Selective oxidation of sulfides to sulfoxides using 30% hydrogen peroxide catalyzed with a recoverable silica-based tungstate interphase catalyst

Article abstract of DOI:10.1021/ol047635d

(Chemical Equation Presented) Various types of aromatic and aliphatic sulfides are selectively oxidized to sulfoxides and sulfones in good to excellent yields using 30% H₂O₂ in the presence of catalytic amounts of a novel recoverable silica-based tungstate interphase catalyst at room temperature. The catalyst can be recovered and reused for at least eight reaction cycles under the described reaction conditions without considerable loss of reactivity.

Full text of DOI:10.1021/ol047635d

ORGANIC
LETTERS
2
005
Vol. 7, No. 4
25-628
Selective Oxidation of Sulfides to
Sulfoxides Using 30% Hydrogen
Peroxide Catalyzed with a Recoverable
Silica-Based Tungstate Interphase
Catalyst
6
Babak Karimi,*,†,‡ Maryam Ghoreishi-Nezhad, and James H. Clark§
†
Department of Chemistry, Institute for AdVanced Studies in Basic Sciences (IASBS),
P.O.Box 45195-1159, GaVa Zang, Zanjan, Iran, Institute for Fundamental Research
(IPM), Farmanieh, P.O.Box 19395-5531, Tehran, Iran, and Clean Technology Center,
UniVersity of York, York YO10 5DD, England
karimi@iasbs.ac.ir
Received November 17, 2004
ABSTRACT
2 2
Various types of aromatic and aliphatic sulfides are selectively oxidized to sulfoxides and sulfones in good to excellent yields using 30% H O
in the presence of catalytic amounts of a novel recoverable silica-based tungstate interphase catalyst at room temperature. The catalyst can
be recovered and reused for at least eight reaction cycles under the described reaction conditions without considerable loss of reactivity.
The selective oxidation of sulfides to sulfoxides is an
attractive and important method in organic chemistry, since
sulfoxides are useful building blocks especially as chiral
problem during the oxidation of sulfides. In recent years,
the newly coined term “green chemistry” has become
increasingly important, with the objective to create new
products, industrial and laboratory processes, and services
1
auxiliaries in organic synthesis They also play key roles in
2
the activation of enzymes. However, this transformation is
that achieve social and economic progress without environ-
5
conventionally achieved using stoichiometric amounts of both
mental detriment. The use of H
O
2 2
as final oxidant offers
3
3h,4
organic and inorganic
reagents, most of which are not
the advantages that it is a cheap, environmentally benign,
and readily available reagent and produces water as the only
suitable for medium to large scale operations and which also
lead to large a volume of toxic wastes. Moreover, over-
oxidation of the sulfoxides to their sulfones is a common
(3) (a) Venier, C. G.; Squires, T. G.; Chen, Y.-Y.; Hussmann, G. P.;
Shei, J. C.; Smith, B. F. J. Org. Chem. 1982, 47, 3773. (b) Murray, R. W.;
Jeyaraman, R. J. Org. Chem. 1985, 50, 2847. (c) Adam, W.; Hadjiarapoglou,
L. Tetrahedron Lett. 1992, 33, 469. (d) Breton, G. W.; Fields, J. D.; Kropp,
P. J. Tetrahedron Lett. 1995, 36, 3825. (e) Kaldor, S. W.; Hammond, M.
Tetrahedron Lett. 1991, 32, 5043. (f) Paquette, L. A.; Carr, R. V. C. Organic
Syntheses; Wiley: New York, 1990; Collect. Vol. VII, p 453. (g) Xiong,
Z.-X.; Huang, N.-P.; Zhong, P. Synth. Commun. 2001, 31, 245. For a review
see: (h) Mata, E. G. Phosphrus, Sulfur Silicon 1996, 117, 231.
(4) (a) Barton, D. H. R.; Li, W.; Smith, J. A. Tetrahedron Lett. 1998,
39, 7055. (b) Hirano, M.; Yakabe, S.; Clark, J. H.; Morimoto, T. J. Chem.
Soc., Perkin Trans. 1 1996, 2693.
†
Institute for Advanced Studies in Basic Sciences.
Institute for Fundamental Research.
University of York.
‡
§
(
1) (a) Soladie, G. Synthesis 1981, 185. (b) Carreno, M. C. Chem. ReV.
995, 95, 1917.
2) (a) Fuhrhop, J.; Penzlin, G. Organic Synthesis, Concepts, Methods,
1
(
Starting materials, 2nd ed.; VCH: Weinheim, 1994. (b) Block, E. Reaction
of Organosulfur Compounds; Academic Press: New York, 1978.
1
0.1021/ol047635d CCC: $30.25
© 2005 American Chemical Society
Published on Web 01/25/2005

6
byproduct. This feature has stimulated the development of
useful procedures for H oxidation, especially with the
aminopropyl group on the surface of commercially available
mesoporous silica followed by acidification of amino groups
using triflic acid and ion exchange of triflate ion by tungstate
(Scheme 1).
2 2
O
7
use of various types of tungsten-based catalyst systems. Very
recently, the elegant work of Noyori and co-workers has
2 4 6 5 3 2
shown that a combination of Na WO /C H PO H and a
quaternary ammonium hydrogen sulfate as an acidic phase
transfer catalyst can be effectively applied for selective
Scheme 1
2 2
oxidation of sulfide to sulfoxides or sulfones using 30% H O
8
under halide-free conditions. Although using this protocol
represents a considerable progress, the protocol needs
homogeneous reaction conditions, and therefore the catalyst
is difficult to recover and reuse. Since the replacement of
current homogeneous oxidation procedures for the production
of fine chemicals by environmentally acceptable protocols
based on recoverable catalysts is one of the major tasks in
green chemistry, solid oxidation catalysts are called to play
9
a crucial role to accomplish this issue. One way to attain
this goal is to immobilize one or more components of the
catalytic systems onto a large surface area solid carrier to
10
create new organic-inorganic hybrid (interphase) catalysts.
An interphase is defined as a region within a material in
which a stationary (organic-inorganic hybrid catalyst) and
mobile component (solvent and reactants) penetrate each
other on a molecular level. According to the definition, an
interphase catalyst is composed of three parts. An inert matrix
8
b
(support), a flexible organic spacer, and an active center.
In contrast to traditional physisorbed heterogeneous catalysts,
in the interphase counterparts the organic spacer provides
sufficient mobility of the reactive center and diminishes
undesired steric effect of the matrix over the accessibility
of the reactive center. Therefore, these systems are able to
simulate homogeneous reaction conditions, and at the same
time they have the advantage of easy separation and recovery
of the heterogeneous catalysts. Owing to the relative mobility
of the reactive center in the interphase catalyst, we hypoth-
esized that it might be possible to replace the phase transfer
catalyst in Noyori’s protocol with a silica matrix having a
quaternary organic spacer. In the present work we wish to
report the results obtained with a novel silica-functionalized
ammonium tungstate as a recoverable heterogeneous catalyst
for selective oxidation of sulfide to sulfoxides using 30%
Typically, a surface-bound amino group at a loading ca.
-
1
0.31 mmol‚g (by TGA/DTG analysis) was obtained.
However, from the simultaneous XRF analysis of the catalyst
for tungsten and sodium it was calculated that the loading
-
1
of the former in the solid was 0.15 mmol‚g , while a trace
amount (less than 0.4 ppm) of the latter was detected. The
major weight loss at high temperature in TGA is character-
istic of chemisorbed materials and confirmed that the
aminopropyl group is covalently bound on the surface of
11
silica. From this result, in combination with those obtained
from TGA and XRF analyses, we can clearly conclude that
the catalyst corresponds to a 2:1 ratio between the surface-
2
-
H
2
O
2
. The catalyst is simply prepared by building up an
bound ammonium group and WO
4
anion (Scheme 1,
compound 1).
(
5) (a) Clark, J. H. Pure Appl. Chem. 2001, 73, 103. (b) Clark, J. H.
Green Chem. 1999, 1, 1. (c) Ghosh, A. et al. Pure Appl. Chem. 2001, 73,
13.
6) For a review on metal-catalyzed epoxidation using H2O2, see: Lane,
B. S.; Burgess, K. Chem. ReV. 2003, 103, 2457.
7) (a) Schultz, H. S.; Freyemuth, H. B.; Buc, S. R. J. Org. Chem. 1963,
8, 1140. (b) Ishii, Y.; Tanaka, H.; Nisiyama, Y. Chem. Lett. 1994, 1. (c)
Stec, Z.; Zawadiak, J.; Skibinski, A.; Pastuch, G. Polish J. Chem. 1996,
0, 1121. (d) Neumann, R.; Juwiler, D. Tetrahedron 1996, 52, 8781. (e)
To test the catalytic activity of 1 we selected the oxidation
of sulfides using 30% H as the model reaction. To
increase accessibility of the H to the catalyst we chose a
solvent mixture CH Cl /MeOH (1:1). We first examined the
oxidation of methyl phenyl sulfide (2 mmol) using 30% H
3 equiv) and 1 (1 mol %, 0.133 g) in CH Cl /MeOH (10
2
O
2
O
2 2
1
(
2
2
(
2 2
O
2
(
2
2
7
mL) at room temperature. We observed that the reaction was
sluggish and only low yields of the corresponding sulfoxide
were formed after 18 h. However, when a similar oxidation
reaction was conducted in the presence of 1 (2 mol %, 0.266
g), methyl phenyl sulfoxide was efficiently formed in
excellent yields within 1.5 h (Table 1, entry 1).
Cresley, N. M.; Griffith, W. P.; Laemmel, A. C.; Nogueira, H. I. S.; Perkin,
B. C. J. Mol. Catal. 1997, 117, 397. (f) Collins, F. M.; Lucy, A. R.; Sharp,
C. J. Mol. Catal. 1997, 117, 397.
(
8) (a) Sato, K.; Hyodo, M.; Aoki, M.; Zheng, X.-Q.; Noyori, R.
Tetrahedron 2001, 57, 2469. (b) Noyori, R.; Aoki, M.; Sato, K. Chem.
Commun. 2003, 1977.
(
9) (a) Corma, A.; Garcia, H. Chem. ReV. 2002, 102, 3837. (b) Mallat,
T.; Baiker, A. Chem. ReV. 2004, 104, 3037.
10) (a) Corma, A.; Garcia, H. Chem. ReV. 2002, 102, 3879. (b) Lu, Z.
(
In a blank experiment no considerable oxidation was
observed under similar reaction conditions in the absence
L.; Lindner, E.; Mayer, H. A. Chem. ReV. 2002, 102, 3543. (c) Wight, A.
P.; Davis, M. E. Chem. ReV. 2002, 102, 3589. (d) Lindner, E.; Kemmler,
M.; Auer, F.; Mayer, H. A. Angew. Chem., Int. Ed. 1999, 38, 2155. (e)
Clark, J. H.; Macquarrie, D. J. Chem. Commun. 1998, 853.
(11) See Supporting Information for details.
626
Org. Lett., Vol. 7, No. 4, 2005

ing sulfoxide was obtained in excellent yields (Table 1, entry
1).
The formation of sulfoxides from diaryl sulfides is difficult
to achieve under standard oxidation procedures using 30%
. Interestingly, under the described reaction conditions
1
Table 1. Oxidation of Aryl Sulfides to Sulfoxide Using 30%
Catalyzed by Silica-Based Ammonium Tungstate
Interphase Catalyst 1
2 2
H O
2 2
H O
even hindered diaryl sulfides furnished the corresponding
sulfoxides in good to excellent yields (Table 1, entries 12-
1
4). It is also worth mentioning that even the strong
withdrawing NO group in the phenyl ring of diaryl sulfides
2
does not affect the synthetic efficiency (Table 1, entry 14).
On the other hand, when using the protocol for the
oxidation of dialkyl sulfides, the formation of the corre-
sponding sulfones was observed along with sulfoxides almost
simultaneously. Decreasing the amount of either catalyst 1
2 2
or H O did not affect the concomitant formation of
sulfoxides and sulfone. Therefore, we decided to pursue the
oxidation of dialkyl sulfides directly to the corresponding
sulfones. We found that under the optimum reaction condi-
2 2
tion by using dibutyl sulfide (2 mmol) and 30% H O (10
mmol) in the presence of 1 (2 mol %) the corresponding
dibutyl sulfone was obtained in excellent yield after 5 h at
room temperature (Table 2, entry 2). In the same way
dibenzyl sulfide and dimethyl sulfide both furnished the
corresponding sulfones in high yields (Table 2, entries 1 and
3
).
Table 2. Oxidation of Alkyl Sulfides to Sulfones Using 30%
Catalyzed by Silica-Based Ammonium Tungstate
2 2
H O
Interphase Catalyst 1
a
Yields refer to isolated yield of sulfones unless otherwise stated. b GC
yields of sulfones.
Catalyst reuse studies were carried out by recycling the
catalyst without further conditioning. Recycling experiments
were examined for the oxidation of methyl phenyl sulfide
on a 5 mmol scale. This was done by decanting the liquid
from the reaction mixture and charging the reaction vessel
a
Isolated yields. b All reactions were completed with >99% GC conver-
c
d
sion unless otherwise stated. Recycling experiment. No epoxidation
products was detected. The reaction was not completed within the indicated
time, yields after column chromatography.
e
2 2
with fresh substrate and 30% H O and then repeating the
of 1 within 1.5 h and the reaction required 24 h time to reach
a reasonable conversion. In a similar way, various types of
structurally diverse aryl alkyl sulfides underwent smooth
oxidation to selectively afford the corresponding sulfoxides
in good to excellent yields (entries 2-10). Another useful
feature of the presented protocol can be seen in the selective
oxidation of allyl phenyl sulfide to the corresponding
sulfoxide. Neither overoxidation to the sulfone nor epoxi-
dation of the double bond was observed, and the correspond-
experiment. Interestingly, the recycled catalyst could be used
for at least eight reaction cycles, corresponding to a overall
turnover number of 340 (Table 1, entry 1). These results
clearly show the practical reusability of the present tungstate
intephase catalyst under the described reaction conditions.
In conclusion, we have shown that the novel silica-based
tungstate interphase catalyst 1 can be easily prepared from
commercially available starting materials. This catalyst
efficiently affects the selective oxidation of a variety of
Org. Lett., Vol. 7, No. 4, 2005
627

sulfides to sulfoxides or sulfones. The catalyst 1 can be
considered as a heterogeneous version of Na WO , and
therefore it is possible to easily recover and reuse for several
reaction cycles without considerable loss of activity. The
oxidation procedure using 1 is free from additives such as
Acknowledgment. The authors acknowledge Institute for
Advanced Studies in Basic Sciences (IASBS) Research
Councils and Institute for Fundamental Research (IPM) for
support of this work. We also acknowledge Mr. Mehdi
Davari for XRF analyses.
2
4
soluble phase transfer catalysts and cocatalysts such as C
6 5
H -
Supporting Information Available: Experimental pro-
cedures and TGA for catalyst 1. This material is available
free of charge via the Internet at http://pubs.acs.org.
PO , which makes it a reasonably environmentally benign
3 2
H
chemical process in terms of potential industrial application
for this transformation. The work on other applications of 1
is currently underway in our laboratories.
OL047635D
628
Org. Lett., Vol. 7, No. 4, 2005