formed via a 1,2 hydride shift process following the formation of 5-member ring intermediate. The barriers for Brønsted acid-catalyzed glucose reactions are largely solvent induced due to the competition for proton from the solvent molecules. [ABSTRACT FROM AUTHOR]

The use of inorganic salts as catalysts for the reactions of d-glucose in aqueous solutions in a batch reactor is reported. The type of salt and effect of reaction time were examined in detail at a fixed salt (5 mM) and d-glucose concentration (0.1 M) and at a temperature of 140 °C. Al(III) and Cr(II) salts gave the highest conversion of d-glucose. Typical reaction products were organic acids like lactic acid, levulinic acid, furanics like hydroxymethylfurfural and insoluble products (humins). The chemo-selectivity is a clear function of the type of inorganic salt. For Al(III), the major water soluble product was lactic acid, for Zn(II) HMF was formed in the highest yields. A reaction scheme is proposed to explain the observed product compositions. [ABSTRACT FROM AUTHOR]

Furan derivatives, such as 5-hydroxymethylfurfural (HMF), obtained from acid-catalyzed dehydration of carbohydrates, can serve as renewable chemical platforms for the production of fuels and chemical intermediates. Addition of an inorganic salt to concentrated aqueous solutions of fructose (30 wt% fructose on salt free basis) in biphasic systems containing an organic extracting phase improves HMF yields by increasing the partitioning of HMF into the extracting phase, as measured by the partition coefficient, R, equal to the concentration of HMF in the organic phase normalized by the concentration in the aqueous phase. We have studied the impact of solvent choice on HMF yield using primary and secondary alcohols, ketones, and cyclic ethers in the C3–C6 range as extracting solvents in biphasic systems saturated with NaCl. Biphasic systems containing C4 solvents generated the highest HMF yields within each solvent class. Tetrahydrofuran demonstrated the best combination of high HMF selectivity (83%) and high extracting power ( R = 7.1) at 423 K. The presence of NaCl provided the additional benefit of creating biphasic systems using solvents that are completely miscible with water in the absence of salt. We have also studied the impact of different salts on HMF yield in systems using 1-butanol as the extracting solvent. Na+ and K+ showed the best combination of extracting power and HMF selectivity of the monovalent and divalent chloride salts tested. Changing the anion of the salt from Cl− to Br− resulted in R-values and HMF selectivity values resembling the non-salt system, while changing to the SO4 2− divalent species generated a high R-value (8.1), but a low HMF selectivity value (71%). [ABSTRACT FROM AUTHOR]