Dehydration of glucose to 5-hydroxymethylfurfural and 5-ethoxymethylfurfural by combining Lewis and Br?nsted acid

Article abstract of DOI:10.1039/c7ra07684c

In this work, glucose was transformed into 5-hydroxymethylfurfural (HMF) and 5-ethoxymethylfurfural (EMF) in the presence of AlCl₃·6H₂O and a Br?nsted solid acid catalyst (PTSA-POM). GVL (γ-valerolactone)-water and ethanol-water solvent systems were evaluated in the dehydration reaction of glucose into HMF and EMF, respectively. Water content and dosage of AlCl₃·6H₂O were examined in the conversion of glucose into HMF, and some valuable chlorides (FeCl₃·6H₂O, NiCl₂·6H₂O, CrCl₃·6H₂O etc.) were also used in contrast with AlCl₃·6H₂O. Some different organic solvents were added to the ethanol-water system to explore whether it would be beneficial to the generation of EMF. A high yield of HMF (60.7%) was obtained at 140 °C within 60 min in GVL-water (10:1) solvent system, and total yield 42.1% of EMF and HMF (30.6% EMF, 11.5% HMF) was achieved at 150 °C after 30 min in an ethanol-water (9:1) solvent system.

Full text of DOI:10.1039/c7ra07684c

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Dehydration of glucose to 5-hydroxymethylfurfural
and 5-ethoxymethylfurfural by combining Lewis
and Brønsted acid
Cite this: RSC Adv., 2017, 7, 41546
b
b
Haosheng Xin,ab Tingwei Zhang,
Wenzhi Li,
Mingxue Su,b Song Li,c
*
a
Qun Shao and Longlong Mac
*
In this work, glucose was transformed into 5-hydroxymethylfurfural (HMF) and 5-ethoxymethylfurfural
(EMF) in the presence of AlCl3$6H2O and Brønsted solid acid catalyst (PTSA–POM). GVL
a
(g-valerolactone)–water and ethanol–water solvent systems were evaluated in the dehydration reaction
of glucose into HMF and EMF, respectively. Water content and dosage of AlCl3$6H2O were examined in
the conversion of glucose into HMF, and some valuable chlorides (FeCl3$6H2O, NiCl2$6H2O, CrCl3$6H2O
etc.) were also used in contrast with AlCl3$6H2O. Some different organic solvents were added to the
ethanol–water system to explore whether it would be beneficial to the generation of EMF. A high yield
of HMF (60.7%) was obtained at 140 ꢀC within 60 min in GVL–water (10 : 1) solvent system, and total
yield 42.1% of EMF and HMF (30.6% EMF, 11.5% HMF) was achieved at 150 ꢀC after 30 min in an ethanol–
water (9 : 1) solvent system.
Received 13th July 2017
Accepted 19th August 2017
DOI: 10.1039/c7ra07684c
rsc.li/rsc-advances
can be obtained in the dehydration of fructose.11 Compared to
the one-step method, the current two-step process is studied
Introduction
more extensively and Lewis acid plays a vital role for the isom-
erization of glucose into fructose in two-step process.12 There-
fore, the combination of Lewis acid and Brønsted acid is
extremely important in order to transform glucose efficiently.13
Nikolla et al. exploited the synthesis of HMF from glucose in the
combination of HCl and Sn-beta catalyst in THF/H2O–NaCl
system, HMF yield (56.9%) and glucose conversion (79%) was
Urged by the rapid depletion of fossil fuels and increased
environmental issues, great efforts have been devoted to the
production of sustainable biofuels from biomass.1,2 In
comparison with other sugars, glucose is the most abundant
hexose contained in lignin biomass, considered as the most
valuable bio-derived carbon resource, and it plays a vital role in
the conversion of biomass to biofuels and chemicals.3–5 Thus,
the high-efficiency transformation of glucose to platform
chemicals has aroused much attention in recent years.6 Among
those prospective chemicals, HMF and EMF are thought highly
of as promising building blocks for the application of renewable
resources.
5-hydroxymethylfurfural (HMF), a valuable biomass-derived
platform compound, referred as the bridge between renew-
able resources and chemistry chemicals.7–9 Glucose, a most
widely distributed monosaccharide in nature, has been exploi-
ted in the production of HMF and furan compounds.10 There
are two ways to convert glucose to HMF, one is direct dehy-
dration of glucose to HMF; the other mainly comprises two
steps, rstly, glucose is isomerized to fructose, aer that, HMF
obtained aer 70 min at 180 C.14 In contrast to homogeneous
ꢀ
catalyst (HCl, H2SO4, H3PO4), solid acid catalyst shows many
advantages such as low corrosivity to the reactor, easy separa-
tion aer reaction and more stable at high temperatures.15
Thus, the production of HMF over solid acid catalysts have been
studied diffusely in recent years. Ohara et al. synthesized
a catalyst with combination of Amberlyst-15 and hydrotalcite to
catalyze glucose to HMF in DMF solvent system, HMF yield
(41%) and glucose conversion (71%) was achieved at 373 K in
3 h.16 Thombal et al. prepared a solid acidic catalyst by mixing
b-cyclodextrin and p-toluenesulfonic acid, with a reaction time
of 5 h at 453 K, the HMF yield was 47% in DMSO.17 In addition,
enormous attention was paid to ionic liquids (ILs) in recent
period time. By combining and modifying the cations and
anions properly, the properties of obtained ILs (polarity,
hydrophobicity and dissolving capacity) could be t better to
adapt to the reaction.18–21 Detail works with careful design of IL
has been done systemic which demonstrated that the trans-
formation of glucose to HMF could be enhanced signi-
cantly.22,23 Zhang et al. prepared a heterogeneous catalyst (Cr-
HAP) by combining hydroxyapatite and chromium chloride,
aInstitute of Materials and Chemical Engineering, Anhui Jianzhu University, Hefei
230022, China
bLaboratory of Basic Research in Biomass Conversion and Utilization, Department of
Thermal Science and Energy Engineering, University of Science and Technology of
China, Hefei 230026, China. E-mail: liwenzhi@ustc.edu.cn
cCAS Key Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion,
Chinese Academy of Sciences, Guangzhou 510640, China
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and the catalyst was used in the dehydration of glucose in obtained from biomass, was selected and proved to be a good
[BMIM]Cl, HMF yield of 40.2% with glucose conversion of solvent in the conversion of carbohydrates into furan
77.9% were obtained in 2.5 min with the aid of microwave compounds.38–40 Ethanol plays a decisive role in the ether-
irradiation.24 Chen et al. utilized Cr(CO)6 as catalyst for the ication of HMF to EMF, not only acted as a green solvent, but
transformation of glucose into HMF in [EMIM]Cl, aer 6 h at also as a reactant.
120 ꢀC, affording the HMF yield of 50%.25 Although ILs has
achieved great progress, its exorbitant price impose restrictions
on the production of HMF and subsequent separation aer
reaction is also difficult. In this work, HMF is also a crucial
Experimental
intermediate product in the process of glucose conversion to
EMF.
p-toluenesulfonic acid monohydrate (PTSA$H2O, 98.5%), para-
formaldehyde (POM, AR), D-(+)-glucose (GC, 99.5%), HMF
(99%), EMF (97%) were purchased from Aladdin Industrial, Inc.
(Shanghai, China). GVL (95%) was obtained from LangFang
Hawk Technology and Development Co, Ltd. AlCl3$6H2O(AR),
CrCl3$6H2O(AR), CrCl2(AR), MgCl2$6H2O(AR), CaCl2(AR),
NiCl2$6H2O(AR), NH4Cl(AR), FeCl3$6H2O(AR), CoCl2$6H2-
O(AR), MnCl2$4H2O(AR), SnCl4$5H2O(AR), SnCl2$2H2O(AR),
H2SO4 (96–98%, AR), MIBK(AR), THF(AR), DMSO(AR) and
dioxane(AR) were supplied by Sinopharm Chemical Reagent
Co., Ltd (Shanghai, China). All the chemicals were used without
further purication.
5-ethoxymethylfurfural (EMF), regarded as fuels or fuel
additives, has high energy density (8.7 kW h Lꢁ1) close to diesel
(9.7 kW h Lꢁ1) and regular gasoline (8.8 kW h Lꢁ1), far better
than ethanol (6.1 kW h Lꢁ1).26 According to the previous liter-
atures, EMF was mainly synthesized not directly from carbo-
hydrates, the intermediate products such as HMF, 5-
(chloromethyl)furfural (CMF) and 5-(bromomethyl)furfural
BMF were rstly obtained, and then etheried into EMF.27–31 Liu
et al. studied the EMF production from HMF, fructose and
glucose, respectively.32 In accordance with expectation, the
reaction efficient improved in the order: glucose < fructose <
HMF. Compared with fructose and HMF, glucose has a good
stability and pricing advantage in the formation of EMF. In the
earlier time, Christopher M. Lew et al. used Sn-BEA and
Amberlyst-131 as catalysts to catalyze glucose into EMF in
According to our reported literature,37 the details of synthesis
of PTSA–POM as following: rstly, 0.2 ml sulphuric acid (98%)
and 10.0 g PTSA–H2O were put to a three-necked round-
bottomed ask with magnetic stirring and reux condensa-
ꢀ
tion which was heated at 110 C. Then 4 g POM added imme-
ꢀ
a single reactor at 90 C, 31% yield of EMF was achieved aer
diately aer PTSA–H2O melted completely. The reaction
temperature was kept at 110 ꢀC for 8 h, then adjusted to 130 ꢀC
for 24 h to form a black solid. Aer that, the obtained solid was
ltered and washed to pH ¼ 7 with deionized water. Drying at
120 ꢀC is necessary and then ground to powder. Finally, the
24 h.33 For the long time cost and low yield of EMF, people were
inspired to hammer at ameliorating catalyst. In Yan's work,
CrCl3 showed excellent catalytic efficiency in the conversion of
carbohydrates.34 But as it known to us, Cr belongs to heavy
metal and do harm to the environment with some toxicity.
Recently, via the good deal of work of Yu Yang and Hu, Li,
AlCl3$6H2O was also proved to be a preeminent catalyst in the
production of EMF, high yield with expectation achieved.35,36
Both HMF and EMF are the vital platform chemicals in the
conversion of carbohydrates, of which is worthy studied in
depth, furthermore, EMF was obtained in the further ether-
ication of HMF.14–21,24,25,27–36 And the study of direct conversion
from glucose to EMF is particularly deserved. Thus, in this
study, the dehydration of glucose to HMF was investigated by
regulating reaction times, temperatures and the ratio of
deionized water to organic solvent, some valuable chlorides
(FeCl3$6H2O, SnCl4$5H2O, CrCl3$6H2O, etc.) were also been
compared. The further etherication from HMF to EMF in the
process of glucose conversion was also explored in ethanol/H2O.
Apart from the inuence of reaction times and temperatures,
DMSO, dioxane, THF, MIBK, GVL were added extra to ethanol/
H2O to explore the inuence of added second organic solvent.
Previously, in the transformation of corn stalk into furfural,
our group prepared a novel heterogeneous strong acid catalyst
(PTSA–POM) by polymerizing p-toluenesulfonic acid (PTSA) and
paraformaldehyde (POM) in the presence of H2SO4, and ach-
ieved signicant results.37 Due to its easy preparation and
excellent recyclability, the further application of PTSA–POM was
explored in the dehydration of glucose in this paper. As for
solvent, g-valerolactone (GVL), a green solvent that can be
ꢀ
resulting sample was calcined in muffle at 185 C for 6 h.
For the production of HMF, reactions were carried out in
a 48 ml pressure thick wall tube with oil-bath heating accom-
panied by 500 rpm magnetic stirring. As for EMF, because of the
high temperature, a certain pressure will be produced in the
reaction process by ethanol. Therefore, taking security into
account, glucose, catalysts and solvents were loaded and sealed
in a 25 ml autoclave. The autoclave was heated to desired
temperature from room temperature in 30 min and also stirred
magnetically at 500 rpm. Aer the reaction, both tube and
autoclave were immersed in cold water immediately to termi-
nate the reaction. Diluted and ltered liquid was analyzed using
HPLC.
HPLC (waters 515 pump, equipped with an UV/Vis Detector
(Waters 2489) using Waters Symmetry-C18 column(5 mm, 4.6 ꢂ
150 mm) and a Rrefractive Index Detector (Waters 2414) using
Waters XBridge Amide column (5 mm, 4.6 ꢂ 150 mm)) was used
to analyze diluted samples for HMF yield, EMF yield and
glucose conversion.33–35 Authentic samples of HMF and EMF
were used as standards, which calibration curves were applied
to quantify.
HMF yield, EMF yield and glucose conversion were calcu-
lated as follows:
HMF yield ¼ (moles of HMF in products/
moles of initial glucose) ꢂ 100%,
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the lines, it can be seen that temperature has profound impact
on HMF yield. At 130 ꢀC, HMF yield increased with the increase
of reaction time, but relatively low HMF yield was obtained even
in 90 min. By comparison, when the temperature are 140 ꢀC and
150 ꢀC, with reaction time goes by, HMF yield rstly increased,
and decreased severally aer reached the optimal values. Indi-
cated that in higher temperatures, prolonged reaction time
rstly promoted the transformation of glucose to HMF, aer
reached the optimal values, the effect of time on the reaction is
not as obvious as at low temperature on HMF production.
Throughout the whole reactions, highest yield 60.7% of HMF
EMF yield ¼ (moles of EMF in products/
moles of initial glucose) ꢂ 100%,
HMF selectivity ¼ (HMF yield/glucose conversion) ꢂ 100%
Glucose conversion ¼ 1 ꢁ (moles of glucose in products/
moles of initial glucose) ꢂ 100%
Results and discussion
ꢀ
was achieved at 140 C in a short time (60 min).
Except the dosage of AlCl3$6H2O, other parameters employed in
the reaction are on the basis of previous literatures of our
group.37,39 Initially, in order to make the dosage of AlCl3$6H2O
appropriately, some probe trials at a mild temperature 140 C
with 20 min were explored in autoclave.
The results are shown in Table 1, as it showing to us (entry 3),
a maximum yield was obtained when 0.15 g AlCl3$6H2O was
loaded. Herein, 0.15 g dosage of AlCl3$6H2O was adopted in the
further reactions.
Production of HMF from the dehydration of glucose was
carried out at 130 ꢀC, 140 ꢀC and 150 ꢀC, with time from 30 min
to 90 min (10 min interval), respectively, both HMF yield and
glucose conversion are shown in Fig. 1. Obviously, according to
Glucose is well converted in GVL/H2O solution and almost all
the reactions conversion were over 90% even though the
temperature was as low as 130 ꢀC. As for higher temperature of
140 ꢀC and 150 ꢀC, complete conversion of glucose was achieved
both in 60 min. It was clear that higher temperatures is more
conducive to the conversion of glucose.
In this section, based on the optimal conditions found
above, comparative experiment was also made on acid added.
The results are shown in Table 2. From which we can learn that
the yield of HMF was much promoted on the dehydration of
glucose by combining PTSA–POM and AlCl3$6H2O, compared
with only PTSA–POM or AlCl3$6H2O added. To our knowledge,
compared with PTSA–POM, glucose is isomerized to fructose
easily in the presence of AlCl3$6H2O, and some H+ will also be
formed when AlCl3$6H2O dissolved in water, and the produc-
tion of HMF from fructose is easy to carry out in GVL/H2O with
H+. Then, with PTSA–POM added, the dehydration of fructose to
HMF could be enhanced and the yield of HMF could be
promoted. Therefore, the activity in the reaction may due to the
conjunction of these two acids.
ꢀ
Table 1 Effect of AlCl3$6H2O dosage on the dehydration of glucose
into HMFa
Entry
Dosage
Yield/%
1
2
3
4
5
6
0.05 g
0.10 g
0.15 g
0.20 g
0.25 g
0.30 g
50.3
54.0
57.8
54.3
51.7
49.4
Apart from the effects of temperature and time, we judged
that different water content could also has a signicant inu-
ence on the dehydration of glucose to HMF. In view of this
conjecture, great deal of efforts was made for the study of the
effect of different water content. The results were summarized
at Table 3, and results are highly consistent with our expecta-
tions, water added has a signicant effect on HMF production.
a
Reaction conditions: 0.4 g glucose, 0.2 g PTSA–POM, 15 ml GVL and
1.5 ml DIW, 140 ꢀC (30 min heating-up time), 20 min, 500 rpm.
Fig. 1 Effects of temperature and time on the conversion of glucose into HMF. Reaction conditions: 0.4 g glucose, 0.2 g PTSA–POM, 0.15 g
AlCl3$6H2O, 15 ml GVL and 1.5 ml DIW, 500 rpm.
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Table 2 Comparative experiment on acid addeda
Table 5 Available chlorides compared with AlCl3$6H2Oa
Entry
Acid added
Yield/% Entry
Chloride
Dosage/g
HMF yield/%
Conversion
1
2
3
PTSA–POM
AlCl3$6H2O
PTSA–POM/AlCl3$6H2O
9.4
50.8
60.7
1
2
3
4
5
6
7
8
FeCl3$6H2O
CoCl2$6H2O
MnCl2$4H2O
MgCl2$6H2O
NiCl2$6H2O
SnCl2$2H2O
SnCl4$5H2O
CaCl2
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
4.5
5.4
7.0
65.0
93.7
92.9
91.1
90.1
84.1
79.1
96.0
92.8
96.9
91.8
13.3
13.8
14.2
16.3
18.0
18.8
46.1
60.4
a
Reaction conditions: 0.4 g glucose, 15 ml GVL and 1.5 ml DIW, 140 ꢀC,
60 min, 500 rpm, PTSA–POM: 0.2 g, AlCl3$6H2O: 0.15 g.
9
10
11
NH4Cl
CrCl2
CrCl3$6H2O
As for entry 1 and 2, we applied pure water and GVL as solvent
under the optimum reaction condition, respectively. Appar-
ently, very low yields of HMF were obtained both of them, only
1.2% in 16.5 ml water and 3.5% in pure GVL. Moreover, reaction
with much water could pull down the conversion of glucose
conspicuously, from 98.1% to 14.3%. From entry 3 to 11,
different water content (0.5 ml, 1.5 ml, 3 ml) and xed addition
of 15 ml GVL solvent systems were evaluated at three time
points (40 min, 60 min and 80 min). On the overall trend, the
yield of HMF was increased with the increase of water content
from 0.5 ml to 1.5 ml and decreased aerwards with the water
content continue increase to 3 ml. Besides, higher water content
in the reactions would do harm to the conversion, 100%
conversion of glucose was achieved in lower water content of
0.5 ml and decreased with the increase of water content, which
was in line with entry 1 and 2. Furthermore, the highest HMF
yield was obtained under the optimized condition in 1.5 ml
H2O/15 ml GVL system (entry 7). In fact, though glucose
a
Reaction conditions: 0.4 g glucose, 0.2 g PTSA–POM, 1.5 ml DIW,
15 ml GVL, temperature: 140 ꢀC, time: 60 min, 500 rpm.
conversion decreased apparently with increase of water content
from 1.5 ml to 3 ml, the selectivity was almost keep the same,
which indicated that when the water content has arrivals
a certain value there is no signicant effect on selectivity of
HMF production. And the comparison with previous catalytic
system are shown in Table 4. From Table 4, we can also learn
that low yields of HMF were obtained in pure water and GVL
solvent (entry 1 and 2), which keeps consistent with the results
we mentioned above.
In addition to the effect of reaction temperature, time and
water content, here some valuable chlorides are compared with
Table 3 Effect of water contenta
Entry
Solution
Time/min
HMF yield/%
Conversion/%
Selectivity/%
1
2
3
4
5
6
7
8
16.5 ml water
16.5 ml GVL
60
60
40
60
80
40
60
80
40
60
80
1.2
3.5
14.3
98.1
100
100
100
93.7
100
100
78.1
84.3
85.6
8.4
3.6
41
0.5 ml H2O + 15 ml GVL
0.5 ml H2O + 15 ml GVL
0.5 ml H2O + 15 ml GVL
1.5 ml H2O + 15 ml GVL
1.5 ml H2O + 15 ml GVL
1.5 ml H2O + 15 ml GVL
3 ml H2O + 15 ml GVL
3 ml H2O + 15 ml GVL
3 ml H2O + 15 ml GVL
41.0
39.6
37.3
40.9
60.7
56.6
33.8
49.4
45.0
39.6
37.3
42.7
60.7
56.6
43.3
58.5
53
9
10
11
a
Reaction conditions: 0.4 g glucose, 0.2 g PTSA–POM, 0.15 g AlCl3$6H2O, temperature: 140 ꢀC, 500 rpm.
Table 4 The comparison with previous catalytic system
Entry
Catalyst
Solvent
HMF yield/%
Glucose conversion/%
Ref.
1
2
3
4
5
6
TiO2
Water
DMSO
H2O–DMSO
H2O–THF–NaCl
[Bmim]Cl
18.6
19.2
37.3
45.3
43.2
68
63.8
95.2
100
100
94.7
99
43
44
45
46
47
48
SO42ꢁ/ZrO2
[Sn,Al]-beta
PTA–PCP(Cr)–SO3H(Cr3+
Zr–P–Cr
)
LCCa
DMSO–[Bmim]Cl
a
LCC ¼ lignin-derived carbonaceous catalyst.
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Table 7 Effects of temperature and time on EMF production from
AlCl3$6H2O and results were gathered in Table 5. As exhibited in
Table 5, the HMF yield arranged from entry 1 to 11 in ascending
order. Among those chlorides, FeCl3$6H2O performed the worst
both in HMF yield and glucose conversion, lowest 4.5% HMF
yield and 65.0% conversion were received. With regard to
CoCl2$6H2O and MnCl2$4H2O, HMF yield were both below 10%
while the conversion of glucose were over 90%. Entry 4, 5 and 8,
9, MgCl2$6H2O and NiCl2$6H2O, CaCl2 and NH4Cl shows alike
catalytic effects with almost the same results in HMF yield and
glucose conversion. Unfortunately, except CrCl2 and CrCl3-
$6H2O, low HMF yield were obtained in the presence of other
chlorides in Table 5. HMF yield was obviously promoted to
46.1% in the presence of CrCl2, and higher glucose conversion
96.9% was obtained. Compared with CrCl2, higher HMF yield
60.4% was gained in the case of CrCl3$6H2O added, 91.8% of
glucose conversion was observed in the meantime. Combined
with previous reports illuminated that the hydrolyzed Cr(III)
complex [Cr(H2O)5OH]2+ may provide a bifunctional site of
Lewis acid–Brønsted base in glucose isomerization, and some
water molecules in the rst coordination sphere of Cr was dis-
placed by glucose to promote the isomerization of glucose.41
Relate to AlCl3, the kinetics results in conjunction with reaction
network expounded that the hydrolyzed Al(III) complex
[Al(OH)2(aq)]+ is the most active Al species enable the isomeri-
zation of glucose.42
Abovementioned, glucose was transformed into HMF in the
rst place and EMF was obtained with further etherication. In
order to explore whether second organic solvent added will
promote the production of EMF from glucose, in this section,
DMSO, dioxane, THF, MIBK and GVL were added extra to
ethanol/H2O system, respectively. As Table 6 demonstrated,
highest HMF yield of 48% was obtained while lowest EMF yield
of only 2.9% was achieved in entry 1 (DMSO added). Other
organic solvents, including dioxane, THF, MIBK and GVL
showed low selectivity towards HMF and EMF, and it is indi-
cated that there is useless with organic solvent added in the
production of EMF from glucose. Therefore, in the following
study, ethanol/H2O solvent system without second organic
solvent was employed in glucose-to-EMF.
glucosea
Time/
min
EMF
yield/%
Glucose
conversion/%
Temperature/ꢀC
HMF yield/%
140
140
140
140
140
150
150
150
150
150
160
160
160
160
160
10
15
20
25
30
10
15
20
25
30
10
15
20
25
30
11.8
15.6
18.5
19.9
22.5
21.0
25.8
26.4
27.9
30.6
26.7
28.8
28.4
28.5
27.9
19.9
19.2
17.9
17.8
15.1
19.5
14.6
14.2
11.3
11.5
15.6
11.7
9.8
61.7
65.9
71.9
78.6
86.0
93.5
94.9
96.3
97.8
97.8
95.6
98.2
98.4
99.2
99.0
8.8
7.7
a
Reaction conditions: 0.4
g glucose, 0.2 g PTSA–POM, 0.15 g
AlCl3$6H2O, 1 ml DIW and 9 ml ethanol, 500 rpm.
rate of EMF formation was rather quick when the temperature
ꢀ
was raised to 160 C, and EMF yield kept at a relatively stable
value as time increased. Highest EMF yield 30.6% was obtained
at optimal temperature and reaction time (150 ꢀC, 30 min) with
glucose conversion of 97.9%.
Throughout the whole reaction progress, HMF was rstly
produced and then etheried into EMF. As Table 7 showing,
HMF yields gradually reduced with reaction time extended
during all temperature. Both higher reaction temperature and
longer reaction time facilitated the further conversion of HMF
to EMF, but HMF yield of 11.5% was still retained under the
optimum reaction conditions, which highest EMF yield was
achieved. Consistent with previous reports35,36,49 that as an
intermediate product, HMF could not etheried into EMF
completely. EMF production process has similar glucose
conversion trend with HMF production, the longer the reaction
time and the higher the reaction temperature, the higher the
conversion of glucose.
Table 7 exhibits the effects of temperature and time on EMF
production from glucose by conducting the reactions in
ꢀ
ꢀ
ꢀ
ethanol/H2O at 140 C, 150 C, and 160 C. It can be observed
that prolonged reaction time facilitated the production of EMF
at 140 ꢀC and 150 ꢀC. In comparison to lower temperatures, the
Conclusions
In conclusion, successfully furans' (HMF and EMF) preparation
from glucose were carried out in different solvents in the pres-
ence of AlCl3$6H2O and a solid acid PTSA–POM, a series of
inuencing parameters were evaluated and signicant results
were acquired. The inuence of water content has been studied
and found that certain water content (1.5 ml) in reaction system
is benecial to HMF production. Some other available chlorides
were also explored to compare with AlCl3$6H2O on the conver-
sion of glucose into HMF, the efficiency of CrCl2 and CrCl3-
$6H2O are better than others. And we further discovered that
extra organic solvent (DMSO, dioxane, THF, MIBK and GVL)
added to ethanol/H2O system couldn't promote the production
of EMF from glucose. Under the optimized conditions, 60.7%
Table 6 Effect of second organic solvent addeda
Entry
Organic solvent
HMF/%
EMF/%
Conversion/%
1
2
3
4
5
DMSO
Dioxane
THF
MIBK
GVL
48
2.9
6.7
6.8
13.2
15.7
100
27.4
28.6
25.5
21.6
98.5
96.8
99.2
97.9
a
Reaction conditions: 0.4
g glucose, 0.2 g PTSA–POM, 0.15 g
AlCl3$6H2O, 1 ml DIW, 9 ml ethanol and all the additive amount of
organic solvent is 9 ml, temperature: 150 ꢀC, time: 30 min, 500 rpm.
41550 | RSC Adv., 2017, 7, 41546–41551
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Conflicts of interest
3972.
There are no conicts to declare.
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Acknowledgements
This study was nancially supported by the State Key Program
of National Natural Science Foundation of China (51536009),
Science and Technological Fund of Anhui Province for
Outstanding Youth (1508085J01), the National Key Technology
R&D Program of China (No. 2015BAD15B06) and the interna-
tional technology cooperation plan of Anhui (No. 1503062030).
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