Green catalysis for the selective oxidation of sulfides with high turnover numbers in water at room temperature

Article abstract of DOI:10.1039/c8nj05170d

A hybrid catalyst based on monoprotonated divanadium-substituted phosphotungstate ([γ-HPV₂W₁₀O₄₀]^4?) was synthesized and used for the selective oxidation of sulfides. The catalytic system was carried out in water with hydrogen peroxide at room temperature. Unprecedented turnover numbers (TONs) for all substrates were obtained, which are much higher than previous reports.

Full text of DOI:10.1039/c8nj05170d

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Green catalysis for the selective oxidation of
sulfides with high turnover numbers in water at
Cite this: New J. Chem., 2018,
room temperature†
4
2, 19349
Received 12th October 2018,
Accepted 6th November 2018
a
a
a
a
b
Wei Zhao, * Chunxia Yang, Hongxian Sun, Zhiguo Cheng and Tao Chang
*
DOI: 10.1039/c8nj05170d
rsc.li/njc
A hybrid catalyst based on monoprotonated divanadium-substituted to develop a new catalytic system which provides high activity as
4
À
phosphotungstate ([c-HPV
2
W
10 40
O ]
) was synthesized and used for well as easy recycling of catalysts.
In this paper, a hybrid catalyst based on N-octyldecyl-N,N-
the selective oxidation of sulfides. The catalytic system was carried out
in water with hydrogen peroxide at room temperature. Unprecedented dimethyl-3-propanesulfonic acid ammonium (Sulfobetaine 18) and
turnover numbers (TONs) for all substrates were obtained, which are a monoprotonated divanadium-substituted phosphotungstate
4À
much higher than previous reports.
([g-HPV W O ] ) was designed and synthesized. The catalytic
2 10 40
activities for several oxidation reactions have been reported
Due to its invaluable outcomes, the selective oxidation of sulfides using diprotonated divanadium-substituted phosphotungstate
3À
to sulfoxides or sulfones has attracted significant interest in ([g-H
organic and synthetic chemistry, particularly for the intermediate the reaction of [g-HPV
products of sulfoxides, which are used widely in the fields of worth noting that the activity of monoprotonated [g-HPV
biology, medicine, oxidative desulfurization and industrial has been rarely reported. In this paper, SO H-fuctionalized
chemistry. Earlier traditional methods for obtaining sulfoxides quaternary ammonium was fabricated on the monoprotonated
2 2 10 40
PV W O ] ), which was commonly obtained in situ by
4
À
23,30,33
2
W
10
O
40
]
and perchloric acid.
It is
4À
2
W O ]
10 40
3
1–3
4
À
used stoichiometric oxidants, such as peracids, iodic acid, hydro- polyoxometalate [g-HPV W O ] by electrostatic interaction to
2
10 40
4–6
2
peroxides, N-oxides and so on. However, the strong and excess form a hybrid catalyst (denoted as S18-HPV W10) (Scheme 1). The
oxidants bring some additional environmental problems. By obtained catalyst has special hydrophilic characteristics in water,
contrast, hydrogen peroxide aqueous solution, as an inexpensive, and it was used as catalyst for sulfide oxidation with hydrogen
readily available, safe and clean oxidant, is an attractive and peroxide. High yields of sulfoxides or sulfones were obtained in
desirable choice that has been used with active catalysts in recent water at room temperature. Surprisingly, the highest TON
7
oxidative transformations. Polyoxometalates, as well-defined reached 33 796, which is much higher than that of reported
inorganic transition-metal oxide clusters, have been employed systems. In addition, the separation of products from the
8
–10
widely as catalysts for several types of oxidation processes,
especially in liquid oxidation with hydrogen peroxide, e.g., olefin
catalytic system is very easy, and the catalytic system is reusable.
Sulfobetaine 18, a SO H-functionalized salt with quaternary
3
11–15
16–18
19–21
epoxidation,
and alkane oxidation.
oxidation using polyoxometalates with hydrogen peroxide have Because of the hydrophilic group of –SO
alcohol oxidation,
pyridine N-oxidation
ammonium, was used to encapsulate the monoprotonated
2
2–24
4À
Some catalytic systems for sulfide divanadium-substituted phosphotungstate ([g-HPV
2
W
10
O
40
]
).
+
3
H and the –N cation,
25–32
also been developed.
Nevertheless, most of these systems
often require toxic organic solvents and rigorous reaction condi-
tions, and these have a negative effect on catalyst recycling and
cause low TONs of the catalyst. Therefore, there is an urgent need
a
College of Chemistry and Pharmaceutical Engineering, Nanyang Normal
University, Nanyang 473061, China. E-mail: zhaowei1231@163.com;
Fax: +86 377 63525055; Tel: +86 377 63525056
b
Key Laboratory for Resource Exploration Research of Hebei Province,
College of Material Science and Engineering, Hebei University of Engineering,
Handan 056038, China. E-mail: changtao@hebeu.edu.cn
†
Electronic supplementary information (ESI) available: General experimental
Scheme 1 Selective oxidation of sulfides to sulfoxides catalyzed by
18-HPV 10 in water.
information and characterization of the catalyst. See DOI: 10.1039/c8nj05170d
S
2
W
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Letter
the formed catalyst (S18-HPV
NJC
2
W
10) has particular property in water, Table 2 Selective oxidation of sulfides in water to sulfoxides catalyzed by
a
S
2 10
18-HPV W
forming a stable water gel. During reaction, an emulsion was
formed when the sulfide and hydrogen peroxide were added. The
b
Reaction Conversion Selectivity
4À
c
anion [g-HPV W O ] was active for the oxidation of sulfides, Entry Substrate Product time (h) (%)
(%)
TON
2
10 40
34
and the –SO H on the cation also reinforces the catalytic activity.
3
Based on the above multiple effects, high TONs were obtained in
the emulsive system.
1
2
3
2
6
6
99
93
99
87
29 700
23 090
31 066
72
To demonstrate the advantages of the catalytic system described
in this paper, several reported systems for the selective oxidation of
methyl phenyl sulfide based on different catalysts with hydrogen
peroxide are shown in Table 1. The system reported in this paper
reveals better results, with the highest turnover number in water as
a green solvent (entries 1–7 vs. 8). The control experiment was
performed under the same reaction conditions and showed that
the oxidation only obtained o3% yield of sulfoxide without the
catalyst (entry 9). With excess hydrogen peroxide, the product
produced sulfone instead of sulfoxide (entry 10, 99% conversion,
91
4
6
99
82
27 993
d
e
5
5
6
99
99
84
85
28 676
29 017
6
2
3% selectivity of sulfoxide).
e
e
7
8
9
5
6
6
90
99
99
76
80
86
23 586
27 310
29 359
The results of catalytic oxidation of different sulfides in this
aqueous system are summarized in Table 2. With one equivalent
of hydrogen peroxide, several kinds of sulfides were successfully
oxidized to the corresponding sulfoxides with high yields
and TONs (about 30000). For aromatic sulfides, ethyl phenyl
sulfide was more difficult to oxidize than methyl phenyl sulfide.
f
10
2
99
85
29 017
g
11
2
95
88
28 827
2-Methoxythioanisole more easily oxidized to sulfoxide than
4-methoxythioanisole and 3-methoxythioanisole because of the
a
Reaction conditions: catalyst (0.58 mmmol), substrate (20 mmol), H
2 2
O
steric effect. Aliphatic sulfides (including ethyl propyl sulfide, (30% aq., 20 mmol) and H
2
O (1 mL) at 298 K. Conversions and
selectivities were determined by gas chromatography using an internal
standard technique and are based on sulfides. The products were
dipropyl sulfide and dibutyl sulfide) were also oxidized to sulfoxides
with high yields and selectivities. The cation and anion in the
combined catalyst all play particular roles during the reaction.
The selective oxidation of sulfides to sulfones catalyzed by
b
identified by GC-MS. The by-products were the corresponding sulfones.
c
d
TON = mole of sulfoxide product/mole of catalyst used. 5 mL of water
used as solvent. 3 mL of water used as solvent. Reuse catalyst of
cycle 1. Reuse catalyst of cycle 5.
e
f
g
S
18-HPV
2
W10 in water was also explored, and results are shown
in Table 3. With excess hydrogen peroxide (5 equivalents),
several kinds of sulfides were successfully oxidized to the easily separated by extraction with ethyl acetate. The catalyst with
corresponding sulfones with high conversions and selectivities. good hydrophilic properties was dispersed in aqueous phase and
The TONs of the catalyst for oxidation to sulfones were much used for the next cycle without isolation. The catalyst reuse activity is
2
8,29,31,32
higher than in previous reports.
listed in the Table 2 (entries 10 and 11) and Table 3 (entries 7 and 8).
The whole reaction procedure containing the catalyst recycling is The TONs of catalyst and the yields of products were not reduced
demonstrated in Fig. 1. Before reaction, the catalyst (S18-HPV
has particular property in water, forming a stable water gel. During
2
W
10
)
obviously, revealing that this system is effective and sustainable.
The obtained catalyst was characterized by IR (shown in
2
reaction, an emulsion was formed when the sulfide and hydrogen Fig. S1, ESI†). The catalyst S18-HPV W10 (Fig. S1a, ESI†), tetra-
peroxide were added. After oxidation, the organic products were n-butylammonium salt of the monoprotonated derivative
a
Table 1 Selective oxidation of methyl phenyl sulfide in different catalytic systems
b
Entry
1
Catalyst
[C 12SO
Solvent
Reaction time (h)
Yield (%)
TON
Ref.
8
H
3
N]
2
TiF
6
[Bpy]BF
Water
Water
4
2
0.75
6
92.15
93.5
84.6
99
2
33
13.16
9350
1410
990
34
31
29
30
30
30
30
c
2
Mo132
3
4
5
6
7
8
CeMe
2
N-PS-SiV
2
W
10
3
À
[g-PW10
O
38
V
2
(m-OH)
2
]
CH
CH
CH
CH
3
3
3
3
CN/t-BuOH
2
TBA
TBA
TBA
4
4
4
[a-PVW11
[a-H PV
[g-SiW10
O
40
]
O
CN
CN
CN
0.5
0.5
0.5
1
2
6
—
330
170
2
3
W
9
40
]
O34(H
2
O)
2
]
17
85
S
18-HPV
No catalyst
18-HPV
2
W
10
Water
Water
Water
29 310
—
7931
This paper
This paper
This paper
9
1
o3
c
0
S
2
W
10
23
a
b
c
Substrate : H
2
O
2
(30%) = 1 : 1, room temperature. TON = mole of sulfoxide product/mole of catalyst used. Substrate : H
2
O
2
(30%) = 1 : 2.
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Letter
Table 3 Selective oxidation of sulfides to sulfones in water catalyzed by
a
S
2 10
18-HPV W
b
c
Entry Substrate Product
Conversion (%) Selectivity (%) TON
1
2
99
97
99
87
33 796
29 100
3
4
95
99
82
97
26 862
2 10
Fig. 2 Proposed mechanism of sulfide oxidation catalyzed by S18-HPV W
with hydrogen peroxide in water.
33 114
33 796
5
6
99
99
99
96
were also detected by UV-vis. As shown in Fig. S2 (ESI†), the
32 772 absorbance values at 230 and 300 nm in Fig. S2a and b (ESI†)
4
À
are similar, attributed to [g-HPV W O ] . In addition, the
2
10 40
d
7
99
99
99
99
33 796
33 796
catalyst S -HPV W was also checked by SEM images (shown
1
8
2
10
in Fig. S3, ESI†). The catalyst was assembled with irregular
clavate structure (o1 mm).
e
8
2
3,35
According to the reports
and based on the above results,
a
Reaction conditions: catalyst (0.58 mmmol), substrate (20 mmol) and
(30% aq., 100 mmol) at 298 K, 6 h. Conversions and selectivities
2 10
a possible mechanism for the oxidation catalyzed by S18-HPV W
2 2
H O
were determined by gas chromatography using an internal standard in water with hydrogen peroxide is proposed in Fig. 2. The catalyst
technique and are based on sulfides. The products were identified by
reacts with hydrogen peroxide in water to form a vanadium oxygen
b
c
GC-MS. The by-products were the corresponding sulfoxides. TON =
d
species, which was analyzed and discussed in detail in a previous
mole of sulfone product/mole of catalyst used. Reuse experiment of
e
35
cycle 1. Reuse experiment of cycle 2.
report. The active vanadium oxygen species reacts with sulfides to
form the corresponding sulfoxides, thus playing an important role
in the oxidation.
Conclusions
In summary, a green and practical system for the synthesis of
sulfoxides was developed, which had the following features:
4À
(
1) the use of monoprotonated polyoxometalate [g-HPV W O ]
2 10 40
without strong acid; (2) high turnover numbers (about 30 000); (3) a
green solvent, water; (4) mild reaction conditions; and (5) recycling
of the catalytic system.
2
Fig. 1 Illustration of the catalytic reaction based on S18-HPV W10 in water
with hydrogen peroxide.
Conflicts of interest
There are no conflicts to declare.
[
n-(C
4 9 4 4 2 10 3
H ) N] [g-HPV W O40] (Fig. S1b, ESI†) and SO H-function-
alized cation part of Sulfobetaine 18 (Fig. S1c, ESI†) were
characterized by IR, shown in Fig. S1 (ESI†). The bands at 1096, Acknowledgements
À1
1
062, 1039, 957, 873, 805, 754, 535 and 489 cm in Fig. S1b
This work was financially supported by the National Natural
Science Foundation of China (No. 21703109), the Funds of Young
Teachers of Colleges of Henan Province (No. 2017GGJS131),
the Natural Science Foundation of Nanyang Normal University
(No. QN2017061, QN2016020), and the Natural Science Foun-
dation of Hebei Province (No. B2016402030).
(
ESI†) of [n-(C
4
H
9
)
4
N]
4 2 10
[g-HPV W O40] were consistent with the
23
reference and attributed to the monoprotonated polyoxometalate
4À
[g-HPV W O ] . From Fig. S1a (ESI†) of S -HPV W , several bands
2 10 40 18 2 10
À1
at 1097, 1049, 961, 875, 805 and 530 cm showed high similarity with
4À
[g-HPV
2
W
10
O
40
]
. Meanwhile, the bands at 1196, 1470, 1636, 2357,
À1
2
850 and 2920 cm in Fig. S1a (ESI†) corresponded to the SO
3
H-
fuctionalized cation part of Sulfobetaine 18 (Fig. S1c, ESI†). The
above results show that the obtained catalyst S18-HPV 10 was
fabricated by the SO H-fuctionalized quaternary ammonium and
monoprotonated polyoxometalate [g-HPV W O ]
2
W
Notes and references
3
4À
.
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40
]
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19352 | New J. Chem., 2018, 42, 19349--19352 This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018