Defunctionalization of fructose and sucrose: Iron-catalyzed production of 5-hydroxymethylfurfural from fructose and sucrose

Article abstract of DOI:10.1016/j.cattod.2011.03.003

A highly efficient iron-catalyzed production of 5-hydroxymethylfurfural (HMF) from sugar is reported. The dehydration of fructose and sucrose has been studied in the presence of different iron salts and co-catalysts. As a result, it was found that fructose and sucrose could be efficiently and selectively converted to HMF using a combination of environmentally friendly FeCl ₃ and tetraethyl ammonium bromide (Et₄NBr) as the catalytic system. For instance, 86% HMF yield at full conversion of fructose was obtained for 2 h at 90 ° C in air. The effects of catalyst concentration, reaction time and reaction temperature were investigated in detail. The electronic absorption spectra of different catalysts were recorded, and the FeCl₃Br^- ion was considered as the active catalyst species.

Full text of DOI:10.1016/j.cattod.2011.03.003

Catalysis Today 175 (2011) 524–527
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Defunctionalization of fructose and sucrose: Iron-catalyzed production of
5-hydroxymethylfurfural from fructose and sucrose
Xinli Tonga, Mengran Lia, Ning Yanb, Yang Maa, Paul J. Dysonb, Yongdan Lia,∗
a Tianjin Key Laboratory of Catalysis Science and Technology and State Key Laboratory for Chemical Engineering (Tianjin University), School of Chemical Engineering, Tianjin University,
Tianjin 300072, China
b Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
A highly efficient iron-catalyzed production of 5-hydroxymethylfurfural (HMF) from sugar is reported.
The dehydration of fructose and sucrose has been studied in the presence of different iron salts and
co-catalysts. As a result, it was found that fructose and sucrose could be efficiently and selectively con-
verted to HMF using a combination of environmentally friendly FeCl3 and tetraethyl ammonium bromide
(Et4NBr) as the catalytic system. For instance, 86% HMF yield at full conversion of fructose was obtained
for 2 h at 90 ◦C in air. The effects of catalyst concentration, reaction time and reaction temperature were
investigated in detail. The electronic absorption spectra of different catalysts were recorded, and the
FeCl3Br− ion was considered as the active catalyst species.
Received 12 October 2010
Received in revised form 15 February 2011
Accepted 1 March 2011
Available online 9 April 2011
Keywords:
Fructose
Sucrose
5-Hydroxymethylfurfural
Iron catalysis
© 2011 Elsevier B.V. All rights reserved.
Biomass transformation
1. Introduction
may be achieved with negligible acid by-product. For example,
Zhao et al. [27] have reported a metal chloride/1-ethyl-3-methyl-
The use of biomass as a source of liquid fuels and chemi-
cals represents a sustainable approach for obtaining energy and
carbon-based compounds [1–3]. Conversion of sugars, such as fruc-
tose and sucrose, to valuable chemicals is very important in the
chemical processing from biomass resources [4–6]. The impor-
tant compound 5-hydroxymethylfurfural (HMF), which originates
from the dehydration of sugar, is a valuable intermediate used
in the production of fine chemicals, pharmaceuticals and numer-
ous polymers [7–9]. In recent years, the development of novel
and efficient catalytic systems for the dehydration of sugars to
HMF has become a hot topic [10–12]. Traditionally, acid cata-
lysts, such as mineral acids [13,14], strong acid cation exchange
resins [15–17], H-form zeolites [18,19], and supported heteropoly-
acids [20], have been employed for the dehydration fructose to
HMF. In addition, acidic ionic liquids have been used as catalysts
or solvents in sugar dehydration [21–24]. However, these cata-
lysts may have favored the subsequent dehydration of HMF to
levulinic and formic acids, which ultimately lowers the yield of
HMF [25,26].
imidazolium chloride ([EMIM]Cl) system that gives moderate
to good HMF yields from fructose (ca. 83% with Pt or Rh
chloride) and glucose (ca. 68% with CrCl2); Yong et al. [28]
further found that a system based on N-heterocyclic carbene-
Cr/1-butyl-3-methyl imidazolium chloride ([BMIM]Cl) was more
efficient for the dehydration of sugars to HMF. However, in
these catalytic systems, only noble metals (Ru and Pt chlo-
ride) or potentially toxic metals (Cr chlorides) resulted in a
good catalytic performance. It is well-known that developing
more cost-efficient and environmentally friendly metal catalysts
remains an issue of scientific interest and industrial significance.
In this respect, iron salts are ideal candidates due to their low
cost, non-toxicity, ready availability and environmentally benign
character [29,30].
Iron-based catalysis is effective in the cross-coupling [31–33],
oxidation [34,35] and hydrogenation reaction [36], as well as in
the Fischer–Tropsch synthesis [37]. However, iron-catalyzed sugar
conversion remains a challenge and warrants further investiga-
tion. In this paper, we describe the iron-catalyzed dehydration of
fructose and sucrose to HMF. It was found that a FeCl3–tetraethyl
ammonium bromide (Et4NBr) system resulted in a high catalytic
performance and HMF was obtained in good yield under mild
conditions. Moreover, the catalytic system was further optimized
and attempts to delineate the nature of the active catalyst were
made.
Recently, the metal-catalyzed dehydration of sugar has received
considerable attention due to the high selectivity of HMF that
∗
Corresponding author. Tel.: +86 022 27405613; fax: +86 022 27405243.
E-mail address: ydli@tju.edu.cn (Y. Li).
0920-5861/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2011.03.003

X. Tong et al. / Catalysis Today 175 (2011) 524–527
525
Table 1
Dehydration of fructose with different catalystsa.
Entry
Catalyst
Time (h)
Yield (%)b
Sel. (%)b
1
2
3
4
5
6
7
8
FeCl2
FeCl3
FeCl3–NH4Br
FeCl3–Et4NBr
Et4NBr
2
2
2
2
3
3
2
2
2
2
2
2
2
2
2
1
–
42
84
86
<1
0
65
69
61
77
80
74
82
<1
<1
43
84
86
–
Scheme 1. Synthesis of HMF from fructose.
no
–
FeCl3–LiCl
FeCl3–NaCl
FeCl3–KCl
FeCl3–LiBr
FeCl3–NaBr
FeCl3–KBr
FeCl3–Et4NCl
Fe(NO3)2–Et4NBr
Fe(NO3)3–Et4NBr
70
70
64
80
82
76
82
–
2. Experimental
9
2.1. Reagents
10
11
12
13
14
15
Fructose, glucose, sucrose, iron salts, Et4NBr and other co-
catalysts are of analytical quality and were obtained from
Tianjin Guangfu Fine Chemical Research Institute. NMP, DMF
and DMSO were purified by distillation prior to use. Pure H2O
was prepared using a Ultrapure Water System (electrical resis-
tivity = 10−12 mꢀ cm). The HMF used as the standard sample was
purchased from Alfa Aesar.
–
a
Reaction conditions: 1.0 g d-fructose, 0.56 mmol iron salt, and 1.0 mmol co-
catalyst in 10 mL NMP solvent, temperature = 90 ◦C, in air.
b
The yield and selectivity are obtained by HPLC analysis and product separation
method.
2.2. General procedure for the dehydration of sugars and the
products analysis method
(Table 1, entry 1) under the employed conditions. In the presence
of 10.0 mol% FeCl3 the yield of HMF increased to 42% (Table 1, entry
2), and HMF was obtained in 84% yield with ammonium bromide
(NH4Br) as a co-catalyst (Table 1, entry 3). Further investigations
showed that the coupled FeCl3–Et4NBr system exhibited a better
catalytic activity, with an 86% yield of HMF at full fructose con-
version (Table 1, entry 4). Note, the yield of HMF was <1% when
only Et4NBr was used as the catalyst (Table 1, entry 5), and a blank
experiment was also carried out in the absence of any catalyst and
nearly no reaction occurred (Table 1, entry 6).
In order to further understand the reaction characteristics, dif-
ferent alkali metal halides were also used as co-catalysts in place
of Et4NBr. Lower yields of HMF were obtained with LiCl, NaCl or
KCl co-catalyst (Table 1, entries 7–9). Moreover, when LiBr, NaBr or
KBr were employed, HMF yields of 74%–80% were obtained (Table 1,
entries 10–12). The bromide ion appears to exhibit a superior activ-
ity, especially when coupled with the tetraethyl ammonium cation,
which is probably linked to the weaker ion pairing present in this
salt compared to the others used in the study. In agreement with
this hypothesis, further investigations showed that the yield of
HMF reached 82% employing Et4NCl as a co-catalyst (Table 1, entry
13). In addition, other combinations of iron salts with Et4NBr were
evaluated and conversions to HMF were very low (Table 1, entries
14–15). Overall, the FeCl3–Et4NBr system proved to be the best cat-
alyst system. Here, the obtained yield of HMF is analogous to that
with Cr [27,28], La [38], Sn [39] and W catalyst [40]; however, the
low cost and non-toxicity of Fe catalyst is more competitive in a
large scale production.
Furthermore, the separation and reusability of Fe catalyst has
been examined. The investigations are performed at 90 ◦C for 2 h.
After the dehydration reaction, the mixture is first distilled under
the reduced pressure. The pure NMP is collected and the left mix-
ture is extracted four times by 10 mL of ethyl acetate after adding
0.5 g of water. The fructose and Fe catalyst are found to be almost
insoluble in ethyl acetate; thus, the amount of HMF in ethyl acetate
is accounted as total separation yield of HMF. The obtained mix-
ture after extraction is heated at 75 ◦C for 12 h in a vacuum oven
to remove water and residual ethyl acetate. It is then used directly
in the next run by adding the distilled NMP and an equal amount
of fructose. The results indicated that the HMF yield gradually
decreased a little in three recycle reactions, which can be attributed
to the partial lose of catalyst during the separation process. This is
accord with a common feature of homogeneous catalyst.
All the dehydration reaction experiments were performed in a
100 mL flask equipped with magnetic stirrer and a condenser. A
typical procedure for dehydration of fructose is as follows: a solu-
tion of fructose (1.0 g, 5.6 mmol), FeCl3 (0.56 mmol), co-catalyst
(1.0 mmol) and solvent (10 mL) were charged into the flask. Under
stirring, the flask was heated to 90 ◦C in an oil bath for 2 h in air.
After 2 h the reaction mixture was decanted to a volumetric flask
with pure H2O or ethanol, and then analyzed by an HPLC equipped
with UV and refractive index detectors.
The HPLC measurements are conducted using an Agilent
1200 HPLC with UV and Refractive Index detector. The Eclipse
Plus-C18 (4.6 mm × 150 mm) column and an Aminex HPX-87C
(300 mm × 7.8 mm) column are employed to separate the reac-
tion mixture. General HPLC conditions for analysis of HMF yield:
variable UV detector; C18 column temperature: 30 ◦C; eluent:
0.5 mL/min H2O: CH3CN (1:4); injection amount: 1 ␮L. General
HPLC conditions for analysis of fructose and sucrose conversion:
Refractive Index detector; Aminex HPX-87C column temperature:
30 ◦C; eluent: 0.2 mL/min water; injection amount: 2.5 ␮L.
2.3. Purification of 5-hydroxymethylfurfural
The reaction mixture was transferred into a flask and was
distilled under reduced pressure. The remaining mixture was
extracted with ethyl acetate (10 mL × 4) and afterwards water
(0.5 g) was added, and then the organic phase was collected. After
drying with anhydrous sodium sulfate, the organic layer was dis-
tilled under reduced pressure to obtain HMF as the main product.
The total isolated yield of HMF is about 78% with FeCl3–Et4NBr sys-
tem, and the purity was more than 97% from HPLC analysis. 1HNMR
spectrum (DMSO-d6): 3.396–3.438 (d, 1H, J = 7.078), 4.483 (s, 2H),
6.580–6.586 (d, 1H, J = 3.417) 7.466–7.473 (d, 1H, J = 3.417), 9.522
(s, 1H); 13CNMR spectrum (DMSO-d6): ␦ 56.524, 56.650, 110.385,
152.413, 162.805, and 178.667.
3. Results and discussion
3.1. Dehydration of fructose to 5-hydroxymethylfurfural
Initially, the dehydration of fructose was evaluated with differ-
ent iron salts and co-catalysts in N-methylpyrrolidone (NMP), see
Scheme 1 and Table 1. HMF was obtained in 1% yield using FeCl2

526
X. Tong et al. / Catalysis Today 175 (2011) 524–527
Table 2
Dehydration of sugar with FeCl3–Et4NBr systema.
Entry
Substrate
Solvent
Time (h)
Yield (%)b
1
Sucrose
Glucose
NMP
NMP
NMP
DMF
3
3
3
2
3
3
5
2
5
40
3
2
3c
4
Fructose + Glucose
Fructose
Sucrose
Fructose
Sucrose
41
62
38
53
27
70
21
5
6
DMF
DMSO
DMSO
H2O + NMP
H2O + NMP
7
8d
9d
Fructose
Sucrose
a
Reaction conditions: 1.0 g substrate, 0.56 mmol FeCl3·H2O, and 1 mmol co-
catalyst in 10 mL solvent, temperature = 90 ◦C, in air.
b
The yield of HMF is obtained by HPLC analysis and product separation method.
The mass ratio of fructose and glucose is 1:1.
The volume ratio of H2O and NMP is 1:1.
c
d
of HMF is obtained for the dehydration of sucrose (Table 2, entry 1),
in keeping with results obtained using mineral acid catalysts [41].
However, in the dehydration of glucose the yield of HMF is only 3%
(Table 2, entry 2). Furthermore, when the mixture of fructose and
glucose is used as a substrate HMF is obtained in 41% yield (Table 2,
entry 3). These data show that the ketose is more easily dehydrated
than aldose using this catalytic system. On the way from glucose
to HMF the first step is probably the isomerization of glucose to
fructose, which should be the reason for low yield. For the con-
version of sucrose, it can be firstly hydrolyzed to one molecule of
glucose and one molecule of fructose, and then the glucose and
fructose are dehydrated to produce HMF. Seen from the obtained
data, it can be concluded that the hydrolysis of sucrose occurs with
good yield but only fructose dehydration takes place. Furthermore,
the NMP solvent is replaced by N,N-dimethyl-formamide (DMF)
or dimethylsulfoxide (DMSO). In DMF, a 62% or 38% yield of HMF
is obtained for the dehydration of fructose or sucrose, respectively
(Table 2, entries 4 and 5). In DMSO, the yield of HMF is 53% or 27% in
the dehydration of fructose or sucrose, respectively (Table 2, entries
6 and 7). In addition, when the mixture of NMP and water (1:1, vol-
ume ratio) is used as the reaction medium, the yield of HMF from
fructose and sucrose is 70% and 21%, respectively (Table 2, entries
8 and 9). It is noteworthy that water does not decrease the yield
too much and also ensures the reaction may be conducted without
precautions to exclude air or moisture.
Fig. 1. The effect of catalyst concentration in the dehydration of fructose (reaction
conditions: 1.0 g fructose, 90 ◦C, 2 h, 10 mL NMP, the molar ratio of FeCl3 and Et4NBr
is 1:1).
3.2. Effect of catalyst concentration
The effect of catalyst concentration was investigated, see Fig. 1,
and it was found that good yields of HMF could be obtained at lower
catalyst loadings. In the presence of 2.5 mol% catalyst the yield of
HMF still reaches 75%.
3.3. Effect of reaction time and reaction temperature
The effect of reaction time is presented in Fig. 2. As expected, the
yield of HMF increases rapidly and the selectivity decreases appre-
ciably during the first 30 min. After 1 h the yield and selectivity of
HMF remains almost unchanged showing that further dehydration
of HMF to unwanted acid by-products is not favored by the catalyst.
The reaction temperature proved to be critical with very low
yields observed below 70 ◦C and the system becoming very efficient
above 75 ◦C.
3.4. Dehydration of sucrose and glucose to
5-hydroxymethylfurfural
3.5. The investigations on the active catalyst species
The dehydration of sucrose and glucose were also studied using
the FeCl3–Et4NBr system. In Table 2, it can be seen that a 40% yield
To gain the insights into the nature of the active catalyst,
the electronic absorption spectra of FeCl3, FeCl3–Et4NCl and
FeCl3–Et4NBr in NMP were recorded. The addition of Et4NCl or
Et4NBr to FeCl3 results in a change in the absorption spectra, indi-
cating the formation of new species (Fig. 3). Moreover, the obtained
−
spectrum of FeCl3–Et4NCl corresponds to that of the FeCl4 anion,
i.e., the peaks centered at 310 and 364 nm belong to the lowest-
6
energy charge transfer (CT) transitions 6A1 → T2 (literature data:
312 and 361 nm in acetonitrile) and the very weak absorption bands
at 530, 616 and 686 nm (literature data: 530, 616 and 686 nm
in acetonitrile) corresponding to d–d forbidden transitions [42].
For the FeCl3–Et4NBr system the spectrum may be tentatively
assigned to the FeCl3Br− anion. Replacing one chloride with a
bromide in the tetrahalogeno-ferrate (III) anion should lead to a
decrease in the ligand field strength and the transition energies
are expected to increase according to the Tanabe–Sugano diagram
[43], as observed in our experiments, with the bands for 6A1 → T2
6
transitions for FeCl3–Et4NBr undergoing a blue shift in compari-
son with those of FeCl30–Et4NCl (304, 358 nm compared to 310 and
364 nm, see Fig. 3). Additionally, the molar extinction coefficient for
FeCl3–Et4NBr in the visible region is significantly higher than that
Fig. 2. The influence of reaction time in the dehydration of fructose (reaction con-
ditions: 1.0 g fructose, 5.0 mol% FeCl3, 7.5 mol% Et4NBr, 90 ◦C, 10 mL NMP, in air).

X. Tong et al. / Catalysis Today 175 (2011) 524–527
527
support of the Natural Science Foundation of China under contract
number 20425619. The work has been also supported by the Pro-
gram of Introducing Talents to the University Disciplines under
file number B06006, and the Program for Changjiang Scholars and
Innovative Research Teams in Universities under file number IRT
0641.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.cattod.2011.03.003.
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Acknowledgements
Tong thanks the financial support from the China Postdoctoral
Science Foundation (20080440676 and 200902273). Li thanks the