The synthesis of Fe-containing ionic liquid and its catalytic performance for the dehydration of fructose

Article abstract of DOI:10.1007/s11696-017-0148-1

Four Fe-containing ionic liquids (ILs) were synthesized by coupling of conventional imidazole ionic liquids [C_xmim]Cl (x = 4, 8, 12, 16) with FeCl₃ and were characterized by FT-IR, Raman, ESI-MS and TG. All of the Fe-containing ILs were applied to the conversion of fructose into 5-hydroxymethylfurfural (HMF) in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) subsequently and the result showed that [C₁₆mim]FeCl₄ exhibited excellent catalytic performance. Then the different reaction parameters with [C₁₆mim]FeCl₄ as catalyst were studied in detail. A 92.8% yield of HMF was obtained with 0.03 g [C₁₆mim]FeCl₄ and 0.1 g fructose in 1.0050 g [Bmim]Cl at 80 °C for 40 min in fructose/[Bmim]Cl solution.

Full text of DOI:10.1007/s11696-017-0148-1

Chem. Pap.
DOI 10.1007/s11696-017-0148-1
ORIGINAL PAPER
The synthesis of Fe-containing ionic liquid and its catalytic
performance for the dehydration of fructose
Hui Liu1 Yue Wang1 Wanxia Ma1 Hongwei Wang1 Deping Wang1
•
•
•
•
•
Wei Jiang2 Ming Zhang2 Cunshan Zhou3 Huaming Li1
•
•
•
Received: 26 August 2016 / Accepted: 15 February 2017
Ó Institute of Chemistry, Slovak Academy of Sciences 2017
Abstract Four Fe-containing ionic liquids (ILs) were
synthesized by coupling of conventional imidazole ionic
liquids [Cxmim]Cl (x = 4, 8, 12, 16) with FeCl3 and were
characterized by FT-IR, Raman, ESI–MS and TG. All of
the Fe-containing ILs were applied to the conversion of
fructose into 5-hydroxymethylfurfural (HMF) in 1-butyl-3-
methylimidazolium chloride ([Bmim]Cl) subsequently and
the result showed that [C16mim]FeCl4 exhibited excellent
catalytic performance. Then the different reaction param-
eters with [C16mim]FeCl4 as catalyst were studied in detail.
A 92.8% yield of HMF was obtained with 0.03 g [C16-
mim]FeCl4 and 0.1 g fructose in 1.0050 g [Bmim]Cl at
80 °C for 40 min in fructose/[Bmim]Cl solution.
received particular attention and become the most impor-
tant renewable resources to replace petroleum feedstock
(Rosatella et al. 2011; Melero et al. 2012). It is an
important process of preparing 5-hydroxymethylfurfural
(HMF) from biomass for this purpose (Takagaki et al.
2012; Van Putten et al. 2013). HMF is well known as
‘‘important platform compound’’ due to its great potential
application as a versatile intermediate between biomass-
based carbohydrate chemistry and petroleum-based indus-
trial organic chemistry (Gallezot 2012), which can be
converted into spices, pharmaceuticals, transportation fuel
and fine chemicals (Rosatella et al. 2011; Dutta et al. 2012;
Sun et al. 2016). Fructose, an abundant C6-sugar molecule,
is a potential feedstock for preparing HMF, and the interest
in converting it to HMF is increased sharply, recently
(Zhao et al. 2016; Zhou et al. 2014) .
Keywords HMF Á Fe-containing ionic liquid Á
Dehydration Á Fructose
For the conversion of fructose to HMF was described
using different catalysts or reaction mediums. Various
catalytic systems including mineral and organic acids
(Yang et al. 2011; Harmer et al. 2009), salts (Zhou et al.
2014; Liu et al. 2015), zeolites(Li et al. 2013; Dornath and
Fan, 2014), and ion-exchange resin have been broadly
studied (Li et al. 2013). However, those catalytic systems
usually suffer from some drawbacks, such as long reaction
time, the hazard of toxicity, high prices and lower fructose
conversion. In our previous works, D001-cc ion-exchange
resin is utilized for the dehydration of fructose and indi-
cates excellent catalytic performance (Li et al. 2013). The
D001-cc ion-exchange resin is inexpensive, non-poisonous
and useable. But the D001-cc ion-exchange resin is easily
broken over 100 °C and its channels are easy to be blocked
by the formed polymer in the process of fructose dehy-
dration. It restricts its application in the future. Hence,
developing an efficient and economic system for fructose
dehydration is still essential.
Introduction
Sustainable concerns and the rising of crude oil prices
prompted a surge in research for renewable feed-stock.
Biomass, as an abundant and sustainable resource, has been
& Hui Liu
lh7544@ujs.edu.cn
& Huaming Li
lihm@ujs.edu.cn
1
School of Chemistry and Chemical Engineering, Jiangsu
University, Zhenjiang 212013, People’s Republic of China
2
Institute for Energy Research, Jiangsu University,
Zhenjiang 212013, People’s Republic of China
3
School of Food and Biological Engineering, Jiangsu
University, Zhenjiang 212013, People’s Republic of China
123

Chem. Pap.
At present, Fe-containing ionic liquid is subjected to high
attention by researchers (Yao & Chu, 2013; Martinez-Ma-
gadan et al. 2012; Wang et al. 2010, 2012). Alexander et al.
(2004) reported the sulfonylation of benzene and its deriva-
tives using [Bmim]ClÁFeCl3 ionic liquid under mild condi-
tions. Wang et al. (Wang et al. 2010) studied the
depolymerization of poly(ethylene terephthalate) in ethylene
glycolusing[Bmim]FeCl4 andgoodconversionwasobtained.
Due to its excellent performance, it is widely used in different
organic reaction, such as the polymerization reaction (Kim
et al. 2008; Wei et al. 2010), Friedel–Crafts reaction of aro-
matic (HoangTran et al. 2014; Csihony et al. 2001), and AryI
Grignard cross-coupling reaction (Bica and Gaertner 2006;
Xia et al. 2012). In addition, Fe-containing ionic liquid occurs
a particular magnetization in the presence of external mag-
netic field, which makes it possible to be separated from the
reaction mixture (Lee et al. 2007). Hence, Fe-containing ionic
liquid has more valuable compared to conventional catalysts
in catalysis (Nguyen et al. 2008) and synthesis (Shang et al.
2009). However, the application of Fe-containing ionic liquid
in the dehydration of fructose has not been reported. It is,
therefore, of interest to study the catalytic performance of Fe-
Containing ionic liquids for the dehydration of fructose.
In this paper, four Fe-containing ionic liquids CxmimFeCl4
(x = 4, 8, 12 and 16) are synthesized and employed for the
dehydration of fructose. The catalytic properties of different
Fe-containing ionic liquids are studied and the optimum cat-
alyst are screened out by the preparing experiments of 5-hy-
droxymethylfurfural (HMF) from fructose. Finally, the effect
of different reaction parameters to fructose dehydration are
investigated for optimized reaction conditions in [Bmim]Cl.
40 °C for 24 h in the oil bath and a yellow solution was
obtained. Then, the solvent (ethanol) in the solution was
evaporated. Finally, the residue was washed with ethanol
and dried in vacuum at 80 °C for 24 h. Thus, the
[Bmim]FeCl4 catalyst was prepared. According to the same
method, [Cxmim]FeCl4 (x = 8, 12, 16) catalysts were
prepared by replacing [Bmim]Cl with [Cxmim]Cl (x = 8,
12, 16), respectively. [Bmim]FeCl4, [Omim]FeCl4 and
[C12mim]FeCl4 existed as liquids, whereas [C16mim]FeCl4
existed as solid at room temperature.
Characterization of catalysts
Raman tests were performed by a Thermo Scientific
DXR Smart Raman spectrometer equipped with
a
532 nm excitation. The Fourier transform infrared (FT-
IR) spectra (KBr disc) were recorded on Nicolet Model
Nexus 470 FT-IR instrument in the mid IR region
(400–4000 cm-1). Thermogravimetric scanning (TG)
analysis was performed in STA-449C Jupiter (NETZSCH
Corp) under N2 atmosphere. The testing process was
carried out from 30 to 1000 °C at a heating rate of
10 °C/min with N2 flow rate of 30 mL/min. The m/z
parameters of Fe-containing ionic liquid were character-
ized by Electrospray ionization tandem mass (ESI–MS)
(Thermo LXQ, USA).
Typical procedure for fructose dehydration
Fructose (0.1 g) and [Bmim]Cl (1.0 g) were firstly added
into the reaction bulb. The mixture was heated to form a
clear solution by an oil bath with a magnetic stirrer at a
desired reaction temperature. Then, the reaction started
after adding a certain amount of Fe-containing ionic liquid
into the mixture. After the desired time, the reaction bulb
was immediately cooled with cold water. Finally, the
reaction mixture was diluted with pure water to a certain
concentration and filtered through a syringe filter before the
HPLC analysis (Scheme 1).
Experiment
HMF (99% purity) was purchased from Wutong Spice Co.,
Ltd. 1-butyl-3-methylimidazolium chloride ([Bmim]Cl),
1-Octyl-3-methylimidazolium
chloride
([Omim]Cl),
1-lauryl-3-methylimidazolium chloride ([C12mim]Cl) and
1-cetyl-3-methylimidazolium chloride ([C16mim]Cl) were
obtained from Shanghai Cheng Jie Chemical Co., Ltd.
Fructose (B. R. grade), iron chloride (FeCl3Á6H2O, A.R.
grade), DMSO (A. R. grade), methanol alcohol (CH3OH,
L. C. grade) and ethanol (C2H5OH, L. C. grade) were
purchased from Sinopharm Chemical Reagent Co., Ltd. All
of them were used without further purification.
Preparation of Fe-containing ionic liquid
Firstly, 1-butyl-3-methylimidazolium chloride ([Bmim]Cl,
0.1 mol) was added in an ethanol solution of iron chloride
(0.1 mol) (Warnke et al. 2010). The mixture was stirred at
Scheme 1 The dehydration of fructose to HMF
123

Chem. Pap.
Analysis of product
[C mim]FeCl
16
Quantitative analysis of HMF was performed by high per-
formance liquid chromatography (HPLC), which was
equipped with a Varian ProStar325 UV–Vis detector, an
Agilent TC-C (18) column and two Varian ProStar210
pumps. The using ultraviolet wavelength was 283 nm. All
the measured parameter and the calculated formula of HMF
yield were consistent with the literature (Li et al. 2013).
4
[C mim]FeCl
4
12
[Omim]FeCl
4
[Bmim]FeCl
4
2874
Results and discussion
3141
1569
3080
3000
1164
1000
1488
1500
4000
3500
2500
2000
500
Characterization of catalysts
Temperature-responsive behavior
-1
Wavenumber(cm
)
Fig. 2 FT-IR spectra of different form Fe-containing ionic liquids
Compared with other Fe-containing catalysts, [C16-
mim]FeCl4 exists as solid under room temperature, which
is due to the long carbon chain in [C16mim]FeCl4. The
temperature-responsive behavior of [C16mim]FeCl4 is
shown in Fig. 1. [C16mim]FeCl4 is in solid state at room
temperature and starts to melt at 38.8 °C. When the tem-
perature rises to 40 °C, high-viscosity liquid is observed.
Similarly, the ionic liquid changes into solid state with the
decrease of temperature. The temperature-control effect of
[C16mim]FeCl4 can make it spontaneously separated from
the reaction system.
ring. The characteristic peaks at 1569 and 1463 cm-1 can
be attributed to the stretch vibration of C=N on the imi-
dazole ring. The characteristic peak at 1488 cm-1 is
attributed to the bending vibration of C–H. The strong peak
at 1164 cm-1 belongs to the stretch vibration of imidazole
ring (Bahr et al. 2001). According to the results, it is found
that the structures of imidazole ring is not destroyed in the
preparing process of catalysts, which may be attributed that
the cationic [Cxmim]? in [Cxmim]Cl is not involved in the
preparing process of catalysts.
FT-Raman spectroscopy
FT-IR spectroscopy
The Raman spectrum of Fe-containing catalysts is shown
in Fig. 3. Only an identical peak at 330 cm-1 is observed
in all of the Fe-containing catalysts. According to the lit-
erature, the identical peaks at 330 and 370 cm-1 in Raman
spectrum were, respectively, represented the totally sym-
metric Fe–Cl stretch vibration of FeCl4- and Fe2Cl7- (Del
Sesto et al. 2008; Pei et al. 2010). The result of Fig. 3
The FT-IR spectra of different Fe-containing ionic liquids
are presented in Fig. 2. As can be seen from the spectra, the
bands in all of the catalysts within the range from 4000 to
500 cm-1 are similar, indicating that the catalysts have a
similar structure. The bands at 3130 and 3082 cm-1 come
from the stretch vibration of heterocyclic C-H. The
adsorption at 2960 and 2874 cm-1 are assigned to the
stretch vibration of C–H of substituent on the imidazole
-
shows that only FeCl4 is existed in all of Fe-containing
catalysts, which is due to the mole ratio of 1:1 between
FeCl3 and [Cxmim]Cl (x = 4, 8, 12, 16).
ESI–MS analysis
To analyze the structures and purities of the synthesized Fe-
containing ionic liquids, ESI–MS spectra were carried out
and the results are shown in Fig. 4. It can be seen from the
positive ESI–MS of catalysts (Fig. 4a) that the characteristic
ionic peaks at m/z: 139.1, 195.2, 251.3 and 307.4 are found,
respectively, which correspond to the [Bmim]?, [Omim]?,
[C12mim]? and[C16mim]? in the Fe-containing ILs,
respectively. Hence, the cationic structures of Fe-containing
ILs have been determined. The negative spectra of Fe-
Fig. 1 Reversible
[C16mim][FeCl4]
melting
and
solidifying
behavior
of
123

Chem. Pap.
gravimetric scanning technology and the results are shown
in Fig. 5. Compared with [Cxmim]Cl (x = 4, 8, 12, 16), the
thermal stability of Fe-containing ILs is improved after the
combination of [Cxmim]Cl (x = 4, 8, 12, 16) with FeCl3.
There is no obvious mass loss before 340 °C under nitro-
gen atmosphere for all of Fe-containing ILs. The significant
weight loss is observed with temperature from 341.0 to
510.5 °C, which can be attributed to the decomposition of
imidazole ring substituent and iron chlorides. According to
the DSC results (data not shown), the corresponding
endothermic peak in the region of 310–320 k can be
attribute to the melting point of Fe-containing ILs. The
results illustrate that Fe-containing ILs are almost in the
form of liquid at room temperature.
[C16mim]FeCl4
[Bmim]FeCl4
[Omim]FeCl4
[C12mim]FeCl4
260
280
300
320
340
360
380
400
Raman shift(/cm)
The hydrophobic property
Fig. 3 Raman spectrum of different Fe-containing ionic liquids
The hydrophobic property of Fe-containing ILs is shown in
Fig. 6. It is obvious that the hydrophobic property of Fe-
containing ILs increases with the increasing length of
carbon chain on imidazole ring.
containing ILs are quite similar and a characteristic ionic
peak at m/z: 197.7 belonging to FeCl4- is observed (Fig. 4b)
in all of Fe-containing ILs. The intensity of the characteristic
ionic peak is nearly 100%, indicating that Fe-containing ILs
have been synthesized with high purities. Test results are as
follows: Electrospray MS?m/z: 139.1 [Bmim]?; MS-m/z:
197.7 [FeCl4]-; Electrospray MS?m/z: 195.2 [Omim]?;
MS-m/z: 197.7 [FeCl4]-; Electrospray MS?m/z: 251.3
[C12mim]?; MS-m/z: 197.7 [FeCl4]-; Electrospray MS?m/
z:307.06 [C16mim]?; MS-m/z: 197.7 [FeCl4]-.
Catalytic performance of Fe-containing ILs
for the dehydration of fructose
Effect of different cation in Fe-containing ILs
on the dehydration of fructose
In order to investigate the effect of different cation in Fe-
containing ILs on the dehydration of frucose, a series of
experiments were carried out under the same conditions
using four different Fe-containing ionic liquids including
[Bmim]FeCl4, [Omim]FeCl4, [C12mim]FeCl4 and [C16-
mim]FeCl4. As shown in Table 1, only 4.3% Yield of HMF
The TG curves
To carefully explore the thermal properties of Fe-contain-
ing ILs, the TG analysis were investigated by using thermal
a
b
100
50
197.66
(a-1)
(a-2)
307.36
Calculated Mass: 307.54
Calculated Mass: 251.43
Calculated Mass: 195.32
(b-1)
(b-2)
(b-3)
FeCl4- Calculated Mass197.66
50
N
N
0
100
0
197.67
197.67
251.28
50
50
N
N
0
0
100
195.19
(a-3)
(a-4)
50
50
N
N
0
0
100
197.77
139.06
Calculated Mass: 139.22(b-4)
50
50
0
N
N
0
100
200
300
400
500
600
100 150 200 250 300 350 400 450 500 550 600
m/z
m/z
Fig. 4 ESI–MS spectrum of Fe-containing ionic liquids. a and b The negative and positive EMI-MS spectrum, respectively. a-1 and b-1
[C16mim]FeCl4, a-2 and b-2 [C12mim]FeCl4, a-3 and b-3 [Omim]FeCl4, a-4 and b-4 [Bmim]FeCl4
123

Chem. Pap.
Fig. 5 TG curves of different
samples
100
80
[Omim]FeCl
OmimCl
4
[Bmim]FeCl
BminCl
4
60
40
20
0
100
80
60
40
20
0
[C mim]FeCl
12
[C mim]FeCl
C
mimCl
4
16
4
C
mimCl
12
16
0
200
400
600
800
0
200
400
600
800
o
o
T( C)
T( C)
Table 1 The effects of different catalysts on the dehydration of
fructose
Entry
Catalyst
HMF yield/%
1a
2a
3a
4a
5a
6b
7b
8b
No catalyst
4.3
70.6
75.1
78.5
86.7
65.8
66.2
66.9
72.7
68.4
5.6
[Bmim]FeCl4
[Omim]FeCl4
[C12mim]FeCl4
[C16mim]FeCl4
[Bmim]FeCl4
[Omim]FeCl4
[C12mim]FeCl4
[C16mim]FeCl4
FeCl3Á6H2O
9b
10a
11a
12a
13c
[C16mim]Cl
[C16mim]Cl ? FeCl3Á6H2O
HCl
79.0
81.9
Conditions a: catalyst 0.1 g, fructose 0.1 g, [Bmim]Cl 1.0050 g,
80 °C, 20 min
Fig. 6 The hydrophobic property of Fe-containing ILs
Conditions b: catalyst 0.1 g, fructose 0.1 g, DMSO 1.0050 g, 120 °C,
20 min
can be observed in the blank experiment (without catalyst),
showing a negligible catalytic activity of [Bmim]Cl. When
the Fe-containing ILs are applied as catalyst in [Bmim]Cl
(entry 2, entry 3, entry 4, entry 5), the HMF yield are
improved and ranges from 70.6 to 86.7%, indicating that
the catalytic activity of Fe-containing ILs is excellent.
Moreover, the catalyst activity of Fe-containing ILs
increases with the increasing of carbon chain length on
imidazole ring. This may be attributed that the hydrophobic
property and the carbon chain are beneficial to the con-
version of fructose (Zhao et al. 2007). The longer carbon
Conditions c: catalyst 2 lL, fructose 0.1 g, [Bmim]Cl 1.0050 g,
80 °C, 20 min
chain is, the more easily the enolization carries out and the
stronger hydrophobic property is, the higher the catalyst
activity.
Similar results are observed when DMSO is used as
solvent (entry 6, entry 7, entry 8, entry 9), indicating that
123

Chem. Pap.
the sequence of catalytic activity for different Fe-contain-
ing ILs is not affected by the solvent.
Table 2 The effect of the dosages of [C16mim]FeCl4 on the dehy-
dration of fructose
From the results of entry 5, entry 10, entry 11 entry 12
and entry 13, Only 5.6% yield of HMF can be obtained
when [C16mim]Cl was used as catalyst(entry 11). The
HMF yield increases to 68.4% when FeCl3 (entry 10) is
used as catalyst. This may be due to FeCl3 owns Lewis
acidity and a new catalyst ([Bmim]FeCl4) is formed
through the interaction of FeCl3 and [Bmim]Cl in the
process of fructose dehydration. When the mixture of
FeCl3 and [C16mim]Cl with the mole ratio of 1:1 is added
as catalyst(entry 12), the yield of HMF increases to 79.0%.
A 81.9% yield of HMF was obtained when HCl was used
as catalyst(entry 13). It proves that Brønsted acid exhibites
good catalytic activity for the dehydration of fructose.
However, compared with the above catalysts, [C16-
mim]FeCl4 (entry 5) has the best catalytic performance and
HMF yield reaches 86.7%. It proves that the existence of
Entry
[C16mim]FeCl4
HMF yield/%
1
2
3
4
5
6
7
0
4.3
51.5
88.5
85.2
80.7
78.2
76.9
0.02
0.03
0.05
0.09
0.12
0.15
Conditions: fructose 0.1 g, [Bmim]Cl 1.0050 g, 80 °C, 20 min
100
90
80
70
60
50
-
FeCl4 is in favor of the dehydration of fructose to HMF.
-
This may be due to the spatial structure of FeCl4 is dif-
ferent from FeCl3 (Martinez-Magadan et al. 2012).
According to all above results, [C16mim]FeCl4 has the
best catalytic activity compared to other Fe-containing
ionic liquids. Therefore, [C16mim]FeCl4 as an acid catalyst
was chosen in all the following experiments.
60oC
40
30
20
10
70oC
80oC
90oC
100oC
Effect of catalyst dosage on the dehydration of fructose
0
The dehydration reaction of fructose with different catalyst
dosage was carried out and the results are presented in
Table 2. Only 4.3% yield of 5-HMF is observed without
[C16mim]FeCl4 at 80 °C for 20 min; however, the 5-HMF
yield reaches to 51.5% when 0.02 g [C16mim]FeCl4 is
added in the same conditions. It confirmedly proved that
[C16mim]FeCl4 shows remarkable catalytic activity for the
dehydration reaction of fructose. It can be observed that
88.5% yield was obtained when the catalyst dosage
increased to 0.03 g, which stems from the fact that the
catalytic sites increase with the increase of the amount of
catalyst. Therefore, the catalytic performance is improved.
However, the HMF yield decreases gradually with con-
tinuous increasing the dosage of [C16mim]FeCl4 to 0.15 g,
which may be attributed that the over-using of catalysts
also accelerates the side reaction.
0
10
20
30
40
50
60
t(min)
Fig. 7 Temporal HMF as a function of the reaction time at different
temperatures. Conditions: [C16mim]FeCl4 0.03 g, fructose 0.1 g,
[Bmim]Cl 1.0050 g
observed at different temperatures, which shows a sharp
increase in the initial phase and then a gradual decrease.
This behavior is due to that the polycondensation of HMF
is boosted with prolonging reaction time to generate
insoluble humins and other by-products (De et al. 2011).
Meanwhile, the high temperature is beneficial to the for-
mation of HMF at initial stage. Increasing the temperature
can reduce the time of reaching the highest yield. It only
tooks 20 min to reach the maximum yield of HMF at
100 °C, but at 90, 80, 70 and 60 °C, the time consumed are
30, 40, 50 and 60 min, respectively. This is due to the face
that the dehydration of fructose is an endothermic reaction
(Choudhary et al. 2012). It is worth noting that the higher
temperature is, the faster HMF yield descends with the
prolonging reaction time. It may be because the undesir-
able side reactions are also promoted while the dehydration
reaction is accelerated under too high reaction temperature.
The effect of different temperatures on the dehydration
of fructose
The influence of different reaction temperatures, including
60, 70, 80, 90 and 100 °C, respectively, on the dehydration
of fructose is depicted in Fig. 7. It is obvious that different
temperature and time had a significant influence on the
dehydration reaction. A similar tendency of HMF yield is
123

Chem. Pap.
Therefore, the optimum condition of dehydration reaction
comprehensive consideration of the yield and economy, the
mass of 0.1 g is chosen as the optimum dosage of fructose.
is 80 °C for 40 min.
Effect of the initial addition amount of fructose on its
dehydration
Effect of different solid acid catalysts on the dehydration
of fructose
To achieve the industrialized production of HMF, it is
indispensable to explore the influence of initial addition
amount of substrate on the dehydration reaction. As can be
shown in Table 3, the HMF yield constantly rises with the
increasing addition amount of fructose when adding less
initial amount of substrate. The highest yield reaches
92.8% with 0.10 g fructose as substrate. However, when
the initial amount of fructose is over 0.10 g, HMF yield
gradually decreases with the increasing of the initial
addition amount of fructose. Especially when initial
amount of fructose increases to 0.4 g, HMF yield declines
sharply. This may be ascribed that the catalytic sites of the
reaction system are relatively high with the low initial
amount of fructose, leading to better promote dehydration
of fructose. However, when the initially added dosage of
fructose is too large, the probability of collision between
molecules is improved. The coking reaction and the cross-
linking polymerizations between generated HMF or
between fructose and HMF are conducted to generate
soluble polymers and insoluble humins, leading to decrease
the HMF yield (Chheda and Dumesic 2007). From
For further exploring the advantage of C16mimFeCl4, a
series of solid acid catalysts (resins, salts, organic–inor-
ganic hybrid, SO3H-functionalized acidic mesoporous
materials) in other researchers’ work was compared and the
result is shown in Table 4. The HMF yield reaches
75.3–90.8% in other catalytic system, which is lower than
that in C16mimFeCl4–[Bmim]Cl system (our work).
Moreover, obvious advantage of reaction time and tem-
perature is observed in our work. Hence, the C16mimFeCl4
used in synthesis of HMF from fructose has remarkable
application prospects in the future.
Recycling of C16mimFeCl4/[Bmim]Cl system
To investigate the recycling performance of the catalyst,
the reusability of the catalyst system [C16mim]FeCl4/
[Bmim]Cl is explored in the experiment. Experiment was
carried out at 80 °C for 40 min. The dosage of [C16-
mim]FeCl4, [Bmim]Cl and fructose was 0.03, 1.0050 and
0.1 g, respectively. After the first reaction stopped run, 1 g
of distilled water was added to reduce the viscosity of ionic
liquid, thus facilitating the subsequent extraction of HMF.
The separation of HMF from the mixture was carried out
by extracting with ethyl acetate (Qi et al. 2009). It can be
found through UV–Vis that 90–95% of HMF could be
extracted by using ethyl acetate as extraction agent. Sub-
sequently, the rest of ethyl acetate and water was removed
by vacuum drying at 60 °C for 24 h. Fresh fructose was
directly added into the dried mixture for the next reaction.
As shown in Fig. 8, the yield of HMF decreases gradually
in the former three experiments, and declines obviously
with the increasing recycle times. The results indicate that
the catalyst system has better recycle performance in lim-
iting recycling runs. However, with the increasing times of
the catalytic system, the water generated during the
Table 3 The effect of the dosages of fructose on the the HMF yield
Entry
Ma/g
Mb/g
Cc/%
HMF yield/%
1
2
3
4
5
0.05
0.10
0.20
0.30
0.40
0.03
0.03
0.03
0.03
0.03
4.7
9.0
89.7
92.8
90.5
87.6
75.2
16.6
23.0
28.5
Conditions: [Bmim]Cl 1.0050 g, 80 °C, 40 min
a
The initial addition amount of fructose
b
The addition amount of [C16mim]FeCl4
c
The initial concentration of fructose
Table 4 The effect of different solid acid catalysts on the HMF yield
Substrate
Solvent
Catalyst
Temperature and time
HMF yield/%
References
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
[Bmim]Cl
[Bmim]Cl
[Bmim]Cl
[Bmim]Cl
[Bmim]Cl
[Bmim]Cl
[Bmim]Cl
Amberlyst-15 resin
Dowex-50wx8-100 resin
SO42-/ZrO2
80 °C, 10 min
80 °C, 10 min
100 °C, 30 min
120 °C, 1 h
100 °C, 120 min
200 °C, 4 h
83.0
81.0
88.4
80.3
75.3
90.8
92.8
Qi et al. (2009)
Qi et al. (2011)
Guo et al. (2012)
Cao et al. (2011)
Zhou et al. (2014)
Our work
SBA-15-SO3H
CrCl3Á6H2O
FeCl3
C
16mimFeCl4
80 °C, 40 min
123

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Fig. 8 Recycling of C16mimFeCl4–[Bmim]Cl system. Conditions:
fructose 0.1 g, [C16mim]FeCl4 0.03 g, [Bmim]Cl 1.0050 g, 80 °C,
40 min
reaction contacts with the active centers of the catalyst,
meanwhile the by-product generated during the reaction
covers the surface of the catalyst and reduces the active
site, ultimately leads to a decline of catalytic activity.
Meanwhile, a slight effect on the results of the recycling
experiment may be caused by the incompletely extracted
HMF and the unreacted fructose in the previous reaction.
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Conclusion
Four Fe-containing ILs were prepared and determined by
different characterization methods. All of Fe-containing
ILs still maintained the imidazole cation structure in the
original ionic liquids and owned FeCl4- anion. The effects
of cation on the dehydration of fructose were discussed and
[C16mim]FeCl4 had the excellent catalytic performance.
The yield of HMF reached to 92.8% with 0.03 g
[C16mim]FeCl4 and 0.1 g fructose in 1.0050 g [Bmim]Cl at
80 °C for 40 min.
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Acknowledgments The authors thank the financial support for this
study by the National Natural Science Foundation of China
(21106057, 21406092, 21506080, 31170672), and Advanced Talents
of Jiangsu University (10JDG143), China Postdoctoral Science
Foundation (2014T70489, 2013M541621, 1302152C).
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