A facile acidic choline chloride-p-TSA DES-catalysed dehydration of fructose to 5-hydroxymethylfurfural

Article abstract of DOI:10.1039/c4ra07065h

The conversion of lignocellulosic biomass to biofuel precursors has recently been a focus of intensive research due to the essential role of biofuels as transport fuels in the future. Specifically, the conversion of fructose to 5-hydroxymethylfurfural (5HMF) has gained momentum, as 5HMF is a versatile bio-based platform molecule that leads to a plethora of high-value chemicals and biofuel molecules, such as DMF. Herein, we report the use of an environmentally friendly, Bronsted acidic, deep eutectic mixture consisting of choline chloride (ChCl) and p-TSA for the dehydration of fructose to 5HMF. Unlike previous systems, the use of ChCl-p-TSA plays a dual role, as both a hydrogen bond donor (HBD) and a catalyst for the dehydration reaction, thus obviating the addition of an external acid. The reaction was examined and optimised in a batch system, where it was found that fructose was readily dehydrated to 5HMF. The best reaction conditions, with the highest 5HMF yield of 90.7%, were obtained at a temperature of 80 °C using a DES molar mixing ratio of 1 : 1 ChCl : p-TSA and feed ratio of 2.5%, and with a reaction time of one hour.

Full text of DOI:10.1039/c4ra07065h

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A facile acidic choline chloride–p-TSA DES-
catalysed dehydration of fructose to 5-
hydroxymethylfurfural
Cite this: RSC Adv., 2014, 4, 39359
*
Amhamed A. Assanosi, Mohamed M. Farah, Joseph. Wood and Bushra Al-Duri
The conversion of lignocellulosic biomass to biofuel precursors has recently been a focus of intensive
research due to the essential role of biofuels as transport fuels in the future. Specifically, the conversion
of fructose to 5-hydroxymethylfurfural (5HMF) has gained momentum, as 5HMF is a versatile bio-based
platform molecule that leads to a plethora of high-value chemicals and biofuel molecules, such as DMF.
Herein, we report the use of an environmentally friendly, Brønsted acidic, deep eutectic mixture
consisting of choline chloride (ChCl) and p-TSA for the dehydration of fructose to 5HMF. Unlike previous
systems, the use of ChCl–p-TSA plays a dual role, as both a hydrogen bond donor (HBD) and a catalyst
for the dehydration reaction, thus obviating the addition of an external acid. The reaction was examined
and optimised in a batch system, where it was found that fructose was readily dehydrated to 5HMF. The
best reaction conditions, with the highest 5HMF yield of 90.7%, were obtained at a temperature of 80 ꢀC
using a DES molar mixing ratio of 1 : 1 ChCl : p-TSA and feed ratio of 2.5%, and with a reaction time of
one hour.
Received 13th July 2014
Accepted 8th August 2014
DOI: 10.1039/c4ra07065h
www.rsc.org/advances
which lead to low 5HMF yields because of the rehydration of the
product 5HMF.4,13,14
1. Introduction
To overcome the drawbacks of aqueous systems, different
organic solvents, such as dimethyl sulfoxide (DMSO),
The depletion of petroleum resources, subsequent changes in
world economies, the increase in greenhouse gas emissions,
and the associated climate change are a few of the issues that
reveal the urgent need for renewable and green energy
resources.1 Lignocellulosic biomass is predominant among the
renewable sources for future bioenergy. It is low-cost, abundant,
and does not compete with food resources. Fructose derived
from lignocellulosic biomass has been found to be among the
best carbohydrate sources of furans.2
One of the most important block intermediate materials
obtained from the direct dehydration of fructose is 5HMF. The
fructose dehydration reaction mechanism and its possible side
reactions are illustrated in Scheme 1. 5HMF is regarded as an
important block material, as it has many derivatives that can be
used as biofuel precursors and useful chemicals.4–6 The main
derivatives of 5HMF are illustrated in Scheme 2.
5HMF was rst produced by Dull et al. in the 19th century by
pressurised heating of inulin in oxalic acid.8 Subsequently,
different acid catalysis systems consisting of mineral acids,9,10
solid acids,11,12 and metallic acids10 were studied to improve the
yields of 5HMF in aqueous medium by catalytic fructose dehy-
dration reactions. The common drawback of these systems was
the requirement for relatively high reaction temperatures,
School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham,
B15 2TT, UK. E-mail: b.al-duri@bham.ac.uk; Tel: +44 (0)121 414 3969
Scheme 1 Schematic diagram of acid-catalyzed fructose dehydration
reaction and the possible subreaction pathways.3
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amines, alcohols and different acids.22 Briey, the chemistry
concept of these mixtures is an ionic interaction between the
hydrogen bond donor (HBO) and the salt, which leads to a
decrease in both melting and freezing points of the mixture.23,24
In addition to sharing similar properties with normal ionic
liquids, DES mixtures retain superior advantages; they have low
cost and are biodegradable and easy to prepare. Choline chlo-
ride–urea is the most commonly used DES mixture;25 it has been
widely used as solvent and co-solvent in many catalytic chemical
synthesis applications.26,27
DES have been found to be active catalytic mixtures in
biomass hydrolysis.27 Hayyan et al. used a DES mixture of N,N-
diethylenethanol ammonium chloride and p-TSA for free fatty
acid esterication to biodiesel fuel28 and a mixture of p-toluene
sulfonic acid monohydrate (p-TSA) and allyltriphenyl-
phosphonium bromide to produce biodiesel from low-grade
palm oil.29
Scheme 2 Possible derivatives of 5HMF.7
dimethylformamide (DMF), acetic acid and methanol have been
investigated. Despite a higher yield of 5HMF obtained with
these solvents, some limitations were encountered. The poor
solubility of sugars in many organic solvents, the difficult
separation of 5HMF in high boiling point organic solvents and
the poor extraction efficiency of low boiling point organic
solvents pose a barrier to utilizing these systems. Similar chal-
lenges are faced with biphasic systems, such as methyl isobutyl
ketone (MIBK) and n-butanol (BuOH) in water to extract the
produced 5HMF.7
Recently, the use of ionic liquids (ILs) in fructose dehydra-
tion to 5HMF showed increased promise because of their
unique properties, namely, low vapour pressure, non-amma-
bility, high chemical and thermal stability, and ability to adjust
solvent power.15
Lansalot obtained 5HMF yield of 68% when 5 wt% of fruc-
tose was solubilised in dimethyl sulfoxide (DMSO) and cata-
lysed by p-TSA in 1-butyl-3-methylimidazolium as ionic liquid
solvent for 32 h.16
Quan Cao studied the fructose dehydration to 5HMF in
different imidazolium ionic liquids. He concluded that the
acidic C-2 hydrogen of imidazolium cations acts as catalyst for
the fructose dehydration reaction, even when no catalyst was
used.17
Liu reported the synthesis of 5HMF from concentrated
solutions of fructose by using a DES mixture formed from
choline chloride and carbon dioxide; a yield of 62% was
obtained.30
In all of the above studies, a range of DES has previously
been utilised for the hydrolysis of fructose to 5HMF requiring
the addition of an acid catalyst, which is generally undesirable
from a processing viewpoint.
This work investigates an acidic DES derived from choline
chloride (ChCl) and p-toluene sulfonic acid monohydrate (p-
TSA) to dehydrate fructose to 5HMF, which obviates the addi-
tion of an acid catalyst. The selected DES was found to be highly
efficient, and 90.7% yield of 5HMF was obtained. It was
produced from cheap and renewable materials, rendering it
environmentally friendly. The use of p-TSA as both HBO and
catalyst would reduce the processing cost.
2. Results and discussion
2.1 The effect of feed ratio
As illustrated in section 5, the feed mass ratio was calculated as
the percentage of fructose in the reaction mixture at the start. As
shown in Fig. 1, the 5HMF yield decreases with increasing
Although the use of ionic liquids highly improved the 5HMF
yields obtained from fructose dehydration, the elevated cost
and unclear environmental effects of the conventional ionic
liquids still pose a challenge for establishing a robust produc-
tion process of 5HMF using the I system. Therefore, research
attention has turned to room temperature ILs. Those liquids
ꢀ
contain organic salts with melting point below 100 C, namely
choline chloride-based ILs18 and amino acid based ILs.19
In this matter, Suqin and others conducted a fructose
dehydration reaction to 5HMF using
a biphasic system
comprised of renewable ionic liquid and ethyl acetate as
extraction solvent.20
The latest form of these solvents are the deep eutectic
solvents (DES), developed by Abbott.21 DES are mixtures made of
different ammonium salts, such as choline chloride, and
different spaces of hydrogen bond donors, namely amides,
Fig. 1 Effect of feed ratio on 5HMF yield and fructose conversion.
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fructose mass ratio. This may be attributed to 5HMF being
rehydrated by the presence of water produced from the dehy-
dration reaction of fructose. The highest yield obtained was
90.7% at a mass ratio of 2.5%, aer which the yield sharply
decreased to 52.3% at a feed mass ratio of 10%. As the feed ratio
increased from 20% to 100%, the 5HMF yield decreased grad-
ually. The lowest yield was 20.5% at a feed ratio of 100%. This
can be attributed to the fact that increasing the initial fructose
concentration could result in subsequently high 5HMF
concentration, which then leads to the occurrence of unwanted
side reactions.31 These reactions are expected to produce
insoluble humins and/or soluble polymers,32 which lead to a
decrease in 5HMF yield. The change of the sample colour to a
darker brown by increasing the fructose ratio is another sign for
the production of these undesirable by-products in the dehy-
dration reaction. Self-polymerization of 5HMF and cross-poly-
merization between fructose and 5HMF could produce
polymers in fructose dehydration reactions.33 It was mentioned
that the increase of initial fructose concentration would
encourage the occurrence of polymerization reactions, which
would decrease the 5HMF selectivity7 as illustrated in Fig. 2. The
highest yield was obtained at a feed ratio of 2.5%. Upon analysis
2.5% feed ratio gave unstable results, therefore 5% feed ratio
was selected for subsequent experiments.
Fig. 3 The effect of reaction time on HMF yield, HMF selectivity and
fructose conversion.
2.3 The effect of reaction temperature
The effect of reaction temperature on the dehydration reactions
ꢀ
ꢀ
was investigated in a temperature range of 50 C to 110 C, as
shown in Fig. 4. The recorded temperature was the oil bath
temperature, and not the temperature inside the reaction
beaker.
A DES mixture of 1 : 1 ChCl to p-TSA was used. Fructose
ꢀ
conversion increased with temperature from 77.1% at 50 C to
99% at 110 ꢀC, keeping a generally high conversion over the
whole temperature range.
2.2 The effect of reaction time
On the other hand, 5HMF yield was almost steady at 65.0%,
65.2% and 63.8%, when the reactions were conducted at 50 ꢀC,
60 ꢀC and 70 ꢀC, respectively. A highest yield of 70.6% was
obtained at 80 ꢀC, aer which the yield started to decrease with
increasing reaction temperature. The lowest yield recorded was
The effect of reaction time on the fructose dehydration reaction
was investigated in 10 minute intervals up to 120 minutes of
reaction time, as shown in Fig. 3.
Fructose conversion was mostly steady for the entire reaction
timescale. The yield and selectivity of 5HMF showed almost
similar trends. 5HMF yield of 57.5% was obtained at 10 minutes
reaction time, then it increased to 63.7% at 30 minutes. The
selectivity showed a slight increase from 65.5% at 10 minutes to
68.3% at 30 minutes. Over the course of 40 to 120 minutes of
reaction time, the yield and selectivity did not show a denite
trend, except for wavering around 70% yield ꢁ10%. This could
only be attributed to the possible rehydration of 5HMF and the
formation of side products by degradation.34 For this reason, a
reaction time of 1 h was selected as the optimum time.
ꢀ
50.6% at 110 C, where the sample colour was very dark. This
might be due to thermal degradation to humins. Based on these
ꢀ
results, 80 C was selected as the best reaction temperature.
As for 5HMF selectivity, Fig. 4 shows a general decrease with
increasing reaction temperature, while remaining generally
high. The highest 5HMF selectivity was 84.3% at 50 ꢀC, and the
ꢀ
lowest selectivity was 51.1% at 110 C. On the other hand, the
highest fructose conversion was 99% at 110 ꢀC, while the lowest
ꢀ
was 77.1% at 50 C.
Fig. 2 Effect of feed ratio on 5HMF selectivity.
Fig. 4 Effect of reaction temperature.
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Table 1 Parameters studied and their ranges
A similar effect of the DES ratio on yield was seen on 5HMF
selectivity. The lowest selectivity of 33.9% was obtained at a 1 : 2
molar mixing ratio, while the highest selectivity of 92.6% was
obtained at a 1 : 1.5 molar mixing ratio.
Variable
Range
Temperature ꢀ
C
50, 60, 70, 80, 90, 100, and 110
10–120
2.5–100
The effect of DES molar mixing ratio on fructose conversion
was not prominent. It was steady around the range of 84.5% to
93.3% at molar mixing ratio of 1 : 1.5 and 1 : 1, respectively.
Other experiments were conducted, where 5HMF yield was
investigated as function of DES ratio, keeping the feed ratio
constant at 2.5 wt%. Fig. 6 shows that a maximum 5HMF yield
of 90.7% was obtained at 1 : 1 DES molar mixing ratio. It
decreased to 58.4% when the DES molar mixing ratio was
increased to 1 : 1.5. This further proves that the 2.5 wt% feed
ratio, 1 : 1 DES molar mixing ratio and 80 ꢀC at 1 hour of
reaction time are the best operating conditions for the investi-
gated system.
Reaction time (minute)
Feed mass ratio (%)
DES mixing molar ratio (%)
ChCl : p-TSA
1 : 0.5, 1 : 1, 1 : 1.5 and 1 : 2
2.4 The effect of DES mixing molar ratio
Deep eutectic solvent (DES) molar mixing ratio had great effect
on the 5HMF yield and selectivity in fructose dehydration
reactions, as DES plays a dual role as solvent and catalyst. In this
work, different DES mixing molar ratios were investigated as
shown in Table 1, at constant feed ratio of 5 wt%, in order to
have a clear assessment of the effect of the DES mixing ratio.
As shown in Fig. 5, changing the ratio from 1 : 0.5% to
1 : 1.5% had a positive effect on 5HMF yield and selectivity. The
yield increased from 53% at a molar mixing ratio of 1 : 0.5 to
70% at a 1 : 1 molar mixing ratio, reaching a value of 78.3% at a
molar mixing ratio of 1 : 1.5. On the other hand, when the
mixing molar ratio of DES increased to 1 : 2, a severe decrease in
the 5HMF yield, down to 29.2%, was observed.
3. Experimental
3.1 Materials
Fructose (99%), 5-hydroxymethylfurfural (99%) and p-toluene
sulfonic acid monohydrate (p-TSA) (98.5%) were ordered from
Sigma Aldrich; choline chloride (99%) was ordered from Acros;
and calcium hydroxide analytical reagent was ordered from
Riedel-DeHaen. All materials were used with no further
purication.
3.2 Preparation of deep eutectic solvent (DES)
Choline chloride and p-toluene sulfonic acid (p-TSA) were dried
under vacuum at 60 ꢀC for 2 h prior to use, and then mixed
together in different molar ratios at 80 ꢀC, using an oil bath and
magnetic stirrer at 300 rpm. Aer half an hour, a colourless,
thick, homogenous liquid mixture was obtained. The prepara-
tion was carried out in a fume hood. A similar procedure was
used by Hayyan to prepare DES of p-TSA and N,N-diethanol
ammonium chloride to produce biodiesel from fatty acid.28
3.3 Fructose dehydration reaction in DES procedure
All the fructose dehydration reactions were carried out in a 100
mL glass beaker clamped in an oil bath, using a magnetic stirrer
at 300 rpm. Aerwards, the required amount of fructose was
added and stirred at 300 rpm for 1 hour at 80 ꢀC. At the end of
the reaction, the thick dark brown reaction mixture was cooled
down to room temperature and then dissolved in 10 mL of
HPLC-grade water. Next, the initial pH was measured by using a
pH meter and then adjusted to neutral by using 2 M of calcium
hydroxide solution (Ca(OH)2). The entire sample was poured
into a 100 mL calibration ask and then diluted by HPLC-grade
water to 100 mL. 2 mL of the sample was passed through a
syringe lter, bottled in HPLC vials, and then shaken for HPLC
analysis.
Fig. 5 Effect of DES mixing molar ratio.
4. HPLC analysis
The reactant fructose and product 5HMF were analysed by an
HPLC 1100 Agilent series equipped with a refractive index
Fig. 6 5HMF yield % vs. DES mixing ratio at a feed ratio of 2.5%.
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detector and Rezex RCM-monosaccharide column (300 ꢂ 7.8
mm), ordered from Phenomenex. The analytical method used
100% HPLC-grade water from VWR as mobile phase, at ow rate
2 Y. Roman-Leshkov, J. N. Chheda and J. A. Dumesic, Science,
2006, 312, 1933–1937.
3 Y. Roman-Leshkov and J. A. Dumesic, Top. Catal., 2009, 52,
297–303.
of 0.5 mL minꢃ1, column oven temperature of 75 C, injection
ꢀ
volume of 20 mL and total time of 40 minutes.
4 B. F. M. Kuster, Starch/Staerke, 1990, 42, 314–321.
5 A. Gandini and M. N. Belgacem, Prog. Polym. Sci., 1997, 22,
1203–1379.
6 A. Gandini and M. N. Belgacem, Actual. Chim., 2002, 56–61.
7 R. J. van Putten, J. C. van der Waal, E. de Jong,
C. B. Rasrendra, H. J. Heeres and J. G. de Vries, Chem. Rev.,
2013, 113, 1499–1597.
8 A. A. Rosatella, S. P. Simeonov, R. F. M. Frade and
C. A. M. Afonso, Green Chem., 2011, 13, 754–793.
9 D. W. Harris and M. S. Feather, J. Am. Chem. Soc., 1975, 97,
178–181.
10 B. F. M. Kuster and H. S. Vanderbaan, Carbohydr. Res., 1977,
54, 165–176.
5. Variables and equations
The 5HMF yield, selectivity and fructose conversion were
calculated as follows:
ꢀ
ꢁ
moles of 5HMF yield produced
initial moles of fructose
5HMF yield% ¼
ꢂ 100
ꢀ
ꢁ
moles of 5HMF yield produced
converted moles of fructose
5HMF selectivity% ¼
ꢂ 100
11 C. Moreau, R. Durand, S. Razigade, J. Duhamet, P. Faugeras,
P. Rivalier, P. Ros and G. Avignon, Appl. Catal., A, 1996, 145,
211–224.
12 X. H. Qi, M. Watanabe, T. M. Aida and R. L. Smith, Green
Chem., 2008, 10, 799–805.
ꢀ
ꢁ
total fructose moles converted
Fructose conversion% ¼
ꢂ100
initial fructose moles
13 A. Corma, S. Iborra and A. Velty, Chem. Rev., 2007, 107, 2411–
2502.
fructose mass
Feed mass ratio ¼
total mass of DES
14 J. Lewkowski, ARKIVOC, 2001, 17–54.
15 M. C. Kroon, V. A. Toussaint, A. Shariati, L. J. Florusse, J. van
Spronsen, G. J. Witkamp and C. J. Peters, Green Chem., 2008,
10, 333–336.
16 C. Lansalot-Matras and C. Moreau, Catal. Commun., 2003, 4,
517–520.
17 Q. Cao, X. C. Guo, S. X. Yao, J. Guan, X. Y. Wang, X. D. Mu
and D. K. Zhang, Carbohydr. Res., 2011, 346, 956–959.
18 M. Avalos, R. Babiano, P. Cintas, J. L. Jimenez and
J. C. Palacios, Angew. Chem., Int. Ed., 2006, 45, 3904–3908.
19 G. H. Tao, L. He, W. S. Liu, L. Xu, W. Xiong, T. Wang and
Y. Kou, Green Chem., 2006, 8, 639–646.
20 S. Q. Hu, Z. F. Zhang, Y. X. Zhou, B. X. Han, H. L. Fan,
W. J. Li, J. L. Song and Y. Xie, Green Chem., 2008, 10, 1280–
1283.
ꢀ
ꢁ
pTSA moles
DES molar mixing ratio ¼
ChCl moles
The experimental conditions and variable ranges investi-
gated in this work are listed in Table 1.
6. Conclusion
The deep eutectic solvent mixture of ChCl–p-TSA was found to
be a highly promising catalytic solvent mixture for the reaction
of fructose dehydration to 5HMF, giving a high yield and
selectivity. The dehydration process using such mixture was
found to be efficient, as the DES mixture comprised renewable,
non-toxic and cheap materials. The process did not require
21 A. P. Abbott, G. Capper, D. L. Davies and R. Rasheed, Inorg.
Chem., 2004, 43, 3447–3452.
ꢀ
severe reaction conditions, as 80 C was found to be the best
22 Z. Maugeri and P. D. de Maria, RSC Adv., 2012, 2, 421–425.
23 M. Figueiredo, C. Gomes, R. Costa, A. Martins, C. M. Pereira
and F. Silva, Electrochim. Acta, 2009, 54, 2630–2634.
24 K. Haerens, E. Matthijs, A. Chmielarz and B. Van der
Bruggen, J. Environ. Manage., 2009, 90, 3245–3252.
25 A. P. Abbott, G. Capper, D. L. Davies, R. K. Rasheed and
V. Tambyrajah, Chem. Commun., 2003, 70–71, DOI:
10.1039/b210714g.
26 D. Lindberg, M. D. Revenga and M. Widersten, J. Biotechnol.,
2010, 147, 169–171.
27 J. T. Gorke, F. Srienc and R. J. Kazlauskas, Chem. Commun.,
2008, 1235–1237, DOI: 10.1039/b716317g.
reaction temperature. There was no need to use an external
catalyst, as the p-TSA serves as both hydrogen bond donor
(HBD) and acid catalyst for the dehydration reaction. The DES
mixture was easy to prepare and had no contamination effect, as
it is not reactive. The best yield obtained was 90.7% at a feed
ratio of 2.5 wt%, DES mixing molar ratio of 1 : 1, 80 ꢀC
temperature and 1 h reaction time. Further investigations are
required for an efficient separation process for the nal product
5HMF. Also, further analysis is required to identify the by-
products obtained from the concurrent side reactions.
28 A. Hayyan, M. A. Hashim, M. Hayyan, F. S. Mjalli and
I. M. AlNashef, Ind. Crops Prod., 2013, 46, 392–398.
References
1 Y. Roman-Leshkov, C. J. Barrett, Z. Y. Liu and J. A. Dumesic, 29 A. Hayyan, M. A. Hashim, F. S. Mjalli, M. Hayyan and
Nature, 2007, 447, 982–985.
I. M. AlNashef, Chem. Eng. Sci., 2013, 92, 81–88.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 39359–39364 | 39363

View Article Online
RSC Advances
Paper
30 F. Liu, J. Barrault, K. D. Vigier and F. Jerome, ChemSusChem, 33 F. F. Wang, A. W. Shi, X. X. Qin, C. L. Liu and W. S. Dong,
2012, 5, 1223–1226. Carbohydr. Res., 2011, 346, 982–985.
31 F. Ilgen, D. Ott, D. Kralisch, C. Reil, A. Palmberger and 34 Q. Zhao, L. Wang, S. Zhao, X. Wang and S. Wang, Fuel, 2011,
B. Konig, Green Chem., 2009, 11, 1948–1954.
32 C. Sievers, I. Musin, T. Marzialetti, M. B. V. Olarte,
P. K. Agrawal and C. W. Jones, ChemSusChem, 2009, 2,
665–671.
90, 2289–2293.
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