Ionic liquids (ILs) as additives were used in the selective conversion of bio-based carbohydrates to 5-hydroxymethylfurfural (HMF) in this work. The effect of adding various imidazole-based ionic liquids with different anion structures on the production of HMF from fructose was firstly investigated in aqueous media. The presence of 15 wt% 1-butyl-3-methylimidazole chloride ([Bmim]Cl) ionic liquids in water with Fe₂(SO₄)₃ as the homogeneous catalyst provided a more effective HMF synthesis compared to that without [Bmim]Cl addition. The enhanced HMF yield was mainly attributed to the fact that [Bmim]Cl might play a vital role in stabilizing the HMF molecule, which could thereby suppress side reactions involving HMF (e.g., its rehydration to levulinic acid or/and polymerization to humins). NMR and FTIR analyses suggested that such a stabilization effect stemmed from the interaction of [Bmim]Cl with the hydroxyl and aldehyde groups of HMF through hydrogen bonding. By performing the operation in a biphasic system (i.e., with the biomass-derived THF solvent as the organic phase and the addition of NaCl salt into water for improving HMF partition), the HMF yield over the Fe₂(SO₄)₃ catalyst in the presence of the [Bmim]Cl additive could be further improved. The catalyst and ionic liquids were quite stable, and could be reused for more than five cycles with a consistent activity. A similar enhancement effect of [Bmim]Cl was also demonstrated in HMF synthesis with better yields from other biomass feedstocks or derivatives (including glucose, sucrose, cellobiose, inulin and starch) in aqueous media.

中文翻译：

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硫酸铁催化水/ [Bmim] Cl的混合物中糖脱水为5-羟甲基糠醛

在这项工作中，使用离子液体（ILs）作为添加剂将生物基碳水化合物选择性转化为5-羟甲基糠醛（HMF）。首先在水性介质中研究了添加各种具有不同阴离子结构的咪唑基离子液体对由果糖生产HMF的影响。以Fe ₂（SO ₄）₃为均相催化剂的水中15 wt％的1-丁基-3-甲基咪唑氯化物（[Bmim] Cl）离子液体的存在与没有[Bmim] Cl的情况相比，提供了更有效的HMF合成加成。HMF产量提高的主要原因是[Bmim] Cl可能在稳定HMF分子方面起着至关重要的作用，从而可以抑制涉及HMF的副反应（例如，将其复水为乙酰丙酸或/和聚合为腐殖质）。NMR和FTIR分析表明，这种稳定作用源于[Bmim] Cl通过氢键与HMF的羟基和醛基的相互作用。通过在双相系统中进行操作（即以生物质衍生的THF溶剂为有机相，并向水中添加NaCl盐以改善HMF分配），HMF的收率超过了Fe ₂（SO ₄）₃在[Bmim] Cl添加剂存在下，催化剂可以得到进一步改善。催化剂和离子液体非常稳定，可以重复使用超过五个周期，且活性一致。在HMF合成中还证明了[Bmim] Cl的类似增强作用，在水性介质中，其他生物质原料或衍生物（包括葡萄糖，蔗糖，纤维二糖，菊粉和淀粉）的收率更高。