Carbohydrate Research 350 (2012) 20–24

Contents lists available at SciVerse ScienceDirect

Carbohydrate Research

journal homepage: www.elsevier .com/locate /carres

Conversion of fructose into 5-hydroxymethylfurfural (HMF) and itsderivatives 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, Chinab Key Laboratory Of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, Chinac Tianjin Key Laboratory for Modern Drug Delivery & High-Efficiency, School of Pharmaceutical Science and Technology, Tianjin University, Tianjin 300072, China

a r t i c l e i n f o

Article history:Received 18 September 2011Received in revised form 28 November 2011Accepted 6 December 2011Available online 5 January 2012

Keywords:FructoseHMFEMFInorganic saltAlcohol

0008-6215/$ - see front matter � 2012 Elsevier Ltd. Adoi:10.1016/j.carres.2011.12.006

⇑ Corresponding authors. Tel.: +86 532 80662706;E-mail addresses: tangyu114@gmail.com (Y. Tang)

a b s t r a c t

The conversion of D-fructose to 5-hydroxymethylfurfural (HMF) on a 1 mmol scale was achieved in goodyield (68%) using NH4Cl as catalyst in isopropanol at 120 �C. About 3% of 5-i-propoxymethylfurfural wasformed. The reaction in ethanol at 100 �C on a 10 g scale gave a total yield of HMF and 5-ethoxymethyl-furfural of 42%. No mineral acid such as H2SO4 and HCl are required.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Fossil fuels such as coal, petroleum, and natural gas providemore than three quarters of the world’s energy today. In additionto producing most of the transportation fuel, petroleum is alsothe feedstock used for the production of over 96% of the carbon-containing chemicals used in our society.1 But in less than two dec-ades petroleum production is unlikely to meet the growing needsof humanity and natural gas resources will be increasingly inacces-sible.2–5 5-Hydroxymethylfurfural (HMF) (2) and its derivatives arevaluable biomass-derived intermediates for plastics, pharmaceuti-cals, fine chemicals, and liquid fuel.6–8 Many important scientificstudies have been reported recently on the synthesis and applica-tions of these biomaterials.9–24 5-Ethoxymethylfurfural (EMF) (3a),a liquid with a boiling point of 235 �C, is already considered to be apromising alternative fuel or fuel additive.25–28 However, HMF andEMF are not readily accessible, partly due to high productioncosts.29–31

The dehydration of fructose has long been an intriguing projectboth from a mechanistic point of view and as a source of HMF (2)and levulinic acid. Recent interest has grown quickly in developingcheap, effective methods to produce HMF which are readily usablefor industrial scale-up. The newer methods described for HMFproduction are also facing isolation problems from polar solvents

ll rights reserved.

fax: +86 532 80662778., cuiqiu@qibebt.ac.cn (Q. Cui).

such as dimethylsulfoxide (DMSO), DMF, DMP, sulfolane.20,32–34

To overcome this disadvantage, the use of organic and inorganicsalts in the synthesis of HMF in aqueous solution was the subjectof numerous works.35–39 Recent reports illustrate that the use ofexpensive ionic liquid (ILs) gave excellent yields in the conversionof saccharides into HMF.40–50 Along the same lines Dumesic and hisco-workers have developed a two-phase (aqueous/organic) systemfor the separation and stablization of the HMF product.10,51 Micro-wave instead of oil-bath as the heating source was developed.52–54

In this work, we developed an efficient and environment-friendly process for the conversion of fructose into HMF and EMF(Scheme 1), in which ethanol was used as the solvent and saltsas the promoter. In an optimized process, fructose was convertedinto HMF and EMF in 46% isolated yield at 100 �C for a reactiontime of 12 h. Levulinic acid ethyl ester (LAEE 6) was formed asthe only byproduct in less than 2% yield.

2. Results and discussion

Firstly, the influence of addition of different inorganic salts onthe yield of EMF and HMF was surveyed, which is summarized inTable 1. The stronger Lewis acids showed higher activity in theconversion of fructose to HMF and EMF at 100 �C. For example,HMF and EMF yields ranging from 23% to 46% were achieved ofFeCl3, CrCl3, SnCl4, NH4Cl. The reaction mixtures were very clean.The weaker Lewis acids, for example, CuCl2, FeCl2 are not efficient,and LiCl, NaCl did not work. NH4Cl was found to be the optimal

Figure 1. Conversion of D-fructose (1) into HMF (2), EMF (3a), and 3b in varietysolvents.

Table 2HMF and its derivatives converted from fructose in the ethanol catalyzed by NH4Cla

1 D-Fructose

OHO O

OEtO O EtO

O

O2 HMF 3a EMF 6 LAEE

O

OHHO

H+

EtOH

4 Ethyl fructofuranosideH+

+ +

O

OHHO

OEtOH

OH

HO OH

O

OHHO

OHHO OH

OEt

5 Ethyl fructopyranoside

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

J. Liu et al. / Carbohydrate Research 350 (2012) 20–24 21

inorganic salt and gave best overall yields of HMF and EMF. Controlexperiment showed that the salt plays a key role in the dehydra-tion of D-fructose. Some salts gave very low yields of HMF andEMF with high D-fructose conversion. The major reason is that inthe first step of D-fructose dehydration, ethyl fructofuranoside(4), and ethyl D-fructopyranoside (5)55,56 (a:b = 4:1) were formedas the major products but could not be dehydrated further whenweak Lewis acids such as NaCl was used as the catalyst. For in-stance, when the reaction was carried out at 100 �C using NaCl(50 mol %) as the catalyst, no HMF or EMF was formed after 12 h.But after NH4Cl (50 mol %) was added, the reaction mixture wasstirred for another 12 h. 27% yield of HMF, and 4% yield of EMFwere obtained with 92% conversion of fructose. Effect of the anionon the hydrolysis was investigated. Based on the low yield of HMFand EMF in the presence of (NH4)2SO4 and NH4NO3, the nitrate andsulfate are most likely unfavorable to the reaction. The yields ofHMF and EMF decreased by using bromide as the halide anion.

Furthermore, we tested the effect of solvent on the conversionof D-fructose (Fig. 1). With 50 mol % NH4Cl at 100 �C for 12 h, thereaction proceeded smoothly in most common solvents. Acetone,ethyl acetate, and Ethanol gave moderate to good yields of HMFand EMF. Isopropanol is the best solvent to form HMF as it gavethe total yield of 61% (HMF (58%), 3b (3%)). MeOH gave very goodconversion of fructose, but no desired product was obtained.Methyl fructofuranoside and methyl D-fructopyranoside were

Table 1Effect of salts on the conversion of D-fructose to HMF and EMF in ethanola

Catalyst Conversion (%) 4b (%) 5b (%) EMFb (%) HMFc (%)

— 1 0 0 0 0LiCl 87 30 22 0 0CuCl2�2H2O 100 0 0 12 0NiCl2�6H2O 96 2 6 5 19SnCl4�5H2O 100 0 5 23 0NaCl 83 32 27 0 0FeCl2�4H2O 90 9 4 0 12FeCl3 100 0 0 28 0CrCl3�6H2O 100 0 0 33 8NH4Cl 97 0 0 10 36(NH4)2SO4 87 30 26 0 0NH4NO3 91 24 29 0 1NH4Br 96 10 4 7 16NaCl/NH4Cld 92 — — 4 27

aD-Fructose (1 mmol) was mixed with inorganic salts (0.5 mmol) at 100 �C for

12 h in ethanol (2 mL).b Yield based on NMR analysis.c Yield based on NMR and HPLC analysis.d The reaction was carried out at 100 �C using NaCl (50 mol %) as the catalyst for

12 h. then NH4Cl (50 mol %) was added, the reaction mixture was stirred for another12 h.

obtained in 45% yield and 35% as the major products. H2O is aninefficient solvent for dehydration of fructose to form HMF.

After choosing NH4Cl as the most promising catalyst for theconversion of fructose to HMF and EMF, the reaction conditionswere further optimized (Table 2). Other factors, such as concentra-tion of the catalyst, temperature, and reaction time were taken intoaccount. Entries 1–3 showed the effect on concentration of NH4Clon the yield. When the concentration of NH4Cl was controlled at50 mol % (entry 2), the best overall yield was obtained.

Higher temperature was beneficial for the formation of HMFand EMF (entries 4 and 5), and the better yield and selectivity ofEMF was obtained after prolonging reaction time (entries 2, 7–9).The highest yield and selectivity of HMF was obtained in isopropa-nol which only gave trace isoproxymethylfurfural (3b) (entry 11).

We tested the scalability of our optimized conditions for HMFand EMF production by performing reactions on 10 g of fructose.These conditions consistently provide HMF and EMF in total yieldof 42% (entry 13). Microwave irradiation in EtOH gave good yieldsof HMF and EMF compared with oil-bath heating, and shortenedthe reaction time from 12 h to 10 min (entry 14). But lower yieldof HMF was obtained when the reaction was carried out in isopro-panol with mocrowave heating (entry 15). No humin was found inthe solution, as evidenced by the absence of insoluble material in

Entry T (�C) Time (h) Conversion (%) Ratio (2/3) Total yieldb (%)

1c 100 12 92 100/0 82 100 12 97 79/21 453d 100 12 97 86/14 414 78 12 94 92/8 145 120 12 99 78/22 476 100 24 99 66/34 577 100 6 93 94/6 168 100 18 97 71/29 519 120 24 100 41/59 5410e 100 24 100 94/6 6111f 120 12 100 96/4 7112g 100 12 — 85/15 2613h 100 12 98 81/19 4214i 120 10 min 99 86/14 6515f,i 120 10 min 92 100/0 37

a Reaction were carried out with D-fructose 1 (1 mmol), NH4Cl (0.5 mmol), EtOH(2 mL) in seal tube unless otherwise noted.

b Yield was calculated by HPLC, 1H NMR and verified by isolation.c NH4Cl (0.1 mmol) was added.d NH4Cl (1 mmol) was added.e The reaction was run in air pressure.f Reaction was run in isopropanol.g Inulin as substrate.h Reaction were carried out with D-fructose 1 (55.6 mmol), NH4Cl (28 mmol),

EtOH (60 mL).i The reaction was carried out with D-fructose 1 (6 mmol), NH4Cl (3 mmol),

alcohol (12 mL) and microwave heating.

Table 3Recycling of the catalyst system in the dehydration of D-fructose

Run Num. Conversion (%) HMF (%) 3ba (%)

1 100 65 62 100 61 43 99 55 64 99 52 45 90 38 0

a Yield calculated by HPLC, 1H NMR.

22 J. Liu et al. / Carbohydrate Research 350 (2012) 20–24

the reaction vessel using ethanol as solvent. We also found thatafter reaction most of the NH4Cl was dissolved in ethanol whileNH4Cl was almost insoluble in isopropanol. So recycling of the cat-alyst and solvent was possible.

The ability to recycle the catalyst is an important criterion forpractical biomass transformations. The catalyst remains activeafter carefully removing the solvent and product. Experimentswere conducted at 120 �C for a reaction time of 12 h in isopropanol.After removal of the organic layer, isopropanol was added to washthe residue three times after each reaction cycle. An equal amountof fructose was added and used for next reaction cycle. As shown inTable 3, the yield of HMF and EMF gradually decreased from 71% to56% after four cycles, which might be due to the catalyst loss in therecovering process. In the fifth cycle, there was a dramatic decreaseof the yield, and we attributed this to humin formation, which pre-cipitated on the surface of the catalyst that slows the further dehy-dration process down. It is worth noting that when NH4Cl waspredissolved in isopropanol under standard reaction conditionswithout fructose for 12 h and the reaction mixture was filtered,and the filtrate was then subjected into the reaction with fructoseunder typical conditions resulted in 46% yield of HMF as well as 1%of isoproxymethylfurfural (3b). The success of this experiment hasdemonstrated the high degree of homogenous catalysis usingNH4Cl during this reaction as well as heterogenous fashion.

From the above experimental results, the dehydration of fruc-tose to HMF catalyzed by salts is a very complex process. As shownin Scheme 2, take Bronsted acid for example, intermediate 7 wasformed first and then can be transformed into intermediate (8)or ethyl fructoside. Intermediate (8) was treated with ethanol toform ethyl D-fructopyranoside (5). HMF can be obtained from ethylfructofuranoside (4) through removal of two water molecules and

OHO

HO OH

OH

OH

O

HO OH

O

H

OHO

HO OH

OH

HO

2

7

OHO

HO OH

OH

OEtH

OHO

HO OH

OH

H

EtOH (-H+)

(-H+)

(-H+)

(-2H2O) ROH

1 4

OH O

OH

LA

Scheme 2. Putative mechanism for

one ethanol molecule. Under similar conditions, reaction of HMF(2) was indeed converted into EMF (3a) as we postulated inScheme 2.

3. Experimental

3.1. Materials

Fructose (extra pure, average particle size) was a commercialproduct from Solarbio Company (Beijing, China); ethanol (AR,>99.7%), ethyl acetate (AR, >99.5%) were purchased from FuyuChemical Company (Tianjin, China); methanol (AR, >99.5%), isopro-panol (AR, >99.7%), tert-Butanol (AR, >99.5%), acetone (AR, >99.5%)were purchased from Jiangtian Chemical Company (Tianjin,China); Deionized water was used for the preparation of aqueoussolutions. All other reagents and solvents were reagent grade andwere used without further purification.

3.2. Dehydration of fructose by oil-bath heating

In a typical run, 0.18 g of fructose (1 mmol) and 27 mg of NH4Cl(0.5 mmol) were loaded into a 25 mL glass tube (predried)equipped with a magnetic stirring bar, then 2.0 mL ethanol wasadded. The glass tube was sealed with a stopper and a screw capand then heated at 100 �C in an oil-bath for a prescriptive time.After reaction, the solution was transparent and there were no hu-mins or insoluble solid visible.

3.3. Typical procedure for carbohydrate dehydration bymicrowave heating

The synthesis was performed in the Anton Paar Synthos 3000,using Rotor XF100 (80 mL quartz vessels, 80 bar) with immersedT-probe. The vessel, equipped with a stirring bar, was charged with1.08 g fructose (6 mmol), 162 mg of NH4Cl (3 mmol), and 12 mLethanol. Special openings in the rotor lid give access to the ade-quate bayonet adaptors on the vessel caps. This allows to prepareand seal the vessel, place it in the rotor, close the rotor accordinglyand put it into the instrument. As a noteworthy safety measure,there is no need to carry around pressurized reaction vessels. Final-ly, with a maximum of 600 W the mixtures were heated at 120 �Cfor a total time of 10 min.

OOH

OHOH

HO

O

OHOH

HO

OEt

OH

5

O

3a (R = Et)

OR O

8

EtOH (-H+)LA

(-H2O)

3b (R = i-Pr)

the dehydration of D-fructose.

J. Liu et al. / Carbohydrate Research 350 (2012) 20–24 23

3.4. Fructose analysis

The Fructose concentration after reaction was determined usinghigh performance ion chromatography (Dionex ICS3000) equippedwith electrochemical detector and CarboPac PA-20 column (col-umn temperature was set at 303 K and flow rate at 0.5 mL/min).Fructose retention time is 10.3 min.

3.5. Analysis of EMF and LAEE

HMF was analyzed by HPLC(Waters) equipped with Waters2489 UV/Visible Detector, Waters 1525 Binary Pump, C18 column(SunFire C18 5 lm 250 � 4.6 mm). EMF and LAEE yields were ob-tained via 1H NMR using 25 lL of mesitylene as the standard.EMF and LAEE yields were calculated by the integration of protonpeaks of EMF (4.52 ppm), LAEE (2.76 ppm) and mesitylene(6.80 ppm). The yield of HMF is the average of three different typesof methods.

5-i-Propoxymethylfurfural (3b). Rf = 0.35 [20% EtOAc–hexane];1H NMR (400 MHz, CDCl3) d 1.21(d, 6H J = 6.0 Hz), 3.73 (sep, 1H,J = 6.0 Hz), 4.54 (s, 2H), 6.51 (d, 1H, J = 3.6 Hz), 7.21 (d, 1H,J = 3.6 Hz), 9.61 (s, 1H); 13C NMR (100 MHz, CDCl3) d 21.9, 62.5,72.1, 110.7, 122.1, 152.5, 159.4, 177.6.

Ethyl fructofuranoside (4). Rf = 0.60 [CH2Cl2–CH3OH = 7:1]; 1HNMR (600 MHz, CD3OD, ppm) d 1.17 (t, 3H, J = 7.2 Hz), 3.56–3.67 (m, 4H), 3.69 (d, 1H, J = 12.0 Hz), 3.74 (dd, 1H, J = 2.8,3.0 Hz), 3.82–3.90 (m, 2H), 4.04 (d, 1H, J = 4.8 Hz); 13C NMR(150 MHz, CD3OD, ppm) d 16.1, 57.7, 61.5, 62.7, 78.6, 83.1, 84.1,108.9.

Ethyl a-fructopyranoside (5). Rf = 0.42 [CH2Cl2–CH3OH = 7:1];1H NMR (600 MHz, CD3OD, ppm) d 1.15 (t, 3H, J = 7.2 Hz), 3.51–3.61 (m, 3H), 3.64–3.79 (m, 4H), 3.94 (t, 1H, J = 7.8 Hz), 4.09 (d,1H, J = 7.8 Hz); 13C NMR (150 MHz, CD3OD, ppm) d 16.1, 57.9,61.9, 65.0, 77.3, 78.3, 83.4, 105.3; mass spectrum (ESI+ Na)+: m/e(% relative intensity) 231.0 (100).

Ethyl b-fructopyranoside (5). Rf = 0.42 [CH2Cl2–CH3OH = 7:1];1H NMR (600 MHz, CD3OD, ppm) d 1.18 (t, 3H, J = 7.2 Hz), 3.51–3.61 (m, 3H), 3.64–3.79 (m, 4H), 3.83 (t, 1H, J = 7.8 Hz), 3.90 (d,1H, J = 9.6 Hz); 13C NMR (150 MHz, CD3OD, ppm) d 15.9, 57.3,63.4, 65.2, 70.4, 71.1, 71.6, 101.8; mass spectrum (ESI+ Na)+: m/e(% relative intensity) 231.0 (100).

Methyl fructofuranoside. Rf = 0.48 [CH2Cl2–CH3OH = 7:1]; 1HNMR (600 MHz, D2O, ppm) d 3.31 (s, 1H), 3.65–3.70 (m, 2H), 3.78(d, 1H, J = 12.6 Hz), 3.80 (dd, 1H, J = 2.6, 2.8 Hz), 3.94–3.98 (m,2H), 4.09 (d, 1H, J = 2.8 Hz); 13C NMR (150 MHz, D2O, ppm) d48.1, 57.5, 61.2, 77.3, 79.9, 83.3, 108.2.

Methyl a-fructopyranoside. Rf = 0.32 [CH2Cl2–CH3OH = 7:1]; 1HNMR (600 MHz, D2O, ppm) d 3.31 (s, 1H), 3.63–3.66 (m, 2H), 3.71(d, 1H, J = 12.6 Hz), 3.77–3.87 (m, 3H), 4.05 (t, 1H, J = 7.8 Hz),4.16 (d, 1H, J = 8.4 Hz); 13C NMR (150 MHz, D2O, ppm) d 48.7,59.5, 62.5, 74.8, 76.6, 81.1, 103.6.

Methyl b-fructopyranoside. Rf = 0.32 [CH2Cl2–CH3OH = 7:1] 1HNMR (600 MHz, D2O, ppm) d 3.28 (s, 3H), 3.63–3.66 (m, 2H), 3.71(d, 1H, J = 12.6 Hz), 3.77–3.87 (m, 3H), 3.91 (d, 1H, J = 10.2 Hz),3.97 (m, 1H); 13C NMR (150 MHz, D2O, ppm) d 48.3, 60.7, 63.7,68.2, 69.0, 69.5, 100.3.

In conclusion, we have demonstrated that HMF and EMF can beobtained in good yields through the NH4Cl promoted dehydrationof D-fructose either in ethanol or in isopropanol. Isopropanolshowed better selectivity toward HMF. No mineral acids such asHCl or H2SO4 are required. Although challenges remain forcommercial application, this research opens a new environment-friendly path for HMF and EMF production as biomass-derivedliquid transportation fuels.

Acknowledgments

This work was funded by grants KSCX2-YW-G-066 from TheChinese Academy of Science, 30970050 from the National NaturalScience Foundation of China, 1102 from Fund Foundation of TianjinUniversity. We thank Dr. Xiaobo Wan for prof-reading.

References

1. Facing the Hard Truths about Energy; U.S. National Petroleum Council:Washington, DC, 2007.

2. Riduan, S. N.; Zhang, Y. G.; Ying, J. Y. Angew. Chem., Int. Ed. 2009, 48,3322–3325.

3. Special issue in Science: Sustainability and Energy: Science 2007, 315, 781–813.

4. Ragauskas, A. J.; Williams, C. K.; Davison, B. H.; Britovsek, G.; Cairney, J.; Eckert,C. A.; Frederick, W. J.; Hallett, J. P.; Leak, D. J.; Liotta, C. L.; Mielenz, J. R.;Murphy, R.; Templer, R.; Tschaplinski, T. Science 2006, 311, 484–489.

5. Parikka, M. Biomass Bioenergy 2004, 27, 613–620.6. Gandini, A. Macromolecules 2008, 41, 9491–9504.7. Huber, G. W.; Iborra, S.; Corma, A. Chem. Rev. 2006, 106, 4044–4098.8. Werpy, T.; Petersen, G. National Renewable Energy Laboratory (NREL) Golden,

CO, 2004.9. Roman-Leshkov, Y.; Barrett, C. J.; Liu, Z. Y.; Dumesic, J. A. Nature 2007, 447,

U982–U985.10. Lewkowski, J. Arkivoc 2001, 2, 17–54.11. Hu, X.; Lievens, C.; Larcher, A.; Li, C. Z. Bioresour.Technol. 2011, 102, 10104–

10113.12. Benoit, M.; Brissonnet, Y.; Guélou, E.; De Oliveira Vigier, K.; Barrault, J.; Jérôme,

F. ChemSusChem 2010, 3, 1304–1309.13. Kim, B.; Jeong, J.; Shin, S.; Lee, D.; Kim, S.; Yoon, H.-J.; Cho, J. K. ChemSusChem

2010, 3, 1273–1275.14. Lai, L.; Zhang, Y. ChemSusChem 2010, 1257–1259.15. Tao, F.; Song, H.; Chou, L. ChemSusChem 2010, 3, 1298–1303.16. Subrahmanyam, A. V.; Thayumanavan, S.; Huber, G. W. ChemSusChem 2010, 3,

1158–1161.17. Thananatthanachon, T.; Rauchfuss, T. B. ChemSusChem 2010, 3, 1139–1141.18. Watanabe, M.; Aizawa, Y.; Iida, T.; Nishimura, R.; Inomata, H. Appl. Catal., A

2005, 295, 150–156.19. Chheda, J. N.; Dumesic, J. A. Catal. Today 2007, 123, 59–70.20. Ohara, M.; Takagaki, A.; Nishimura, S.; Ebitani, K. Appl. Catal., A 2010, 383, 149–

155.21. Takagaki, A.; Ohara, M.; Nishimura, S.; Ebitani, K. Chem. Commun. 2009, 6276–

6278.22. Tuercke, T.; Panic, S.; Loebbecke, S. Chem. Eng. Technol. 2009, 32, 1815–1822.23. Li, C. Z.; Zhao, Z. K.; Wang, A. Q.; Zheng, M. Y.; Zhang, T. Carbohydr. Res. 2010,

345, 1846–1850.24. Tong, X.; Li, Y. ChemSusChem 2010, 3, 350–355.25. Mascal, M.; Nikitin, E. B. Angew. Chem., Int. Ed. 2008, 47, 7924–7926.26. gen Klaas, M. R.; Schone, H. ChemSusChem 2009, 2, 127–128.

27. Gruter, G. J. M.; Dautzenberg, F.; Gruter, G. Eur. Pat. 1834950A1, 2007.28. Ras, E. J.; Maisuls, S.; Haesakkers, P.; Gruter, G. J.; Rothenberg, G. Adv. Synth.

Catal. 2009, 351, 3175–3185.29. Chheda, J. N.; Huber, G. W.; Dumesic, J. A. Angew. Chem., Int. Ed. 2007, 46, 7164–

7183.30. Chheda, J. N.; Roman-Leshkov, Y.; Dumesic, J. A. Green Chem. 2007, 9, 342–350.31. Kuster, B. F. M. Starch/Starke 1990, 42, 314–321.32. Brown, D. W.; Floyd, A. J.; Kinsman, R. G.; Roshanali, Y. J. Chem. Technol.

Biotechnol. 1982, 32, 920–924.33. Shimizu, K.; Uozumi, R.; Satsuma, A. Catal. Commun. 2009, 10, 1849–1853.34. Caes, B. R.; Raines, R. T. ChemSusChem 2011, 4, ASAP.35. Mednick, M. L. J. Org. Chem. 1962, 27, 398–403.36. Fayet, C.; Gelas, J. Carbohydr. Res. 1983, 122, 59–68.37. Nakamura, Y. Japan Pat. 8,013,243, 1980.38. Garber, J. D.; Jones, R. E. US Pat. 2,929,823, 1960.39. Hales, R. A.; Le Maistre, J. W.; Orth, G. O. US Pat. 3,071,599, 1963.40. Sievers, C.; Musin, I.; Marzialetti, T.; Valenzuela Olarte, M. B.; Agrawal, P. K.;

Jones, C. W. ChemSusChem 2009, 2, 665–671.41. Lima, S.; Neves, P.; Antunes, M. M.; Pillinger, M.; Ignatyev, N.; Valente, A. A.

Appl. Catal., A 2009, 363, 93–99.42. Binder, J. B.; Raines, R. T. J. Am. Chem. Soc. 2009, 131, 1979–1985.43. Chan, J. Y.; Zhang, Y. ChemSusChem 2009, 2, 731–734.44. Yong, G.; Zhang, Y.; Ying, J. Y. Angew. Chem., Int. Ed. 2008, 47, 9345–9348.45. Zhao, H. B.; Holladay, J. E.; Brown, H.; Zhang, Z. C. Science 2007, 316, 1597–

1600.46. Hu, S. Q.; Zhang, Z. F.; Zhou, Y. X.; Han, B. X.; Fan, H. L.; Li, W. J.; Song, J. L.; Xie,

Y. Green Chem. 2008, 10, 1280–1283.47. Qi, X. H.; Watanabe, M.; Aida, T. M.; Smith, R. L. Green Chem. 2009, 11, 1327–

1331.48. Hu, S. Q.; Zhang, Z. F.; Zhou, Y. X.; Song, J. L.; Fan, H. L.; Han, B. X. Green Chem.

2009, 11, 873–877.49. Bao, Q.; Qiao, K.; Tomida, D.; Yokoyama, C. Catal. Commun. 2008, 9, 1383–1388.

24 J. Liu et al. / Carbohydrate Research 350 (2012) 20–24

50. Tong, X. L.; Ma, Y.; Li, Y. D. Carbohydr. Res. 2010, 345, 1698–1701.51. Roman-Leshkov, Y.; Chheda, J. N.; Dumesic, J. A. Science 2006, 312, 1933–

1937.52. Hansen, T. S.; Woodley, J. M.; Riisager, A. Carbohydr. Res. 2009, 344, 2568–2572.53. Qi, X. H.; Watanabe, M.; Aida, T. M.; Smith, R. L. Catal. Commun. 2008, 9, 2244–

2249.

54. Qi, X. H.; Watanabe, M.; Aida, T. M.; Smith, R. L. ChemSusChem 2010, 3, 1071–1077.

55. Ferrieres, V.; Benvegnu, T.; Lefeuvre, M.; Plusquell-ec, D.; Mackenzie, G.;Watson, M. J.; Haley, J. A.; Goodby, J. W.; Pindak, R.; Durbin, M. K. J. Chem. Soc.,Perkin. Trans. 2 1999, 951–959.

56. Kuang, H. X.; Kasai, R.; Ohtani, K. Chem. Pharm. Bull. 1989, 37, 2232–2233.