Y. Xiao, Y.-F. Song / Applied Catalysis A: General 484 (2014) 74–78
75
2.4. Yield and selectivity definitions
The fructose conversion (mol%), 5-HMF yield (mol%) and selec-
tivity (mol%) were evaluated on a carbon basis as shown below:
Fructose conversion (mol%):
ꢀ
ꢁ
Scheme 1. Three different catalytic systems for dehydration of the fructose to 5-
HMF [12,14,15,23].
Moles of fructose in product
Starting amount of fructose
X = 1 −
× 100%
5-HMF yield (mol%):
2. Experimental
Moles of 5-HMF in product
Starting amount of fructose
Y =
× 100%
2.1. Chemical materials
5-HMF selectivity (mol%):
Yield of 5-HMF
Fructose (purity: 99%), 5-hydroxymethylfurfural, H2SO4,
HCl, H3PO4, HNO3, NaVO3, Na2WO4·2H2O, Na2HPO4·2H2O,
Na2MoO4·2H2O, Na2SiO3·9H2O, diethyl ether and the ionic
liquids including [BMIM]Cl, [BMIM]BF4, [BMIM]PF6 (BMIM = 1-
S =
× 100%
Fructose conversion
methylimidazolium chloride ([C2OHMIM]Cl) were purchased from
Sigma–Aldrich and used directly without further purification. The
HPAs including H3PW12O40 [24], H4SiW12O40 [25], H3PMo12O40
[25], H4SiMo12O40 [25], H4PMo11VO40 [26], H5PMo10V2O40 [26],
and H6PMo9V3O40 [26], were synthesized and characterized
according to the reported procedures. The characterization data
were summarized in the supporting information.
3.1. Investigation of different catalysts for dehydration of the
fructose
Firstly, two classical Keggin clusters of H3PW12O40 (PW12
)
and/or H4SiW12O40 (SiW12) have been applied as catalysts in the
presence of [BMIM]Cl for the fructose dehydration. HPLC analysis
shows that both the 5-HMF yield and selectivity reach as high as
99% in only 5 min. To have a better understanding of the efficiency of
HPAs as catalysts, contrast experiments have been carried out using
different non-HPAs catalysts in ionic liquids for the fructose dehy-
dration to 5-HMF, and the results have been presented in Table 1. It
can be seen that in the presence of [EMIM]Cl, CrCl2 could catalyze
conversion of the fructose to 5-HMF at 80 ◦C in 180 min with the
yield of 83% (entry 5), whereas CrCl3, FeCl3, and GeCl4 at 100 ◦C
in the presence of ionic liquids exhibit the yield of 5-HMF ranging
from 59% to 92.1% (entries 8–10). In the case of H2SO4, only 80%
5-HMF can be obtained at 120 ◦C in 240 min (entry 11). In contrast,
the PW12 and/or SiW12 in the presence of [BMIM]Cl show shorter
reaction times, relatively lower temperature and higher yield for
dehydration of the fructose to 5-HMF (entries 1–2).
2.2. Analysis
FT-IR spectra were recorded on a Bruker Vector 22 infrared spec-
trometer by using KBr pellets. 13C NMR spectra were recorded on
a Bruker AV400 NMR spectrometer at 400 MHz, and the chemi-
cal shifts are given using TMS as internal reference. The content
of 5-HMF was analyzed on an Agilent 1260 HPLC (UV wavelength:
284 nm; C18 column 5 m; 250 mm × 4.6 mm), using 60% methanol
in ultrapure water as mobile phase at a flow rate of 1 mL min−1
.
2.3. Dehydration of the fructose to 5-HMF
Further investigation has been carried out by using various HPAs
such as H3PMo12O40, H4SiMo12O40, H4PMo11VO40, H5PMo10V2O40
and H6PMo9V3O40 as catalysts. As shown in Fig. 1, the highest
yield of 99% with H3PW12O40 and H4SiW12O40 as catalysts can
be obtained under the experimental conditions. Furthermore, it
should be noted that all the used HPAs exhibit better catalytic
conversion results than that of H2SO4 and HCl.
The effect of the catalyst dosage on the fructose dehydration has
been investigated. As shown in Fig. 2, almost no conversion can be
found in the absence of catalyst. Even the reaction time is extended
In a typical reaction, 0.5 g of fructose (2.78 mmol) was dissolved
in 0.6 g of ILs firstly, and 0.1 mmol catalyst was added. The reaction
mixture was stirred at 80 ◦C in oil bath. After reaction, each sample
was diluted with 10 g of ultra-pure water before analysis.
For recycling of the ionic liquid and the catalyst, 3 mL of water
and 8 mL of ethyl acetate were added to the above reaction mixture.
Then, the organic phase was extracted out from the mixture. After
extraction, the ionic liquid was heated at 60 ◦C for 24 h in a vacuum
oven, and it can be used directly for the next run.
Table 1
Effect of different catalysts on the fructose dehydration in ILs.
Entry
Solvent
Catalyst
T (◦C)
t (min)
Conv. (%)
Yield (%)
Ref.
1a
2a
3
4
5
6
7
8
9
[BMIM]Cl
[BMIM]Cl
Water-MIBK
Water-MIBK
[EMIM]Cl
DES
[BMIM]Cl
[BMIM]Cl
ChCl
H3PW12O40
H4SiW12O40
Cs2.5H0.5PW12O40
Ag3PW12O40
CrCl2
Citric acid
TfOH
GeCl4
CrCl3
FeCl3
H2SO4
[MIMPS]3PW12O40
80
80
115
120
80
5
5
>99
>99
78.1
82.8
92
93.2
96
100
–
99
99
74
77.7
83
77.8
88
92.1
60
59
80
This work
This work
[14]
[15]
[23]
[27]
[28]
[29]
[30]
60
60
180
60
60
5
30
30
240
120
80
100
100
100
100
120
120
10
11
12
ChCl
[BMIM]Cl
sec-Butanol
–
[30]
[12]
[31]
100
99.7
99.1
a
Reaction conditions: fructose (2.78 mmol), catalyst (0.1 mmol), [BMIM]Cl (1 g), 80 ◦C, 5 min. MIBK: methylisobutylketone; [EMIM]Cl: 1-ethyl-3-methylimidazolium
chloride; ChCl: choline chloride; TfOH: trifluoromethanesulfonic acid; MIMPS: 1-(3-sulfonicacid)propyl-3-methyl imidazolium; DES: deep eutectic solvent.