The oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) using oxygen (1 atm) with a TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl) and CuCl catalyst system is investigated using a range of imidazolium-based ionic liquids (ILs) and various bases at different HMF substrate loadings (10–50%). This represents the first example of HMF to DFF conversion in ionic liquid media under homogeneous catalysis conditions, revealing dramatic differences in performance between the ILs. In the noncoordinating, hydrophobic ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][NTf₂]), 90% DFF yield is obtained at 5 mol % catalyst loading after 6 h at 80 °C at a very high 40% HMF loading. Increasing the temperature to 100 °C leads to a lower yield, attributed to the loss of volatile TEMPO from the reaction medium. A system using TEMPO and pyridine immobilized within the ionic liquid [bmim][NTf₂] results in selective conversion of HMF to high purity DFF. It also allows the DFF formed to be isolated by sublimation in 81% yield before a further cycle is performed. Subsequent catalyst deactivation is probed by X-ray photoelectron spectroscopy (XPS). Synthesis from fructose in a two-step process achieves a 55% isolated DFF yield. This approach overcomes significant drawbacks previously reported for this transformation, such as solvent toxicity, separation and purification problems, and the need for high oxygen pressures. Further oxidation of HMF with this system leads to a 62% yield of 5-formyl-2-furancarboxylic acid (FFCA). The separation of this compound can be achieved by sublimation of DFF followed by solvent extraction.

中文翻译：

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在高底物负载和低氧气压力下通过升华分离在离子液体中高效形成2,5-二甲酰呋喃

使用氧气（1 atm）和TEMPO（（2,2,6,6-四甲基哌啶-1-基）氧基）和CuCl催化剂体系将5-羟甲基糠醛（HMF）氧化为2,5-二甲酰呋喃（DFF）为使用一系列基于咪唑鎓的离子液体（IL）和各种碱在不同的HMF底物负载量（10–50％）上进行了研究。这代表了在均相催化条件下离子液体介质中HMF转化为DFF的第一个例子，揭示了IL之间性能的巨大差异。在非配位疏水离子液体中，1-丁基-3-甲基咪唑鎓双（三氟甲基磺酰基）酰亚胺（[bmim] [NTf ₂]），在80℃下以非常高的40％HMF负载量在6 h后以5 mol％的催化剂负载量获得90％的DFF收率。将温度升高至100°C会导致产率降低，这归因于反应介质中挥发性TEMPO的损失。使用TEMPO和吡啶固定在离子液体[bmim] [NTf ₂ ]中的系统]导致HMF选择性转化为高纯度DFF。它还允许在进行进一步的循环之前通过升华以81％的产率分离形成的DFF。随后的催化剂失活通过X射线光电子能谱（XPS）进行探测。由果糖分两步合成可以达到55％的分离DFF收率。该方法克服了先前报道的该转化的显着缺点，例如溶剂毒性，分离和纯化问题以及对高氧压的需求。用该系统进一步氧化HMF可以使62％的5-甲酰基-2-呋喃甲酸（FFCA）收率。该化合物的分离可通过升华DFF，然后进行溶剂萃取来实现。