Journal of Materials Chemistry A
Paper
has a high energy density of 30.3 MJ Lꢁ1, which is similar to that Chemical Reagent Co., Ltd (Shanghai, China), and was freshly
of diesel (33.6 MJ Lꢁ1). Several methods have been reported for distilled before use.
the synthesis of EMF from either HMF or glucose/fructose in
excess ethanol with homogeneous acid catalysts or solid acid
2.2 Synthesis of bis-vinylimidazolium dibromide salt
catalysts.17–20 Homogeneous acid catalysts usually show high
Scheme 1 illustrates the steps for the synthesis of bis-vinyl-
catalytic activity for the synthesis of EMF. However, the furan
imidazolium dibromide salt, prepared according to a known
ring of HMF is prone to hydrolytic cleavage under acidic
conditions and, besides the desired EMF, a fair amount of ethyl
vinylimidazole (0.02 mol) in toluene (20 mL) was heated for 24 h
levulinate (EL) is also formed. For example, an EMF yield of 75%
method.26 A solution of 1,2-dibromoethane (0.01 mol) and 1-
ꢀ
in an oil bath at 90 C with magnetic stirring. Aer cooling to
and EL yield of 15% were produced from the reaction of HMF
room temperature, the mixture was ltered and washed several
times with diethyl ether to remove the unreacted starting
materials including 1-vinylimidazole and dibromoethane. In
order to further purify the as-prepared bis-vinylimidazolium
dibromide salt, active carbon was generally used to remove the
colored and organic impurities present in trace amounts, which
were not easily detected by other technologies.27 The solid
product was dissolved in methanol and stirred overnight in the
presence of activated carbon then ltered and dried at 40 ꢀC
under reduced pressure to give rise to bis-vinylimidazolium
dibromide salt in a yield of 96%. 1H NMR (400 MHz, CDCl3): d ¼
9.48 (s, 2H), 8.12–8.10 (d, 2H), 7.77–7.5 (d, 2H), 4.35–4.31 (t, 4H),
5.90–5.94 (t, 2H), 5.42–5.46 (d, 4H). 13C NMR (100 MHz, CDCl3):
52.6, 110.6, 121.3, 124.5, 129.7, 135.8.
ꢀ
with ethanol at 100 C aer 24 h by the use of H2SO4 as cata-
lyst.21 Some heterogeneous catalysts have been used for the
synthesis of EMF. However, some of the heterogeneous catalysts
have low acidity, resulting in low EMF yield, and the mass
transformation is limited due to the limited surface area and
narrow pore size.
Polyionic liquids (PILs) refer to a subclass of polyelectrolytes
that feature an IL species in each monomer repeat unit, con-
nected through a polymeric backbone to form a macromolec-
ular architecture. PILs have recently received a lot of attention
in catalyst preparation for many chemical reactions.22,23 Some of
the unique properties of ILs are incorporated into the polymer
chains, giving rise to a new class of polymeric materials. In
addition, PILs facilitate reactant transfer from the reaction
solution to the catalyst sites and product release from the
catalyst to the reaction solution. Acidic ILs have been used for
the synthesis of EMF from renewable carbohydrates;24,25
however, it seemed that the recycling of the catalyst is difficult.
In this study, we describe a new kind of magnetic material
supporting PILs with high acidity by a highly cross-linked imi-
dazolium network obtained by radical oligomerization of bis-
vinylimidazolium salts on the surface of mercaptopropyl-
modied silica-coated Fe3O4. This magnetic material is insen-
sitive to air and requires no special care during its handling.
With these considerations in mind, we tried to evaluate our
solid acid catalyst for the synthesis of the promising liquid fuel
EMF from HMF and fructose-based carbohydrates. To the best
of our knowledge, this is the rst report of the use of magnetic
material-supported PILs as acid catalyst for the synthesis of
EMF.
2.3 Polymeric ILs supported on magnetic Fe3O4@SiO2
material
Mercaptopropyl-modied silica-coated Fe3O4 was prepared and
characterized according to our previous work.28 In a round-
bottom ask, 500 mg of Fe3O4@SiO2–SH was added into 20 mL
of methanol, and sonicated for 30 min to homogeneously
disperse in the methanol. Then, bis-vinylimidazolium dibro-
mide salt (673 mg) and azobisisobutyronitrile (16.3 mg) were
added into the above mixture. The whole reaction system was
degassed by bubbling argon for 15 min. The mixture was heated
ꢀ
at 78 C under argon atmosphere with stirring for 24 h. Aer
reaction, the reaction mixture was cooled to room temperature,
ltered under reduced pressure and washed with hot methanol,
then with diethyl ether. The obtained material was dried in an
ꢀ
oven at 40 C overnight.
In order to prepare acidic magnetic catalyst, the bromide
ions were exchanged with hydrosulfate ions. In a three-necked
round-bottom ask equipped with stirrer, the above obtained
material (0.4 mg) was suspended in 3 cm3 of water. During
vigorous stirring, 0.15 g of concentrated H2SO4 (98%) was
introduced drop by drop at 0 ꢀC. Then the mixture was heated to
room temperature, and was reuxed for 24 h. Then water and
the formed HBr were removed under reduced pressure. The
remaining H2SO4 was continuously washed by water until no
2. Experimental section
2.1 Materials
FeSO4$7H2O (99.5%), FeCl3$6H2O (99.5%), 1,2-dibromoethane
(99%) and tetraethoxysilane (TEOS, 99.5%) were purchased
from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China).
1-Vinylimidazole (98%) and g-mercaptopropyltrimethoxysilane
(MPTMS) (98.5%) were purchased from Aladdin Chemicals Co.
Ltd (Beijing, China). Fructose was purchased from Sanland-
Chem International Inc. (Xiamen, China). Inulin and sucrose
were purchased from the J&K Chemical Co. Ltd (Beijing, China).
HMF (98%) was purchased from Beijing Chemicals Co. Ltd
(Beijing, China). 5-Ethoxymethylfurfural (98%) was purchased
from Hangzhou Imaginechem Co., Ltd (Zhejiang, China).
Acetonitrile (HPLC grade) was purchased from Tedia Co. (Fair-
Scheme
1 Schematic illustration of the synthesis of bis-vinyl-
eld, USA). Ethanol (99.5%) was purchased from Sinopharm imidazolium dibromide salt.
J. Mater. Chem. A
This journal is © The Royal Society of Chemistry 2015
Yin, Shanshan
