Properties and catalytic activity of magnetic and acidic ionic liquids: Experimental and molecular simulation

Article abstract of DOI:10.1016/j.carbpol.2014.01.071

The exploitation of dual functional magnetic and acidic ionic liquids (MAILs) for hydrolysis of cellulose to platform chemicals can solve some practical challenges through easy separation of products and efficient catalyst recyclability. In this work, seven C_nmim/FeCl₄ MAILs were synthesized and investigated with combined experimental and molecular dynamics. The MAILs contained FeCl₄^- anions and exhibited a typical hard magnetic materials behavior with rather strong magnetic susceptibilities. These MAILs were stable up to 250-310 C, the decomposition was started up at 250/310-480-810 C in two steps with the formation of the undecomposed residue. The Gibbs energy for the reaction of glucose/xylose conversion to 5-hydroxymethylfurfural by metal chlorides in the C_nmimCl ionic liquid was studied using the density functional theory calculations and the results that C₃mim/WCl₃ may be the most hopeful catalyst. The MAILs have the potential to open up promising new catalytic systems because of their easy product separation and efficient catalyst recyclability.

Full text of DOI:10.1016/j.carbpol.2014.01.071

Carbohydrate Polymers 105 (2014) 300–307
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Properties and catalytic activity of magnetic and acidic ionic liquids:
Experimental and molecular simulation
Cunshan Zhoua,b,c,d, Xiaojie Yu , Haile Maa,b,c,∗, Xingyi Huang , Henan Zhang , Jian Jin
a
a
a
a
a
School of Food and Biological Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China
Jiangsu Provincial Research Center of Bio-process and Separation Engineering of Agri-products, Jiangsu University, 301 Xuefu Road,
b
Zhenjiang 212013, China
c
Jiangsu Provincial Key Laboratory for Physical Processing of Agricultural Products, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013, China
Heddle Initiative Research Unit, Advanced Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
d
a r t i c l e i n f o
a b s t r a c t
Article history:
The exploitation of dual functional magnetic and acidic ionic liquids (MAILs) for hydrolysis of cellulose to
platform chemicals can solve some practical challenges through easy separation of products and efficient
catalyst recyclability. In this work, seven Cnmim/FeCl4 MAILs were synthesized and investigated with
combined experimental and molecular dynamics. The MAILs contained FeCl4 anions and exhibited a
typical hard magnetic materials behavior with rather strong magnetic susceptibilities. These MAILs were
Received 22 November 2013
Received in revised form 14 January 2014
Accepted 21 January 2014
Available online 31 January 2014
−
◦
◦
stable up to 250–310 C, the decomposition was started up at 250/310–480–810 C in two steps with the
formation of the undecomposed residue. The Gibbs energy for the reaction of glucose/xylose conversion
to 5-hydroxymethylfurfural by metal chlorides in the CnmimCl ionic liquid was studied using the density
functional theory calculations and the results that C3mim/WCl3 may be the most hopeful catalyst. The
MAILs have the potential to open up promising new catalytic systems because of their easy product
separation and efficient catalyst recyclability.
Keywords:
Catalytic activity
Recyclability
Platform chemical
Dual functional ionic liquids
Molecular dynamics
©
2014 Elsevier Ltd. All rights reserved.
1
. Introduction
hydrolysis of cellulose with cellulases, mineral acids and solid acids.
Enzymatic hydrolysis of cellulose is rather effective, but the reac-
tion is sensitive to environmental contaminants, and suffers from
inefficiency and a high enzyme cost (Engel et al., 2010; Salvador
et al., 2010). Mineral acids have been comprehensively investi-
gated to catalyze the degradation of cellulose at a variety of acid
The exploitation and usage of fossil fuel is widely thought
to be the cause of serious problems such as, climate anomalies
Friedlingstein & Solomon, 2005). Reserves of fossil fuels will even-
tually disappear and this will lead energy crisis (Shafiee & Topal,
005). To prevent the imminent problems, alternative biofuels have
(
◦
2
concentrations, high temperatures (180–250 C) and high pressure.
been explored and successful stories such as first-generation bio-
fuels from corn and soybean edible oil have confirmed the practical
feasibility of biomass-to-biofuel (edible oil to gasoline) conver-
sion. However, with the use of dependent survival agricultural and
edible products and in this choice may create their own fatal prob-
lems such as food supply shortages as the world population grows
and social issues (Godfray et al., 2010). Another option is typical
and important chemical alternatives such as second-generation
biofuels, feedstocks and platform chemicals produced from non-
edible lignocellulosic biomass from agricultural waste (which has
attracted most attention to date). Since considered and recognized
as a particularly attractive option owing to its potential greener,
and sustainability and carbon neutrality (Scheme 1) (Nel & Cooper,
Furthermore, as far as safety and green concerned, degradation of
the resulting glucose and some intermediates becomes an issue at
such high temperatures. Meanwhile, large-scale use of mineral acid
suffers from several related problems such as reactor corrosion,
catalyst recovery/reuse and requires treatment of the waste, pro-
ducing lots of pollution (Torget et al., 2000). The catalytic hydrolysis
of cellulose into glucose with solid acids has the advantage of
avoiding some of the above shortcoming owing to the ease of cat-
alytic separation, recyclability and reduced damage to the corrosion
(Shimizu & Satsum, 2011). Significant progress of this catalytic con-
version has been made by using various types of particles acids with
large pore size and super acid strength. As far as the real biomass
feedstock and practical process for the hydrolysis of cellulose to glu-
cose is concerned, challenges still exist for the solid acids catalytic
system (Xu et al., 2011; Lange et al., 2012). Solid acids catalysts can-
not be directly separated when residues are formed as solid power
in the reaction process. Additionally, several important aspects also
need to be looked at, and such as economic feasible, simplicity to
2
009). Until now, a great deal of work has been carried on the
∗ Corresponding author. Tel.: +86 511 88790958; fax: +86 511 88780201.
E-mail address: mhl@ujs.edu.cn (H. Ma).
0
144-8617/$ – see front matter © 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carbpol.2014.01.071

C. Zhou et al. / Carbohydrate Polymers 105 (2014) 300–307
301
Dissolution
Levulinic
acid
Cellulose
Hemicellulose
Lignin
Hydrolysis
Glucose
Xylose
HMF
Dehydration
IL
Biomass
Furfural
Formic acid
H
O
C
n
mim+
+
-
H O
n
+ C mim /MCl
4
O
H
-
O H
MCl
4
HO
HO
HO
HO
HO
+
-
O
OH
+H O
+C
mim /MCl
O
O
2
O
n
4
O
H
O
HO
HO
4
HO
OH
ClH
O
n
+
-
OH
+C mim /MCl
OH
HO
n
OH
OH
OH
Cl
O
OH
OH
OH
OH
+
-
Cellulose
C mim /MCl
n
3
+
-
C mim /MCl
n
3
+
-
+
-
-C
n
mim /MCl4
C mim /MCl
O
n
4
+
-
OH OH
O
HO
H
HO
H
OH
-C
n
mim /MCl
4
OH OH
+
-
HO
+C mim /MCl
n
4
O
H
OH
OH
HO
OH
OH
HO
HO
OH
OH
OH
OH OH H
OH
O
2
H
2O
-
3
-3H
-
l
4
C
+
im
/M
O
m
n
HO
O
C
-
HMF
Scheme 1. Possible dissolution mechanism of cellulose in Cnmim/MCl4 MAILs and conversion of cellulose to HMF catalyzed with Cnmim/MCl4MAILs (n = 4, 6, 8, 10, 12, 14,
6).
1
enlarge, efficiency and environmental green (Huang & Fu, 2013).
Overall, economic, environmental, and sustainable aspects should
be of concern when designing new catalytic systems.
(Zhao, Holladay, Brown, & Zhang, 2007) discovered that CrCl2 in
[EMIM]Cl (1-ethyl-3-methylimidazolium chloride; an imidazolium
type ionic liquid) can efficiently catalyze the conversion of glucose
to HMF.
Ionic liquids (ILs) have gained enormous attention in the past
3
0 years. They are solvents and are often regarded as “green”,
Despite all the researches carried out in this area, there is little
explanation on the reaction mechanism for the glucose/fructose
conversion to HMF. Especially, glucose/fructose degradation in
ionic liquid/metal halide catalysts remains poorly understood
mechanistically, although somewhat experimental results have
confirmed the essential nature of Cr species and the coordination
characteristics of the complex between metal salts and sugars (Hu
et al., 2009). However, in a recent DFT computations combined with
EXAFS study, a transient binuclear Cr(II) species was reported to
be in charge of the glucose/fructose isomerization necessary step
(Pidko, Degirmenci, van Santen, & Hensen, 2010).
“
designable”, “friendly”, “non-coordinating” etc., nevertheless it is
increasingly recognized that none of these tags could be used eas-
ily. Yet, considerable research in ILs green chemistry is still learned
by trial-and-error method rather than fundamental principle of
understanding and reasonable design. Not enough is known to date
about properties and structures of these new materials in the liquid
phase nor are all observed differences in reaction outcomes as com-
pared to “conventional” solvents explained satisfactorily (Zhou, Yu,
Ma, He, & Vittayapadung, 2013a; Zhou et al., 2013b). Recently, ILs
have attracted more and more attention and have been utilized
as catalysts for the hydrolysis of lignocellulosic biomass. The first
mention of the dissolution of cellulose in an ILs was in 1934, but
the utilization of ILs in the lignocellulose biofuel conversion only
started from 2000 as a result of the energy crisis. In many of the pos-
sible biomass based chemicals, 5-hydroxymethylfurfural (HMF) is
derived from dehydration of saccharides, such as pentose, hexoses,
sucrose, cellulose and inulin, and is considered as a pivotal building
block in biomass biorefinery because it can derive a variant of ben-
eficial derivatives, including 2, 5-dimethylfuran, which is a hopeful
biofuel, 2, 5-diformylfuran, 2, 5-furandicarbaldehyde and 2, 5-
furandicarboxylic acid (Zakzeski et al., 2010). Catalytic dehydration
of pentose (fructose) to HMF making use of both homogeneous
and heterogeneous catalytic reaction systems has been investi-
gated extensively (Nishiyama et al., 2002). Notwithstanding the
conversion of fructose to HMF without catalysts, higher yields of
HMF have been realized with many catalysts, such as ion-exchange
resins, ionic liquids, zeolites, and metal halide. In 2007, Zhao et al.
Magnetic 1-butyl-3-methylimidazolium tetrachloroferrate
(bmim/FeCl ) was synthesized and first reported by Hayashi et al.
4
(Hayashi, Saha, & Hamaguchi, 2006), but they did not mention the
acidic property of the tested ILs at the same time in the paper. It
would be extremely interesting and necessary to investigate the
macroscopic and microscope responses of those multifunctional
ionic liquids to a magnet in quantitative ways. Magnetic and acidic
ionic liquids (MAILs) not only have the excellent properties of
conventional ionic liquids, such as wide liquid range, higher ionic
conductivity, excellent solubility, thermal stability and designabil-
ity by appropriate modifications of cations or anions in structures,
but also exhibit an unexpectedly strong response to an additional
magnetic field and acidic catalytic activity. These properties make
MAILs have more advantages and potential application prospects
than conventional ILs in the fields of catalytic reactions (Wang
et al., 2011; Misuka et al., 2011), solvent effects (Kim et al., 2008)
and separation processes (Pei et al., 2010; Wang et al., 2010).

3
02
C. Zhou et al. / Carbohydrate Polymers 105 (2014) 300–307
In this paper, seven Cnmim/FeCl4 MAILs with the same imid-
Thermo gravimetric analysis (TGA) was measured on a TG-DSC
PerkinElemer Pyris Diamond thermal analyzer at a heating rate of
10 C min under N2 atmosphere.
The magnetic susceptibilities of MAILs were carried out with a
MPMS (SQUID) (America, Quantum Design).
azole cationic rings were synthesized and tested in a combined
experimental and molecular dynamics simulation study, which has
not previously been reported in the literature. The catalytic activity
of the reaction of glucose and xylose conversion to HMF by metal
◦
−1
chlorides (MCl , M=Cr, Fe, Mo, W) in CnmimCl (n = 2,3,4) ionic liquid
3
(
Scheme 1) has been studied using DFT calculations. These studies
2
.4. Computational details
will provide important and fundamental references for further syn-
thesizing MAILs with stronger magnetism, and offer more chances
for the usage of MAILs in utilization of lignocellulose and for the
conversion of biomass to biofuel or derived chemicals challenging
which can solve energy crisis in future.
The coordination condition of the chromium center in the
MMIM]+ (M = methyl) cation and CrCl3 anion for ionic liquid
MMIM]/CrCl3 was studied with the method of DFT (density func-
−
[
[
tional theory) calculations (Pidko et al., 2010). In order to explain
the complex influence of the type with different cations and anions
in ILs on the catalyzed hydrolysis reaction, and to acquire molec-
ular level mechanism of the exclusive efficiencies of chromium
N-heterocyclic carbenes, a reduced model was put forward in
this work. In the initial and preliminary geometry, the deproto-
nated [BMIM] (1-butyl-3-methylimidazolium) ligand was bound
2
. Methods
2
.1. Materials
N-Methylimidazole (≥99.0%), methanesulfonyl chloride
III
to Cr Cl3 through the lone pair of electrons of the carbon atom
(
≥99.7%), triethyl amine (≥99.5%), diethylene glycol (≥99.0%),
which is located between two highly electronegative nitrogen
atoms, resulting in the construction of a direct Cr C bond and a
tetrahedral Cr Cl species. It is known that the structure of depro-
tonated [BMIM] ligand bears very similarity to the well-outlined
N-heterocyclic carbenes that have been engaged to stabilize and
maintain catalysts based on Cr and other elements of transition
metals (Bourissou et al., 2000). Further more, the addition of glu-
triethylene glycol (≥99.0%), tetra ethylene glycol (≥95.0%),
FeCl ·6H O, pyridine, n-chlorobutane, acetonitrile and ethyl
3
2
acetate were of analytical grade and were used without further
purification.
2
.2. Preparation of magnetic ionic liquids
cose or other monosaccharides to the [BMIM]/CrCl site comes into
being six-coordinated Cr intermediates, which were often and eas-
ily found in the crystal structures of Cr (III) complexes.
3
In the present study, the preparation of MAILs (shown in
Scheme 2), such as C mim/FeCl , was synthesized according to
4
4
the following methods (Bourissou, Guerret, Gabbai, & Bertrand,
000). Firstly, N-butylpyridiumchloride intermediates were pre-
DFT calculations were carried out using the B3LYP of nonlo-
cal three-parameter density functional, which joins the Becke’s
exchange and Lee et al. (Lee et al., 1988) conjunction functionals
(Hatakeyama et al., 2009).
2
pared by reacting of 0.2 mol N-methylpyrrolidine with 0.24 mol
◦
n-chlorobutane at 80 C for 48 h with magnetic stirring. The reac-
tion intermediate products were purified and recrystallized from
acetonitrile repeatedly, subsequently washed with ethyl acetate
for four times and dried in a vacuum oven at 60 C for 24 h. Sec-
The LANL2DZ bases fix with relativistic effective core poten-
tial (RECP) of Hay and Wadt (Hay & Wadt, 1985) was applied to
describe the transition metal elements (Cr, Fe, Mo and W), and the
6–31 G + (d,p) for all the remaining elements (Liang et al., 2009).
◦
ondly, the intermediates CnmimCl were mixed with equimolar of
FeCl ·6H O under N atmosphere with magnetic stirring at room
3
2
2
◦
temperature (∼25 C). The final products were washed with ether
3. Results and discussion
and deionized water repeatedly, purified by reduced pressure dis-
◦
tillation and dried in a vacuum oven at 60 C for 24 h successively.
3.1. Properties of the MAILs
The MAILs, Cnmim/FeCl , were obtained for further experiments.
4
The obtained Cnmim/FeCl MAILs were characterized by Raman
4
2
.3. Characterization
spectroscopy, FTIR, ultraviolet and visible absorption spectrum,
TGA and magnetic susceptibility. The MAILs represented a painted
liquid with brown or green colors. The physical characterization
was carried out by Raman spectroscopy (LabRAM HR-800) with
the ꢀ = 532 nm line from an air-cooled Nd:YAG laser at room tem-
Raman spectra were recorded by a microscopic confocal
LabRAM HR-800 Raman spectroscopy (France, Jobin-Yvon) using a
32 nm laser (He–Ne 632.8 nm, Nd:YAG laser 532 nm) beam and an
5
−
1
◦
air-cooled charge-coupled detector (CCD) with 4 cm resolution.
Fourier transform infrared spectroscopy (FTIR) spectra of the
samples (as pellets in KBr) were recorded by a Thermo Electron
Nicolet Nexus 670 FTIR spectrometer in a wavenumber range of
perature (∼25 C) under atmospheric pressure from raman shift
−
1
−1
−1
0 cm to 3500 cm with resolution 4 cm overlay times 20 at
laser power of 8 mW. The raman spectra of Cnmim/FeCl are shown
4
in Fig. 1. As shown in Fig. 1, the observed raman spectra of the
Cnmim/FeCl4 showed the very similar patterns as that of CnmimCl,
indicating that the Cnmim cation predominates. Those peaks at
−1
−1
.
4
00–4000 cm at a resolution of 4 cm
The ultraviolet and visible absorption spectrum (200–500 nm)
was detected using a Hitachi U-3500 UV–vis spectrometer.
−
1
332 cm were reported and assigned very well to the symmetric
R
R
RCl
FeCl 6H O
3 2
N
N
N
N
N
N
Cl
FeCl4
Scheme 2. Synthetic pathway of Cnmim/FeCl4 MAILs (n = 4, 6, 8, 10, 12, 14, 16). 1. R=C4H9, 2. R=C6H13, 3. R=C8H17, 4. R=C10H21, 5. R=C12H25, 6. R=C14H29, 7. R=C16H33.

C. Zhou et al. / Carbohydrate Polymers 105 (2014) 300–307
303
3
500
000
500
000
1500
3
3
2
2
1
1
500
000
500
000
500
000
C mim/FeCl
4
4
C4mim/FeCl4
C6mim/FeCl4
C8mim/FeCl4
C mim/FeCl
3
1
00
2
2
10
4
C mim/FeCl
4
1
2
80
C mim/FeCl
4
1
4
1000
C16mim/FeCl
4
5
00
6
0
0
0
5
00
100
200
Raman shit/cm
300
400
-1
0
4
4000
3500
3000
2500
2000
1500
1000
500
0
0
500
1000
1500
2000
2500
3000
3500
Wavenumbers/cm-1
-1
Raman shit/cm
Fig. 1. Raman spectra of the synthetic Cnmim/FeCl4 MAILs (n = 4, 6, 8, 10, 12, 14, 16).
C mim/FeCl
4
4
−
Fe Cl bond stretch vibrations of [FeCl4] in the literature (Lin &
C mim/FeCl
6
4
Vasam, 2005).
−1
Finding FeCl4
in these liquids is not accidental and surpris-
ing, as it has been found as the primary Fe-containing compounds
C mim/FeCl
8
4
in basic chloroaluminate melts prepared with N-n-butypyridinium
−
1
−1
C10mim/FeCl
4
chloride. However, the peak observed at 72 cm
does not correspond with a known FeCl4 feature, and this feature
and 109 cm
−
12
C mim/FeCl4
may be due to the Cnmim cation. Thus, it can also be confirmed that
−
the tested samples contain the same [FeCl4] anions (Wang et al.,
2
012).
Infrared spectra of imidazolium salts have revealed particu-
C mim/FeCl
4
1
4
lar information about metal halide interactions through hydrogen
bonding force. By comparing the FTIR spectra of Cnmim/FeCl4
with each other (shown in Fig. 2), it can be seen that the spectra
are quite similar to each other. From fingerprint area (400–1750
cm ) to characteristic frequency area (2500–4000 cm ), there
are no differences except the sharper peaks arising from the
C mim/FeCl
1
6
4
−
1
−1
3
500
3000
2500
2000
1500
1000
500
Wavenumbers/cm -1
complexes spectra. The stretching mode of the aromatic C
H
bonds (C(2)-H, C(4)-H and C(5)-H) originate from the imidaz-
olium ring structural features. The two higher frequency bands in
Fig. 2. FTIR spectra of the synthetic Cnmim/FeCl4 MAILs (n = 4, 6, 8, 10, 12, 14, 16).
−
1
−1
the range of 3149–3151 cm and 3110–3117 cm are assigned
to the stretching modes of C(4)-H or C(5)-H bond, the band
assigned to the C(2)-H stretching mode appeared at lower fre-
−1
quency regions of 3093–3096 cm . IR (KBr) of C mim/FeCl :
4
4
1
.0
3
097 m, 3112 s, 3145 s (C H aromatic); 2963 m, 2933 s, 2876 s
C mim/FeCl
4
4
4
4
−1
(
C H aliphatic) cm . In all the examined MAILs exist absorp-
C mim/FeCl
6
tion bands of imidazole ring (ꢁ
=
= ꢁ
= 3100–31,501;
= 621 cm–1).
amide III
0.8
C C ring
C − Harom
C mim/FeCl
8
for C4mim/FeCl4
ꢁ
= 1467, 1164;
ꢁ
as ring
C mim/FeCl
1
0
4
4
4
4
The analysis indicates that the Cnmim/FeCl4 MAILs have sim-
ilar cationic structures as the CnmimCl and the anions of
complexes have little effect on the chemical shifts of MAILs com-
plexes.
The ultraviolet and visible absorption spectrum of Cnmim/FeCl4
is shown in Fig. 3. The spectra resemble each other and show
four characteristic bands of the [FeCl] ion at 227, 262, 327, and
0
.6
C mim/FeCl
12
C mim/FeCl
14
0.4
C mim/FeCl
1
6
0
.2
3
54 nm (Friedman, 1952). The spectra in the ultraviolet and visible
regions indicate the presence in the composition of MAILs of parti-
cle [FeCl4 ] in the form of the anion. Similar spectra for MAILs based
0.0
–
on derivatives of imidazolium and FeCl are presented in published
3
200
250
300
350
400
450
500
data (Hayashi et al., 2006).
Wavelengh/nm
Moreover, the TGA shows that the sample does not lose weight
◦
when heated until 250 C. Contrary to what was reported by
Fig. 3. Ultraviolet and visible absorption spectra of the synthetic C mim/FeCl4
n
Holbrey and Seddon (Holbrey & Seddon, 1999) that all the ILs
samples underwent drying at 100 C at pressure of 0.5 Torr, the
MAILs (n = 4, 6, 8, 10, 12, 14, 16).
◦

3
04
C. Zhou et al. / Carbohydrate Polymers 105 (2014) 300–307
N
N
CH CH CH
+
3
2
3
CH Cl +
N
N
3
4
2.08
50.49
N
N
+
CH CH2
2
N
N
FeCl4
28.06
CH CH Cl + CH CH2
3
2
2
CH CH CH CH Cl
Molecular Weight
336.88
N
N
+
3
2
2
2
28.06
92.57
CH Cl + CH
CH
CH
3
3
2
3
50.49
42.08
Scheme 3. Possible mechanism for the two steps decomposition of Cnmim/FeCl4 MAILs (n = 4, 6, 8, 10, 12, 14, 16).
water content was calculated to be lower than 200 ppm. It can
thus be considered that the synthetic ILs contain almost no free
water (Song et al., 2010; Zhou et al., 2013c). The weight losses
1
.0
.8
0
C mim/FeCl4
4
2
6
C mim/FeCl4
of Cnmim/FeCl4 (n = 4, 6, 8, 10, 12, 14, 16) in a N atmosphere
0.6
◦
occurring in the range of 250/310 C (onset decomposition temper-
ature, Tonset) to 480 C varied from 62.01%, 60.61%, 64.14%, 66.64%,
C mim/FeCl4
0
.4
.2
8
◦
0
7
2.86%, 66.29% and 66.38% (Fig. 4) respectively, due to the decom-
position temperature (T ). In the rapid decomposition process from
0.0
0.2
d
◦
2
50 C to T , the anions thermally decompose through dealkylation,
d
-
whereas the cations mainly undergo alkyl migration and elimina-
C10mim/FeCl4
C12mim/FeCl4
C14mim/FeCl4
C16mim/FeCl4
◦
-0.4
-0.6
tion reactions (Scheme 3). In the temperature range of 480–810 C,
the weight loss 11–17%; unburned residue 12–23% remains after
◦
8
10 C.
The magnetic susceptibilities of the MAILs were carried out by
-0.8
the MPMS (SQUID), and the results are shown in Fig. 5. A small
amount of Cnmim/FeCl4 (0.0030–0.0070 g) was enclosed in a cap-
sule and measured at 293.15 K in the magnetic field range from
-1.0
-1000 -800 -600 -400 -200
0
200
400
600
800 1000
Coercivity (KA/m)
−
1
−1
−800 KA m
to 800 KA m . It can be seen that magnetization
intensities of the seven MAILs exhibit a hysteresis loop behavior in
the magnetic field (Hao et al., 2010; Li et al., 2009). The hysteresis
loop measurement was used to determine the magnetic parame-
ters such as the specific saturation magnetization (Ms), coercivity
Fig. 5. Hysteresis loops of the synthetic Cnmim/FeCl4 MAILs (n = 4, 6, 8, 10, 12, 14,
16).
3
.2. Catalytic activity of the MAILs
(
Hc) and remanence (Mr). The hysteresis loop for Cnmim/FeCl4 is
shown in Fig. 5. From the hysteresis loop, the Cnmim/FeCl4 shows
a typical hard-magnetic materials behavior, and the characteristics
parameters are shown in Table 1.
We also present an attempt to adopt the DFT calculations to
predict the reaction mechanism for glucose/xylose conversion to
HMF catalyzed by Cnmim/MCl3 complexes, and then to find out
the dependence of the reactivity difference on various MCl (M=W,
3
Mo, Cr and Fe) in the same oxidation states. Scheme 1 shows
the reaction mechanism of cellulose dissolved in Cnmim/MCl4
1
10
00
1
C mim/FeCl
and conversion of cellulose to HMF catalyzed with Cnmim/MCl .
4
4
4
4
4
III
III
III
The trivalent Cr , Mo and W complexes were processed in
high spin-state. The choice for the spin state was supported by
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
C mim/FeCl
6
C mim/FeCl
8
III
III
previous works on Cr chlorides (Robertson et al., 2003). The Fe
-
C10mim/FeCl4
C12mim/FeCl4
C14mim/FeCl4
C16mim/FeCl4
containing complex was in line with a low spin-state. In addition,
in the light of B3LYP energetics, the step related to the first water
removal is the most different of the three steps dehydration, fol-
lowed by the release of the second water, while the loss of the
Table 1
The magnetic susceptibilities of Cnmim/FeCl4 MAILs at temperature 293.15 K (n = 4,
6, 8, 10, 12, 14, 16).
2
2
Compound
Ms/(AM /kg)
Hc(KA/m)
Mr/(AM /kg)
Mr/Ms
C4mim/FeCl4
C6mim/FeCl4
C8mim/FeCl4
C10mim/FeCl4
C12mim/FeCl4
C14mim/FeCl4
C16mim/FeCl4
0.19
0.20
0.44
0.89
0.23
0.66
0.90
8.1
18.8
16.2
24.5
25.7
59.3
36.2
0.018
0.032
0.042
0.118
0.050
0.147
0.167
0.095
0.160
0.095
0.133
0.217
0.223
0.186
0
200
400
600
800
1000
Temperature/
C
º
Fig. 4. TGA curves of the synthetic Cnmim/FeCl4 MAILs in a nitrogen atmosphere
n = 4, 6, 8, 10, 12, 14, 16).
(

C. Zhou et al. / Carbohydrate Polymers 105 (2014) 300–307
305
Fig. 6. The equilibrium and transition structure geometries of the optimized state on the reaction coordinate of glucose (a)/xylose (b) dehydrations to HMF catalyzed by
Cnmim/MCl3 (n = 2, 3, 4; M=Cr, Fe, Mo, W) complexes. C2mim-E, C3mim-A, C4mim-B.
third water is considered to be the easiest step dehydration. Fig. 6
described the DFT-optimized structures of CrCl , FeCl , MoCl and
FeCl3 for xylose, respectively, in which C mim/WCl3 may be
the most promising catalyst. These preliminary calculations with
DFT simulation are intrinsically more difficult to happen than
3
3
3
3
WCl3 containing complexes involved in the dehydration at the
first water removal. The change of Gibbs energy (ꢀG) is deter-
mined at 293.15 K and the results are shown in Table 2. The Gibbs
energy barriers at 293.15 K indicated that the reaction activities
of the dehydration processes over different Cnmim/MCl3 (n = 2, 3
and 4; M=W, Mo, Cr and Fe) active sites decrease in the order
actual using CrCl , MoCl3 and WCl3 catalysts put into practice.
3
Accordingly, C mim/WCl3 possesses the highest activities in the
3
conversion of glucose/xylose to HMF and may be the most hopeful
catalyst. It comes out that various intermediates and forma-
tions along with the reaction coordinate are predicted to be
thermodynamically potential confirmed, in which the removal
of the first water is the rate control step in the reaction,
of C mim/WCl > C mim/CrCl > C mim/MoCl > C mim/FeCl for
3
3
3
3
3
3
3
3
glucose and C mim/WCl > C mim/MoCl > C mim/CrCl > C mim/
3
3
3
3
3
3
3

3
06
C. Zhou et al. / Carbohydrate Polymers 105 (2014) 300–307
Table 2
Gibbs energy of glucose/xylose dehydrations into HMF catalyzed by Cnmim/MCl3 at
reagents: A new catalyst combination of N-heterocyclic carbenes and iron,
cobalt, and nickel fluorides. Journal of the American Chemical Society, 131,
11949–11963.
2
93.15 K (n = 2, 3, 4; M=Cr, Fe, Mo, W).
Hay, P. J., & Wadt, W. R. (1985). Ab initio effective core potentials for molecular
calculations. Potentials for K to Au including the outermost core orbitals. Journal
of Chemical Physics, 82, 299–310.
Hayashi, S., Saha, S., & Hamaguchi, H. (2006). A new class of magnetic fluids:
bmim[FeCl4] and nbmim[FeCl4] ionic liquids. IEEE Transactions on Magnetics,
Cnmim/MCl3
Gibbs energy (kcal/mol)
Glucose
Xylose
C2mim/CrCl3
C2mim/FeCl3
C2mim/MoCl3
C2mim/WCl3
C3mim/CrCl3
C3mim/FeCl3
C3mim/MoCl3
C3mim/WCl3
C4mim/CrCl3
C4mim/FeCl3
C4mim/MoCl3
C4mim/WCl3
46.42
48.23
44.86
44.45
44.21
46.01
44.67
44.01
46.41
47.25
44.75
44.31
43.87
44.17
43.31
42.70
43.63
43.78
42.61
42.58
44.45
45.09
42.93
42.66
4
2, 12–14.
Hu, S. Q., Zhang, Z. F., Song, J. L., Zhou, Y. X., & Han, B. X. (2009). Efficient conversion of
glucose into 5-hydroxymethylfurfural catalyzed by a common Lewis acid SnCl4
in an ionic liquid. Green Chemistry, 11, 1746–1749.
Huang, Y. B., & Fu, Y. (2013). Hydrolysis of cellulose to glucose by solid acid catalysts.
Green Chemistry, 15, 1095–1111.
Kim, J. Y., Kim, J. T., Song, E. A., Min, Y. K., & Hamaguchi, H. O. (2008). Polypyrrole
nanostruc-tures self-assembled in magnetic ionic liquid as a template. Macro-
molecules, 41, 2886–2889.
Lange, J. P., Heide, E., Buijtenen, J., & Price, R. (2012). Furfural—A Promising platform
for lignocellulosic biofuels. ChemSusChem, 5, 150–166.
Lee, C., Yang, W., & Parr, G. (1988). Development of the colle-salvetti correlation-
energy formula into a functional of the electron density. Physical Review B, 37,
785–789.
Li, L., Huang, Y., Yan, G. P., Liu, F. J., Huang, Z. L., & Ma, Z. B. (2009). Poly (3, 4-
ethylenedioxythiophene) nanospheres synthesized in magnetic ionic liquid.
Materials Letters, 63, 8–10.
while the release of the second and third waters can become
easier.
Liang, Y., Zhou, H. L., & Yu, Z. X. (2009). Why is copper (I) complex more competent
than dirhodium(II) complex in catalytic asymmetric OH insertion reactions? A
computational study of the metal carbenoid OH insertion into water. Journal of
the American Chemical Society, 131, 17783–17785.
Lin, I. J. B., & Vasam, C. S. (2005). Metal containing ionic liquids and ionic liquid
crystals based on imidazolium moiety. Journal of Organometallic Chemistry, 690,
4
. Conclusions
−
The synthesized MAILs contained anion [FeCl4 ] and various
+
cations based on Cnmim . It was established that all synthesized
MAILs were stable up to 250–310 C. The decomposition was car-
3498–3512.
◦
Misuka, V., Breucha, D., & Löwe, H. (2011). Paramagnetic ionic liquids as “liq-
ried out in two steps with the formation of difficult decomposed
residue (Scheme 3). The MAILs display a typical hard magnetic
materials characteristic and with rather strong magnetic suscep-
tibilities. The Gibbs energy barriers at 293.15 K indicated that
C3mim/WCl3 may be the most active catalyst for breakage of glu-
cosidic bonds and hydrolysis of glucose/xylose to HMF platform
compound. As far as the advantages and potential application is
concerned, the MAILs also have the potential to open up more
promising new catalytic systems.
uid fixed-bed” catalysts in flow application. Chemical Engineering Journal, 173,
536–540.
Nel, W. P., & Cooper, C. J. (2009). Implications of fossil fuel constraints on economic
growth and global warming. Energy Policy, 37, 166–180.
Nishiyama, Y., Langan, P., & Chanzy, H. (2002). Crystal structure and hydrogen-
bonding System in cellulose I␤ from synchrotron X-ray and neutron fiber
diffraction. Journal of the American Chemical Society, 124, 9074–9082.
Pei, X. W., Yan, Y. H., Yan, L. Y., Yang, P., Wang, J. L., Xu, R., et al. (2010). A mag-
netically responsive material of single-walled carbon nanotubes functionalized
with magnetic ionic liquid. Carbon, 48, 2501–2505.
Pidko, E. A., Degirmenci, V., van Santen, R. A., & Hensen, E. J. M. (2010). Glucose
+2
activation by transient. Cr dimers. Angewandte Chemie-International Edition, 49,
2530–2534.
Robertson, N. J., Carney, M. J., & Halfen, J. A. (2003). Chromium(II) and chromium(III)
complexes supported by tris(2-pyridylmethyl)amine: Synthesis, structures, and
reactivity. Inorganic Chemistry, 42, 6876–6885.
Acknowledgements
The authors would like to thank Dr Jonathan G. Heddle and Dr
Ting-yu Lin, Advanced Science Institute, RIKEN, who gave valu-
able suggestions that have contribute to enhance the quality of
the manuscript. The work was funded by National Natural Science
Foundation of China (Nos. 31170672, 30940058), China Post-
doctoral Science Foundation (2013M541621; 1302152C), Jiangsu
Government Scholarship Fund for Study Abroad, the Foundation for
the Eminent Talents and Research Foundation for Advanced Talents
of Jiangsu University (12JDG074) and the Project Funded by the Pri-
ority Academic Program Development of Jiangsu Higher Education
Institutions.
Salvador, A. C., Santos, M. C., & Saraiva, J. A. (2010). Effect of the ionic liquid
[
6
bmim]Cl and high pressure on the activity of cellulose. Green Chemistry, 12,
32–635.
Shafiee, S., & Topal, E. (2005). When will fossil fuel reserves be diminished? Energy
Policy, 37, 181–189.
Shimizu, K., & Satsum, A. (2011). Toward a rational control of solid acid catalysis for
green synthesis and biomass conversion. Energy and Environmental Science, 4,
3
140–3153.
Torget, R. W., Kim, J. S.,
dilute acid hydrolysis/fractionation kinetics of hardwood carbohydrates.
&
Lee, Y. Y. (2000). Fundamental aspects of
1.
cellulose hydrolysis. Industrial and Engineering Chemistry Research, 39,
2817–2825.
Wang, H., Yan, R. Y., Li, Z. X., Zhang, X. P., & Zhang, S. J. (2011). Fe-containing mag-
netic ionic liquid as an effective catalyst for the glycolysis of poly(ethylene
terephthalate). Catalysis Communications, 11, 763–767.
Wang, M., Li, B., Zhao, C. J., Qian, X. Z., Xu, Y. L., Chen, G. R., et al. (2010). Recovery
of [BMIM] FeCl4 from homogeneous mixture using a simple chemical method.
Korean Journal of Chemical Engineering, 27, 1275–1277.
References
Xu, J., Chen, H., Z, Kádár, Thomsen, Z., Schmidt, A. B., Peng, J. E., & H. (2011). Opti-
mization of microwave pretreatment on wheat straw for ethanol production.
Biomass and Bioenergy, 35, 3859–3864.
Wang, J., Yao, H., Nie, Y., Zhang, X., & Li, J. (2012). Synthesis and characterization
of the iron-containing magnetic ionic liquids. Journal of Molecular Liquids, 169,
Bourissou, D., Guerret, O., Gabbai, F. P., & Bertrand, G. (2000). Stable carbenes. Chem-
ical Reviews, 100, 39–91.
Engel, P., Mladenov, R., Wulfhorst, H., Jäger, G., & Spiess, A. (2010). Point by point
analysis: How ionic liquid affects the enzymatic hydrolysis of native and modi-
fied cellulose. Green Chemistry, 12, 1959–1966.
1
52–155.
Holbrey, J. D., & Seddon, K. R. (1999). Ionic liquids. Journal of Cleaner Production, 1,
23–236.
Friedman, H. L. (1952). The visible and ultraviolet absorption. Spectrum of the tetra-
chloroferrate(III) ion in various media. Journal of the American Chemical Society,
2
74, 5–10.
Song, F., Shen, X., Liu, M., & Xiang, J. (2010). Formation and characterization of mag-
netic barium ferrite hollow fibers with high specific surface area via sol–gel
process. Solid State Sciences, 12, 1603–1607.
Zakzeski, J., Bruijnincx, P. C. A., Jongerius, A. L., & Weckhuysen, B. M. (2010). The cat-
alytic valorization of lignin for the production of renewable chemicals. Chemical
Review, 110, 3552–3599.
Friedlingstein, P., & Solomon, S. (2005). Contributions of past and present human
generations to committed warming caused by carbon dioxide. Proceedings of
the National Academy of Sciences, 102, 10832–10836.
Godfray, H. C. J., Beddington, J. R., Crute, I. R., Haddad, L., Lawrence, D., Muir, J. F.,
et al. (2010). Food security: The challenge of feeding 9 billion people. Science,
327, 812–818.
Zhao, H., Holladay, J., Brown, H.,
ionic liquid solvents convert sugars to 5-hydroxymethylfurfural. Science, 316,
597–1600.
& Zhang, Z. C. (2007). Metal chlorides in
Hao, Y., Peng, J., Hu, S. W., Li, J. Q., & Zhai, M. L. (2010). Thermal decomposition
of allyl-imidazolium-based ionic liquid studied by TGA–MS analysis and DFT
calculations. Thermochimica Acta, 501, 78–83.
Hatakeyama, T., Hashimoto, S., Ishizuka, K., & Nakamura, M. (2009). Highly selec-
tive biaryl cross-coupling reactions between aryl halides and aryl grignard
1
Zhou, C., Yu, X., Ma, H., He, R., & Vittayapadung, S. (2013). Optimization on the con-
version of bamboo shoot shell to levulinic acid with environmentally benign

C. Zhou et al. / Carbohydrate Polymers 105 (2014) 300–307
307
acidic ionic liquid and response surface analysis. Chinese Journal of Chemical
Engineering, 21, 544–550.
Zhou, C., Yu, X., Ma, H., Zhang, Z., Lin, L., Yagoub, A., et al. (2013). Solid–liquid extrac-
tion kinetics of flavonoids from okra (Abelmoschus esculentus L. Moench) pods
with applicability analysis. Advanced Materials Research, 750, 1560–1566.
Zhou, C., Yu, X., Yang, H., Zhang, Y., Wang, Y., Lin, L., et al. (2013). Preparation of
levulinic acid by acid-catalysed hydrolysis of bamboo shoot shell in the pres-
ence of acidic ionic liquid using Box–Behnken design. Energy Sources Part A, 35,
1852–1862.