Selective oxidation of sulfides to sulfones using H2O 2 and anderson-type hexamolybdochromate(III) as catalyst

Article abstract of DOI:10.1080/10426500902922958

An Anderson-type hexamolybdochromate(III) is found to be an effective catalyst for the selective oxidation of sulfides to their corresponding sulfones. The reaction was carried out in 60% aq. acetonitrile (v/v) using 30% H2O2 at 60C. Various dialkyl, alkyl-aryl, and diaryl sulfides were selectively oxidized, giving high yields of sulfones after a simple workup procedure.

Full text of DOI:10.1080/10426500902922958

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Selective Oxidation of Sulfides to
Sulfones Using H O and Anderson-Type
2
2
Hexamolybdochromate(III) as Catalyst
a
a
Amit R. Supale & Gavisiddappa S. Gokavi
a
Kinetics and Catalysis Laboratory, Department of Chemistry, Shivaji
University, Kolhapur, India
Published online: 23 Mar 2010.
To cite this article: Amit R. Supale & Gavisiddappa S. Gokavi (2010) Selective Oxidation of Sulfides to
Sulfones Using H O and Anderson-Type Hexamolybdochromate(III) as Catalyst, Phosphorus, Sulfur, and
2
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Silicon and the Related Elements, 185:4, 725-731, DOI: 10.1080/10426500902922958
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Phosphorus, Sulfur, and Silicon, 185:725–731, 2010
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ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902922958
SELECTIVE OXIDATION OF SULFIDES TO SULFONES
USING H O AND ANDERSON-TYPE
2
2
HEXAMOLYBDOCHROMATE(III) AS CATALYST
Amit R. Supale and Gavisiddappa S. Gokavi
Kinetics and Catalysis Laboratory, Department of Chemistry, Shivaji University,
Kolhapur, India
An Anderson-type hexamolybdochromate(III) is found to be an effective catalyst for the
selective oxidation of sulfides to their corresponding sulfones. The reaction was carried
◦
out in 60% aq. acetonitrile (v/v) using 30% H2O2 at 60 C. Various dialkyl, alkyl-aryl, and
diaryl sulfides were selectively oxidized, giving high yields of sulfones after a simple workup
procedure.
Keywords Hexamolybdochromate (III); homogeneous catalysis; hydrogen peroxide; oxida-
tion; sulfones
INTRODUCTION
Sulfoxides and sulfones play an important role in organic synthetic chemistry.1–2
Sulfones are valuable intermediates for the formation of chemically and biologically im-
3
4–8
portant molecules. Among the various oxidants employed for the oxidation of sulfides,
hydrogen peroxide is an ideal oxidant, having water as the only byproduct with high oxygen
9
content. In the case of sulfoxide preparation, careful monitoring of the reaction is required
to minimize the amount of sulfone as a side product, while oxidation of sulfide to sulfone
requires a long reaction time and lengthy treatment with the use of toxic materials and
heavy metals. Several catalysts have also been utilized for oxidation of sulfides by aqueous
10
H2O2, but most of them have one or more drawbacks such as long reaction time, toxic
byproducts, unavailability, and high cost of reagents, as well as selectivity. Polyoxometa-
1
1–13
lates are very good catalysts
for both gas and liquid phase oxidation reactions. They
in various organic transformations. Most of the polyoxomet-
were successfully utilized1
4–17
12
alate catalysis is concentrated on Keggin and Dawson types, and less attention is given to
the other type of polyoxometalates such as Anderson-type compounds.
18
Sodium hexamolybdochromate(III) is an Anderson-type polyoxometalate. Detailed
19
analysis of the structure of catalyst is reported. Among the oxidation states of chromium,
chromium(VI) is carcinogenic, while chromium(III) is required for carbohydrate and lipid
Received 11 January 2009; accepted 24 March 2009.
A. R. Supale gratefully acknowledges UGC, New Delhi, India, for Research Fellowship.
Address correspondence to Dr. Gavisiddappa S. Gokavi, Kinetics and Catalysis Laboratory, Department of
Chemistry, Shivaji University, Kolhapur 416004, India. E-mail: gsgokavi@hotmail.com
7
25

726
A. R. SUPALE AND G. S. GOKAVI
metabolism in mammals.20 In continuation of our work21–24 on catalyzed oxidation reac-
tions, we now present a novel catalytic system for oxidation of sulfides to sulfone by using
aqueous H2O2 and sodium hexamolybdochromate(III) as catalyst, as shown in Scheme 1.
Hexamolybdochromate(III),
O
0
3
0%H O ,60 C
S
2
2
R1
S
R2
R1
R2
60% aq. Acetonitrile (v/v)
O
1a-1l
Scheme 1 Oxidation of sulfide to sulfone catalyzed by hexamolybdochromate(III).
RESULTS AND DISCUSSION
To study the catalytic oxidation of sulfides mediated by Na3[CrMo6O24H6]·8H2O,
methyl phenyl sulfide was chosen as a model compound, and the reaction conditions
were optimized. At room temperature, the reaction is slow and requires 2 h for complete
◦
conversion into sulfone. The reaction proceeds smoothly at 60 C and requires only 10
min for completion. Under these conditions, the presence of sulfoxide was not observed.
Other catalytic derivatives such as molybdenum oxide and ammonium molybdate have
25
been used previously for oxidation of sulfides. These methods only afford sulfoxide as a
major product. Oxidation of sulfides directly into sulfones is the advantage of the method
presented in this article. The present method is compared with previous reports; Table I
indicates the advantages of the present catalytic system over previous methods.
Since the solvent has a pronounced effect on the reaction, it was carried out in various
solvents and the results are shown in Table II. Among the various solvents used, aqueous
acetonitrile (60% v/v) was found to be the most effective solvent, giving a high yield with
comparatively low reaction time. In pure aqueous medium, there was no reaction even after
12 h. In the absence of the catalyst, the reaction did not afford sulfone even after 3 h.
The yield and rate of the reaction were also found to be dependent on the concentration
of the catalyst and oxidant. As the catalyst was decreased from 2 mol% to 0.5 mol%,
the yield of product sulfone decreased, and the reaction time also increased considerably.
The effect of catalyst variation on the reaction rate and yield are tabulated in Table III.
Table I Comparison of the present system with previous systems
Sr. No.
Catalytic system
Time
45 min
3 h
(%) Yield
Ref.
8
1
2
3
4
MoO2Cl2/H2O2 sulfide (4 mmol), 30% H2O2 (4 eq.),
MoO2Cl2(15 mol%) in 10 mL CH3CN at RT.
Titanium catalyst TiO2–400 (37.4 mg), sulfide (0.4 mmol),
H2O2 (1.2 mmol) in 4 mL CH3CN at 80 C
Silica sulfuric acid/ H2O2 SSA(0.2 g), sulfide (1 mmol), 30%
H2O2(3 eq.), in 5 mL CH3CN at RT
95
96
96
94
26
27
—
◦
45 min
10 min
Present system Na3[CrMo6H6O24] (2 mol%), sulfide (1 mmol),
◦
3
0% H2O2(2 eq.) in 10 mL 60% CH3CN (v/v) at 60 C

SELECTIVE OXIDATION OF SULFIDES TO SULFONES
727
Table II Reaction in various solventsa
Solvent
Time (min)
Yield (%)b
Acetonitrile
Methanol
Ethanol
10
20
45
94
85
75
—
Water
720
a
Reaction conditions: sulfide (1 mmol), 2 mol% hexamolybdochromate(III), H2O2
◦
(
2 equivalent) at 60 C in 60% aq. acetonitrile(v/v).
b
Isolated yield.
To study the scope of the reaction, a series of sulfides having dialkyl, diaryl, and alkyl-
aryl groups were chosen. Sulfides including furfuryl methyl sulfide (1i) were selectively
converted into sulfones in high yields as shown in Table IV. It is clear from Table IV that
dialkyl sulfides (1j–1l) afford sulfones in less time in comparison with diaryl (1g) and
alkyl-aryl (entries 1a–1f, 1h) sulfides. It is seen that the substrates containing an electron-
donating group are more reactive than the substrates having electron-withdrawing groups
due to the deactivating effect in the oxidation procedure by diaryl and electron-withdrawing
groups. Since the uncatalyzed reaction is slow under the experimental conditions and the
rate of the reaction depends on both the catalyst and oxidant concentrations, the catalyzed
reaction proceeds with the interaction of the catalyst and the oxidant. We have reported
21
earlier that the oxidation of sulfide takes place via complex formation between Cr(III)
and sulfides. In the present study, the catalyst is a heteropolyoxometalate in which the
hetero atom, Cr(III), is buried within the six molybdate octahedrons, which does not favor
the formation of a complex between the catalyst and the substrate, thus making it an
inert redox catalyst. Therefore, the initiation of the reaction occurs by the oxidation of
the catalyst to its higher oxidation state by hydrogen peroxide, which then affects the
oxidation of the substrate. In order to get further support for the proposed mechanism, the
interaction between the catalyst and oxidant was examined separately under the reaction
conditions. The violet solution of hexamolybdochromate(III) turns green when treated with
H2O2, and the green solution was evaporated to get the crystals of oxidized form of the
catalyst, hexamolybdochromate(V). The FT-IR spectra of both oxidized and unoxidized
hexamolybdochromate(III) were recorded as KBr pellets. The comparison of both the
−
1
spectra indicates that the polyoxometalate characteristic M–Oc–M peak at 643 cm was
29
found to be split into two peaks in the oxidized form due to a change in the oxidation state
of chromium. There was also a new peak at 829 cm , characteristic of Cr = O in the
−1
V
Table III Effect of catalyst on oxidation reactiona
Entry
Catalyst (mol%)
Time (min)
Yield (%)b
1
2
3
4
2
1
0.8
0.5
10
35
40
60
94
85
82
85
a
◦
Reaction conditions: sulfide (1 mmol), H2O2 (2 equivalent) at 60 C in
0% aq. acetonitrile (v/v).
6
b
Pure isolated yield.

728
A. R. SUPALE AND G. S. GOKAVI
Table IV Selective oxidation of sulfides to sulfones catalyzed by hexamolybdochromate(III)a
Time
(min)
Yield
(%)
b
◦
Entry
Sulfide
Sulfone
M.P. C (Rep.)
1
a
SCH3
SCH3
O
S
30
26
88
90
102 (101–102)27
CH3
Br
Cl
O
Br
1
b
O
97 (95–97)27
S
CH
3
O
Cl
1
1
c
SCH3
O
20
20
90
95
76 (76–79)28
S
CH3
F
O
F
d
SCH3
O
85 (88)27
S
CH3
H C
3
O
H C
3
1
e
SCH3
O
S
10
94
85 (86–88)27
CH3
O
O
S
1
1
1
f
SC H
10
10
15
91
94
85
43 (42–43)28
126 (128–130)27
oil
2
5
C H
2
5
O
g
h
S
O
S
O
O
S
CH(CH3)2
S
CH(CH3)2
O
1
i
O
25
74
69
CH SCH3
2
O
CH2
S
CH3
O
O
28
1
1
1
j
k
l
(CH3)2S
(CH3CH2)2S
(CH3CH2)3)2S
(CH3)2SO2
(CH3CH2)2SO2
(CH3CH2)3)S2
6
6
8
92
88
92
109 (108–110)
27
73 (73–75)
27
45 (46)
a
◦
Reaction conditions: sulfide (1 mmol), H2O2 (2 equivalent) at 60 C and 2 mol% hexamolybdochromate(III)
◦
at 60 C in 60% acetonitrile(v/v).
b
Pure isolated yield.
1
All products characterized by H NMR and mass spectrometry.

SELECTIVE OXIDATION OF SULFIDES TO SULFONES
729
FT-IR of the oxidized form of hexamolybdochromate.
III
V
Cr Mo6O24H6(H2O) + H2O2 → (Cr = O)Mo6O24H6 + 2H2O
(1)
On the basis of FT-IR spectral examination of both the unoxidized and oxidized form
V
of hexamolybdochromate, the formation of Cr can be shown as in Equation (1), and the
V
Cr = O formed acts as an oxidant in the present study. The proposed mechanism is shown
in Scheme 2.
2
CrIII
R SO R
1 2 2
2
H O
2 2
2
H O
V
R SR2
1
2
2Cr =O
Scheme 2 A plausible catalytic cycle.
Initially H2O2 reacts with CrIII and forms Cr = O. This Cr = O oxidizes sulfide
to sulfone. The conditions used in the system allowed the use of organic solvents to be
reduced as much as possible. The catalyst used is easy to prepare and is very effective with
H2O2. The method is more advantageous than previous reports due to its green approach.
V
V
CONCLUSION
In summary, the reaction is one-step, rapid, mild, and environmentally benign, giv-
ing high yields of sulfone after a simple workup procedure. The sulfides having various
substituents were selectively oxidized to their respective sulfones. The catalytic role of
hexamolybdochromate is briefly described.
EXPERIMENTAL
All the products are known compounds and were identified by comparison of their
1
0,27 1
physical and spectral data with previous reports in the literature.
H NMR was recorded
onBruker Avance 300MHzspectrometer. Mass spectra were recorded onShimadzuGCMS-
QP2010. Melting points were determined in an open capillary and are uncorrected. Sulfides
were purchased from Lancaster. Acetonitrile and dichloromethane were purchased from
SD Fine Chemicals (Mumbai, India) and used without further purification. All yields refer
to isolated yields.
Catalyst Preparation
The catalyst sodium hexamolybdochromate(III) was prepared by the previously re-
ported method.19 The pH of a solution containing Na2MoO4.2H2O (14.5 g in 30 mL of
water) was adjusted to 4.5 with concentrated HNO3. A second solution was made by dis-
solving Cr(NO3)3 .9H2O (4.0 g in 5 mL of water). The solutions were mixed together,
and the mixture was boiled for 1 min and filtered while hot. The filtrate was set aside for
crystallization, and crystals started to appear in 1 h. the solution was allowed to stand for

730
A. R. SUPALE AND G. S. GOKAVI
2
weeks before the precipitate was filtered off and washed several times with cold water.
Reddish-purple crystals were obtained.
Catalyst Characterization
The complex Na3[CrMo6O24H6]·8H2O was studied by AAS analysis. 100 mg of
recrystallized sample was dissolved in doubly glass-distilled water. 5 mL of this stock
solution was diluted to 100 mL and used for AAS analysis of Cr and Mo metals using
Perkin-Elmer Analyst-300. The complex Na3[CrMo6O24H6]·8H2O shows (Theoretical):
Na—5.6303% (5.6052%), Cr—4.2227% (4.2242%), and Mo–46.217% (46.2109%).
General Procedure for Oxidation of Sulfide
In a typical experiment, methyl phenyl sulfide (1 mmol, 0.124 g) and 30% H2O2
(
2 mmol, 0.22 mL) were taken in 10 mL 60% acetonitrile (v/v) in a round bottom flask. The
◦
catalyst Na3[CrMo6H6O24] (2 mol%) was added. The reaction mixture was stirred at 60 C.
The progress of the reaction was monitored by TLC. After completion of the reaction, the
mixture was treated with dichloromethane (2 × 25 mL). The organic layer was dried by
anhydrous MgSO4 and concentrated to obtain the required product, methyl phenyl sulfone.
It was further purified by column chromatography (silica gel, using hexane:ethyl acetate
◦
9
0:10, v/v). (94% yield, mp = 75 C).
REFERENCES
1
. J. Drabowicz, P. Kielbasinski, and M. Mikolaiczyk, Synthesis of Sulfoxides (Wiley, New York,
994).
1
2. H. L. Holland, Chem. Rev., 88, 473 (1988).
3
. S. Patai andZ. Rappoport, Synthesis ofSulfones Sulfoxides and CyclicSulfides (Wiley, Chichester,
UK, 1994).
4. R. S. Verma, R. K. Saini, and H. M. Meshram, Tetrahedron Lett., 38, 6525 (1997).
5. X. Liang, J. Cheng, and M. Trudell, J. Org. Chem., 68, 5388 (2003).
6. Y. Sasaki, K. Ushimaru, K. Itey, H. Nakayam, S. Yamaguchi, and J. Ichihara, Tetrahedron Lett.,
45, 9513 (2004).
7. A. R. Hajipour, B. Kooshki, and A. E. Ruoho, Tetrahedron Lett., 46, 5503 (2005).
8. A. R. Hajipour, M. El-Shadpour, and A. Hadi, J. Org. Chem., 67, 8666 (2002).
9. G. T. Brink, I. W. C. Arends, and R. A. Sheldon, Science, 287, 1636 (2000).
1
1
1
1
1
1
1
1
1
1
2
2
2
0. K. Jayakumar and D. K. Chand, Tetrahedron Lett., 47, 4573 (2006) and references cited therein.
1. M. T. Pope, Isopoly and Heteropoly Anions (Springer, Berlin, Germany, 1983).
2. A. Muller, Polyoxometalate Chemistry (Kluwer Academic: Dordrecht, The Netherlands, 2001).
3. I. V. Kozhevnikov, Catalysis by Polyoxometalates (Wiley, Chichester, UK, 2002).
4. A. M. Khenkin and R. Neumann, Adv. Synth. Catal., 344, 1017 (2002).
5. R. Neumann and M. Levin, J. Am. Chem. Soc., 114, 7278 (1992).
6. A. M. Khenkin and R. Neumann, J. Am. Chem. Soc., 123, 6437 (2001).
7. S. P. Mardur and G. S. Gokavi, Catal. Commun., 8, 279 (2007).
8. A. M. Khenkin and R. Neumann, Adv. Synth. Catal., 344, 1017 (2002).
9. A. Perloff, Inorg. Chem., 9, 2228 (1970).
0. J. B. Vincent, Polyhedron, 20, 1 (2001).
1. A. R. Supale and G. S. Gokavi, Catal. Lett., 124, 284 (2008).
2. A. R. Supale and G. S. Gokavi, React. Kinet. Catal. Lett., 93, 141 (2008).

SELECTIVE OXIDATION OF SULFIDES TO SULFONES
731
2
2
2
2
2
2
3. S. P. Mardur, S. B. Halligudi, and G. S. Gokavi, Catal. Lett., 96, 165 (2004).
4. A. R. Supale and G. S. Gokavi, React. Kinet. Catal. Lett., 96, 83 (2009).
5. P. P. Samatov, U. V. Dzhemilev, and A. K. Sharipov, Petroleum Chem., 46, 468 (2006).
6. W. Al-Maksoud, S. Daniele, and A. B. Sorokin, Green Chem., 10, 447 (2008).
7. A. Shaabani and A. H. Rezayan, Catal Commun., 8, 1112 (2007).
8. Catalogue Handbook of Fine Chemicals (Lancaster Synthesis Inc., Windham, UK, 2001), pp.
93, 822, 912, 964.
9. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 3rd ed.
Wiley Interscience, New York, 1978).
7
2
(