[O:1]=[CH:2][C@@H:3]([C@H:5]([C@@H:7]([C@@H:9]([CH2:11][OH:12])[OH:10])[OH:8])[OH:6])[OH:4].[OH:13]CC([C@H:17]([C@@H:19]([C@@H:21]([CH2:23][OH:24])O)O)O)=O.[Cl-:25].C([N+]1C=CN(C)C=1)C.[Na+:34].[Br-].B([O-])([O-])[O-]>[Cr].Cl.CN(C)C=O.CC(N(C)C)=O.O>[O:1]=[CH:2][C@@H:3]([C@H:5]([C@@H:7]([C@@H:9]([CH2:11][OH:12])[OH:10])[OH:8])[OH:6])[OH:4].[ClH:25].[OH2:13].[Na+:34].[Cl-:25].[CH2:19]1[CH2:17][O:24][CH2:23][CH2:21]1Recent studies have been published on developing new processing strategies focused on isomerizing glucose to fructose with a subsequent acid-catalyzed dehydration of fructose to HMF. Lewis acid catalysts in ionic liquids have been shown to be the most promising systems for the conversion of glucose to HMF.1e Zhao, et al. first reported HMF yields of 68-70% in a system consisting of 1-ethyl-3-methyl-imidazolium chloride and a CrCl2 catalyst.1b It is believed that the high activity and selectivity observed for the production of HMF in ionic liquids with chromium catalysts are caused by the stabilization of the transition state for ring opening of glucose by the Lewis acidic Cr center during glucose isomerization.7 Other studies have been carried out on this same reaction using different ionic liquids or Lewis acid catalysts.8 However, the reactions require ionic liquids, which are expensive and subject to deactivation by small amounts of water formed during dehydration reactions.9 Binder, et al. reported that a mixture consisting of dimethylacetamide (DMA), NaBr, and a Lewis acid, CrCl2, could reach HMF yields of 81%, being as effective as ionic liquid systems.1c Huang, et al. reported an HMF yield of 63% from glucose by a two-step process consisting of the isomerization of glucose to fructose in the presence of glucose isomerase and borate ions, followed by the acid catalyzed dehydration of fructose to HMF using HCl as a catalyst in a biphasic system.10 Takagaki, et al. reported HMF yields of 42% at a 73% conversion by a similar two step process by combining a solid acid catalyst, Amberlyst-15, and a solid base catalyst, Mg—Al hydrotalcite, in N,N-dimethylformamide.11 Nikolla, et al. reported HMF yields of 57% at 79% conversion of glucose using a Lewis acidic Sn-Beta zeolite and HCl in a water/NaCl/THF biphasic reaction system.12
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