Dehydration of glucose into 5-hydroxymethylfurfural in SO 3H-functionalized ionic liquids

Article abstract of DOI:10.1016/j.cclet.2014.01.044

The continuous dehydration of d-glucose into 5-hydroxymethylfurfural (HMF) was carried out under mild conditions, using SO₃H-functionalized acidic ionic liquids as catalysts and H₂O-4-methyl-2-pentanone (MIBK) biphasic system as solvent. High glucose conversion of 97.4% with HMF yield of 75.1% was obtained at 120 °C for 360 min, also, small amounts of levulinic acid (LA) and formic acid were generated. Generally, the dosage of catalyst and the initial content of glucose influenced the reaction significantly; the HMF selectivity decreased with the excessive elevation of temperature and prolonging of time; and water content in the system had a negative effect on the reaction. The ionic liquid catalyst could be recycled and exhibited constant activity for five successful runs. This paper provided a new strategy for HMF production from glucose.

Full text of DOI:10.1016/j.cclet.2014.01.044

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Chinese Chemical Letters xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Original article
Dehydration of glucose into 5-hydroxymethylfurfural
in SO3H-functionalized ionic liquids
*
Fu-Rong Tao , Chen Zhuang, Yue-Zhi Cui, Jing Xu
Shandong Provincial Key Laboratory of Fine Chemicals, Qilu University of Technology, Ji’nan 250353, China
A R T I C L E I N F O
A B S T R A C T
Article history:
The continuous dehydration of D-glucose into 5-hydroxymethylfurfural (HMF) was carried out under
Received 11 November 2013
Received in revised form 13 January 2014
Accepted 15 January 2014
Available online xxx
mild conditions, using SO3H-functionalized acidic ionic liquids as catalysts and H2O-4-methyl-2-
pentanone (MIBK) biphasic system as solvent. High glucose conversion of 97.4% with HMF yield of 75.1%
was obtained at 120 8C for 360 min, also, small amounts of levulinic acid (LA) and formic acid were
generated. Generally, the dosage of catalyst and the initial content of glucose influenced the reaction
significantly; the HMF selectivity decreased with the excessive elevation of temperature and prolonging
of time; and water content in the system had a negative effect on the reaction. The ionic liquid catalyst
could be recycled and exhibited constant activity for five successful runs. This paper provided a new
strategy for HMF production from glucose.
Keywords:
Glucose
Dehydration
HMF
ß 2014 Fu-Rong Tao. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Acidic ionic liquids
1. Introduction
tates difficult and energy-intensive isolation procedures. There-
fore, an efficient dehydration system is greatly needed.
With the diminishing of fossil fuels, the search for sustainable,
alternative energy has become critically important in recent
decades. Increasing interest has been devoted to the selective
dehydration of hexose to 5-hydroxymethylfurfural (HMF) [1,2], as
HMF and its derivatives have potential applications in the
production of fine chemicals, pharmaceuticals, plastics [3], and
liquid alkanes [4]. Presently, HMF is formed with high yield by the
acid-catalyzed dehydration of fructose [5,6]. However, the key
problem with the use of fructose is its high cost. One of the most
important starting chemicals from biomass is glucose. With its low
cost and wide supply, the conversion of glucose to HMF has
attracted much attention [7–9].
Room temperature ionic liquids (ILs), which could dissolve
carbohydrates effectively [17–19], have attracted much attention
in recent years. In pure water, the dehydration of monosaccharide
is generally nonselective, leading to many by-products besides
HMF [20]. Biphasic systems, in which a water-immiscible organic
solvent is added to extract continuously the HMF from the aqueous
phase, have also been investigated [21]. In our previous work [22],
we studied the conversion of xylose to furfural with an acidic ionic
liquid. Here, we describe an efficient method for the dehydration of
glucose into HMF with a biphasic system and SO3H-functionalized
ionic liquids as catalysts. The HMF production from glucose is
shown in Scheme 1.
For the dehydration of glucose, the selection of catalysts is very
important. Several kinds of catalysts, such as HCl, H2SO4 [10,11],
CrCl3–hydroxyapatite [9], and TiO2 [12] have been investigated.
However, the catalysts mentioned above have some disadvan-
tages, such as pollution, separation, and recycling problems. The
development of environmental friendly catalysts with high activity
is expected. In addition, the conversion of monosaccharides has
been carried out in some polar organic solvents, dimethylsulfoxide
[13], dimethylformamide [14], or acetone [11], and sub-critical or
high temperature water [15,16]. However, this approach necessi-
2. Experimental
2.1. Materials
D-Glucose (98%) was a commercial product from Sinopharm
Chemical Reagent Co., Ltd.; 5-HMF (>99%) was from Aldrich; 4-
methyl-2-pentanone (AR, >90%), formic acid (AR, >98%), and
acetonitrile (HPLC) were purchased from Tianjin chemical reagent
company (Tianjin, China); 1-methyl imidazole, 1-butyl imidazole,
1-vinyl imidazole, and 1,4-butanesultone were from Alfa Aesar and
all of them were CP grade (>99%); levulinic acid was purchased
from DaoCheng chemical company (Hong Kong, China); all other
*
Corresponding author.
E-mail address: taofurong17329@126.com (F.-R. Tao).
1001-8417/$ – see front matter ß 2014 Fu-Rong Tao. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2014.01.044
Please cite this article in press as: F.-R. Tao, et al., Dehydration of glucose into 5-hydroxymethylfurfural in SO3H-functionalized ionic
liquids, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.01.044

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35.560, 48.810, 49.985, 122.049, 123.551, 125.252, 129.353,
135.775, 139.435, 142.334. ESI-MS: m/z (+) 218.8, m/z (À) 170.7.
IL-5: 1H NMR (400 MHz, CDCl3):
0.731–0.856 (m, 2H), 0.942–
0.997 (m, 2H), 1.892 (t, 2H), 2.809 (s, 3H), 3.146 (t, 2H), 7.361 (s,
1H), 7.384 (s, 1H), 8.517 (s, 1H); 13C NMR (100 MHz, CDCl3):
OH
O
OH OH
OH
OH
HO
O
H
OH
H
HO
HO
HO
OH
d
OH
H
OH
OH
β-Glucopyranose
O
OH
Fructofuranose
-3H2O
Open-f ructose
d
20.612, 28.207, 36.114, 49.031, 50.698, 118.444 (JCF = 224.3 Hz),
122.477, 123.948, 136.025. ESI-MS: m/z (+) 218.9, m/z (À) 148.6.
O
IL-6: 1H NMR (400 MHz, D2O):
d 1.531–1.607 (m, 2H), 1.802–
OH
+2H2O
HO
HCOOH
1.915 (m, 2H), 2.724 (t, 2H), 3.675 (s, 3H), 4.028 (t, 2H), 7.179 (s,
1H), 7.242 (s, 1H), 8.471 (s, 1H); 13C NMR (100 MHz, D2O):
+
CHO
O
O
d
5-Hydroxymethyl furfural (HMF)
Formic acid
Levulinic acid (LA)
20.907, 28.204, 35.851, 49.063, 50.258, 122.336, 123.719, 136.018.
Scheme 1. A typical reaction scheme for HMF production from glucose.
ESI-MS: m/z (+) 218.6, m/z (À) 96.3.
IL-7: 1H NMR (400 MHz, CDCl3):
d 0.643–0.697 (m, 2H), 0.842–
0.913 (m, 2H), 1.255 (t, 1H), 1.884 (t, 2H), 2.252 (d, 2H), 3.166 (t,
2H), 7.342 (s, 1H), 7.742 (s, 1H), 8.724 (s, 1H); 13C NMR (100 MHz,
reagents and solvents were commercially available and used
without further purification.
CDCl3):
122.374, 135.107. ESI-MS: m/z (+) 230.9, m/z (À) 96.6.
IL-8: 1H NMR (400 MHz, D2O):
0.766 (t, 3H), 1.114–1.207 (m,
d 23.016, 23.769, 29.134, 35.735, 48.414, 74.063, 122.198,
2.2. Typical procedure for synthesis of SO3H-functionalized ionic
liquids
d
2H), 1.554–1.632 (m, 2H), 1.669–1.865 (m, 2H), 1.884–1.921 (m,
2H), 2.794 (t, 2H), 4.056 (t, 2H), 4.106 (t, 2H), 7.364 (s, 1H), 7.379 (s,
1H), 8.670 (s, 1H); 13C NMR (100 MHz, D2O):
d 12.536, 18.664,
20.862, 28.009, 31.094, 48.859, 49.266, 49.980, 122.198, 122.417,
135.115. ESI-MS: m/z (+) 260.9, m/z (À) 96.6.
The ionic liquids used in this study (Fig. 1) were synthesized as
described in the literature [23,24]. IL-1, for example, was prepared
as follows: 1-methylimidazole (16.4 g, 0.2 mol) and 1, 4-butane-
sultone (27.28 g, 0.2 mol) were mixed in a 100 mL round bottom
flask. The mixture was stirred at 42–45 8C for 17 h. The white solid
zwitterion was washed repeatedly with ether to remove non-ionic
residues, filtrated through a Buchner funnel, and dried in vacuum
for 4 h. A stoichiometric amount of trifluoroacetic acid (22.8 g,
0.2 mol) was added dropwise, and the mixture was stirred for 6 h
at 80 8C. The viscous liquid was washed three times with ether and
2.3. Typical procedure for glucose dehydration
The as-received glucose was dried for 24 h at 90 8C prior to
dehydration reaction. Experiments were carried out in a Teflon-
lined stainless steel autoclave equipped with a heating jacket. After
the catalysts (typically 0.3 g) and glucose (0.7 g) were added into
the autoclave pre-charged with water and 4-methyl-2-pentanone
(MIBK) (typically 8 mL), the reaction was started under spontane-
ous pressure by heating the mixture to the reaction temperature.
After the reaction, the reactor was removed and quickly quenched
in a cool water bath. Subsequently, filtration, extraction, and
separation were conducted; and then the organic and aqueous
phases were collected to characterize the products. For the
recycling of IL-5, HMF was extracted out from the water phase
5 times with 8 mL of ethyl acetate, after extraction, the aqueous
phase was heated at 60 8C for 24 h in a vacuum oven to remove
water and residual ethyl acetate. The IL-5 was then used directly
for the next run by adding glucose and MIBK. All results were
replicated at least three times.
dried in vacuum to form IL-1. 1H NMR (400 MHz, CDCl3):
d 1.197–
1.215 (m, 2H), 1.232–1.245 (m, 2H), 1.739 (t, 2H), 3.490 (s, 3H),
3.880 (t, 2H), 7.436 (s, 1H), 7.541 (s, 1H), 9.026 (s, 1H); 13C NMR
(100 MHz, CDCl3):
d 21.544, 27.932, 36.121, 48.857, 50.074,
116.042 (1JCF = 289.3 Hz), 120.274, 122.093, 123.902, 135.579,
162.157 (2JCF = 36.6 Hz). ESI-MS: m/z (+) 218.8, m/z (À) 112.7.
The synthesis of ionic liquids IL-2 to IL-8 followed the same
protocol as was used for the preparation of IL-1. Their NMR and
ESI-MS spectral characteristics are shown as follows:
IL-2: 1H NMR (400 MHz, D2O):
2.046 (m, 2H), 2.903 (t, 2H), 3.852 (s, 3H), 4.210 (t, 2H), 7.400
(s, 1H), 7.462 (s, 1H), 8.707 (s, 1H); 13C NMR (100 MHz, D2O):
d 1.664–1.741 (m, 2H), 1.947–
d
20.877, 28.055, 35.607, 48.865, 50.009, 122.120, 123.606, 135.934,
176.615. ESI-MS: m/z (+) 218.8, m/z (À) 58.9.
IL-3: 1H NMR (400 MHz, D2O):
d
1.615–1.668 (m, 2H), 1.875–
2.4. Analyses
1.948 (m, 2H), 2.832 (t, 2H), 3.783 (s, 3H), 4.135 (t, 2H), 7.329
(s, 1H), 7.389 (s, 1H), 8.627 (s, 1H); 13C NMR (100 MHz, D2O):
20.837, 28.010, 35.580, 48.823, 49.978, 122.076, 123.569, 135.871.
d
After each dehydration run, the consumption of glucose was
confirmed by the phenol-sulfuric acid method [25]. A mixture
containing 0.1 mL reaction samples (water-soluble portion),
0.9 mL deionized water, 1 mL 5% phenol (freshly distilled), and
5 mL 98% concentrated sulfuric acid was prepared. The analysis
was performed on an HP 8453 UV–vis spectrophotometer at about
490 nm with a slit width of 0.06 mm. The concentration of glucose
in the reacted solution was calculated based on the standard curve
obtained with glucose.
ESI-MS: m/z (+) 218.8, m/z (À) 96.5
IL-4: 1H NMR (400 MHz, D2O):
d 1.568–1.645 (m, 2H), 1.826–
1.901 (m, 2H), 2.260 (s, 3H), 2.813 (t, 2H), 3.735 (s, 3H), 4.074
(t, 2H), 7.227 (d, 2H), 7.273 (s, 1H), 7.331 (s, 1H), 7.555 (d, 2H),
8.563 (s, 1H); 13C NMR (100 MHz, D2O):
d 20.406, 20.852, 28.010,
Analysis of HMF was performed by HPLC on an HP 1090 series
equipped with a photodiode array UV detector and a zorbax eclipse
plus C18 reversed-phase column (150 mm  4.6 nm, 0.5
mm).
During this process, the column temperature remained constant at
30 8C, while the mobile phase applied was water–acetonitrile
(15:85, v/v) at the flow rate of 0.5 mL/min with UV detection at
280 nm.
In addition, for the characterization of ionic liquids, NMR
spectra were recorded on an INOVA-400 spectrometer; ESI-MS
analyses were performed by using a Waters micromass ZQ alliance
Fig. 1. Ionic liquids used in this study.
Please cite this article in press as: F.-R. Tao, et al., Dehydration of glucose into 5-hydroxymethylfurfural in SO3H-functionalized ionic
liquids, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.01.044

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3
100
95
90
85
80
75
70
spectrometer. The Hammett acidity function of ionic liquids was
recorded on an HP 8453 UV–vis spectrophotometer.
3. Results and discussion
Glucose conversion
HMF yield
3.1. Glucose dehydration in SO3H-functionalized ionic liquids
With increasing concerns on environmental protection and
sustainable development, ionic liquids as catalysts were studied in
our work. Fig. 2 shows the dehydration of glucose in eight SO3H-
functionalized ionic liquids. The catalysts were efficient for glucose
dehydration, and the acidity of the ionic liquid had large effects on
the reaction. The nature of the anion influence on the catalytic
activity of such SO3H-functionalized ionic liquids is well known.
Ionic liquids with anions p-CH3C6H4SO3À, CF3SO3À, and HSO4À (IL-
4 to IL-8) resulted in high yields of HMF. When IL-5 was used as
catalyst, glucose conversion was 97.4% and HMF yield reached
75.1%. However, SO3H-functionalized ionic liquids with anions
CF3COOÀ and CH3COOÀ (IL-1 and IL-2) showed remarkably poor
activities, perhaps because of the weak acidity of trifluoroacetic
acid and acetic acid. Phosphoric acid as anion (IL-3) showed
slightly lower activity than IL-6, most probably because of its
weaker acidity, too. The Hammett acidity functions (H0) of the
eight ionic liquids were calculated (not shown), which suggested
that the order of acidity reflected the catalytic activities of ionic
liquids.
Collectively, the results above indicated that strong acidity of
the ionic liquid was an important aspect in glucose dehydration.
Meanwhile, the structure of ionic liquids was also investigated.
Fig. 2 shows that while the anion was HSO4À and position 1 in the
imidazole ring was occupied by methyl, ethylene, n-C4H9 (IL-6 to
IL-8, respectively), the results of glucose dehydration were almost
equivalent, which means that the influence of an ionic liquid’s
structure on dehydration reaction was not as significant as that of
its acidity. Therefore, we could confirm that the acidity of the
solution had a large effect on glucose dehydration into HMF.
0.1 g
0.2 g
0.3 g
m (IL-5)/g
0.4 g
0.5 g
Fig. 3. Influence of IL-5 dosage on glucose dehydration (0.7 g glucose, 1 mL H2O,
8 mL MIBK, T = 120 8C, t = 360 min, P = 2.5 atm.).
Fig. 3, when the dosage of IL-5 was 0.1 g, the glucose conversion
reached 93.9% and HMF yield was 68.1%; while the IL-5 amount
increased from 0.1 g to 0.3 g, the yield of HMF increased from 68.1%
to 76.9%, and glucose conversion was up to 99.8%; however, when
the dosage of IL-5 increased from 0.3 g to 0.5 g, both glucose
conversion and HMF yield decreased. We considered that when IL-
1 dosage was above 0.3 g, side effects occurred, such as aldol
condensation and rehydration of HMF, which led to the decrease of
HMF selectivity and glucose conversion. The HMF yield did not
increase with IL-5 amounts over 0.3 g, which implied that there
were sufficient catalytic sites available for the substrate glucose
(0.7 g) in our system at the experimental conditions.
3.3. Effects of initial glucose concentration, reaction temperature and
time
Generally, in the dehydration of glucose, in the first step, the
reaction of glucose-fructose isomerization occurred, and then
fructose dehydrated into HMF, as indicated in Scheme 1. Kuster
et al. [26] demonstrated that in the dehydration of fructose, the
product HMF can combine with fructose and cross-polymerize to
form humins, especially in aqueous systems and aqueous mixture
systems, so initial fructose concentration has a large effect on the
selectivity of HMF. We considered that in our system, the initial
concentration of glucose also influenced the HMF yield. Table 1
shows the effects of initial glucose concentration, reaction
3.2. Influence of IL-5 dosage on glucose dehydration
As IL-5 was the most effective catalyst in our study, we chose IL-
5 as the probe to investigate the influence of reaction conditions.
Fig. 3 shows the effects of IL-5 dosage on glucose conversion and
HMF yield. The amounts of IL-5 used were 0.1 g, 0.2 g, 0.3 g, 0.4 g,
0.5 g. In the absence of IL-5, at a reaction temperature of 120 8C, no
HMF yield was observed for 120 min reaction time, and the
conversion of glucose was only 7.8% (not shown). As shown in
Table 1
100
Effects of initial glucose concentration, reaction temperature and time (0.2 g IL-5,
Glucose conversion
1 mL H2O, 8 mL MIBK, P = 2.5 atm.).
HMF yield
80
Entry
Amount of
glucose (g)
T (8C)
t (min)
Conv. (%)
Yield (%)
HMF
LA
HCOOH
60
40
20
1
2
0.3
0.5
0.7
0.9
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
120
120
120
120
80
360
360
360
360
360
360
360
360
360
180
240
300
360
420
99.8
98.7
97.4
92.4
82.5
89.6
97.4
99.3
99.7
87.5
89.6
93.1
97.4
98.6
78.4
77.1
75.1
71.7
55.2
63.3
75.1
78.5
77.9
57.4
62.8
68.3
75.1
77.2
3.20
2.95
2.79
2.48
0.98
1.77
2.79
3.42
3.51
1.98
2.15
2.44
2.79
2.83
1.27
1.17
1.11
0.98
0.39
0.70
1.11
1.36
1.39
0.79
0.85
0.97
1.11
1.12
3
4
5
6
100
120
140
150
120
120
120
120
120
7
8
0
9
IL-1 IL-2 IL-3 IL-4 IL-5 IL-6 IL-7 IL-8
10
11
12
13
14
Ionic liquids
Fig. 2. Glucose dehydration in various SO3H-functionalized ionic liquids (0.7 g
glucose, 0.2 g ionic liquids, 1 mL H2O, 8 mL MIBK, T = 120 8C, t = 360 min,
P = 2.5 atm.).
Please cite this article in press as: F.-R. Tao, et al., Dehydration of glucose into 5-hydroxymethylfurfural in SO3H-functionalized ionic
liquids, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.01.044

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temperature and time on glucose dehydration. When the glucose
weight changed from 0.3 g to 0.9 g (Table 1, entries 1–4), the yield
of HMF decreased from 78.4% to 71.7%, glucose conversion also
decreased to 92.4%. Additional increase in glucose weight led to
lower HMF selectivity and glucose conversion. This may have been
due to the generation of humins in the aqueous-MIBK biphasic
system, or that reactive compounds, such as glucose and HMF,
would collide with each other or cross polymerize. Considering the
cost of the reaction, we chose 0.7 g as the optimum initial glucose
amount.
As shown in Table 1, the reaction time and temperature played
important roles both in glucose conversion and HMF yield (entries
5–14). With the elevation of temperature and prolonging of time,
the conversion of glucose and HMF yield improved correspond-
ingly. The glucose conversion was up to 99.7% with a HMF yield of
77.9% at 150 8C for 360 min. The HMF yield increased from 55.2% to
78.5% when reaction temperature changed from 80 8C to 140 8C; as
the reaction time increased from 180 min to 360 min, the glucose
conversion changed from 87.5% to 97.4% at 120 8C.
Glucose conversion
HMF yield
100
80
60
40
20
0
1
2
3
4
5
Runs number
Fig. 5. Recycling of IL-5 catalyst (0.7 g glucose, 0.2 g IL-5, 1 mL H2O, 8 mL MIBK,
T = 120 8C, t = 360 min, P = 2.5 atm.).
The color of the solution changed from colorless to deep brown
as the reaction proceeded, which may be evidence for the
decomposition of the formed HMF. From Table 1 we could see
that when the temperature changed from 140 8C to 150 8C, HMF
yield decreased little and the yields of LA and HCOOH increased.
Three side-reactions are possible. One is the rehydration of HMF
into levulinic acid (LA) and formic acid; the second is the Aldol
condensation between HMF molecules into soluble polymers; and
the third is the cross-polymerization between HMF and glucose to
form insoluble humins. The color of reacted solutions was brown;
remaining even after HMF was extracted from the mixture. The
brown by-products were thought to be soluble polymers and
humins, which could not be quantified according to the present
methods. In our work, the decrease in HMF selectivity was due to
the side-reactions, which consumed the initial glucose and the
formed HMF, and hence reduced the yield of HMF.
slightly. When H2O:MIBK was 1:8 (v/v), we got the optimum
results. The conversion of glucose was 97.4% and HMF yield
reached 75.1%. Fig. 4 also indicates that the yield of HMF decreased
with the increase of water content. The reason was that when the
dosage of water increased, the side effects of HMF rehydration
happened, and the yield of by-product (LA) correspondingly
increased. Therefore, water content in our system had a large
influence on glucose dehydration, and also, water-MIBK biphasic
system was an effective method for the reaction. Previous study
[20] indicated that in pure water, the dehydration of fructose is
generally nonselective; in our system, MIBK was added to extract
continuously the HMF from the aqueous phase, so as to minimize
degradation reactions arising from extended HMF residence in the
reactive aqueous phase and to achieve more efficient recovery of
HMF in the subsequent isolation step.
3.4. Effect of water content on glucose dehydration
3.5. Recycling of catalyst IL-5
Water is generally thought to have a negative effect on glucose
dehydration into HMF [27,28]. Since IL-5 is a hydrophilic ionic
liquid, the influence of water content in the system on glucose
dehydration was studied. As shown in Fig. 4, when the water
content was 0.5 mL, the conversion of glucose was 95.6%, HMF and
LA yield were up to 76.3% and 2.51%, respectively. However, as
water content increased from 0.5 mL to 2.5 mL, HMF selectivity
decreased significantly, while glucose conversion increased
To study the reusability of the catalyst IL-5, the main product
HMF was separated from reaction mixture using extraction. After
the first reaction run for glucose, only the catalyst IL-5 existed in
the aqueous phase, so the organic phase was separated. Then 1 g of
distilled water was added into the reaction liquid to decrease the
viscosity of the ionic liquid and facilitate the extraction of HMF.
Subsequently, the HMF was separated from the aqueous phase by
extracting 8 times with 5 mL ethyl acetate [29]. The amount of
extracted product was examined by HPLC, which demonstrated
that ethyl acetate extraction could recover about 85%–90% of HMF.
After extraction, the solution was heated at 60 8C in a vacuum drier
until the water and residual ethyl acetate were removed
absolutely. The dried IL-5 catalyst was used directly in the next
run by adding fresh glucose and MIBK under the same reaction
conditions. In order to examine the reusability of IL-5, the recycling
tests were conducted five times. As shown in Fig. 5, the catalytic
activity of the IL-5 for the dehydration of glucose did not decrease
significantly after five runs, which demonstrated that the catalyst
IL-5 was stable in this system. The non-complete extraction of HMF
and LA and the residue of unreacted glucose in the previous run
may have slight influence on the results of the recycling test. So,
the separation and purification of HMF is a remaining subject of
future study.
Glucose conversion
HMF yield
LA yield
100
80
60
40
20
0
0.5
1.0
1.5
2.0
2.5
4. Conclusion
V (H2O)/mL
In summary, we demonstrated that SO3H-functionalized acidic
ionic liquids were efficient and excellent catalysts for the
Fig. 4. Influence of water content on the dehydration of glucose (0.7 g glucose, 0.2 g
IL-5, 8 mL MIBK, T = 120 8C, t = 360 min, P = 2.5 atm.).
Please cite this article in press as: F.-R. Tao, et al., Dehydration of glucose into 5-hydroxymethylfurfural in SO3H-functionalized ionic
liquids, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.01.044

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dehydration of glucose into 5-hydroxymethylfurfural (HMF). The
acidity of the solution had a large effect on glucose conversion and
HMF yield; the results showed that stronger acidity led to higher
catalytic activity. The dosage of the catalyst and the initial amount of
glucose also played important roles in the reaction. With the
excessive elevation of temperature and prolonging of reaction time,
the selectivity of HMF decreased, which suggested the occurrence of
the side reactions, such as rehydration, condensation, and reversion
of HMF. Glucose conversion reached 99.3% and HMF yield was 78.5%
when the reaction was performed at 140 8C for360 min. The catalyst
IL-5 was recycled, which exhibited favorable catalytic activity over
five repeated runs. The simple, efficient, low toxicity, and reusable
catalytic system has great potential for application.
Acknowledgments
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from d-fructose in subcritical water, Ind. Eng. Chem. Res. 45 (2006) 2163–2173.
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We gratefully acknowledge the financial support of the
National Natural Science Foundation of China (No. 21276149),
Shandong National Natural Science Funds (No. ZR2013BQ014) and
the Program for Scientific Research Innovation Team in Colleges
and Universities of Shandong Province.
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adsorption by ammonium sulfamate-bacterial cellulose in aqueous solutions,
Chin. Chem. Lett. 24 (2013) 253–256.
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Please cite this article in press as: F.-R. Tao, et al., Dehydration of glucose into 5-hydroxymethylfurfural in SO3H-functionalized ionic
liquids, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.01.044