Amphiphilic porous polyhedral oligomeric silsesquioxanes (POSS) incorporated polyoxometalate-paired polymeric hybrids: Interfacial catalysts for epoxidation reactions

Article abstract of DOI:10.1039/c4ra16956e

A new strategy to fabricate amphiphilic polyoxometalate (POM)-paired polymeric hybrids via a free radical polymerization process using polyhedral oligomeric vinylsilsesquioxanes (POSS) and ionic liquids as the building block, followed by ion exchange was designed. The obtained hybrids were demonstrated to be porous materials with excellent amphiphilic properties, and can behave as efficient interfacial catalysts for the epoxidation of alkenes with H₂O₂ by stabilizing Pickering emulsions. The catalysts could be recovered by centrifugation and reused with no appreciable deactivation. The unique amphiphilic porous structure is revealed to be responsible for the catalysts' excellent performances in the epoxidation reaction by accelerating the mass transfer. This journal is

Full text of DOI:10.1039/c4ra16956e

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PAPER
Amphiphilic porous polyhedral oligomeric
silsesquioxanes (POSS) incorporated
polyoxometalate-paired polymeric hybrids:
interfacial catalysts for epoxidation reactions†
a
Cite this: RSC Adv., 2015, 5, 17709
Yan Leng, Jiwei Zhao,a Pingping Jianga and Jun Wangb
*
A new strategy to fabricate amphiphilic polyoxometalate (POM)-paired polymeric hybrids via a free radical
polymerization process using polyhedral oligomeric vinylsilsesquioxanes (POSS) and ionic liquids as the
building block, followed by ion exchange was designed. The obtained hybrids were demonstrated to be
porous materials with excellent amphiphilic properties, and can behave as efficient interfacial catalysts
for the epoxidation of alkenes with H2O2 by stabilizing Pickering emulsions. The catalysts could be
recovered by centrifugation and reused with no appreciable deactivation. The unique amphiphilic porous
structure is revealed to be responsible for the catalysts' excellent performances in the epoxidation
reaction by accelerating the mass transfer.
Received 24th December 2014
Accepted 5th February 2015
DOI: 10.1039/c4ra16956e
www.rsc.org/advances
and recycling aer operation. However, this method still
involves cumbersome and lengthy catalyst preparation proce-
1. Introduction
dures, and leaching of the active components. Therefore, a
novel methodology for creating amphiphilic POM-based cata-
lyst systems is needed.
The construction and exploration of amphiphilic structures is
an area of growing research interest and technical importance
in the design of advanced functional materials and devices.1,2 In
this context a variety of materials involving metal ions, bioma-
terials, and copolymers, have been constructed and explored for
their potential applications in diverse elds.3–5 Poly-
oxometalates (POMs) are a class of transition metal oxygen
cluster and have been widely used as homogeneous catalysts for
H2O2-based oxidation reactions.6–9 Nevertheless, when (hydro-
philic) aqueous H2O2 is used as the oxidant in organic trans-
formations, one of the most troublesome problems is the
insolubility of organic substances. Inspired by conventional
amphiphiles, a number of amphiphilic POM catalytic systems
have been reported, including phase transformation10 and
microemulsion formation.11–13 However, most of these systems
are homogeneous and suffer from poor catalyst recovery.
Recently, the surface modication of metal oxide or silica
matrix supported POM catalysts with hydrophilic and hydro-
phobic functional groups has proved to be an effective solution
to form amphiphilic solid POM catalysts,14,15 which can be
utilized in heterogeneous catalysis, allowing facile separation
Poly(ionic liquids) (PILs) resulting from the polymerization
of ionic liquids (IL) monomers or copolymerization of ILs with
other monomers are shown to constitute an interesting system
to develop amphiphilic materials.16,17 By varying the cations
and/or anions with specic functions that constitute IL's
structure, it is possible to design abundant PILs with required
functionalities.18,19 Indeed, POM-anions have been used as the
counter anions for preparing “task-specic” ionic hybrids,20,21
and several IL–POMs have been reported as efficient homoge-
neous, heterogeneous, or phase-separation catalysts for organic
transformations.22–25 In our recent work, an amphiphilic POM-
paired PIL catalyst was prepared by employing the long chain
alkyl imidazole ILs and carboxylic acid-functionalized imid-
azole ILs, and used as a highly efficient and recyclable hetero-
geneous catalyst in epoxidation of olens with H2O2.26,27
Polyhedral oligomericsilsesquioxanes (POSS) are organic–
inorganic molecules, with the general formula R8Si8O12 where R
is hydrogen or organic groups, such as alkyl, aryl or any of their
derivatives.28,29 Their unique star-shaped nanostructures and
chemical properties, such as facile chemical modication, good
pH tolerance, high temperature and oxidation resistance
properties, make POSS an excellent building block for con-
structing multi-functional materials.30–32 Taking into account
that the incorporation of POSS into organic or inorganic poly-
mer could create a micro/mesoporous matrix33,34 and the fact
that porous framework structure of the solid catalysts would
aThe Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School
of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China.
E-mail: lengyan1114@126.com; Fax: +86-510-85917763; Tel: +86-510-85917090
bState Key Laboratory of Materials-Oriented Chemical Engineering, College of
Chemistry and Chemical Engineering, Nanjing Tech University, Nanjing 210009,
China
† Electronic
supplementary
information
(ESI)
available:
Catalyst
characterizations. See DOI: 10.1039/c4ra16956e
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favor the increase of their catalytic performances because of
[3-Propionic acid-1-vinylimidazolium]Br (CIM): N-vinyl-
benets of structural stability and mass transfer, to construct imidazole (9.42 g, 0.10 mol) and 3-bromopropionic acid (15.30
POSS-containing porous POM-based PIL hybrids with more g, 0.10 mol) were dissolved in ethanol (50 mL). Then, the
structural stability for application in H2O2-based oxidation mixture was stirred at 80 ꢁC for 24 h under nitrogen atmo-
catalysis is not only feasible but also protable, and the multi- sphere. On completion, the white solid of CIM was obtained
functional designability of polymeric IL cations can meet the aer the removing of solvent and washing with acetonitrile for
1
requirement described above.
three times. H NMR (400 MHz, D2O, TMS) for CIM d (ppm) ¼
Herein, an innovative exploitation of POSS as building block 3.01 (t, 2H, –CH2), 4.72 (t, 2H, –CH2), 5.45 (d, 1H, –CH), 5.81 (d,
for constructing porous POM-based polymeric hybrid catalysts 1H, –CH), 7.17 (m, 1H, –CH), 7.63 (s, 1H, –CH), 7.79 (s, 1H,
(POSS–DIMx–CIMy–PW) with amphipathicity is proposed. –CH), 9.12 (s, 1H, –CH) (ESI, Fig. S2†).
POSS–DIMx–CIMy–PW are prepared by copolymerization of
Preparation of octavinyl POSS. Octavinyl POSS was prepared
octavinyl POSS, dodecyl imidazole IL (DIM), and carboxylic acid- according to the previous literature.35 Typically, in a 250 mL
functionalized imidazole IL (CIM) without using any templates, ask, vinyltriethoxysilane (19 g, 0.1 mol) was dissolved in 50 mL
followed by ion exchange with the [PO4(WO3)4]3ꢀ species. The anhydrous ethanol. Then 10 mL hydrochloric acid and 8 mL
resulting catalysts are fully characterized by SEM, TEM, CHN deionized water were added into the above solution with
elemental analysis, BET, contact angles (CA) tests, FT-IR, TG, vigorous stirring. The above reaction mixture was allowed to
and Raman (ESI†). Catalytic tests have shown that the POSS– react for 48 h at room temperature. On completion, the white
DIMx–CIMy–PW exhibit extraordinary catalytic activities and crystalline powder was ltered, washed with anhydrous ethanol,
recyclability in epoxidation of alkenes with H2O2.
recrystallized in tetrahydrofuran/methanol (volume ratio: 1 : 3)
mixture solvent and dried in vacuum at 80 ꢁC for 10 h. 29Si NMR
(400 MHz, CDCl3, TMS) d (ppm) ¼ 80.19 (ESI, Fig. S3†).
Preparation of POSS–DIMx–CIMy. POSS–DIMx–CIMy (x and y
stands for the molar ratio of DIM with POSS and CIM with
POSS, respectively) were synthesized through free radical poly-
merization of octavinyl POSS, DIM, and CIM. As a typical run for
the synthesis of POSS–DIM3–CIM5, the obtained octavinyl POSS
(0.63 g, 1 mmol), DIM (1.03 g, 3 mmol), CIM (1.24 g, 5 mmol),
and azodiisobutyronitrile (AIBN, 0.06 g) were dissolved in a
mixture solvent (1,4-dioxane 20 mL and methanol 20 mL). Then
the solution was stirred at 75 ꢁC for 24 h. Aer reaction, the
above mixture was added dropwise into deionized water (100
mL) to afford the solid product. Elemental analysis, found: C:
45.32%, N: 7.93%, and H: 6.08%. Then the solid product POSS–
DIMx–CIMy was ltered, washed with ethanol and dried under
vacuum. The control polymers of POSS–DIM8 and POSS–CIM8
were prepared accordingly.
Preparation of POSS–DIMx–CIMy–PW. POM-paired ionic
copolymer POSS–DIMx–CIMy–PW was prepared from the reac-
tion between POSS–DIMx–CIMy and phosphotungstate
(H3PO4(WO3)4, abbreviate as PW) in aqueous solution at room
temperature for 2 h. The starting molar ratio of POSS–DIMx–
CIMy to PW was 1 : (x + y)/3. Typically, a solution of H3PO4 (0.25
g, 2.5 mmol) in water (5 mL) was added to a solution of 2.5 g
H2WO4 (10 mmol) in water (15 mL) and 30 wt% H2O2 (7 mL), the
mixture was reacted for 30 min at room temperature with stir-
2. Experimental section
2.1 Materials and methods
All chemicals were analytical grade and used as received. FT-IR
spectra were recorded on a Nicolet 360 FT-IR instrument (KBr
discs) in the 4000–400 cmꢀ1 region. 1H-NMR and 29Si NMR
spectra were measured with a Bruker DPX 400 spectrometer at
ambient temperature in D2O or CDCl3 using 2,2-dimethyl-2-
silapentane-5-sulfonate or TMS as internal reference. SEM
image was performed on a HITACHI S-4800 eld-emission
scanning electron microscope. TG analysis was carried out
ꢁ
with a STA409 instrument in dry air at a heating rate of 10 C
minꢀ1. TEM images were obtained with JEOL JEM-2100 electron
microscope operated at 200 kV. The pore size distribution was
derived from the desorption branch of N2 isotherms using
Barrett–Joyner–Halenda (BJH) method. Water repellency was
checked by the contact angle of a pure water droplet using a
contact angle meter of OCA 40. Elemental analyses (C, H, N)
were performed on a CHN elemental analyzer (FlashEA 1112).
The amount of leached tungsten species in the ltrate was
measured using a Jarrell-Ash 1100 ICP-AES spectrometer.
2.2 Catalyst preparation
Preparation of IL monomers DIM and CIM. [3-Dodecyl-1- ring. Then POSS–DIMx–CIMy (2.0 g) dissolved in anhydrous
vinylimidazolium]Br (DIM): N-vinylimidazole (9.42 g, 0.10 ethanol (20 mL) was added drop wise into the above solution.
mol) and bromododecane (25.0 g, 0.10 mol) were dissolved in The mixture was stirred vigorously at room temperature for 2 h.
ethanol (50 mL). Then, the mixture was stirred at 80 ꢁC for 48 h The solid product POSS–DIM3–CIM5–PW was ltered, washed
under nitrogen atmosphere. On completion, the solvent was with small amount of water and ethanol, and dried. Elemental
removed by distillation, and the solid product was washed with analysis, found: C: 25.76%, N: 4.59%, and H: 3.66%.
anhydrous acetone for three times to remove the unreacted
1
substrates. Aer drying under vacuum, DIM was obtained. H
2.3 Catalytic tests
NMR (400 MHz, CDCl3, TMS) d (ppm) ¼ 0.97 (s, 3H, –CH3), 1.28
(m, 18H, –CH2), 1.87 (m, 2H, –CH2), 3.32 (m, 2H, –CH2), 5.48 (d, Cyclooctene (10 mmol), acetonitrile (10 mL), and catalyst (0.1 g,
1H, –CH), 5.95 (d, 2H, –CH2), 7.15 (d, 2H, –CH), 7.68 (d, 1H, 0.035 mmol) were added into a 25 mL ask. Then 30 wt% H2O2
ꢁ
–CH) (ESI, Fig. S1†).
(12 mmol) was added into the solution at 70 C within 10 min
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under vigorous stirring. Aer reaction, the reaction mixture was
centrifuged to remove the solid catalyst, and the liquid was
analyzed by
a gas chromatography (GC). Other alkene
substrates were tested accordingly. A ve-run catalyst recycling
was carried out for testing the reusability of catalyst. The cata-
lyst was recovered by a centrifugation, washed with ethanol, and
dried in vacuum.
3. Results and discussion
3.1 Catalyst preparation and characterization
The preparation of the POM-paired polymeric hybrids was
carried out according to the procedures shown in Fig. 1. The IL
monomers DIM and CIM were rst prepared and characterized
1
by H NMR. The PIL POSS–DIMx–CIMy was synthesized by the
free radical copolymerization of octavinyl POSS, DIM and CIM
using AIBN as the initiator. By varying the molar ratio of DIM
and CIM to octavinyl POSS, a series of ionic copolymers POSS–
DIMx–CIMy could be prepared in the same way. The nal cata-
lyst POSS–DIMx–CIMy–PW was obtained by the anion-exchange
of POSS–DIMx–CIMy with the previously prepared
H3[PO4(WO3)4] in aqueous solution. Typically, the SEM image of
POSS–DIM3–CIM5–PW shows the irregular coral-shaped
morphology with micrometer size and nanoscale hollow struc-
ture (Fig. 2A). The TEM image in Fig. 2B conrms the amor-
phous nature of the polymeric hybrid POSS–DIM3–CIM5–PW. In
the high-resolution TEM image, the observed dark nano-
particles with small size of about 1 nm indicate that the intro-
duced PW has been uniformly dispersed in the PIL network.
The TG patterns (Fig. 2C) for the POSS–DIM3–CIM5–PW shows a
high thermal stability up to ca. 250 ꢁC, which is higher than that
of the conventional organic polymers. In addition, these
obtained polymeric hybrids are insoluble in most common
solvents, including water, acetonitrile, methanol, ethyl acetate,
DMF, DMSO, and acetic acid at low temperatures, and thus can
be used as the heterogeneous catalysts.
Fig. 2D illustrates the FT-IR spectra of polymeric hybrids
POSS–DIM3–CIM5 and POSS–DIM3–CIM5–PW. The FT-IR spec-
trum of POSS–DIM3–CIM5 (Fig. 2D, curve a) clearly shows the
band at 1113 cmꢀ1 assigned to asymmetric vibration of Si–O–Si
and the characteristic bands at 1740, 1570, and 2854–2930 cmꢀ1
that are attributed to C]O, C]N, and CH2 stretching vibra-
tions, respectively, indicating the coexistence of POSS and IL
units. Aer the combination of POSS–DIM3–CIM5 with
H3[PO4(WO3)4] (Fig. 2D, curve b), the peaks assigned to Si–O–Si
Fig. 2 (A) SEM image of POSS–DIM3–CIM5–PW; (B) TEM image of
POSS–DIM3–CIM5–PW; (C) TG curves of (a) POSS–DIM3–CIM5–PW
and (b) POSS–DIM3–CIM5; (D) FT-IR spectra of (a) POSS–DIM3–CIM8
and (b) POSS–DIM3–CIM5–PW.
and organic moiety in POSS–DIM3–CIM5–PW are consistent with
those of the IR spectrum for individual POSS–DIM3–CIM5.
Moreover, characteristic vibration bands for the [PO4(WO3)4]3ꢀ
species are observed for POSS–DIM3–CIM5–PW at 1080, 951, 883
and 820 cmꢀ1, assignable to vibrations of P–Oa, W]Od, W–Ob–
W and W–Oc–W, respectively, which are in reasonable agree-
ment with those of the IR spectra for [PO4(WO3)4]3ꢀ in previous
literatures.10,36–39 Additionally, the Raman spectrum of POSS–
DIM3–CIM5–PW (ESI, Fig. S6†) shows the characteristic bands at
951, 989, and 1007 cmꢀ1 for tungstate polyoxoanion vibrations,40
which further conrms the structure of [PO4(WO3)4]3ꢀ anion.
Fig. 3A and B show the N2 adsorption–desorption isotherms
and the corresponding pore size distributions of the prepared
polymeric hybrids, respectively. The POSS-free polymeric hybrid
DIM3–CIM5–PW is a nonporous material with a surface area of
only 6.2 cm2 gꢀ1 (curve e in Fig. 3A and B, Table 1, entry 5). For
the POSS-containing polymeric hybrids POSS–DIMx–CIMy–PW,
all the samples display a typical IV type isotherm, giving a steep
increase at a relative pressure of 0.8 < P/P0 < 1, indicating the
presence of porous structures, including mesopores and mac-
ropores. This demonstrates that the POSS plays an important
role in the pore formation. The optimum specic surface 24.2
cm2 gꢀ1 and pore volume 0.175 cm3 gꢀ1 are obtained when the
Fig. 1 Schematic illustration outlining the preparation and structure of the catalyst POSS–DIMx–CIMy–PW.
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Fig. 4 (A) Water droplets and (B) cyclooctene droplets on the surface
of catalysts (a) POSS–DIM3–CIM5–PW, (b) POSS–DIM5–CIM5–PW, (c)
POSS–DIM5–CIM3–PW, and (d) POSS–DIM8–CIM6–PW.
Fig. 3 (A) Nitrogen adsorption–desorption isotherms and (B) BJH
pore size distributions of (a) POSS–DIM3–CIM5–PW, (b) POSS–DIM5–
CIM5–PW, (c) POSS–DIM5–CIM3–PW, (d) POSS–DIM8–CIM6–PW, (e)
DIM3–CIM5–PW.
observed in a short reaction time of 1 h. It is noteworthy that
peroxyacids generated from the oxidation of carboxylic acid with
H2O2 in acetic acid solvent may take part in the epoxidation. In
order to conrm this, a control experiment without the addition
of catalyst was performed, and a conversion of 84.4% with 95%
selectivity was obtained in the reaction time of 4 h. When the
catalyst was added, the reaction rate signicantly increased, the
reaction proceeded well and completed within only 15 min. For
ethanol and methanol solvents, high conversions were also
obtained by prolonging the reaction time to 4 h. When ethyl
acetate and dichloroethane were used as a solvent, a liquid–
liquid biphasic reaction system was formed due to the immis-
cibility of these solvents with aqueous H2O2. Aer the addition
of POSS–DIM3–CIM5–PW, the catalyst tends to migrate toward
the oil/aqueous interface due to their amphiphilic feature
(Fig. 6a), and stable emulsions were formed aer stirring
(Fig. 6b). The optical microscopy image of the emulsion (Fig. 6c)
shows droplet sizes in the range of 5–10 mm. Aer the reaction,
the solid catalyst can be separated by centrifugation and recycled
in the next run. The phenomenon observed here is very similar
to that of the Pickering Interfacial Catalysis,41,42 that the
amphiphilic catalysts localized at the interface of both phases
can stabilize emulsions, allowing facile separation and recycling.
Herein, the formation of the Pickering emulsion enhances the
contact region, the substrates cyclooctene and H2O2 molecules
could inltrate into the amphiphilic catalyst effectively (Fig. 6d).
mole ratio of DIM to CIM is 3 : 5 (Table 1, entry 1). The higher
molar ratio of DIM to CIM leads to less porous systems, most
probably due to the blockage of channel by long chain dodecyl
in DIM.
The combination of the hydrophilic CIM with hydrophobic
DIM into a single POSS-containing polymeric hybrid structure
could generate unique amphiphilic property in principle. To
understand the wettability of these hybrids POSS–DIMx–CIMy–
PW, we carried out the CA tests. As can be seen in Fig. 4A, when
a water droplet is brought in contact with the surface of the
samples, it yields a CA of 62.8ꢁ on the surface of POSS–DIM3–
CIM5–PW, implying its hydrophilicity. The CAs increased from
62.8ꢁ to 105.8ꢁ as the molar ratio of DIM to CIM increased, the
enhanced hydrophobicity is attributable to the surface chem-
istry change due to the increasing of hydrophobic DIM in the
hybrid catalysts. With cyclooctene as the testing droplet, the
CAs were measured to be less than 5ꢁ for all samples (Fig. 4B),
demonstrating excellent surface lipophilicity. Therefore, the
above results indicate that the unique amphiphilic PW-paired
polymeric hybrids could be obtained through tuning the
content of DIM and CIM in POSS–DIMx–CIMy–PW.
3.2 Catalytic activity in the epoxidation reaction
The catalytic activity of the POSS–DIM3–CIM5–PW was tested in Thus, with ethyl acetate and dichloroethane as the solvent, very
the epoxidation of cyclooctene using H2O2 in various solvents high conversions (>98%) were obtained as well.
over the reaction times of 1 h, 2 h, and 4 h, respectively (Fig. 5).
Considering that the chlorocarbons have environment safety
During the reaction process, the catalyst POSS–DIM3–CIM5–PW problems such as high toxicity and carcinogenicity. Moreover,
was insoluble in all cases, and exhibited different catalytic the epoxidation process using acetic acid and H2O2 may cause
activities with satisfying selectivity above 99%. In the acetonitrile severe safety and corrosion problems relative to the peroxyacids.
and acetic acid solvents, excellent conversions ($99%) were Therefore, acetonitrile and ethyl acetate were selected as the
Table 1 The textural parameters of POSS–DIMx–CIMy–PW catalysts
SBETa (m2 gꢀ1
)
Vpb (cm3 gꢀ1
)
Dav (nm)
c
Entry
Samples
1
2
3
4
5
POSS–DIM3–CIM5–PW
POSS–DIM5–CIM5–PW
POSS–DIM5–CIM3–PW
POSS–DIM8–CIM6–PW
DIM3–CIM5–PW
24.2
18.6
18.8
12.9
6.2
0.175
0.11
0.113
0.101
0.062
30.3
28.6
29.4
24.3
15.2
a
BET surface area. b Total pore volume. c Average pore diameter.
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Table 2 Catalytic performances of various catalysts for the epoxida-
a
tion of cyclooctene with H2O2
Acetonitrile
Ethyl acetate
Entry Catalyst
Conb (%) Selc (%) Conb (%) Selc (%)
1
2
3
4
POSS–DIM3–CIM5
POSS–DIM8–PW
POSS–CIM8–PW
7
63
68
100
100
100
100
4
67
18
98
100
100
100
100
Fig. 5 Catalytic activities of POSS–DIM3–CIM5–PW in epoxidation of
cyclooctene with H2O2 in different solvents.a Reaction conditions:
catalyst (0.1 g), cyclooctene (10 mmol), 30% H2O2 (12 mmol), solvent
(10 mL), 70 ꢁC.
POSS–DIM3–CIM5–PW 100
a
Reaction conditions: 0.1 g catalyst, 10 mmol cyclooctene, 12 mmol
b
H2O2 (30%), 10 mL solvent, 70 ꢁC, 4 h. Conversion of the substrate.
c
Selectivity for the epoxide product.
solvent for the following catalytic investigation. The catalytic
activities of various control catalysts were assessed in compar-
ison to POSS–DIM3–CIM5–PW for epoxidation of cyclooctene
with H2O2. The results are shown in Table 2, it can be seen that
the POSS containing hybrids are all insoluble in the reaction
system, and caused heterogeneous catalysis. However, the PW-
free polymer POSS–DIM3–CIM5 shows very low activities (Table
2, entry 1), and CIM-free POSS–DIM8–PW and DIM-free POSS–
CIM8–PW (Table 2, entries 2 and 3) affords much lower
conversions than that POSS–DIM3–CIM5–PW did in both
acetonitrile and ethyl acetate solvents. It appears that the low
catalytic activities of POSS–DIM8–PW and POSS–CIM8–PW are
mostly due to the poor interfacial interaction, since the systems
using ethyl acetate as the solvent could hardly form an emul-
sion. Therefore, all the above comparisons suggest that the
coexistence of DIM and CIM unites in polymeric cations endows
the hybrid catalyst with unique amphiphilic feature, and plays
an important role for the emulsion catalytic system, which
account for the excellent catalytic performance.
To illustrate the inuence of the content of DIM and CIM on
the catalytic activity of hybrid catalysts, we also tested the
catalytic kinetics of POSS–DIMx–CIMy–PW for the epoxidation
of cyclooctene in acetonitrile and ethyl acetate, respectively
(Fig. 7). Pickering emulsions taking place in all cases, and very
high conversions are observed over these polymeric catalysts
with a reaction time of about 3 h. However, the reaction rates of
POSS–DIMx–CIMy–PW gradually decreased as the molar ratio of
DIM to CIM increased. This variation was also reected in their
pore structure as suggested by Nitrogen adsorption–desorption
characterization. It is thus propose that the catalytic activity of
POSS–DIMx–CIMy–PW is reasonably related to its porous
structure, and the comparatively high surface area and large
pore volume favor higher catalytic rate.
In order to investigate the scope of the amphiphilic porous
catalyst for epoxidation reactions, the substrates such as
cyclohexene, 1-octene, 1-hexene, cis-3-hexenol, and bipentene
were also investigated on the catalyst POSS–DIM3–CIM5–PW,
with the results shown in Table 3. It can be seen that the present
catalyst POSS-DIM3–CIM5–PW could be applied to the epoxi-
dation of various alkenes using H2O2, and good to excellent
activities and selectivity were obtained.
Fig. 6 (a) Photograph of POSS–DIM3–CIM5–PW appeared at the
H2O2/(cyclooctene + ethyl acetate) interface; (b) photograph of the
reaction system after stirring for 10 min; (c) optical micrograph of the Fig.
7
Time profile of epoxidation of cyclooctene catalyzed by
emulsions; (d) scheme of amphiphilic catalysts located at the H2O2/ different catalysts in (A) acetonitrile and (B) ethyl acetate solvents.
(cyclooctene + ethyl acetate) interface for the epoxidation of cyclo- Reaction conditions: 0.1 g catalyst, 10 mmol cyclooctene, 12 mmol
octene with H2O2.
H2O2 (30%), 10 mL solvent, 70 ꢁC.
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Table 3 Epoxidation of various alkenes with H2O2 catalyzed by POSS–
DIM3–CIM5–PWa
Entry
Substrate
Reaction time (h)
Conb (%)
Selc (%)
1
2
3
4
5
6
Cyclooctene
Cyclohexene
1-Octene
1-Hexene
cis-3-Hexenol
Bipentene
1
3
6
4
4
4
99
98
56
49
99
86
100
95
100
100
94
98
a
Reaction conditions: catalyst (0.1 g), substrate (10 mmol), 30% H2O2
b
(12 mmol), acetonitrile (10 mL), 70 ꢁC. Conversion of the substrate.
Fig. 9 FTIR spectra of (a) fresh POSS–DIM3–CIM5–PW and (b) recy-
cled POSS–DIM3–CIM5–PW.
c
Selectivity for the epoxide product. Byproducts for entry 2: 2-
cyclohexen-1-ol (0.93 mmol) and 2-cyclohexen-1-one (0.51 mmol);
entry 3: octylaldehyde; entry 4: 2-hexenone; entry 5: 3,4-epoxyhexane-1-
aldehyde; entry 6: 1,2:8,9-diepoxy-p-menthane and 1,2-ene-p-menth-
8,9-epoxy.
4. Conclusion
In summary, we have demonstrated the successful application
of octavinyl POSS and IL as building blocks for constructing
amphiphilic porous POM-paired ionic hybrids POSS–DIMx–
CIMy–PW via free radical polymerization and ion exchange
reaction. The obtained hybrids were found to be highly efficient
interfacial catalysts for epoxidation of alkenes with H2O2 as
oxidant. The catalyst was recovered easily and reused for ve
runs without observing loss in catalytic activity. The overall
superior catalytic activity, high selectivity and excellent recy-
clability of POSS–DIM3–CIM5–PW as a heterogeneous catalyst
could be attributed to its amphiphilic surface and pore struc-
ture, which allow for a rapid diffusion of the reactants into the
reactive PW centers.
3.3 Catalyst reusability
Finally, the reusability of amphiphilic porous catalyst was
evaluated on the epoxidation of cyclooctene over POSS–DIM3–
CIM5–PW. Aer each cycle, the catalyst was separated from the
reaction system by centrifugation, washed with ethanol, and
ꢁ
dried at 80 C. As shown in Fig. 8, the ve-run test gave 100%
selectivity without signicant loss of conversion. It is explicitly
more stable than our previous prepared POSS-free polymeric
POM hybrid.27 The IR spectrum for the recovered POSS–DIM3–
CIM5–PW in Fig. 9 was well consistent with that of the fresh one,
revealing a durable catalyst structure. However, the intensities
of the IR bands for the PW decreased lightly. Moreover, the
results of ICP-AES analysis for the reacted ltrate showed that
about 3.1 wt% W in the catalyst has been leached into the
reaction media in the rst run, but in the followed runs, the
Acknowledgements
leaching amounts were negligible. It is thus supposed that there The authors thank the National Natural Science Foundation of
is a small amount of PW in the fresh catalyst that only losely
interacts with polymeric cations tends to leach into the liquid
phase in the rst reaction run. The above result implies that the
featured three dimensional network framework of POSS–DIM3–
CIM5–PW derived from POSS units endows the catalyst with
excellent structural stability, and accounts for the steadily
catalytic reuse.
China (no. 21206052 and 21136005), the Opening Foundation
of the State Key Laboratory of Materials-Oriented Chemical
Engineering (no. KL13-09), and MOE & SAFEA for the 111
Project (no. B13025).
Notes and references
1 T. Chen, S. Xu, T. Zhao, L. Zhu, D. Wei, Y. Li, H. Zhang and
C. Zhao, ACS Appl. Mater. Interfaces, 2012, 4, 5766–5774.
2 W. Cao and L. Zhu, Macromolecules, 2011, 44, 1500–1512.
3 B. S. Souza, E. C. Leopoldino, D. W. Tondo, J. Dupont and
F. Nome, Langmuir, 2012, 28, 833–840.
4 J. Hu, T. Wu, G. Zhang and S. Liu, J. Am. Chem. Soc., 2012,
134, 7624–7627.
5 Y. M. A. Yamada, S. M. Sarkar and Y. Uozumi, J. Am. Chem.
Soc., 2012, 134, 9285–9290.
6 Y. Song and R. Tsunashima, Chem. Soc. Rev., 2012, 41, 7384–
7402.
7 H. Lv, Y. V. Geletii, C. Zhao, J. W. Vickers, G. Zhu, Z. Luo,
J. Song, T. Lian, D. G. Musaev and C. L. Hill, Chem. Soc.
Rev., 2012, 41, 7572–7589.
8 Y. Zhou, G. Chen, Z. Long and J. Wang, RSC Adv., 2014, 4,
42092–42113.
Fig. 8 Catalytic reusability of POSS–DIM3–CIM5–PW for the epoxi-
dation of cyclooctene with H2O2. Reaction conditions: catalyst (0.1 g),
cyclooctene (10 mmol), 30% H2O2 (12 mmol), acetonitrile (10 mL), 70
ꢁC, 2 h.
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Paper
RSC Advances
9 N. Mizuno, K. Yamaguchi and K. Kamata, Coord. Chem. Rev., 26 Y. Leng, J. Zhao, P. Jiang and J. Wang, ACS Appl. Mater.
2005, 249, 1944–1956. Interfaces, 2014, 6, 5947–5954.
10 Z. Xi, N. Zhou, Y. Sun and K. Li, Science, 2001, 292, 1139– 27 Y. Leng, J. Wu, P. Jiang and J. Wang, Catal. Sci. Technol.,
1141. 2014, 4, 1293–1300.
11 J. Xu, S. Zhao, Y. Ji and Y. Song, Chem.–Eur. J., 2013, 19, 709– 28 K. Tanaka, F. Ishiguro and Y. Chujo, J. Am. Chem. Soc., 2010,
715. 132, 17649–17651.
12 J. Gao, Y. Zhang, G. Jia, Z. Jiang, S. Wang, H. Lu, B. Song and 29 M. C. Kung, M. V. Riofski, M. N. Missaghi and H. H. Kung,
C. Li, Chem. Commun., 2008, 332–334. Chem. Commun., 2014, 50, 3262–3276.
13 P. Yin, J. Wang, Z. Xiao, P. Wu, Y. Wei and T. Liu, Chem.–Eur. 30 J. Han, Y. Zheng, S. Zheng, S. Li, T. Hu, A. Tang and C. Gao,
J., 2012, 18, 9174–9178. Chem. Commun., 2014, 50, 8712–8714.
14 K. Inumaru, T. Ishihara, Y. Kamiya, T. Okuhara and 31 Z. Ruan, W. Rong, X. Zhan, Q. Li and Z. Li, Polym. Chem.,
S. Yamanaka, Angew. Chem., Int. Ed., 2007, 46, 7625–7628. 2014, 5, 5994–6002.
15 F. Su, L. Ma, Y. Guo and W. Li, Catal. Sci. Technol., 2012, 2, 32 K. Tanaka and Y. Chujo, J. Mater. Chem., 2012, 22, 1733–
2367–2374. 1746.
16 Y. M. A. Yamada, S. M. Sarkar and Y. Uozumi, J. Am. Chem. 33 M. Seino, W. Wang, J. E. Lofgreen, D. P. Puzzo, T. Manabe
Soc., 2012, 134, 9285–9290.
17 D. Mecerreyes, Prog. Polym. Sci., 2011, 36, 1629–1648.
18 D. Chaturvedi, Curr. Org. Chem., 2011, 15, 1236–1248.
and G. A. Ozin, J. Am. Chem. Soc., 2011, 133, 18082–18085.
34 H. Lin, J. Ou, Z. Zhang, J. Dong and H. Zou, Chem. Commun.,
2013, 49, 231–233.
¨
19 N. R. Sahraie, J. P. Paraknowitsch, C. Gobel, A. Thomas and 35 H. He, B. Li, J. Dong, Y. Lei, T. Wang, Q. Yu, Y. Feng and
P. Strasser, J. Am. Chem. Soc., 2014, 136, 14486–14497. Y. Sun, ACS Appl. Mater. Interfaces, 2013, 5, 8058–8066.
20 R. N. Biboum, F. Doungmene, B. Keita, P. Oliveira, L. Nadjo, 36 J. Gao, Y. Chen, B. Han, Z. Feng, C. Li, N. Zhou, S. Gao and
B. Lepoittevin, P. Roger, F. Brisset, P. Mialane, A. Dolbecq, Z. Xi, J. Mol. Catal. A: Chem., 2004, 210, 197–204.
I. M. Mbomekalle, C. Pichon, P. Yin, T. Liu and 37 J. Li, S. Gao, M. Li, R. Zhang and Z. Xi, J. Mol. Catal. A: Chem.,
R. Contant, J. Mater. Chem., 2012, 22, 319–323. 2004, 218, 247–252.
21 S. Doherty, J. G. Knight, J. R. Ellison, D. Weekes, 38 Y. Sun, Z. Xi and G. Cao, J. Mol. Catal. A: Chem., 2001, 166,
R. W. Harrington, C. Hardacre and H. Manyar, Green
Chem., 2012, 14, 925–929.
22 Y. Leng, J. Wang, D. Zhu, X. Ren, H. Ge and L. Shen, Angew.
Chem., Int. Ed., 2009, 48, 168–171.
219–224.
39 S. Zhang, S. Gao, Z. Xi and J. Xu, Catal. Commun., 2007, 8,
531–534.
40 E. P. Ferreira-Neto, S. Ullah, F. L. S. de Carvalho, A. L. de
23 S. Doherty, J. G. Knight, J. R. Ellison, D. Weekes,
R. W. Harrington, C. Hardacre and H. Manyar, Green
Chem., 2012, 14, 925–929.
Souza,
M.
de
Oliveira
Jr,
J.
F.
Schneider,
Y. P. Mascarenhas, A. M. Jorge Jr and U. P. Rodrigues-
Filho, Mater. Chem. Phys., 2015, 153, 410–421.
24 G. Chen, Y. Zhou, P. Zhao, Z. Long and J. Wang, 41 W. Zhou, L. Fang, Z. Fan, B. Albela, L. Bonneviot, F. De
ChemPlusChem, 2013, 78, 561–569.
25 P. Zhao, J. Wang, G. Chen, Y. Chen and J. Huang, Catal. Sci.
Technol., 2013, 3, 1394–1404.
Campo, M. Pera-Titus and J. Clacens, J. Am. Chem. Soc.,
2014, 136, 4869–4872.
42 H. Tan, P. Zhang, L. Wang, D. Yang and K. Zhou, Chem.
Commun., 2011, 47, 11903–11905.
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