Catalytic conversion of cellulose to 5-hydroxymethyl furfural using acidic ionic liquids and co-catalyst

Article abstract of DOI:10.1016/j.carbpol.2012.05.083

Efficient catalytic conversion of microcrystalline cellulose (MCC) to 5-hydroxymethyl furfural (HMF), is achieved using acidic ionic liquids (ILs) as the catalysts and metal salts as co-catalysts in the solvent of 1-ethyl-3-methylimidazo-lium acetate ([emim][Ac]). A series of acidic ILs has been synthesized and tested in conversion of MCC to HMF. The effect of reaction conditions, such as reaction time, temperature, catalyst dosage, metal salts, water dosage, Cu²⁺ concentration and various acidic ILs are investigated in detail. The results show that CuCl₂ in 1-(4-sulfonic acid) butyl-3-methylimidazolium methyl sulfate ([C₄SO ₃Hmim][CH₃SO₃]), is found to be an efficient catalyst for catalytic conversion of MCC to HMF, and 69.7% yield of HMF is obtained. A mechanism to explain the high activity of CuCl₂ in [C₄SO₃Hmim][CH₃SO₃] is proposed. To the best of our knowledge, this report first proposes that the Cu²⁺ and [C₄SO₃Hmim][CH₃SO₃] show better catalytic performance in catalytic conversion of MCC to HMF.

Full text of DOI:10.1016/j.carbpol.2012.05.083

Carbohydrate Polymers 90 (2012) 792–798
Contents lists available at SciVerse ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Catalytic conversion of cellulose to 5-hydroxymethyl furfural using acidic ionic
liquids and co-catalyst
∗
Zhen-Dong Ding, Jin-Cai Shi, Jing-Jing Xiao, Wen-Xiu Gu, Chang-Ge Zheng, Hai-Jun Wang
School of Chemical and Material Engineering, Jiangnan University, Wuxi, Jiangsu 214122, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Efficient catalytic conversion of microcrystalline cellulose (MCC) to 5-hydroxymethyl furfural (HMF),
is achieved using acidic ionic liquids (ILs) as the catalysts and metal salts as co-catalysts in the sol-
vent of 1-ethyl-3-methylimidazo-lium acetate ([emim][Ac]). A series of acidic ILs has been synthesized
and tested in conversion of MCC to HMF. The effect of reaction conditions, such as reaction time,
Received 12 January 2012
Received in revised form 8 March 2012
Accepted 22 May 2012
Available online 30 May 2012
2
+
temperature, catalyst dosage, metal salts, water dosage, Cu concentration and various acidic ILs are
investigated in detail. The results show that CuCl2 in 1-(4-sulfonic acid) butyl-3-methylimidazolium
methyl sulfate ([C4SO3Hmim][CH3SO3]), is found to be an efficient catalyst for catalytic conversion of
MCC to HMF, and 69.7% yield of HMF is obtained. A mechanism to explain the high activity of CuCl2 in
Keywords:
Cellulose
Hydrolysis
Ionic liquids
[
C4SO3Hmim][CH3SO3] is proposed. To the best of our knowledge, this report first proposes that the Cu2+
5
-Hydroxymethyl furfural
and [C4SO3Hmim][CH3SO3] show better catalytic performance in catalytic conversion of MCC to HMF.
2012 Elsevier Ltd. All rights reserved.
©
1
. Introduction
the sustainable production of HMF, a versatile and key intermedi-
ate in the bio-fuel chemistry and petrochemical industry. But it is
practically difficult to dissolve cellulose in most common organic
solvents, because of their stiff molecules and close chain packing
via numerous intermolecular and intramolecular H-bonds (Zhang,
Wu, Zhang, & He, 2005). The tight H-bond network and van der
Waals interactions greatly stabilize it, which makes it notoriously
resistant to hydrolysis.
With the rapid development of society, energy demand is
increasing, and it is projected to grow by more than 50% by 2025
Ragauskas et al., 2006). However, the exhaustible fossil fuels repre-
(
sent ∼80% of the total world energy supply. For constant production
and consumption, the presently known reserves of oil will last
around 36 years, natural gas 59 years and coal 150 years. It can
be speculated that fossil fuels cannot be considered as the world’s
main source of energy for more than one hundred years. Besides,
the use of fossil fuels presents serious environmental problems,
particularly global warming. In addition, their production costs
will increase as reserves approach exhaustion and as more expen-
sive technologies are used to explore and extract fewer attractive
resources (Goldemberg, 2007). Therefore, it can be concluded that
a sustainable energy in future depends on an increased share of
renewable energy. One of the best ways to achieve such a goal
is to convert renewable biomass to valuable fuels and products.
Key global biomass resources come from agricultural residues,
wood and herbaceous energy crops. Cellulose, the most abun-
dant biomass resource, is a key component of grass, agricultural
and wood waste, and has a highly crystalline linear polymer of
d-an-hydroglucopyranose units join together in long chains by ␤-
Recently, some researchers have investigated the dissolu-
tion and hydrolysis of cellulose. For the dissolution of cellulose,
ILs have been received attention as green solvents for cel-
lulose. Prior to the studies by Robin Rogers demonstrated
1-butyl-3-methylimidazolium salts as good solvents for cellulose
(Swatloski, Spear, Holbrey, & Rogers, 2002), and the dissolution
mechanism of cellulose in ILs was also investigated by NMR
spectroscopy (Mikkola et al., 2007). From then on, the disso-
lution of cellulose has attracted much attention. It has been
reported that some hydrophilic ILs can dissolve cellulose. For exam-
ple, 1-allyl-3-methylimidazolium chloride ([amim][Cl]) (Kosan,
Michels, & Meister, 2008), 1-ethyl-3-methyli-midazolium acetate
([emim][Ac]) (Fukaya, Sugimoto, & Ohno, 2006) and 1-allyl-3-
methyli-midazolium formate ([amim][Fo]) (Fu, Mazza, & Tamaki,
2010). Due to the increased interest and demand for industrial
application, substantial effort has been devoted to the development
of appropriate hydrolysis schemes, including catalysis using min-
eral acids, enzyme-drivenreactions and heteropolyacid. However,
there are many disadvantages of these processes, such as the use
1
,4-glycosidic bonds (Zhang & Lynd, 2004). Moreover, it has the
potential to become a promising alternative to fossil resources for
◦
∗ Corresponding author.
E-mail address: wanghj329@hotmail.com (H.-J. Wang).
of mineral acids is efficient at high temperature (170–240 C), the
corrosion of equipments is very serious, and the generation of large
0
144-8617/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carbpol.2012.05.083

Z.-D. Ding et al. / Carbohydrate Polymers 90 (2012) 792–798
793
amounts of acid waste water; In enzymatic hydrolysis, the obvious
disadvantages are the low activity, high cost of enzymes; In het-
eropoly acids hydrolysis, the inherent advantages are their high
catalytic activity, reusability, fewer side reactions, strong Brønsted
acidity and so on. Moreover, a remarkably high yield of glucose
0.2 mol [emim][Br] and 0.1 mol Pb(Ac) ·3H O were separately dis-
2
2
solved in solutions of methanol–water (4:1, v/v). Upon mixing the
two solutions, a precipitate of PbBr2 was produced, which was
◦
removed by filtration after cooling at −20 C overnight. The solvent
was removed from the filtrate by rotary evaporation, and the prod-
uct [emim][Ac] was obtained by being dried in vacuum for 2 days
(
82.4%) is obtained (Cheng et al., 2011), but the disadvantage is the
◦
1
low selectivity of HMF. Therefore, the development of a new, green
and economical process for the conversion of cellulose into HMF
under mild conditions with high selectivity is essential. Raines’s
group reported that N,N-dimethylacetamide containing lithium
chloride is a privileged solvent that enables the synthesis of HMF in
a single step, producing HMF from cellulose to obtain with a yield
of 50% (Binder & Raines, 2009). Zhao, Holladay, Brown, and Zhang
at 80 C. H NMR (400 MHz, D O): ıH (ppm) = 1.46–1.52 (m, 3H),
2
1.89–1.94 (t, 3H), 3.88–3.90 (t, 3H), 4.18–4.26 (m, 2H), 7.42–7.43
(d, 1H), 7.49–7.50 (d, 1H), 8.72 (s, 1H).
2
.2.2. Preparation of [C SO Hmim][HSO ]
4 3 4
Methylimidazole (0.11 mol) and 1,4-butane sulfone (0.10 mol)
◦
were dissolved in toluene (20 mL) and stirred for 3 h at 80 C under
a nitrogen atmosphere. A white precipitate formed which was fil-
tered, washed with diethyl ether three times, and then dried in a
vacuum. The resulting white precipitate (0.06 mol) was added to
an aqueous solution of H SO (0.06 mol), and then the mixture was
(
2007) first reported metal chlorides in IL converts sugars to 5-HMF,
the yield nearly 70% can be obtained. Zhang et al. studied the con-
version of lignocellulose into furans in the presence of CrCl3 under
microwave irradiation, the yield of HMF could be up to 45–52%
2
4
(
Zhang & Zhao, 2010). Chou’s group investigated the hydrolysis of
stirred at room temperature for 2 h. Water was removed in vacuum
cellulose by using catalytic amounts of FeCl2 in ILs, and the HMF
yield of 34% was achieved (Tao, Song, & Chou, 2010). Tao, Song,
and Chou (2011), Tao, Song, Yang, and Chou (2011) also indicated
1
to give the product. H NMR (400 MHz, D O): ıH (ppm) = 1.74–1.78
2
(
(
m, 2H), 1.99–2.06 (m, 2H), 2.93–2.96 (q, 2H), 3.89 (s, 3H), 4.23–4.26
t, 2H), 7.44 (t, 1H), 7.49–7.50 (t, 1H), 8.73 (s, 1H).
that the catalytic hydrolysis of cellulose to HMF in MnCl –IL sys-
2
tem, HMF yield was up to 37%. It can be speculated that the metal
ion in IL is demonstrated to be an efficient catalyst system for the
conversion of cellulose to HMF.
2
.2.3. Preparation of [NMP][CH SO ]
Under vigorous stirring, benzene (30 mL) was mixed with N-
3 3
methyl-2-pyrrolidone (0.1 mol) in a 50 mL flask. Then, methane
sulfonic acid (0.1 mol) was dropped slowly into the flask within
3
The catalytic conversion of cellulose to HMF consists of hydroly-
sis of cellulose to ␤-glucose, isomerization of ␤-glucose to fructose,
and fructose dehydration to HMF. Furthermore, metal ions mainly
act as the catalyst for promoting rapid conversion of the ␣-glucose
to the ␤-glucose and isomerization of ␤-glucose to fructose (Zhao
et al., 2007), while cellulose hydrolysis and fructose dehydration
can be simply achieved at acidic condition. Herein, we investigate
the conversion of MCC to HMF with several acidic ILs and metal salts
in the solvent of [emim][Ac] under mild conditions, and the high-
est yield of HMF can be obtained when the optimal conditions of
catalytic conversion of cellulose to HMF in [emim][Ac] are selected.
0 min in an ice-bath. The reaction lasted for another 4 h at room
temperature. Benzene was removed under reduced pressure and
◦
was further dried at 90 C in vacuum for 1 h, giving [NMP][CH SO ]
3
3
as a light yellow viscous liquid. 1H NMR (400 MHz, D O): ıH
2
(ppm) = 2.0–2.08 (m, 2H), 2.42–2.48 (t, 2H), 2.78 (s, 3H), 2.83 (s,
3
H), 3.48–3.54 (t, 2H).
2.2.4. Preparation of [Hmim][HSO4]
[Hmim][HSO ] was obtained by mixing 1-methylimidazole with
4
◦
concentrated sulfuric acid at 0–5 C and stirring for 2 h at room tem-
perature. The liquid was washed with ether several times and dried
2
. Methods
for 5 h in vacuum. 1H NMR (400 MHz, D O): ıH (ppm) = 1.46–1.52
2
(
7
m, 3H), 1.89–1.94 (t, 3H), 3.88–3.90 (t, 3H), 4.18–4.26 (m, 2H),
.42–7.43 (d, 1H), 7.49–7.50 (d, 1H), 8.72 (s, 1H).
2.1. Materials
MCC (AR, average particle size 90 ␮m) is a commercial prod-
uct from J&K Chemical Company. N-methylimidazole is obtained
from Changzhou Chemical Factory and further purified by distilla-
tion. 1,4-Butyl sultone is obtained from Shanghai Chemical Factory.
Bromoethane and ethyl acetate are distilled and then are stored
over molecular sieves in tightly sealed glass bottles, respectively.
N-methyl-2-pyrrolidone (99%), methane sulfonic acid (99%) and
other chemicals (AR) are commercially available and used without
further purification unless otherwise stated.
2.2.5. Preparation of [C SO Hmim][CH SO ]
4 3 3 3
Methylimidazole (0.11 mol) and 1,4-butane sulfone (0.10 mol)
were dissolved in toluene (20 mL) and stirred for 3 h at 80 C under
◦
a nitrogen atmosphere. A white precipitate formed, which was
filtered, washed with diethyl ether three times, then dried in a vac-
uum. The resulting white precipitate (0.06 mol) was dissolved in
water, and equal mole methane sulfonic acid was dropped slowly at
room temperature. After dropping, the reaction mixture was slowly
◦
heated up to 90 C and was stirred for 2 h, and then the water was
◦
removed under vacuum at 90 C, giving [C SO Hmim][CH SO ]
2.2. Synthesis procedure and characterization data of ILs
4
3
3
3
as a light yellow viscous liquid. 1H NMR (400 MHz, D O): ıH
2
(
3
(
ppm) = 1.74–1.78 (m, 2H), 1.99–2.06 (m, 2H), 2.93–2.96 (q, 2H),
.89 (s, 3H), 4.23–4.26 (t, 2H), 7.44 (t, 1H), 7.49–7.50 (t, 1H), 8.73
s, 1H).
The ILs used in this study (Fig. 1) are synthesized as described in
the literatures (Ellis, 1996; Junming, Jianchun, Zhiyue, & Jing, 2010;
Tao, Song, & Chou, 2011; Tao, Song, & Yang, et al., 2011; Yang, Zhang,
Wang, & Tong, 2006; Zhang et al., 2009).
2.2.6. Preparation of [NMP][HSO4]
[
NMP]HSO4 was obtained by mixing N-methyl-2-pyrrolidone
2
.2.1. Preparation of [emim][Ac]
◦
(
0.1 mol) with concentrated sulfuric acid (0.1 mol) at 0–5 C and
stirring for 4 h at room temperature. The liquid was then washed
[
emim][Ac] was prepared following the reported procedures:
[
emim][Br] was synthesized by refluxing the N-methylimidazole
◦
◦
with ethyl acetate (3× 10 mL) and dried at 80 C in vacuum. The
with excess bromoethane at 50 C for 48 h. The excess bromoethane
was removed by evaporation and the crude product was recrystal-
lized twice by ethyl acetate. The resulting precipitate was brownish
and was dried in vacuum for 24 h under reduced pressure. Then
IL was obtained in quantitative yield. 1H NMR (400 MHz, D O): ıH
2
(
(
ppm) = 2.01–2.09 (m, 2H), 2.42–2.48 (t, 2H), 2.84 (s, 3H), 3.50–3.54
t, 2H).

7
94
Z.-D. Ding et al. / Carbohydrate Polymers 90 (2012) 792–798
O
S
O
_
O
HO
O
N
N
CH3
O_
HO
S
N
C
O
N
O
1-ethyl-3-methylimidazolium acetate
1-(4-sulfonic acid) butyl-3-methylimidazolium
(
[emim][Ac]).
hydrogen sulfate ([C
4 3 4
SO Hmim][HSO ] )
O
O
_
O
S
+
N
_
N HO
S
O
CH3
H
O
N
O
O
N-methyl-2-pyrrolidonium methyl sulfate
N-methylimidazolium hydrogen sulfate
(
3
[NMP][CH SO
3
])
([Hmim][HSO
4
])
O
O
S
O
S
O
_
+
_
N CH3
O
N
HO
O
HO
S
N
O
H
O
O
1
-(4-sulfonic acid) butyl-3-methylimidazolium
N-methyl-2-pyrrolidonium hydrogen sulfate
([NMP][HSO ])
methyl sulfate ([C SO Hmim][CH SO ])
4
3
3
3
4
Fig. 1. Structures of ILs prepared and used in this paper.
2.3. Thermo gravimetric analyzer (TGA) of ILs
column (250 mm × 4.6 mm, 5 ␮m). The mobile phase was water-
acetonitrile (15:85, v/v) at a flow rate of 0.6 mL/min. HMF was
detected at 280 nm, and the volume for each injection was 20 ␮L.
The concentration of HMF was calculated based on the standard
curve obtained with known concentrations of the standard sub-
stance. The yield of HMF was calculated from the equation: yield
(wt%) = (weight of HMF)/(weight of cellulose put into the reac-
tor) × 100.
Considering that the thermal stability of ILs in cellulose
◦
hydrolysis temperature ranges (130–180 C). So the thermal
decomposition curves of the ILs were determined using a precisa
TGA/DSC1/1100 SF thermo gravimetric analyzer. Each sample was
analyzed in a platinum pan with nitrogen as the purge gas. In all
◦
experiments, the temperature was increased from 25 to 600 C at
◦
−1
.
a constant rate of 20 C min
3. Results and discussion
2.4. Catalytic conversion of MCC to HMF
3.1. The thermal stability of ILs
The catalytic conversion of MCC to HMF was carried out in a
round bottom flask that was heated in the oil-bath in the range
The thermal decomposition curves of the ILs were determined
◦
◦
from 130 C to 180 C. Typically, 0.5 g MCC was added into 10.0 mL
emim][Ac] solvent that was preheated under vigorous stirring
using TGA. Neglecting small initial drops in weight occurring
◦
[
near 100 C due to evaporation of retained moisture, a sin-
until a transparent solution was obtained, followed by the addi-
gle pronounced decomposition event followed by slow loss of
mass was observed in all cases. The maximum decomposition
rate temperature (Tmax) computed from the TGA traces of the
ILs. It is found that the ranges of Tmax values of [emim][Ac],
[C SO Hmim][CH SO ], [C SO Hmim][HSO ], [NMP][CH SO ],
tion of the desired 0.05–0.30 mol/L acidic IL catalyst and H O at the
2
reaction temperature. At different time intervals, 0.5 mL samples
were extracted, and quenched immediately with NaOH solution.
The solution was centrifuged at 15,000 rpm for 10 min and further
employed for the product analysis.
4
3
3
3
4
3
4
3
3
◦
◦
[NMP]HSO4 and [Hmim][HSO ] are about 230–310 C, 330–390 C,
4
◦ ◦ ◦ ◦
3
10–390 C, 150–280 C, 190–280 C and 340–400 C, respectively.
Clearly, these ILs have good thermal stability in the temperature
ranges of 130–180 C.
2.5. HMF analysis
◦
The catalytic conversion of MCC to HMF by the acidic ILs
is an extremely complex process in which a variety of reac-
tions can take place together and many products will be formed.
Based on our observation that the products detected is only HMF.
The HMF was analyzed by high performance liquid chromatog-
raphy (HPLC) on a Waters Alliance 2695 series chromatograph
equipped with UV detector and a ODS-EP C18 reversed-phase
3.2. Influence of reaction conditions on catalytic conversion of
MCC to HMF
3.2.1. Effect of reaction temperature and time
The reaction temperature is a key parameter to determine the
yield of HMF, the results on the effect of temperature are presented

Z.-D. Ding et al. / Carbohydrate Polymers 90 (2012) 792–798
795
Fig. 3. Effect of the catalyst dosage: MCC (0.35 g), [emim][Ac] (10 mL), H2O (0.4 mL),
◦
T = 160 C, t = 3.5 h.
HMF under such reaction conditions, and the conversion of MCC to
HMF can be promoted by using acid catalysts. With increasing the
dosage of catalyst 0.5–2.5 mL, the yield of HMF increases from 20.5%
and 35.3%. This increase can be attributed to an increase in the avail-
ability of the number of catalytically active sites. As mentioned by
Shimizu, Furukawa, Kobayashi, Itaya, and Satsuma (2009), the acid
catalyst with stronger Brønsted acidity could result in the higher
relative rate of acid-catalyzed cellulose hydrolysis. It should be
noted that the HMF yield shows little additional increase within
higher catalyst dosage over 1.5 mL, which implies that there are
sufficient catalytic active sites available for the substrate MCC in
the system under the experimental conditions. Therefore, consid-
ering the cost of the experiment, we chose 1.5 mL as the dosage of
[
C SO Hmim][HSO ].
4 3 4
3.2.3. Effect of metal salts
Knowing that the metal salts in IL was demonstrated to be an
efficient catalyst system for the conversion of cellulose to HMF
Binder & Raines, 2009; Zhao et al., 2007). In present work, some
(
metal salts are investigated and we first chose CuCl in our present
2
Fig. 2. (a) Effect of the reaction temperature: MCC (0.35 g), [emim][Ac] (10 mL), H2O
system. As shown in Fig. 4, the existence of metal salts can improve
the yield of HMF. Compared with other metal salts, the promoting
effect of copper salt is remarkable. In the presence of Cu2+, the yield
of HMF increases about 30%. The reason for the promotional effect
(
(
0.4 mL), [C4SO3Hmim][HSO4] (2 mL), t = 5.5 h. (b) Effect of the reaction time: MCC
0.35 g), [emim][Ac] (10 mL), H2O (0.4 mL), [C4SO3Hmim][HSO4] (2 mL), T = 160 C.
◦
in Fig. 2(a). It can be seen that the yield of HMF increases fast
2+
of the copper salt may be due to the Cu coordination interaction.
◦
◦
from 130 C to 160 C. However, the HMF yield decreases gradu-
ally when the temperature is further elevated to the higher range.
2+
In addition, the Cu could play an important role in promoting
rapid conversion of the ␣-glucose to the ␤-glucose and isomer-
ization of ␤-glucose to fructose, which improves the yield of HMF
(Zhao et al., 2007). Moreover, the comparison of the promoting cat-
alytic activity of CuCl2 and FeCl2 indicates that the yield of HMF is
higher when CuCl2 is used as co-catalyst, therefore we conclude
◦
These results show that the optimal temperature is 160 C in the
acidic IL [C SO Hmim][HSO ] catalytic conversion of MCC to HMF.
4
3
4
To show the relationship between reaction time and the yield of
HMF, the effect of reaction time is shown in Fig. 2(b). It is found
that the yield of HMF increases gradually during the reaction from
2+
2+
that the promoting effect of Cu is larger than Fe in catalytic
conversion of MCC.
0.5 h to 3.5 h. When the time is extended to 3.5 h or even longer,
the yield of HMF decreases, which indicates that the conversion to
byproducts is probably more rapid than the generation of HMF. It
is consistent with the reported results that the HMF can be con-
verted to levulinic acid, formic acid and furfural (Tao et al., 2010).
3
.2.4. Effect of water dosage
Shimizu, Uozumi, and Satsuma (2009) found in the conversion
of fructose to HMF under acidic condition, full removal of water
decreased the HMF yield while mild evacuation could improve the
HMF yield. Considering that water dosage may affect conversion
of cellulose to HMF, in this study several special experiments are
designed in order to investigate the influence of water on the con-
version of cellulose to HMF. As listed in Fig. 5, it is shown that the
◦
The highest HMF yield of 34.9% can be obtained at 160 C for 3.5 h.
3.2.2. Effect of the catalyst dosage
The performance of acid catalyst [C SO Hmim][HSO ] is exam-
4
3
4
ined under reaction conditions, such as 0.35 g MCC and 0.5–2.5 mL
◦
catalyst at 160 C for 3.5 h in 0.4 mL distilled water. It can be seen
optimal dosage of H O is 0.2 mL, we obtain the maximal yield of
2
from Fig. 3 that without catalyst, the MCC cannot be hydrolyzed into
HMF reached 62.6%. While the dosage of H O is 0.6 mL, the yield of
2

7
96
Z.-D. Ding et al. / Carbohydrate Polymers 90 (2012) 792–798
Fig. 4. Effect of metal salts: MCC (0.35 g), [emim][Ac] (10 mL), H2O (0.4 mL,
◦
C = 0.2 mol/L), [C4SO3Hmim][HSO4] (1.5 mL), T = 160 C, t = 3.5 h.
2+
Fig. 6. Effect of Cu concentration: MCC (0.35 g), [emim][Ac] (10 mL), H2O (0.2 mL),
◦
T = 160 C, t = 3.5 h, [C4SO3Hmim][HSO4] (1.5 mL).
HMF is only 47.9%. The results confirm that the presence of a small
amount of water in the reaction system does promote the reaction,
but more water has a negative effect on the conversion of cellulose
to HMF and results in the decomposition of HMF to levulinic acid,
which is consistent with the previous reports by Hu et al. (2008).
In addition, with the water content increasing, the selectivity of
the HMF decreases, the results are also in a good agreement with
previous reported by Qi, Watanabe, Aida, and Smith (2008).
3.2.6. Effect of various acidic ILs
The results of conversion of cellulose to HMF by the various
acidic ILs catalysts with co-catalyst of 0.1 mol/L CuCl2 are exhib-
ited in Fig. 7. With various acidic ILs as catalysts, the present
system is effective on the MCC conversion to HMF. It is remark-
able that the presence of SO H-functionalized ILs shows better
3
catalytic performance than other ILs and results in higher yield of
HMF. In case of [C SO Hmim][HSO ] and [C SO Hmim][CH SO ],
4
3
4
4
3
3
3
the yield of HMF is 64.9%, 69.7%, respectively. It should be noted that
[
[
C SO Hmim][HSO ] and [C SO Hmim][CH SO ] have same cation
4 3 4 4 3 3 3
3
.2.5. Effect of Cu2+ concentration
+
−
−
C SO Hmim] , but the anions are HSO , CH SO3 , respectively.
4
3
4
3
Conversion of MCC to HMF by varying the concentration of Cu2+
This implies that the anions can influence the catalytic activity of
such as SO H-functionalized ILs. Moreover, the ILs have the same
cation but containing CH SO3 anion exhibits better catalytic per-
formance than those containing HSO4 under the same conditions.
from 0.05 to 0.30 mol/L was investigated under reaction conditions:
1
can be seen that the HMF yield increases first, and then decreases
with increasing concentration of Cu2 . The HMF yield reaches a
maximum of 64.9%, when concentration of Cu2 was 0.1 mol/L.
3
◦
.5 mL of catalyst, 0.2 mL of water and at 160 C for 3.5 h (Fig. 6). It
−
3
−
+
+
◦
Fig. 5. Effect of H2O dosage: MCC (0.35 g), [emim][Ac] (10 mL), T = 160 C, t = 3.5 h,
Fig. 7. Effect of various acidic ILs: MCC (0.35 g), [emim][Ac] (10 mL), H2O (0.2 mL),
◦
C(Cu2+ = 0.2 mol/L, [C4SO3Hmim][HSO4] (1.5 mL).
C(Cu2+ = 0.1 mol/L, T = 160 C, t = 3.5 h.
)
)

Z.-D. Ding et al. / Carbohydrate Polymers 90 (2012) 792–798
797
Fig. 8. (a) Putative mechanism of CuCl2 and [C4SO3Hmim][CH3SO3] promote conversion of cellulose into ␤-glucose. (b) Putative mechanism of CuCl2 and
C4SO3Hmim][CH3SO3] promote conversion of ␤-glucose into HMF.
[

7
98
Z.-D. Ding et al. / Carbohydrate Polymers 90 (2012) 792–798
It can be concluded that the acidity and structure of ILs had large
effects on the conversion of MCC to HMF.
University Student Investigation Program (101029520) for finan-
cial support.
3.3. Mechanism of cellulose transforming to HMF
References
Binder, J. B., & Raines, R. T. (2009). Simple chemical transformation of lignocellulosic
biomass into furans for fuels and chemicals. Journal of the American Chemical
Society, 131, 1979–1985.
Cheng, M., Shi, T., Guan, H., Wang, S., Wang, X., & Jiang, Z. (2011). Clean production
of glucose from polysaccharides using a micellar heteropolyacid as a heteroge-
neous catalyst. Applied Catalysis B: Environmental, 107, 104–109.
Ellis, B. (1996). Int Pat, WO 96/18459.
Fu, D., Mazza, G., & Tamaki, Y. J. (2010). Lignin extraction from straw by ionic liquids
and enzymatic hydrolysis of the cellulosic residues. Journal of Agricultural Food
Chemistry, 58, 2915–2922.
Fukaya, Y., Sugimoto, A., & Ohno, H. (2006). Superior solubility of polysaccha-
rides in low viscosity, polar, and halogen-free 1,3-dialkylimidazolium formates.
Biomacromolecules, 7, 3295–3297.
As we know, the glycosidic bonds in cellulose are weakened
by Brønsted acid attack. A Lewis acid can also weaken the gly-
cosidic bonds through binding with a glycosidic oxygen atom in
a similar manner to protic acid, leading to the dehydration of
polysaccharide to produce monosaccharides (Guan, Cao, Guo, & Mu,
2
011). To explain the results of conversion of MCC to HMF, we pro-
pose a mechanism in which CuCl2 in [C SO Hmim]CH SO forms
4
3
3
3
n−
[
CuCl (CH SO )n]
complexes in a similar manner to LnCl3 as
reported by Hines et al. (2008). We suggest that [CuCl (CH SO )]
2
3
3
−
2
3
3
plays a role in proton transfer, and facilitates mutarotation of ␣-
Goldemberg, J. (2007). Ethanol for a sustainable energy future. Science, 315, 808–810.
Guan, J., Cao, Q., Guo, X., & Mu, X. (2011). The mechanism of glucose conversion to 5-
hydroxymethylfurfural catalyzed by metal chlorides in ionic liquid: A theoretical
study. Computational and Theoretical Chemistry, 963, 453–462.
Hines, C. C., Cordes, D. B., Griffin, S. T., Watts, S. I., Cocalia, V. A., & Rogers,
R. D. (2008). Flexible coordination environments of lanthanide complexes
grown from chloride-based ionic liquids. New Journal of Chemistry, 32,
872–877.
Hu, S., Zhang, Z., Zhou, Y., Han, B., Fan, H., Li, W., et al. (2008). Conversion of fruc-
tose to 5-hydroxymethylfurfural using ionic liquids prepared from renewable
materials. Green Chemistry, 10, 1280–1283.
Junming, X. U., Jianchun, J., Zhiyue, Z., & Jing, L. (2010). Synthesis of tributyl citrate
using acid ionic liquid as catalyst. Process Safety and Environmental Protection,
glucose. These complexes would promote rapid conversion of the
␣
-glucose to the ␤-glucose through hydrogen bonds between the
chloride anions and the hydroxyl groups (as shown in Fig. 8(a)).
The putative mechanism of CuCl2 and [C SO Hmim]CH SO pro-
4
3
3
3
mote conversion of ␤-glucose into HMF is shown in Fig. 8(b).
Intermediate 1 is generated through the interactions between the
−
hydroxyl groups in ␤-glucose and Cu atom in [CuCl (CH SO )] ,
2
3
3
characterized by binding of CHO group in the open form of glu-
−
cose to [CuCl (CH SO )] , then intermediate 1 is transformed into
2
3
3
1
,2-enediol intermediate 2, which involves the formation of a five-
8
8, 28–30.
membered-ring chelate between the two neighboring hydroxyl
groups in glucose and Cu atom, the next step occurs with the
Kosan, B., Michels, C., & Meister, F. (2008). Dissolution and forming of cellulose with
ionic liquids. Cellulose, 15, 59–66.
conversion of the enolate 2 into intermediate 3, which can finally
Mikkola, J. P., Kirilin, A., Tuuf, J. C., Pranovich, A., Holmbom, B., Kustov, L.
M., et al. (2007). Ultrasound enhancement of cellulose processing in ionic
liquids: From dissolution towards functionalization. Green Chemistry, 9,
−
release the [CuCl (CH SO )] moiety and convert into fructose via
2
3
3
a ring closure. Then loses a water molecule and change to ene-
diol intermediate 5 and rapidly isomerizes into its aldehyde form
1229–1237.
Qi, X., Watanabe, M., Aida, T. M., & Smith, R. L., Jr. (2008). Catalytic dehydration of
fructose into 5-hydroxymethylfurfural by ion-exchange resin in mixed-aqueous
system by microwave heating. Green Chemistry, 10, 799–805.
Ragauskas, A. J., Williams, C. K., Davison, B. H., Britovsek, G., Cairney, J., Eckert, C.
A., et al. (2006). The path forward for biofuels and biomaterials. Science, 311,
6
, and then [C SO Hmim][HSO ] interacts with the oxygen atoms
4 3 4
connected with C2 and aldehyde group leading to the formation
of intermediate 7, Subsequently releases a water molecule to pro-
duce the C1 C2 in 7, follows by the removal of a water molecule
to give the C3 C4 in the product HMF. Then with the effect of
484–489.
Shimizu, K., Furukawa, H., Kobayashi, N., Itaya, Y., & Satsuma, A. (2009). Effects
of Brønsted and Lewis acidities on activity and selectivity of heteropolyacid-
based catalysts for hydrolysis of cellobiose and cellulose. Green Chemistry, 11,
[
C SO Hmim][HSO ], the HMF is combined with water to generate
4 3 4
1627–1632.
levulinic acid or lost formaldehyde to produce furfural.
Shimizu, K., Uozumi, R., & Satsuma, A. (2009). Enhanced production of hydrox-
ymethylfurfural from fructose with solid acid catalysts by simple water removal
methods. Catalysis Communications, 10, 1849–1853.
4
. Conclusion
Swatloski, R., Spear, S., Holbrey, J., & Rogers, R. (2002). Dissolution of cellose with
ionic liquids. Journal of American Chemical Society, 124, 4974–4975.
Tao, F., Song, H., & Chou, L. (2010). Hydrolysis of cellulose by using catalytic amounts
of FeCl2 in ionic liquids. ChemSusChem, 3, 1298–1303.
Tao, F., Song, H., & Chou, L. (2011). Hydrolysis of cellulose in SO3H-functionalized
ionic liquids. Bioresource technology, 102, 9000–9006.
Preparation of HMF through the conversion of MCC is one of
the most important approaches to utilize biomass as promising
substitutes for petroleum-based chemicals, and efficient catalytic
conversion of cellulose to HMF has been achieved using small
amounts of acidic ILs as catalysts and metal salts as co-catalysts
under mild conditions. [C SO Hmim][CH SO ] shows higher cat-
Tao, F., Song, H., Yang, J.,
& Chou, L. (2011). Catalytic hydrolysis of cellu-
lose into furans in MnCl -ionic liquid system. Carbohydrate Polymers, 85,
2
363–368.
4
3
3
3
2
+
Yang, J. Z., Zhang, Q. G., Wang, B., & Tong, J. (2006). A theoretical investigation of the
interactions between water molecules and ionic liquids. The Journal of Physical
Chemistry B, 110, 22521–22524.
Zhang, H., Wu, J., Zhang, J., & He, J. (2005). 1-Allyl-3-methylimidazolium chloride
room temperature ionic liquid: A new and powerful nonderivatizing solvent for
cellulose. Macromolecules, 38, 8272–8277.
Zhang, L., Xian, M., He, Y., Li, L., Yang, J., Yu, S., et al. (2009). A Brønsted acidic
ionic liquid as an efficient and environmentally benign catalyst for biodiesel
synthesis from free fatty acids and alcohols. Bioresource Technology, 100,
alytic activity among different ILs. Moreover, Cu could play an
important role in the conversion of cellulose to HMF as co-catalyst.
9.7% yield of HMF was obtained for 3.5 h at 160 C in the pres-
◦
6
ence of 1.5 mL [C SO Hmim][CH SO ] and 0.2 mL H O (C
2+
=
4
3
3
3
2
(Cu
)
0
.1 mol/L). The effective catalyst system may be proved valuable
in facilitating the conversion of cellulose into HMF. To better under-
stand the catalysis of Cu2+, the influence of different copper salts
4368–4373.
on the reaction will be studied in our future work. In addition, the
effect of MCC dosage and ILs recycling on the conversion of MCC is
remaining subjects in future studies.
Zhang, Y. H. P., & Lynd, L. R. (2004). Toward an aggregated understanding of enzy-
matic hydrolysis of cellulose: Noncomplexed cellulase systems. Biotechnology
and Bioengineering, 88, 797–824.
Zhang, Z.,
& Zhao, Z. K. (2010). Microwave-assisted conversion of lignocel-
lulosic biomass into furans in ionic liquid. Bioresource Technology, 101,
1111–1114.
Zhao, H., Holladay, J. E., Brown, H., & Zhang, Z. C. (2007). Metal chlorides in
ionic liquid solvents convert sugars to 5-hydroxymethylfurfural. Science, 316,
Acknowledgements
The authors are grateful to the Fundamental Research Funds
for the Central Universities (JUSRP211A08) and the National
1597–1600.