Efficient and reusable SBA-15-immobilized Br?nsted acidic ionic liquid for the ketalization of cyclohexanone with glycol

Article abstract of DOI:10.1039/c7ra13385e

Ketalization of cyclohexanone with glycol has been carried out using molecular sieve SBA-15 immobilized Br?nsted acidic ionic liquid catalyst. The properties of the heterogeneous catalysts were characterized by elemental analysis, Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), thermogravimetry/differential scanning calorimetry (TG/DSC), and N₂ adsorption-desorption (BET). The results suggested that Br?nsted acidic ionic liquid [BSmim][HSO₄] had been successfully immobilized on the surface of SBA-15 and the catalytic performance evaluation demonstrated that the catalyst BAIL@SBA-15 exhibited excellent catalytic activities in the ketalization of cyclohexanone with glycol. In addition, the effects of reaction temperature, catalyst loading, reaction time, and reactant molar ratio have also been investigated in detail, and a general reaction mechanism for the ketalization of cyclohexanone with glycol was given. The SBA-15 immobilized ionic liquid can be recovered easily and after reusing for 5 times in the ketalization reaction, the catalyst could still give satisfactory catalytic activity.

Full text of DOI:10.1039/c7ra13385e

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Efficient and reusable SBA-15-immobilized
Brønsted acidic ionic liquid for the ketalization of
cyclohexanone with glycol
Cite this: RSC Adv., 2018, 8, 7179
ab
Heyuan Song, Guoqin Wang and Jing Chen*a
ab
ab
Ruiyun Li,
Ketalization of cyclohexanone with glycol has been carried out using molecular sieve SBA-15 immobilized
Brønsted acidic ionic liquid catalyst. The properties of the heterogeneous catalysts were characterized by
elemental analysis, Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM),
2
thermogravimetry/differential scanning calorimetry (TG/DSC), and N adsorption–desorption (BET). The
results suggested that Brønsted acidic ionic liquid [BSmim][HSO ] had been successfully immobilized on
4
the surface of SBA-15 and the catalytic performance evaluation demonstrated that the catalyst
BAIL@SBA-15 exhibited excellent catalytic activities in the ketalization of cyclohexanone with glycol. In
addition, the effects of reaction temperature, catalyst loading, reaction time, and reactant molar ratio
have also been investigated in detail, and a general reaction mechanism for the ketalization of
cyclohexanone with glycol was given. The SBA-15 immobilized ionic liquid can be recovered easily and
after reusing for 5 times in the ketalization reaction, the catalyst could still give satisfactory catalytic activity.
Received 16th December 2017
Accepted 26th January 2018
DOI: 10.1039/c7ra13385e
rsc.li/rsc-advances
Compared to other well-known acid catalysts, immobilized
ILs have several advantages. The most important may be the
1
. Introduction
Currently, ionic liquids (ILs) are receiving widespread attention easily adjustable acidity, and the possibilities given by the
17,18
as media for a variety of reactions because of their unique selection of support materials.
Recently, rapidly increasing
properties such as low vapor pressure, high chemical and reports have become available describing the application of task
1–4
thermal stability, and adjustable structure.
Compared to specic ionic liquids (TSILs) immobilized on various supports.
conventional acid catalysts, acidic ionic liquids possess several The immobilized TSILs show additional advantages, such as
advantages, such as, reactions can be carried out under solvent- decreasing consumption of ionic liquids, the facilitation of
free conditions, and the physical and chemical properties of catalyst separation and recycling from reaction system, lower
5
,6
ionic liquids can be tailored by varying cations and anions.
contamination of product, and the ability of using in gas phase
7
19
8
Since 2002 when Cole et al. rst reported SO
3
H-functionalized reactions. In 2007, Sugimura et al. investigated the copoly-
ionic liquids with strong Brønsted acidity, the applications of merization of 1-vinylimidazolium based acidic ionic liquid with
the Brønsted acidic ionic liquids (BAILs) with alkyl sulfonic acid styrene and its use as effective and reusable catalyst for acetal
1
7
groups in cations as a replacement for conventional homoge- formation under mild reaction condition. In 2011, Miao et al.
7–10
nous and heterogeneous acids have received great attention.
And BAILs have been used as acid catalysts for esterication, catalyzed by SG-[(CH
reported acetalization of different aldehydes with alcohols
2
)
3
SO H-HIM]HSO . The yields range from
3
4
alkylation,
oligomerization.
Pechmann
reactions,
acetalization
and 85% to 98.5% under condition of 4 wt% catalyst amount,
1
1–13
ꢀ
110 C. In 2004, a novel micropore zeolite MOR supported
20
Although ionic liquids have become commercially available, acidic ionic liquids was prepared. It possesses an excellent
several drawbacks, such as unendurable viscosity, high cost and performance for ketalization of cyclohexanone with glycol. The
tedious purication procedure of the product, restricted their conversion of cyclohexanone can reach 69.5%.
14
widespread applications.
In order to solve problems
More recently, it has reported on the preparations of a series
mentioned above, immobilized ionic liquids catalysts of organic–inorganic hybrid mesoporous materials incorpo-
21
combining the characteristics of ionic liquids, inorganic acids rated with ionic liquids. The commonly used solid supports
1
5,16
and solid acids had been proposed.
may be subdivided into resins, nanotubes, bers, zeolites and
22
mesoporous silicas (MSs). Mesoporous materials possess the
excellent characteristics of stable mesoporous structure, high
surface area, controllable pore size, and thermal stability, which
make them attractive supports for the preparation of immobi-
a
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of
Chemical Physics (LICP), Chinese Academy of Sciences, Lanzhou, 730000, P. R. China.
E-mail: chenj@licp.cas.cn; Fax: +86-931-496-8129; Tel: +86-931-496-8068
23
b
lized ionic liquid catalyst. Mesoporous materials, mostly
University of Chinese Academy of Sciences, Beijing, 100049, P. R. China
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ordered mesoporous molecular sieves (MCM-41, SBA-15), have
been used as efficient catalysts and supports for many catalytic
24–29
reactions.
As an appealing type of mesoporous material,
SBA-15 has relatively large specic surface area, controlled pore
size and pore volumes. Besides, the abundant hydroxyl group
on surface of SBA-15 could render it convenient for chemical
modication and suitable for specic catalytic applications.
Furthermore, the surface of the molecular sieves are sensitive to
hydrothermal treatment, and the hydrothermal treatment could
be used to activate the surface of SBA-15 and increase its
capacity for graing. Additives NaCl, KCl and NaF etc. are
usually used to moderate the wall thickness and the degree of
polymerization during post-synthesis hydrothermal treatments
30,31
of SBA-15.
as suitable supports.
In these papers, a series of heterogeneous catalysts, meso-
porous materials SBA-15 and amorphous SiO immobilized
All these make SBA-15 a potential candidate to act
32–35
2
SO H-functionalized ionic liquid was synthesized. And the
3
surface properties of the obtained catalysts were characterized
by elemental analysis, Fourier transform infrared (FT-IR)
4
Scheme 1 Synthesis of [BSmim][HSO ]@SBA-15.
spectra,
thermogravimetry/differential scanning calorimetry (TG/DSC)
and N adsorption–desorption isotherms (BET). Moreover, the
scanning
electron
microscopy
(SEM),
2
effects of reaction parameters such as reaction time, reaction 2.3. Synthesis of SBA-15 immobilized ionic liquid
temperature and catalyst loading were studied and the recy-
SBA-15 supported acidic ionic liquid was synthesized according
clability of the catalyst was also examined. A general reaction
38
to the literature. Activated SBA-15 (5 g) was suspended in 50 ml
dry toluene and an excess of 3-chloropropyl-triethoxysilane (6 g)
mechanism for ketalization of cyclohexanone with glycol was
given.
was added. The mixture was reacted under stirring for 24 h at
ꢀ
90
C. Upon the reaction was completed, the products was
collected by ltration and washed with toluene and ethyl ether
in turn for three times. Aer dried under vacuum at 70 C for
2. Experimental
ꢀ
2.1. Material
8 h, SBA-15-Cl was obtained as a white powder.
Subsequently, SBA-15-Cl (all product obtained from the last
step) was placed in a reaction ask containing 50 ml toluene
and an excess of imidazole (3 g) was added. The mixture was
Silica gel (35–60 mesh) was purchased from Sigma-Aldrich. SBA-15
was purchased from Nanjing XFNANO Materials Tech Co., Ltd. 3-
Chloropropyltriethoxysilane (CPES, purity $ 98%), 1,4-butane
sultone (purity $ 99%) and 1-methylimidazole (purity $ 99%) was
purchased from Aladdin Reagent Co, Ltd (Shanghai, China).
Toluene, anhydrous ethanol, ethyl ether, anhydrous methanol,
acetone, sulfuric acid were purchased from Rianlon Chemical Co.,
Ltd. Cyclohexanone and toluene were dried according to standard
ꢀ
reuxed with stirring for 24 h at 90 C. Then the products was
disposed in the same way as the last step to acquire interme-
diate [SBA-15-im]Cl. The obtained [SBA-15-im]Cl and 1,4-butane
sultone (4.0 g) were added in a 200 ml ask containing 50 ml
toluene. The mixture was reacted with magnetic stirring for
ꢀ
another 24 h at 100 C, to undergo a condensation reaction to
ꢀ
operations and stored over 4 A molecular sieves. Other reagents
form the silica chemically bonded sultone. Aer the same
were of analytical grade and used without any further purication.
ꢀ
treatment, [SBA-15-Bs-im]Cl was dried under vacuum at 60 C
for 8 h.
Finally, [SBA-15-Bs-im]Cl was added in a round-bottom ask
containing 100 ml 1,2-dichloromethane. 1,2-Dichloromethane
2
.2. Synthesis of [BSmim][HSO
4
]
[BSmim][HSO ] was synthesized and puried according to the
4
diluted 2.5 g of sulphuric acid was slowly added into the ask at
36,37
literature.
1,4-Butane sultone (27.23 g, 0.2 mol) was dissolved
ꢀ
0
C with stirring. The mixture was gradually heated to room
in toluene, and 1-methylimidazole (16.42 g, 0.2 mol) was added
dropwisely. The mixture was stirred at 60 C for 8 h under
temperature and reacted for 48 h. Then, the mixture was
washed and ltered with 1,2-dichloromethane and ethyl ether
until the pH of the ltrate reached 7.0. The prepared SBA-15
immobilized ionic liquid BAIL@SBA-15 was dried under
ꢀ
vigorous stirring to obtain the white precipitate. The generated
white solid zwitterion was ltrated and washed with toluene for
three times. Aer dried in vacuum to remove unreacted mate-
rials, the zwitterion was mixed with H SO in a molar ratio of 1 : 1
in anhydrous toluene, and stirred magnetically at 60 C for 8 h.
Finally, the mixture was dried in vacuum to form corresponding
BAILs.
ꢀ
vacuum at 60 C for 12 h to remove the residual volatiles and
2
4
moisture before use (Scheme 1).
ꢀ
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.4. Catalyst characterization
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2
Elemental analysis was performed on an Elementar Vario EL
cube analyzer (Elementar Analysensysteme GmbH, Germany)
and the graing amount of ILs on supports was determined by
the contents of the N element. Fourier transform infrared (FT-
ꢁ
1
IR) spectra in the frequency range of 4000–400 cm
measured at room temperature on a Nexus 870 spectrometer
Nicolet Instruments Co., USA). Thermogravimetry/differential
were
(
scanning calorimetry (TG/DSC) was performed on a Netzsch
Model STA 449 F3 simultaneous thermal analyzer (Netzsch,
Germany) in an air atmosphere. The shape and surface
morphology of the catalysts were examined via scanning elec-
tron microscopy (SEM) (Model SU8020, Hitachi, Japan). N
2
adsorption–desorption isotherms were recorded using a Tris-
tarII 3020 instrument (Micromeritics, USA) and pore size
distribution curves were calculated from the analysis of
desorption branch of the isotherm by the BJH (Barrett–Joyner–
Halenda). Before adsorption, samples were degassed at 473 K
for 4 h.
2.5. Catalytic activity evaluation
Catalytic activity experiments were conducted in a 25 ml round-
bottom ask. Immobilized ILs, cyclohexanone and glycol were
added quantitatively into the reactor successively. The mixture
was heated to a desired temperature and stirred at a speed of
ꢁ
1
6
00 rad min . Upon reaction completion, the qualitative
Fig. 1 Fourier transform infrared spectra of (a) molecular sieve and
supported catalysts; and (b) the fresh and five times reused catalysts.
analysis of products was performed by Agilent 7980A/5975C GC-
MS. The products were quantied by GC Smart equipped with
a hydrogen ame ionization detector (FID). A capillary column
ZB-WAX (30 m ꢂ 0.25 mm ꢂ 0.25 mm) was used to determine
the composition of the samples with nitrogen as the carrier gas
at a ow rate of about 3 ml min . 1,2-Dichloroethane was used
as the internal standard for the quantitative analysis of the
products.
3.2. SEM
ꢁ1
Fig. 2 shows the scanning electron microscopy (SEM) images of
the samples. It can be seen from the pictures that samples are
amorphous and accumulations of small particles. Compared
with the catalyst in Fig. 2(b), the patent material in Fig. 2(a) is
smother than the former because of immobilization of the IL.
3. Results and discussion
3.1. FT-IR
To conrm the immobilization of active component on the
mesoporous structure, FT-IR spectroscopic studies were carried
ꢁ
1
out in the frequency range of 4000–400 cm . The FT-IR spectra
of molecular sieve SBA-15, amorphous SiO and immobilized
2
ionic liquids catalysts were shown in Fig. 1(a), respectively. As
can be seen from the spectra of BAIL@SBA-15, the characteristic
ꢁ
1
ꢁ1
ꢁ1
peaks of [BSmim][HSO ] around 3150 cm , 2970 cm
1
,
4
ꢁ1
ꢁ1
ꢁ1
ꢁ1
571 cm , and 1176 cm , 1058 cm , 626 cm , 525 cm
could be clearly observed. They were ascribed to N–H, C–H,
C]C and C]N stretching vibrations of the imidazole ring, and
S]O symmetric stretching vibrations of the SO
hydrogen sulfate, respectively.
3
H group and
The typical peaks of Si–O–Si
on SBA-15 supported ionic liquids could be observed around
39,40
ꢁ
1
ꢁ1
ꢁ1
4
3
60 cm , 769 cm and 954 cm and the strong absorbance at
ꢁ
1
ꢁ1
440 cm
and 1630 cm
corresponds to the stretching
frequency of physical adsorbed water. Hence, the above results
conrm that the ILs were successfully immobilized onto the
supports by covalent bonds.
Fig. 2 SEM images of (a) BAIL@SBA-15; (b) SBA-15; (c) BAIL@Silica gel;
(d) silica gel.
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From all the above surface analysis data, it is conrmed that the
3-chloropropyl-triethoxysilane and ionic liquid is modied into
the framework of the molecular sieve and amorphous silica.
3.4. TG-DSC
The TG-DSC analysis was employed to investigate the thermal
stability of the catalysts. The thermograms of the samples are
presented in Fig. 4. The thermogravimetric (TG) curve of
BAIL@SBA-15 showed an initial weight loss of ꢃ10% up to
ꢀ
1
00 C, which is attributed to the release of physisorbed water
and residual solvent in supported catalysts. A signicant weight
ꢀ
loss of ꢃ30% was found in the temperature range of 200–400 C
because of the organic components of ionic liquid and the
propyl of 3-chloropropyltriethoxysilane separated from the
surface of support. The peaks in the DSC curve also prove this
Fig. 3
2
N adsorption–desorption isotherms of the catalysts.
process. Therefore, the catalysts can be operated stably under
ꢀ
1
00 C (Table 1).
Table 1 Physical properties of the supported ionic liquid
3.5. Ketalization of cyclohexanone with glycol
BET
surface area,
Pore
volume,
Bonding
amount
The catalytic activity of several supported ILs were evaluated on
the ketalization of cyclohexanone with glycol under the opti-
mized reaction condition and the results were listed in Table 2.
It can be observed that the molecular sieve SBA-15 as catalyst
has 22.6% conversion of cyclohexanone (CYC), which demon-
strates molecular sieve SBA-15 has relatively poor catalytic
activity (Table 2, entry 4). With the successful immobilization of
2
ꢁ1
3
ꢁ1
ꢁ1
ꢀ
p
D (A) (mmol g )
Samples
SBET (m g
)
V
p
(cm g
)
SBA-15
BAIL@SBA-15
Silica gel
541.8
42.9
297.1
1.3
0.2
0.5
0.4
97.2
125.2
65.0
0
1.5342
0
0.4418
BAIL@Silica gel 262.9
73.8
ionic liquid [Bsmim][HSO ] on molecular sieve, the BAIL@SBA-
4
15 gave a drastic increase in the catalytic activity and the
conversion of cyclohexanone was 85.2% (Table 2, entry 1).
However, there is little inferior to the corresponding homoge-
neous catalyst of [BSmim][HSO ] (Table 2, entry 3) under the
4
And the ionic liquid [BSmim][HSO ] had been immobilized on
the surface of SBA-15.
4
same condition. The heterogeneous catalyst BAIL@SBA-15 can
remain high catalytic performance, even though the catalyst
loading content of Brønsted acidic ionic liquid was obviously
less than the pure BAIL. Therefore, the molecular sieve SBA-15
plays a signicant roles on the immobilized catalyst. The
cooperative pathway of catalyst system enhances the conversion
of cyclohexanone in the ketalization reaction. It could also be
found that the SBA-15 supported acidic ionic liquid has much
higher activity than the support materials of silica gel.
3
.3.
N
2
adsorption–desorption
The N
2
adsorption–desorption isotherms and pore size distri-
bution of the mesoporous materials and catalysts are depicted
in Fig. 3. The textural properties such as the BET surface areas,
pore diameter and pore volume derived from the N adsorp-
tion–desorption measurements are included in Table 1. It is
clear that the obtained isotherms are similar to type IV isotherm
curve with H1-type hysteresis loop, characteristic of highly
ordered mesoporous materials according to the IUPAC classi-
2
3.6. Inuence of reaction parameters on the ketalization

cation. Adsorption data were obtained over a relative pressure
ranging from 0.01 Pa to 0.99 Pa. The BAIL@SBA-15 exhibits SBA-15 supported acidic ionic liquid was selected as catalyst in
a hysteresis loop and a sharp increase in pore volume adsorbed the ketalization reaction to optimize the reaction condition
above a relative pressure (P/P ) at 0.7 Pa.
since BAIL@SBA-15 showed excellent catalytic activity. The
0
The physical properties of molecular sieve, silica gel and effect of reaction parameters such as reaction temperature,
immobilized catalysts are shown in Table 1. Compared to parent reaction time, catalyst loading, reactant molar ratio were
mesoporous materials, the surface area of SBA-15 decreased from investigated.
2
ꢁ1
2
ꢁ1
5
41.8 m g to 42.9 m g with the increasing of pore size from
3.6.1. Effect of reaction temperature. The effect of reac-
9
.7 nm to 12.5 nm. This is attributed to the immobilization of tion temperature was performed in the presence of
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
BAIL onto the framework of molecular sieve. The immobilization BAIL@SBA-15 at 30 C, 40 C, 50 C, 60 C, 70 C. As shown in
of ionic liquids blocked a small fraction of the pores, which leads Fig. 5, the conversion of cyclohexanone increased from
to the increasing of the average pore size and the aggregation of 73.9% to 85.2% when the reaction temperature increased
adjacent plate-like particles. The surface modication is probably from 30 C to 50 C. And the conversion of cyclohexanone
a multi-layered process, in which additional ILs molecules increased rapidly when the temperature is lower than 50 C
ꢀ
ꢀ
ꢀ
ꢀ
interact with those covalent attached to the supports surface. and slowly aer 50 C. A reasonable explanation for this
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observation may be that the ketalization reaction is an
ꢀ
endothermic reaction and reached equilibrium at 50 C.
ꢀ
Therefore, 50 C is the optimum reaction temperature.
3.6.2. Effect of catalyst loading. The conversion of cyclo-
hexanone increased signicantly when the catalyst loading is
lower than 1.3% (Fig. 6), which means that increase of catalyst
loading is conductive to the ketalization reaction. It can be
seen that the conversion of cyclohexanone was enhanced with
the increasing of the catalyst loading content from 0.33% to
1
.3%. However, there is little change in the conversion of
cyclohexanone when the amount of catalyst was increased
from 1.3% to 3.9%. This implies that further increase in the
amount of catalyst is not necessary for the conversion of
Fig. 5 Effect of reaction temperature on the conversion of cyclo-
cyclohexanone. Therefore, the preferable catalyst loading hexanone. Reaction conditions: n(EG) : n(CYC) ¼ 2, n(IL) : n(CYC) ¼
1
.3%, 3 h.
content of supported catalyst is 1.3%.
a
Table 2 Ketalization of cyclohexanone with glycol
3.6.3. Effect of reaction time. In order to study the reaction
time on the ketalization reaction, the experiment was per-
formed taking reaction time ranging from 0.5 h to 5 h. As can be
seen from Fig. 7, the conversion of cyclohexanone increases
from 40.9% to 85.1% by increasing the reaction time from 0.5 h
to 3 h. Extending reaction time to 5 h, the conversion of cyclo-
henxanone increased to 86.4%. Hence, it is not practical to
promote the conversion of cyclohexanone by prolonging reac-
tion time and the required time to reach the equilibrium is 3 h.
Conversion
of CYC/(%)
Entry
Catalyst
Selectivity/(%)
1
2
3
4
5
BAIL@SBA-15
BAIL@Silica gel
[BSmim][HSO
SBA-15
85.2
79.1
88.7
22.6
0.5
100
100
100
100
100
b
4
]
Blank
a
Reaction conditions: cyclohexanone (30 mmol), glycol (60 mmol),
catalyst (1.3%, based on the mole ratio of cyclohexanone), reaction
3.6.4. Effect of reactant molar ratio. The effect of the molar
ꢀ
b
ratio of ethylene glycol (EG) to cyclohexanone (CYC) in the range
of 1.0 to 2.5 on the conversion of cyclohexanone was shown in
Fig. 8. It can be seen that the conversion of cyclohexanone is
sensitive to the reactant molar ratio. With EG : CYC increased
from 1 : 1 to 2 : 1, the conversion of cyclohexanone was
enhanced from 58.1% to 85.1%. However, further increase of
the molar ratio to 2.5 : 1 resulted in a decrease in conversion
due to the reduction of catalyst concentration . Thus the most
suitable molar ratio of EG : CYC was 2 : 1.
temperature (50 C), reaction time 3 h. The molar ratio of
BSmim][HSO ] is 10%.
[
4
3.7. Mechanism
The possible mechanism for hydrogen bond between anion of
ionic liquid and support was shown in Scheme 2. The supported
Fig. 6 Effect of catalyst dosage on the conversion of cyclohexanone.
Reaction conditions: n(EG) : n(CYC) ¼ 2, 3 h, 50 ꢀC.
Fig. 4 TG-DSC curves of supported ILs (a) BAIL@SBA-15; (b) BAIL@-
Silica gel.
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Fig. 7 Effect of reaction time on the conversion of cyclohexanone. Fig. 8 Effect of catalyst dosage on the conversion of cyclohexanone.
ꢀ
ꢀ
Reaction conditions: n(EG) : n(CYC) ¼ 2, n(IL) : n(CYC) ¼ 1.3%, 50 C.
Reaction conditions: n(IL) : n(CYC) ¼ 1.3%, 3 h, 50 C.
hydrogen bonding with supports. Therefore, the supported
ionic liquid can be reused for several times with small loss in
the selectivity and cyclohexanone conversion.
Ketalization is a reversible reaction and the possible two-step
mechanism for ketalization of cyclohexanone with glycol over
17,41
BAIL@SBA-15 was consistent with the reported ones.
Scheme 3 envisages the mechanism of the ketalization of
cyclohexanone with glycol using SBA-15 supported ionic liquid.
In the rst step, the cyclohexanone is protonated by the acid site
+
of BAIL@SBA-15 (H ions of the catalyst) to produce the inter-
mediate 2 and then activated for nucleophilic addition of O
atom of the alcohol to form the hemiacetal 4. Protonation of 4
leads to intermediate 5 which undergoes subsequent dehydra-
tion to give 6. It accepted a second molecule of alcohol hydroxyl
group to give intermediate 7. This step is also an exothermic
reaction, and last, removal of a proton from 7 leads to the
formation of the ketal 8.
Scheme 2 The possible mechanism for hydrogen bond between
anion of ionic liquid and support.
ionic liquids catalyst system is likely operated in a cooperative
pathway. Cation of ionic liquid was rmly immobilized through
the covalent bonds to the surface of the supports and the anion
was also not easily lost because of ionic bonding with cation and 3.8. Recycling of catalyst
The recovery of catalyst is highly preferable from both envi-
ronmental and economic points of view. The reusability of the
SBA-15 supported ionic liquid was investigated in the ketaliza-
tion of cyclohexanone with glycol, and the result was shown in
Fig. 9. In each cycle, the catalyst was easily recovered by
centrifugation and washed with dichloromethane for three
Scheme
3
General reaction mechanism for the ketalization of Fig. 9 The recycle test of BAIL@SBA-15 in the ketalization of cyclo-
cyclohexanone with glycol.
hexanone with glycol.
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times, followed by drying under vacuum before the next run. As
shown in Fig. 9, the catalyst BAIL@SBA-15 can be readily
9 H. H. Wu, F. Yang, P. Cui, J. Tang and M. Y. He, Tetrahedron
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9
2.0%, respectively.
The recovered catalyst that reused for ve times has no obvious
12 P. Wasserscheid, M. Sesing and W. Korth, Green Chem.,
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analysis, the graing amount of ionic liquid on BAIL@SBA-15
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ꢁ
1
ꢁ1
decreased from 1.5342 mmol g
to 0.4820 mmol g
aer 15 C. Feher, E. Krivan, J. Hancsok and R. Skoda-Foeldes, Green
ꢁ
being used for 5 times. It was found that the loss of anion HSO4
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1
7 J. Miao, H. Wan, Y. Shao, G. Gua and B. Xu, J. Mol. Catal. A:
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4
. Conclusions
In summary, a series of mesoporous materials SBA-15 and amor- 18 P. Sharma and M. Gupta, Green Chem., 2015, 17, 1100–1106.
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the Brønsted acidic ionic liquid [BSmim][HSO ] was proved to be 20 Z. M. Li, Y. Zhou, D. J. Tao, W. Huang, X. S. Chen and
2
4
successfully immobilized onto mesoporous materials and the
results show that BAIL@SBA-15 is more active in the ketalization 21 H. Jin, M. B. Ansari and S. E. Park, Catal. Today, 2015, 245,
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of BAIL@SBA-15 as catalyst, initial molar ratio of EG : CYC was 2 24 W. Xie and C. Zhang, Food Chem., 2016, 211, 74–82.
ꢀ
and reaction temperature is 50 C for 3 h. The possible mechanism 25 B. Lebeau, A. Galarneau and M. Linden, Chem. Soc. Rev.,
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general reaction mechanism for ketalization reaction was given. 26 K. A. Shah, J. K. Parikh and K. C. Maheria, Catal. Today, 2014,
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237, 29–37.
for ve times without a signicant loss of catalytic activity.
27 H. Zhao, N. Yu, Y. Ding, R. Tan, C. Liu, D. Yin, H. Qiu and
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2
8 S. Udayakumar, S. W. Park, D. W. Park and B. S. Choi, Catal.
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Conflicts of interest
There are no conicts to declare.
29 Z. Alothman, Materials, 2012, 5, 2874–2902.
30 F. Zhang, Y. Yan, H. Yang, Y. Meng, C. Yu, B. Tu and D. Zhao,
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1 C. Pirez, A. F. Lee, J. C. Manayil, C. M. A. Parlett and
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32 J. N. Appaturi, M. R. Johan, R. J. Ramalingam and H. A. Al-
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