Highly efficient selective oxygenation of sulfides to sulfoxides by oxalic acid dihydrate in the presence of h2o2

Article abstract of DOI:10.1155/2012/412798

A highly efficient method for the oxidation of sulfides to sulfoxides using oxalic acid dihydrate in the presence of hydrogen peroxide has been developed. A versatile procedure for the oxidation of sulfides to sulfoxides without any over-oxidation to sulf

Full text of DOI:10.1155/2012/412798

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.ejchem.net
2012, 9(2), 863-868
Highly Efficient Selective Oxygenation of
Sulfides to Sulfoxides by Oxalic Acid
Dihydrate in the Presence of H2O2
MASOUD MOKHTARY1*, MOHAMMAD QANDALEE 2 and
MASOUMEH RASTEGAR NIAKI 3
1Department of Chemistry
Rasht Branch, Islamic Azad University, Rasht, Iran
2Department of Biology, Garmsar Branch
Islamic Azad University, Garmsar, Iran
3Department of Chemistry, Science and Research, Amol Branch
Islamic Azad University, Amol, Iran
mmokhtary@iaurasht.ac.ir
Received 15 August 2011; Accepted 4 October 2011
Abstract: A highly efficient method for the oxidation of sulfides to sulfoxides
using oxalic acid dihydrate in the presence of hydrogen peroxide has been
developed. A versatile procedure for the oxidation of sulfides to sulfoxides
without any over-oxidation to sulfones has been reported. This procedure
cleanly oxidizes sulfides to the corresponding sulfoxides in excellent yields at
ambient temperature.
Keywords: Oxidation, Oxalic acid dehydrate, Sulfides, Sulfoxides, Hydrogen peroxide.
Introduction
The ready oxidation of sulfur compounds by appropriate reagents is a key feature of
organosulfur chemistry. Especially, sulfoxides deserved much attention as important chiral
auxiliary in asymmetric synthesis1. However, this transformation is conventionally achieved
using both organic and inorganic reagents2-24, but most of are not suitable for medium to
large scale operations and which also lead to large a volume of toxic wastes. Therefore,
development of green, environmentally acceptable oxidative methodologies has emerged as
an urgent task in this field. Furthermore, over oxidation of the sulfoxides to their sulfones is
a common problem during the oxidation of sulfides. Also, the use of H2O2 as a final oxidant
offers the advantages that it is a cheap and is a readily available reagent and produces water
as the only by product25. Organocatalysis26,27, has gained widespread attention as a result of
the efficiency and selectivity of many organocatalytic reactions. Novel methods employing
organic molecules are advantageous from both a practical and an environmental standpoint
due to their ability to perform in wet solvents under an aerobic atmosphere and to avoid the

864 MASOUD MOKHTARY et al.
possibility of metal contamination that may occur with traditional metal catalyst systems.
Recently, oxalic acid was efficiently used as catalyst in variety of chemical reactions like,
imino Diels-Alder reaction28, Beckmann rearrangement29, synthesis of coumarins30,
protection of carbonyl to thioacetal and deprotection of thioacetal to carbonyl as well31.
In this research we introduce the use of oxalic acid dihydrate as an eco-friendly
promoter for oxidation of sulfides to sulfoxides by hydrogen peroxide at room
temperature (Scheme 1). The use of oxalic acid dihydrate/H2O2 system offers the
advantages that it is an inexpensive, environmentally benign and easy available reagent.
O
HOOC-COOH.2H2O/H2O2
R
S
R'
R
S
R'
CH3OH/ r.t.
Scheme 1
Experimental
All chemicals were purchased from Merck chemical company. A number of sulfides were
prepared using the standard synthetic method.32 Melting points were recorded on an electro
thermal melting point apparatus. The NMR spectra were recorded in CDCl3 with TMS as an
internal standard on a Bruker advance DRX 400 MHz spectrometer. IR spectra were
determined on a SP-1100, P-UV-Com instrument. Purity determination of the products was
accomplished by TLC on silica gel poly gram SIL G/UV 254 plates. Products were
1
separated and identified by comparison IR and H NMR spectra, with those reported for
authentic samples.
Typical Procedure for Oxidation of Sulfides
A solution of sulfide (1 mmol) and 35% hydrogen peroxide (3 mmol) in 5 mL mehtanol was
prepared. Oxalic acid dihydrate (0.5 mmol) was added to the solution and the reaction
mixture was stirred for 2-3 h at room temperature until TLC analysis showed that no sulfide
remained. Then, the mixture of reactions was extracted with dichloromethane (20 mL) and
the combined organic fraction was washed with 3% NaHSO3 and dried over Na2SO4.
Evaporation of the solvent gave the corresponding sulfoxide in 88-98% yields.
Results and Discussion
To select the best solvent, the oxidation of methylphenyl sulfide was studied in a variety of
organic solvents such as methanol, acetonitrile, n-hexane and dichloromethane. Among
them, methanol was found to be the best solvents for oxidation of sulfides to sulfoxides
(Table 1). So, a protic solvent such as methanol is required to facilitate the oxygenation of
sulfide to give the corresponding sulfoxide in excellent yield. To show the role of the oxalic
acid dihydrate in this oxidation reaction, the oxidation of methylphenyl sulfide was carried
out in the absence of the catalyst. The oxidation was very slow and a low yield of
corresponding sulfoxide was formed. As seen in Table 2, the optimized stoichiometric ratio
of RSR′:H2O2 for the conversion of sulfides to sulfoxides was found to be 1:3 using 0.5
mmol of the oxalic acid in methanol at room temperature. We examined the oxidation
reaction of structurally different sulfides with an oxalic acid/H2O2 system in methanol at
room temperature. All reactions were carried out under the optimized conditions and the
results are summarized in Table 3.

Highly Efficient Selective Oxygenation of Sulfides 865
Table 1. Oxidation of methylphenyl sulfide to corresponding sulfoxide in different
solventsa.
Entry
Sulfide, 1 mmol
PhSMe
Solvent
CH2Cl2
CH3OH
CH3CN
n-hexane
Time, h
Yield, %b
1
2
3
4
4
38
96
78
56
PhSMe
1.5
3
3.5
PhSMe
PhSMe
aAll reactions were carried out using 0.5 mmol oxalic acid and 3 mmol of H2O2.
bThe yield was determined by GC analysis of the crude product.
Table 2. Effect of oxalic acid on oxidation of methylphenyl sulfidea.
Entry
Sulfide
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
H2O2, mmol
Oxalic acid, mmol
Yield, %b
1
2
3
4
5
6
1
2
3
1
2
3
0. 25
0. 25
0. 25
0.5
0.5
0.5
42
58
78
56
84
96
aReactions were carried out in methanol at room temperature in 1.5 h. bThe yield was
determined by GC analysis of the crude product.
a,b
Table 3. Oxidation of sulfides to sulfoxides using oxalic acid dihydrate/H2O2
.
Entry
Sulfides
Time/h
Yield, %c
96
M.P.°C (Lit.) 11,14
1
1.5
SCH3
33-34 (31-33)
CH2SCH2
2
2
98
130-132 (131-133)
SCH2
SCH2
3
4
5
6
1.5
2.5
2
96
96
97
90
121-123 (122-123)
178-180 (178-179)
129-131 (128-130)
oil
Br
Cl
SCH2
SCH2-CH=CH2
2
SCH2-CH2OH
SCH2CN
7
8
8
9
2
2
96
93
94
97
150-152 (151-152)
69-71 (70-71)
Cl
H3C
SCH2
SCH2
1.5
2
137-139 (136-137)
104-106 (105-107)
MeO
(CH2=CH-CH2)2S
(CH3CH2CH2)2S
10
11
12
2
2
2
88
94
94
39-41 (40-41)
oil
oil
(CH3CH2CH2CH2)2S
a All the products were characterized by IR, 1H-NMR spectra and comparison with authentic
samples. bReaction conditions: sulfide (1 mmol), oxalic acid dihydrate (0.5 mmol), H2O2 (3
mmol), CH3OH, r.t. c All yields refer to isolated products.

866 MASOUD MOKHTARY et al.
It is clear that sulfide bearing sensitive to oxidation such as hydroxy and carbon–
carbon double bonds are completely unaffected under the reaction conditions (Table 3, entry
6, 7, 10). In order to show the advantages and disadvantages of our method, some of our
results in oxidation of sulfides were compared with some of those reported in literature
(Table 4).
Table 4. Comparison of HOOC-COOH.2H2O/H2O2 with some other catalyst for oxidation
of PhSMe.
Entry
1
Reagent
Conditions
Time Yield (%)a Ref.
Silica-Based Ammonium Tungstate
/H2O2 (30%)
CH2Cl2/MeOH,
r.t.
1.5 h
82
6
3
4
Mont. K10/H2O2 (35%)
Ce(OTf)4·xH2O/H2O2 (50%)
CuBr2/t-BuOOH
MeOH, r.t
THF, r.t
2.5 h
95
93
94
95
90
93
91
85
87
92
89
95
11
12
13
15
16
17
18
19
20
21
22
23
42 min
5
MeCN/reflux 45 min
6
DBUH-Br3/H2O2 (30%)
Ca(OCl)2/moist Alomina
N2O4/Charcoal
MeCN, r.t.
CH2Cl2, r.t.
CH2Cl2, r.t.
MeCN/ reflux
4 oC
1 h
40 min
3 h
7
8
9
PhCH2Ph3PHSO5
2 h
10
11
12
12
13
(Bu4N)[PMo12O40 ]/ UHP
2-PSBA or 2-IBA/ H2O2
HAuCl4.4H2O
72 h
5 h
MeOH, r. t
r.t.
1 h
Cyclohexylidenebishydroperoxide
Thiourea dioxide/ t-BuOOH
CH2Cl2, r.t.
CH2Cl2, r.t.
0.5 h
3.5 h
14
15
fluorous thiourea/H2O2 (30%)
CH2Cl2, r.t.
MeOH, r.t
12 h
95
96
24
-
HOOC-COOH.2H2O/H2O2 (35%)
1.5 h
aYield refers to the corresponding sulfoxide.
It is evident that the oxalic acid dihydrate/H2O2 system allows these
transformations to proceed with excellent selectivity, good yield and milder conditions.
Furthermore, the use of oxalic acid dihydrate makes this method simple, inexpensive, more
convenient and practical. Additionally, competitive oxalic acid dihydrate catalyzed
oxidation reaction of equimolar amounts of methylphenyl sulfide and benzaldehyde at room
temperature lead to the selective formation methylphenyl sulfoxide in good yield, whereas
benzaldehyde remaind unchanged (Scheme 2).
PhSOMe
+
(96%)
PhSMe
+
PhCHO
HOOC-COOH.2H2O/H2O2
CH3OH, r.t. 2 h
PhCOOH (0%)
Scheme 2

Highly Efficient Selective Oxygenation of Sulfides 867
It is suggested that the acid interaction or hydrogen bonding of oxalic acid with
hydrogen peroxide would enhance the electrophilicity and reactivity of hydroperoxy
intermediate (I) much higher than inactivated hydrogen peroxide. At the same time, the
deporting of water as a leaving group would be assisted by nucleophilic attack of sulfide
(Scheme 3).
HO
C
O
C
O
O
O
O
C
O
C
O
O
C
O
C
H
H
HO
OH
HO
OH
R-S-R' +
R-S-R'
H
H2O2
O
R
:
S
H2O
R'
(I)
Scheme 3
Conclusion
Acknowledgment
We are grateful to Islamic Azad University of Rasht Branch and Islamic Azad University,
Science and Research, Amol Branch, for financial assistance of this work.
References
1.
2.
Curreno M C, Chem Rev., 1995, 95, 1717.
Paquette L A and Carr R V C, Organic Syntheses, Wiley: New York, Collect. Vol.
VII, 1990, 453.
3.
4.
5.
Xiong Z X, Huang N P and Zhong P A, Synth Commun., 2001, 31, 245.
Mata E G, Phosphrus, Sulfur Silicon, 1996, 117, 231.
Hirano M, Yakabe S, Clark J H and Morimoto T, J Chem Soc Perkin Trans 1, 1996,
2693.
6.
7.
8.
9.
Karimi B, Ghoreishinezhad M and Clark J H, Org Lett., 2005, 7, 625.N
Ali M H and Bohnert G J, Synthesis, 1998, 1238.
Kim S S, Nehru K, Kim S S, Kim D W and Jung H C, Synthesis, 2002, 2484.
Baciocchi E, Gerini M F and Lapi A, J Org Chem., 2004, 69, 3586.
10. Ali M H, Kriedelbaugh D and Wencewicz T, Synthesis, 2007, 3507.
11. Lakouraj M M, Tajbakhsh M and Tashakkorian H, Lett Org Chem., 2007, 4, 75.
12. Raju B R, Sarkar S, Reddy U C and Saikia A K, J Mol Catal A: Chem., 2009, 308, 169.
13. Das R and Chakraborty D, Tetraheron Lett., 2010, 51, 6255.
14. Mohammadpoor-Baltork I, Memarian H R, Bahrami K and Esmayilpour K,
Phosphrus, Sulfur Silicon, 2005, 180, 2751.
15. Bakavoli M, Motavalizadeh Kakhky A, Shiri A, Ghabdian M, Davoodnia A, Eshghi
H and Khatami M, Chin Chem Lett., 2010, 21, 651.
16. Hirano M, Yakabe S, Itoh S, Clark J H and Morimotoa T, Synthesis, 1997, 1161.
17. Iranpoor N, Firouzabadi H and Pourali A R, Synlett, 2004, 347.
18. Hajipour A R, Mallakpour S E and Adibi H, J Org Chem., 2002, 67, 8666.

868 MASOUD MOKHTARY et al.
19. Sasaki Y, Ushimaru K, Iteya K, Nakayama H, Yamaguchi S and Ichihara J,
Tetrahedron Lett., 2004, 45, 9513.
20. Drabowicz J, Byżwa P, Buczak J, MikoBajczyk M and Laur P, Phosphrus Sulfur
Silicon, 1997, 120, 425.
21. Yuan Y and Bian Y Tetrahedron Lett., 2007, 48, 8518.
22. Suresh S V, Rajesh K, Babu D C, Suryakiran N and Venkateswarlu Y, Tetrahedron
Lett., 2008, 49, 3463.
23. Kumar S, Verma S, Jain L S and Sain B, Tetrahedron Lett., 2011, 52, 3393.
24. Huang Y B, Yi W B and Cai C, J Fluor Chem., 2011, 132, 554.
25. Lane B S and Burgess K, Chem Rev., 2003, 103, 2457.
26. Lelais G Frontiers in Asymmetric Catalysis, Mikami K and Lautens M, (Eds.), Wiley,
New York, 2007.
27. Dalko P I and Moisan L, Angew Chem Int Ed., 2004, 116, 5138.
28. Najarajan R and Perumal P T, Synth Commun., 2001, 31, 1733.
29. Chandrasekhar S and Gopalaiah K, Tetrahedron Lett., 2003, 44, 7437.
30. Kokare N D, Sangshetti J N and Shinde D B, Chin Chem Lett., 2007, 18, 1309.
31. Miyake H, Nakao Y and Sasaki M, Chem Lett., 2007, 36, 104.
32. Lakouraj M M, Movassagh B and Fadaei Z, Synth Commun., 2002, 32, 1237.

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