PyHBr3/TBN/H2O as catalytic system for the oxidation of sulfides to sulfoxides with air as the oxidant

Article abstract of DOI:10.1016/j.tetlet.2013.10.102

Pyridinium bromide perbromide (PyHBr₃) and tert-butyl nitrite (TBN) catalytic system was used for the oxidation of sulfides with air as the oxidant. Under mild conditions (at room temperature), a series of sulfide substrates have been oxidized

Full text of DOI:10.1016/j.tetlet.2013.10.102

Tetrahedron Letters 55 (2014) 56–58
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
PyHBr3/TBN/H2O as catalytic system for the oxidation of sulfides
to sulfoxides with air as the oxidant
⇑
Hua Zhang , Guibin Wang
State Key Laboratory of Fine Chemicals, Dalian University of Technology, No. 2 Linggong Road, 116024 Dalian, Liaoning Province, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2013
Revised 15 October 2013
Accepted 21 October 2013
Available online 28 October 2013
Pyridinium bromide perbromide (PyHBr3) and tert-butyl nitrite (TBN) catalytic system was used for the
oxidation of sulfides with air as the oxidant. Under mild conditions (at room temperature), a series of sul-
fide substrates have been oxidized to their corresponding sulfoxides with high conversion rate. To the
best of our knowledge, for the first time, the PyHBr3/TBN/H2O is reported as exceptional catalyst system
for the oxidation discussed in this Letter.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Sulfides
Oxidation
Sulfoxides
Pyridinium bromide perbromide
tert-Butyl nitrite (TBN)
Air
Introduction
O
S
PyHBr3/TBN/H2O
air CH3CN
room temperature
S
R1
R2
R1
R2
The oxidation of sulfides to their corresponding sulfoxides is
one of the most important transformations in the synthesis of dif-
ferent organisms. Sulfoxides can be used as synthetic intermedi-
ates for the construction of various chemically and biologically
significant molecules,1,2 as well as oxidant for the oxidation of
alcohols.3 Therefore, different methods have been developed to
oxidize various sulfides. However, most of the methods need a
stoichiometric amount of oxidants.4,5 In recent years, hydrogen
peroxide and molecular oxygen as oxidant have attracted much
attention6–10 and have been extensively developed due to environ-
mental protection, low cost, easy handling, safe storage, and pro-
ducing water as the only by-product. Unfortunately, hydrogen
peroxide being a kind of strong oxidizing agent, sometimes is hard
to control, and over-oxidation occurs easily in the reactions.11–14
Compared with hydrogen peroxide, molecular oxygen is easily
controlled. In the previous reports, a lot of high-efficiency catalyst
systems, such as the rhenium,15 ruthenium,16 palladium,17 cobalt,6
copper,18,19 iron,20 and gold21 were used in the reactions with
molecular oxygen as oxidant. However, transition metal catalysts
are commonly expensive and it may also be hard to be removed
from the reaction substrates, which might lower the purity of the
products. Therefore, the new catalysts with no transition metal,
will be of great value.
R1 , R2 = Aryl and Alkyl
Scheme 1.
Our research was initially inspired by the mechanism of selec-
tive catalysis of sulfide oxidations from Ref. 22, in which Bosch
et al. reported that, by using dioxygen and catalytic amounts of
nitrogen dioxide, the alkyl and aryl thioethers can be oxidized into
their corresponding sulfoxides. Our group has carried out some rel-
ative research work23–25 and found DBDMH/NaNO2, Br2/NaNO2/
H2O, and HBr/t-BuONO catalyst systems for catalysis of the aerobic
oxidation of a wide range of sulfides. Meanwhile, it has been re-
ported the use of pyridinium bromide perbromide as oxidant for
the oxidation of sulfides and alcohols.26,27 In this Letter, a novel
metal-free catalytic system PyHBr3/TBN/H2O was applied for the
oxidation of sulfides to their corresponding sulfoxides with air as
the terminal oxidant at room temperature (Scheme 1). This cata-
lytic system is reported for the first time.
Results and discussion
The initial experiment was carried out using methyl phenyl sul-
fide as the substrate with different catalytic systems: PyHBr3/H2O,
tert-butyl nitrite(TBN)/H2O, PyHBr3/TBN, and PyHBr3/TBN/H2O,
⇑
Corresponding author. Tel./fax: +86 0411 849 86205.
E-mail address: zhanghua@dlut.edu.cn (H. Zhang).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.10.102

H. Zhang, G. Wang / Tetrahedron Letters 55 (2014) 56–58
57
Table 1
respectively at 25 °C for 3 h in CH3CN solution. TBN as a source of
NO has easy accessibility and has unique oxidation ability. The re-
sults are listed in Table 1. The entries 1 and 2 showed the first two
catalytic systems have no catalysis activities. Entry 3 showed
better conversion, which indicated the PyHBr3 requiring a co-cata-
lyst to activate the molecular oxygen and reoxidize the HBr to Br2,
and then Br2 can oxidize the sulfide to the corresponding sulfoxide.
The 3 mol % of PyHBr3, 4 mol % of TBN, and 1 ml of H2O system
show the most effective catalytic activity (entry 4), which were
applied to all the experiments below.
The catalysts’ effect on the reactiona
Entry
PyHBr3 (mol %)
t-BuONO (mol %)
H2O (ml)
Conversionb(%)
1
2
3
4
3
0
3
3
0
4
4
4
1
1
0
1
0
0
73
100
a
Reaction conditions: methyl phenyl sulfide (10 mmol), PyHBr3 (0.3 mmol,
0.096 g), t-BuONO (0.4 mmol, 50 l), H2O (1 ml), CH3CN (20 ml), air, 25 °C.
Conversions were determined by GC with area normalization.
l
b
Table 2
Oxidation of sulfides to sulfoxidesa
Entry
Substrate
Product
Time (h)
3
Conversionb (%)
>99
Yieldc (%)
91
S
O
S
1
S
O
S
2
3
3
5
>99
>99
92
94
S
O
S
O
O
S
O
S
4
5
3
>99
>99
84
91
F
F
S
O
S
4.5
Cl
O
Cl
O
S
O
S
6
7.5
>99
71
S
O
S
7
8
9
11
5
>99
>99
>99
88
93
90
O2N
O2N
S
O
S
O
S
O
O
S
9.5
Cl
S
Cl
O
S
10
11
12
24
2
10
>99
95
8
92
80
S
O
S
S
O
S
OH
4
OH
a
b
c
Reaction conditions: substrates (10 mmol), PyHBr3 (0.3 mmol, 0.096 g), t-BuONO (0.4 mmol, 50
Conversions were determined by GC with area normalization.
Isolated yield.
ll), H2O (1 ml), CH3CN (20 ml), air, 25 °C.

58
H. Zhang, G. Wang / Tetrahedron Letters 55 (2014) 56–58
PyHBr3
TBN
NO
Supplementary data
H2O
2H+
R1R2S
Br2
I
O2
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.
10.102. These data include MOL files and InChiKeys of the most
important compounds described in this article.
II
R1R2S+-Br
H2O
NO2
Br
References and notes
R1R2SO+2H+
Scheme 2.
1. Carreno, M. C. Chem Rev. 1995, 95, 1717.
2. Pradilla, R. F. D. L.; Colomer, I.; Colomer, A. Org. Lett. 2012, 14, 3068.
3. Sousa, S. C. A.; Bernardo, J. R.; Fernandes, A. C. Tetrahedron Lett. 2012, 53, 6205.
4. Xiong, Z. X.; Huang, N. P.; Zhong, P. Synth Commun. 2001, 31, 245.
5. Kowalskia, P.; Mitka, K.; Ossowska, K.; Kolarska, Z. Tetrahedron 2005, 61, 1933.
6. Anna, M. M. D.; Mastrorilli, P.; Nobile, C. F. J. Mol. Cata. A- Chem. 1996, 108, 57.
7. Kiriharaa, M.; Yamamoto, J.; Noguchi, T.; Hirai, Y. Tetrahedron Lett. 2009, 50,
1180.
8. Lindén, A. A.; Kruger, L.; Backvall, J. E. J. Org. Chem. 2003, 68, 5890.
9. Trevisan, V.; Signoretto, M.; Colonna, S.; Pironti, V.; Strukul, G. Angew Chem.
2004, 116, 4189.
10. Iwahama, T.; Sakaguchi, S.; Ishii, Y. Tetrahedron Lett. 1998, 39, 9059.
11. Bäckvall, J. E. Modern Oxidation Methods; Wiley-VCH: Weinheim, Gemany,
2004. 119–163.
12. Kon, Y.; Yokoi, T.; Yoshioka, M.; Uesaka, Y.; Kujira, H.; Sato, K.; Tatsumi, T.
Tetrahedron Lett. 2013, 54, 4918.
13. Kirihara, M.; Yamamoto, J.; Noguchi, T.; Itou, A.; Naito, S.; Hirai, Y. Tetrahedron.
2009, 65, 10477.
14. Rahimi, R.; Tehrani, A. A.; Fard, M. A.; Sadegh, B. M. M.; Khavasi, H. R. Catal
Commun. 2009, 11, 232.
15. Huang, R.; Espenson, J. H. J. Mol. Cat. A- Chem. 2001, 168, 39.
16. Zhou, X. T.; Ji, H. B.; Cheng, Z.; Xu, J. C.; Pei, L. X.; Wang, L. F. Bioorg. Med. Chem.
Lett. 2007, 17, 4650.
10 mmol substrates of methyl phenyl sulfide analogues were
reacted with 3 mol % PyHBr3, 4 mol % of TBN, and 1 ml H2O in
20 ml CH3CN at 25 °C with air as oxidant, in which, good conver-
sion rates were found, as shown in Table 2.
With this oxidation system, a variety of sulfides were success-
fully converted to sulfoxides with high conversion rate. From Ta-
ble 2, it has been found that most of the substrates including
electron-rich and nucleophilic-rich aromatic compounds take
more time in the reaction than methyl phenyl sulfide. Substrates
with electron-withdrawing groups take more time than those with
electron-donating groups. This oxidation system did not show a
good oxidation for diphenyl sulfide (entry 10). As we all know,
2-(phenylthio)ethanol (entry 12) has both the sulfide and hydroxyl
functional groups, which may also be oxidized simultaneously. But
this catalytic system has achieved the selective oxidation of the
sulfide without oxidizing the hydroxyl group.
A possible mechanism for this new transition-metal-free cata-
lytic oxidation process can be described by the dual cycle shown
in Scheme 2. Firstly, sulfide was oxidized to the sulfoxide with
Br2 as the oxidant provided by the composition of PyHBr3, in this
reaction H2O can provide the oxygen atom which is needed for
the oxidation of sulfide to sulfoxide. Secondly, through cycle I,
the BrÀ is continuously reoxidized to Br2 by NO2, which is the
key for a catalytic amount of Br2 to oxidize sulfide substrates,
meanwhile, the NO2 is reduced to NO. The NO is easily released
from TBN as an efficient NO equivalent and NO can easily be oxi-
dized to NO2 by O2 through cycle II, at this cycle H+ are easy turn
to H2O. The coupling of the two cycles formed a novel and efficient
aerobic sulfide oxidation system.
17. Aldea, R.; Alper, H. T. J. Org. Chem. 1995, 64, 8365.
18. Song, G.; Wang, F.; Zhang, H.; Lu, X.; Wang, C. Synth Commun. 1998, 28, 2783.
19. Firouzabadi, H.; Iranpoor, N.; Zolfigol, M. A. Synth Commun. 2006, 28, 1179.
20. Martin, S. E.; Rossi, L. I. Tetrahedron Lett. 2001, 42, 7147.
21. Boring, E.; Geletii, Y. V.; Hill, C. L. J. Am. Chem. Soc. 2001, 123, 1625.
22. Bosch, E.; Kochi, J. K. J. Org. Chem. 1995, 60, 3172.
23. Chen, C. Y.; Zhang, H.; Zhang, L. X.; Li, L. D.; Yan, Y. L. Chin. J. Org. Chem. 1978,
2008, 28.
24. Zhang, H.; Chen, C.; Liu, R. Molecules 2010, 15, 83.
25. Zhang, H.; Chen, C.; Liu, R. Synth Commun. 2012, 42, 811.
26. Ali, M. H.; Stricklin, S. Synth Commun. 2006, 36, 1779.
27. Yang, S. H. Synlett 2009, 1351. General procedure for the oxidation of sulfides:
Dissolve PyHBr3 (0.3 mmol) in water (1 ml). Transfer the solution into a 100 ml
round bottom flask with substrate (10 mmol), CH3CN (20 ml), and TBN
(0.4 mmol). The reaction mixture was stirred at room temperature (ꢀ25 °C)
and air condition. Progress of the reaction was monitored by TLC and GC. Upon
completion, the mixtures were removed and dissolved with CH2Cl2. Wash the
mixtures with HCl (1 Â 10 ml), saturated sodium bicarbonate ((2 Â 10ml), and
water (10 ml). The organic layer was dried over anhydrous Na2SO4. The yield
was calculated on the basis of 10 mmol of substrate. Products are determined
by GC, 1H NMR, and 13C NMR.
In conclusion, we have found a highly efficient catalytic system
for the oxidation of different sulfides with air as oxidant and have
provided a very mild method for the oxidation of sulfides without
using any transition metal.
Acknowledgment
The research was supported by Program for Changjiang Schol-
ars and Innovative Research Team in University (IRT0711).