Peroxotungstates immobilized on multilayer ionic liquid brushes-modified silica as an efficient and reusable catalyst for selective oxidation of sulfides with H2O2

Article abstract of DOI:10.1016/j.molcata.2011.03.024

Peroxotungstates held in a series of different supported ionic liquid brush catalysts were synthesized and characterized. Their catalytic performance towards the selective oxidation of sulfides with aqueous hydrogen peroxide was investigated under mild conditions. We found that the catalytic activities of the different catalysts depend on the number of supported ionic liquid layers and N-end-capped alkyl group on the imidazole ring. The highest yield of methyl phenyl sulfoxide was obtained using the BisILs-C₈H₁₇-W2 catalyst under optimum conditions. The sulfides were selectively oxidized to sulfoxides in high yields with trace sulfones detected by GC upon using 1.1 equivalents of H₂O₂. At 2.5 equivalents of H ₂O₂ the sulfones were found to be the main products. It is noteworthy that the catalyst resulted in high chemoselectivity towards sulfur groups with unsaturated double bonds even though excess hydrogen peroxide was used in addition to exhibiting high catalytic activity. There was no apparent loss of catalytic efficiency until the 8th cycle.

Full text of DOI:10.1016/j.molcata.2011.03.024

Journal of Molecular Catalysis A: Chemical 341 (2011) 57–62
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Peroxotungstates immobilized on multilayer ionic liquid brushes-modified silica
as an efficient and reusable catalyst for selective oxidation of sulfides with H O
2
2
a,b,∗
, Xiaoyan Hana,b, Wenjuan Maa,b, Junfa Weia,b,c,∗, Jing Lia,b, Qiang Zhanga,b
,
Xianying Shi
a,b
Zhanguo Chen
a
School of Chemistry and Material Science, Shaanxi Normal University, Xi’an 710062, China
Key Laboratory for Macromolecular Science of Shaanxi Province, Xi’an 710062, China
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Peroxotungstates held in a series of different supported ionic liquid brush catalysts were synthesized
and characterized. Their catalytic performance towards the selective oxidation of sulfides with aqueous
hydrogen peroxide was investigated under mild conditions. We found that the catalytic activities of
the different catalysts depend on the number of supported ionic liquid layers and N-end-capped alkyl
group on the imidazole ring. The highest yield of methyl phenyl sulfoxide was obtained using the BisILs-
C8H17-W2 catalyst under optimum conditions. The sulfides were selectively oxidized to sulfoxides in
high yields with trace sulfones detected by GC upon using 1.1 equivalents of H2O2. At 2.5 equivalents of
H2O2 the sulfones were found to be the main products. It is noteworthy that the catalyst resulted in high
chemoselectivity towards sulfur groups with unsaturated double bonds even though excess hydrogen
peroxide was used in addition to exhibiting high catalytic activity. There was no apparent loss of catalytic
efficiency until the 8th cycle.
Received 19 November 2010
Received in revised form 28 February 2011
Accepted 28 March 2011
Available online 6 April 2011
Keywords:
Hydrogen peroxide
Heterogeneous catalysis
Supported ionic liquid
Selective oxidation
Sulfide
©
2011 Elsevier B.V. All rights reserved.
1
. Introduction
of sulfides [29–33]. However, these catalytic systems suffer from
at least one of the following shortcomings: long reaction time,
low conversion of sulfide, bad selectivity between sulfoxide and
sulfone, high catalyst quantities and excessive H O .
The increasing amount of interest directed towards sulfoxides
and sulfones has stimulated research on their efficient synthesis
because of their extensive applications as synthetic intermediates
for the construction of various chemically and biologically active
molecules [1,2]. The selective oxidation of sulfides is a simple tech-
nique that can be used to obtain sulfoxides and sulfones. Many
reagents are available for the oxidation of sulfides such as halogen
compounds [3–6], nitrates [7], transition metal oxides [8], oxygen
and hydrogen peroxide [9–17]. Among them, hydrogen peroxide
has attracted much attention over the years because it forms harm-
less by-products and product work-up is simple [18–21].
Previous research has shown that soluble transition metal based
complexes are effective catalysts for the oxidation of sulfides
when using hydrogen peroxide as an oxidant [22–26]. Although
homogenous catalysts have favorable catalytic abilities [27,28],
heterogeneous catalysts are of significant industrial interest as they
can be easily separated from the reaction mixture and recycled.
Some heterogeneous catalysts have been applied to the oxidation
2
2
In our previous work, we found that the catalysts of per-
oxotungstates that were immobilized on mono-layered ionic
liquid-modified silica worked well for the oxidation of sulfides
[34]. However, the narrow imidazoliums on the carrier limited the
amount of catalytic active centers because only one imidazolium
was present on each of the side chains. Recently, we reported that
a series of supported multilayered ionic liquids, which have more
imidazoliums on each of the side chains (referred to as “ionic liq-
uid brushes”) because of their brush-like features were useful as
efficient and multifunctional catalysts for the Suzuki reaction [35].
These coral-like brushes provide an ionic liquid micro-environment
for substrates, reactants and active species, and have the advantage
of ease separation by simple filtration. The recovery and recycling
of these brushes provides environmental benefits and economical
viability. As a part of our ongoing research about the use of ionic liq-
uid brushes as promoters for organic reactions, peroxotungstates
that are held in ionic liquid brushes (Fig. 1) were prepared and
their catalytic properties were determined during the oxidation
of sulfides under mild conditions because a variety of tungsten-
based homogeneous catalysts are known to have high activities in
useful oxidation procedures when using hydrogen peroxide as an
oxidant.
∗ Corresponding authors at: School of Chemistry and Material Science, Shaanxi
Normal University, Xi’an 710062, China. Tel.: +86 29 85303734; fax: +86 29
8
5307774.
E-mail addresses: ying1075@sina.com (X. Shi), weijf@snnu.edu.cn (J. Wei).
1
381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.03.024

5
8
X. Shi et al. / Journal of Molecular Catalysis A: Chemical 341 (2011) 57–62
After the reaction, the obtained materials were washed consecu-
◦
tively with water and acetone, then, dried under vacuum at 70 C
over night.
−
SiO -BisILs-CH3 (R = CH3 ): Elemental analysis: C, 12.35%; H,
2
−
1
2
1
1
.38%; N, 2.01%. IR (KBr disk): 3050, 2937, 2866 cm , ␯(C–H);
−
1
−1 −
642 cm
,
␯(C N); 833 cm
, ␯(PF6 ). BET surface areas:
N
N
N
N
N
N
2
07 m /g.
−
SiO -BisILs-C H (R = n-C H9 ): Elemental analysis: C, 17.03%; H,
2
4
9
4
−
1
2
1
.09%; N, 2.69%. IR (KBr disk): 3055, 2942, 2882 cm , ␯(C–H);
627 cm , ␯(C N); 822 cm , ␯(PF ). BET surface areas: 67 m /g.
−
1
−1
−
2
6
N
N
N
N
N
N
−
SiO -BisILs-C H (R = n-C H
): Elemental analysis: C, 12.48%;
2
8
17
8
17
−
1
H, 1.80%; N, 2.96%. IR (KBr disk): 3162, 2938, 2860 cm , ␯(C–H);
636 cm , ␯(C N); 832, ␯(PF6 ). BET surface areas: 117 m /g.
SiO -BisILs-C12H25 (R = n-C12H25 ): Elemental analysis: C, 13.22%;
N
N
N
−1
−
2
1
−
2
N
N
N
−
1
H, 1.96%; N, 2.34%. IR (KBr disk): 3061, 2939, 2867 cm , ␯(C–H);
− −1 −
1
2
1
639 cm , ␯(C N); 830 cm , ␯(PF6 ). BET surface areas: 82 m /g.
−
2 6 2 6 2
5 5
SiO -BisILs-C H CH (R = C H CH ): Elemental analysis: C,
N
N
N
−
1
EtO
EtO
EtO
Si
14.22; H, 1.68; N 3.01%. IR (KBr disk): 3053, 2928, 2882 cm
,
Si
Si
N
N
N
−1 −1 −
O
O
O
␯(C–H); 1641 cm , ␯(C N); 828 cm , ␯(PF6 ). BET surface areas:
O
O
O
2
3
4 m /g.
EtO
EtO
EtO
Si
Si
Si
2
.2.2. Preparation of BisILs-R-W2 catalysts
O
O
O
SiO2
1
0 ml 30% H O2 was added to the solution of K WO ·2H O
O
O
O
2
2
4
2
(0.725, 2 mmol) in 10 ml water while being stirred at room tem-
perature [36,37], the resulting yellow solution was treated with
dilute HCl until it just turned colorless. 1 g of the SiO -BisILs-R was
2
-
1
2-
=
PF , / [W O (O ) ]
added to this colorless solution and the suspension was stirred at
room temperature for 24 h. During the reaction, binuclear peroxo-
tungstate anions were exchanged on the ionic liquid-modified silica
6
2
2
3
2 4
Fig. 1. Silica immobilized peroxotungstates ionic liquids brushes.
SiO -BisILs-R. After filtration and dry, the bis-layered ionic liquid
2
modified SiO2 catalysts were obtained.
2
. Experimental
2
.1. Materials and apparatus
−
BisILs-CH -W2 (R = CH3 ): Elemental analysis: C, 11.88; H,
3
−
1
1
1
8
.93; N, 1.98%. IR (KBr disk): 3162, 2940, 2866 cm , ␯(C–H);
␯(C N); 833 cm
43 cm , ␯(O–O); 727 cm , ␯(W O); 559 cm , ␯(W(O )). BET
surface areas: 71 m /g. The loading amount of tungsten and phos-
phorus are 0.332 and 0.103 mmol/g respectively.
Unless otherwise stated, all reagents were purchased from
−1
−1
−1
−
−1
641 cm
,
,
␯(PF6 ); 934 cm
, ␯(W O);
commercial sources and used without purification. Flash chro-
matography was performed with freshly distilled solvents.
Columns were typically packed as slurry and equilibrated with the
appropriate solvent system prior to use. The SEM-EDAX was per-
formed on a Philips-FEI Quanta 200 scanning electron microscopy
equipped with an EDAX energy dispersive X-ray analysis. The BET
surface areas of materials were measured by nitrogen adsorption
Peking Pioneer-2002 ST-03A. C, H and N element analyses were per-
formed on a Perkin-Elmer 2400 CHN elemental analyzer. IR spectra
were recorded separately on a Bruker Equinox-55 spectrophotome-
−1
−1
2
2
2
−
BisILs-C H -W2 (R = n-C H9 ): Elemental analysis: C, 15.62;
4
9
4
−1
H, 1.93; N, 2.38%. IR (KBr disk): 3079, 2942 cm , ␯(C–H);
␯(C N); 821 cm
44 cm , ␯(O–O); 686 cm , ␯(W O); 559 cm , ␯(W(O )). BET
surface area: 68 m /g. The loading amount of tungsten and phos-
phorus are 0.326 and 0.559 mmol/g respectively.
−1
−1
−1
−
−1
1
8
625 cm
,
,
␯(PF6 ); 932 cm
, ␯(W O);
−1
−1
2
2
2
−
BisILs-C H -W2 (R = n-C H
): Elemental analysis: C, 12.06; H,
8
17
8
17
−
1
ter (KBr pellets in the range 400–4000 cm ). ICP-MS was measured
by X series ꢀ mass spectrometer. 1H NMR and C MNR spectra
were recorded on a Bruker AVANCE300 MHz spectrometer (TMS
as an internal standard). GC analysis was performed on an Agilent
−1
1
1
8
.71; N, 2.64%. IR (KBr disk): 3166, 2937, 2864 cm , ␯(C–H);
␯(C N); 831 cm
44 cm , ␯(O–O); 731 cm , ␯(W O); 560 cm , ␯(W(O )). BET
surface area: 103 m /g. The loading amount of tungsten and phos-
phorus are 0.334 and 0.165 mmol/g respectively.
BisILs-C12H25-W2 (R = n-C12H25 ): Elemental analysis: C, 11.99;
H, 1.72; N, 1.82%. IR (KBr disk): 3057, 2931 cm , ␯(C–H);
␯(C N); 828 cm
75 cm , ␯(O–O); 685 cm , ␯(W O); 560 cm , ␯(W(O )). BET
surface areas: 65 m /g. The loading amount of tungsten and phos-
phorus are 0.312 and 0.51 mmol/g respectively.
13
−1
−1
−1
−
−1
638 cm
,
,
␯(PF6 ); 935 cm
, ␯(W O);
−1
−1
2
2
2
6
890N using a capillary column (HP-5 30 m × 0.25 mm × 0.53 ␮m)
with a FIT detector.
−
−
1
−
1
1
−1
−
−1
1
8
642 cm
,
,
␯(PF6 ); 942 cm
, ␯(W O);
2
2
.2. Preparation of catalysts
−
−1
−1
2
2
2
.2.1. Preparation of SiO -BisILs-R
2
SiO -1 and SiO -2 were synthesized according to previous
2
2
−
BisILs-C H5CH -W2 (R = C H5CH ): Elemental analysis: C, 13.27;
report [34,35]. The mixture of 2.0 g SiO -2 and 0.034 mol alkyl
6
2
6
2
2
−
1
H, 1.58; N, 2.63%. IR (KBr disk): 3072, 2932 cm , ␯(C–H);
␯(C N); 830 cm
82 cm , ␯(O–O); 726 cm , ␯(W O); 564 cm , ␯(W(O )). BET
surface area: 20 m /g. The loading amount of tungsten and phos-
phorus are 0.326 and 0.284 mmol/g respectively.
halide was vigorously stirred in refined toluene under refluxed con-
dition for 24 h. After filtered, the resulting materials were washed
by Soxhlet extraction with ethanol as solvent. The ionic liquid mod-
ified silica SiO -BisILs-R was prepared by the direct reaction of the
above precursor and KPF6 in CH CN at room temperature for 24 h.
−
1
1
−1
−
−1
1
8
636 cm
,
,
␯(PF6 ); 928 cm
, ␯(W O);
−
−1
−1
2
2
2
2
3

X. Shi et al. / Journal of Molecular Catalysis A: Chemical 341 (2011) 57–62
59
2.3.2. The typical procedure for the selective oxidation of sulfides
to sulfones
The methods of oxidizing sulfides to sulfones were similar to
that of sulfoxides except that the ratio of catalyst, H2O2, and sulfide
was changed from 1.5:110:100 to 2:250:100.
Scheme 1. Synthesis of 1-(4-bromobutyl)-3-methylimidazolium bromide.
2
.2.3. Preparation of SiO -TriILs-CH3
The mixture of 1-methylimidazole (3.52 g, 43 mmol) and 1,4-
2
3
. Results and discussion
◦
dibromobutane (20 ml) was heated to 60 C under strongly stirring
for 10 h. Then the mixture was cooled to room temperature
and extracted by deionized water. After the removal of residual,
a yellow viscous liquid 1-(4-bromobutyl)-3-methylimidazolium
bromide was obtained in 84% yield (Scheme 1). Anal. Calc. for
C8H14Br N : C, 32.23%; H, 4.70%; N, 9.40%; Found: C, 32.10%; H,
3.1. Catalysts preparation
The peroxotungstates in the ionic liquid brushes (Scheme 2)
were prepared by ion-exchange between the immobilized ionic liq-
uid brushes and aqueous K [W O (O ) ], as shown in Scheme 2.
The results of elemental analysis, IR spectra and SEM–EDAX stud-
2
2
3
2 4
2
2
4
.75%; N, 9.43%.
The suspension of SiO -2 (2.45 g) and 1-(4-bromobutyl)-3-
−
ies of the catalysts showed that the ionic liquid anion PF6 was
2
not exchanged completely by the binuclear peroxotungstate anion.
Therefore, the characteristic homogeneous reaction of the ionic liq-
uid changed to that of a heterogeneous catalyst. Additionally, the
grafted ionic liquid avoids the increase in cost associated with some
loss in the homogeneous system.
methylimidazolium bromide (0.90 g, 3.02 mmol) in DMF (20 ml)
was stirred at 90 C for 24 h. After filtered and washed with ethano,
the powder was extracted by Soxhlet Extractor with ethanol as sol-
vent and dried overnight. The SiO -TriILs-CH was prepared by the
◦
2
3
direct reaction of the above precursor and KPF6 in CH CN at room
3
temperature for 24 h. After the completion of reaction, the obtained
material was washed consecutively with water and acetone, then,
3
.2. Characterization of the intermediates and catalysts
◦
dried under vacuum at 70 C over night. Elemental analysis: C,
The elemental analysis, BET surface areas, and metal loading
−
1
1
␯
2
2.10%; H, 1.93%; N, 3.19%. IR (KBr disk): 3084, 2925, 2851 cm
,
of intermediates and catalysts are summarized in Table 1. Ele-
mental analysis revealed that the amount of nitrogen in three
intermediates was different (entries 2, 5 and 7). The nitrogen atom
content in the multilayered ionic liquids were higher than that in
the monolayer ionic liquid, which shows that there are more imi-
dazolium ions in the multilayered ionic liquids. Accordingly, they
could provide more abundant reaction environment of ionic liquid.
Compared with the amount of tungsten loaded onto the catalysts
−1
−1
−
(C–H); 1568 cm , ␯(C N); 826 cm , ␯(PF6 ). BET surface areas:
2
29 m /g.
2
.2.4. Preparation of TriILs-CH -W2 catalyst
3
The preparation of SiO -TriILs-CH -W2 catalyst was similar
2
3
to that of BisILs-CH -W2. Elemental analysis: C, 11.23; H, 1.82;
3
−1
−1
N, 2.87%. IR (KBr disk): 2925, 2843 cm , ␯(C–H); 1655 cm ,
− − −1 −1
1
␯
6
(C N); 835 cm , ␯(PF6 ); 951 cm , ␯(W O); 882 cm , ␯(O–O);
(entries 3, 6, and 8), the amounts of tungsten loaded onto the sur-
− −1
98 cm , ␯(W O); 557 cm , ␯(WO ). BET surface area: 211 m /g.
2 2
1
2
face of the multilayered ionic liquids were obviously higher than
that of the monolayer ionic liquid. Compared with the initial inter-
mediate SiO -1, the BET surface areas of the other intermediates
The loading amount of tungsten and phosphorus are 0.506 and
0.607 mmol/g respectively.
2
and the final catalysts decreased significantly. This is consistent
with the decrease in BET surface area of the carrier upon subsequent
modification by organic groups.
2
2
.3. Catalytic reactions
.3.1. The typical procedure for the selective oxidation of sulfides
to sulfoxides
3
3
.3. The catalytic abilities of different supported catalysts
To a 25 ml flask with a mixed solvent of MeOH/CH Cl2 (1:1
volume ratio), the catalyst (1.5 mol% with respect to substrate),
2
.3.1. The influence of the number of layers of ionic liquid on the
sulfide (1 mmol) and 30% aqueous hydrogen peroxide (1.1 mmol)
were added successively. The resulting mixture was stirred elec-
tromagnetically at room temperature. The reaction was monitored
by TLC. After the completion of the reaction, the catalysts were
separated by filtration, washed with EtOAc (3 × 5 ml), and dried
in vacuum. The combined organic layer was dried with anhydrous
catalytic ability
The catalytic abilities of the different catalysts were investi-
gated using methyl phenyl sulfide as a model substrate under the
same reaction conditions. The results are listed in Table 2 and show
that although the sulfoxides could be obtained in high yields using
3
0% hydrogen peroxide upon catalysis by various catalysts, the cat-
MgSO , and concentrated under reduced pressure to give the crude
4
alytic activities of these catalysts greatly depend on the number of
loaded ionic liquid layers and the end-capped groups. As expected,
the multilayer catalysts performed better than the monolayer cat-
product, which was purified by silica gel column chromatography
using petroleum ether-EtOAc as eluent.
Table 1
Analytical data of intermediates and catalysts.
BET SA (m2
g
−1
)
Metal loading (mmol/g)
Entry
Compound
Elemental analysis (%)
C
H
N
a
1
2
3
SiO2-1
6.46
6.03
5.08
19.57
12.35
11.88
12.10
11.23
1.09
0.89
0.74
2.88
2.38
1.93
1.93
1.82
325
300
199
285
107
71
a
SiO2-2-Im (mono)
Mono-W2-Im
SiO2-2
SiO2-BisILs-CH3
BisILs-CH3-W2
SiO2-TriILs-CH3
TriILs-CH3-W2
1.65
1.35
7.39
2.01
1.98
3.19
2.87
a
0.22
4
5
6
7
8
0.332
0.506
229
211
a
The intermediates and catalyst are reported in literature [34].

6
0
X. Shi et al. / Journal of Molecular Catalysis A: Chemical 341 (2011) 57–62
Scheme 2. Preparation of silica-immobilized ionic liquid brush catalysts.
alyst (entry entries 1, 2, 7). For instance, in the reaction where a
1.9% yield of phenyl methyl sulfoxide was obtained when using
3.3.2. The influence of N-end-capped alkyl groups on the catalytic
ability
9
the monolayer ionic liquid modified catalyst, 2.5 h (entry 1) was
required. By comparison, a yield of up to 91% was obtained after
only 1.5 h when using the multilayer ionic liquid catalysts (entries
The experimental results also show that the end-capped alkyl
groups on the imidazole ring affect the reaction significantly. From
Table 2 the catalyst with n-octyl as the terminal alkyl group is the
most effective for the oxidation reaction as it affords the highest
product yield (entry 4). The catalysts with methyl, n-butyl, ben-
zyl or n-dodecyl are less reactive. These results indicate that the
catalysts bearing more or less than eight carbons in the chain
of alkyl group are less effective. This may be because the octyl
group is more efficient in balancing the critical hydrophobic and
hydrophilic parameters and thus provides a suitable hydropho-
bic and hydrophilic environment for substrates to move into the
brushes where the catalytically active species is attached and for
the product and byproduct (water) to move out of the brushes. As
for benzyl, its rigid structure makes it difficult for the reagents to
approach the catalytically active site.
2
, 7).
The reason for this may be that compared with the monolayer
ionic liquid catalyst, the multilayer ionic liquid catalysts have more
prominent three-dimensional environment characteristics, which
closely resembles the liquid phase character of ionic liquids and
thus eases the approach of substrates or reagents to the catalytic
species.
Additionally, the multilayer ionic liquid catalysts show good
flexibility because of the larger amount of imidazoliums on each
of the side chains. These properties give them better mobility,
hydrophobicity and homogeneity, which provide a good environ-
ment for the reaction. However, the catalytic activity of the trilayer
analogue was unexpectedly lower than that of the dilayer ana-
logues (entry 2 vs 7). This may be because the imidazolium ions
and the near the surface of the silica could not play their rules com-
pletely in the catalytic reaction since the reactants might access the
deeper layer with difficulty.
3
.4. Catalytic abilities of catalyst BisILs-C H17-W2
8
3.4.1. Oxidation of sulfides to sulfoxides
The catalyst BisILs-C H17-W2 showed the best catalytic activity
8
in all of the catalysts. Therefore, this catalyst was applied to the
oxidation of other various sulfides with aqueous H O (Table 3).
2
2
Table 2
The data in Table 3 displayed that both aromatic and aliphatic sul-
foxides could be obtained in high yields. Meanwhile, only trace
amounts of over-oxidation products of sulfones were detected by
GC after reaction. Control experiments indicate that in the absence
of the catalyst, the oxidation of thioanisole at the same condition
gives methyl phenyl sulfoxide in a rather low yield of 18.3%, which
indicated that the catalyst played important role in the reaction.
Compared with a previous report about using an ordinary silica-
a
The catalytic abilities of different catalysts in oxidation of methyl phenyl sulfoxides.
Entry
Catalyst
Time (h)
Yield (%)b
1c
Mono-W2-Im
2.5
1.5
1.5
1.5
1.5
1.5
1.5
91.9
93.4
94.1
95.5
87.9
88.5
91.0
2
3
4
5
6
7
BisILs-CH3-W2
BisILs-C4H9-W2
BisILs-C8H17-W2
BisILs-C12H25-W2
BisILs-C6H5CH2-W2
TriILs-CH3-W2
based tungstate catalyst [38], the amount of H O2 needed in the
2
catalytic oxidation system was reduced greatly from 3 equivalents
to 1.1 equivalents (based on the amount of sulfide). The catalyst
provides excellent chemoselectivity for sulfides containing other
functional groups that are susceptible to oxidation. For instance,
a
Reaction conditions: 1.5 mol% of catalyst (W), 1.1 equiv of H2O2, were stirred at
room temperature.
b
Isolated yields (average in two runs).
The catalyst was reported in literature [34].
c

X. Shi et al. / Journal of Molecular Catalysis A: Chemical 341 (2011) 57–62
61
Table 3
The catalytic ability of catalyst BisILs-C8H17-W2 in oxidation of sulfide to sulfoxide.a
.
Entry
1
Sulfide
Time (h)
1.0
Conv. (%)
99.8
Yield (%)b
89.2
90.0
92.2
2
3
1.5
1.5
100
99.2
4
5
4.0
4.0
1.5
94.6
93.7
98.6
89.9
83.1
95.5
6
a
Reaction conditions: 1.5 mol% of catalyst (W), 1.1 equiv of H2O2, were stirred at room temperature.
Isolated yields (average in two runs).
b
allyl methyl sulfoxide and allyl sulfoxide were obtained in high
the catalytic oxidation system possesses excellent chemoselectiv-
ity.
yields of 92.2% and 90.0%, respectively, and no epoxidation products
were detected by GC. In addition, the yield of diphenyl sulfoxide
was lower than that of methyl phenyl sulfoxide because of steric
effects. Although the strong electron withdrawing group NO2 is
present in the phenyl ring of these sulfides, the sulfoxide yield was
not affected.
3
.4.3. The recycling of catalyst BisILs-C H17-W2
8
It is noteworthy that the work-up of the reaction mixture
is rather simple since the catalyst can be recovered by simple
filtration. The recovered catalyst is capable of being reused in
subsequent cycles. Eight consecutive preparations of the methyl
phenyl sulfoxide showed no significant loss in yield (Table 5), which
indicates that the catalytic activity of the catalyst did not change
significantly compared with the fresh catalyst. In each case, the
catalyst was recovered by filtration, washing with ethanol and
water, and the experiment repeated. ICP-MS analysis of the reaction
solution after filtration of the brushes shows that only 0.58 mg/l
tungsten was present, which indicates that there is almost no loss
of metal components.
3.4.2. Oxidation of sulfides to sulfones
When the molar ratio of the catalyst:H O :sulfide was changed
2
2
from 1.5:110:100 to 2:250:100, the sulfones were obtained at room
temperature within 5 h (Table 4). From Table 4, the BisILs-C H17-
8
W2 catalyst gave high catalytic activity in all the reactions and the
conversion of sulfides were all 100% without exception. Similar to
the oxidation of sulfides to sulfoxides, unsaturated double bonds
are also tolerated during these reactions where aqueous hydrogen
peroxide was used in large excess. This result further showed that
Table 4
The catalytic ability of catalyst BisILs-C8H17-W2 in oxidation of sulfide to sulfone.a
.
Entry
Sulfide
Time (h)
2.5
Yield (%)b
96.2
1
2
3.0
92.8
3
4
2.5
2.5
86.5
90.8
5
6
5.0
5.0
4.0
85.3
80.6
98.8
7
a
Reaction conditions: 2 mol% of catalyst (W), 2.5 equiv of H2O2, were stirred at room temperature.
Isolated yields (average in two runs).
b

6
2
X. Shi et al. / Journal of Molecular Catalysis A: Chemical 341 (2011) 57–62
Table 5
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