Catalytic conversion of glucose to 5-hydroxymethyl furfural using inexpensive co-catalysts and solvents

Article abstract of DOI:10.1016/j.carres.2011.06.007

Efficient conversion of glucose to 5-hydroxymethyl furfural (5-HMF), a platform chemical for fuels and materials, was achieved using CrCl₂ or CrCl₃ as the catalysts with inexpensive co-catalysts and solvents including halide salts in dimethyl sulfoxide (DMSO) and several ionic liquids. 5-HMF (54.8%) yield was achieved with the CrCl₂/tetraethyl ammonium chloride system at mild reaction conditions (120 °C and 1 h). The 5-HMF formation reaction was found to be faster in ionic liquids than in the DMSO system. Effects of water in the reaction system, chromium valence and reaction temperature on the conversion of glucose into 5-HMF were discussed in this work.

Full text of DOI:10.1016/j.carres.2011.06.007

Carbohydrate Research 346 (2011) 2019–2023
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Note
Catalytic conversion of glucose to 5-hydroxymethyl furfural using
inexpensive co-catalysts and solvents
c
c
Zhongshun Yuan a,b, Chunbao (Charles) Xu a,b, , Shuna Cheng , Mathew Leitch
⇑
a Department of Chemical Engineering, Lakehead University, Thunder Bay, ON, Canada P7B 5E1
b Department of Chemical & Biochemical Engineering, The University of Western Ontario, London, ON, Canada N6A 5B9
c Faculty of Forestry and Forest Environment, Lakehead University, Thunder Bay, ON, Canada P7B 5E1
a r t i c l e i n f o
a b s t r a c t
Article history:
Efficient conversion of glucose to 5-hydroxymethyl furfural (5-HMF), a platform chemical for fuels and
materials, was achieved using CrCl2 or CrCl3 as the catalysts with inexpensive co-catalysts and solvents
including halide salts in dimethyl sulfoxide (DMSO) and several ionic liquids. 5-HMF (54.8%) yield was
achieved with the CrCl2/tetraethyl ammonium chloride system at mild reaction conditions (120 °C and
1 h). The 5-HMF formation reaction was found to be faster in ionic liquids than in the DMSO system.
Effects of water in the reaction system, chromium valence and reaction temperature on the conversion
of glucose into 5-HMF were discussed in this work.
Received 21 April 2011
Received in revised form 1 June 2011
Accepted 6 June 2011
Available online 12 June 2011
Keywords:
5-Hydroxymethyl furfural
Glucose
Ó 2011 Elsevier Ltd. All rights reserved.
Chromium dichloride
Chromium trichloride
Ionic liquids
In the past 150 years, fossil fuels (petroleum, coal, and natural
gas) have been the dominant sources for energy and chemicals.1
However, due to the rapid economic development and population
growth, fast consumption of these resources has accelerated their
depletion. The global concerns over energy security, the environ-
mental issues related to the use of fossil fuels, as well as the sustain-
ability of the economic development have intensified the efforts in
seeking alternative resources for energy and chemical production.
Biomass, with a total annual production of 2.74 Â 1019 Btu equiva-
lent of about eight times of the energy consumed each year in the
world, offers an immense, renewable, and carbon-neutral source
for fuels and chemicals.
Glucose is the main building block of biomass, for example, cel-
lulose and starch. Although it has been successful in bio-conver-
sion of cellulose and starch to ethanol fuel, the process to
convert a 6-C glucose molecule into two molecules of ethanol (plus
two molecules of CO2) has an inherently lower efficiency with
respect to energy and carbon utilization efficiency. Moreover,
ethanol is not an ideal transportation fuel because of its low energy
density (23 M J/L),2 high volatility, and its readiness in water
absorption from air. The ethanol-fueled vehicles have only about
66% of efficiency compared with those fueled with gasoline. In this
regard, it is urgently needed to explore conversion technologies to
convert plentiful biomass resources into bio-fuels with higher
energy contents. 5-Hydroxymethyl furfural (5-HMF), is a dehydra-
tion intermediate product in glucose fermentation processes.3
5-HMF can be easily converted to dimethylfuran (DMF) with fur-
ther improved energy content through hydrogenation.4 The energy
content of DMF (31.5 M J/L) is comparable to that of gasoline
(35 M J/L) and 40% greater than that of ethanol.2 Furthermore,
DMF (bp = 92–94 °C) is less volatile than ethanol (bp = 78 °C) and
is immiscible with water, making it a better candidate for alterna-
tive liquid transportation fuels. 5-HMF can also be a platform
chemical for a variety of synthetic materials.5
The conversion of fructose to 5-HMF is a readily straightforward
process that has been demonstrated in water and organic solvents,6
in multiphase systems,7,8 and in ionic liquids.9,10 However, fructose
is not an abundant building block in cellulose and starch, although
fructose can be produced from glucose via some expensive isomer-
ization processes. Obviously, direct conversion of glucose into 5-
HMF offers a better economic value. Zhao et al.10 have successfully
produced 5-HMF from glucose at a high yield (69%) with chromium
chlorides as the main catalysts combined with expensive alkylimi-
dazolium chloride ionic liquids, such as 1-ethyl-3-methylimidazo-
lium chloride ([EMIM]Cl), as the co-catalyst. Separation of 5-HMF
product from the ionic liquids may be achieved by solvent extrac-
tion with low boiling point organic solvents followed by evapora-
tion and purification. Li et al.11 obtained a surprisingly high yield
(91%) of 5-HMF from glucose using the same catalyst/co-catalyst
system as was used by Zhao et al.,10 but under the microwave irra-
diation conditions. While promising, this catalytic method has
⇑
Corresponding author. Tel.: +1 519 661 2111x86414.
E-mail address: cxu6@uwo.ca (C. (Charles) Xu).
0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2011.06.007

2020
Z. Yuan et al. / Carbohydrate Research 346 (2011) 2019–2023
limitation in the process economics due to the use of a large amount
of expensive ionic liquid solvents. Binder and Raines5 demonstrated
that with chromium chlorides as the main catalyst, polar aprotic or-
ganic solvent combined with some halide (Cl, Br) salts could replace
ionic liquid as a co-catalyst to convert glucose to 5-HMF at a high
yield up to 80%. The drawbacks of this approach may be the diffi-
culty in separation of the 5-HMF product from the high boiling
point solvents and recovery of large amount of halide salts used
in the process (the addition amount of these salts was over 10% of
solvent in weight).
The main objective of the present research was to produce 5-
HMF from glucose using CrCl2 or CrCl3 as the main catalysts with
different inexpensive co-catalysts and solvents including halide
salts in dimethyl sulfoxide (DMSO) and several new ionic liquids
synthesized by ourselves.
1.2. Experimental methods for conversion of glucose to 5-HMF
In a typical run for the synthesis of 5-HMF in DMSO, a 100 mL
three-neck reactor was equipped with Dean-stark trap, a con-
denser, a purge gas (nitrogen) inlet, nitrogen outlet and a ther-
mometer in the three necks, respectively. The reactor was first
evacuated and purged with nitrogen, then 25.00 g DMSO, 5.00 g
glucose, and 0.110 g CrCl2 (0.03 M), 0.150 g (0.03 M) tetraethyl
ammonium chloride, and 3.0 mL of benzene (as a stripping reagent
for water removal via azeotropic evaporation) were added to the
reactor. The Dean-stark was filled with benzene. The reactor was
put into an oil bath preheated at 130 °C. The reaction mixture
was stirred with a magnetic stirrer under nitrogen protection for
2 h. The reaction mixture was analyzed with HPLC to determine
the contents of remaining glucose and 5-HMF in the product.
Synthesis of 5-HMF from glucose in ionic liquid solvents was
conducted following the similar procedure as above in a 50 mL
three-neck reactor with nitrogen purge or a 15 mL sealed reactor
with nitrogen protection. In a typical run, 1.00 g glucose and
5.00 g ionic liquid and 0.03 M chromium chloride (CrCl2 or CrCl3)
were reacted at 120 °C for 1 h. The reported yield of 5-HMF was
calculated to be % of the moles of 5-HMF actually produced in each
test to the theoretical maximum moles of 5-HMF if assuming 100%
conversion. Duplicate tests were performed for most reaction con-
ditions, and the maximum relative errors were ensured within 10%,
as demonstrated in Figure 1.
1. Experimental
1.1. Materials
The raw materials and chemicals used in this research mainly
include: glucose, fructose, dimethyl sulfoxide (DMSO), chromium
dichloride (CrCl2), chromium trichloride (CrCl3), tetraethyl ammo-
nium chloride (TEAC), epichlorohydrin, pyridine, dimethyl sulfate,
lithium chloride, potassium bromide, zinc chloride, H2SO4-
pretreated zeolite as a solid ultra acid, 5-HMF standard, and 0.005 M
H2SO4 HPLC-grade water. All the raw materials and chemicals as
listed above were ACS reagent-grade chemicals from Sigma–Aldrich
and were used as received without further treatment.
The reaction products were analyzed by HPLC and quantified
withcalibrationcurvesgeneratedfromcommerciallyavailablestan-
dards. As the typical measurement procedure, the product mixture
was first diluted with HPLC grade 0.005 M H2SO4 water, filtered with
Several new ionic liquids were synthesized and tested as the
reaction co-catalysts and solvents. (3-chloro-2-hydroxypropyl)
pyridinium chloride (CHPPC) was synthesized following Zhao’s
procedure.12 That is, to a stirred solution of pyridine in ethanol
at room temperature was added concentrated hydrochloric acid.
After addition of the acid, the mixture was cooled to room tem-
perature, and epichlorohydrin was added dropwise with stirring.
Then the reactor flask was irradiated in the water bath of a lab-
oratory ultrasonic cleaner at 25 °C for 2 h. Upon completion, the
solvent was removed by evaporation under reduced pressure
with heating at 60 °C, followed by vacuum drying to yield a col-
orless liquid of CHPPC. (3-chloro-2-methoxypropyl) pyridinium
chloride (CMPPC) was synthesized by reacting CHPPC with di-
methyl sulfate in the presence of barium hydroxide at room
temperature for 8 h.13 Poly(triethylammonium methylene ethyl-
ene oxide) (PTEAMEO) salt was synthesized by first cationic
polymerization of epichlorohydrin with BF3 plus ethanol as the
initiator at 0 °C,14 then reacting polyepichlorhydrin with triethyl-
amine in ethanol under reflux for 10 h.15 The synthetic proce-
dures for these ILs are depicted schematically in the following
Scheme 1.
0.45 lm filters, and analyzed using a Waters Breeze GPC–HPLC (gel
permeation chromatography–high performance liquid chromatog-
raphy) instrument (1525 binary pump with refractive index (RI)
and UV detector). The analysis was conducted with Bio-Rad HPX-
87H column (300 Â 7.8 mm) using HPLC grade 0.005 M H2SO4 water
solution as the eluent at a column temperature of 65 °C and a flow
rate of 0.8 mL/min. Glucose and 5-HMF were detected with an RI
detector and a UV detector, respectively. The reaction mixtures (di-
luted with methanol) were also analyzed by GC–MS (Varian 1200
Quadrupole GC/MS (EI), Varian CP-3800 GC) using a silicon column
with temperature programming from an initial temperature of
65 °C to a final temperature of 280 °C at 10 °C/min with 2 min of ini-
tial and final time, to verify the formation of 5-HMF.
2. Results and discussion
2.1. Catalytic conversion of glucose to 5-HMF in DMSO
Zhao et al.10 reported that CrCl2 combined with an expensive io-
nic liquid ([EMIM]Cl) as a co-catalyst or solvent could effectively
CH2Cl
OMe
CH2Cl
Pyridine
Cl
Me2SO4
KOH
Cl
N
OH
N
CH2Cl
CH2Cl
HCl
O
CMPPC
CHPPC
NEt3
*
CH2 CHO
CH2NEt3
*
*
CH2 CHO
CH2Cl
*
n
n
O
Cl
PTEAMEO
Scheme 1. Synthesis of ionic liquids of CHPPC, CMPPC, and PTEAMEO.

Z. Yuan et al. / Carbohydrate Research 346 (2011) 2019–2023
2021
in the reaction process did increase 5-HMF yield from glucose by
3–5%.
2.2. Conversion of glucose to 5-HMF in ionic liquids
Since 5-HMF has a very high boiling point (114 °C at 1 bar) and
is easy to transform to levulinic acid, it renders a challenge in sep-
aration of 5-HMF from a high boiling point aprotic solvent like
DMSO. In this regard, employing ionic liquid (salts in liquid state
or salts whose melting point is below 50 °C) as the reaction co-
catalyst and solvent could be advantageous, since the 5-HMF prod-
uct can be separated by extraction using low boiling point solvents
(acetone, ethyl acetate, diethyl ether, etc.). After the product sepa-
ration, the ionic liquid and catalyst may be recycled and reutilized.
Since the ionic liquids used by Zhao et al.,10 such as 1-ethyl-3-
methylimidazolium chloride ([EMIM]Cl), are very expensive, four
inexpensive ionic liquids (three of them were prepared by our-
selves in the lab) were investigated in this work for the conversion
of glucose to 5-HMF.
Figure 1. Conversion of fructose and glucose to 5-HMF with various catalysts.
Reaction conditions: 5.00 g glucose in 25.0 mL DMSO at 130 5 °C for 3 h with 2–
3 mL of benzene to remove water by azeotropic distillation. The concentration of
the catalyst (CrCl2, CrCl3 or other co-catalysts) was 0.03 M. (⁄): without addition of
the azeotropic solvent.
2.2.1. Effects of ionic liquids
Figure 2 shows the results of synthesis of 5-HMF from glucose
with CrCl2 as the main catalyst in various ionic liquids as reaction
solvents. The reaction was carried out in a 15 mL sealed reactor
with 1.00 g glucose in 5.00 g ionic liquid with 0.03 M CrCl2 at
120 °C for 1 h under N2 protection. The ionic liquids (ILs) tested in-
clude tetraethyl ammonium chloride (TEAC), (3-chloro-2-hydroxy-
propyl) pyridinium chloride (CHPPC), (3-chloro-2-methoxypropyl)
pyridinium chloride (CMPPC), and poly(triethylammonium methy-
lene ethylene oxide) chloride (PTEAMEO). Among the four ILs,
TEAC (a commercial ionic liquid) produced the best results with
51.6% 5-HMF yield and 100% glucose conversion. The other three
self-prepared ionic liquids (as displayed in Scheme 1), that is,
CHPPC, CMPPC, and PTEAMEO, produced 100% glucose conversion
too, but a lower 5-HMF yield of 29.6%, 38.3%, and 48.4%, respec-
tively, suggesting that more side reactions occurred in these ionic
liquid systems. Especially for CHPPC, the hydroxyl group in the
molecule may not be stable and easy to undergo dehydration to
form double bond and subsequently undergo polymerization.
König et al.17 used a similar catalyst choline chloride combined
with CrCl2 for this transformation with an optimal yield of 45%
achieved. Comparing the structure of the two ionic liquids, CHPPC
is more likely undergo dehydration.
convert glucose to 5-HMF. Binder and Raines5 reported that chro-
mium chloride(II, III) combined with many less expensive co-
catalysts such as a variety of halides in dimethyl acetamide
produced similar or even better results than the ionic liquid system
used by Zhao et al.10 We began with our investigation of converting
glucose and fructose to 5-HMF in dimethyl sulfoxide solution.
Compared with the work of Binder and Raines,5 we used a higher
concentration of glucose (about two times) and a lower concentra-
tion of cocatalysts (1/15th to 1/10th). Figure 1 presents the yields
from the tests for conversion of glucose (or fructose) to 5-HMF in
DMSO with CrCl2 or CrCl3 as the main catalyst and KBr, tetraethy-
lammonium chloride (TEAC), LiCl as a co-catalyst. The results in
Figure 1 show that CrCl2 is a more active catalyst than CrCl3 as sim-
ilarly demonstrated by Zhao et al.10 Among different halides as the
co-catalysts, TEAC led to the highest HMF yield from glucose, that
is, 49.3% with CrCl2 as the main catalyst. This could be owing to the
fact that TEAC has higher solubility and weaker ionic bonding in
the DMSO solvent. Without the addition of a co-catalyst, the con-
version of glucose into 5-HMF was much lower, which could be ex-
plained with the glucose conversion mechanism proposed by Zhao
et al.10 and Binder and Raines.5 That is, conversion of glucose to 5-
HMF is through a fructose intermediate: glucose was first isomer-
ized to fructose followed by conversion of fructose into 5-HMF.10
The halide anion could act as a chelating ligand to coordinate with
chromium ion in the transition state for the transformation of glu-
cose to fructose. The presence of a co-catalyst could promote this
isomerization process, hence enhance the HMF yield. As clearly
shown in Figure 1, the 5-HMF yield from fructose was very high,
71.1% in the test with CrCl3 catalyst, more than double that from
glucose using the same catalyst. Fructose might be the key inter-
mediate in the reaction of converting glucose into 5-HMF, as trace
of fructose was detectable by HPLC in the final reaction mixture.
Compared with CrCl2 or CrCl3, the use of other Lewis acid catalysts,
that is, ZnCl2 and the solid ultra acid (acidified zeolite) produced
very low yield of 5-HMF (<2%). Thus, chromium salts played a cru-
cial catalytic role in the conversion of glucose or fructose to 5-HMF.
5-HMF is well known to be unstable and it can undergo hydro-
lytic decomposition when being heated in the presence of water.
For instance, Shimizu et al.16 reported that mild evacuation of
water from the reaction process could significantly increase the
5-HMF product yield from fructose. As shown in Figure 1, the
use of benzene as a azeotropic solvent to remove water produced
Figure 2. Conversion of glucose to 5-HMF with CrCl2 catalyst in various ionic
liquids. Reaction conditions: 1.00 g glucose in 5.00 g ionic liquid with 0.03 M CrCl2
at 120 °C for 1 h under N2 protection in a closed system.

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Z. Yuan et al. / Carbohydrate Research 346 (2011) 2019–2023
Table 1
Glucose conversion and 5-HMF yields from the tests using different reactor
configurationsa
Reactor configuration
Glucose
5-HMF
conversion (%)
yield (%)
15 mL sealed reactor
Three necked 50 mL reactor under high
vacuum
ꢀ100
ꢀ100
51.6
49.7
Three necked 50 mL reactor under
continuous nitrogen purge
ꢀ100
54.8
a
Reaction conditions: 1.00 g glucose in 5.00 g TEAC with 0.03 M CrCl2 at 120 °C
for 1 h.
2.2.2. Effects of water in the reaction system
Water is a by-product of the reaction. The presence of water
was believed to promote the decomposition of 5-HMF to levulinic
acid.18 Removal of water could suppress two undesired reactions:
hydrolysis of 5-HMF to levulinic acid, and the reactions that par-
tially dehydrate the intermediates into condensation products. In
contrast, Shimizu, et al16 found in the conversion of fructose to
5-HMF under acidic condition, full removal of water decreased
the 5-HMF yield while mild evacuation could improve the 5-HMF
yield. In this study several special experiments were designed in
order to investigate the influence of water in the reaction mixture
on the conversion of glucose into 5-HMF. The tests were performed
with three different reactor configurations as follows: in a 15 mL
sealed reactor, in a three-neck 50 mL reactor under high vacuum,
and in a three-neck 50 mL reactor under continuous nitrogen
purge. In all tests, the conversion of glucose were all around
100% after 1 h at 120 °C, while the 5-HMF yield varied with differ-
ent reactor configurations as presented in Table 1. Although the 5-
HMF yield (54.8%) was the highest in the three-neck 50 mL reactor
under continuous nitrogen purge, the 5-HMF yield in the 15 mL
sealed reactor was 51.6%, even higher than that (49.7%) in the
three-neck 50 mL reactor under high vacuum. This implies that
without the existence of water in the 50 mL three-neck reactor un-
der high vacuum (water was removed under high vacuum), the 5-
HMF yield actually reduced, being lower than that from a sealed
reactor where water was always present. It should be noted, how-
ever, under the nitrogen purge condition water vapor could only be
partially removed, and there should always be some water present
in the reaction mixture. These results are thus in a good agreement
with those reported by Shimizu et al.,16 where mild evacuation of
the reactor could improve the 5-HMF yield, but full removal of
water decreased the 5-HMF yield. Thus, the presence of a small
amount of water in the reaction system can help the reaction,
probably because water can increase the solubility of chromium
catalyst in the reaction medium.
Figure 3. Conversion of glucose to 5-HMF in various ILs with CrCl2 or CrCl3 as the
main catalyst. Reaction conditions: 1.00 g glucose in 5.00 g ionic liquid with 0.03
CrCl2 or CrCl3 at 120 °C for 1 h in a closed reactor system under N2 protection or in a
three-necked reactor with continuous nitrogen purge (⁄).
Figure 4. Conversion of glucose to 5-HMF at different temperatures. Reaction
conditions: 1.00 g glucose in 5.00 g ionic liquids with 0.03 M CrCl2 or CrCl3 at 120 °C
for 1 h or at 100 °C for 1.5 h in a closed reactor system under N2 protection.
2.2.4. Effects of reaction temperature
Effects of reaction temperature on the glucose conversion to
5-HMF were investigated under the following reaction conditions:
1.00 g glucose in 5.00 g ionic liquids with 0.03 M CrCl2 or CrCl3 at
120 °C for 1 h or at 100 °C for 1.5 h in a closed reactor system under
N2 protection. The results are shown in Figure 4. Although in all
tests at 120 °C for 1 h or at 100 °C for 1.5 h with the CHPPC/CrCl2,
CMPPC/CrCl2 and CMPPC/CrCl3 catalyst system, the glucose con-
version attained 100%, the 5-HMF yields were about 6–10% higher
at 100 °C than those at 120 °C. This result might suggest that
although the reaction was faster at a higher temperature, more
side reactions occurred, resulting in reduced yields of 5-HMF.
2.2.3. Effects of chromium valence
Zhao et al.10 first found that chromium chlorides were very
effective catalysts for glucose to 5-HMF conversion and CrCl2
(70%) gave a much better yield than CrCl3 (45%). The study of
Binder and Raines5 showed that there was no difference in the
activities of CrCl2 and CrCl3 for the glucose to 5-HMF conversion,
which is very interesting due to the fact that the cost of CrCl3 is
much lower than CrCl2, while their finding seems to be question-
able. In the present study, CrCl2 was found to be more effective
than CrCl3 for catalyzing the conversion of glucose to 5-HMF in
ILs (TEAC and CMPPC). The use of CrCl2 led to about 10% higher
yields of 5-HMF at 120 °C for 1 h either in a closed reactor system
under N2 protection or in a three-neck reactor with continuous
nitrogen purge, as shown in Figure 3. This probably because CrCl3
is a strong Lewis acid, so it can cause glucose dehydration to olig-
omers. As such, for glucose to 5-HMF conversion in ionic liquids,
CrCl2 is a better catalyst than CrCl3 with respect to the 5-HMF yield.
3. Conclusions
Efficient conversion of glucose to 5-HMF was achieved with
CrCl2 and CrCl3 as the main catalysts in DMSO and several new io-
nic liquids as co-catalyst or solvents. When using DMSO, the high-
est 5-HMF yield obtained was ꢀ50% with the CrCl2/TEAC catalyst
system. The yield of 5-HMF attained ꢀ55% using CrCl2 catalyst
with TEAC ionic liquid as the co-catalyst or solvent. The reaction
was faster in ionic liquids than in DMSO solvent. CrCl2 was demon-
strated to be more effective than CrCl3 for converting glucose into
5-HMF in either DMSO or ionic liquids. Nitrogen purging to remove

Z. Yuan et al. / Carbohydrate Research 346 (2011) 2019–2023
2023
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Acknowledgments
The authors are grateful for the financial support from the On-
tario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)
through the New Directions Program Grant, as well as the funding
from FedNor and NOHFC. One of the authors (C.X.) also acknowl-
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