Metal-free dehydration of glucose to 5-(hydroxymethyl)furfural in ionic liquids with boric acid as a promoter

The dehydration of glucose and other hexose carbohydrates to 5-(hydroxymethyl)furfural (HMF) was investigated in imidazolium-based ionic liquids with boric acid as a promoter. A yield of up to 42% from glucose and as much as 66% from sucrose was obtained. The yield of HMF decreased as the concentration of boric acid exceeded one equivalent, most likely as a consequence of stronger fructose-borate chelate complexes being formed. Computational modeling with DFT calculations confirmed that the formation of 1:1 glucose-borate complexes facilitated the conversion pathway from glucose to fructose. Deuterium-labeling studies elucidated that the isomerization proceeded via an ene-diol mechanism, which is different to that of the enzyme-catalyzed isomerization of glucose to fructose. The introduced non-metal system containing boric acid provides a new direction in the search for catalyst systems allowing efficient HMF formation from biorenewable sources.     

离子液体催化制备5-羟甲基糠醛的研究进展

本文综述了离子液体催化制备5-羟甲基糠醛的研究进展。运用离子液体作为反应溶剂和催化剂,与常规合成HMF的方法相比,其反应在常压、低温下进行,更易于操作控制;副反应数量明显减少,HMF的产率稳定,可达90%;离子液体催化活性稳定,可重复利用,减少了有机溶剂的使用量;利用离子液体作为媒介,能将反应原料从单一的果糖扩展到葡萄糖和纤维素等廉价原料,降低了生产成本。由此可见,运用离子液体催化制备HMF将是今后研究的重点和发展的必然趋势。     

磺酸多相催化剂用于二甲基亚砜中C6-单糖脱水制5-羟甲基糠醛（英）

Sulfonic acid-functionalized heterogeneous catalysts have been evaluated in the catalytic dehydration of C(,monosaccharides into 5-hydroxymethylfurfural(HMF) using dimethyl sulfoxide(DMSO)as solvent.Sulfonic commercial resin Amberlyst-70 was the most active catalyst,which was ascribed to its higher concentration of sulfonic acid sites as compared with the other catalysts,and it gave 93 mol%yield of HMF from fructose in 1 h.With glucose as the starting material,which is a much more difficult reaction,the reaction conditions(time,temperature,and catalyst loading) were optimized for Amberlyst-70 by a response surface methodology,which gave a maximum HMF yield of 33 mol%at 147 °C with 23 wt%catalyst loading based on glucose and 24 h reaction time.DMSO promotes the dehydration of glucose into anhydroglucose,which acts as a reservoir of the substrate to facilitate the production of HMF by reducing side reactions.Catalyst reuse without a regeneration treatment showed a gradual but not very significant decay in catalytic activity.     

果糖催化合成5-羟甲基糠醛研究的新进展

5-羟甲基糠醛(HMF)是一种具有重要应用价值的原材料和中间体,以果糖脱水合成HMF具有实现生物质转化利用的重大意义。本文综述了近三年来果糖制备HMF过程的两大关键因素:催化剂和反应介质的重要进展。固体酸(特别是杂多酸及其盐)、离子液体(ILs)中添加卤化物或ILs作为催化剂是近几年来研究的热点,固体酸的优点是可多次重复使用且易于分离,而ILs中果糖的降解条件较温和,副反应较少。目前,用于果糖转化HMF的反应溶剂优、缺点并存。最后对该反应存在的问题和今后的研究进行了总结和展望。     

果糖在酸性离子液体中脱水制备5-羟甲基糠醛

制备了多种离子液体,并将其作为催化剂和溶剂催化果糖脱水制备5-羟甲基糠醛（HMF）。 制备的酸性离子液体包括磺酸基功能化酸性离子液体、咪唑类酸性离子液体和吡啶类酸性离子液体。 利用核磁共振仪和红外光谱仪对离子液体的结构进行表征。 利用紫外可见光分光光度计结合Hammett指示剂计算Hammett酸度函数,比较了酸强度的大小对反应的影响。 结果表明,离子液体的酸强度对反应有较大影响,在无其它催化剂和溶剂的情况下,离子液体具有较高的催化活性,通过使用1-丁基-3-甲基咪唑氯盐(BmimCl)作为催化剂,当反应温度为120 ℃,反应进行到4 h时,HMF收率可以达到74.97%。     

Preparation of 5-Hydroxymethylfurfural from Cellulose via Fast Depolymerization and Consecutively Catalytic Conversion

The conversion of cellulose to 5-hydroxymethylfurfural (HMF) has been investigated by a one-pot consecutive reaction. At first, cellulose was depolymerised into glucose via a fast degradation of cellulose in molten ZnCl2 in the presence of hydrochloric acid, and the yield of glucose is 75% in 120 s at reaction temperature of 95 oC. Then, DMSO was used as solvent and different kinds of metal chloride were added as catalysts, and the conversion was carried out continuously at 110-130 oC for 0.5-4 h. The yield of HMF was 53% when CrCl3 were used as catalyst. The one-pot two steps conversion was carried out at atmosphere pressure, and it is a simple route to prepare HMF from lignocellulosic feedstock on a large scale.     

离子液体中磺化无定形炭催化菊糖制备5-羟甲基糠醛

研究了以1-丁基-3-甲基咪唑氯盐([Bmim]Cl)离子液体作溶剂,磺化无定形炭为催化剂催化菊糖脱水制5-羟甲基糠醛(HMF)的反应.考察了溶剂、水量、反应温度、反应时间和催化剂用量对HMF收率的影响.实验结果表明,反应温度为100°C,反应时间60min,R=5(R为水的物质的量与菊糖中所含果糖单位的物质的量的比值),m(催化剂):m(菊糖)=1:3时,HMF的收率可达50%.     

离子液体中微波辅助的 Lewis 酸催化纤维素制备 5-羟甲基糠醛

 以离子液体 1-丁基-3-甲基咪唑氯为溶剂, 以 CrCl3•6H2O 为催化剂, 直接转化纤维素生成 5-羟甲基糠醛 (HMF). 考察了微波辐射条件、反应温度、反应时间及催化剂用量对 HMF 产率的影响. 结果表明, 在最佳条件下, HMF 产率可达 55%.     

Conversion of Glucose to Valuable Platform Chemicals over Graphene Solid Acid Catalyst

Biomass-derived hexose sugars, the most abundant renewable resources in the world, have potential to be the sustainable resources for production of platform chemicals. Here, conversion of glucose is investigated by using sulfonated graphene (rGO-SO₃H) as solid acid catalyst in water without any organic solvent. At first, graphene functionalized with sulfonic acid groups is prepared by using NaH and propane sultone, and then it is characterized by means of XPS, FT-IR, and TEM to confirm the existence of the sulfonic acid groups. The catalytic activity of rGO-SO₃H in the conversion of glucose to valuable chemicals is studied under different reaction conditions. The maximum yield of 5-hydroxymethylfurfural (HMF) is 28.8%, and the total yield of formic acid, lactic acid and HMF is 51.94% when the reaction is conducted at the optimized reaction condition. In addition, the rGO-SO₃H gives a relatively high total yield of the three kinds of products after five run experiments, indicating that the catalyst shows good thermal stability.     

An unexpected reaction between 5-hydroxymethylfurfural and imidazolium-based ionic liquids at high temperatures

A new compound was detected during the production of 5-hydroxymethylfurfural (HMF) from glucose and cellulose in the ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) at high temperatures. Further experiments found that it was derived from the reaction of HMF with [Bmim]Cl. The structure of new compound was established as 1-butyl-2-(5'-methyl-2'-furoyl)imidazole (BMI) based on nuclear magnetic resonance and mass spectrometry analysis, and a possible mechanism for its formation was proposed. Reactions of HMF with other imidazolium-based ionic liquids were performed to check the formation of BMI. Our results provided new insights in terms of side reactions between HMF and imidazolium-based ionic liquids, which should be valuable for designing better processes for the production of furans using biomass and related materials.     

硅胶固定功能化离子液体的制备及其在5-羟甲基糠醛合成中的应用

通过γ-氯丙基三甲氧基硅烷将磺基功能化离子液体-N-磺丙基咪唑盐化学键合到微球硅胶上,制得微球硅胶固定化离子液体(IL3). 用FTIR、TG、~(13)C NMR、SEM、BET及酸度测定等测试技术对IL3进行了表征,并考察其在果糖脱水合成5-羟甲基糠醛(HMF)过程中的催化性能. 研究结果表明,氯丙基三甲氧基硅烷可以将磺基功能化咪唑型离子液体化学键合到微球硅胶上. 微球硅胶固定化磺基咪唑离子液体能有效催化果糖脱水生成HMF. 果糖在固载率45.4%的IL3催化下、乙二醇甲醚(EGME)溶剂中、115 ℃反应5 h,HMF收率可达82.1%. 催化剂循环使用4次后,HMF的收率下降为53.0%.     

MCM‐41 Immobilized Acidic Functional Ionic Liquid and Chromium(III) Complexes Catalyzed Conversion of Hexose into 5‐Hydroxymethylfurfural

The development of novel methods to obtain biofuels and chemicals from biomass has been an immediate issue in both academic and industrial communities. In this work, a series of novel catalysts were prepared and characterized by FT‐IR , TGA , XRD , SEM , TEM , ICP‐AES , NH₃‐TPD and BET , which were applied for the conversion of hexose to 5‐hydroxymethylfurfural (HMF ). The Cr(Salten)‐MCM ‐41‐[(CH₂ )₃SO₃HVIm ]HSO₄ catalyst was the most active catalyst, and a glucose conversion of 99.8% with 50.2% HMF yield was obtained at 140 °C for 4 h in dimethyl sulfoxide (DMSO ). The effects of reaction temperature, reaction time, solvents and catalyst dosages were investigated in detail. MCM ‐41 immobilized acidic functional ionic liquid and chromium(III ) Schiff base complexes as heterogeneous catalysts can be easily recovered by simple filter treatment, exhibiting excellent stability and activity towards hexose conversion. Thus the heterogeneous catalysts were environment‐friendly for transforming biomass carbohydrates into fine chemicals.     

双相体系中凹土负载型固体酸 SO42-/In2O3-ATP催化己糖降解5-羟甲基糠醛

凹土(ATP)有“千用之土、万土之王”之美誉,我国江苏省盱眙凹土矿资源量占世界储量的49%和我国储量的74%. ATP是一种天然链层状结构的含水镁铝硅酸盐黏土矿物,其分子式为(Mg,Al)4(Si)8(O,OH,H2O)26·nH2O. ATP具有一定酸性,层结构中的结构羟基可形成 Br?nsted酸位点,暴露的 Al3+离子可形成 Lewis酸位点. ATP经酸化或离子交换后作为催化剂直接应用较少.由于 ATP具有较大的比表面积和较好的热稳定性,是良好的催化剂载体,因此多将 ATP作为载体负载催化活性组分制备负载型催化剂. 5-羟甲基糠醛(HMF)是由生物质得到的十二种平台化合物之一,是非常重要的中间体,可用于生产呋喃类衍生物,制备精细化学品、液体燃料和多种聚合物,还可生产5-羟基-4-酮-2-戊烯酸和乙酰丙酸.γ-戊内酯(GVL)是一种乙酰丙酸的加氢产物,可以代替乙醇作为汽油添加剂,也可用来生产丁烯同分异构体等化学品.本文以天然 ATP为载体,通过浸渍-焙烧法设计和制备了兼具 Br?nsted酸和 Lewis酸的新型固体酸催化剂 SO42?/In2O3-ATP.该催化剂可催化己糖直接转化为 HMF. ATP固有的微观结构和高比表面积使反应选择性提高.同时,结合固体酸活性位表征技术探索了己糖转化历程和 HMF生成机制.结果表明, In(III)的引入使 ATP催化性能更加优越.固体酸的 Lewis酸位和 Br?nsted酸位能分别有效催化葡萄糖异构和果糖脱水.优化的最佳反应条件为： GVL：H2O双相体系比例9：1,反应温度180oC,反应时间60 min.底物为葡萄糖时, HMF最高收率为40%. SO42?/In2O3-ATP固体酸比纯 ATP酸性更强,可重复使用4次,且不腐蚀设备,后处理简单,绿色环保.     

Cellulose sulfuric acid as a bio-supported and recyclable solid acid catalyst for the synthesis of 5-hydroxymethylfurfural and 5-ethoxymethylfurfural from fructose

In this study, we have developed a new and green method for the synthesis of 5-hydroxymethylfurfural (HMF) and 5-ethoxymethylfurfural (EMF) from fructose using cellulose sulfuric acid as catalyst. Firstly, HMF was synthesized from fructose, and a high yield of 93.6 % was obtained in DMSO for 45 min in the presence of cellulose sulfuric acid. Cellulose sulfuric acid also showed high catalytic activity for the synthesis of EMF. EMF was obtained in a high yield of 84.4 % by the etherification of HMF under the optimal reaction conditions. More importantly, a high EMF yield of 72.5 % was also obtained from fructose through one-pot reaction strategy, which integrated the dehydration of fructose into HMF and the followed etherification of HMF into EMF. The reaction work-up was very simple and the catalyst could be reused several times without the loss of its catalytic activity.     

硅胶固定功能化离子液体的制备及其在HMF合成中的应用

通过氯丙基三甲氧基硅烷将磺基功能化离子液体--N-磺丙基咪唑盐化学键联到微球硅胶上,制得微球硅胶固定化离子液体（IL3）。用FTIR、TG、13C-NMR、SEM、BET及酸度测定等方法对IL3进行了表征,并考察其在果糖脱水合成5-羟甲基糠醛（HMF）过程中的催化性能。研究结果表明：氯丙基三甲氧基硅烷可以将磺基功能化咪唑型离子液体化学键联到微球硅胶上。微球硅胶固定化磺基咪唑离子液体能有效催化果糖脱水生成HMF。在45.4-IL3催化下、乙二醇甲醚(EGME)溶剂中、115℃反应5小时, HMF收率可达82.1％。使用后的催化剂可以方便地循环使用。但随次数增加,HMF收率明显下降。45.4-IL3催化剂循环使用四次后,HMF的收率下降为53.0%。     

Effect of Brønsted/Lewis Acid Ratio on Conversion of Sugars to 5‐Hydroxymethylfurfural over Mesoporous Nb and Nb‐W Oxides

A series of mesoporous Nb and Nb‐W oxides were employed as highly active solid acid catalysts for the conversion of glucose to 5‐hydroxymethylfurfural (HMF ). The results of solid state ³¹P MAS NMR spectroscopy with adsorbed trimethylphosphine as probe molecule show that the addition of W in niobium oxide increases the number of Brønsted acid sites and decreases the number of Lewis acid sites. The catalytic performance for Nb‐W oxides varied with the ratio of Brønsted to Lewis acid sites and high glucose conversion was observed over Nb₅W₅ and Nb₇W₃ oxides with high ratios of Brønsted to Lewis acid sites. All Nb‐W oxides show a relatively high selectivity of HMF , whereas no HMF forms over sulfuric acid due to its pure Brønsted acidity. The results indicate fast isomerization of glucose to fructose over Lewis acid sites followed by dehydration of fructose to HMF over Brønsted acid sites. Moreover, comparing to the reaction occurred in aqueous media, the 2‐butanol/H₂O system enhances the HMF selectivity and stabilizes the activity of the catalysts which gives the highest HMF selectivity of 52% over Nb₇W₃ oxide. The 2‐butanol/H₂O catalytic system can also be employed in conversion of sucrose, achieving HMF selectivity of 46% over Nb₅W₅ oxide.     

Aluminum alkoxy-catalyzed biomass conversion of glucose to 5-hydroxymethylfurfural: Mechanistic study of the cooperative bifunctional catalysis

Density functional theory calculations were performed to understand the detailed reaction mechanism of aluminum alkoxy-catalyzed conversion of glucose to 5-hydroxymethylfurfural (HMF) using Al(OMe)₃ as catalyst. Potential energy surfaces were studied for aggregates formed between the organic compounds and Al(OMe)₃ and effects of the medium were considered via continuum solvent models. The reaction takes place via two stages: isomerization from glucose to fructose (stage I) and transformation of fructose to HMF (stage II). Stage II includes three successive dehydrations, which begins with a 1,2-elimination to form an enolate (i.e., B), continues with the formation of the acrolein moiety (i.e., D), and ends with the formation of the furan ring (i.e., HMF). All of these steps are facilitated by aluminum alkoxy catalysis. The highest barriers for stage I and stage II are 23.9 and 31.2 kcal/mol, respectively, and the overall catalytic reaction is highly exothermic. The energetic and geometric results indicate that the catalyzed reaction path has feasible kinetics and thermodynamics and is consistent with the experimental process under high temperature (i.e., 120 °C). Remarkably, the released water molecules in stage II act as the product, reactant, proton shuttle, as well as stabilizer in the conversion of fructose to HMF. The metal–ligand functionality of the Al(OMe)₃ catalyst, which combines cooperative Lewis acid and Lewis base properties and thereby enables proton shuttling, plays a crucial role in the overall catalysis and is responsible for the high reactivity. © 2019 Wiley Periodicals, Inc.     

Rapid conversion of cellulose to 5-hydroxymethylfurfural using single and combined metal chloride catalysts in ionic liquid

Direct conversion of cellulose into 5-hydroxymethylfurfural(HMF) was performed by using single or combined metal chloride catalysts in 1-ethyl-3-methylimidazolium chloride(Cl) ionic liquid.Our study demonstrated formation of 2-furyl hydroxymethyl ketone(FHMK),and furfural(FF) simultaneously with the formation of HMF.Various reaction parameters were addressed to optimize yields of furan derivatives produced from cellulose by varying reaction temperature,time,and the type of metal chloride catalyst.Catalytic reaction by using FeCl3 resulted in 59.9% total yield of furan derivatives(HMF,FHMK,and FF) from cellulose.CrCl3 was the most effective catalyst for selective conversion of cellulose into HMF(35.6%) with less concentrations of FHMK,and FF.Improving the yields of furans produced from cellulose could be achieved via reactions catalyzed by different combinations of two metal chlorides.Further optimization was carried out to produce total furans yield 75.9% by using FeCl3/CuCl2 combination.CrCl3/CuCl2 was the most selective combination to convert cellulose into HMF(39.9%) with total yield(63.8%) of furans produced from the reaction.The temperature and time of the catalytic reaction played an important role in cellulose conversion,and the yields of products.Increasing the reaction temperature could enhance the cellulose conversion and HMF yield for short reaction time intervals(5~20 min).     

Production of 5‐Hydroxymethylfurfural from Fructose in Ionic Liquid Efficiently Catalyzed by Cr(III)‐Al2O3 Catalyst

A series of metal‐Al₂O₃ catalysts were prepared simply by the conventional impregnation with Al₂O₃ and metal chlorides, which were applied to the dehydration of fructose to 5‐hydroxymethylfurfural (HMF). An agreeable HMF yield of 93.1% was achieved from fructose at mild conditions (100°C and 40 min) when employing Cr(III)‐Al₂O₃ as catalyst in 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl). The Cr(III)‐Al₂O₃ catalyst was characterized via XRD, DRS and Raman spectra and the results clarified the interaction between the Cr(III) and the alumina support. Meanwhile, the reaction solvents ([Bmim]Cl) collected after 1^st reaction run and 5^th reaction run were analyzed by ICP‐OES and LC‐ITMS and the results confirmed that no Cr(III) ion was dropped off from the alumina support during the fructose dehydration. Notably, Cr(III)‐Al₂O₃ catalyst had an excellent catalytic performance for glucose and sucrose and the HMF yields were reached to 73.7% and 84.1% at 120°C for 60 min, respectively. Furthermore, the system of Cr(III)‐Al₂O₃ and [Bmim]Cl exhibited a constant stability and activity at 100°C for 40 min and a favorable HMF yield was maintained after ten recycles.     

Furfural and 5-Hydroxymethylfurfural Production from Sugar Mixture Using Deep Eutectic Solvent/MIBK System

Choline chloride (ChCl) / glycolic acid (GA) deep eutectic solvent (DES) media with high water content but without any additional catalyst are introduced in furfural and 5-hydroxymethylfurfural (HMF) production. The effects of water content, reaction time, and reaction temperature are investigated with two feedstocks: a glucose/xylose mixture and birch sawdust. Based on the results, 10 equivalent quantities of water (32.9 wt.%) were revealed to be beneficial for conversions without rupturing the DES structure. The optimal reaction conditions were 160 °C and 10 minutes for the sugar mixture and 170 °C and 10 minutes for birch sawdust in a microwave reactor. High furfural yields were achieved, namely 62 % from the sugar mixture and 37.5 % from birch sawdust. HMF yields were low, but since the characterization of the solid residue of sawdust, after DES treatment, was revealed to contain only cellulose (49 %) and lignin (52 %), the treatment could be potentially utilized in a biorefinery concept where the main products are obtained from the cellulose fraction. Extraction of products into the organic phase (methyl isobutyl ketone, MIBK) during the reaction enabled the recycling of the DES phase, and yields remained high for three runs of recycling.