Tetrahedron Letters 50 (2009) 5403–5405

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Tetrahedron Letters

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Direct conversion of glucose and cellulose to 5-hydroxymethylfurfuralin ionic liquid under microwave irradiation

Changzhi Li a, Zehui Zhang a,c, Zongbao K. Zhao a,b,*

a Dalian Institute of Chemical Physics, CAS, Dalian 116023, PR Chinab Dalian National Laboratory of Clean Energy, Dalian 116023, PR Chinac Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China

a r t i c l e i n f o a b s t r a c t

Article history:Received 7 April 2009Revised 28 May 2009Accepted 10 July 2009Available online 15 July 2009

0040-4039/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.tetlet.2009.07.053

* Corresponding author. Tel./fax: +86 411 8437 921E-mail address: zhaozb@dicp.ac.cn (Z.K. Zhao).

An efficient strategy for CrCl3-mediated production of 5-hydroxymethylfurfural (HMF) in ca. 60% and 90%isolated yields from cellulose and glucose, respectively, in ionic liquid under microwave irradiation ispresented.

� 2009 Elsevier Ltd. All rights reserved.

Studies on conversion of cellulose into biofuels and other bio-materials have been currently one of the most intensive pursuitsworldwide.1 One major approach is to hydrolyze cellulose to glu-cose followed by fermentation for biofuels and related chemicals.However, the overall energy efficiency of these biochemical routesis under debate.2 Thus, a workable non-fermentative process forthe conversion of cellulose to bio-based products remainsimperative.

The five-membered ring compound, 5-hydroxy-methylfurfural(HMF), is one of the top bio-based platform compounds. HMFcan be converted to a novel biofuel molecule 2,5-dimethylfuran3

via selective hydrogenation. Thus, making HMF with renewablefeedstock is highly demanding. Because glucose is liable to forma stable six-membered pyranoside structure,4 it failed to formHMF with satisfactory yields under those known conditions.5 Fur-thermore, a direct cellulose-to-HMF process (Scheme 1), which iseconomically more attractive, has yet to be developed.

We present herein an efficient strategy for direct production ofHMF in ca. 90% and 60% isolated yields from glucose and cellulose,respectively, in ionic liquids under microwave irradiation (MI) inthe presence of CrCl3. This approach greatly advanced our utiliza-tion of lignocellulose for bioenergy through a chemical transforma-tion strategy.

After a solution of glucose and CrCl3 (3.6 wt%) in [C4mim]Cl wassubjected to MI at 400 W for 1 min, the entire reaction mixture waspurified by column chromatography on silica gel (ethyl ace-tate:petroleum ether = 1:10 to 1:1), affording HMF in 91% yield(Table 1, entry 1). In contrast, HMF was obtained in 17% yield ifthe reaction was done under oil-bath heating at 100 �C for60 min (entry 2). If water was used as the solvent, glucose dehy-dration was essentially suffocated (entry 3). When sulfuric acid

ll rights reserved.

1.

was employed in lieu of CrCl3, the dehydration reaction affordedHMF in only 49% yield (entry 4), and formation of insoluble huminswas observed in this case. Careful comparison of these data indi-cated that (1) MI had a drastic effect on HMF formation; (2)[C4mim]Cl was a solvent superior to water, and (3) CrCl3 was apowerful catalyst for selective dehydration of glucose. More de-tailed explanation will be discussed thereafter. Taken together,efficient dehydration of glucose to HMF was achieved in [C4mim]Clwith a catalytic amount of CrCl3 under MI.

We have demonstrated recently that cellulose could be effec-tively hydrolyzed in ionic liquids to produce glucose.6 It was thuslogic to pursue a direct transformation of cellulose into HMF. In-deed, we were able to obtain HMF in 61% isolated yield and totalreducing sugars (TRS) in 16% yield when Avicel cellulose andCrCl3�6H2O (10 wt%) were mixed in [C4mim]Cl and irradiated at400 W for 2 min (Table 2, entry 1). These data are close to the bestknown result from glucose.5b Other cellulose samples showed sim-ilar results in the range of 53–62% (entries 2–4). Apparently, thismethod worked almost equally well regardless of the cellulosetype and the degree of polymerization. Although our method affor-ded TRS in around 20% yield based on analysis with the 3,5-dinitro-salicylic acid (DNS) reagent,7 further analysis revealed that glucosehad little contribution, indicating that other byproducts or sugaroligomers might be formed. In sharp contrast, when an identicalreaction of Avicel cellulose was heated with oil-bath at 100 �C for240 min, HMF and TRS were obtained in 17% and 45% yields,respectively (entry 5). It should be noted that the initial water con-tent in the system was estimated about 170 mM, a quite low con-centration compared to about 1000 mM in our early cellulosehydrolysis work.6a Yet, as there are three water molecules releasedfor the formation of one HMF molecule, cellulose hydrolysis is ex-pected auto-accelerated during the process. On the other hand, alower water concentration would also slow down HMF rehydrationand humins formation.4

Table 1HMF production from glucose under various conditionsa

Entry Catalyst Catalyst loading (wt%) Time (min) Yieldb (%)

1 CrCl3 3.6 1 912c CrCl3 3.6 60 173d CrCl3 3.6 10 <14 H2SO4 10 1 49

a Unless otherwise specified, conditions were glucose (100 mg) in [C4mim]Cl(1.0 g) under MI at 400 W.

b Isolated yields.c Heated with an oil-bath at 100 �C.d Water (1.0 g) was used in lieu of [C4mim]Cl as the solvent.

Table 2HMF production from cellulose in [C4mim]Cl under MIa

Entry Substrate Time (min) YieldHMFb (%) YieldTRS

c (%)

1 Avicel 2 61 162 Spruce 2 53 263 Sigmacell 2 55 234 a-Cellulose 2 62 205d Avicel 240 17e 456d,f Avicel 240 2.0e 157f Avicel 2 1.6e 9.7

a Unless otherwise specified, reaction conditions were cellulose (100 mg) andCrCl3�6H2O (10 mg) in [C4mim]Cl (2.0 g) under 400 W MI.

b Isolated yield unless otherwise specified.c Determined by the DNS method.7d Heated by oil-bath at 100 �C.e Determined spectrophotometrically at 282 nm.f Three equiv of 2,20-bipyridine (17.5 mg) were introduced thereafter the addi-

tion of CrCl3�6H2O (10 mg).

Hydrolysis Dehydration OOOH

Cellulose

HMF

HO O

HOOH

OH

OH

Glucose

O

HO

OH

OHO

O

HOOH

HO

HO O

HOOH

HO

OO

HO

OH

OHOHO

n

O

2,5-dimethylfuran

Scheme 1. Schematic illustration of the steps for cellulose-to-HMF.

5404 C. Li et al. / Tetrahedron Letters 50 (2009) 5403–5405

Based on current data, the reasons that a combination of[C4mim]Cl, CrCl3, and MI generates the magic power for conversionof cellulose into HMF may be imagined. First, complete dissolutionof cellulose in [C4mim]Cl leaves the cellulose chains accessible tochemical transformation.8 Second, [C4mim]Cl has excellent dielec-tric properties for transformation of microwave into heat.9 UnderMI, alternating electric field induces vibrational motion of ions,and resistance of the reaction mixture to ion flux leads to heat evo-lution, the higher the concentration of ions, the stronger the heat-ing effect.10 Because the reaction in ionic liquids had nearly a pureionic circumstance, it was heated up rapidly, volumetrically andsimultaneously by this ‘specific microwave effects’. Therefore, itcircumvented some known problems such as partly overheatingunder conventional oil-bath conditions.11 Other microwave ef-fects,12 such as lowering activation energy or increasing the pre-exponential factor in the Arrhenius law due to orientation effectof polar species in an electromagnetic field,13 might also contrib-ute. Moreover, [C4mim]Cl may also act as a water scavenger bydilution, circumventing water-associated HMF decomposition asfound in these aqueous systems.14 Thus, a combination of ionic li-quid and MI might be an interesting condition to try newchemistry.

Although an exact catalytic mechanism for the exceptionaleffectiveness of CrCl3 in the conversion of cellulose remains elu-sive, we would like to offer some insights into the reaction. Asillustrated in Scheme 2, we imagined that CrCl3 in [C4mim]Cl mightform complexes [C4mim]n[CrCl3+n] (n = 1–3) in a way similar toLnCl3 reported by Rogers and co-workers.15 In the cellulose hydro-lysis step, the 1,4-glucosidic bonds were weakened partially be-cause of coordination with [CrCl3+n]n�, resulting in more liable towater attack to form glucose and oligomers. Then, the complexpromoted rapid mutarotation of the a-anomer of glucose to theb-one through hydrogen bonds of chloride anions with the hydro-xyl groups similar to what was proposed for CrCl2 in an earlywork.5b The hemiacetal portion of b-glucopyranose then formsCr(III) enolate anion complex leading to isomerization of glucoseto fructose, which would be dehydrated to HMF simultaneouslyin the reaction condition (vide ante). There are additional data sup-porting our speculation. We found that a strong coordinating li-gand, 2,20-bipyridine, strongly inhibited the reaction, as HMFyield dropped from 61% to 1.6% (Table 2, entry 1 vs entry 7). More-over, under oil-bath heating conditions, both HMF yield and TRSyield dropped substantially in the presence of 2,20-bipyridine (Ta-ble 2, entry 5 vs entry 6). These results suggested that 2,20-bipyri-dine restrained both cellulose hydrolysis and glucose dehydrationreactions. Thus, coordination chemistry involving CrCl3 played akey role not only for glucose dehydration but also for cellulosehydrolysis.

Zhang and co-workers reported a method for dehydration ofglucose to HMF and claimed that CrCl2 was more efficient as a cat-alyst than CrCl3 under conventional heating condition.5b However,near identical HMF yields were observed in our system, that is,when the reaction was heated under MI, implying that the valencestate of Cr is not the determinant in the transformation. Moreover,one might consider to formulate complexes [C4mim]n[CrCl2+n](n = 1–4) for CrCl2 in [C4mim]Cl according to Scheme 2. We alsonoticed that in Zhang’s work, glucose was introduced into the mix-ture of CrCl2 and ionic liquid pretreated at 150 �C for 20 min withvigorous stirring in a sealed tube because CrCl2 could not be easilysolubilized in [C4mim]Cl. When CrCl3 was used in our method, incontrast, stirring at 80 �C for 1 min under ambient pressure en-sured a solution of CrCl3 in [C4mim]Cl. Thus, it was more practi-cal.16 More significantly, for the glucose-to-HMF process, ourmethod afforded 91% isolated yield whereas a 68% HPLC yieldwas reported in the literature.5b When cellulose was employed asthe substrate, we also obtained HMF in over 60% isolated yield.

As very high isolated yield for HMF was realized with our meth-od, it was appealing to envision a more practical process. Notingthat ionic liquids have little vapor pressure, and HMF has a boilingpoint of 85–88 �C at 0.01 torr,17 one can take the advantages of thissystem and engineer a continuous reaction-distillation process toproduce HMF using carbohydrates as the feedstock. In this sce-nario, both ionic liquids and catalyst may be recycled.

In conclusion, we showed multiple beneficiary effects under MIin ionic liquid for carbohydrate chemistry. For the conversion of

Cellulose

HO O

HOOH

OH

OH

Glucose

O

HO

OH

OHO

O

HOOH

HO

HO O

HOOH

OH

OO

HO

OH

OHOHO

n

OHO

HOOH

OH

OH

OHO

HOOH

OH

OH

(a-glucopyranose anomer)Glucose

Glucoseβ( -glucopyranose anomer)

[CrCl3+n] n-

H2O

OHO

OOH

OH

HO

CrCl(2+n)

ClH

n-

OHO

OOH

OH

HO CrCl(2+n)

ClH

n-

[CrCl3+n] n-

[CrCl3+n] n-

+ [CrCl4]-

HO OH

HO

OH

OH

OH

Cr

Cl ClCl

Cl

OHO

H

H

OH

OH

H

OHOH O

HO O

- [CrCl4]-

_

- 3 H2O

- 3 H2 O

- [CrCl4 ] -

HOO

H

OH

OH

OH

OH

Fructose HMF

Scheme 2. Direct conversion of cellulose to HMF catalyzed with CrCl3 in [C4mim]Cl (n = 1–3).

C. Li et al. / Tetrahedron Letters 50 (2009) 5403–5405 5405

glucose and cellulose, respectively, HMF was obtained in 91% and61% isolated yields in the presence of a catalytic amount of CrCl3.Thus, this work achieved a direct transformation of cellulose intoHMF technically escaping a sugar separation step. Our method pro-vided a new opportunity for transformation of abundant and inex-pensive cellulosic biomass through a non-fermentative processinto biofuels and bio-based products.

Acknowledgments

We acknowledge financial supports from the National HighTechnology Research and Development Program of China (No.2007AA05Z403) and the Knowledge Innovation Program of CAS(No. KGCX2-YW-336).

Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.tetlet.2009.07.053.

References and notes

1. (a) Suganuma, S.; Nakajima, K.; Kitano, M.; Yamaguchi, D.; Kato, H.; Hayashi, S.;Hara, M. J. Am. Chem. Soc. 2008, 130, 12787–12793; (b) Schmidt, L. D.;

Dauenhauer, P. J. Nature 2007, 447, 914–915; (c) Rinaldi, R.; Palkovits, R.;Schüth, F. Angew. Chem., Int. Ed. 2008, 47, 8047–8050.

2. Klemm, D.; Heublein, B.; Fink, H.-P.; Bohn, A. Angew. Chem., Int. Ed. 2005, 44,3358–3393.

3. Román-Leshkov, Y.; Barrett, C. J.; Liu, Z. Y.; Dumesic, J. A. Nature 2007, 447,982–985.

4. Kuster, B. M. F. Starch 1990, 42, 314–321.5. (a) Qi, X.; Watanabe, M.; Aida, M. T. Green Chem. 2008, 10, 799–805;

(b) Zhao, H.; Holladay, J. E.; Brown, H.; Zhang, Z. C. Science 2007, 316,1597; (c) Chheda, J. N.; Román-Leshkov, Y.; Dumesic, J. A. Green Chem.2007, 9, 342–350; (d) Seri, K.; Inoue, Y.; Ishida, H. Bull. Chem. Soc. Jpn.2001, 74, 1145–1150.

6. (a) Li, C. Z.; Zhao, Z. K. B. Adv. Synth. Catal. 2007, 349, 1847–1850; (b) Li, C. Z.;Wang, Q.; Zhao, Z. K. Green Chem. 2008, 10, 177–182.

7. Miller, G. L. Anal. Chem. 1959, 31, 426–428.8. Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. J. Am. Chem. Soc. 2002,

124, 4974–4975.9. de la Hoz, A.; Diaz-Ortiz, A.; Moreno, A. Chem. Soc. Rev. 2005, 34, 164–

178.10. Kappe, C. O. Chem. Soc. Rev. 2008, 37, 1127–1139.11. Nuchter, M.; Ondruschka, B.; Bonrath, W.; Gum, A. Green Chem. 2004, 6, 128–

141.12. Kappe, C. O. Angew. Chem., Int. Ed. 2004, 43, 6250–6284.13. Hosseini, M.; Stiasni, N.; Barbieri, V.; Kappe, C. O. J. Org. Chem. 2007, 72, 1417–

1424.14. Asghari, F. S.; Yoshida, H. Ind. Eng. Chem. Res. 2007, 46, 7703–7710.15. Hines, C. C.; Cordes, D. B.; Griffin, S. T.; Watts, S. I.; Cocalia, V. A.; Rogers, R. D.

New J. Chem. 2008, 32, 872–877.16. A recent publication reported similar observations: Binder, J. B.; Raines, R. T. J.

Am. Chem. Soc. 2009, 131, 1979–1985.17. Fayet, C.; Gelas, J. Carbohydr. Res. 1983, 122, 59–68.

Supporting Information

Direct conversion of cellulose to 5-hydroxymethylfurfural in ionic liquids

Changzhi Li a, b, Zehui Zhang a, b, Zongbao K. Zhao a, c *

a Dalian Institute of Chemical Physics, CAS, Dalian 116023, P. R. China

b Graduate School of the Chinese Academy of Sciences, Beijing 100039, P. R. China

c Dalian Laboratory of Clean Energy, Dalian 116023, P. R. China

Contents

1. Materials and Instruments (S1)

2. Preparation of [C4mim]Cl (S2)

3. Typical Procedure for Glucose Dehydration (S2)

4. Typical Procedure for Conversion of Cellulose into HMF (S3)

5. HMF Quantification Procedure (S3)

6. Total Reducing Sugar Analysis (S4)

7. Glucose Analysis (S4)

8. Catalyst Screening (S4)

9. References (S5)

10. Figure and Table (S6)

11. Spectra (S8)

Materials and Instruments

The cellulose samples Avicel, Sigmacell cellulose, cellulose powder from spruce and

α-cellulose were purchased from Sigma (St Louis, USA), and were dried under vacuum at 100 °C

for 24 h before use. N-Methylimidazole (99%) was obtained from J&K Chemical Ltd. (Beijing,

China). 1-Chlorobutane (98%) was purchased from ABCR Gmbh & Co. (Karlsruhe, Germany)

and freshly distilled before use. All other chemicals were supplied by local suppliers and used

without further purification. WBFY-205 microwave reactor (Rating power 1100 W, rating output

power 650 W, maximal input electric current 7.8 cA, working voltage 220 V, microwave

frequency 2450 ± 50 MHz, lumen size 290 mm × 295 mm × 190 mm) was purchased from

Gongyi City Yuhua Instrument Co. Ltd, China. JASCO V-530 spectrophotometer was product of

JASCO Inc., Japan. SBA-50B glucose analyzer was purchased from Shandong Academy of

Sciences, Jinan, China.

1

Preparation of [C4mim]Cl1

A mixture of N-Methylimidazole (41 g, 0.50 mol) and 1-chlorobutane (61 g, 0.65 mol) was

refluxed at 80 °C for 48 h. After cooling, the reaction mixture formed two phases. The lower layer

was separated and was washed with ethyl acetate (30 mL × 3), dried in vacuum at 70 °C for 5 h.

The crude product was then taken in water (150 mL) and treated with activated charcoal (5 g) at

room temperature for 24 h. The solution was filtered through Celite, dried in vacuum at 70 °C for

12 h to give 80.2 g yellowish liquid in 92% yield, which crystallized as a white solid at room

temperature. 1H NMR (400 Hz, CDCl3): δ 10.55(s, 1H), 7.62 (d, J=1.6 Hz, 1H), 7.46 (t, J=1.6 Hz,

1H), 4.25 (t, J=7.2 Hz, 2H), 4.04 (s, 3H), 1.78-1.86 (m, 2H), 1.25-1.34 (m, 2H), 0.87 (t, J=7.2 Hz,

3H). 13C NMR (100 Hz, CDCl3): δ 137.84, 123.70, 122.01, 49.72, 36.50, 32.14, 19.42, 13.41.

Typical Procedure for Glucose Dehydration

Glucose (100 mg) and appropriate amount catalyst (6 mg CrCl3·6H2O, or 10 mg 98 wt%

sulfuric acid) were subsequently dissolved in 1.0 g [C4mim]Cl at 100 oC, and the reaction mixture

was immediately subjected to 400 W microwave irradiation for the setting reaction time. After

reaction, the entire reaction mixture was purified by column chromatography on silica gel (ethyl

acetate : petroleum ether = 1 : 10 to 1 : 1) to afford HMF. 1H NMR (400 Hz, CDCl3): δ 9.70 (s,

1H), 7.35 (d, J=2.8 Hz, 1H), 6.65 (d, J=2.8 Hz, 1H), 4.84 (s, 2H). 13C NMR (100 Hz, CDCl3): δ

178.2, 161.2, 152.8, 123.4, 110.5, 58.0.

Typical Procedure for Conversion of Cellulose into HMF

Cellulose (100 mg) in [C4mim]Cl (2.0 g) was heated with stirring at 100 °C until a clear

solution was formed. To this cellulose solution was added 10 mg CrCl3·6H2O. The reaction was

then vigorously stirred under 400 W MI for appropriate time. Sample was withdrawn, weighed

(recorded as M1, usually less than 50 mg), and quenched immediately with cold water. The

aqueous solutions was neutralized with 0.5 mol/L NaOH, centrifuged at 10,000 rpm for 5 min,

measured the volume (recorded as V1) and subjected to total reducing sugar (TRS) and glucose

analysis. The residue reaction mixture was purified by column chromatography on silica gel (ethyl

acetate : petroleum ether = 1 : 10 to 1 : 1) to afford HMF.

HMF Quantification Procedure

Reaction samples (M1, ca 50 mg) were diluted with deionized water to 2 ml, centrifuged at

10,000 rpm for 5 min. Then 25 µl of the upper clear liquid was pipetted off and diluted with

deionized water to 4.025 ml for analysis. HMF concentration was measured on a JASCO V-530

Model spectrophotometer at 282 nm using standard curve method with 0.06 mm width of quartz

cell. The mass of HMF MH was calculated as follows,

MH (mg) = HMF concentration (×10-3 mg/mL) × 4.025 (mL) × (2 ÷ 0.025) × (M0 ÷

M1)

For gluc r as calculated as follows,

For cellul alculated as follows,

ose used as subst ate, the yield of HMF w

HMF Yield = MH ÷ (100 × 0.7) × 100%

ose used as substrate, the yield of HMF was c

2

HMF Yield = MH ÷ (100 ÷ 0.9 × 0.7) × 100%

In which, MH is the mass of HMF, M0 is the total mass of the reaction solution and M1 is the

To

ed to room temperature and diluted with deionized water to 1000 mL to give the DNS

re

ained with glucose. The mass of TRS

MT and the

M 5 (mL) × (V1 ÷ 0.5) × (M0 ÷ M1)

T 1 olume of the sample, M0 is the total mass of the

d M1 is the mass of sample.

G

as determined using a SBA-50B glucose analyzer (Shandong Academy

ina).

Cata

various metal

atalysts. Table S1 shows the best results obtained in the reactions of Fig. S1.

son, S.; Slawin, A. M. Z.; Cole-Hamilton, D.

Miller, G. L. Anal. Chem. 1959, 31, 426-428.

mass of sample.

tal Reducing Sugar Analysis2

In 500 mL of hot deionized water (50 °C) was added 182 g of potassium sodium tartrate, 6.3 g

of 3, 5-dinitrosalicylic acid (DNS) and 262 mL of 2 M NaOH, after dissolved, 5 g of phenol and 5

g of sodium sulfite were added in the solution, stirring until homogeneous solution was formed,

then cool

agent.

A mixture contained 0.5 mL of DNS regent and 0.5 mL of cellulose reaction sample was heated

for 5 min in a boiling water bath, then cooled to room temperature, and mixed with 4 mL of

deionized water. The color intensity of the mixture was measured on a JASCO V-530 Model

spectrophotometer at 540 nm with 0.06 mm width of glass cell. The concentration of total

reducing sugars was calculated based on a standard curve obt

yield of TRS were calculated as follows,

T (mg) = TRS concentration (mg/mL) ×

TRS Yield = MT ÷ (100 ÷ 0.9) × 100%

In which, M is the mass of TRS, V is the v

reaction solution an

lucose Analysis

Glucose concentration w

of Sciences, Jinan, Ch

lyst Screening

Ionic liquid C4mimCl (1.0 g) and catalyst (see Table S1) was stirred at 100 oC to form a

homogeneous solution, to which was added glucose (100 mg) and the mixture was transferred into

microwave reactor, irradiating at 400 W. At different time intervals, samples were withdrawn,

weighed, and quenched immediately with cold water. The aqueous solutions were centrifuged at

10,000 rpm for 5 min, measured the volume and subjected for HMF quantification. Fig. S1 shows

the time course of HMF yields in the process of glucose dehydration promoted by

c

References

(1) Webb, P. B.; Sellin, M. F.; Kunen, T. E.; William

J. J. Am. Chem. Soc. 2003, 125, 15577-15588.

(2)

3

0 2 4 6 8 10 12 14 160

20

40

60

80

100

HM

F y

ield

(%

)

Time (min)

CrCl3 NiCl2 MgCl2 MnCl2 CuCl2 CuCl InCl3 Ti(SO4)2

Nocatalyst

Fig. S1 Results of glucose conversion in the presence of various metal catalysts under 400 W

microwave irradiation.

Reaction condition: 1.0 g of ionic liquid C4mimCl, at 100 oC added setting amount of

catalyst (see Table S1), 100 mg of glucose was added in and the reaction mixture was transferred

into microwave rector, reacting at 400 W for appropriate time.

4

Table S1 Best results of glucose conversion in the presence of various metal catalysts under 400 W

microwave irradiation. a

Entry Catalyst MCat.(mg) ncat./nglucose(%) Time (min) Yield (%)

1 CrCl3 3.6 4 1 96 (91) b

2 No -- -- 8.5 47

3 NiCl2 16.4 23 3.5 46

4 CuCl 11.0 20 3.5 43

5 InCl3 24.5 20 6 37

6 MgCl2 5 9 9 35

7 MnCl2 9.1 13 7 30

8 CuCl2 15 20 2.5 32

9 Ti(SO4)2 27 20 4 23

a. Unless otherwise specified, reaction condition is: At 100 oC, in 1.0 g of C4mimCl was added

the appropriate amount of catalyst, after dissolution, 100 mg of glucose was added in and the

reaction mixture was transferred into microwave reactor, reacting at 400 W for the desired time.

b. The data in the blanket is the isolated yield.

5

6

7

HMF spectra:

8