Polyvinylpolypyrrolidone-supported boron trifluoride (PVPP-BF3): Highly efficient catalyst for chemoselective oxygenation of sulfides to sulfones by H2O2

Article abstract of DOI:10.1080/10426507.2011.610849

A highly efficient method for the oxidation of sulfides to sulfones using polyvinylpolypyrrolidone-supported boron trifluoride (PVPP-BF₃) in the presence of (35%) hydrogen peroxide has been developed. This procedure cleanly oxidizes dialkyl and alkyl aryl sulfides to the corresponding sulfones in excellent yields at room temperature.

Full text of DOI:10.1080/10426507.2011.610849

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Phosphorus, Sulfur, and Silicon and the
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Polyvinylpolypyrrolidone-Supported
Boron Trifluoride (PVPP-BF ): Highly
3
Efficient Catalyst for Chemoselective
Oxygenation of Sulfides to Sulfones by
H O
2
2
a
b
Masoud Mokhtary , Moslem Mansour Lakouraj & Masoumeh
c
Rastegar Niaki
a
Department of Chemistry , Islamic Azad University, Rasht Branch ,
Rasht , Iran
b
Department of Organic Chemistry , Mazandaran University ,
Babolsar , Iran
c
Department of Chemistry , Islamic Azad University, Amol Branch ,
Amol , Iran
Published online: 31 Jan 2012.
To cite this article: Masoud Mokhtary , Moslem Mansour Lakouraj & Masoumeh Rastegar Niaki (2012)
Polyvinylpolypyrrolidone-Supported Boron Trifluoride (PVPP-BF ): Highly Efficient Catalyst for
3
Chemoselective Oxygenation of Sulfides to Sulfones by H O , Phosphorus, Sulfur, and Silicon and the
2
2
Related Elements, 187:3, 321-326, DOI: 10.1080/10426507.2011.610849
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Phosphorus, Sulfur, and Silicon, 187:321–326, 2012
Copyright ꢀ
Taylor & Francis Group, LLC
C
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2011.610849
POLYVINYLPOLYPYRROLIDONE-SUPPORTED BORON
TRIFLUORIDE (PVPP-BF ): HIGHLY EFFICIENT CATALYST
3
FOR CHEMOSELECTIVE OXYGENATION OF SULFIDES
TO SULFONES BY H O2
2
1
2
Masoud Mokhtary, Moslem Mansour Lakouraj,
3
and Masoumeh Rastegar Niaki
1
Department of Chemistry, Islamic Azad University, Rasht Branch, Rasht, Iran
Department of Organic Chemistry, Mazandaran University, Babolsar, Iran
Department of Chemistry, Islamic Azad University, Amol Branch, Amol, Iran
2
3
GRAPHICAL ABSTRACT
O
R S R'
O
PVPP-BF /H O (35%)
3
2
2
R S R'
CH NO
3
2
Abstract A highly efficient method for the oxidation of sulfides to sulfones using
polyvinylpolypyrrolidone-supported boron trifluoride (PVPP-BF3) in the presence of (35%)
hydrogen peroxide has been developed. This procedure cleanly oxidizes dialkyl and alkyl aryl
sulfides to the corresponding sulfones in excellent yields at room temperature.
Keywords Polyvinylpolypyrrolidone; boron trifluoride etherate; hydrogen peroxide; sulfides;
sulfones
INTRODUCTION
The ready oxidation of sulfur compounds by appropriate reagents is a key feature of
organosulfur chemistry. The oxidation of sulfides is the most straightforward method for
1
the synthesis of sulfoxides and sulfones. Sulfones can be prepared both by direct oxidation
of sulfides and by oxidation of sulfoxides. The use of H2O2 as a final oxidant offers the
advantages that it is a cheap, environmentally benign and is a readily available reagent and
produces water as the only by product.2
There are some alternative catalysts for oxidation of sulfides to sulfones in the pres-
3
ence of hydrogen peroxide such as Na2WO4.2H2O/[CH3(n-C8H17)3N]HSO4/C6H5PO3H2,
β-cyclodextrin,4 MoO2Cl2,5 titanium alkoxide/ionic liquid, manganese complex of
6
Received 25 May 2011; accepted 26 July 2011.
We are grateful to Islamic Azad University of Rasht Branch for financial assistance of this work.
Address correspondence to Masoud Mokhtary, Department of Chemistry, Islamic Azad University, Rasht
Branch, Rasht, Iran. E-mail: mmokhtary@iaurasht.ac.ir
3
21

3
22
M. MOKHTARY ET AL.
ꢁ
ꢁꢁ
9
7
benzo-18-crown-6,8 silica-
N,N ,N -tris(2-hydroxypropyl)-1,4,7-triazacyclononane,
10
vanadia, tantalum(V) or niobium(V), TiO2 nanoparticles and Preyssler-type heteropoly
11
12
acid modified nano-sized TiO2, boric acid, and Silica immobilized peroxotungstates
ionic liquids brushes.13 Also, N-methylpyrolidin-2-one hydrotribromide as a oxidant for
14
the oxygenation of sulfides to sulfoxides and sulfones has been developed. Recently, the
transition metal compounds, such as (Bu PPh3)2Cr2O7/AlCl3 N,N-dibenzyl-N,N,N,N-
tetramethylethylene diammonium permanganate, and Hexamolybdochromate (III),
n
15
16
17
have been used as catalyst for the oxidation of sulfides to sulfones. However, some of
1
4,15,17
8,10
these methods involve drastic reaction conditions,
costly reagents, toxic transition
5,7,14–17
7,13
metal compounds and corrosive wastes,
preparation of complex catalyst, and the
Polymer supported catalysts and reagents have become
tedious work-up procedure.3
,8,17
popular in organic synthesis over the past decades. The high catalytic activity, low toxicity,
stability, their recyclability, and environmentally safe condition make the use of a polymer
supported reagent attractive alternatives to conventional reagents. Also, the application of
polymer supported reagents and catalysts has received special attention due to easy work
up of reaction products and some selectivity that is undoubtedly attractive features of this
18
methodology.
In connection of our studies on oxygenation of sulfides to sulfoxides by
polyvinylpyrrolidone-Vilsmeier adduct with (35%) hydrogen peroxide,19 in this research
we introduce the use of polyvinylpolypyrrolidone-boron trifluoride (PVPP-BF3) as a
heterogeneous catalyst for oxidation of sulfides to sulfones in the presence of hydrogen
peroxide.
RESULTS AND DISCUSSION
In this method, BF3 etherate was immobilized on PVPP to give a stable polymeric
20
Lewis acid reagent according to our previous article. Characterization of the Lewis acid
sites present on the polymer was performed by recording the FT-IR spectrum of PVPP-BF3,
−
1
which shows a strong broad absorption at 1000–1060 cm for the BF bonds and a moderate
−1
absorption at 1646 cm corresponds to the imine group on the backbone.
The capacity of the reagent was determined by titration and found to be 10 mmol/g,
2
1,22
whereas its silica supported analogue has a loading capacity of less than 4 mmol/g.
In spite of BF3.Et2O, the PVPP-BF3 is more water tolerant, noncorrosive, and stable solid
catalyst with an elevated Lewis acid property. Interestingly, this reagent not only gives
excellent yields of the products but also PVPP-BF3 is easily regenerated and can be reused
several times and retains its activity after several months of storage (Scheme 1).
To select the best solvent, the oxidation of methylphenylsulfide was studied in a
variety of organic solvents such as methanol, acetonitrile, nitromethane, dioxane, and
dichloromethane. Among them, nitromethane was found to be the best solvent for oxida-
tion of sulfides to sulfones (Table 1). To show the role of the PVPP-BF3 in this oxidation
reaction, the oxidation of methylphenylsulfide was carried out in the absence of the catalyst.
The oxidation was not successful, and a low yield of corresponding sulfoxide and trace of
sulfone was formed. The oxidation reaction of sulfides via PVPP-BF3 in the presence of hy-
drogen peroxide in methanol at room temperature led to mixture of sulfoxides and sulfones
based on GC-MS analysis. So, to increase of chemoselectivity, we examined the oxidation
reaction of structurally different sulfides with PVPP-BF3/H2O2 system in nitromethane at
ꢁ
room temperature. As seen in Table 2, the optimized stoichiometric ratio of RSR :H2O2 for

PVPP-BF3 FOR CHEMOSELECTIVE OXYGENATION OF SULFIDES
323
BF .Et O
3
2
CH Cl2
2
n
n
N
-
O
N
+
OBF3
H O
2
2
PVPP
CH NO /r.t.
3
2
PVPP-BF3
O
S
R
S
R'
R
R'
O
Scheme 1
the conversion of sulfides to sulfones was found to be 1:3 using 0.1 g of the PVPP-BF3 in
nitromethane at room temperature. All reactions were carried out under the optimized con-
ditions, and the results are summarized in Table 3. It is clear that sulfides bearing sensitive
to oxidation such as hydroxy, and carbon–carbon double bonds are completely unaffected
under the reaction conditions and the sulfones are obtained in excellent yields (Table 3,
Entry 6, 9, 10). In order to show the advantages and disadvantages of our method, some of
our results in oxidation of sulfides were compared with some of those reported in litera-
ture (Table 4). It is evident that the PVPP-BF3/H2O2 in nitromethane solvent allows these
transformations to proceed with excellent selectivity and excellent yield. In order to check
the reusability of the catalyst, it was employed for the oxidation of dibenzylsulfide fourth
cycles under the optimum conditions. In the first run, 97% of sulfone was obtained. The cat-
alyst powder was recovered by filtration, washed with dichloromethane, and immediately
reused for oxidation processes again, taking into account the partial loss of catalyst during
the recovery. The second cycle was performed with the recovered catalyst and addition of
three equimolecular amount of H2O2 gave corresponding sulfone in 90% yield. The third
and fourth cycles were performed with the recovered catalyst similar to above method and
78% and 67% of sulfone were obtained, respectively (Table 5). To improve the catalytic
activity of catalyst after three cycles, it is favored to separate the PVPP by filtration, washed
carefully from dichloromethane, and dried, then treated with BF3 etherate again to prepared
fresh PVPP immobilized BF3 catalyst. The polymer support can be used several times for
the immobilization of BF3.
Table 1 Oxidation of methylphenylsulfide to corresponding sulfone in different solventsa
Entry
Solvent
Time (h)
Yield (%)b
1
2
3
4
5
CH2Cl2
CH3OH
CH3CN
CH3NO2
Dioxane
4
2.5
3
2.5
3.5
38
76
68
99
56
aAll reactions were carried out using 0.1 g of the polymeric reagent, 1 mmol sulfide,
and 3 mmol of H2O2.
b
The yield was determined by GC analysis of the crude product.

3
24
M. MOKHTARY ET AL.
Table 2 Effect of PVPP-BF3 loading and H2O2 concentration on oxidation of methylphenylsulfide in ni-
tromethane at room temperature in 2.5 h
Entry
H2O2 (mmol)
PVPP-BF3 (g)
Yield (%)a
1
2
3
4
5
6
1
2
3
1
2
3
0.05
0.05
0.05
0.1
0.1
0.1
42
68
77
56
81
99
aThe yield was determined by GC analysis of the crude product.
In conclusion, we have developed a simple methodology that exhibits excellent
selectivity for oxygenation of sulfides to sulfones in the presence of hydrogen peroxide
using PVPP-BF3 as a high loading of Lewis acid, which is stable and easy to prepare and
handle. In addition, this method is suitable both for preparative and industrial usage because
of its low cost, biocompatibility, and recyclability of the PVPP as a safe polymer support.
Table 3 Oxidation of sulfides to sulfones using PVPP-BF3/H2O2a
Entry
1
Sulfides
Time (h)
Yield (%)b
99
mp (Ref.)
86–87(85)16
2.5
SCH3
2
3
4
5
6
7
8
9
3
2.5
3
97
98
98
97
96
96
97
148–150(149)16
145–147(147)16
198–200(195–197)15
143–144(142–143)15
119–120(121.5)16
99–101
CH SCH
2
2
SCH2
SCH2
Br
3
Cl
SCH2
2.5
2
SCH -CH OH
2
2
S
CH2
2
144–145(146)16
Me
SCH2
15
15
15
Ph—SCH2 CH CH2
(CH2 CH CH2)2S
(CH3CH2CH2)2S
3
3
2.5
2.5
99
99
98
97
Oil
Oil
Oil
1
1
1
0
1
2
16
(CH3CH2CH2CH2)2S
44–45(45)
aReaction conditions: sulfide (1 mmol), PVPP-BF3 (0.1 g), H2O2 (3 mmol), CH3NO2, r.t.
b
Isolated yields.

PVPP-BF3 FOR CHEMOSELECTIVE OXYGENATION OF SULFIDES
325
Table 4 Comparison of our reagent with some other reagents in oxidation of sulfides to sulfones
Substrate
Reagent
Conditions
Time Yield (%)a
Ref.
◦
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
Na2WO4/C6H5PO3H2/PTC/H2O2
β-cyclodextrin/H2O2
MoO2Cl2/H2O2
Benzo-18-crown-6/H2O2
H3BO3/H2O2
BisILs-C8H17-W2/H2O2
Caro’s acid/SiO2
PVPP-BF3/H2O2
50 C
2 h
4 h
0.75 h
4 h
0.5 h
97
91
95
64
94
98.8
92
99
93
99
20
94
88
97
3
4
5
8
12
13
25
◦
H2O, 75 C
MeCN, r.t.
EtOH, 40 C
Neat, r.t.
CH2Cl2/MeOH, r.t. 4 h
MeCN, reflux
MeNO2, r.t.
MeOH, r.t.
MeOH, 45 C
Im/MeCN/H2O, r.t. 0.5 h
MeCN/r.t. 80 min
◦
4.5 h
2.5 h
2.5 h
2.5 h
This work
(
(
(
(
(
(
PhCH2)2S Ti4[(OCH2)3CMe]2 (i-PrO)10/H2O2
PhCH2)2S TaCl5/H2O2
PhCH2)2S Mn(III)–Salophen/NaIO4
PhCH2)2S SSA/H2O2
6
10
24
26
27
◦
PhCH2)2S Silica-based Ammonium Tungstate/H2O2 CH2Cl2/MeOH, r.t. 4.5 h
PhCH2)2S PVPP-BF3/H2O2
MeNO2, r.t.
3 h
This work
aYield refers to the corresponding sulfone.
EXPERIMENTAL
The PVPP was purchased from Fluka. Other chemicals were purchased from Merck.
A number of sulfides were prepared using a standard synthetic method.23 Melting points
were recorded on an electro thermal melting point apparatus. The NMR spectra were
recorded in CDCl3 with TMS as an internal standard on a Bruker Avance DRX 400 MHz
spectrometer. IR spectra were determined on a SP-1100, P-UV-Com instrument. Purity
determination of the products was accomplished by TLC on silica gel poly gram SIL G/UV
2
54 plates. Products were separated by simple filtration, and identified by comparison IR,
1
and H NMR spectra, with those reported for authentic samples.
General Procedure for Oxidation of Sulfides to Sulfones
To a suspension of sulfide (1 mmol) and PVPP-BF3 (0.1 g) in nitromethane (5 mL),
3
2
5% hydrogen peroxide (3 mmol) was added dropwise. The reaction mixture was stirred for
–3 h at room temperature. After completion of the reaction (TLC), the mixture was filtered
and washed with Et2O (5 mL). The filtrates were extracted with diethyl ether (20 mL), and
the combined organic fraction was washed with 3% NaHSO3 and dried over Na2SO4.
Evaporation of the solvent gave the corresponding sulfone in 96%–99% yields.
Table 5 The recycling of PVPP-BF3 in the oxidation of dibenzylsulfide to sulfonsa
Run
1
2
3
4
Yield (%)b
97
90
78
67
aAll reactions were carried out using 0.1 g of the polymeric reagent,
mmol sulfide, and 3 mmol of H2O2.
1
b
Isolated yields.

3
26
M. MOKHTARY ET AL.
Benzyl Cyclohexyl Sulfone (Entry 7)
◦
◦
−1
Mp = 99 C–101 C; IR (KBr): (υmax, cm ) = 2927, 2854, 1486, 1452, 1295, 1261,
1
1
2
124, 1027. H NMR (400 MHz, CDCl3) δ = 1.26–2.21 (m, 10H), 2.78 (m, 1H), 4.23 (s,
+
H), 7.41–7.46 (m, 5 H) ppm. MS (m/z) 238 (M ).
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