The efficient and chemoselective MoO3-catalyzed oxidation of sulfides to sulfoxides and sulfones with H2O2

Article abstract of DOI:10.1139/V06-177

Hydrogen peroxide together with MoO₃ as catalyst can efficiently and chemoselectivity oxidize sulfides to sulfoxides and sulfones in the presence of other oxidized functional groups in ethanol at 50°C in short reaction times.

Full text of DOI:10.1139/V06-177

7
The efficient and chemoselective MoO3-catalyzed
oxidation of sulfides to sulfoxides and sulfones
with H2O2
Mohammad Mehdi Khodaei, Kiumars Bahrami, and Mohammad Khedri
Abstract: Hydrogen peroxide together with MoO3 as catalyst can efficiently and chemoselectivity oxidize sulfides to
sulfoxides and sulfones in the presence of other oxidized functional groups in ethanol at 50 °C in short reaction times.
Key words: oxidation, sulfides, sulfoxides, sulfones, H2O2–MoO3 system.
Résumé : En opérant dans l’éthanol à 50 °C pour de courtes périodes, le peroxyde d’hydrogène en présence de MoO3
comme catalyseur peut oxyder d’une façon efficace et chimiosélective les sulfures en sulfoxydes et en sulfones, en pré-
sence d’autres groupes fonctionnels oxydés.
Mots-clés : oxydation, sulfures, sulfoxydes, sulfones, système H2O2–MoO3.
[Traduit par la Rédaction] Khodaei et al. 11
Introduction
A range of sulfides, dialkyl, diaryl, alkyl, aryl, and cyclic
sulfides were subjected to the developed reaction procedure
to afford sulfoxides with high chemoselectivity and excellent
yields. The procedure proved to be compatible with other
functional groups and to work under neutral conditions. Hy-
drogen peroxide was used as a 30% solution in water.
We carried out our initial studies with dibenzyl sulfide to
find optimal reaction conditions. After studying various
amounts of catalyst, we found that 0.05 equiv. of the catalyst
was the best choice. Ethanol was selected as the best solvent
as lower catalytic activity was observed with other solvents
such as chloroform, dichloromethane, acetonitrile, and wa-
ter. The optimum amount of H2O2 (30%) in this system was
found to be 1.3 mmol; when higher amounts of oxidant was
employed, a significant increase in the sulfone was ob-
served. For dibenzyl sulfide, a separate experiment showed
that the presence of the catalyst is necessary, since oxidation
with H2O2 alone occurs rather slowly. Looking at the results
reported in Table 1, it is readily seen that the reaction is very
efficient, affording excellent yields of sulfoxides, generally
around 95%, with a reaction time as short as 9 min. The se-
lectivity with respect to the formation of sulfone is also
high.
Sulfoxides are important intermediates in organic chemis-
try because of their application in fundamental research and
other extended usage (1–7). As the sulfoxides are important
for carbon–carbon bond formation and functional group
transformation, the search for new methods for the selective
oxidation of sulfides to sulfoxides continues despite the exis-
tence of a number of methods available for this transforma-
tion. Selective oxidation of sulfides to sulfoxides and
sulfones with the same reagent system under adjusted reac-
tion conditions is an important process in synthetic organic
chemistry and only a few reports are available in the litera-
ture (8–13).
Aqueous hydrogen peroxide is an attractive oxidant be-
cause it is cheap, safely stored and handled, environmentally
friendly, contains effective oxygen, and produces only water
as a byproduct, which is easy to deal with after reactions.
There are many reports on oxidation reactions of sulfides
carried out by a combination of H2O2 and a catalyst that of-
ten increase the efficiency of the oxidant, and therefore the
presence of the catalyst as an activator in the reaction can be
necessary (14–26).
The chemoselectivity of sulfoxidation of sulfides contain-
ing a double bond was examined. As shown in Table 1, entry
13, high chemoselectivity was found as the sulfoxide was
obtained in high yield without any detectable epoxidation of
the double bond. Further selectivity of the proposed method
was investigated and the results are indicated in Scheme 2.
As can be seen, sulfides were selectively converted to
Results and discussion
In continuation of our research on the oxidation of organic
compounds (27–29), we report here our efforts in developing
new catalytic procedures for the oxidation of sulfides to
sulfoxides and sulfones using aqueous hydrogen peroxide
catalyzed by MoO3 (Scheme 1).
Received 20 September 2006. Accepted 17 November 2006. Published on the NRC Research Press Web site at
http://canjchem.nrc.ca on 6 January 2007.
M.M. Khodaei,1 K. Bahrami, and M. Khedri. Department of Chemistry, Faculty of Science, Razi University, Kermanshah 67149,
Iran.
1Corresponding author (e-mail: mmkhoda@razi.ac.ir).
Can. J. Chem. 85: 7–11 (2007)
doi:10.1139/V06-177
© 2007 NRC Canada

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Can. J. Chem. Vol. 85, 2007
Scheme 1.
O
O
S
O
S
H2O2 (2.6 equiv.), MoO3(0.05 equiv.)
EtOH, 50 °C
H2O2 (1.3 equiv.), MoO3 (0.05 equiv.)
EtOH, 50 °C
S
O
O
O
Scheme 2.
sulfoxides, while the oxime, acylal, and alcohol remained
untouched under the same reaction conditions.
Experimental
For the synthesis of sulfones several experiments were
carried out with a 2.0:1 H2O2–substrate molar ratio to check
whether sulfone could be efficiently obtained by using just a
stoichiometric amount of oxidant and also whether in this
case the high chemoselectivity found in the synthesis of
sulfoxides could be observed. It was found that with 2.6
equiv. of oxidant a very efficient synthesis of sulfones is
possible using higher concentrations of catalyst and longer
reaction times than those used for the synthesis of
sulfoxides. In all cases sulfones were isolated in almost
quantitative yields. Sulfones were also obtained without any
detectable formation of the corresponding epoxides (Table 2,
entry 24). The results of the synthesis of sulfoxides from
sulfides in different reaction conditions are listed in Table 3,
which shows that our conditions were more effective than
some others with respect to the yield and to the time of the
reaction.
General experimental procedure for the preparation of
sulfoxides
In
a round-bottomed flask, H2O2 30% (0.15 mL,
1.34 mmol) was added to a mixture of sulfide (1 mmol) and
MoO3 (0.05 mmol, 0.007 g) in EtOH (2 mL). This mixture
was stirred at 50 °C for the appropriate time according to
Table 1. The progress of the reaction was followed by TLC.
After completion of the reaction, H2O (15 mL) was added to
the reaction mixture and filtered. The solid residue was
recrystallized from ethanol to obtain the pure product in
95%–98% yields.
General experimental procedure for the preparation of
sulfones
To a mixtuure of sulfide (1 mmol) and MoO3 (0.05 mmol,
0.007 g) in EtOH (2 mL), 30% aq. H2O2 (0.3 mL,
2.67 mmol) was added and the mixture was refluxed for 8–
30 min (Table 2). The progress of the reaction was followed
by TLC. After completion of the reaction, H2O (15 mL) was
added to the reaction mixture and filtered. The solid residue
was recrystallized from ethanol to obtain the pure product in
92%–98% yields.
In conclusion, this catalytic system efficiently promoted
the oxidation of sulfides to sulfoxides and sulfones. The
method is simple, mild, and inexpensive. A further advan-
tage of this method is its chemoselectivity in the presence of
other oxidized functional groups.
© 2007 NRC Canada

Khodaei et al.
9
Table 1. Oxidation of sulfides to sulfoxides using an H2O2–MoO3 system in ethanol.
Yield
(%)a
Time
(min)
Entry
1
Substrate
Product
O
S
S
12
14
15
9
98
96
97
97
96
O
CH2
2
3
4
5
S
CH2
CH2
S
CH2
O
S
CH2
CH2
S
O
S
Me
Br
CH2
CH2
S
S
Me
Br
O
S
CH2
11
CH2
O
S
6
7
8
17
16
14
95
97
96
CH2
O2N
O2N
CH2 S
O
S
Me
CH2
Me
CH2
S
O
Br
Br
S
CH2
Br
S
CH2
O
9
10
11
18
12
16
97
97
96
CH2
S
Br
Br
Br
Br
CH2
CH2
S
Br
O
S
Me
Br
Br
CH2
S
Me
O
S
CH2
O
CH2
CH2
S
CH2
12
13
13
15
98
94
Me
S CH2
Me
Me
S CH2
Me
O
S
S
O
O
S
40
14
98
S
O
Note: All products were identified by comparison of their physical and spectral data with those reported
in the literature.
aIsolated yields.
© 2007 NRC Canada

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Can. J. Chem. Vol. 85, 2007
Table 2. Oxidation of sulfides to sulfones using an H2O2–MoO3 system in ethanol.
Note: All products were identified by comparison of their physical and spectral data with those re-
ported in the literature.
aIsolated yields.
© 2007 NRC Canada

Khodaei et al.
11
Table 3. Comparison of the effects of different conditions for diphenylsulfoxide preparation from diphenylsulfide.
Entry
Conditions
Yield (%)
Time (min)
Ref.
12
120
35
1
MoO3 (0.05 mmol), H2O2 (1.34 mmol), 50 °C, EtOH
98
95
91
89
99
85
90
2
PMo11VO40H3Py (0.01mol), H2O2 (2 equiv.), RT, CH3CN
30
24
31
25
32
26
3
Mn (III) Schiff-base complex (0.03 mmol), H2O2 (4 equiv.), RT, CH3COOH
MoO2Cl2 (1.5 mol%), H2O2 (1.05 equiv.), RT, CH3COCH3–H2O (1.5:1.0)
TEMPO (0.01 mmol), Cu (II) complex (0.005 mmol), H2O2 (2 equiv.), 20 °C, CH3CN
(Bu4N)3[PMo12O40] (0.01 mmol) – FAp (1 g), H2O2 (1.05 equiv.), 4 °C, solvent-free
SeO2 (1 equiv.), H2O2 (1 equiv.), RT, MeOH
4
20
5a
6a
7
270
4320
10
aThe sulfide was methyl phenyl sulfide.
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1
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Acknowledgments
We are thankful to the Razi University Research Council
for partial support of this work.
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© 2007 NRC Canada