1,2-dipyridiniumditribromide-ethane (DPTBE) as a new oxidizing agent for the chemoselective oxidation of sulfides to the sulfoxides

Article abstract of DOI:10.1080/10426500902849565

A wide range of aliphatic or aromatic sulfides is selectively oxidized to the corresponding sulfoxides using 1,2-dipyridiniumditribromide-ethane (DPTBE) in a mixture of CH2Cl2/H2O under heterogeneous conditions in moderate to high yields. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Full text of DOI:10.1080/10426500902849565

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1,2-Dipyridiniumditribromide-ethane
(DPTBE) as a New Oxidizing Agent for the
Chemoselective Oxidation of Sulfides to
the Sulfoxides
Arash Ghorbani-Choghamarani a , Mohammad Ali Zolfigol b & Tahereh
Azadbakht b
a Department of Chemistry, Faculty of Science , Ilam University ,
Ilam, Iran
b Faculty of Chemistry , Bu-Ali Sina University , Hamadan, Iran
Published online: 24 Feb 2010.
To cite this article: Arash Ghorbani-Choghamarani , Mohammad Ali Zolfigol & Tahereh Azadbakht
(2010) 1,2-Dipyridiniumditribromide-ethane (DPTBE) as a New Oxidizing Agent for the Chemoselective
Oxidation of Sulfides to the Sulfoxides, Phosphorus, Sulfur, and Silicon and the Related Elements,
185:3, 573-577, DOI: 10.1080/10426500902849565
To link to this article: http://dx.doi.org/10.1080/10426500902849565
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Phosphorus, Sulfur, and Silicon, 185:573–577, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902849565
1,2-DIPYRIDINIUMDITRIBROMIDE-ETHANE (DPTBE) AS A
NEW OXIDIZING AGENT FOR THE CHEMOSELECTIVE
OXIDATION OF SULFIDES TO THE SULFOXIDES
Arash Ghorbani-Choghamarani,1 Mohammad Ali Zolfigol,2
and Tahereh Azadbakht2
1Department of Chemistry, Faculty of Science, Ilam University, Ilam, Iran
2Faculty of Chemistry, Bu-Ali Sina University, Hamadan, Iran
A wide range of aliphatic or aromatic sulfides is selectively oxidized to the corresponding sul-
foxides using 1,2-dipyridiniumditribromide-ethane (DPTBE) in a mixture of CH2Cl2/H2O
under heterogeneous conditions in moderate to high yields.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords 1,2-Dipyridiniumditribromide-ethane (DPTBE); oxidation; sulfides; sulfoxides
INTRODUCTION
The chemistry of sulfoxides has been attractive to organic chemists. Interest in the
chemistry of sulfoxides is due to the fact that sulfoxides are important synthetic interme-
diates in the preparation of biologically and medicinally useful compounds.1–3 Sulfoxides
have also been used extensively in C C bond-forming, molecular rearrangements, and
functional group transformations.4–8
There are several reports on the oxidation of sulfides to the sulfoxides with molecular
bromine.9–12 However to decrease the toxicity of molecular bromine, a wide variety of
organic tribromide reagents were reported and applied in different functional group trans-
formations.13–21 Also, recently we have synthesized ({[K.18-crown-6]Br3}n); this reagent
was applied for the oxidative coupling of thiols and bromination of some aromatic com-
pounds.22
Although a number of methods for sulfoxidation have emerged in recent years,23–34
the development of environmentally benign oxidants has become increasingly important.
Received 11 January 2009; accepted 25 February 2009.
Financial support for this work by the Center of Excellence of Development of Chemical Methods (CEDCM)
of Bu-Ali Sina University, Hamadan, Iran is gratefully acknowledged.
Address correspondence to A. Ghorbani-Choghamarani, Department of Chemistry, Faculty of Science, Ilam
University, Ilam, Iran. E-mail: arashghch58@yahoo.com and M. A. Zolfigol, Faculty of Chemistry, Bu-Ali Sina
University, Hamadan, Iran. E-mail: Zolfi@basu.ac.ir
573

574
A. GHORBANI-CHOGHAMARANI ET AL.
-
N+
Br3
-
N+
Br3
DPTBE
Figure 1 1,2-Dipyridiniumditribromide-ethane.
RESULTS AND DISCUSSION
In continuation of our studies on the application of new oxidizing reagents in organic
transformations,35–41 we became interested in introducing a new oxidizing media, based on
in situ generation of Br2 with 1,2-dipyridiniumditribromide-ethane (DPTBE) (Figure 1) as
a new oxidizing agent.
1,2-Dipyridiniumditribromide-ethane has been synthesised previously by Kavala
et al.42 and has been applied for the bromination of a wide variety of organic compounds. In
this communication, we decided to apply 1,2-dipyridiniumditribromide-ethane DPTBE for
the oxidation of different types of sulfides 1 to the corresponding sulfoxides 2 in a mixture
of dichloromethane and H2O at room temperature with reasonable yields (Scheme 1 and
Table I).
O
S
S
DPTBE
CH2Cl2/H2O, rt
R1
R2
R1
R2
1
2
Scheme 1 Oxidation of sulfides into sulfoxides.
Sulfoxidation reactions were selectively carried out under mild conditions, and no
impurity of sulfone was observed whatsoever. The catalytic oxidation procedure is very
simple, and the products are easily isolated from the reaction media by simple filtration and
evaporation of dichloromethane.
To investigate the chemoselectivity of the described system, a sulfide containing an al-
cohol group was subjected to the sulfoxidation reaction, but alcohol oxidation did not occur
under the above-mentioned conditions, and the primary hydroxyl groups remained intact
during the reaction (Table I, entry 5, and Scheme S1, available online in the Supplemental
Materials).
A plausible mechanism of this oxidation is shown in Scheme S2 (see the Supplemental
Materials online) based on the reported pathway in the literature,37,43 our observations, and
obtained results.
To show the efficiency of the described system in comparison with previously reported
bromine-containing reagents, we compared our obtained results for the oxidation of dibutyl
sulfide and dibenzyl sulfide with the best of the well-known data from the literature, as
shown in Table II.
Initially, a reaction between an organic sulfide and bromine (from DPTBE) produces
bromosulfonium as an unstable intermediate. Finally in the presence of water, bromosul-
fonium decomposes to the corresponding sulfoxide.

CHEMOSELECTIVE OXIDATION OF SULFIDES
575
Table I Oxidation of sulfides 1 to the corresponding sulfoxides 2 using 1,2-dipyridiniumditribromide-ethane
DPTBE in CH2Cl2/H2O at room temperaturea
Entry
1
Substrate
Substrate
Time (min)
20
Yield (%)b
73
Ref. c
44
O
S
O
S
O
2
5
87
45–46
S
O
S
3
4
10
10
90
93
27, 44–46, 48
27, 44–46, 48
S
S
S
O
O
S
5
6
20
15
79
85
46, 48
46
S
O
S
OH
OH
O
S
S
S
OMe
OMe
O
O
7
8
5
45
78
46, 47
O
S
CHO
Ph
CHO
Ph
12 h
27, 44–48
S
O
S
aSubstrate/DPTBE for entries 1–7 = 1 mmol: 0.7 g; for entry 8 = 1 mmol: 0.9 g.
bIsolated yield after short column chromatography.
cAll products are known and were identified using comparison of their physical and spectral data (IR, NMR,
or MS) with those reported in the literature.
Table II Comparison of the different methods used for the oxidation of dibutyl sulfide and dibenzyl sulfide
Entry
Substrate
Reagent
Time (min) Yield (%)a
Ref.
1
2
3
4
5
6
Dibutyl sulfide
Dibenzyl sulfide DPTBE
Dibutyl sulfide
Dibutyl sulfide
Dibenzyl sulfide Cetyltrimethylammonium tribromide
DPTBE
10
10
—
80
120
2
93
90
85
99
92
95
This work
This work
1,4-iazabicyclo(2,2,2) octane tribromide
Pyridinium tribromide
9
13
14
49
Dibutyl sulfide
1-Benzyl-4-aza-1-azonia-bicyclo[2.2.2]
octane tribromide
aIsolated yield.

576
A. GHORBANI-CHOGHAMARANI ET AL.
In summary, we report in this article an efficient method for the selective oxidation of
sulfides to sulfoxides under very mild conditions with moderate to good yields. This method
offers the advantage of shorter reaction times, high selectivity, cost effective reagents, and
easy workup.
EXPERIMENTAL
Chemicals were purchased from Fluka, Merck, and Aldrich chemical companies. The
oxidation products were characterized by comparison of their spectral (IR, 1H NMR, and
13C NMR) and physical data with authentic samples. 1,2-Dipyridiniumditribromide-ethane
(DPTBE) was prepared via a reported procedure by Kavala et al.42
Oxidation of Dibenzyl Sulfide to Dibenzyl Sulfoxide: Typical Procedure
DPTBE (0.7 g) was added to a solution of dibenzyl sulfide (0.214 g, 1 mmol) in
CH2Cl2 (8 mL) and H2O (8 mL). This reaction mixture was stirred at room temperature
for 10 min (the reaction progress was monitored by TLC) and then filtered. The residue
was washed with CH2Cl2 (20 mL). Anhydrous Na2SO4 (4 g) was added to the filtrate and
filtered off after 20 min, then CH2Cl2 was removed by a water bath (40–50◦C) and simple
distillation. The crude product was purified by flash silica gel column chromatography
using acetone:n-hexane (4:6) as an eluent, and the pure product was obtained in 90% yield
(0.207 g).
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