Direct transformation of cellulose into 5-hydroxymethyl-2-furfural using a combination of metal chlorides in imidazolium ionic liquid

Article abstract of DOI:10.1039/c1gc15152e

Direct transformation of cellulose into HMF was carried out using a combination of metal chlorides in ionic liquid [EMIM]Cl. From high throughput screening of various metal chlorides, a combination of CrCl₂ and RuCl₃ was found as the most effective catalyst. HMF was directly afforded from cellulose in nearly 60% yield. Gram scale-up synthesis of HMF was successfully performed from cellulose using CrCl₂ and RuCl ₃. Furthermore, lignocellulosic raw material reed could be directly converted into HMF and furfural in reasonable yields under these conditions.

Full text of DOI:10.1039/c1gc15152e

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COMMUNICATION
Direct transformation of cellulose into 5-hydroxymethyl-2-furfural using a
combination of metal chlorides in imidazolium ionic liquid†
Bora Kim,a Jaewon Jeong,a Dohoon Lee,a Sangyong Kim,a Hyo-Jin Yoon,b Yoon-Sik Leeb and Jin Ku Cho*a
Received 9th February 2011, Accepted 29th March 2011
DOI: 10.1039/c1gc15152e
Direct transformation of cellulose into HMF was carried
out using a combination of metal chlorides in ionic liquid
[EMIM]Cl. From high throughput screening of various
metal chlorides, a combination of CrCl2 and RuCl3 was
found as the most effective catalyst. HMF was directly
afforded from cellulose in nearly 60% yield. Gram scale-up
synthesis of HMF was successfully performed from cellu-
lose using CrCl2 and RuCl3. Furthermore, lignocellulosic
raw material reed could be directly converted into HMF
and furfural in reasonable yields under these conditions.
convert.3 However, the depolymerization step of cellulose into
glucose still remains an expensive and energy-intensive process.
5-Hydroxymethyl-2-furfural (HMF) is a template compound
to synthesize a broad range of chemicals and fuels.4 Although
HMF can be obtained by straightforward dehydration of ketose-
type hexose forming 5-membered ring such as fructose,5 ketose-
type carbohydrates are not abundant in nature and most of them
are sourced from agricultural feedstock. Recently, a remarkable
study by Zhang’s group found that aldose-type glucose could
be converted into HMF in record yield using Cr(II) or Cr(III)
metal catalysts in imidazolium ionic liquid and they revealed
that the Cr metal could assist an isomerization from C1-aldose
to C2-ketose by a specific coordination to the hemiacetal portion
of aldose.6 More recently, HMF synthesis from glucose was
also accomplished by common Lewis acid, SnCl4 in 1-ethyl-
3-methylimidazolium tetrafluoroborate ([EMim]BF4) instead
of Cr metal catalyst,7 effective bulky NHC (N-heterocyclic
carbene) metal ligands,8 and an integration of enzymatic and
chemical conversion.9 Furthermore, some efforts to utilize
cellulose as a starting material for direct synthesis of HMF
by means of a mixed catalyst using Brønsted acid and Lewis
acid10 and a microwave-assisted conversion11 were tried. Herein,
we report an effective direct transformation of cellulose into
HMF using a combination of metal catalysts screened in a
combinatorial manner (Scheme 1).
Over the past 150 years, humankind has consumed carbon
sources in a mostly irreversible manner, which resulted in
diminishing reserves of fossil fuels and global warming by CO2
emission.1 This issue is prompting us to replace fossil-based re-
sources with renewable and sustainable ones.2 With this in mind,
plentiful biomass has the potential as a renewable carbon source
for transportation fuels and chemicals. Actually, bioethanol
produced from corn or sugarcane is used as a transportation
fuel in some countries. There are, however, many arguments
that such a use of crop-based feedstock could bring a food
shortage problem. In an effort to overcome this dispute, cellulose
derived from naturally grown lignocellulosic biomass currently
attracts much attention as a promising carbon source due to
its abundance and limited share of cultivated land. Until now,
studies have mainly focused on the efficient depolymerization
of cellulose into monomeric glucose, because cellulose itself is
too complex and its crystalline structure (formed by internal
hydrogen bonds) is chemically and biologically too stable to
Scheme 1 Direct transformation of cellulose into HMF using a
combination of metal catalysts in imidazolium ionic liquid.
aGreen Chemistry & Engineering R&D Department, Cleaner Production
Technology Division, Korea Institute of Industrial Technology
(KITECH), 35-3, Hongcheon-Ri, Ipchang-Myeon, Cheonan-Si,
Chungnam, 330-825, South Korea. E-mail: jkcho@kitech.re.kr;
Fax: +82-41-589-8580; Tel: +82-41-589-8665
In terms of chemical pathway, a direct transformation of
cellulose into HMF involves three reactions corresponding
to (1) hydrolysis of polymeric cellulose into mono-saccharide
such as glucose, so called saccharification, (2) isomerization
from aldose-type sugar to ketose-type one, allowing five-
membered ring formation, and (3) dehydrations of ketose-type
(or furanose-type if cyclized) sugar to generate final product,
HMF (Scheme 2). It means that various functions of catalysts
bSchool of Chemical and Biological Engineering, Seoul National
University, 599 Gwanak-ro, Gwanak-gu, Seoul, 151-742, South Korea.
E-mail: yslee@snu.ac.kr; Fax: +82-2-876-9625; Tel: +82-2-880-7073
† Electronic supplementary information (ESI) available: Detailed ex-
perimental and analytical procedures, seven figures including UV and
RI HPLC traces, standard curve for quantification of HMF and total
reducing sugars, NMR and MS spectra of synthetic HMF. See DOI:
10.1039/c1gc15152e
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steps, the reaction was tried at a temperature above the boiling
point of water (120 ◦C).
The results were positive to some extent. In most cases using
CrCl2, MnCl2, FeCl2, CoCl2, NiCl2, ZnCl2, higher yields of
HMF were synthesized at 120 ◦C than at 90 ◦C (green bars
in Fig. 1). Particularly, CrCl2 gave more than two times of
HMF yield (7.4% to 19%) when temperature was increased from
90 ◦C to 120 ◦C. As a next attempt, reactions were carried out
for longer reaction time (4 h) and HMF yield was increased
to 27.1% in the presence of CrCl2. Meanwhile, a similar or
less amount of HMF was obtained in the presence of other
metal chlorides. It was believed that the produced HMF was
consumed due to subsequent reaction into levulinic acid by
deformylation for an extended reaction time. In another attempt,
direct transformation of cellulose into HMF was tried under
choline chloride (CC)/citric acid (CA) known as renewable
material based ionic liquid14 and DMSO using CrCl2 at 120 ◦C
for 4 h. In both cases, HMF yields were, however, less than 5%
(inner box in Fig. 1).
Based on the above results, we realized that direct transforma-
tion of cellulose into HMF in the presence of single metal chlo-
ride was unable to afford a yield over 30%. Therefore, in order
to enhance the ability of depolymerizing cellulose, additional
metal chlorides were applied. Cu,15 Fe,16 Ru17 metal chlorides
were employed based on the recent results about hydrolytic
efficiency of cellulose into glucose and CuCl2, FeCl2, FeCl3,
RuCl3 was used in combination with CrCl2 under [EMIM]Cl
(molar ratio between two metal chlorides is CrCl2 : MCln = 4 : 1).
Reactions were carried out at 120 ◦C for 2 h. As expected, HMF
yields were improved and all the yields of HMF were more than
37%. No additional water was required for the depolymerization
of cellulose into glucose. Especially when RuCl3 was added to
CrCl2, HMF was obtained in nearly 60% yield. However, after
the reaction progressed over 4 h, HMF yield was diminished. It
was thought to be due to the same reasons previously mentioned
(Fig. 2).
Scheme 2 Chemical pathway of direct transformation of cellulose into
HMF.
should be simultaneously required for direct transformation of
cellulose into HMF.
In an initial attempt for the ability to transform cellulose into
HMF directly, a wide range of single metal chlorides including
CrCl2, MnCl2, FeCl2, FeCl3, CoCl2·6H2O (simply called CoCl2
in the following), NiCl2, CuCl2, ZnCl2, MoCl3, VCl3, RuCl3
were assayed under imidazolium-type ionic liquid, ethylmethyl-
imdazolium chloride ([EMIM]Cl) that is class of solvents
capable of dissolving cellulose.12 When reactions were carried
out using single metal chloride at 90 ◦C for 2 h, HMF yields
obtained from all the reactions were less than 15% (blue bars
in Fig. 1).13 Although it was reported that HMF synthetic yield
from glucose, using CrCl2 in [EMIM]Cl under these conditions
was approximately 70%,6 only 7.4% of HMF was obtained
from cellulose. It indicates that CrCl2 is the most powerful
metal chloride to catalyze the isomerization of aldose-type
glucose to ketose-type fructose (second step in Scheme 2) but
it is not effective to hydrolyze cellulose into glucose. Expecting
enhancement of catalytic activity in hydrolysis and dehydration
Fig. 2 Direct transformation of cellulose into HMF using two metal
chloridesin [EMIM]Cl (conditions: metal chlorides (10 mol% to cel-
lulose, total equivalent of two metal chlorides), cellulose (50 mg),
[EMIM]Cl (500 mg)); green bars: 120 ◦C, 2 h; red bars: 120 ◦C, 4 h.
Fig. 1 High throughput screening of single metal catalyst for direct
transformation of cellulose into HMF under [EMIM]Cl (conditions:
each metal catalyst (10 mol%), cellulose (50 mg), [EMIM]Cl (500 mg));
blue bars: 90 ◦C, 2 h; green bars: 120 ◦C, 2 h; red bars: 120 ◦C, 4 h
and comparison of solvents including [EMIM]Cl, cholic acid/citric acid
([CA]/[CA] = 2/1), DMSO for HMF synthesis from cellulose using
CrCl2 at 120 ◦C for 4 h (inner box).
Next, the effect of molar ratio of CrCl2 and RuCl3 was
investigated. A series of molar ratios from 10 : 1 (CrCl2 : RuCl3)
to 1 : 4 (CrCl2 : RuCl3) were screened. The reactions were carried
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◦
out at 120 C for 2 h. From the results, a molar ratio of CrCl2
dinitrosalicylic acid) was 14%.18 As previously found in screening
greater than 50% was required for efficient transformation into
HMF, and a molar ratio of 4 : 1 (CrCl2 : RuCl3) showed the
best performance (Fig. 3). In a practical aspect, the amount
of precious metal ruthenium can be reduced to a molar ratio
of 6 : 1 (CrCl2 : RuCl3) with which HMF was still obtained in
over 50% yield. In addition, gram scale-up tests and time course
experiments of HMF synthesis from cellulose using CrCl2 and
RuCl3 were performed. In a 250 mL round-bottomed flask were
placed CrCl2 and RuCl3 (8 mol% of CrCl2 and 2 mol% of RuCl3
to cellulose) and [EMIM]Cl (40 g), the mixture was elevated to
90 ◦C and stirred for 40 min. After cooling to room temperature,
4 g of cellulose was added into the reaction mixture and then it
was re-elevated to 120 ◦C and stirred in a temperature-controlled
oil bath with magnetic stirring. The reaction was a little bit
lagging at the initial stage because of heat transferring time
occurring from scale-up. Nevertheless, maximum yield of HMF
could be achieved in approximately 60% after 3 h (Fig. 4)
and yield of total reducing sugars titrated from DNS (3,5-
experiments, prolonged reaction led to exacerbation of HMF
yields due to subsequent deformylation of produced HMF into
levulinic acid, which could be confirmed from refractive index
HPLC analysis (see Fig. S3 in ESI†).
Finally, the reaction was applied to the conversion of lig-
nocellulosic raw material. Reed (Phragmites communis, Trin.)
naturally grown all over Korea was chosen as a model lignocel-
lulosic raw material.19 Under the conditions using CrCl2/RuCl3
◦
(4 : 1) in [EMIM]Cl at 120 C for 2 h, reed was converted into
HMF and furfural in 41% and 26% of yields, respectively, based
on glucan and xylan contents.
Conclusions
In conclusion, the effective catalytic conditions using CrCl2
and RuCl3 in imidazolium ionic liquid to transform cellulose
into HMF was found by high throughput screening of various
metal chlorides. Under these conditions, gram scale-up synthesis
of HMF was successfully performed and lignocellulosic raw
material, reed could be directly converted into HMF and furfural
in reasonable yields.
Acknowledgements
This work was supported by the Korea Ministry of Environ-
ment as “Converging technology project (202–091–002)” and
we acknowledge Dr Jung Kon Kim in Rural Development
Administration of Korea for generous supply of lignocellulosic
raw materials.
Notes and references
1 (a) A. J. Ragauskas, C. K. Williams, B. H. Davison, G. Britovsek, J.
Cairney, C. A. Eckert, W. J. Frederick, J. P. Hallett, D. J. Leak, C. L.
Liotta, J. R. Mielenz, R. Murphy, R. Templer and T. Tschaplinski,
Science, 2006, 311, 484; (b) G. Stephanopoulos, Science, 2007, 315,
801; (c) Y. Roma´n-Leshkov, C. J. Barrett, Z. Y. Liu and J. A. Dumesic,
Nature, 2007, 447, 982.
2 (a) J. N. Chheda, G. W. Huber and J. A. Dumesic, Angew. Chem.,
Int. Ed., 2007, 46, 7164; (b) A. Corma, S. Iborra and A. Velty, Chem.
Rev., 2007, 107, 2411.
Fig. 3 HMF yields according to molar ratio of two metal chlorides
(conditions: metal chlorides (10 mol% to cellulose, total equivalent of
two metal chlorides), cellulose (50 mg), [EMIM]Cl (500 mg), 120 ◦C,
2 h).
3 (a) Q. Gan, S. J. Allen and G. J. Taylor, J. Chem. Technol. Biotechnol.,
2005, 80, 688; (b) J. F. Saeman, Ind. Eng. Chem., 1945, 37, 43; (c) N.
Mosier, C. Wyman, B. Dale, R. Elander, Y. Y. Lee, M. Holtzapple
and M. Ladisch, Bioresour. Technol., 2005, 96, 673; (d) G. Sanchez, L.
Pilcher, C. Roslander, T. Modig, M. Galbe and G. Liden, Bioresour.
Technol., 2004, 93, 249.
4 (a) T. Werpy, G. Petersen, A. Aden, J. Bozell, J. Holladay, J. White
and A. Manheim, Top value-added chemicals from biomass, volume I:
Results of screening for potential candidates from sugars and synthesis
gas; Report DOE/GO-102004-1992, Office of Scientific and Technical
Information, U.S. Department of Energy, Oak Ridge, TN, 2004;
(b) G. W. Huber, J. N. Chheda, C. J. Barrett and J. A. Dumesic,
Science, 2005, 308, 1446; (c) J. N. Chheda, G. W. Huber and J. A.
Dumesic, Angew. Chem., Int. Ed., 2007, 46, 7164.
5 Y. Roma´n-Leshkov, J. N. Chheda and J. A. Dumesic, Science, 2006,
312, 1937.
6 H. Zhao, J. E. Holladay, H. Brown and Z. C. Zhang, Science, 2007,
316, 1597.
7 S. Hu, Z. Zhang, J. Song, Y. Zhou and B. Han, Green Chem., 2009,
11, 1746.
Fig. 4 Scale-up and time course experiment of direct transformation of
cellulose into HMF using CrCl2/RuCl3 in [EMIM]Cl (conditions: metal
chlorides (10 mol% to cellulose, total equivalent of CrCl2 and RuCl3 in
molar ratio of 4 : 1), cellulose (4 g), [EMIM]Cl (40 g), 120 ◦C).
8 G. Yong, Y. Zhang and J. Y. Ying, Angew. Chem., Int. Ed., 2008, 47,
9345.
9 R. Huang, W. Qi, R. Su and Z He, Chem. Commun., 2010, 1115.
This journal is
The Royal Society of Chemistry 2011
Green Chem., 2011, 13, 1503–1506 | 1505
©

View Article Online
10 (a) J. B. Binder and R. T. Raines, J. Am. Chem. Soc., 2009, 131, 1979;
(b) S. Zhao, M. Cheng, J. Li, J. Tian and X. Wang, Chem. Commun.,
2011, 47, 2176.
11 Z. Zhang and Z. K. Zhao, Bioresour. Technol., 2010, 101, 1111.
12 R. C. Remsing, R. P. Swatloski, R. D. Rogers and G. Moyna, Chem.
Commun., 2006, 1271.
13 HMF yields were determined from HPLC peak area at 280 nm
using standard curve ready-made with authentic HMF (For detailed
analytical procedure, see ESI†); HMF yields obtained from MoCl3,
VCl3, RuCl3were not shown in Fig. 1 due to their negligible yields
less than 5%.
14 S. Hu, Z. Zhang, Y. Zhou, B. Han, H. Fan, W. Li, J. Song and Y. Xie,
Green Chem., 2008, 10, 1280.
15 Y. Su, H. M. Brown, X. Huang, X. Zhou, J. E. Amonette and Z. C.
Zhang, Appl. Catal., A, 2009, 361, 117.
16 F. Tao, H. Song and L. Chou, ChemSusChem, 2010, 3, 1298.
17 (a) A. Fukuoka and P. L. Dhepe, Angew. Chem., Int. Ed., 2006, 45,
5161; (b) H. Kobayashi, T. Komanoya, K. Hara and A. Fukuoka,
ChemSusChem, 2010, 3, 440.
18 G. L. Miller, Anal. Chem., 1959, 31, 426.
19 The components of reed used in this experiment are 40.0% glucan,
22.0% xylan, 26.1% lignin, and 5.2% ashes.
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