The effect of imidazolium ionic liquid on the dehydration of fructose to 5-Hydroxymethylfurfural, and a room temperature catalytic system

Article abstract of DOI:10.1002/cssc.201000201

The catalytic dehydration of fructose into 5-hydroxymethylfurfural is conducted in an HCl-imidazolium ionic liquid (catalyst-solvent) system, in ambient conditions. High yields and excellent recyclability make the system a promising choice for fructose dehydration. DFT calculations suggest that the solvent "switches" the dehydration from thermodynamically unfavorable into a thermodynamically favorable reaction.

Full text of DOI:10.1002/cssc.201000201

DOI: 10.1002/cssc.201000201
The Effect of Imidazolium Ionic Liquid on the Dehydration of Fructose to 5-
Hydroxymethylfurfural, and a Room Temperature Catalytic System
[
a]
Linke Lai and Yugen Zhang*
Biomass-derived carbohydrates are promising as both carbon-
based alternative energy source and sustainable feedstock for
[
1,2]
the chemical industry.
Recently, many efforts have been de-
voted towards converting biomass into 5-hydroxymethylfurfu-
ral (HMF), a versatile and key intermediate in biofuel chemistry
[
3,4]
and the petrochemical industry.
Acidic catalysts have been
employed for the production of HMF from d-fructose in water,
[
5–7]
aprotic solvents (e.g., DMSO), and biphasic systems.
Howev-
er, at elevated temperatures the yields of the target product
have been low owing to side reactions, such as HMF decom-
[
3,8]
position and oligomerization.
Imidazolium-based ionic liq-
uids have been applied for this conversion in a number of
[9–12]
recent reports, with acids or metal salts as catalysts.
Throughout these studies, it was generally accepted that ionic
liquids may stabilize HMF in the reaction mixture and increase
[
10]
the reaction selectivity; however, the detailed role of the imi-
dazolium ionic liquid in the sugar dehydration process re-
mained to be studied. Current protocols conduct the sugar de-
hydration reaction at relatively high temperatures (80–
Scheme 1. Proposed mechanism of fructose dehydration with a metal halide
catalyst at low temperature.
[
9–12]
1208C),
which not only results in significant energy con-
[
a]
sumption but may also have other negative effects, such as
more side reactions and a shorter catalyst lifetime. Fructose de-
hydration was recently demonstrated at 508C and at room
Table 1. Conversion of fructose into HMF in BMIMCl.
[
b]
Entry
Catalyst
TiCl
T [8C]
t [h]
Yield [%]
1
2
3
4
5
6
7
8
9
4
50
50
50
50
50
50
23
23
23
23
23
4
4
4
4
4
6
6
6
48
<5
49
<5
<5
63
45
49
65
72
temperature in
a
1-butyl-3-methylimidazolium chloride
Ti(OEt)
ZrCl
4
[
13]
[14]
(BMIMCl) solvent system, using WCl6 and solid acidic resin
4
catalysts, respectively. In an effort to find more cost-effective
methods for the large-scale synthesis of HMF, we report a recy-
clable HCl–BMIMCl catalytic system for converting fructose into
HMF at room temperature. DFT calculations were carried out in
order to better understand the role of the imidazolium ionic
liquid in this process.
Zr(OEt)4
–
WCl
WCl
6
6
(HCl)
WCl6
(HCl)
–
6
6
24
24
24
10
11
<1
A study of a metal chloride–BMIMCl system (i.e., TiCl -IL) has
4
shown that the metal cation may in fact not be the actual cat-
[a] Reaction conditions: 500 mg BMIMCl, 100 mg fructose, 8 mol% cata-
lyst. [b] Yields determined by NMR analysis of the extracted product with
an external standard.
[
13]
alyst during the reaction (Scheme 1). It is known that early
transition-metal chloride salts (such as TiCl ) easily react with
4
alcohols (e.g. fructose) to form metal alkoxides and HCl. If the
metal cation is the active agent in the catalytic cycle, metal alk-
oxides should also be able to catalyze the fructose dehydration
reaction; however, this is not the case. Metal alkoxides were
found to be inactive towards fructose dehydration (Table 1, en-
tries 2 and 4). We therefore reasoned that the real catalyst
must be the acid (HCl), with metal chloride salts serving as
source. To confirm this hypothesis, the same amounts of HCl
(compared to those generated from metal chlorides) were
used as catalyst for fructose dehydration. As the results show,
HCl indeed promoted the reaction and gave even better re-
[14]
sults than metal chloride systems at low temperatures. En-
couraged by this result, the room-temperature performance of
the HCl–BMIMCl system for fructose dehydration was further
studied. With solid acid catalyst systems, BMIMCl needed to be
preheated with fructose at 808C and mixed with solvent to
[a] L. Lai, Dr. Y. G. Zhang
Institute of Bioengineering and Nanotechnology
3
1 Biopolis Way, The Nanos
Singapore 138669 (Singapore)
Fax: (+65)6478-9020
[15]
form a liquid. In contrast, when using a concentrated HCl
aqueous solution as catalyst the BMIMCl–fructose mixture
forms a low-viscosity liquid at room temperature, with or with-
out adding a small amount of solvent (e.g., CHCl3).
E-mail: ygzhang@ibn.a-star.edu.sg
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201000201.
ChemSusChem 2010, 3, 1257 – 1259
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1257

Tracking the fructose dehydration in HCl-BMIMCl system as a
function of time (Figure 1) showed that the HMF yield quickly
reached 51% in 7 h, and slowly increased to 72% in 24 h. As
expected, the reaction rate at room temperature was slower
was no, or only a trace amount of, HMF formation in the
BMIMCl system without the addition of acid catalyst at room
temperature, or if the reaction was carried out in a solvent
other than the imidazolium ionic liquid. A DFT calculation
(
B3LYP/6-31G level) was conducted to explore the energy pro-
file of the reaction. As shown in Scheme 2, there are three re-
Figure 1. Yield of fructose to HMF in BMIMCl: fructose 100 mg, BMIMCl
500 mg, HCl 50 mol%.
Scheme 2. Proposed three-step dehydration reactions from fructose to HMF.
[
9–12]
[16]
than that at higher temperature.
However, the maximum
action steps for the dehydration of fructose into HMF. Enol
HMF yield reached 80% at room temperature, with simple ad-
dition of HCl as catalyst. Subsequently, a biphasic reaction
model was also tested. Owing to the ambient reaction temper-
ature, a biphasic system was easier be realize and operate with
low-boiling extraction solvents. THF was selected as the organ-
ic phase because it can extract both HMF and a small amount
of water from the HCl–BMIMCl phase. Remarkably, the fructose
dehydration process was sped up in THF–BMIMCl biphasic
system. The yield after 24 h increased to 77%. This may due to
the in situ extraction effect of the THF phase.
2, its tautomeric aldehyde 2a, and 3 are three possible dehy-
dration intermediates. Gas-phase calculations at 298 K suggest
that the energy profiles of the first two dehydration steps (1!
2, 2!2a, and 2a!3) are actually endothermic (Figure 3A),
while the fourth reaction step is slightly exothermal, that is,
The stability of the HCl–BMIMCl catalytic system was further
studied. It was found that the whole system could be recycled
several times without using any additional HCl catalyst. The
HMF product was extracted after each run, and fructose was
added directly for the next run. The HMF yield stabilized at
81–85% (Figure 2) and the HCl catalyst was fully retained in
the ionic liquid system, as monitored by pH measurement. At
ambient temperature, the high HMF yield, low catalyst cost
and toxicity, and excellent recyclability make this simple HCl–
BMIMCl system a promising choice for fructose dehydration.
These results encouraged us to further investigate the de-
tails of the reaction. Control experiments showed that there
Figure 3. Energy diagram of fructose dehydration, calculated by DFT.
A) Energy profile calculated without adding stabilizing solvent molecules;
B) Energy profile calculated with two BMIMCl solvent molecules.
1
kcal=4.184 kJ.
the complete process from fructose to HMF is endothermic
ꢀ
1
process with a positive energy difference DE=+28.8 kcalmol
1 kcal=4.184 kJ). This would means that the fructose dehydra-
(
tion reaction is a thermodynamically unfavorable process that
should not take place at ambient conditions. Modifying the
DFT calculation model by including two imidazolium molecules
to mimic a possible (and likely hydrogen-bond mediated and
specific) solvent effect rectifies this error. As shown in Fig-
Figure 2. Yields of fructose to HMF from recycled batches in BMIMCl: fruc-
tose 180 mg, BMIMCl 1000 mg, HCl 50 mol%.
1
258
www.chemsuschem.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2010, 3, 1257 – 1259

ure 3B, the first two steps of the reaction (1!2 and 2a!3)
become slightly exothermal. Together with the exothermal
third reaction step, the energy difference of whole process is
Keywords: biomass
calculations · ionic liquids · platform chemicals
·
catalysis
·
density functional
ꢀ
1
then negative (DE=ꢀ13.3 kcalmol ) explaining why fructose
can be dehydrated into HMF at ambient conditions in the
BMIMCl system, but not in other solvents.
[1] Special issue in Science: Sustainability and Energy, Science 2007, 315,
781.
Thus, in the imidazolium IL system, acidic imidazolium mole-
cules may take the role of activating the reactants and stabiliz-
ing the products of each step through hydrogen-bonding in-
teractions (see Supporting Information). These computational
results support observations from previous experiments.
In summary, the catalytic dehydration of fructose into HMF
was conducted in an HCl–BMIMCl (catalyst–solvent) system at
ambient conditions. High HMF yields and excellent recyclability
make this simple HCl-BMIMCl system a promising choice for
fructose dehydration. DFT calculations suggest that the
BMIMCl solvent turns fructose dehydration from a thermody-
namically unfavorable into a thermodynamically favorable re-
action.
[
2] a) For recent Reviews, see: J. N. Chheda, G. W. Huber, J. A. Dumesic,
Angew. Chem. 2007, 119, 7298; Angew. Chem. Int. Ed. 2007, 46, 7164;
b) G. W. Huber, A. Corma, Angew. Chem. 2007, 119, 7320; Angew. Chem.
Int. Ed. 2007, 46, 7184; c) B. Kamm, Angew. Chem. 2007, 119, 5146;
Angew. Chem. Int. Ed. 2007, 46, 5056; d) J. O. Metzger, Angew. Chem.
2
006, 118, 710; Angew. Chem. Int. Ed. 2006, 45, 696; e) G. W. Huber, S.
Iborra, A. Corma, Chem. Rev. 2006, 106, 4044; f) J. N. Chheda, J. A. Du-
mesic, Catal. Today 2007, 123, 59; g) Y. G. Zhang, J. Y. G. Chan, Energy
Environ. Sci. 2010, 3, 408.
[
[
3] H. E. van Dam, A. P. G. Kieboom, H. van Bekkum, Starch/Staerke 1986,
3
8, 95.
4] F. W. Lichtenthaler, Acc. Chem. Res. 2002, 35, 728.
[5] Y. Roman-Leshkov, J. N. Chheda, J. A. Dumesic, Science 2006, 312, 1933.
[6] B. M. F. Kuster, Starch/Staerke 1990, 42, 314.
[
7] a) M. Mascal, E. B. Nikitin, Angew. Chem. 2008, 120, 8042; Angew. Chem.
Int. Ed. 2008, 47, 7924; b) J. B. Binder, R. T. Rainers, J. Am. Chem. Soc.
2
2
009, 131, 1979; c) F. Salak Asghari, H. Yoshida, Int. Eng. Chem. Res.
006, 45, 2163; d) K. Seri, Y. Inoue, H. Ishida, Bull. Chem. Soc. Jpn. 2001,
Experimental Section
7
4, 1145; e) S. Hu, Z. Zhang, Y. Zhou, B. Han, H. Fan, W. Li, J. Song, Y.
Xie, Green Chem. 2008, 10, 1280.
8] L. Cottier, G. Descotes, C. Neyret, H. Nigay, Ind. Aliment. Agric. 1989,
Conversion of fructose into HMF: 0.18 g fructose and 1 g BMIMCl
were mixed well in a 15 mL glass vial (predried), equipped with a
magnetic stirrer bar, with the aid of several drops of chloroform.
[
[
5
67.
9] a) C. Moreau, A. Finiels, L. Vanoye, J. Mol. Catal. A: Chem. 2006, 253,
65; b) C. Lansalot-Matras, C. Moreau, Catal. Commun. 2003, 4, 517.
10] H. Zhao, J. E. Holladay, H. Brown, Z. C. Zhang, Science 2007, 316, 1597.
0
.04 mL of concentrated HCl (50 mol%) was then added to the
1
mixture. The mixture was stirred for several minutes, after which it
became homogenous in appearance. The reaction was set aside at
room temperature for different time intervals. The reaction mixture
was then extracted with 3ꢁ10 mL of THF, and the combined THF
layers were evaporated to dryness to obtain the product, HMF.
[
[11] G. Yong, Y. Zhang, J. Y. Ying, Angew. Chem. 2008, 120, 9485; Angew.
Chem. Int. Ed. 2008, 47, 9345.
[12] a) A. Takagaki, M. Ohara, S. Nishimura, K. Ebitani, Chem. Commun. 2009,
6276; b) X. Qi, M. Watanabe, T. M. Aida, R. L. Smith, Jr., Green Chem.
2
009, 11, 1327.
Recycling experiments: Into the previous extracted ionic liquid
[13] J. Y. G. Chan, Y. G. Zhang, ChemSusChem 2009, 2, 731.
(
very low HMF concentration), a new batch of fructose (0.18 g) was
[14] a) J. B. Binder, A. V. Cefali, J. J. Blank, R. T. Raines, Energy Environ. Sci.
2010, 3, 765; b) W. Yang, A. Sen, ChemSusChem 2010, 3, 597.
added and the reaction was treated according to the procedure
described above. After the third round, the already extracted
BMIMCl was heated at 508C in vacuo to remove the dissolved
water.
[
15] X. Qi, M. Watanabe, T. M. Aida, R. L. Smith, Jr., ChemSusChem 2009, 2,
44.
9
[
16] X. Tong, Y. Li, ChemSusChem 2010, 3, 350.
[
17] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone,
B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsu-
ji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Na-
kajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Och-
terski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,
A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham,
C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wallingford
CT, 2004.
Calculation method: DFT calculations were carried out with Gaussi-
an 03 software. We employed the Becke, three-parameter, Lee–
Yang–Parr (B3LYP) exchange-correlation functional,
cludes a fraction of Hartree–Fock exchange to reduce the self-inter-
action error. In this study, 6-31(G) basis sets were used. After fully
optimizing the structure of each compound we obtained its total
energy. For each reaction, the stationary structures were obtained
by optimizing the complex structures along the intrinsic reaction
coordinate of the reaction pathway.
[17]
[18]
which in-
Further experimental details are provided in the Supporting Infor-
mation.
Acknowledgements
[
18] a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648; b) C. T. Lee, W. T. Yang, and
R. G. Parr, Phys. Rev. B 1988, 37, 785.
This work was funded by the Institute of Bioengineering and
Nanotechnology (Biomedical Research Council), Agency for Sci-
ence, Technology and Research, Singapore).
Received: July 6, 2010
Published online on September 1, 2010
ChemSusChem 2010, 3, 1257 – 1259
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
1259