Facile isomerization of glucose into fructose using anion-exchange resins in organic solvents and application to direct conversion of glucose into furan compounds

Article abstract of DOI:10.1007/s11164-017-2942-3

The facile isomerization of glucose into fructose has been developed using commercially available anion-exchange resins (AERs) in organic solvents. Following extensive screening for the amount and type of AERs, solvents and reaction time, glucose was transformed into fructose in yields of up to 50% using Amberlite A-26 with macroreticular morphology and tertiary amine functionality in a protic solvent (ethanol). AERs could be used five times without a significant loss of activity. This isomerization method could be applied to the direct conversion of glucose into furan compounds by integrating the dehydration of fructose with cation-exchange resins.

Full text of DOI:10.1007/s11164-017-2942-3

Res Chem Intermed
DOI 10.1007/s11164-017-2942-3
Facile isomerization of glucose into fructose using
anion-exchange resins in organic solvents
and application to direct conversion of glucose
into furan compounds
1
,2
1,3
•
Dasom Mun
Seunghan Shin
Yong-Gun Shul
•
Nhan Thanh Thien Huynh
1,3
1
,3
1,3
•
•
Yong Jin Kim
1,3
Jin Ku Cho
•
Sangyong Kim
2
•
Received: 12 September 2016 / Accepted: 20 March 2017
Ó Springer Science+Business Media Dordrecht 2017
Abstract The facile isomerization of glucose into fructose has been developed
using commercially available anion-exchange resins (AERs) in organic solvents.
Following extensive screening for the amount and type of AERs, solvents and
reaction time, glucose was transformed into fructose in yields of up to 50% using
Amberlite A-26 with macroreticular morphology and tertiary amine functionality in
a protic solvent (ethanol). AERs could be used five times without a significant loss
of activity. This isomerization method could be applied to the direct conversion of
glucose into furan compounds by integrating the dehydration of fructose with
cation-exchange resins.
Keywords Isomerization Á Glucose Á Fructose Á Anion-exchange resins Á Organic
solvents Á Direct conversion
Introduction
Bio-based chemicals from renewable and sustainable resources are attracting
attention as substitutes for fossil-based chemicals [1]. Biomass-derived carbohy-
drates such as cellulose and starch represent 75% of the annually regenerated
biomass [2]. Glucose, as a repeating unit of cellulose and starch, is considered the
&
Jin Ku Cho
jkcho@kitech.re.kr
1
2
3
Green Chemistry and Engineering R&D Department, Korea Institute of Industrial Technology
(KITECH), 89 Yangdaegiro-gil, Ipjang-myeon, Seobuk-gu, Cheonan, Chungnam 31056, Korea
Department of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro,
Seodaemun-gu, Seoul 03722, Korea
Department of Green Process and System Engineering, Korea University of Science &
Technology (UST), 89 Yangdaegiro-gil, Ipjang-myeon, Seobuk-gu, Cheonan,
Chungnam 31056, Korea
123

D. Mun et al.
most abundant bio-refinery starter [3]. However, fructose—an isomer of glucose—is
attracting research as a more effective starter for creating furan compounds, which
possess great potential in industrial applications [4]. For example, 5-hyroxymethyl-
2
-furfural (HMF) obtained from the dehydration of fructose is a versatile platform
chemical that can be converted into fuels and a variety of monomers for bioplastics.
Due to lack of availability, the isomerization of glucose into fructose appears to
be a crucial step for the development of a furan platform. The commercialized
isomerization of glucose into fructose is conducted using glucose isomerase (also
known as xylose isomerase) [5]. This method suffers from various drawbacks due to
the sensitive nature of the enzymatic procedure and complications in integrating a
chemical process. Other non-biological approaches have been attempted for the
isomerization of glucose into fructose. Zhang’s group reported that chromium
chlorides (CrCl or CrCl ) in ionic liquid [(EMIM)Cl] could efficiently assist the
2
3
isomerization of glucose into fructose [6]. More recently, glucose was isomerized
into fructose in N,N-dimethylformamide (DMF) using hydrotalcite as an inorganic
solid base [7]. In addition, Sn-containing zeolite could convert glucose into fructose
under aqueous acidic conditions [8]. However, these previously reported procedures
still possess drawbacks, including the use of environmentally non-benign chromium
salts and relatively expensive ionic liquids, the difficulty in removing and recycling
high boiling reaction media, and low yields.
Glucose can be converted into isomers such as fructose and mannose through a
proton transfer mechanism called a Lobry–de Bruyn–van Ekenstein transformation
under aqueous basic conditions [9]. The isomerization proceeds via an enediol
intermediate formed by the base-catalyzed deprotonation of a-carbonyl carbon of
glucose [10]. There are several studies on the isomerization of aldose into ketose
with an inorganic base or solid base in water [11–13]. However, aqueous conditions
reduce the stability of monosaccharides in the presence of basic catalysts. Therefore,
we present a facile method for the isomerization of glucose into fructose using
anion-exchange resins (AERs) in organic solvents (Scheme 1).
Scheme 1 Isomerization of glucose into fructose using anion-exchange resin
1
23

Facile isomerization of glucose into fructose using…
Experimental
Materials and analysis
D-Glucose, D-Fructose, and 5-hydroxymethyl furfural (HMF) (all with[99% purity)
were purchased from Sigma-Aldrich and used as reagents or HPLC standards
accordingly. Five types of ion-exchange resins including Amberlite IRA-743 (IRA-
743), Amberlite IRA-400 (IRA-400), Amberlite IRA-900 (IRA-900), Amberlyst
A-26 (A-26), and Amberlyst 15 were purchase from Sigma-Aldrich and used as
catalysts. Several solvents such as dimethylsulfoxide (DMSO, C99.9%), DMF
anhydrous, 99.8%), ethanol (anhydrous, C99.5%), 1,4-dioxane (dioxane, anhy-
(
drous, 99.8%), and isopropyl alcohol (IPA, 99.5%) were also acquired from Aldrich.
The loading amount of nitrogen on the anion-exchange resins were determined by a
CHN elemental analysis (Automatic Elemental analyzer, FLASH 2000 Series;
Thermo Scientific, USA) and the specific surface area of the resins was determined
on a BET surface analyzer (Brunanuer–Emmett–Teller, ASAP2010; Micromeritics,
USA) using N as the adsorbent at liquid nitrogen temperature (77 K) in a relative
2
pressure (P/P ) range of 0–0.25. The resin samples (in powder forms) were
0
degassed in air for over 12 h at 100 °C prior to analysis. The yields of fructose and
HMF were determined using high-performance liquid chromatography (HPLC;
Agilent 1200 series) equipped with a refractive index detector and an Aminex HPX-
8
7H column (Bio-Rad). The analysis conditions were as follows: eluent, 0.01 N
-
1
H SO ; flow rate, 0.6 ml min ; and column temperature, 45 °C. Prior to HPLC
2
4
analysis, all samples were subjected to dilution with water (HPLC grade) to prevent
signal overload and damage to the system.
Isomerization of glucose into fructose
The isomerization of glucose into fructose was carried out in a tubular-type
Carousel 12 Plus Reaction Station reactor (Radley, UK) equipped with a cross-
shaped magnetic stirrer. Prior to the reaction, the AER catalysts were treated by
shaking in a saturated aqueous NaHCO solution at room temperature for 5 h and
3
then dried under vacuum. Glucose samples (100 mg) were placed in the reactor, and
the designated amounts of AER and solvent (3 mL) were added. After the reactors
were installed into the Carousel 12 Plus Reaction Station, the reaction mixtures
were heated and stirred at 700 rpm for a designated time. After the reaction, the
AER catalysts were filtered, and the reaction mixtures were cooled to room
temperature and diluted with water (HPLC grade) for HPLC analysis.
Direct conversion of glucose into HMF
The direct conversion of glucose to HMF was performed by using both AERs and
cation-exchange resins (CERs) simultaneously or sequentially. In a simultaneous
system, both AERs and CERS were added from the onset (with the AERs being
treated prior to use) and treated for a designated time. On the other hand, in a
123

D. Mun et al.
sequential system, the reactions were performed in cycles. In each cycle, the resins
were employed by turns: the AER was used first for the isomerization of glucose
and then altered by the CER for the conversion into HMF. The resin was filtered out
after each turn and new resin was added for the next turn. In our research, the
sequential system was repeated up to 6 cycles with varied reaction times for each
resin-employed turn. Reaction scales and equipment are similar to the procedure for
the isomerization of glucose into fructose. Glucose (100 mg) and a designated
amount of ion-exchange resins in solvent (3 mL) were added to the tubular type
reactor (Radley), heated and stirred at 700 rpm for a designated time or cycles (in
cases of the sequential system studied). After completion, the resins were filtered,
the reaction mixtures were cooled to room temperature, diluted with water (HPLC
grade) and analyzed by HPLC.
Results and discussion
Characterization of AERs
Four commercially available AERs (IRA-743, IRA-400, A-26 and IRA-900) with
differences in resin morphology and terminal-group functionality were evaluated for
the isomerization of glucose into fructose (Table 1). IRA-743 is a rigid macroporous
resin with a high cross-linking degree, and its terminal is functionalized with N-
methyl-glucamine. IRA-400 is a gel-type resin with a low cross-linking degree,
allowing a substrate that can access the resin surface when sufficiently swollen.
IRA-400 has a tetraalkyl ammonium terminal group. A-26 and IRA-900 are
macroreticular-type resins composed of small spherical microgel particles agglom-
erated to form clusters. Their terminal groups are tertiary amine and tetraalkyl
ammonium forms, respectively. As for strength of basicity, IRA-400 and IRA-900
are stronger than IRA-743 and A-26 because the basicity of IRA-400 and IRA-900
is provided by counter anions of a quaternary ammonium terminal group, whereas
Table 1 Morphology of anion-exchange resins and functionality of their terminal groups
Name
Morphology of resin
Macroporous
Functionality of terminal group
CH3 OH OH
Amberlite IRA-743 (IRA-743)
N
OH
OH OH
H
3
C
Amberlite IRA-400 (IRA-400)
Amberlyst A-26 (A-26)
Gel
CH3
N
HCO
3
CH
3
CH
N
3
Macroreticular
Macroreticular
CH
3
H
3
C
Amberlite IRA-900 (IRA-900)
CH3
N
HCO
3
3
CH
1
23

Facile isomerization of glucose into fructose using…
that of IRA-743 and A-26 is provided by unshared electrons of a tertiary amine
terminal group.
The amount of basic functional groups on each AER was determined by the
-
1
loading level of the nitrogen contents per weight of the resin (mmol of ‘N’ g of
resin) using a CHN elemental analysis of dried AERs. The loading level of IRA-743
-
1
-1
was less than 2.0 mmol g , and those of the other AERs were over 3.0 mmol g
These results originate from the molecular weights of the attached moieties. IRA-
43 has a higher molecular weight moiety (N-methyl-glucamine compared to
.
7
trimethyl or dimethyl moieties of other AERs) and increment in total weight of
resin. The surface area of each AER was investigated using a BET analysis. As
expected, the gel-type IRA-400 showed very low surface area and the macroporous-
2
-1
type IRA-743 showed the highest surface area at over 18 m g . The surface areas
-1
2
of the macroreticular-type A-26 and IRA-900 were 6.62 and 2.00 m g
respectively (Table 2).
,
The swelling property of the AERs in organic solvents was also examined.
Taking the solubility of glucose into account, water miscible solvents with high
polarity such as DMSO, DMF, dioxane, IPA, and ethanol were selected for
screening (Fig. 1). Swelling property is often an important factor in polymer-based
heterogeneous catalysis because it can enhance the accessibility of the substrate.
The gel-type IRA-400 offered no swelling ability in any of the solvents except
ethanol. It was considered that hydrophilic solvents would be limited in accessing
hydrophobic polystyrene-based resins with low surface areas. Meanwhile,
macroreticular-type AERs (IRA-900 and A-26) showed relatively high swelling
abilities. All AERs were best swollen in ethanol with IRA-900 swollen up to nearly
2
00% of the ratio.
Isomerization of glucose into fructose
All four types of AERs were treated with aqueous NaHCO at room temperature for
3
5
anions of IRA-400 and IRA-900 were exchanged into hydrogen carbonate (HCO )
h and dried with a vacuum prior to use. Because of this treatment, the counter
-
3
and the tertiary amine groups of IRA-743 and A-26 were changed to free amine.
Isomerization was carried out in a tubular-type reactor; a designated amount of AER
and 3 mL of solvent were added to 100 mg of D-glucose. The reaction tubes were
heated at 80 °C and stirred at 700 rpm for 3 h. After the reaction, the mixture was
Table 2 Loading level and surface area of anion-exchange resins
Name
Loading level
mmol of ‘N’/g)
Surface area
2
(m /g)
(
Amberlite IRA-743
Amberlite IRA-400
Amberlyst IRA-26
Amberlite IRA-900
1.9
3.3
3.2
3.8
18.76 ± 0.08
0.03 ± 0.02
6.62 ± 0.03
2.00 ± 0.01
123

D. Mun et al.
DMSO
DMF
Dioxane
IPA
2
1
1
00
50
00
Ethanol
5
0
0
4
3
te IRA-900
berlite IRA-7
Amberlyst A-26
Amberli
Am
Amberlite IRA-400
Anionic exchange resins
Fig. 1 Swelling properties of AERs in various water-miscible organic solvents
cooled to room temperature, diluted with water (HPLC grade) and analyzed with
HPLC. Isomerization of the glucose into fructose was performed in the presence of
two different amounts of AERs (20 and 50 mol% of basic moiety based on glucose)
using five different solvents, namely DMSO, DMF, dioxane, IPA, and ethanol.
All the results are listed in Table 3. When DMSO (Table 3, entries 1–8) or DMF
(
Table 3, entries 9–16) was used as a high polar aprotic solvent, low conversions of
glucose were shown on all AERs. In particular, the gel-type IRA-400 showed the
lowest conversion, with more than 90% of the glucose still remaining even in the
presence of large amounts of resin (50 mol%) (Table 3, entries 6 and 14). It appears
that the glucose was unable to gain access to the gel-type resin. However, IRA-743
and A-26, having tertiary amine terminal groups, provided a higher conversion of
glucose than the IRA-400 and IRA-900 with quaternary ammonium terminal
groups. Dioxane increased glucose conversions, but provided a low selectivity of
fructose—below 70% regardless of the AERs, their amounts and reaction time
(
Table 3, entries 17–24). Conversions of glucose were conspicuously improved
using a protic solvent such as IPA or ethanol. In particular, higher polar ethanol
produced a remarkable difference in the selectivity of fructose compared to IPA. A
high conversion (53%) and superior selectivity (94%) of fructose was observed
using ethanol in the presence of A-26 (Table 3, entry 35). A larger amount of A-26
(
50 mol%) in ethanol enhanced the conversion to 64%, but the selectivity then fell
to 70% (Table 3, entry 39). Moreover, the undesired decomposition of glucose
could be suppressed in organic solvent at increased temperatures.
The fructose yields obtained from screening the AERs and solvents are depicted
in Fig. 2a. Based on this figure, the following facts were clearly confirmed: (1)
protic solvents were superior to aprotic solvents; (2) macroporous and macroretic-
ular resins provided higher yields of fructose than gel-type resins; and (3) tertiary
1
23

Facile isomerization of glucose into fructose using…
Table 3 Conversion of glucose
Entry Catalyst
CoG SoF Mol% Solvent
Polar Index
7.2
(
(
CoG) and selectivity of fructose
SoF) by isomerization of
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
IRA-743 11.3 91.5 20 DMSO
glucose using AERs in various
organic solvents
IRA-400
A-26
1.8 60.0
15.8 71.2
6.2 61.3
IRA-900
IRA-743 19.7 88.6 50
IRA-400
A-26
6.1 53.9
24.6 87.6
IRA-900 14.0 79.5
IRA-743 18.5 92.5 20
DMF
6.4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
IRA-400
A-26
4.2 40.1
11.1 96.6
7.4 73.7
IRA-900
IRA-743 28.3 89.2 50
IRA-400
A-26
8.4 37.2
37.8 73.3
IRA-900 18.1 74.0
IRA-743 51.3 67.5 20
Dioxane 4.8
IRA-400
A-26
8.4
0.0
31.5 62.8
IRA-900 15.3 38.3
IRA-743 60.1 61.9 50
IRA-400 10.7
5.1
A-26 42.5 65.8
IRA-900 25.1 65.3
IRA-743 45.0 75.3 20
IRA-400 22.2 94.0
IPA
3.9
A-26
44.4 79.0
IRA-900 36.6 84.0
IRA-743 54.8 73.6 50
IRA-400 27.0 94.6
A-26
61.9 72.6
IRA-900 38.7 76.5
IRA-743 57.1 72.3 20
IRA-400 28.7 86.5
Ethanol
5.2
A-26
53.1 93.6
IRA-900 34.3 95.1
IRA-743 67.6 66.8 50
IRA-400 29.0 96.3
A-26
64.1 70.0
IRA-900 61.1 69.5
123

D. Mun et al.
(a)
DMSO
DMF
Dioxane
IPA
Ethanol
5
4
3
2
1
0
0
0
0
0
Amberlite IRA-743
Amberlite IRA-400
Amberlyst A-26
Amberlite IRA-900
0
2
0
50
20 50
20 50
20 50
20 50
Amount of AER (mol%)
(b)
Amberlite IRA-743
Amberlite A-26
5
0
0
0
0
0
4
3
2
1
0
1
2
3
4
5
Run
Fig. 2 a Fructose yields after isomerization of glucose using AER in organic solvents, and b reuse of
AERs for isomerization of glucose into fructose
amine functionalities were beneficial compared to tetraalkyl ammonium function-
alities. Furthermore, reuse tests of IRA-743 and A-26 were carried out for the
isomerization of glucose into fructose, demonstrating that both AERs can be used
five times in ethanol without a significant loss of activity (Fig. 2b).
From a mechanistic point of view, it is well known that aldose has been
isomerized into ketose via a proton transfer mechanism called the Lobry–de Bruyn–
van Ekenstein transformation (see yellow area in Fig. 3) under aqueous basic
condition [9, 14]. The isomerization proceeds with base-catalyzed deprotonation of
the a-carbonyl carbon of aldose to form enolates [10]. There have been several
1
23

Facile isomerization of glucose into fructose using…
Fig. 3 Proposed mechanism of isomerization of glucose into fructose in organic solvents via the Lobry–
de Bruyn–van Ekenstein transformation (proton transfer) and the Meerwein–Ponndorf–Verley reaction
(hydride transfer). (Color figure online)
studies on the isomerization of aldose into ketose with general base [11] or solid
base [12, 13] in water. However, the situation is more complicated when organic
solvents are used. The isomerization of aldose into ketose in organic solvents can
also occur via intramolecular transfer of hydride by the similar pathway such as the
Meerwein–Ponndorf–Verley reaction (see green area in Fig. 3), [15] which can lead
to an enhancement of isomerization. Indeed, the isomerization was markedly
accelerated by the addition of organic solvents such as ethanol and acetone [16, 17].
Additionally, the enhanced effect can be explained by the increasing amount of the
a-pyranose form of glucose in organic solvents [18].
Direct conversion of glucose into HMF
As previously mentioned, HMF is a versatile platform that can be converted into a
variety of valuable fuels and chemicals [19]. It can be readily transformed from
fructose by dehydration using a CER as a solid acid catalyst in DMSO [20], DMF
[
21], dioxane [22], and ethanol [23]. Therefore, the direct conversion of glucose into
Scheme 2 Direct conversion of glucose into furan compounds using AERs and CERs
123

D. Mun et al.
HMF was explored by integrating an isomerization step with AERs and a
dehydration step with CERs (Scheme 2).
The direct conversion of glucose into HMF was initially performed in DMSO and
DMF (Table 4). Both solvents are well known as preferred media for the
dehydration of fructose in the presence of CERs. A negligible amount of HMF
was created with a CER (Amberlyst 15) in DMSO at 100 °C after 5 h because the
isomerization of glucose into fructose scarcely occurred (Table 4, entry 1). When
AER (IRA-743) was simultaneously used with a CER (wt/wt = 1:1) under the same
conditions (DMSO, 100 °C, 5 h), HMF was formed at a yield below 10% (Table 4,
entry 2). DMF was more effective than DMSO, in creating HMF at a yield greater
than 10% (Table 4, entry 3). Increasing the ratio of AER to CER (wt/wt = 2:1)
produced a greater yield of HMF (23%) (Table 4, entry 4) but a prolonged reaction
time was unnecessary (Table 4, entry 5). Next, just an AER was initially treated in
DMSO at 100 °C for 3 h. CER was then added, and the reaction was continued for
another 2 h to produce an HMF yield of 16%, slightly higher than the simultaneous
treatment of AER and CER from the onset (Table 4, entry 2 vs. 6). In an attempt to
improve the HMF yield, turn-by-turn treatments of AER and CER were repetitively
performed in multiple cycles. In each cycle, the AER was treated and then filtered
out, and the CER was subsequently added to the filtrate (reaction mixture). After the
turn-by-turn treatment of the AER and CER for 1 h each in three cycles and for
0
1
.5 h each in six cycles (in both cases, the total reaction time was 6 h) in DMSO at
00 °C, 29 and 26% yields of HMF were obtained, respectively (Table 4, entries 7
and 8). Using DMF as a solvent can improve HMF yield to 34% (Table 4, entry 9).
A direct conversion of glucose into HMF was then conducted in ethanol. The use
of ethanol in glucose isomerization has several advantages. First, ethanol is a
renewable solvent and is now produced on an industrial scale from biomass.
Table 4 Direct conversion of glucose into HMF using AER and CER in DMSO and DMF
a
a
b
Entry
Solvent
AER (mg)
CER (mg)
Reaction time (h)
HMF yield (%)
1
2
3
4
5
6
7
8
9
a
DMSO
DMSO
DMF
–
100
100
100
100
100
100
100
100
100
5
\1
7
c
100
100
200
200
100
200
200
200
5
c
5
13
23
23
16
29
26
34
c
DMF
5
c
DMF
9
DMSO
DMSO
DMSO
DMF
3 ? 2
(1 ? 1) 9 3
(0.5 ? 0.5) 9 6
(1 ? 1) 9 3
IRA-743 and Amberlyst 15 were used as an anion-exchange resin (AER) and a cation-exchange resin
CER), respectively
(
b
Notation of treatment time: (b ? a) 9 t, where b and a are the times for basic AER and acidic CER
treatments, respectively; t is the number of turns
c
AER and CER were used together from the onset (simultaneous system)
1
23

Facile isomerization of glucose into fructose using…
Second, ethanol has a low boiling point (78 °C) and can be easily removed after the
reaction compared to other high-boiling solvents such as DMSO (189 °C) and DMF
(
153 °C). Third, the dehydration of fructose in ethanol can produce 5-ethoxymethyl-
-furfural (EMF), a promising candidate for bio-fuels and a more stable platform
2
chemical than HMF for use as a precursor for valuable chemicals. This reaction
employed a turn-by-turn treatment of AER and CER at 80 °C for 1 h each in three
repeated cycles. HMF and EMF were obtained in 23 and 11% yields, respectively. A
total of 20% glucose and 34% fructose remained after the reaction, and it was
believed that the dehydration of fructose into furan compounds was incomplete at
this low temperature. An investigation of the reaction profile clearly showed that
fructose was produced during the treatment of the AER, whereas furan compounds
(
(
HMF and EMF) formed as fructose was consumed during the treatment of the CER
Fig. 4).
Conclusion
A facile isomerization of glucose into fructose was developed using AERs in an
organic solvent. Fructose yields of 40–50% of were achieved with Amberlyst A-26
and Amberlite IRA-743 bearing tertiary amine functionalities in a protic solvent,
namely ethanol. The AERs could be used five times without a significant loss of
AER
CER
AER
CER
AER
CER
100
40
80
30
60
20
40
1
0
20
0
0
0
1
2
3
4
5
6
Time (h)
Fig. 4 Reaction profiles according to ion-exchange resin treatment: Glucose (300 mg) and ethanol
9 mL) were used as substrate and solvent, respectively. IRA-743 (600 mg) was used for anion-exchange
(
resin treatment and Amberlyst 15 (300 mg) was used for cation-exchange treatment at 80 °C. Each
symbol represents the conversion of glucose (open triangle) and the yields of fructose (filled circle), HMF
(filled inverted triangle), and EMF (filled square). Solid and dotted arrows indicate sections for anion-
exchange resin and cation-exchange resin treatments, respectively
123

D. Mun et al.
activity. This procedure has the advantage of using common industrial solvents and
commercially available AERs. Applying an organic solvent reaction system and a
heterogeneous catalyst allows for easy separation of the product as well as recovery
and reuse of the solvent and catalyst. In addition, the sequential dehydration of
fructose into furan compounds could be integrated without replacing the solvent
system.
Acknowledgements We would like to acknowledge the financial support from the R&D Convergence
Program of NST (National Research Council of Science and Technology) of the Republic of Korea and
KITECH (Korea Institute of Industrial Technology) and from the Internal Research Program (PEO17250)
of KITECH.
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