Conversion of Fructose Into 5-Hydroxymethylfurfural (HMF).Pdf

Carbohydrate Research 350 (2012) 20–24

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Carbohydrate Research

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Conversion of fructose into 5-hydroxymethylfurfural (HMF) and its derivatives promoted by inorganic salt in alcohol ⇑ ⇑ ⇑ Jitian Liu a,b, Yu Tang b,c, , Kaigui Wu a, Caifeng Bi a, , Qiu Cui b, a College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266101, China b Key Laboratory Of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China c Tianjin Key Laboratory for Modern Drug Delivery & High-Efﬁciency, School of Pharmaceutical Science and Technology, Tianjin University, Tianjin 300072, China article info abstract

Article history: The conversion of D-fructose to 5-hydroxymethylfurfural (HMF) on a 1 mmol scale was achieved in good Received 18 September 2011 yield (68%) using NH4Cl as catalyst in isopropanol at 120 °C. About 3% of 5-i-propoxymethylfurfural was Received in revised form 28 November 2011 formed. The reaction in ethanol at 100 °C on a 10 g scale gave a total yield of HMF and 5-ethoxymethyl- Accepted 6 December 2011 furfural of 42%. No mineral acid such as H SO and HCl are required. Available online 5 January 2012 2 4 Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Fructose HMF EMF Inorganic salt Alcohol

1. Introduction such as dimethylsulfoxide (DMSO), DMF, DMP, sulfolane.20,32–34 To overcome this disadvantage, the use of organic and inorganic Fossil fuels such as coal, petroleum, and natural gas provide salts in the synthesis of HMF in aqueous solution was the subject more than three quarters of the world’s energy today. In addition of numerous works.35–39 Recent reports illustrate that the use of to producing most of the transportation fuel, petroleum is also expensive ionic liquid (ILs) gave excellent yields in the conversion the feedstock used for the production of over 96% of the carbon- of saccharides into HMF.40–50 Along the same lines Dumesic and his containing chemicals used in our society.1 But in less than two dec- co-workers have developed a two-phase (aqueous/organic) system ades petroleum production is unlikely to meet the growing needs for the separation and stablization of the HMF product.10,51 Micro- of humanity and natural gas resources will be increasingly inacces- wave instead of oil-bath as the heating source was developed.52–54 sible.2–5 5-Hydroxymethylfurfural (HMF) (2) and its derivatives are In this work, we developed an efficient and environment- valuable biomass-derived intermediates for plastics, pharmaceuti- friendly process for the conversion of fructose into HMF and EMF cals, fine chemicals, and liquid fuel.6–8 Many important scientific (Scheme 1), in which ethanol was used as the solvent and salts studies have been reported recently on the synthesis and applica- as the promoter. In an optimized process, fructose was converted tions of these biomaterials.9–24 5-Ethoxymethylfurfural (EMF) (3a), into HMF and EMF in 46% isolated yield at 100 °C for a reaction a liquid with a boiling point of 235 °C, is already considered to be a time of 12 h. Levulinic acid ethyl ester (LAEE 6) was formed as promising alternative fuel or fuel additive.25–28 However, HMF and the only byproduct in less than 2% yield. EMF are not readily accessible, partly due to high production 29–31 costs. 2. Results and discussion The dehydration of fructose has long been an intriguing project both from a mechanistic point of view and as a source of HMF (2) Firstly, the influence of addition of different inorganic salts on and levulinic acid. Recent interest has grown quickly in developing the yield of EMF and HMF was surveyed, which is summarized in cheap, effective methods to produce HMF which are readily usable Table 1. The stronger Lewis acids showed higher activity in the for industrial scale-up. The newer methods described for HMF conversion of fructose to HMF and EMF at 100 °C. For example, production are also facing isolation problems from polar solvents HMF and EMF yields ranging from 23% to 46% were achieved of

FeCl3, CrCl3, SnCl4,NH4Cl. The reaction mixtures were very clean. ⇑ Corresponding authors. Tel.: +86 532 80662706; fax: +86 532 80662778. The weaker Lewis acids, for example, CuCl2, FeCl2 are not efﬁcient, E-mail addresses: [email protected] (Y. Tang), [email protected] (Q. Cui). and LiCl, NaCl did not work. NH4Cl was found to be the optimal

OEt O HO OH

HO OH OH O 4 Ethyl fructofuranoside HO OH H+ H+ OEt EtOH O HO OH OH 1 D-Fructose HO OH OH 5 Ethyl fructopyranoside O O O HO O ++EtO O EtO Figure 1. Conversion of D-fructose (1) into HMF (2), EMF (3a), and 3b in variety 3a EMF 6 LAEE O 2 HMF solvents.

Scheme 1. Conversion of D-fructose (1) into HMF (2) and EMF (3a).

obtained in 45% yield and 35% as the major products. H2Oisan inefficient solvent for dehydration of fructose to form HMF. inorganic salt and gave best overall yields of HMF and EMF. Control After choosing NH Cl as the most promising catalyst for the experiment showed that the salt plays a key role in the dehydra- 4 conversion of fructose to HMF and EMF, the reaction conditions tion of D-fructose. Some salts gave very low yields of HMF and were further optimized (Table 2). Other factors, such as concentra- EMF with high D-fructose conversion. The major reason is that in tion of the catalyst, temperature, and reaction time were taken into the first step of D-fructose dehydration, ethyl fructofuranoside 55,56 account. Entries 1–3 showed the effect on concentration of NH4Cl (4), and ethyl D-fructopyranoside (5) (a:b = 4:1) were formed on the yield. When the concentration of NH Cl was controlled at as the major products but could not be dehydrated further when 4 50 mol % (entry 2), the best overall yield was obtained. weak Lewis acids such as NaCl was used as the catalyst. For in- Higher temperature was beneficial for the formation of HMF stance, when the reaction was carried out at 100 °C using NaCl and EMF (entries 4 and 5), and the better yield and selectivity of (50 mol %) as the catalyst, no HMF or EMF was formed after 12 h. EMF was obtained after prolonging reaction time (entries 2, 7–9). But after NH Cl (50 mol %) was added, the reaction mixture was 4 The highest yield and selectivity of HMF was obtained in isopropa- stirred for another 12 h. 27% yield of HMF, and 4% yield of EMF nol which only gave trace isoproxymethylfurfural (3b) (entry 11). were obtained with 92% conversion of fructose. Effect of the anion We tested the scalability of our optimized conditions for HMF on the hydrolysis was investigated. Based on the low yield of HMF and EMF production by performing reactions on 10 g of fructose. and EMF in the presence of (NH ) SO and NH NO , the nitrate and 4 2 4 4 3 These conditions consistently provide HMF and EMF in total yield sulfate are most likely unfavorable to the reaction. The yields of of 42% (entry 13). Microwave irradiation in EtOH gave good yields HMF and EMF decreased by using bromide as the halide anion. of HMF and EMF compared with oil-bath heating, and shortened Furthermore, we tested the effect of solvent on the conversion the reaction time from 12 h to 10 min (entry 14). But lower yield of D-fructose (Fig. 1). With 50 mol % NH Cl at 100 °C for 12 h, the 4 of HMF was obtained when the reaction was carried out in isopro- reaction proceeded smoothly in most common solvents. Acetone, panol with mocrowave heating (entry 15). No humin was found in ethyl acetate, and Ethanol gave moderate to good yields of HMF the solution, as evidenced by the absence of insoluble material in and EMF. Isopropanol is the best solvent to form HMF as it gave the total yield of 61% (HMF (58%), 3b (3%)). MeOH gave very good conversion of fructose, but no desired product was obtained. Table 2 HMF and its derivatives converted from fructose in the ethanol catalyzed by NH Cla Methyl fructofuranoside and methyl D-fructopyranoside were 4 Entry T (°C) Time (h) Conversion (%) Ratio (2/3) Total yieldb (%) 1c 100 12 92 100/0 8 2 100 12 97 79/21 45 Table 1 3d 100 12 97 86/14 41 a Effect of salts on the conversion of D-fructose to HMF and EMF in ethanol 4 78 12 94 92/8 14 5 120 12 99 78/22 47 Catalyst Conversion (%) 4b (%) 5b (%) EMFb (%) HMFc (%) 6 100 24 99 66/34 57 — 1 000 0 7 100 6 93 94/6 16 LiCl 87 30 22 0 0 8 100 18 97 71/29 51

CuCl2Á2H2O 100 0 0 12 0 9 120 24 100 41/59 54 e NiCl2Á6H2O96265 19 10 100 24 100 94/6 61 f SnCl4Á5H2O 100 0 5 23 0 11 120 12 100 96/4 71 NaCl 83 32 27 0 0 12g 100 12 — 85/15 26 h FeCl2Á4H2O90 9 4 0 12 13 100 12 98 81/19 42 i FeCl3 100 0 0 28 0 14 120 10 min 99 86/14 65 f,i CrCl3Á6H2O 100 0 0 33 8 15 120 10 min 92 100/0 37 NH Cl 97 0 0 10 36 4 a Reaction were carried out with D-fructose 1 (1 mmol), NH4Cl (0.5 mmol), EtOH (NH4)2SO4 87 30 26 0 0 NH NO 91 24 29 0 1 (2 mL) in seal tube unless otherwise noted. 4 3 b 1 NH Br 96 10 4 7 16 Yield was calculated by HPLC, H NMR and veriﬁed by isolation. 4 c NaCl/NH Cld 92 — — 4 27 NH4Cl (0.1 mmol) was added. 4 d NH4Cl (1 mmol) was added. a e D-Fructose (1 mmol) was mixed with inorganic salts (0.5 mmol) at 100 °C for The reaction was run in air pressure. 12 h in ethanol (2 mL). f Reaction was run in isopropanol. b Yield based on NMR analysis. g Inulin as substrate. c h Yield based on NMR and HPLC analysis. Reaction were carried out with D-fructose 1 (55.6 mmol), NH4Cl (28 mmol), d The reaction was carried out at 100 °C using NaCl (50 mol %) as the catalyst for EtOH (60 mL). i 12 h. then NH4Cl (50 mol %) was added, the reaction mixture was stirred for another The reaction was carried out with D-fructose 1 (6 mmol), NH4Cl (3 mmol), 12 h. alcohol (12 mL) and microwave heating. 22 J. Liu et al. / Carbohydrate Research 350 (2012) 20–24

Table 3 one ethanol molecule. Under similar conditions, reaction of HMF Recycling of the catalyst system in the dehydration of D-fructose (2) was indeed converted into EMF (3a) as we postulated in Run Num. Conversion (%) HMF (%) 3ba (%) Scheme 2. 1 100 65 6 2 100 61 4 3. Experimental 399556 499524 3.1. Materials 590380

a 1 Yield calculated by HPLC, H NMR. Fructose (extra pure, average particle size) was a commercial product from Solarbio Company (Beijing, China); ethanol (AR, >99.7%), ethyl acetate (AR, >99.5%) were purchased from Fuyu the reaction vessel using ethanol as solvent. We also found that Chemical Company (Tianjin, China); methanol (AR, >99.5%), isopro- after reaction most of the NH4Cl was dissolved in ethanol while panol (AR, >99.7%), tert-Butanol (AR, >99.5%), acetone (AR, >99.5%) NH4Cl was almost insoluble in isopropanol. So recycling of the cat- were purchased from Jiangtian Chemical Company (Tianjin, alyst and solvent was possible. China); Deionized water was used for the preparation of aqueous The ability to recycle the catalyst is an important criterion for solutions. All other reagents and solvents were reagent grade and practical biomass transformations. The catalyst remains active were used without further purification. after carefully removing the solvent and product. Experiments were conducted at 120 °C for a reaction time of 12 h in isopropanol. 3.2. Dehydration of fructose by oil-bath heating After removal of the organic layer, isopropanol was added to wash the residue three times after each reaction cycle. An equal amount In a typical run, 0.18 g of fructose (1 mmol) and 27 mg of NH4Cl of fructose was added and used for next reaction cycle. As shown in (0.5 mmol) were loaded into a 25 mL glass tube (predried) Table 3, the yield of HMF and EMF gradually decreased from 71% to equipped with a magnetic stirring bar, then 2.0 mL ethanol was 56% after four cycles, which might be due to the catalyst loss in the added. The glass tube was sealed with a stopper and a screw cap recovering process. In the fifth cycle, there was a dramatic decrease and then heated at 100 °C in an oil-bath for a prescriptive time. of the yield, and we attributed this to humin formation, which pre- After reaction, the solution was transparent and there were no hu- cipitated on the surface of the catalyst that slows the further dehy- mins or insoluble solid visible. dration process down. It is worth noting that when NH4Cl was predissolved in isopropanol under standard reaction conditions 3.3. Typical procedure for carbohydrate dehydration by without fructose for 12 h and the reaction mixture was filtered, microwave heating and the filtrate was then subjected into the reaction with fructose under typical conditions resulted in 46% yield of HMF as well as 1% The synthesis was performed in the Anton Paar Synthos 3000, of isoproxymethylfurfural (3b). The success of this experiment has using Rotor XF100 (80 mL quartz vessels, 80 bar) with immersed demonstrated the high degree of homogenous catalysis using T-probe. The vessel, equipped with a stirring bar, was charged with

NH4Cl during this reaction as well as heterogenous fashion. 1.08 g fructose (6 mmol), 162 mg of NH4Cl (3 mmol), and 12 mL From the above experimental results, the dehydration of fruc- ethanol. Special openings in the rotor lid give access to the ade- tose to HMF catalyzed by salts is a very complex process. As shown quate bayonet adaptors on the vessel caps. This allows to prepare in Scheme 2, take Bronsted acid for example, intermediate 7 was and seal the vessel, place it in the rotor, close the rotor accordingly formed ﬁrst and then can be transformed into intermediate (8) and put it into the instrument. As a noteworthy safety measure, or ethyl fructoside. Intermediate (8) was treated with ethanol to there is no need to carry around pressurized reaction vessels. Final- form ethyl D-fructopyranoside (5). HMF can be obtained from ethyl ly, with a maximum of 600 W the mixtures were heated at 120 °C fructofuranoside (4) through removal of two water molecules and for a total time of 10 min.

H OH H OEt O O HO OH HO OH

HO OH HO OH 1 4 EtOH (-H+) LA OH OEt H O O O O O + OH HO OH (-H+) OH LA EtOH (-H ) HO OH HO OH HO OH HO OH 7 OH OH 8 5 (-H+)

H O OH O OR O (-2H O) O O HO OH 2 ROH (-H2O) HO OH 2 3a (R = Et) 3b (R = i-Pr)

Scheme 2. Putative mechanism for the dehydration of D-fructose. J. Liu et al. / Carbohydrate Research 350 (2012) 20–24 23

3.4. Fructose analysis Acknowledgments

The Fructose concentration after reaction was determined using This work was funded by grants KSCX2-YW-G-066 from The high performance ion chromatography (Dionex ICS3000) equipped Chinese Academy of Science, 30970050 from the National Natural with electrochemical detector and CarboPac PA-20 column (col- Science Foundation of China, 1102 from Fund Foundation of Tianjin umn temperature was set at 303 K and ﬂow rate at 0.5 mL/min). University. We thank Dr. Xiaobo Wan for prof-reading. Fructose retention time is 10.3 min. References

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