Highly Efficient and Convenient Supported Ionic Liquid TiCl5-DMIL@SiO2@Fe3O4-Catalyzed Cycloaddition of CO2 and Epoxides to Cyclic Carbonates

Article abstract of DOI:10.1007/s10562-017-2051-3

Abstract: A series of silica coated magnetic nanoparticles supported ILs were prepared, characterized and their catalytic performances in cycloaddition of CO₂ to epoxides were investigated. The influences of various reaction parameters including catalyst selection, catalyst amount, reaction time, and reaction temperature were studied. Research shows that TiCl₅-DMIL@SiO₂@Fe₃O₄ could be used as the highest efficient catalyst in cycloaddition of CO₂ and epoxides to gives the corresponding cyclic carbonates. Good to excellent yields were achieved for this reaction under mild conditions. The heterogeneous supported catalyst is easily recoverable by filtration, and could be used for five consecutive runs without significant loss in catalytic activity.

Full text of DOI:10.1007/s10562-017-2051-3

Catal Lett
DOI 10.1007/s10562-017-2051-3
Highly Efficient and Convenient Supported Ionic Liquid
TiCl -DMIL@SiO @Fe O -Catalyzed Cycloaddition of CO
5
2
3
4
2
and Epoxides to Cyclic Carbonates
Yu Lin Hu1,2 · Rong Xing3
Received: 24 January 2017 / Accepted: 2 April 2017
©
Springer Science+Business Media New York 2017
Abstract A series of silica coated magnetic nanoparti-
Graphical Abstract
cles supported ILs were prepared, characterized and their
O
R
1
CO2
O
catalytic performances in cycloaddition of CO to epox-
2
O
R1
O
ides were investigated. The influences of various reaction
parameters including catalyst selection, catalyst amount,
reaction time, and reaction temperature were studied.
R
2
R
2
O
O
O
S
S
O
O
O
O
i
Research shows that TiCl -DMIL@SiO @Fe O could be
O
i
N
Si
Fe
O
5
2
3
4
Fe
O
Si
N
N
3
4
2
2
3
4
N
used as the highest efficient catalyst in cycloaddition of
TiCl
5
TiCl
5
CO and epoxides to gives the corresponding cyclic car-
2
bonates. Good to excellent yields were achieved for this
reaction under mild conditions. The heterogeneous sup-
ported catalyst is easily recoverable by filtration, and could
be used for five consecutive runs without significant loss in
catalytic activity.
Recycled catalytic system
Keywords Supported ionic liquid · Cycloaddition ·
Epoxides · CO · Heterogeneous catalysis
2
1
Introduction
Carbon dioxide is an attractive C1 source that have been
widely used for the production of a variety of chemicals
[
1, 2]. Nowadays, numerous methods have been devel-
oped for the preparation of these molecules, and one of the
most attractive synthetic protocols constitutes the cycload-
dition of CO to epoxides to afford cyclic carbonates [3].
2
Conventionally, the common protocol for the assembly of
these compounds is the use of alkali metal catalysts [4, 5].
However, these protocols suffered from some drawbacks
such as the use of stoichiometric amount of catalysts and
generation of vast amounts of corrosive wastes. In order to
overcome these problems, many efforts have been devel-
oped for this transformation, and various catalysts have
*
Yu Lin Hu
huyulin1982@163.com
1
College of Materials and Chemical Engineering,
China Three Gorges University, Yichang 443002,
People’s Republic of China
2
3
Key Laboratory of Inorganic Nonmetallic Crystalline
and Energy Conversion Materials, China Three Gorges
University, Yichang 443002, People’s Republic of China
been developed including PS-TBMAC/ZnI [6], salen-
2
complexes [7–11], bromide [12], K S O /NaBr [13], MOFs
2
2
8
[
14–21], quaternary ammonium hydroxide [22], sup-
College of Chemistry and Environmental Engineering,
Yancheng Teachers University, Yancheng 224002,
People’s Republic of China
ported imidazole [23], organocatalysts [24, 25], and others
26–29]. However, some of these procedures still require
[
Vol.:(0
1
123456789)
3

Y. L. Hu, R. Xing
harsh reaction condition, the cost and instability of cata-
lysts. Therefore, the design and explore of environmentally
benign and efficient catalysts that address these drawbacks
are highly desirable.
X-ray (EDX) analysis were carried out on a JSM-7500F
Scanning Electron Microscope. FTIR spectra were
recorded on a Nicolet Nexus 470 Fourier transform infra-
red spectrometer. UV–Vis spectra were recorded on a Shi-
madzu UV-2450 spectrometer. Magnetic properties were
carried out using a vibrating sample magnetometer (PPMS-
9T, Quantum Design, USA) in the magnetic field range of
−10,000 to 10,000 Oe at room temperature. Thermogravi-
metric analysis (TG) were measured on a Netzsch Thermo-
analyzer STA 449. GC experiments were performed on a
Ionic liquids (ILs) are well-known green reaction media
and catalysts because of their outstanding and unique prop-
erties [30–32]. Examples of their applications in the syn-
thesis of cyclic carbonates from CO and epoxides were
2
reported [33–37]. Although their good catalytic activi-
ties in the reaction, they have some problems such as par-
tially ILs wasted and difficulties in separating catalysts
from products after the reaction. Immobilized ILs have the
attractive features of ILs and heterogeneous catalysis, such
as easy catalyst recovery, high efficiency, high stability
and recyclability. Thus, this problem can be overcome by
immobilizing the traditional IL on solid supports [38–46].
Various methods have been developed for immobilization
of ILs on solid supports such as alumina, titania, silica, etc,
and among these solid supports, silica was found to be one
of the most effective one [41]. In the present study, a series
of silica coated magnetic nanoparticles supported function-
alized ionic liquids anion-DMIL@SiO @Fe O have been
1
Shimadzu GC-2014C chromatograph. H NMR spectra
were recorded in CDCl at room temperature on a Bruker
3
400 MHz spectrometer. Elemental analysis were performed
on a Vario EL III instrument.
2.2 Supported ILs Anion-DMIL@SiO @Fe O
4
2
3
Preparation
Supported ILs were prepared according to reported process
[40–44] and shown in Scheme 2. Preparation of SiO @
2
Fe O : Fe O (2 g), ethanol (400 mL) were sonicated at
3
4
3
4
room temperature for 60 min, and tetraethyl orthosilicate
2
3
4
prepared and characterized, which exhibited good chemical
and thermal stability, and were applied as a novel hetero-
geneous catalyst in the preparation of cyclic carbonates by
(4 mL), NH ·H O (28%) (12 mL) were added. The mix-
3
2
ture was stirred at room temperature for 24 h. The nano-
particles were isolated by filtration and washed with H O
2
cycloaddition of CO to epoxides (Scheme 1). As well as
(3×20 mL), EtOH (3×20 mL), and dried under vacuum
2
this, the reusability of the supported functionalized IL was
to afford the silica-coated Fe O nanoparticles. Preparation
3
4
also studied.
of Cl-DMIL: 1,4-di(1H-imidazol-1-yl)butane (0.5 mol),
(
(
3-chloropropyl) triethoxysilane (2.2 mol), toluene
400 mL) were refluxed for 36 h under N2 atmosphere, and
2
Experimental
then the solvent was removed by liquid–liquid separation,
and the residue was evaporated under vacuum to give Cl-
DMIL. Preparation of anion-DMIL: Cl-DMIL (0.05 mol)
was dispersed in CH Cl /CH CN (120 mL) and stirred vig-
2
.1 General
2
2
3
The reagents and solvents were purchased from Aldrich.
All the chemicals were from commercial sources without
any pretreatment. Powder X-ray diffraction (XRD) patterns
were collected on a Rigaku Ultima IV diffractometer. Scan-
ning electron microscopy (SEM) and Energy dispersive
orously with KPF (0.11 mol)/ZnCl or TiCl (0.11 mol) for
6 2 4
24 h under reflux conditions. After cooled down to room
temperature, the resulting material was isolated by filtra-
tion, washed with H O (3×20 mL), EtOH (3×20 mL), and
2
evaporated under vacuum to give PF -DMIL, ZnCl -DMIL
6
3
Scheme 1 Catalytic preparation
R1
R2
R1
R2
O
O
CO2
of cyclic carbonates by cycload-
O
O
dition of CO to epoxides
2
anion-DMIL@SiO @Fe O
4
2
3
R = aryls, alkyls; R = H, alkyls
1
2
O
O
O
O
O Si
O
N
Si
Fe O
3
4
N
Fe O
N
3
4
N
[
anion]
[anion]
anion = PF , HSO , CF SO , p-CH C H SO , ZnCl , TiCl
5
6
4
3
3
3
6
4
3
3
1
3

Highly Efficient and Convenient Supported Ionic Liquid…
N
toluene
reflux 24 h
N
N
N
Cl
Si(OEt)3
N
Si(OEt)3
N
(
EtO) Si
N
3
N
Cl
Cl
Cl-DMIL
TiCl4
KPF6
ZnCl2
H SO
2
4
CF SO H
p-CH C H SO H
3 6 4 3
3
3
CH Cl2
2
O
O
O
O
O Si
O
N
Si
N
N
[
N
[
anion]
anion]
anion-DMIL
anion = PF , HSO , CF SO , p-CH C H SO , ZnCl , TiCl
6
4
3
3
3
6
4
3
3
5
Fe O
3
4
toluene, reflux 24 h
SiO @Fe O
4
2
3
O
O
O
O
O Si
O
N
Si
Fe O
3 4
N
Fe O
N
3
4
N
[
anion]
[
anion]
anion-DMIL@SiO @Fe O
4
2
3
anion = PF , HSO , CF SO , p-CH C H SO , ZnCl , TiCl
5
6
4
3
3
3
6
4
3
3
Scheme 2 Preparation of supported ILs
or TiCl -DMIL; Cl-DMIL (0.05 mol), H SO , p-CH C H-
0.8 MPa at 100°C. The reaction mixture was stirred at 100°C
for the desired time. The reaction progress was monitored by
GC. When the pressure of reactor was fall down to a preset-
5
2
4
3 6
SO H or CF SO H (0.1 mol) were stirred vigorously at
4
3
3
3
5
0°C for 12 h, then the resulting material was dried under
vacuum to give HSO -DMIL, p-CH C H SO -DMIL or
ting value, then the excess of CO was vented. The resulting
4
3
6
4
3
2
CF SO -DMIL. Preparation of anion-DMIL@SiO @
mixture was distilled under vacuum to afford the desired pure
product. Fresh substrates were then recharged to the recov-
ered catalyst and then recycled under identical reaction con-
ditions. All products were identified by comparing their phys-
ical and GC spectra with those of commercial materials.
3
3
2
Fe O : anion-DMIL (0.01 mol), SiO @Fe O (3 g), and
3
4
2
3
4
toluene (400 mL) were stirred under reflux conditions for
4 h. The resultant solid was separated magnetically and
washed with EtOH (3×20 mL) and dried under vacuum.
2
2
.3 General Procedure for Catalytic Cycloaddition
2.4 Spectral Data of Products
of Epoxides with CO
2
2
.4.1 4‑Methyl‑1,3‑dioxolan‑2‑one (Table 2, Entry 1)
Typically, epoxide (0.1 mol) and TiCl -DMIL@SiO @Fe O
5
2
3
4
2
1
(
0.5 g) were introduced into a stainless-steel autoclave. CO
H NMR: δ 1.41 (dd, CH , 3H), 3.96 (m, CH, 1H), 4.52
3
was charged in the autoclave and the pressure was raised to
(m, CH, 1H), 4.83 (m, CH, 1H). Anal. Calcd. for C H O :
4
6
3
1
3

Y. L. Hu, R. Xing
C, 47.02; H, 5.89; O, 47.01. Found: C, 47.06; H, 5.92; O,
3 Results and Discussion
4
7.02.
The characterization of the silica coated magnetic nano-
particles supported ILs were using FT-IR, SEM, EDX,
and XRD analysis. The FT-IR spectra of the supported
ILs are shown in Fig. 1. The characteristic bonds at about
2
.4.2 1,3‑Dioxolan‑2‑one (Table 2, Entry 2)
1
H NMR: δ 4.51 (s, CH CH , 4H). Anal. Calcd. for
2
2
−
1
C H O : C, 40.89; H, 4.55; O, 54.47. Found: C, 40.92; H,
1475, 1538, and 1660 cm , which were assigned to the
C–H bending vibrations, C=C and C=N stretching vibra-
tions of the imidazolium ring [40]. The peaks observed at
3
4
3
4
.58; O, 54.50.
−
1
about 1090 and 980 cm were belonged to the stretching
2
.4.3 4,4‑Dimethyl‑1,3‑dioxolan‑2‑one (Table 2, Entry 3)
−1
vibration of Si–O–Si. The peaks at about 2975, 1320 cm
are attributed to C–H stretching of alkyl chain, and the
1
H NMR: δ 1.43 (s, 2CH , 6H), 4.21 (s, CH , 2H). Anal.
3
2
−
1
peak at about 3480 cm is related to C–H stretching of the
Calcd. for C H O : C, 51.68; H, 6.91; O, 41.32. Found: C,
5
8
3
−
1
absorbed water. The peaks observed at 1542, 1450 cm
5
1.72; H, 6.94; O, 41.34.
−
1
−1
(
Fig. 1a), 1718, 875 cm (Fig. 1b), 827 cm (Fig. 1c),
−
1
−1
1
025 cm (Fig. 1d), 575, 690, 822 cm (Fig. 1e), and
2
.4.4 4‑Propyl‑1,3‑dioxolan‑2‑one (Table 2, Entry 4)
−
1
1
472, 1365, 1269 cm (Fig. 1f), related to vibrational
1
modes of ZnCl , HSO , PF , CF SO , p-CH C H SO , and
3
4
6
3
3
3
6
4
3
H NMR: δ 0.87 (t, CH , 3H), 1.38 (m, CH , 2H), 1.57 (dd,
3
2
TiCl respectively. Moreover, the absorption band at about
5
CH , 2H), 4.09 (m, CH, 1H), 4.53 (t, CH , 1H), 4.71 (t,
2
2
−1
5
75 cm is attributed to the Fe–O stretching vibration of
CH , 1H). Anal. Calcd. for C H O : C, 55.32; H, 7.68; O,
2
6
10
3
Fe O [44].
3
4
3
6.81. Found: C, 55.34; H, 7.71; O, 36.85.
The surface morphology and chemical composition
of the supported ILs were analyzed by SEM and EDX.
SEM images of the supported ILs are shown in Fig. 2,
it clearly observed that all the ILs particles were well-
defined, and the surface of the supported ILs are smooth
and soft, which shows highly uniform particles. Figure 3
displayed the EDX analysis of the supported ILs. EDX
obtained from SEM showed the presence of the expected
elements in their structure. Figure 4 displayed the XRD
diffractograms of the supported ILs. All of the supported
2
.4.5 4‑(Chloromethyl)‑1,3‑dioxolan‑2‑one (Table 2, Entry
5
)
1
H NMR: δ 3.79 (dd, CH , 2H), 4.32 (dd, CH , 1H),
2
2
4
.61 (dd, CH , 1H), 4.92 (m, CH , 1H). Anal. Calcd. for
2 2
C H ClO : C, 35.13; H, 3.64; Cl, 25.91; O, 35.09. Found:
4
5
3
C, 35.19; H, 3.69; Cl, 25.97; O, 35.15.
2
.4.6 Hexahydrobenzo[d] [1,3] dioxol‑2‑one (Table 2,
Entry 6)
1
H NMR: δ 1.83 (m, 2CH, 2H), 2.01 (m, 2CH, 2H), 2.31
m, CH CH , 4H), 5.09 (m, 2CH, 2H). Anal. Calcd. for
(
2
2
C H O : C, 59.11; H, 7.08; O, 33.75. Found: C, 59.14; H,
7
10
3
7
.09; O, 33.77.
2
.4.7 4‑Phenoxymethyl‑1,3‑dioxolan‑2‑one (Table 2, Entry
7
)
1
H NMR: δ 4.18 (m, CH , 2H), 4.61 (m, CH , 2H), 4.95
2
2
(
m, CH, 1H), 6.91–7.06 (m, Ar–H, 3H), 7.35–7.42 (m,
Ar–H, 2H). Anal. Calcd. for C H O : C, 61.81; H, 5.17;
1
0
10
4
O, 32.93. Found: C, 61.85; H, 5.19; O, 32.96.
2
.4.8 4‑Phenyl‑1,3‑dioxolan‑2‑one (Table 2, Entry 8)
1
H NMR: δ 4.34 (t, CH , 1H), 4.77 (t, CH , 1H), 5.65
2
2
Fig. 1 FT-IR spectra of ZnCl -DMIL@SiO @Fe O
(a),
HSO -DMIL@SiO @Fe O (b), PF -DMIL@SiO @Fe O (c),
3
2
3
4
(
t, CH , 1H), 7.31–7.48 (m, Ar–H, 5H). Anal. Calcd. for
2
4
2
3
4
6
2
3
4
C H O : C, 65.85; H, 4.89; O, 29.21. Found: C, 65.85; H,
9
8
3
CF SO -DMIL@SiO @Fe O (d), p-CH C H SO -DMIL @SiO @
3 3 2 3 4 3 6 4 3 2
4
.91; O, 29.24.
Fe O (e), TiCl -DMIL@SiO @Fe O (f)
3 4 5 2 3 4
1
3

Highly Efficient and Convenient Supported Ionic Liquid…
ILs had the diffraction peaks of the cubic structure of
Fe O (JCPDS No.19-0629) [45]. The absence of obvi-
nanocrystalline nature of the prepared supported ILs.
Figure 5 showed the diffuse reflectance UV–Vis spectra
of the supported ILs. All the supported ILs exhibit a peak
around 215 nm, which are assigned to the O–Si transition
[38, 41]. In addition to this peak, another peaks appeared
at around 413, 492, 556 nm in Fig. 5f, which is likely to
3
4
ous characteristic peaks of anions of ILs in the XRD
patterns suggests that the anion is well-dispersed on the
surface in the channels of the silica coated magnetic
nanoparticles, and the broadness of the peaks shows the
Fig. 2 SEM
images
of
ZnCl -DMIL@SiO @Fe O
(a),
Fe O (e), TiCl -DMIL@SiO @Fe O (f), and five times recycled
3
2
3
4
3
4
5
5
2
3
4
HSO -DMIL@SiO @Fe O (b), PF -DMIL@SiO @Fe O (c),
TiCl -DMIL@SiO @Fe O (g)
4
2
3
4
6
2
3
4
2
3
4
CF SO -DMIL@SiO @Fe O (d), p-CH C H SO -DMIL@SiO @
3
3
2
3
4
3
6
4
3
2
Fig. 3 EDX images of
ZnCl -DMIL@SiO @Fe O
3
2
3
4
(
(
(
a), HSO -DMIL@SiO @Fe O
4 2 3 4
b), PF -DMIL@SiO @Fe O
4
6
2
3
c), CF SO -DMIL@SiO @
3
3
2
3
Fe O (d), p-CH C H SO -
3
4
3
6
4
DMIL @SiO @Fe O (e),
2
3
4
TiCl -DMIL@SiO @Fe O (f)
5
2
3
4
1
3

Y. L. Hu, R. Xing
probed in the reaction (Table 1, entries 1–6). Among
the supported ILs, TiCl -DMIL@SiO @Fe O demon-
5
2
3
4
strated the best results in terms of yield and reaction con-
ditions (Table 1, entry 6). The contrast experiments were
studied with bulk IL catalysts, such as ZnCl -DMIL,
3
p-CH C H SO -DMIL, HSO -DMIL (Table 1, entries
3
6
4
3
4
7
–9). Results show that the supported ILs showed much
higher reaction efficiency than the bulk ILs, which might
be due to the increase of the surface area of the catalyst
after supported on silica coated magnetic nanoparticles car-
rier. Therefore, TiCl -DMIL@SiO @Fe O was chosen as
5
2
3
4
the suitable catalyst in the subsequent experiments.
It was found that the cycloaddition was significantly
affected by the amount of supported catalyst (Fig. 6). The
reaction did not perform in the absence of TiCl -DMIL@
5
SiO @Fe O . As expected, the reaction activity was
2
3
4
strengthened with the increase of the catalyst amount, the
product yield and selectivity raised with the amount of cat-
alyst increased to 0.5 g. However, there was no substantial
change in the yield and selectivity with further increasing
the amount of catalyst, while decreased the amount of cata-
lyst resulted in lowering the yield and selectivity. There-
fore, the best result was obtained by carrying out the reac-
tion with a catalyst amount of 0.5 g.
Fig. 4 XRD diffractograms of ZnCl -DMIL@SiO @Fe O (a),
3
6
2
2
3
3
4
4
HSO -DMIL@SiO @Fe O (b), PF -DMIL@SiO @Fe O (c),
4
2
3
4
CF SO -DMIL@SiO @Fe O (d), p-CH C H SO -DMIL @SiO @
3
3
3
2
3
4
2
3
6
4
3
2
Fe O (e), TiCl -DMIL@SiO @Fe O (f)
4
5
3
4
The influence of CO pressure on the cycloaddition were
2
investigated (Fig. 7). It was found that the product yield and
selectivity could be retained at a low CO pressure, dem-
2
onstrating the preferential effect of TiCl -DMIL@SiO @
5
2
Fe O for promoting the reactivity of CO . The reaction
3
4
2
activity was strengthened as CO pressure increased to
2
0
.8 MPa, higher CO pressure can effectively increase the
2
solubility of CO in propylene oxide, enabling the reaction
2
equilibrium to shift towards cycloaddition. However, it was
observed that a decrease in the yield and selectivity with
the further increase of CO pressure. The studies revealed
2
that CO pressure has important influence on the reaction,
2
and 0.8 MPa was identified as the optimal CO pressure.
2
Fig. 5 UV–Vis spectra of ZnCl -DMIL@SiO @Fe O
4
(a),
3
6
2
2
3
3
Figure 8 showed the magnetization curves of the
HSO -DMIL@SiO @Fe O (b), PF -DMIL@SiO @Fe O (c),
4
2
3
4
4
selected supported ILs such as PF -DMIL@SiO @Fe O ,
CF SO -DMIL@SiO @Fe O (d), p-CH C H SO -DMIL @SiO @
6
2
3
4
3
3
3
2
3
4
2
3
6
4
3
2
Fe O (e), TiCl -DMIL@SiO @Fe O (f)
p-CH C H SO -DMIL@SiO @Fe O , and the catalyst
4
5
3
4
3 6 4 3 2 3 4
TiCl -DMIL@SiO @Fe O , and the saturation mag-
5
2
3
4
netizations are 19.2, 21.7, and 49.8 emu/g, respectively.
be associated with the characteristic absorption band of
Ti–Cl [47–49].
Compared to the magnetic property of SiO @Fe O with
2
3
4
saturation magnetization of about 60 emu/g [44], the
In order to optimize the reaction conditions and test
the catalytic activities of the synthesized supported ILs,
initially we selected the cycloaddition of propylene oxide
TiCl -DMIL@SiO @Fe O exhibited a superparamag-
5
2
3
4
netic property with saturation magnetization of 49.8 emu/g,
which is important for the supported catalyst in separation
after the completion of the reaction.
and CO as a model reaction and the proper chosen of
2
ILs were examined for this reaction. A series of sup-
The heterogeneous catalyst TiCl -DMIL@SiO @
5
2
ported IL catalysts such as ZnCl -DMIL@SiO @Fe O ,
Fe O can be easily separated and recovered by filtration
3
2
3
4
3
4
HSO -DMIL@SiO @Fe O , PF -DMIL@SiO @Fe O ,
after the reaction. The cycloaddition results by recovered
4
2
3
4
6
2
3
4
CF SO -DMIL@SiO @Fe O ,
p-CH C H SO -DMIL
TiCl -DMIL@SiO @Fe O are shown in Fig. 9. The over-
3
3
2
3
4
3 6 4 3
5
2
3
4
@
SiO @Fe O , and TiCl -DMIL@SiO @Fe O , were
all thermal stability of the supported IL was conducted
2
3
4
5
2
3
4
1
3

Highly Efficient and Convenient Supported Ionic Liquid…
Table 1 Catalyst screening for
the cycloaddition of propylene
oxide and CO2
Yield (%)a
Entry
Catalyst
Time (h)
Selec-
tivity
b
(
%)
1
2
3
4
5
6
7
8
9
ZnCl -DMIL@SiO @Fe O
2
3
8
3
3
2
5
8
8
91
64
21
72
78
95
82
58
46
97
83
92
78
87
99
91
79
75
3
2
3
4
4
HSO -DMIL@SiO @Fe O
4
2
3
PF -DMIL@SiO @Fe O
4
6
2
3
CF SO -DMIL@SiO @Fe O
4
3
3
2
3
p-CH C H SO -DMIL@SiO @Fe O
4
3
6
4
3
2
3
TiCl -DMIL@SiO @Fe O
5
2
3
4
ZnCl -DMIL
3
p-CH C H SO -DMIL
3
6
4
3
HSO -DMIL
4
Reaction conditions: propylene oxide (0.1 mol), catalyst (0.5 g), CO (0.8 MPa), at 100°C
2
a
Isolated yield
Isolated selectivity
b
Fig. 6 Effect of the amount of catalyst on the cycloaddition. The
reactions were carried out with propylene oxide (0.1 mol), CO
Fig. 8 Magnetization
curves
of
PF6-DMIL@SiO2@Fe3O4,
2
(
0.8 MPa), in different amounts of TiCl -DMIL@SiO @Fe O for 2 h
p-CH3C6H4SO3-DMIL@SiO2@Fe3O4 and TiCl5-DMIL@SiO2@
5
2
3
4
Fe O
3
4
through TG analysis (Fig. 10), the observed weight loss was
associated with the loss of the organic components attached
to the surface. In the TG curve, the observed organic mate-
rials weight loss of the IL showed a mass weight 34.8% on
heating to 700°C. The small weight loss before 110°C is
related to the desorption of adsorbed water and toluene,
9
.1% weight loss occurred before 250°C, indicating a
considerably thermal stability up to 250°C. There existed
drastic weight loss between 250 and 500°C is attributed
to the breakdown of the organic moieties. From the curves
depicted, it demonstrated that the supported IL is thermally
stable below about 250°C. The good thermal stability of
TiCl -DMIL@SiO @Fe O is beneficial to the recycling
5
2
3
4
experiments, and the results showed that the product yield
in each run with no notable decline in catalytic efficiency,
suggesting that the catalyst could be recovered and recycled
Fig. 7 Influence of CO pressure on the cycloaddition. The reac-
2
tions were carried out with propylene oxide (0.1 mol), TiCl -DMIL@
5
SiO @Fe O (0.5 g), in different CO pressure at 100°C
2
3
4
2
1
3

Y. L. Hu, R. Xing
Fig. 11 XRD diffractogram of fresh and recycled TiCl -DMIL@
Fig. 9 Reusability of TiCl -DMIL@SiO @Fe O in cycloaddition of
5
5
2
3
4
SiO @Fe O
4
propylene oxide and CO
2
3
2
epoxides, and these cycloadditions proceeded smoothly and
can be completed in 2 h (Table 2, entries 1, 4, 5, 7 and 8).
However, di-substituted epoxides significantly decreased
the reaction rate, and good yields were obtained after pro-
longed reaction time (Table 2, entries 3 and 6).
From these results, a possible reaction mechanism
using the cycloaddition of propylene oxide with CO as
2
an example is proposed and depicted in Scheme 3 based
on the previous literatures [12, 13, 34–37] and the obser-
vations in this reactions. At first, the substrate epoxide is
activated by TiCl -DMIL@SiO @Fe O to form the com-
5
2
3
4
plex 1 by the coordination of one TiCl anion with O atom
5
of propylene oxide. Meanwhile, nucleophilic attack of the
other TiCl anion on the less sterically hindered carbon
5
atom of propylene oxide the occurred to form the com-
plex 2, which reacts with CO to produce complex 3. Sub-
Fig. 10 TGA profile of TiCl -DMIL@SiO @Fe O
4
2
5
2
3
sequent intramolecular substitution to afford the desired
product.
up to five runs with no significant loss of catalytic activi-
ties. The recovered catalyst after six runs had no obvious
change in the morphology and size, referring to the SEM
image in comparison with fresh catalyst (Fig. 2g). Further-
more, XRD diffractogram of the catalyst after five runs
revealed that TiCl -DMIL@SiO @Fe O preserved its
4 Conclusion
In conclusion, series of silica coated magnetic nanoparti-
cles supported ILs anion-DMIL@SiO @Fe O were pre-
5
2
3
4
2
3
4
original crystallinity during the reaction (Fig. 11).
pared and characterized. anion-DMIL@SiO @Fe O was
2 3 4
In order to study the generality and scope of the cata-
lyst TiCl -DMIL@SiO @Fe O , the catalytic activities of
applied as a new heterogeneous solid catalyst in cycload-
dition of CO to epoxides successfully. Research shows
5
2
3
4
2
CO with various epoxides were assessed and the results
that TiCl -DMIL@SiO @Fe O is the most effective cat-
2
5
2
3
4
were shown in Table 2. A variety of epoxides were reacted
alyst in the titled reaction. Various epoxides were reacted
with CO , which gave the desired cyclic carbonates in good
with CO to give the corresponding cyclic carbonates
2
2
to excellent yields (Table 2, entries 1–8). We found the
in good to excellent yields with high selectivities under
catalyst showed high efficiency toward mono-substituted
mild conditions. This methodology is endowed with
1
3

Highly Efficient and Convenient Supported Ionic Liquid…
Table 2 Catalytic activity of the cycloaddition of various epoxides with CO2
Time
Yield
Selectivity
Entry
1
Epoxide
Product
a
b
(
h)
(%)
(%)
O
O
O
O
O
O
2
95
99
92
97
99
100
100
99
O
O
2
3
4
2
5
2
O
O
O
O
O
O
O
O
O
O
O
5
6
1
5
98
91
99
99
Cl
Cl
O
O
O
O
O
O
O
O
O
O
7
8
O
2
96
99
99
O
O
O
2
98
O
Reaction conditions: epoxide (0.1 mol), TiCl -DMIL@SiO @Fe O (0.5 g), CO (0.8 MPa), at 100°C
5
2
3
4
2
a
Isolated yield
Isolated selectivity
b
some attractive features, such as short reaction times,
high yields, simple experimental procedure, good gen-
erality, easy recoverability and recyclability of catalyst.
Moreover, a possible mechanism is proposed. The above
study would provide a green and efficient route towards
the chemical carbon dioxide fixation.
1
3

Y. L. Hu, R. Xing
Scheme 3 Possible mechanism
for the cycloaddition
N
N
1
TiCl5
O
N
N
TiCl
5
O
N
N
TiCl5
N
N
N
O
N
N
Cl
TiCl5
N
TiCl4
N
TiCl5
N
N
N
TiCl -DMIL@SiO @Fe O
2
5
2
3
4
TiCl5
TiCl5
N
N
O
O
TiCl5
CO2
O
O
O
O
N
N
TiCl
4
Cl
3
Acknowledgements The authors are grateful to the National Natu-
14. Babu R, Roshan R, Kathalikkattil AC, Kim DW, Park DW
(2016) ACS Appl Mater Interfaces 8:33723
ral Science Foundation of China (No. 21506115) for financial support.
1
1
5. Morozan A, Jaouen F (2012) Energy Environ Sci 5:9269
6. Han YH, Zhou ZY, Tian CB, Du SW (2016) Green Chem
1
8:4086
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