A Selective Conversion of Sulfides to Sulfoxides in 3-Fluorophenol

Article abstract of DOI:10.1081/SCC-120027258

A novel, convenient and selective procedure of oxidizing sulfides to sulfoxides with 30% aqueous H₂O₂ in 3-fluorophenol at room temperature was described. The procedure was very simple and no strict conditions were required for the s

Full text of DOI:10.1081/SCC-120027258

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A Selective Conversion of Sulfides to Sulfoxides in 3-
Fluorophenol
a
a
a
a
Wei Liang Xu , Yun Zheng Li , Qing Shan Zhang & He Sun Zhu
a
School of Chemical Engineering and Environment , Beijing Institute of Technology , No.
, Zhang Guan Cun South Avenue, Hai Dian District, Beijing, 100081, P.R. China
5
Published online: 18 Oct 2011.
To cite this article: Wei Liang Xu , Yun Zheng Li , Qing Shan Zhang & He Sun Zhu (2004) A Selective Conversion of
Sulfides to Sulfoxides in 3-Fluorophenol, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 34:2, 231-237, DOI: 10.1081/SCC-120027258
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w
SYNTHETIC COMMUNICATIONS
Vol. 34, No. 2, pp. 231–237, 2004
A Selective Conversion of Sulfides to
Sulfoxides in 3-Fluorophenol
*
Wei Liang Xu, Yun Zheng Li, Qing Shan Zhang,
and He Sun Zhu
School of Chemical Engineering and Environment, Beijing Institute
of Technology, Beijing, P.R. China
ABSTRACT
A novel, convenient and selective procedure of oxidizing sulfides to
sulfoxides with 30% aqueous H O in 3-fluorophenol at room tempera-
2
2
ture was described. The procedure was very simple and no strict con-
ditions were required for the selective conversion. The reaction was
finished within 20 min and the yield was excellent. The specific role of the
solvent in the selectivity was also exhibited.
2 2
Key Words: Sulfide; Sulfoxide; Oxidation; 3-Fluorophenol; H O .
*
Correspondence: Wei Liang Xu, School of Chemical Engineering and Environment,
Beijing Institute of Technology, No. 5, Zhang Guan Cun South Avenue, Hai Dian
District, Beijing 100081, P.R. China; Fax: 86-10-68913293; E-mail: xwl3831@
sina.com.
2
31
DOI: 10.1081/SCC-120027258
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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REPRINTS
2
32
Xu et al.
Organic sulfoxides are useful synthetic intermediates for the construction
[1,2]
of various chemically and biologically significant molecules.
tion of sulfides is still the most common method for preparing sulfoxides.
The oxida-
[3]
[4]
Many oxidants are available to perform this key transformation such as
[9]
KHSO,
Unfortunately, most of these reagents are not satisfactory for the medium to
[
5,6]
[7]
[8]
MnO2, RuO4, and 4-methylmorpholine oxide with OsO4.
[
10]
large-scale synthesis
because they are often harmful or toxic, and have the
problem of over oxidation of sulfoxides to sulfones. Despite careful control of
the reaction temperature, reaction time and the relative amount of oxidants, it
[11]
is frequently difficult to avoid such over oxidation. Consequently, there is a
need for development of a convenient, selective and efficient reagent for the
conversion of sulfide to sulfoxide.
The group of Ravikumar have reported that the perfluoro-cis-2,3-
dialkyloxaziridines oxidize selectively 1-trifluoromethyl vinyl sulfides to the
[
12]
corresponding sulfoxides at 2508C in a fluorous system CHCl /CFCl .
A
fluorous phase has effectively been proved to present several advantages in
3
3
[13–16]
organic synthesis, and in oxidation processes.
The group of K.S.
Ravikumar have also recently described a new operationally simple, non-
catalyzed system of selective oxidation of sulfides using aqueous H O and
2
2
[11]
hexafluoro-isopropanol (HFIP) as fluorous alcoholic solvent.
But the HFIP
used is expensive and volatile which severely restrict the using of it in organic
synthesis.
Now, we wish to report a very convenient, simple and selective method
for the synthesis of sulfoxides through the oxidation of sulfides by the classical
oxidizing reagent H O without any catalyst in 3-fluorophenol [Eq. (1)].
2
2
The oxidation of ethylphenylsulfide (10 mmol) was carried out in 3-
fluorophenol (14 mL) with 30% aqueous H O (20 mmol) at room temperature
2
2
and yielded after 40 min the corresponding ethylphenyl sulfoxide as the only
product in excellent yield (98%). Prolonging the reaction to 4 h didn’t give any
sulfone. When ethylphenyl sulfoxide was allowed to react (14 h) with 30%
aqueous H O in 3-flurophenol at 258C, the starting reactant was recovered
2
2
and remained unchanged.
The advantages of this method is obvious: (1) it does not demand of
catalyzer such as a metal complex or any cooxidant; (2) the 3-fluorophenol
and H O are easily available and the 3-fluorophenol can be recovered and
2
2
reused without any difficulty which meets the spirit of green chemistry; (3) the
reaction is efficient and no overoxidation products are obtained. It is different

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Conversion of Sulfides to Sulfoxides in 3-Fluorophenol
233
[
17]
[18]
from the reactions carried out by using KMnO4, CF CO H or NaClO
[19]
3
3
as oxidant in which both sulfoxide and sulfone are found.
A series of sulfides was then reacted with this remarkably simple
procedure and the results are presented in Table 1. As shown, all the reactions
were finished within a very short time and both aliphatic and aromatic sulfides
were oxidized. All the reactions occurred with complete selectivity for
sulfoxide formation and no overoxidation products such as sulfones were
Table 1. Oxidation of sulfides with 30% aqueous H
2
O
2
in 3-fluorophenol.
React. time Yield
Entry
1
Substrate
Product
(min)
(%)
12
98
2
3
4
5
6
12
12
20
20
30
91
94
95
93
92
7
40
93
(
continued)

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2
34
Xu et al.
Table 1. Continued.
React. time Yield
(%)
Entry
8
Substrate
Product
(min)
12
89
9
12
12
95
92
1
1
0
1
20
12
95
93
1
2
detected in the reaction mixtures. Cyclosulfide gave cyclosulfoxide without
affecting the bended ring group. Allylic and vinylic sulfides yielding the
corresponding sulfoxides without affecting the carbon-carbon double bond.
All reactions proceeded nearly quantitatively.
The efficiency of the oxidation can be explained by the interaction
between the solvent and H O . The hydroxyl proton in the solvent forms a
strong hydrogen bond with H O and activates the hydroxyl leaving group
2
2
2
2
from H O . More striking is that the solvent prevent from any further
2
2
oxidation into sulfone. The formation of a strong hydrogen bond between the
solvent and the oxygen of the sulfoxides could highly decreased the nucleo-
philicity at sulfur of the sulfoxides.
In order to further realize the oxidation reaction and prove the point
above, we adopted acetic acid as reaction medium. When the reaction was
finished, both sulfoxide and sulfone were found. When the reaction was
carried out in iso-propanol, the reaction was incomplete even after a prolonged
time. It was clear that the pK of the reagent played a key role in the oxidation
a
reaction. If the pK is so low, the strong hydrogen bond between the solvent
a

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Conversion of Sulfides to Sulfoxides in 3-Fluorophenol
235
and the H O will excessively activate the oxidizing ability of H O , thus
2
2
2 2
leads to the overoxidation product. If the pK of the solvent is a little high, the
a
interaction between the solvent and H O is feeble and the H O will not be
2 2
2
2
competent to accomplish the oxidation reaction rapidly.
In conclusion, we have found a new, convenient and selective procedure
of oxidizing sulfides to sulfoxides with 30% aqueous H O in 3-fluorophenol.
2
2
All the reagents demanded are cheap and easily available. The reactions were
carried out at room temperature and no strict conditions were required for
these selective conversions. The bended ring and carbon–carbon double bond
are not affected under the present reaction conditions. This novel oxidation
methodology should find widespread use in organic and pharmaceutical
synthesis.
General Procedure for the Oxidation of Ethylphenyl Sulfide in
3-Fluorophenol
To a stirred solution of ethylphenyl sulfide (1.38 g, 10 mmol) in 3-
fluorophenol (14 mL) at 258C was added 30% aqueous H O (2.25 mL,
2
2
2
0 mmol). The reaction was followed by TLC. After complete disappearance
of reactant (12 mm), the excess H O was quenched with saturated Na SO
3
2
2
2
aqueous solution. The two phases were separated and the aqueous layer was
back extracted with CHCl three times. The combined organic layer was
3
washed with water, dried with anhydrous MgSO and the solvent was removed
4
in vacuo to give the product as an oil (1.51 g, yield 98%).
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Received in Japan May 27, 2003

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