Syntheses of 5-hydroxymethylfurfural and levoglucosan by selective dehydration of glucose using solid acid and base catalysts

Article abstract of DOI:10.1016/j.apcata.2010.05.040

Selective dehydration of glucose, the most abundant monosaccharide, was examined using a solid acid catalyst individually or a combination of solid acid and base catalysts to form anhydroglucose (levoglucosan) or 5-hydroxymethylfurfural (HMF), respectively. Glucose was dehydrated to anhydroglucose by acid catalysis in polar aprotic solvents including N,N-dimethylformamide. Amberlyst-15, a strongly acidic ion-exchange resin, functioned as an efficient solid acid catalyst for anhydroglucose production with high selectivity. In the presence of solid base, aldose-ketose isomerization of glucose to fructose preferentially occurred by base catalysis, even in coexistence with the solid acid, resulting in successive dehydration of fructose to 5-hydroxymethylfurfural by acid catalysis with high yield in a one-pot reaction. A combination of Amberlyst-15 and hydrotalcite, an anionic layered clay, afforded high HMF selectivity under a moderate reaction temperature, owing to prevention of anhydroglucose formation.

Full text of DOI:10.1016/j.apcata.2010.05.040

Applied Catalysis A: General 383 (2010) 149–155
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Syntheses of 5-hydroxymethylfurfural and levoglucosan by selective
dehydration of glucose using solid acid and base catalysts
Mika Ohara, Atsushi Takagaki, Shun Nishimura, Kohki Ebitani∗
School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Selective dehydration of glucose, the most abundant monosaccharide, was examined using a solid acid
catalyst individually or a combination of solid acid and base catalysts to form anhydroglucose (levoglu-
cosan) or 5-hydroxymethylfurfural (HMF), respectively. Glucose was dehydrated to anhydroglucose by
acid catalysis in polar aprotic solvents including N,N-dimethylformamide. Amberlyst-15, a strongly acidic
ion-exchange resin, functioned as an efficient solid acid catalyst for anhydroglucose production with high
selectivity. In the presence of solid base, aldose–ketose isomerization of glucose to fructose preferentially
occurred by base catalysis, even in coexistence with the solid acid, resulting in successive dehydration
of fructose to 5-hydroxymethylfurfural by acid catalysis with high yield in a one-pot reaction. A combi-
nation of Amberlyst-15 and hydrotalcite, an anionic layered clay, afforded high HMF selectivity under a
moderate reaction temperature, owing to prevention of anhydroglucose formation.
Received 19 February 2010
Received in revised form 13 May 2010
Accepted 26 May 2010
Available online 4 June 2010
Keywords:
Biorefinery
Dehydration
Carbohydrate
One-pot synthesis
Acid–base catalysis
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
maceuticals [7–10]. These anhydroglucoses are obtained by
dehydration of one water molecule from 1,6-␤-d-glucopyranose
Currently, the world faces serious environmental and economic
issues related to our overwhelming dependence on fossil fuels for
energy and chemical production and the resulting global warming
that arises from their conversion to carbon dioxide. Biomass offers
a promising alternative to fossil fuels as a renewable resource as it
can be produced in a carbon neutral way [1,2]. To avoid competition
for land resources dedicated to food and animal-feed production,
it is strongly desirable to utilize an inedible biomass. Wood-
based biomass offers an abundant resource comprising cellulose
(35–50%), hemicellulose (25–30%) and lignin (25–30%). Cellulose
and hemicellulose can be depolymerized into monosaccharides
including glucose, fructose and xylose. Among them, glucose is the
most abundant monosaccharide, and therefore transformation of
glucose has attracted much attention for the production of alterna-
tive chemicals as an efficient biorefinery [3–5].
Dehydration of glucose is an important and attractive
chemical reaction because it produces two valuable deriva-
tives, anhydroglucose and 5-hydroxymethylfurfural (Fig. 1)
[6]. These anhydroglucoses, 1,6-anhydro-␤-d-glucopyranose and
1,6-anhydro-␤-d-glucofuranose, are highly valuable chemicals.
1,6-Anhydro-␤-d-glucopyranose, also known as levoglucosan,
can be used as an intermediate for biodegradable surfactants,
stereoregular polysaccharides, hyperbranched polymers and phar-
and 1,6-␤-d-glucofuranose, respectively, where the pyranose and
furanose forms are under tautomeric equilibrium. The efficient
production of anhydroglucose has recently been examined in
detail using 2-chloro-1,3-dimethylimidazolinium chloride as a
strong dehydrating agent [11] and hydrophobic ionic liquids
including N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium
bis(trifluoromethanesulfonyl)amide [12].
5-Hydroxymethylfurfural (HMF) as a furan derivative can be
formed by elimination of three water molecules from hexoses
(glucose or fructose), and is a desirable intermediate for plastics,
polymers and fuels [3,4,13]. For instance, HMF can be oxidized
to form 2,5-diformylfuran [14–17] and 2,5-furandicarboxylic
acid [18–21]. These derivatives are expected to be highly useful
intermediates for a variety of polymers and plastics. Levulinic acid,
which is obtained by rehydration of HMF, is also an important
intermediate for polymers [3,4]. Further, Dumesic et al. proposed
that a dimethylfuran derived from HMF is a promising biofuel
with a higher energy density and boiling point than ethanol [22].
Because of the great potential of HMF as a versatile platform, a
large number of researchers have investigated the more efficient
production of HMF by several different methods [23–51]. For
example, efficient production of HMF has been reported using an
organic-water biphasic system, in which hydrochloric acid in the
water phase dehydrates fructose or glucose to form HMF, which
is subsequently extracted into the organic phase, resulting in
high HMF selectivity [25–28]. The use of ionic liquids containing
metal ions such as chromium has also been a notable method for
∗
Corresponding author. Tel.: +81 761 51 1610; fax: +81 761 51 1625.
E-mail address: ebitani@jaist.ac.jp (K. Ebitani).
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.05.040

150
M. Ohara et al. / Applied Catalysis A: General 383 (2010) 149–155
hydroxymethylfurfural, respectively. Fig. 2 illustrates the proposed
reaction pathway for selective dehydration of glucose using the
solid acid and base catalysts. A strong acidic ion-exchange resin,
Amberlyst-15 was used as the solid acid catalyst, and a layered
clay compound, hydrotalcite, was used as the solid base catalyst
[59–68]. The former is a macroreticular sulfonated polystyrene-
based ion-exchange resin with 20% divinylbenzene. The latter is a
3+
layered anionic clay denoted as [M2+
M
x(OH)2]x+An− ·mH2O,
1−x
x/n
where M2+ and M3+ are di- and trivalent metal ions, and An− rep-
resents the interlayer anions. Anionic species such as carbonate
and hydroxide are located to compensate the positively charged
brucite layer. Mg–Al hydrotalcite, i.e. Mg6Al2(OH)16CO3·nH2O, is
generally used as the active solid base catalyst for several reactions
including aldol condensation, Knoevenagel reaction, epoxidation
and transesterification [59–68].
2. Experimental
Fig. 1. Selective dehydration of glucose to anhydroglucose and 5-hydroxymethyl-
furfural.
2.1. Materials
d-glucose and d-fructose were purchased from Wako Pure
Chemical Industries, Ltd. Amberlyst-15 was purchased from
Sigma–Aldrich Corporation. Hydrotalcite (Mg/Al = 3) was supplied
from Tomita Pharmaceutical Co. Ltd. N,N-Dimethylformamide
(DMF), N,N-dimethylacetamide (DMA), dimethyl sulfoxide (DMSO)
and acetonitrile (MeCN) were purchased from Kanto Chemical Co.
Inc. Solvents were used after purification by distillation.
HMF production, providing high selectivity with high conversion
[29–39].
HMF can be much more easily synthesized from fructose than
glucose by dehydration because of the difference in their chemical
structures. Fructose, as a ketohexose, readily dehydrates to form
HMF under mild acid conditions. In contrast, glucose, as an aldo-
hexose, gives poor HMF selectivity in direct dehydration due to side
reactions, including cross-condensation, resulting in the formation
of humins and oligomers.
2.2. Glucose and fructose dehydration
We have adopted an alternative approach for HMF synthe-
sis from glucose through a two-step reaction in one-pot [52].
It is known that glucose can be transformed into fructose by
aldose–ketose isomerization catalyzed by a base [53]. The obtained
fructose could easily be converted into HMF in the presence of acid.
This simple methodology can be performed using a solid acid cata-
lyst along with a solid base catalyst in one-pot. The combination of
solid acid and base catalysts offers the opportunity to utilize acid
or base activity separately even in one reactor, whereas for a liquid
acid–base pair, neutralization and subsequent deactivation would
naturally occur. One-pot reactions using heterogeneous catalysts
afford environmentally friendly benefits, including avoidance of
isolation and purification of intermediate compounds, which saves
time, energy and solvent [54–58].
Glucose and fructose dehydrations were performed using 0.1 g
of glucose or fructose, 3–10 mL of DMF, 0.025–0.1 g of Amberlyst-
15 and/or 0.05–0.2 g of hydrotalcite in an oil bath at 353–413 K. The
experiments were carried out in a Schlenk tube attached to a reflux
condenser under an N2 atmosphere.
2.3. Analytical procedures
The conversions and yields were estimated using high-
performance liquid chromatography (HPLC) (Waters) with an
Aminex HPX-87H column from Bio-Rad Laboratories, Inc. Samples
were diluted with water before HPLC measurement. The products
were analyzed using a refractive index (RI) detector. The anal-
ysis conditions were set as follows: eluent, 10 mM H2SO4; flow
rate, 0.5 mL/min; column temperature, 323 K. The retention times
for detected compounds were 11.6, 12.5, 14.8, 13.6, 38, 20.2 and
In this study, selective dehydration of glucose was examined
using either a solid acid individually or a combination of solid acid
and base catalysts for the production of anhydroglucoses or 5-
Fig. 2. A reaction pathway for anhydroglucose and 5-hydroxymethylfurfural formation from glucose in the presence of solid acid and base catalysts.

M. Ohara et al. / Applied Catalysis A: General 383 (2010) 149–155
151
Scheme 1. Anhydroglucose formation from d-glucose over Amberlyst-15.
17.5 for glucose, fructose, 1,6-anhydro-␤-d-glucopyranose (AGP),
1,6-anhydro-␤-d-glucofuranose (AGF), 5-hydroxymethylfurfural
(HMF), levulinic acid and formic acid, respectively.
3. Results and discussion
3.1. Anhydroglucose formation from glucose by dehydration over
Amberlyst-15
Anhydroglucose was found to be selectively synthesized
from glucose in the presence of Amberlyst-15 in N,N-
dimethylformamide (DMF), whereas no anhydroglucose was
formed in the absence of acid (Scheme 1) [69]. Table 1 summarizes
the formation of anhydroglucose from d-glucose in different vol-
umes of DMF over Amberlyst-15 at 393 K for 3 h. The yields of the
anhydroglucoses (sum of 1,6-anhydro-␤-d-glucopyranose (AGP)
and 1,6-anhydo-␤-d-glucofuranose (AGF)) were not affected much
by the solvent amount. In contrast, glucose conversion decreased
markedly with an increase in solvent amount, resulting in an
increase in anhydroglucose selectivity (from 43% to 78%). Thus,
since a high glucose concentration leads to undesired by-products
such as oligomers, a low concentration of the substrate is therefore
much preferred to ensure high selectivity of anhydroglucose. The
use of 0.1 g of catalyst improved both the conversion and yield
while maintaining the anhydroglucose selectivity (entry 4).
The anhydroglucose yield was found to increase with increas-
ing reaction temperature. Fig. 3 shows the dependence of glucose
conversion, anhydroglucose yield and selectivity on reaction tem-
perature. Both the glucose conversion and the anhydroglucose yield
increased with increasing reaction temperature. The anhydroglu-
cose selectivity remained high at ∼80%. Glucose conversion of 93%
and a selectivity of 77% were obtained at 413 K for 3 h. A similarly
high conversion and selectivity were also observed at 393 K by
increasing the reaction time (76% selectivity and 87% conversion
at 393 K for 5 h). It should be noted that formation of anhy-
droglucose by dehydration was suppressed below 373 K, which
is a beneficial feature for one-pot synthesis of HMF from glucose
(vide infra).
Fig. 3. Dependence of glucose conversion (filled circle), anhydroglucose yield (open
square) and selectivity (filled triangle) on reaction temperature for dehydration of
glucose in DMF solution using Amberlyst-15. Reaction conditions: glucose (0.09 g),
Amberlyst-15 (0.1 g), DMF (10 mL), 3 h.
Scheme 2. Isomerization of glucose over hydrotalcite.
3.2. Isomerization of glucose to fructose over hydrotalcite
In the presence of a base, glucose can be transformed into
fructose by aldose–ketose isomerization. Hydrotalcite is known to
efficiently catalyze this base reaction (Scheme 2) [67,68]. Table 2
summarizes the isomerization of glucose to fructose over hydro-
talcite (0.1 g) at 353–393 K for 3 h with DMF as solvent. Glucose
conversion increased with increasing reaction temperature from
47% at 353 K to 81% at 393 K. Correspondingly, however, the fruc-
Table 1
Anhydroglucose formation from d-glucose in N,N-dimethylformamide over Amberlyst-15.a.
Entry
Solvent amount (mL)
Conv. (%)
Yield (%)
AGPb
Selec. (%)
AGFc
AGP + AGF
1
2
2.5
5
10
10
67
53
30
44
16
16
14
19
13
11
9
29
27
23
35
43
51
77
80
3
4d
16
a
Reaction conditions: glucose (0.09 g), Amberlyst-15 (0.05 g), DMF, 393 K, 3 h.
1,6-Anhydro-␤-d-glucopyranose.
1,6-Anhydro-␤-d-glucofuranose.
b
c
d
Using 0.1 g of Amberlyst-15.

152
M. Ohara et al. / Applied Catalysis A: General 383 (2010) 149–155
Table 2
Fructose formation by isomerization of glucose over hydrotalcite.a.
Reaction temperature (K)
Glucose conversion (%)
Fructose yield (%)
Fructose selectivity (%)
353
373
393
47
62
81
40
38
32
85
62
40
a
Reaction conditions: glucose (0.1 g), hydrotalcite (0.1 g), DMF (3 mL), 3 h.
Fig. 5. Effect of reaction temperature on product distribution of glucose transfor-
mation using Amberlyst-15 and hydrotalcite. Reaction conditions: glucose (0.1 g),
Amberlyst-15 (0.1 g), hydrotalcite (0.1 g), DMF (3 mL), 353–393 K, 3 h.
Fig. 4. Time course of HMF formation from fructose over Amberlyst-15. Reaction
conditions: fructose (0.1 g), Amberlyst-15 (0.1 g), DMF (3 mL), 353 K and 373 K. Fruc-
tose conversion (353 K (ꢀ) and 373 K (᭹)). HMF yield (353 K (ꢀ) and 373 K (ꢁ)).
88% selectivity for 2 h. High selectivity of ∼90% at high yield could
be obtained at both 353 K and 373 K. It should be noted that fructose
dehydration for HMF could proceed at much lower temperatures
(below 373 K) than glucose dehydration for anhydroglucose (above
383 K) using the same catalytic system. This indicates a significant
difference between glucose dehydration and fructose dehydration
over Amberlyst-15 in DMF.
tose yield gradually decreased from 40% at 353 K to 32% at 393 K,
leading to a decrease in fructose selectivity at high tempera-
tures. The appearance of humins was observed on the surface of
hydrotalcite after the isomerization, especially at high temperature
reaction, presumably attributable to base-catalyzed condensa-
tion. Low temperatures are preferred to maintain a high fructose
selectivity even though glucose conversion is relatively low (85%
fructose selectivity and 47% glucose conversion at 353 K) in these
conditions. The aldose–ketose isomerization is an equilibrium reac-
tion. When fructose was first added to DMF containing 0.1 g of
hydrotalcite at 373 K, 20% of the fructose was converted after 3 h,
resulting in a 13% yield of glucose with 64% selectivity, which is
equivalent to glucose isomerization.
3.4. HMF formation from glucose in the presence of solid acid and
base catalysts in one-pot
One-pot synthesis of HMF from glucose was examined using
Amberlyst-15 and hydrotalcite (Scheme 3). This methodology has
the potential to improve HMF selectivity via the formation of fruc-
tose as an intermediate under a moderate temperature. The effects
of reaction temperature on the product distribution of glucose
transformation using Amberlyst-15 and hydrotalcite are shown in
Fig. 5. The reaction was performed using 0.1 g of glucose, 0.1 g of
Amberlyst-15, 0.1 g of hydrotalcite in 3 mL of DMF at 353–393 K
for 3 h. With increasing reaction temperature glucose conversion
increased from 43% at 353 K to 99% at 393 K. HMF yield remained
unchanged from 353 K to 393 K, resulting in a decrease in selec-
tivity from 52% to 18% with increasing temperature. In contrast,
anhydroglucose formation increased with increasing temperature,
giving yields of 7%, 18% and 22% at 353 K, 373 K and 393 K, respec-
tively.
3.3. HMF formation from fructose by dehydration over
Amberlyst-15
In contrast to glucose, fructose readily dehydrates to form HMF
using Amberlyst-15 under mild conditions. Fig. 4 shows the time
course of HMF formation from fructose over Amberlyst-15 at 353 K
and 373 K. At 373 K, 66% of the fructose was converted into HMF
after 15 min. After 1 h, the fructose was fully converted, provid-
ing HMF with considerable selectivity (91%). HMF was successfully
obtained even at 353 K, with a 46% yield for 1 h and a 77% yield with
The product distribution was also influenced by the amounts
of solid acid and base catalyst. Table 3 summarizes the depen-
Scheme 3. One-pot synthesis of 5-hydroxymethylfurfural from glucose using Amberlyst-15 and hydrotalcite.

M. Ohara et al. / Applied Catalysis A: General 383 (2010) 149–155
153
Table 3
One-pot synthesis of 5-hydroxymethylfurfural from glucose using a variety of Amberlyst-15 and hydrotalcite combinations.a.
Entry
Catalyst amount (g)
Amberlyst-15
Glucose conv. (%)
Product yield (%)
HMFb (selec.)
Hydrotalcite
Fructose
AHGc
1
2
3
0.1
0
0
69
62
64
63
63
71
72
73
76
81
0 (0)
0 (0)
0
38
2
32
0
0.1
0.1
0.1
0.1
0.05
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0.1
0.1
0.05
0.025
24 (38)
23 (37)
24 (38)
12 (17)
41 (57)
42 (58)
41 (54)
36 (45)
18
16
16
30
10
13
8
4d
5e
6
Trace
1
0
4
0
4
5
7
8f
9
10
7
a
Reaction conditions: glucose (0.1 g), Amberlyst-15, hydrotalcite, DMF (3 mL), 373 K, 3 h.
b
c
d
e
f
5-Hydroxymethylfurfural.
Anhydroglucose. Sum of 1,6-anhydro-␤-d-glucopyranose and 1,6-anhydro-␤-d-glucofuranose.
2nd use.
3rd use.
353 K, 9 h.
dence on the amount of Amberlyst-15 and hydrotalcite catalysts
were not formed. The mechanism of sequential reactions was con-
firmed by the addition of Amberlyst-15 into a solution containing
fructose formed from glucose in the presence of hydrotalcite, as
shown in Fig. 7. Upon the addition of Amberlyst-15, fructose was
quickly consumed and HMF correspondingly formed, resulting in a
46% yield of HMF with high selectivity (76%) after 4.5 h.
used in a one-pot synthesis of HMF from glucose at 373 K for 3 h
in DMF. In the presence of either the solid acid or the solid base,
HMF was not obtained (entries 1 and 2). The former reaction selec-
tively gave anhydroglucose (entry 1) and the latter gave fructose
(entry 2). A combination using the same amount of solid acid and
solid base (0.1 g) gave a 24% yield of HMF with 38% selectivity
(entry 3). In this case, fructose was slightly formed at 2% yield. The
yield of anhydroglucoses (sum of 1,6-␤-d-anhydroglucopyranose
and 1,6-␤-d-anhydroglucofuranose) was 18%. The combination of
Amberlyst-15 and hydrotalcite could be reused for this HMF syn-
thesis at least three times without loss of activity (entries 4 and 5).
The acid and base catalysts were simply recovered by decantation,
washing with solvent (DMF, 6 mL) and drying in vacuo overnight,
and recycled for further reaction. Decreasing the hydrotalcite from
0.1 g to 0.05 g resulted in a poorer yield of HMF (12%) with 17%
selectivity, attributable to a decrease in fructose formation by
base-catalyzed isomerization (entry 6). In contrast, increasing the
amount of hydrotalcite to 0.2 g improved the HMF yield to 41%
with 57% selectivity (entry 7). Anhydroglucose formation was 10%,
which was lower than that obtained using 0.1 g of hydrotalcite
(entry 3). The formation of anhydroglucose could be suppressed by
reducing the amount of solid acid, Amberlyst-15 (entries 9 and 10).
Using 0.025 g of Amberlyst-15 and 0.2 g of hydrotalcite, 81% glu-
cose conversion and 36% HMF yield (corresponding to 0.2 mmol)
were obtained (entry 10). The amounts of acid and base catalysts
used were 4.8 mmol g−1 for Amberlyst-15 and 0.7 mmol g−1 for
hydrotalcite, respectively. Turnover numbers were estimated to be
1.7 and 1.4 for Amberlyst-15 and hydrotalcite, respectively. These
results showed that the highest HMF selectivity (57%) was obtained
using 0.1 g of Amberlyst-15 and 0.2 g of hydrotalcite at 373 K for 3 h
(entry 7). A similar result was observed at 353 K for 9 h (entry 8).
Fig. 6 shows the time course of HMF formation from glucose in
the presence of Amberlyst-15 and hydrotalcite at 353 K. In the ini-
tial stage of reaction (1 h), fructose formation was clearly observed,
indicating that glucose was firstly transformed into fructose by iso-
merization over the solid base hydrotalcite. The yield of fructose
decreased over the reaction time, falling to zero after 9 h. Corre-
spondingly, the HMF yield increased over this time, indicating that
fructose was successively dehydrated into HMF by acid catalysis by
Amberlyst-15. After 9 h, the glucose conversion and HMF yield were
73% and 42%, respectively. HMF selectivity improved with increas-
ing reaction time, from 31% for 1 h to 58% for 9 h. Anhydroglucose
formation as a side reaction via acid catalysis by Amberlyst-15 also
gradually proceeded during the reaction, giving a yield of 13% for
9 h. Levulinic acid and formic acid as rehydrated products of HMF
Fig. 6. Time courses of HMF formation from glucose over Amberlyst-15 and
hydrotalcite. Reaction conditions: glucose (0.1 g), Amberlyst-15 (0.1 g), hydrotalcite
(0.2 g), DMF (3 mL), 353 K.
Fig. 7. Time course of glucose transformation into fructose and 5-
hydroxymethylfurfural (HMF). Amberlyst-15 was added after 2.5 h. Reaction
conditions: glucose (0.1 g), Amberlyst-15 (0.1 g), hydrotalcite (0.2 g), DMF (3 mL),
373 K.

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M. Ohara et al. / Applied Catalysis A: General 383 (2010) 149–155
Table 4
One-pot synthesis of 5-hydroxymethylfurfural from glucose using Amberlyst-15 and hydrotalcite in various solvents.a.
Entry
Solventb
Glucose conv. (%)
Product yield (%)
HMFc (selec.)
Fructose
AHGd
1
2
DMF
72
97
94
41
88
40
45
31
91
92
91
41 (57)
14 (14)
12 (13)
25 (61)
10 (12)
0 (0)
29 (64)
0 (0)
28 (31)
25 (27)
0 (0)
4
10
Trace
Trace
0
12
0
0
0
12
0
DMAe
Trace
0
0
1
23
0
6
2
2
3
DMSOf
4g
5
DMSOf
MeCNh
6
7
8
9
10
11
H2O
DMF + H2O (3)
DMF + H2O (10)
MeCN + H2O (3)
MeCN + H2O (6)
MeCN + H2O (16)
2
0
a
Reaction conditions: glucose (0.1 g), Amberlyst-15 (0.1 g), hydrotalcite (0.2 g), 373 K, 3 h.
b
c
d
e
f
Values in parentheses are the water concentrations (v/v, %).
5-Hydroxymethylfurfural.
Anhydroglucose. Sum of 1,6-anhydro-␤-d-glucopyranose and 1,6-anhydro-␤-d-glucofuranose.
N,N-dimethylacetamide.
Dimethyl sulfoxide.
353 K.
g
h
Acetonitrile.
Table 4 shows the effect of solvent on HMF formation in the
perature (above 383 K) were preferred, achieving 77% selectivity at
93% conversion in N,N-dimethylformamide at 413 K.
presence of 0.1 g of Amberlyst-15 and 0.2 g of hydrotalcite at
373 K for 3 h. In addition to water, we used polar aprotic solvents
(N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA),
dimethyl sulfoxide (DMSO) and acetonitrile (MeCN)). Glucose could
be fully dissolved at 373 K for all solvents except in the case of
MeCN. HMF was successfully formed in all the polar aprotic solvents
tested (entries 1–5), whereas it was not produced at all in water
(entry 6). The highest yield and selectivity for HMF formation were
observed in DMF (entry 1). Among the other polar aprotic solvents,
the HMF yields were 14%, 12% and 10% for DMA, DMSO and MeCN,
respectively. In DMSO, at 353 K, the HMF yield was higher at 353 K
(25% with 61% selectivity) than at 373 K (entries 3 and 4). In water,
HMF was not obtained due to the loss of activity of Amberlyst-15 in
dehydrating fructose into HMF, meaning the hydrotalcite acts alone
as a base catalyst for isomerization, resulting in fructose formation
at 23% yield (entry 6). The dehydration activity of Amberlyst-15
in forming HMF from fructose and anhydroglucose from glucose
was considerably affected by the presence of water. Addition of a
small amount of water (3 vol%) to DMF diminished anhydroglucose
formation, resulting in a high HMF selectivity (67%) (entry 7). How-
ever, addition of a larger amount of water (10 vol%) gave 0% HMF
yield (entry 8). These results indicate that anhydroglucose forma-
tion from glucose by acid catalysis is much more sensitive to water
than HMF formation from fructose, and in this latter case a small
amount of water could be beneficial. For example, the addition of a
small amount of water (3–6 vol%) to acetonitrile improved the HMF
yieldfrom 10%to 25–28% (entries9and 10), which werehigherthan
those obtained in DMA and DMSO. Because sugars, including glu-
cose, are not fully dissolved in pure acetonitrile, addition of water
to acetonitrile improves the solubility, resulting in enhancement
of the HMF yield. An excess of water (16 vol%), however, leads to
negative effects (0% HMF yield) (entry 11).
In contrast, using a combination of solid acid and base catalysts
afforded selective formation of 5-hydroxymethylfurfural. Hydro-
talcite was used as the base catalyst for isomerization of glucose to
fructose, and Amberlyst-15 was used as the acid catalyst for dehy-
dration of fructose to 5-hydroxymethylfurfural. This system gave a
high HMF yield and selectivity under mild conditions (below 373 K).
For example, using 0.1 g of Amberlyst-15 and 0.2 g of hydrotalcite
at 353 K for 9 h, 58% HMF selectivity and 73% glucose conver-
sion were obtained. A low reaction temperature is advantageous
in formation of fructose from glucose by base catalysis and lim-
its the amount of anhydroglucose formation by acid catalysis. The
preferential formation of fructose results in high selectivity for
HMF. Aprotic polar solvents, including N,N-dimethylformamide,
N,N-dimethylacetamide, dimethyl sulfoxide and acetonitrile can
be used in this system, with the addition of a small amount of
water improving HMF selectivity. The catalysts are recyclable and
the method provides efficient conversion of glucose into important
intermediates by an environmentally friendly catalytic reaction.
Acknowledgements
This work was supported by a Grant-in-Aid for Young Scientists
(Start-up) (No. 20860038) by the Ministry of Education, Culture,
Sports, Science and Technology (MEXT), Japan.
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