Efficient and selective dehydration of fructose to 5-hydroxymethylfurfural catalyzed by br?nsted-acidic ionic liquids

Article abstract of DOI:10.1002/cssc.200900224

The dehydration of d-fructose and glucose has been studied with acidic ionic liquids as catalysts. A series of Br?nsted-acidic ionic liquids has been synthesized and tested in the dehydration of d-fructose. The results showed that N-methyl-2-pyrrolidonium methyl sulfonate [NMP]+[CH₃SO₃]^- and N-methyl-2-pyrrolidonium hydrogen sulfate [NMP]+[HSO₄]^- have high catalytic activity. Highly efficient and selective dehydration of dfructose to 5-hydroxymethylfurfural (HMF) was achieved in dimethyl sulfoxide (DMSO) under mild conditions. For example, a 72.3% yield of HMF with 87.2% selectivity were obtained for 2 h at 90 °C in the presence of 7.5 mol% [NMP]+[CH₃SO₃]^-. The effects of the reaction temperature, time, and solvent were investigated in detail. The catalyst and solvent can be recycled for the dehydration of d-fructose. The Hammett method was used to determine the acidities of these ionic liquids, which indicated that the acidity and molecular structure have strong effects on the catalytic activity of ionic liquids. Based on the experimental results, a possible reaction mechanism for the dehydration of d-fructose is proposed.

Full text of DOI:10.1002/cssc.200900224

DOI: 10.1002/cssc.200900224
Efficient and Selective Dehydration of Fructose to 5-
Hydroxymethylfurfural Catalyzed by Brønsted-Acidic Ionic
Liquids
[a]
Xinli Tong and Yongdan Li*
+
À
The dehydration of d-fructose and glucose has been studied
with acidic ionic liquids as catalysts. A series of Brønsted-acidic
ionic liquids has been synthesized and tested in the dehydra-
tion of d-fructose. The results showed that N-methyl-2-pyrroli-
2 h at 908C in the presence of 7.5 mol% [NMP] [CH SO ] . The
3 3
effects of the reaction temperature, time, and solvent were in-
vestigated in detail. The catalyst and solvent can be recycled
for the dehydration of d-fructose. The Hammett method was
used to determine the acidities of these ionic liquids, which in-
dicated that the acidity and molecular structure have strong
effects on the catalytic activity of ionic liquids. Based on the
experimental results, a possible reaction mechanism for the de-
hydration of d-fructose is proposed.
+
À
donium methyl sulfonate [NMP] [CH SO ] and N-methyl-2-
3
3
+
À
pyrrolidonium hydrogen sulfate [NMP] [HSO ] have high cat-
4
alytic activity. Highly efficient and selective dehydration of d-
fructose to 5-hydroxymethylfurfural (HMF) was achieved in di-
methyl sulfoxide (DMSO) under mild conditions. For example,
a 72.3% yield of HMF with 87.2% selectivity were obtained for
Introduction
[
24]
Renewable biomass resources are promising alternatives for
the sustainable supply of chemical intermediates and liquid
scale continuous production protocol for HMF below 508C.
On the other hand, Bao et al. reported that the Lewis acidic 3-
allyl-1-(4-sulfurylchloride butyl)-imidazolium trifluoromethane-
[
1]
fuels. Particularly, fossil fuels are diminishing and contributing
to global warming; therefore, catalytic biomass conversion has
sulfonate ([ASCBI][Tf]) effectively catalyzed the dehydration of
[
2–4]
[25]
been an attractive hot topic in recent years.
With the con-
d-fructose under microwave irradiation.
Moreover, special
sideration of the downstream chemical processing, catalytic
transformation of sugar to value-added chemicals is important
ILs, such as 1-H-3-methyl imidazolium chloride and choline
chloride/citric acid, have also been used as both solvent and
catalyst for the reaction, with a reported IL to d-fructose molar
[
5,6]
in both science and commerce.
Therefore, much effort has
[26,27]
been devoted to the dehydration of hexoses into 5-hydroxy-
methylfurfural (HMF), a versatile and key intermediate both in
ratio of 12 or 5, respectively.
However, in these reported
works, the ILs mainly played a role as the solvent and were
consumed in considerably large amounts. The merits and de-
tails of the ILs as single catalysts for the dehydration of d-fruc-
tose are still far from being sufficiently understood and need
to be further investigated.
[
7–9]
biofuel chemistry and the petroleum industry.
In literature,
acidic catalysts have been employed for the d-fructose dehy-
[
10,11]
dration reaction, such as mineral acids,
strong acid cation
[
12–14]
[14,16]
exchange resins,
H-form zeolites,
supported heteropo-
[
17]
[18,19]
lyacids,
and metal ions.
In addition, several reaction
Very recently, Chakraborti and Roy put forward the catalytic
concept of ILs based on the O-tert-butoxy-carbonylation of 2-
media, including pure water and organic solvents, and also a
number of biphasic water/organic systems, have been adopt-
[28]
naphthol catalyzed by a catalytic amount of [bmim][OAc],
[
20,21]
ed.
However, the yields of the target product HMF were
which revealed the unique catalytic performance of ILs. Ac-
cordingly, catalysis with a single IL has become a hot and
promising research topic. As far as we know, the efficient dehy-
dration of d-fructose with a catalytic amount of acidic ILs has
not been reported until now.
low because these catalysts may have favored the subsequent
dehydration of HMF to levulinic and formic acids. Moreover, d-
fructose and HMF can be oligomerized or polymerized to give
[21,22]
the other byproducts, which also lowers the HMF yield.
Recently, room temperature ionic liquids (ILs) have also been
In this work, the dehydration of d-fructose to HMF using cat-
alytic amounts of Brønsted-acidic ILs (molar ratio of IL to d-
[
8,23–27]
employed in the dehydration of hexoses into HMF.
The
neutral ILs were used as reaction media in which catalysts and
substrates were dissolved. For example, the IL [Emim]Cl was an
effective solvent in the dehydration of d-fructose to HMF with
a metal chloride as catalyst, in which a 70% yield of HMF was
[
a] Dr. X. Tong, Prof. Y. Li
Tianjin Key Laboratory of Applied Catalysis Science and Technology
and State Key Laboratory of Chemical Engineering
School of Chemical Engineering, Tianjin University
Tianjin, 300072 (PR China)Fax: (+86)22-27405243
E-mail: ydli@tju.edu.cn
[
8]
achieved. Moreau et al. found that [BMIm]PF and [BMIm]BF4
6
were suitable reaction media for the dehydration of d-fructose
[
23]
in the presence of Amberlyst-15. In particular, in the IL–tetra-
hydrofuran biphasic system, tungsten salt promoted a large-
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.200900224.
3
50
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2010, 3, 350 – 355

Efficient and Selective Dehydration of Fructose to 5-Hydroxymethylfurfural
fructose of 0.075 or 0.1) has been investigated in water and or-
ganic solvents. Various acidic ILs, including 1-methylimidazoli-
+
À
um hydrogen sulfate ([MIM] [HSO ] ), N-methyl-2-pyrrolidoni-
4
+
À
um hydrogen sulfate ([NMP] [HSO ] ), 1-methylimidazolium
4
+
À
methyl sulfonate ([MIM] [CH SO ] ), and N-methyl-2-pyrrolido-
3
3
+
À
nium methyl sulfonate ([NMP] [CH SO ] ) were synthesized
3
3
and employed as catalysts for the reaction. Here, the ILs
+
À
+
À
[
NMP] [CH SO ] and [NMP] [HSO ] showed the highest cata-
3 3
4
+
lytic activities in the dehydration of d-fructose; [NMP] -
À
[
CH SO ] also exhibited superior selectivity for HMF.
3
3
Results and Discussion
Basic characterizations of Brønsted-acidic ILs
The preparation procedures of the ILs are similar to those re-
Figure 1. The UV/Vis spectra according to the Hammett method (the ampli-
[
29–31]
fied peaks are presented at the top right corner). Concentrations:
ported in previous literature.
The detailed synthesis condi-
À2
À1
À5
À1
+
À
3.0ꢁ10 molL of ILs and 7.5ꢁ10 molL p-nitroaniline in methanol.
tions are described in the experimental section. [MIM] [HSO ]
4
+
À
and [NMP] [HSO ] are colorless and light yellow liquid at
4
+
À
room temperature, respectively. The fresh [NMP] [CH SO ] is a
3
3
Table 1. Hammett function values of various ILs.
viscous liquid at room temperature; however, it solidifies after
+
À
[a]
+
[b]
[c]
0
several days. [MIM] [CH SO ] is a white solid at room temper-
Ionic liquid
Absorbance
[In] [%]
[InH ] [%]
H
3
3
ature.
none
1.13
1.13
1.12
0.94
0.99
100
100
99.1
83.2
87.6
0
0
0.9
16.8
12.4
–
–
3.03
1.69
1.84
+
À
[
MIM] [HSO
4
]
+
À
[
MIM] [CH
3
SO
3
À
]
+
Hammett acidity of Brønsted-acidic ILs
4
[NMP] [HSO ]
+
À
[
NMP] [CH SO ]
3 3
As the dehydration of d-fructose is closely associated with the
[
32]
[a] [In] represents the molar concentration of the 4-nitroaniline indicator.
acidity of the catalyst, Hammett acidity function of the dif-
ferent ILs was investigated in methanol solution. Based on the
+
[
b] [InH ] represents the molar concentration of the protonated 4-nitroa-
+
niline. [c] H
0
=pK
a
(In)+log([In]/[InH ]), pK
a
=0.99; solvent: methanol;
[
33]
À5
À1
À2
À1
protocol given by Gilbert et al., the acidities of these Brønst-
ed-acidic ILs were characterized using UV/Vis spectroscopy
with p-nitroaniline as the indicator and molecular probe.
Therein, the ILs and 4-nitroaniline were dissolved in methanol
c(In)=7.5ꢁ10
58C.
molL
;
c(sample)=3.0ꢁ10
molL ; temperature=
2
Dehydration of d-fructose to HMF catalyzed by Brønsted-
acidic ILs
À2
À1
À5
À1
with concentrations of 3.0ꢁ10 molL and 7.5ꢁ10 molL ,
respectively. Then, the solutions were mixed for 2 h with mag-
netic stirring, and then their UV spectra were recorded with a
PerkinElmer Lambda 900 UV/Vis spectrometer. The experimen-
tal data are summarized in Figure 1 and Table 1. There was a
noticeable change in the absorption curve of p-nitroaniline in
methanol in the wavelength region from 350 to 400 nm upon
the addition of the acidic ILs (Figure 1); moreover, compared
The dehydration of d-fructose was carried out in a 100 mL
flask with a condenser under a nitrogen atmosphere. After the
reaction, the mixture was decanted into a volumetric flask
using H O or ethanol as diluter, and then analyzed by HPLC
2
equipped with UV and refractive index detectors. In a typical
dehydration reaction, d-fructose loses three water molecules
to produce HMF in the presence of Brønsted-acidic ILs
(Scheme 1).
+
to the addition of [MIM] -based ILs, the change in absorbance
+
was more obvious when [NMP] -based ILs were added to the
p-nitroaniline solution. Correspondingly, the protonic acidity of
In Table 2, the dehydration results of d-fructose with differ-
+
+
+
[NMP] -based ILs is stronger than that of [MIM] -based ILs.
ent ILs as catalysts are summarized. [NMP] -based ILs showed
+
In Table 1, the Hammett acidity function (H ) can be ex-
better catalytic performance than [MIM] -based ILs; moreover,
0
+
À
pressed as the equation H =pK (In)+log([In]/[InH ]), where
the ILs containing [CH SO ] ion exhibited better selectivity
0
a
3
3
À
pK (In) is the pK value of the p-nitroaniline indicator solution
than those containing [HSO4] under the same conditions.
a
a
+
(
about 0.99), [In] and [InH ] are the molar concentrations of
the protonated and unprotonated forms of p-nitroaniline indi-
cator, respectively. Based on the UV spectra of Figure 1, the
quantitative data of H values were obtained. The correspond-
0
+
À
+
À
+
ing H values of [MIM] [CH SO ] , [NMP] [HSO ] , and [NMP] -
0
3
3
4
À
[
CH SO ] were 3.03, 1.69, and 1.84, respectively (Table 1).
3 3
+
À
These results indicated that the acidity of [NMP] [HSO ] was
4
the strongest among these ILs examined, and the acidity of
+
À
+
À
[
NMP] [CH SO ] was very close to that of [NMP] [HSO ] .
Scheme 1. Reaction process for the dehydration of d-fructose.
3
3
4
ChemSusChem 2010, 3, 350 – 355
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
351

Y. Li and X. Tong
[
a]
Table 2. Dehydration of d-fructose catalyzed by the acidic ILs.
[
b]
[b]
Entry
Catalysts
Solvent
Yield [%]
Selectivity [%]
+
À
1
2
3
4
5
6
7
[NMP] [HSO
4
]
]
DMSO
DMSO
DMSO
DMSO
DMSO
69.4
23.6
72.3
25.1
3.2
70.4
51.6
87.2
63.1
68.1
–
+
À
[MIM] [HSO
4
+
À
[NMP] [CH SO ]
3 3
À
SO ]
3 3
+
[MIM] [CH
none
+
À
[NMP] [HSO
4
]
H
H
2
O
O
2.4
2.7
+
À
[NMP] [CH
3
SO
3
]
2
–
[
a] The reaction of d-fructose was performed on a 1.0 g scale, in the pres-
ence of acidic IL (7.5 mol%) under nitrogen atmosphere, in solvent
12 mL); reaction time=2 h, temperature=908C. [b] Yield and selectivity
(
of HMF were obtained by HPLC analysis.
Yields of 69.4% or 72.3% HMF were obtained in dimethylsulf-
Figure 2. Effect of reaction time on the dehydration of d-fructose.
+
À
+
oxide (DMSO) when 7.5 mol% [NMP] [HSO ] or [NMP] -
4
À
[
CH SO ] were employed in the reaction, respectively (Table 2,
3
3
+
À
entries 1 and 3). On the other hand, using [MIM] [HSO ] or
4
+
À
[
MIM] [CH SO ] as a catalyst, only 23.6% or 25.1% yields were
3 3
obtained, respectively (Table 2, entries 2 and 4). In selectivity,
+
8
7.2% and 70.4% of HMF in the presence of [NMP] -based ILs
were also satisfying. For comparison, a blank experiment was
carried out in the absence of any IL, and the HMF yield was
3
.2% (Table 2, entry 5). Furthermore, the dehydration reactions
+
À
of d-fructose in pure water in the presence of [NMP] [HSO ]
or [NMP] [CH SO ] were also carried out, and the yields of
4
+
À
3
3
HMF were 2.4% and 2.7%, respectively (Table 2, entries 6 and
+
À
7
). These results indicated that [NMP] [CH SO ] was the most
3 3
efficient catalyst for the dehydration of d-fructose to HMF in
all four acidic ILs.
Effect of reaction time and temperature for the dehydration
of d-fructose
Figure 3. Effect of temperature on the dehydration of d-fructose.
The effect of reaction time in the dehydration of d-fructose
+
À
catalyzed by [NMP] [CH SO ] is shown in Figure 2. It was
3
3
found that the yield of HMF increased gradually and the selec-
tivity was maintained during the reaction from 0.5 h to 2.0 h.
When the time was extended to 2.5 h and longer, the yield
and selectivity of HMF decreased, which indicated that the
conversion to byproducts was probably more rapid than the
generation of HMF. The effect of temperature is presented in
Figure 3. The yield of HMF increased slowly and the selectivity
hardly changed from 408C to 908C. However, the HMF yield
decreased gradually when the temperature was further elevat-
ed to the higher range. These results showed that the optimal
temperature was 908C in the acidic IL-catalyzed dehydration of
d-fructose.
was superior to 5.9% conversion or 4.2% conversion with eth-
anol or acetonitrile as a solvent. When carbon tetrachloride
was used as a solvent, due to the limited solubility of d-fruc-
tose, the dehydration reaction hardly occurred. It was conclud-
ed that aprotic and polar solvents are more suitable for this re-
action system, which can be attributed to their ability to solu-
bilize and differentiate the structures. However, DMSO is also a
[
a]
Table 3. Dehydration of d-fructose in the different solvents.
[
b]
[b]
Entry
Solvent
Yield [%]
Selectivity [%]
1
2
3
4
5
ethanol
acetonitrile
dimethylacetamide(DMAc)
dimethylsulfoxide (DMSO)
carbon tetrachloride
5.9
4.2
20.5
69.4
0.3
63.5
67.3
75.1
87.8
–
Effect of solvent in the dehydration of d-fructose
Different solvents, including protic (ethanol) and aprotic ones
(
N, N-dimethyl acetamide, acetonitrile, carbon tetrachloride,
[
a] The reaction of d-fructose was performed on a 1.0 g scale, in the pres-
+
À
and DMSO), were employed in the dehydration of d-fructose
for 2 h at 858C (Table 3). Here, 20.5% conversion or 69.4% con-
version with N, N-dimethylacetamide or DMSO as a solvent
ence of [NMP] [CH SO ] (7.5 mol%) under nitrogen atmosphere, in sol-
vent (12 mL); reaction time=2 h, temperature=858C. [b] Yield and selec-
tivity of HMF were obtained by HPLC analysis.
3 3
3
52
www.chemsuschem.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2010, 3, 350 – 355

Efficient and Selective Dehydration of Fructose to 5-Hydroxymethylfurfural
favorable solvent for the dehydration of d-fructose to HMF
due to its ability to prevent the formation of byproducts, such
as levulinic acid and humins.
[
a]
Table 4. Dehydration of glucose in the prensence of Brønsted-acidic ILs.
[
b]
Entry
Catalysts
Solvent
Yield [%]
+
À
1
2
3
4
[NMP] [CH
3
SO
3
À
]
DMSO
DMSO
DMSO
DMSO
3.0
2.4
1.4
+
[NMP] [HSO
sulfuric acid
4
]
Investigations on the recycling of catalyst and solvent
hydrochloric acid
21.2
The recycling of catalyst and the reuse of solvent were exam-
[
a] The dehydration reaction of glucose was performed on a 1.0 g scale,
ined. The investigations were performed at 908C for 2 h in the
+
À
in the presence of acidic IL or mineral acid (10.0 mol%) under a nitrogen
atmosphere, in solvent (12 mL); reaction time=2 h, temperature=908C.
presence of [NMP] [CH SO ] (10.0 mol%). After the dehydra-
3
3
tion reaction, the mixture was first distilled under reduced
pressure. Pure DMSO was collected and the remaining mixture
was extracted with ethyl acetate (10 mLꢁ4) after water (0.5 g)
[
b] Yield and selectivity of HMF were obtained by HPLC analysis.
[27]
was added, similar to other procedures in the literature. d-
+
À
+
À
3
Fructose and [NMP] [CH SO ] were found to be insoluble in
3.0% or 2.4% in DMSO solvent when [NMP] [CH
À
[NMP] [HSO ] was employed as a catalyst (entries 1 and 2).
4
3
SO
]
or
3
3
+
ethyl acetate; thus, the total amount of extracted HMF in the
combined ethyl acetate layers was accounted as the isolated
yield of HMF. The obtained mixture after extraction was heated
at 758C for 12 h in a vacuum oven to remove water and resid-
ual ethyl acetate. It was then used directly in the next run by
adding the distilled DMSO and an equal amount of d-fructose.
The yield of HMF was essentially maintained for the former
three recycled reactions (Figure 4), which showed that the cat-
Moreover, a 1.4% or 21.2% yield of HMF was obtained in the
presence of 10.0 mol% sulfuric acid or hydrochloric acid (en-
tries 3 and 4). Compared to the results on the dehydration of
d-fructose, these data indicate that the catalytic efficiency of
acidic ILs is closely related to the reaction substrate. The differ-
ence between the dehydration of d-fructose and glucose is
helpful to understand the dehydration mechanism of hexoses
+
in the presence of [NMP] -based acidic ILs, which shows that
the ketose is more easily dehydrated than aldose in this cata-
lytic system.
Mechanism of the d-fructose dehydration by acidic ILs
From the above experimental results, it can be shown that the
dehydration of d-fructose to HMF catalyzed by the acidic ILs is
a very complex process. In general, the efficiency in the d-fruc-
tose dehydration is closely related to the acidity of the catalyst.
However, the product selectivity can be affected by numerous
factors, such as the structure effect and solvent effect. Thus,
the cyclic furan and enediol intermediates were proposed to
account for the mechanism of the dehydration of d-fruc-
[34,35]
tose.
NMP] [HSO ] and [NMP] [CH SO ] have higher acidity and
+
À
+
À
3
[
4
3
+
exhibit better activity compared to [MIM] -based acidic ILs.
Figure 4. Recycling of the catalyst system in the dehydration of d-fructose
+
À
+
À
(the reaction condition was similar to that of Table 2, entry 3).
The acidity of [MIM] [HSO ] and [MIM] [CH SO ] are very
4 3
3
weak; accordingly, their catalytic performances are rather poor
in the reaction. In our catalytic system, the conversion of d-
fructose was likely sensitive to the structure of the ionic liquid.
As shown in Scheme 2, the first and third water molecules can
be lost directly under appropriate protonic acidity; neverthe-
less, the loss of the second water molecule is selective and
alyst retained very high activity for the dehydration of d-fruc-
tose. Furthermore, the yield of HMF only decreased slightly
(
about 3.0%) after being recycled five times. All these results
+
À
indicated that the catalyst [NMP] [CH SO ] was efficiently re-
3
3
cycled in the d-fructose dehydra-
tion.
Dehydration of glucose cata-
lyzed by Brønsted-acidic ILs
The dehydration of glucose was
+
investigated using [NMP] -based
acidic ILs and mineral acid under
similar reaction conditions. In
Table 4 the yield of HMF was Scheme 2. Possible mechanism for the dehydration of d-fructose.
ChemSusChem 2010, 3, 350 – 355
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
353

Y. Li and X. Tong
+
À
needs the help of a chemical force, which has been testified
[NMP] [HSO
(
5
]
4
was obtained by mixing N-methyl-2-pyrrolidone
[
36]
+
À
9.9 g, 0.1 mol) with concentrated sulfuric acid (9.6 g, 0.1 mol) at 0–
8C and stirring for 4 h at room temperature. The liquid was then
washed with ethyl acetate (3ꢁ10 mL) and dried at 808C in vacuo.
The ionic liquid was obtained in quantitative yield. H NMR
[D ]DMSO): d=3.266–3.294 (t, 2H, J=7.2 Hz), 2.665 (s, 3H), 2.143–
.175 (t, 2H, J=8.1 Hz), 1.840–1.900 ppm (quint, 2H, J=7.6 Hz).
ESI-MS: m/z (+) 99.9 [NMP] , 96.8 [HSO ] .
by an NMR study.
Here, when [NMP] [CH SO ] was em-
3
3
ployed as a catalyst, the IL may have interacted with d-fructose
or the intermediate through hydrogen bonding and nucleo-
philic effect, owing to the existence of a carbonyl group and
protonated nitrous cation, which led to the production of HMF
with high selectivity. Indeed, in the dehydration of glucose, the
yield of HMF was relatively low due to the difficulty in forming
a penta-ringed structure. Further investigations on the capture
of the intermediates are underway.
1
(
6
2
+
À
4
+
À
The preparation of the ionic liquid [MIM] [HSO ] was similar to
4
+
À
1
that of [NMP] [HSO4] . H NMR (DMSO-d6, 500 MHz): 9.011 (s, 1H),
.626–7.675 (d, 2H, J=25.1 Hz), 3.846 (s, 3H); ESI-MS: m/z 83.2
7
[
+
À
MIM] , 97.0 [HSO ] .
4
Conclusions
Reaction conditions for the dehydration of d-fructose
Efficient synthesis of HMF from d-fructose dehydration has
been achieved using small amounts of acidic ILs as catalysts
All the dehydration reaction experiments were performed in a
1
00 mL flask equipped with magnetic stirring and a condenser.
+
À
under mild conditions. [NMP] [CH SO ] showed very high cat-
3
3
Typical procedure for dehydration of d-fructose is as follows: a so-
lution of d-fructose (1.0 g, 5.6 mmol), acidic ILs (7.5 mol%), and sol-
vent (12 mL) were charged into the flask. The atmosphere inside
was replaced with nitrogen before the flask was airproofed. Under
stirring, the flask was preheated to 908C with an oil bath and then
remained for 2 h under a nitrogen atmosphere. After the reaction,
the mixture was decanted to a volumetric flask with pure H O or
ethanol as diluter, and then analyzed by an HPLC equipped with
UV and refractive index detectors.
alytic activity and selectivity in the dehydration of d-fructose,
and a 72.3% HMF yield and 87.2% selectivity were obtained
when it was employed as a catalyst at 908C after 2 h. Com-
pared to pure water and other solvents, DMSO was a better re-
action medium and exhibited superior performance in the de-
hydration of d-fructose and glucose. The effects of reaction
time and reaction temperature were investigated in detail. The
catalyst and solvent can be recycled for the dehydration of d-
fructose. The relationship between the characteristics of ILs
and the catalytic activity was discussed according to the Ham-
mett acidity function and the experimental results. Further-
more, a possible mechanism for the dehydration of d-fructose
was proposed.
2
Typical separation procedure for HMF
After the dehydration of d-fructose, the reaction mixture was trans-
ferred into a flask and was distilled under reduced pressure. The re-
maining mixture was extracted with ethyl acetate (10 mLꢁ4) after
water (0.5 g) was added, and then the organic phase was collected.
After drying with anhydrous sodium sulfate, the organic layer was
distilled under reduced pressure to obtain pure HMF as the main
product. The purity was more than 95% from HPLC analysis.
Experimental Section
1
Reagents
H NMR spectrum ([D6]DMSO): 3.396–3.483 (d, 1H, J=7.078), 4.483
(
9
1
s, 2H), 6.580–6.586 (d, 1H, J=3.417) 7.466–7.473 (d, 1H, J=3.417),
.522 (s, 1H); C NMR spectrum ([D6]DMSO): d 56.524, 56.650,
10.385, 152.413, 162.805, 178.667. The GC/MS and HPLC spectra
N-methyl-2-pyrrolidone, 1-methylimidazole, H SO , CH SO H, d-fruc-
2
4
3
3
13
tose, and glucose were analytical grade. The anhydrous DMSO was
purified by distillation. The pure water was prepared by the Ultra-
pure Water System (electrical resistivity=10–16 mWcm). The HMF
used as the standard sample was purchased from Alfa Aesar.
of reaction products and detailed HPLC measurement conditions
are contained in the Supporting Information.
Acknowledgements
Synthesis procedure and characterization data of ILs
+
À
X.T. thanks the China Postdoctoral Science Foundation
[
NMP] [CH SO ] was synthesized using the following procedure:
3 3
(
20080440676) for financial support. Y.L. thanks the Natural Sci-
N-methyl-2-pyrrolidone (9.9 g, 0.1 mol) was added to a 50 mL flask
with magnetic stirring. Then, methyl sulfonic acid (9.6 g, 0.1 mol)
was dropped slowly into the flask over approximately 30 min in an
ice bath. The reaction was kept stirring for another 4 h at room
ence Foundation of China under contract number 20425619 for
support. This work was also supported by the Program of Intro-
ducing Talents to the University Disciplines under file number
B06006, and the Program for Changjiang Scholars and Innova-
tive Research Teams in Universities under the file number IRT
temperature. The mixture was washed with ethyl acetate three
1
times and dried at 908C under vacuum. H NMR ([D ]DMSO): d=
6
8
2
1
.568 (s, 1H), 3.270–3.298 (t, 2H, J=7.1 Hz), 2.672 (s, 3H), 2.458–
0
641.
.464 (d, 3H, J=2.2 Hz), 2.144–2.177(t, 2H, J=8.1 Hz) 1.861–
+
.906 ppm (quint, 2H, J=7.6 Hz). ESI-MS: m/z 99.8 [NMP] , 94.8
À
[
CH SO ] .
3
3
Keywords: biomass
· Brønsted acids · carbohydrates ·
+
À
3
dehydration · ionic liquids
The preparation of ionic liquid [MIM] [CH SO ] was similar to that
3
+
À
1
of [NMP] [CH SO ] . H NMR (DMSO-d6, 500 MHz): 9.037 (s, 1H),
3
3
7
.646–7.675 (d, 2H, J=14.5 Hz), 3.851 (s, 3H), 3.390 (s, 1H), 2.328
[1] Y. Roman-Leshkov, J. N. Chheda, J. A. Dumesic, Science 2006, 312, 1933–
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À
(
s, 3H). ESI-MS: m/z 83.2 [MIM] , 95.1 [CH SO ] .
1937.
3
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54
www.chemsuschem.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: September 28, 2009
Revised: October 27, 2009
Published online on January 15, 2010
ChemSusChem 2010, 3, 350 – 355
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
355