Polyethylene Glycol-400-Functionalized Dicationic Acidic Ionic Liquids for Highly Efficient Conversion of Fructose into 5-Hydroxymethylfurfural

Article abstract of DOI:10.1007/s10562-015-1485-8

A variety of polyethylene glycol-400-functionalized dicationic acidic ionic liquids (ILs) (PEG₄₀₀-DAILs) were synthesized and tested in the dehydration of fructose. Among these catalysts, hydrogen sulfate anion-based ILs showed the higher catalytic performance in the conversion of fructose. The highest HMF yield of 96.5 % with 100 % consumption of fructose were obtained after 60 min at 110 °C. The effects of catalyst concentration, reaction time, reaction temperature, and solvents were systematically investigated. In addition, the generality of the catalysts was examined by processing inulin and sucrose to HMF with yield of 71.9 and 52.1 % under certain conditions, respectively. PEG₄₀₀-DAILs possess modified physicochemical properties such as low viscosity, strong hydrophilicity and hydrogen bonding with sugars so as to improve activity for the dehydration of fructose into HMF. The used IL catalyst could be separated and recycled repeatedly without significant loss of catalytic activity. The research emphasizes preparation of the novel catalysts combining polymers with functionalized ILs for conversion of renewable biomass. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-015-1485-8

Catal Lett
DOI 10.1007/s10562-015-1485-8
Polyethylene Glycol-400-Functionalized Dicationic Acidic Ionic
Liquids for Highly Efficient Conversion of Fructose into
5-Hydroxymethylfurfural
•
Wentao Liu Yanfang Wang Wei Li
•
•
•
Yan Yang Ningning Wang Zhanxin Song
•
•
•
Xiao-Feng Xia Haijun Wang
Received: 29 November 2014 / Accepted: 10 January 2015
Ó Springer Science+Business Media New York 2015
Abstract A variety of polyethylene glycol-400-functiona-
lized dicationic acidic ionic liquids (ILs) (PEG400-DAILs)
were synthesized and tested in the dehydration of fructose.
Among these catalysts, hydrogen sulfate anion-based ILs
showed the higher catalytic performance in the conversion of
fructose. The highest HMF yield of 96.5 % with 100 %
consumption of fructose were obtained after 60 min at
110 °C. The effects of catalyst concentration, reaction time,
reaction temperature, and solvents were systematically
investigated. In addition, the generality of the catalysts was
examined by processing inulin and sucrose to HMF with yield
of 71.9 and 52.1 % under certain conditions, respectively.
PEG400-DAILs possess modified physicochemical properties
such as low viscosity, strong hydrophilicity and hydrogen
bonding with sugars so as to improve activity for the dehy-
dration of fructose into HMF. The used IL catalyst could be
separated and recycled repeatedly without significant loss of
catalytic activity. The research emphasizes preparation of the
novel catalysts combining polymers with functionalized ILs
for conversion of renewable biomass.
Graphical abstract
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-015-1485-8) contains supplementary
material, which is available to authorized users.
Keywords Polyethylene glycol ꢀ Ionic liquid ꢀ Fructose ꢀ
5-Hydroxymethylfurfural
W. Liu ꢀ Y. Wang ꢀ W. Li ꢀ Y. Yang ꢀ N. Wang ꢀ Z. Song ꢀ
X.-F. Xia ꢀ H. Wang (&)
1 Introduction
The Key Laboratory of Food Colloids and Biotechnology,
Ministry of Education, School of Chemical and Material
Engineering, Jiangnan University, Wuxi, Jiangsu, China
e-mail: wanghj329@outlook.com
Under the dual pressure of the energy crisis and environ-
mental protection, development and utilization of
123

W. Liu et al.
renewable clean energy have been extensively concerned.
In this respect, biomass, which is affluent, pollution-free
and widespread, provides an ideal substitute to fossil
resources for the production of fine chemicals and fuels [1–
4]. Recently, an increasing efforts have been devoted
towards transforming biomass into 5-hydroxymethylfurf-
ural (HMF), which is one of vitally important versatile
intermediates for preparing a broad of valuable chemicals
[5–11], polymers [12], pharmaceutical [13].
The abundance of differently functionalized ionic liq-
uids are incorporated PEG chain into cationic units, gen-
erating an attractive group of solvents or catalysts that find
applications across a range of disciplines, including
extractions, gas separations, carbohydrate dissolution,
organic synthesis and catalysis [39]. Recent studies have
demonstrated that ether-functionalized ILs tend to present
lower viscosity and reduced toxicity than their aliphatic-
substituted counterparts [40, 41]. Considering the above
factors, we attempted to prepare polyethylene glycol-400-
As a sustainable precursor for monomers and fuel
components, HMF can be synthesized from all types of C6
carbohydrates, including monomeric and polymeric sac-
charides, among which conversion of fructose to HMF is of
significant interest with acidic catalysts. Over the past few
years, all sorts of mineral or organic acids catalysts for
direct production of HMF from fructose have been exten-
sively studied in water [14] and various aprotic organic
solvents [15, 16]. However, the homogenous acid catalysts
show innate drawbacks in corrosion and non-recyclability.
Recently, there were several novel heterogeneous solid
acid catalysts which were employed for the conversion of
fructose to HMF under different conditions, such as silica
materials [17, 18], acid-functionalized carbons [19, 20],
acidic resins [21], zeolites [22, 23], functionalized metal–
organic frameworks (MOFs) [24], graphene oxide (GO)
[25], polyoxometalates (POMs) [26]. Generally, heteroge-
neous catalysis is preferred over homogeneous catalysis
because of the ease of catalyst separation and its reus-
ability. However, soluble polymers and insoluble humins
formed can deposit in the catalyst pores, leading to the
partial deactivation of the catalysts. This suggests a need to
explore efficient homogeneous catalytic processes for HMF
production from fructose.
functionalized dicationic acidic ionic liquids (PEG400
-
DAILs) to broaden homogeneous supported ionic liquids
catalysts applications in the dehydration of fructose into
HMF. In the present study, a variety of PEG400-DAILs
were synthesized and used as catalysts for dehydration of
fructose into HMF. Moreover, the influence of different
anion moieties on the catalytic activity of ionic liquids
were discussed and the effects of various process param-
eters were investigated in detail.
2 Experimental
2.1 Materials and Equipment (General Remark)
1,3-Propanesultone, phosphotungstic acid (H3PW12O40)
and phosphomolybdic acid (H3PMo12O40) were purchased
from shanghai Aladdin Industrial Inc.; HMF used in the
study was obtained from Sigma-Aldrich Co. LLC.; inulin
was obtained from Alfa Aesar; fructose, sucrose, glucose,
cellobiose, polyethylene glycol-400, imidazole, sodium
ethoxide, potassium carbonate, sodium hydroxide, were
purchased from Sinopharm Chemical Reagent Co. Ltd.; All
other reagents and solvents were of analytical grade and
used without further purification unless otherwise stated.
Deionized water was produced by a laboratory water-
purification system (RO DI Digital plus). FT-IR spectra
were recorded on a Nicolet 360 FT-IR instrument (KBr
discs) in the 4,000–500 cm-1 region. 1H NMR spectra
were measured with a Bruker DPX 300 (400 MHz) spec-
trometer and tetramethylsilane (TMS) was used as internal
standard. UV–Vis spectra were performed on TU-1901
spectrophotometer in water.
Interestingly, ionic liquids (ILs) have been defined as a
sort of powerful reaction medium as well as catalysts for
the dehydration of hexose to HMF [27–34], while the use
of innovative catalysts containing ionic liquids have been
scarce and subject to intense research. Lee et al. [35]
reported that functionalized mesoporous silica nanoparti-
cles with both sulfonic acid and ionic liquid were applied
as effective and recyclable catalysts for generating HMF
from fructose. Shi et al. [36] first developed a novel class of
fiber supported ionic liquid to catalyze fructose dehydra-
tion into HMF and showed excellent catalytic activity.
Recently, Jadhav et al. [37, 38] prepared a series of
homogeneous supported dicationic ionic liquids, in which
each IL contains short oligo (ethylene glycol) linkers.
These ionic liquids showed high catalytic activity for
selective dehydration of fructose into HMF. At present, the
functionalized ionic liquid catalysts still exist some defi-
ciencies, thus we need to make further constant efforts to
modify the kind of catalysts to improve catalyst activity for
fructose conversion into HMF.
2.2 Catalysts Preparation
The IL 4 was prepared according to literature procedure
with slight modifications (Fig. 1) (see the Supporting
Information for details).
The PEG400-DAILs used in the study were synthesized
by the treatment of IL 4 or 5 with acid in water. Typically,
the ionic liquid of [4ꢀ2H][HSO4]2 was prepared as follows:
the H2SO4 (0.7 mL, 12 mmol) was added to the IL 4
123

Catalytic Conversion of Fructose into 5-Hydroxymethylfurfural
(4.46 g, 6 mmol) in water (10 mL) followed by stirring of
the mixture at 50 °C for 12 h. On completion, water was
removed in vacuum and the residue was washed with
petroleum ether three times then evaporated under reduced
pressure, and the final product, [4ꢀ2H][HSO4]2 was
obtained as brown viscous liquid and characterized by FI-
IR spectroscopy. The other PEG400-DAILs were prepared
following the above same procedures.
hydrophilicity of the resulting ILs. Figure 1 illustrates method
for synthesis of PEG400-DAILs including several synthetic
1
steps. These ILs were characterized by H NMR, FT-IR
analysis. In this method, PEG-400 is first converted to an alkyl
chloride, followed by reaction with a nucleophilic imidazole
anion. Then, quaternization of the PEG-400-substituted
imidazole with 1,3-propane sultone is performed to produce
functionalized dicationic ionic liquid. Finally, functionalized
dicationic ionic liquids are protonated to achieve ultimate
PEG-400-functionalized dicationic imidazolium acidic ionic
liquids. A similar approach has also been used in the prepa-
ration of PEG-400-functionalized dicationic quaternary
ammonium acidic ionic liquids. The detailed synthesis con-
ditions are described in the Supporting Information.
2.3 General Procedure for the Dehydration of Fructose
to HMF
All the dehydration reaction experiments were performed in
a 5 mL reaction vial equipped with magnetic stirrer. A typ-
ical procedure for dehydration of fructose was as follow:
fructose (50 mg), PEG400-DAIL (7.5 mol%) and DMSO
(2 mL) were added into the reaction vial. The mixture was
stirred vigorously and heated with a thermostatically con-
trolled oil bath for a specific time. After completion of the
reaction, the mixture was decanted into a volumetric flask
using ultrapure water as diluents, and analyzed by high-
performance liquid chromatography (HPLC) system. HMF:
1H NMR (400 MHz, D2O, TMS): d 4.68 (s, 2H), 6.66 (d,
J = 4 Hz, 1H), 7.51 (d, J = 4 Hz, 1H), 9.44 (s, 1H).
3.2 Hammett Acidity of PEG400-DAILs (HSO4)
It has been suggested that the dehydration of fructose to
HMF is proportional to the acidity of catalyst [42], the
Hammett acidity function H0 value of [4ꢀ2H][HSO4]2
and [5ꢀ2H][HSO4]2 were determined using UV–Visible
spectrophotometer with p-nitroaniline as the indicator,
which was similar to the method utilized in the previ-
ous literature [43]. Therein, the IL and p-nitroaniline
were dissolved in water with concentrations of 30 and
0.1 mmol/L, respectively, and then the solution UV
spectra were recorded, the obtained data were listed in
Table 1. The H0 value was calculated by the equation
H0 = pK(I)aq ? log([I]/[IH?]), where pK(I)aq is the pKa
value (about 0.99) of the indicator solution, [IH?] and
[I] are respectively the molar concentrations of the
protonated and unprotonated forms of the indicator. The
maximum absorbance of the unprotonated forms of the
indicator was obtained at 380 nm in water. Furthermore,
the corresponding H0 values of [4ꢀ2H][HSO4]2 and
2.4 Analyses
The liquid solutions were analyzed with HPLC using Ag-
ilent 1100 series with a refractive index detector and a
Shodex SURGER SP-0810 column (300 9 8.0 mm).
Ultrapure water was used as the mobile phase at a flow rate
of 0.7 mL/min, and the column temperature was main-
tained at 70 °C. The amount of HMF and fructose were
determined using an external standard. The conversion of
fructose and the yield of HMF were evaluated as follows:
ꢀ
ꢁ
moles of remaining fructose
Fructose conversion ðmol%Þ ¼ 1 ꢁ
ꢂ 100 %
starting moles of fructose
ꢀ
ꢁ
moles of HMF
HMF yield ðmol%Þ ¼
ꢂ 100 %
starting moles of fructose
[5ꢀ2H][HSO4]2 were 1.42 and 1.72, respectively. The
results demonstrated that the acidity of [4ꢀ2H][HSO4]2
was stronger than [5ꢀ2H][HSO4]2.
3 Results and Discussion
3.1 Preparation and Characterizations of PEG400
DAILs
-
3.3 Conversion of Fructose to HMF by Various
PEG400-DAILs Catalysts
Seekingtoefficientand environment-friendly ionicliquids for
conversion of fructose into HMF, polyethylene glycol (PEG)
is grafted to the cation to lead to variation in viscosity and
HMF is a triple dehydration product of fructose (Fig. 2) in
the presence of acidic catalyst. As shown in Fig. 3a, b, the
123

W. Liu et al.
Fig. 1 Synthesis of PEG400
DAILs
-
Table 1 Comparison of H0 values of different ILs in water (25 °C)
reaction time and temperature were optimized to achieve
maximum quantity of HMF from fructose. Temperature
ranged from 90 to 120 °C were discussed at different time
of 30, 45, 60, 75, 90 and 120 min in the presence of the
equimolar amounts of catalyst (7.5 mol% to fructose) both
for [4ꢀ2H][HSO4]2 and [5ꢀ2H][HSO4]2. For [4ꢀ2H][HSO4]2,
it can be seen that the yield of HMF increased to 91.2 %
after 120 min at 90 °C, while it could reach as high as
96.5 % with a full fructose conversion (Table 2, entry 1) at
110 °C for 1 h in DMSO, confirming that increasing the
reaction temperature facilitates the formation of HMF from
fructose. However, with the further increasing reaction
temperature and time, the main by-products of insoluble
humins were created and HMF decomposed to levulinic
acid and formic acid which coherently leading to reduced
HMF yield. Similarly, for optimization of the reaction
conditions, two parameters such as reaction time and
Ionic liquid
Absorbance
[I] (%)
[IH?] (%)
H0
None
1.34
0.98
1.13
100
0
–
[4ꢀ2H][HSO4]2
[5ꢀ2H][HSO4]2
73.1
84.3
26.9
15.7
1.42
1.72
Indicator: p-nitroaniline, pKa = 0.99
the dehydration of fructose into HMF. These results are
consistent with the Hammett acidity function order of the
ILs.
Moreover, we repeated the reaction with different dos-
ages of anion-based PEG400-DAILs (5 and 10 mol% to
fructose) under 110 °C for 60 min. As a result (Table 2,
entries 3–6), the slight decrease of HMF yield was
observed with 5 or 10 mol% of catalyst, which might be
attributed to a difference in acidic sites. Thus, the optimum
amount of catalyst is 7.5 mol% to fructose.
reaction
temperature
were
investigated
using
[5ꢀ2H][HSO4]2 as a catalyst. These results reflected that the
best HMF yield of 92.7 % (Table 2, entry 2) was achieved
at 110 °C for 60 min. It was noted that both [4ꢀ2H][HSO4]2
and [5ꢀ2H][HSO4]2 showed close catalytic activity toward
In addition, the effect of PEG-400-functionalized het-
eropolyanion based ionic liquids on the dehydration of
fructose was examined and the results were summarized in
123

Catalytic Conversion of Fructose into 5-Hydroxymethylfurfural
Fig. 2 The conversion of
fructose into HMF
Fig. 3 Effect of reaction temperature and time on HMF yield by
conversion of fructose in DMSO with [4ꢀ2H][HSO4]2 (a) or
[5ꢀ2H][HSO4]2 (b). Experiments were performed at 90, 100, 110
and 120 °C in 2 mL DMSO with 7.5 mol% catalyst to fructose at 30,
45, 60, 75, 90, 120 min reaction time
Table 2 (entries 7–14). The reactions were carried out at
110 °C for 60 min using 0.9 or 1.1 mol% of catalyst in
2 mL DMSO. Generally, phosphotungstic anion based ILs
showed excellent to good activity toward the fructose
dehydration. With an increasing catalyst dosage, HMF
gradually increases to a relatively high yield of 94.8 % or
91.8 % with 1.1 mol% of [4ꢀ2H]3[PW12O40]2 or [5ꢀ2H]3
[PW12O40]2. Nevertheless, the low HMF yields (Table 2,
entries 11–14) with phosphomolybdic anion based ILs
catalyst may be explained by taking into account lower
acid strength and thermal stability [44].
On the basis of the above results, we discover that
various PEG400-DAILs exhibit excellent catalytic perfor-
mance which can be attributed to the following aspects. On
the one hand, the wettability of catalyst has great impact on
the HMF stabilization [37, 38].
Literature reported that the addition of alkoxy groups to
the cation remarkably increased the hydrophilicity of ILs
Table 2 Dehydration of
fructose to HMF catalyzed by
the PEG400-DAILs
Entry
Catalyst
Catalyst loading (mol%)
HMF yield (%)a
1
[4ꢀ2H][HSO4]2
[5ꢀ2H][HSO4]2
[4ꢀ2H][HSO4]2
[4ꢀ2H][HSO4]2
[5ꢀ2H][HSO4]2
[5ꢀ2H][HSO4]2
[4ꢀ2H]3[PW12O40 2
[4ꢀ2H]3[PW12O40 2
[5ꢀ2H]3[PW12O40 2
[5ꢀ2H]3[PW12O40 2
[4ꢀ2H]3[PMo12O40 2
[4ꢀ2H]3[PMo12O40 2
[5ꢀ2H]3[PMo12O40 2
[5ꢀ2H]3[PMo12O40 2
7.5
7.5
5
96.5
92.7
89.1
94.4
87.5
92.1
87.6
94.2
86.9
91.8
62.6
59.5
60.2
58.6
2
3
4
10
5
5
6
10
7
]
0.9
1.1
0.9
1.1
0.9
1.1
0.9
1.1
8
]
9
]
10
11
12
13
14
]
]
Reaction conditions: fructose
(50 mg), DMSO (2 mL),
T = 110 °C, t = 60 min
]
]
a
The results are obtained by
HPLC analysis
]
123

W. Liu et al.
References
Table 3 Comparison of different catalysts for the dehydration of fructose
Entry
Catalyst
Catalyst loading
T (°C)
Time (min)
HMF yield (%)
1
2
3
4
5
6
7
8
[NMP]?[CH3SO3]-
[TetraEG(mim)2][OMs]2
[PPFPy][HSO4]
7.5 mol%
100 %
90
120
40
72.3
92.3
82.9
72.5
72.8
92
[30]
120
120
90
[37]
7.5 mol%
25 wt%
30
[36]
[HSO3 ? (ILs/CrCl2)]-MSN
[PSMBIM]HSO4
180
60
[35]
10 wt%
80
[34]
IL-POMs-(PW12O40
)
2.5 mol%
7.5 mol%
1.1 mol%
100
110
110
60
[26]
PEG400-DAILs-(HSO4)
60
96.5
94.2
This work
This work
PEG400-DAILs-(PW12O40
)
60
Table 4 Effect of different solvents on fructose dehydration using [4ꢀ2H][HSO4]2
Entry
Solvent
T (°C)
Time (min)
Conversionc (%)
HMF Yieldc (%)
1
2
3
4
5
6
7
8
9
DMSO
110
110
110
110
110
110
110
80
60
60
60
60
60
60
60
60
60
99.2
89.2
89.7
72.8
88.6
92.5
96.3
91.6
94.7
96.5
54.8
42.7
48.7
37.5
82.5
79.4
60.5
62.8
DMF
DMA
NMP
Isopropanol
H2O-MIBKa
H2O-MIBKb
H2O-acetonea
H2O-acetoneb
80
Reaction conditions: fructose (50 mg), 7.5 mol% [4ꢀ2H][HSO4]2, 2 mL solvent
Volume ratio of H2O/MIBK or H2O/acetone = 1:9
a
b
Volume ratio of H2O/MIBK or H2O/acetone = 2:8
c
The results are obtained by HPLC analysis
[39]. Thus, PEG400-DAILs have aroused the enormous
attention in our study. When prolonging the reaction time,
the hydrophilic groups of PEG400-DAILs have a close
interaction with water molecule, improving the formation
of HMF from fructose. When extending optimized reaction
time, the decrease of HMF yield could be caused, which
indicated by-product formation and product instability at
this stage. What’s more, we speculated that the intermo-
lecular hydrogen bonding between ether chain oxygen
atom and sugar molecules facilitated the sugar dissolution.
To a certain extent, the strong intermolecular interaction is
one factor that contributes to promote the dehydration of
fructose. Besides, HSO4 anion-based PEG400-DAILs dis-
play relative lower viscosity which can accelerate the rate
of mass transport, enhancing the yield of HMF. According
to the above understanding, we can rationally deduce that
PEG400-DAILs show unique physicochemical properties,
which are favorable for conversion of fructose to HMF.
To compare the applicability and the efficiency of
PEG400-DAILs with the reported catalysts for the
dehydration of fructose, we have summarized the results in
Table 3. It can be seen that PEG400-DAILs showed better
catalytic performance than other catalysts.
3.4 Effect of Solvent on Fructose Dehydration
Similarly, A series of solvents, including DMA, DMF,
NMP, isopropanol, MIBK and acetone were also used to
investigate the effect of solvents with respect to the fruc-
tose conversion and HMF yield by using [4ꢀ2H][HSO4]2 as
catalyst. 100 % fructose conversion and 96.5 % HMF yield
were obtained in DMSO. Clearly, DMA, DMF, NMP and
isopropanol were less effective reaction media in the study.
When NMP was used as solvent, the yield of HMF reached
48.7 % with 72.8 % fructose conversion. HMF yield of
37.5 % were achieved in isopropanol. In the polar aprotic
solvent, such as DMA and DMF, 42.7 and 54.8 % HMF
yield were obtained, respectively. It is noteworthy that
DMSO is the most efficient solvent for facilitating the
dehydration of fructose to HMF, which is probably due to
123

Catalytic Conversion of Fructose into 5-Hydroxymethylfurfural
catalyst to research the recyclability for the dehydration
reaction of fructose over five times. All reactions were
conducted at 110 °C for a reaction time of 60 min. The
resulting mixture after reaction was first distilled under
reduced pressure to obtain DMSO and the remaining
mixture was extracted with ethyl acetate. It had been
demonstrated fructose and [4ꢀ2H][HSO4]2 were insoluble
in ethyl acetate and could be easily separated, while HMF
was the sole product in ethyl acetate phase. The obtained
mixture containing IL was dried in vacuum at 60 °C for
12 h to remove water and residual ethyl acetate. It was then
reused for further reaction by adding the same amount of
fructose. As shown in Fig. 4, the yield of HMF was
maintained at 96 % after the first recycle. Furthermore, no
significant loss of HMF yield was observed till the sixth
run, meaning that [4ꢀ2H][HSO4]2 has excellent stability
and catalytic activity.
Fig. 4 Recyclability of [4ꢀ2H][HSO4]2 in fructose conversion to
HMF. Experiments were carried out on 50 mg fructose using
7.5 mol% [4ꢀ2H][HSO4]2 as catalyst in 2 mL DMSO; reaction
time = 60 min, temperature = 110 °C
3.6 Conversion of Other Feedstock to HMF
Apart from the discussion above, fructose-based saccha-
rides such as inulin and sucrose were selected as feedstock
to evaluate catalytic performance using PEG400-DAILs as
catalysts. It can been seen in Table 5, HMF was produced
with 71.9 and 66.6 % yield in the presence of
[4ꢀ2H][HSO4]2 and [5ꢀ2H][HSO4]2, respectively. Then we
also further researched the heteropolyanion based ILs cat-
alyzed inulin transformation to HMF. Among these cata-
lysts, phosphotungstic acid anion based ILs still show the
higher catalytic performance in HMF formation. The ten-
dency is in agreement with the results achieved by fructose
to HMF.
DMSO being as an electron acceptor to improve the
dehydration of fructose [45]. However, the approach make
it unable to separate HMF by distillation owning to the
high boiling point of DMSO. In addition, the catalytic
conversion of fructose into HMF in a biphasic system
including water and organic solvents as well as the
[4ꢀ2H][HSO4]2 to further verify the catalytic activity of the
PEG400-DAILs. It was demonstrated that acetone with the
co-solvent of water gave the good yields of 60.5–62.8 %
(Table 4, entries 8–9). Besides, the results show that water
and MIBK mixtures (1:9) under 110 °C for 60 min of
reaction time obtained the highest yield of 82.5 %
(Table 4, entry 6).
Furthermore, the dehydration of sucrose was also
investigated with PEG400-DAILs as catalyst, the results are
summarized in Table 6. It can be seen that 52.1 % yield of
HMF was obtained with [4ꢀ2H][HSO4]2 as catalyst
(Table 6, entry 1), in keeping with results obtained using
mineral acid catalysts (Table 6, entry 9). Then, catalytic
transformation of sucrose to HMF was researched in the
presence of other PEG400-DAILs. It is well known that
3.5 Recyclability of the Catalysts
From the point of view of economizing resource and pre-
venting pollution, recyclability of the catalysts seems to be
pretty important. Therefore, we chose [4ꢀ2H][HSO4]2 as
Table 5 Dehydration of inulin to HMF catalyzed by the PEG400-DAILs
Entry
Substrate
Catalyst
Catalyst loading (mol%)
Yielda (%)
1
2
3
4
5
6
Inulin
Inulin
Inulin
Inulin
Inulin
Inulin
[4ꢀ2H][HSO4]2
[5ꢀ2H][HSO4]2
7.5
7.5
1.1
1.1
0.9
0.9
71.9
66.6
59.8
56.6
35.7
32.4
[4ꢀ2H]3[PW12O40 2
]
[5ꢀ2H]3[PW12O40 2
[4ꢀ2H]3[PMo12O40 2
[5ꢀ2H]3[PMo12O40 2
]
]
]
Reaction conditions: inulin (50 mg), DMSO (2 mL), T = 120 °C,t = 120 min
a
The results are obtained by HPLC analysis
123

W. Liu et al.
Table 6 Dehydration of
sucrose, glucose and cellobiose
to HMF catalyzed by the
PEG400-DAILs
Entry
Substrate
Catalyst
Catalyst loading (mol%)
HMF yielda (%)
1
Sucrose
Sucrose
Sucrose
Sucrose
Sucrose
Sucrose
Sucrose
Sucrose
Sucrose
Glucose
Glucose
Cellobiose
Cellobiose
[4ꢀ2H][HSO4]2
[5ꢀ2H][HSO4]2
7.5
7.5
1.1
1.1
0.9
0.9
7.5
1.1
0.9
7.5
1.1
7.5
1.1
52.1
47.3
47.8
47.2
31.9
38.7
48.5
41.8
38.2
11.6
12.6
15.4
18.7
2
3
[4ꢀ2H]3[PW12O40 2
]
4
[5ꢀ2H]3[PW12O40 2
[4ꢀ2H]3[PMo12O40 2
]
5
]
6
[5ꢀ2H]3[PMo12O40 2
]
Reaction conditions: sucrose
(50 mg), DMSO (2 mL),
T = 110 °C, t = 120 min
7
H2SO4
8
H3PW12O40
H3PMo12O40
[4ꢀ2H][HSO4]2
9
a
The results are obtained by
HPLC analysis
10b
11b
12b
13b
b
[4ꢀ2H]3[PW12O40 2
]
Reaction conditions: glucose
or cellobiose (50 mg), DMSO
(2 mL), T = 140 °C,
t = 240 min
[4ꢀ2H][HSO4]2
[4ꢀ2H]3[PW12O40 2
]
Acknowledgments This work was financial supported by National
Natural Science Foundation of China (21206057), and the Natural
Science Foundation of Jiangsu Province, China (BK2012118),
(BK2012547), and MOE & SAFEA for the 111 Project (B13025).
sucrose is a disaccharide composed of one molecule glu-
cose and one molecule fructose. These data show that the
ketose is more easily dehydrated to HMF than aldose using
current conditions. When glucose and cellobiose were
subjected to our reaction system, the HMF yield was
remarkably inferior (Table 6, entries 10–13). This result
clearly indicates that PEG400-DAILs as Brønsted acid
catalysts can hardly promote the isomerization of glucose
to fructose.
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