COMMUNICATION
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Highly efficient oxidation of sulfides with hydrogen peroxide catalyzed
2
ꢀ
by [SeO {WO(O ) } ] w
4
2 2 2
Keigo Kamata,ab Tomohisa Hirano and Noritaka Mizuno*ab
a
Received (in Cambridge, UK) 21st April 2009, Accepted 11th May 2009
First published as an Advance Article on the web 2nd June 2009
DOI: 10.1039/b907952a
By using the selenium-containing dinuclear peroxotungstate at
0
.005–0.1 mol%, various kinds of sulfides could be converted
into the corresponding sulfoxides or sulfones in excellent yields
with one or two equivalents of H O with respect to the sulfide,
2
2
respectively.
ð1Þ
Organosulfur compounds such as sulfoxides and sulfones are
important as intermediates in the synthesis of natural products
1
and biologically significant molecules, ligands in asymmetric
To the best of our knowledge, the use of selenium-containing
2
3
catalysis, and oxo-transfer reagents. The selective oxidation
of sulfides to sulfoxides is conventionally achieved by using
2 2
peroxotungstate in the catalytic oxidation of sulfides with H O
has not been previously reported. This study provides the first
example of an artificial catalyst with high catalytic activity
comparable to that of a natural enzyme.
stoichiometric oxidants such as peracids, dioxiranes, NaIO ,
4
4
, and PhIO. These stoichiometric systems
MnO
2
, CrO
3
, SeO
2
are not atom-efficient. In contrast, the catalytic oxidation
of sulfides with H is attractive because H is easily
The catalytic activity of I was compared with those of
selenium and tungsten catalysts for the oxidation of thioanisole
(1a) (Table S2w). Under the stoichiometric conditions using
2
O
2
2 2
O
available and environmentally benign with the formation of
water as the only by-product. There are many reports of
an equimolar amount of H
2 2
O with respect to the sulfide
the H
2
O
2
-based oxidation of sulfides by homogeneous and
2 2
(sulfide : H O : I = 1000 : 1000 : 1), 1a could efficiently be
heterogeneous organocatalysts, acid catalysts, enzymes, and
metal catalysts such as Sc, Ti, V, Cr, Mn, Fe, Cu, Zr, Nb,
oxidized to the corresponding sulfoxide (2a). Among
the catalysts tested, I showed the highest yield (90%) and
the selectivity to 2a was 95%. The oxidation did not proceed in
5
Mo, Ru, Ta, W, Re, Pt, Au, and polyoxometalates.
However, most of them need an excess amount of H O
2
the absence of I. The SeO
various oxidations with H
The catalyst precursor H
present conditions even in the presence of H
2
catalyst, which has been applied to
2
7
(
1.1–8.0 equivalents with respect to sulfide) to achieve high
2
O
2
, showed low catalytic activity.
WO was also inactive under the
SeO . The
yields of the sulfoxides (see Table S1w). While some catalytic
systems such as Ti-, V-, and Fe-based systems show high yield
and selectivity to sulfoxide for the sulfoxidation with an
2
4
2
4
catalytic activities of other peroxotungstates were lower than
equimolar amount of H
2
O
2
, the reactivity and substrate scope
that of I and the reactivities were strongly dependent on the
8
kinds of hetero atoms and the numbers of tungsten atoms.
are not satisfactory. In these contexts, the development of
an efficient oxidation of various kinds of sulfides with an
The reaction rate of I was eight times larger than that of the
equimolar amount of H
demanded.
2
O
2
with respect to the sulfide is still
simple dinuclear peroxotungstate (TBA)
2 2 2 2
[{WO(O ) } (m-O)],
suggesting that the dimeric tungsten unit is activated by the
2
ꢀ
We have reported an efficient and simple route for the
epoxidation of various homoallylic and allylic alcohols
connection with the SeO
4
ligand. The reaction rates of the
nꢀ
dinuclear peroxotungstates with XO
4
ligands (X = Se, S, P,
ꢀ1
with H O2 catalyzed by a selenium-containing dinuclear
2
As, and Si) decreased in the order of Se (25.0 mM min ) 4
1
ꢀ
ꢀ1
peroxotungstate, (TBA)
2
[SeO
N ).z In this communication, we report the
selective oxidation of sulfides with H catalyzed by I.
4
{WO(O
2
)
2
}
2
]
(I, TBA
=
S
(16.0 mM min
ꢀ1
)
4
As (4.1 mM min
ꢀ1
)
4
P
+
6
(
n-C
H
4 9
)
4
(3.7 mM min ) 4 Si (0.5 mM min ). The rates for the
epoxidation of homoallylic alcohols and the pK values of
XO decreased in the same order. Since the pK values of
a
6
2
O
2
a
Notably, use of I at 0.005–0.1 mol% molar concentrations
resulted in the quantitative conversion of sulfides to the
corresponding sulfoxides or sulfones with one or two equivalents
H
n
4
ligands can be an index of the Lewis acidity of transition metal
9
complexes, the strong Lewis acidity of W atoms in I has an
of H
2
O
2
with respect to the sulfide, respectively (eqn (1)).
important role in the oxidation.
The present system also catalyzed the oxidation of various
aromatic and aliphatic sulfides using an equimolar amount of
a
Department of Applied Chemistry, School of Engineering, The
University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656,
Japan. E-mail: tmizuno@mail.ecc.u-tokyo.ac.jp;
Fax: +81-3-5841-7220; Tel: +81-3-5841-7272
Core Research for Evolutional Science and Technology (CREST),
Japan Science and Technology Agency (JST), Japan
2 2
H O with respect to the sulfide (Table 1). The reaction
proceeded smoothly with a substrate/catalyst ratio of 1000
at 293 K. Various kinds of sulfides were selectively oxidized to
the corresponding sulfoxides with high H O efficiency
b
2
2
(95–99%). Thioanisoles 1a–i were oxidized to the corresponding
w Electronic supplementary information (ESI) available: Experimental
details, product data, and Tables S1 and S2. See DOI: 10.1039/b907952a
sulfoxides 2a–i (entries 1–11) and the reaction rates were
3
958 | Chem. Commun., 2009, 3958–3960
This journal is ꢁc The Royal Society of Chemistry 2009
Kamata, Keigo
