Sulfamic acid-catalyzed oxidation of sulfides to sulfoxides and sulfones using H2O2: Green and chemoselective method

Article abstract of DOI:10.1080/00397911.2011.577924

A mild, efficient, green, and selective oxidation method of sulfides to sulfoxides or sulfones using H₂O₂ in the presence of catalytic amounts of sulfamic acid has been developed. Various substituted sulfides having functional groups such as alcohol, ester, and aldehyde are successfully and selectively oxidized without affecting the sensitive functionalities in good to excellent yields at room temperature.

Full text of DOI:10.1080/00397911.2011.577924

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Sulfamic Acid–Catalyzed Oxidation of
Sulfides to Sulfoxides and Sulfones Using
H O : Green and Chemoselective Method
2
2
a
b
b
Hadi Jafari , Amin Rostami , Firoz Ahmad-Jangi & Arash
c
Ghorbani-Choghamarani
a
Department of Chemistry, Faculty of Science, Sanandaj Branch,
Islamic Azad University, Sanandaj, Iran
b
Department of Chemistry, Faculty of Science, University of
Kurdistan, Sanandaj, Iran
c
Department of Chemistry, Faculty of Science, Ilam University, Ilam,
Iran
Accepted author version posted online: 10 Jan 2012.Version of
record first published: 17 Aug 2012.
To cite this article: Hadi Jafari , Amin Rostami , Firoz Ahmad-Jangi & Arash Ghorbani-Choghamarani
(
2012): Sulfamic Acid–Catalyzed Oxidation of Sulfides to Sulfoxides and Sulfones Using H O :
2 2
Green and Chemoselective Method, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 42:21, 3150-3156
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1
Synthetic Communications , 42: 3150–3156, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.577924
SULFAMIC ACID–CATALYZED OXIDATION OF
SULFIDES TO SULFOXIDES AND SULFONES USING
H O : GREEN AND CHEMOSELECTIVE METHOD
2
2
1
2
Hadi Jafari, Amin Rostami, Firoz Ahmad-Jangi, and
2
3
Arash Ghorbani-Choghamarani
1
Department of Chemistry, Faculty of Science, Sanandaj Branch, Islamic
Azad University, Sanandaj, Iran
Department of Chemistry, Faculty of Science, University of Kurdistan,
Sanandaj, Iran
Department of Chemistry, Faculty of Science, Ilam University, Ilam, Iran
2
3
GRAPHICAL ABSTRACT
Abstract A mild, efficient, green, and selective oxidation method of sulfides to sulfoxides or
2 2
sulfones using H O in the presence of catalytic amounts of sulfamic acid has been
developed. Various substituted sulfides having functional groups such as alcohol, ester,
and aldehyde are successfully and selectively oxidized without affecting the sensitive
functionalities in good to excellent yields at room temperature.
Keywords Catalyst; hydrogen peroxide; oxidation; sulfamic acid; sulfide; sulfone;
sulfoxide
INTRODUCTION
Organosulfur compounds, such as sulfoxides and sulfones, are useful
compounds in organic chemistry because they are valuable intermediates that have
been utilized for a long time for the synthesis of fine chemicals and biologically active
[
1]
compounds. Furthermore, sulfoxidation catalysis has assumed special relevance in
[
the deep desulfurization of fuels because of environmental constraints.
2]
Received March 29, 2011.
Address correspondence to Amin Rostami, Department of Chemistry, Faculty of Science,
University of Kurdistan, Sanandaj, Iran. E-mail: arostami372@gmail.com
3
150

SULFAMIC ACID–CATALYZED OXIDATION OF SULFIDES
3151
The main synthetic route for preparation of these valuable materials is oxi-
dation of corresponding sulfides; therefore different synthetic methods have been
[3–6]
developed for this transformation.
However, many of these procedures utilize
environmentally unfavorable reagents, solvents, and catalysts that highlight the
matter of ecoefficiency in our environmentally conscious times. In addition to this,
in the synthesis of sulfones from sulfides, other oxidizable functional groups, such
as alcohols or olefins, sometimes react as well, producing undesirable compounds.
From the standpoint of so-called green and sustainable chemistry, another
approach to create cleaner and more selective catalytic systems for the organic trans-
[
7]
formations has become increasingly important in recent years. In this way, various
types of metal- and non-metal-catalyzed oxidation of sulfides using environmentally
[
8–23]
[24]
friendly character and cheap oxidants such as H O
2
and O2
have been
2
developed. Despite these recent improvements, the sulfide oxidation reaction
requires further studies with particular focus on the chemoselectivity of the
reaction as well as the effective oxygen utilization, avoiding unproductive H O
2
2
decomposition.
Sulfamic acid (SA, H NSO H) is a common inorganic acid with a mild acidity
2
3
that is nonvolatile, noncorrosive, and utilized as a stable, low-cost, and commercially
available reagent. More important, its water resistance and incapability for forma-
tion of complexes make it an outstanding alternative to metal catalysts, in different
[
25,26]
areas of organic synthesis, as an efficient and green heterogeneous catalyst.
RESULTS AND DISCUSSION
In continuation of our studies into environmentally benign chemical pro-
[
27–29]
cesses, we introduce an efficient and clean procedure for the selective oxidation
of sulfides to sulfoxides or sulfones with H O in the presence of sulfamic acid (SA)
as an environmental acceptable catalyst by controlling the amounts of H O and SA
2
2
2
2
(
Scheme 1).
The optimum amount of H O (1.2 equivalent) in the presence of sulfamic acid
2
2
(0.05 mmol) is ideal for complete conversion of sulfides to sulfoxides, and the use of
excess reagent H O (3.6 equivalent) in the presence of sulfamic acid (0.1 mmol)
2
2
affords the corresponding sulfones in a clean reaction. A series of sulfides was then
subjected to oxidation under the specific conditions required for sulfoxide and sul-
fone production. Some synthetic results are presented in Table 1. The reaction shows
satisfactory general applicability for the production of both sulfoxides and sulfones.
The reactions went on well to afford products in short times and good yields. To
show the chemoselectivity, the sulfides were oxidized in the presence of
oxidation-prone functional groups such as OH, CHO, and COOCH (Table 1,
3
Scheme 1. Sulfamic acid (SA) catalyzed the selective oxidation of sulfides to sulfoxides or sulfones with
2 2
H O .

3152
H. JAFARI ET AL.
Table 1. Selective oxidation of sulfides to sulfoxides or sulfones under neat conditions
a
b
Sulfoxide
Sulfone
Entry
1
Substrate
PhSPh
Time (min)
12
Isolated yield (%)
94
Time
Isolated yield (%)
92
55 min
c
93
2
90
90
250 min
3
4
5
6
7
PhSCH
2
Ph
15
15
12
60
45
95
93
94
81
85
55 min
50 min
15 min
120 min
115 min
95
90
95
75
75
PhSCH
3
PhCH
CH
2
3
2
SCH
2
3
2
Ph
SCH
SCH
CH
3
CH
CH
3
8
9
45
88
120 min
85
d
PhSCH
CH SCH
CH SCH
CH SCH CH
2
CH
CH
CH
COOCH
2
OH
OH
CHO
90
90
40
50
91
88
78
85
180 min
180 min
12 h
No reaction
d
1
1
1
0
1
2
3
2
2
No reaction
d
70
3
2
2
d
80
3
2
2
3
120 min
a
b
c
Reaction conditions: sulfide (1 mmol), 30% H
Reaction conditions: sulfide (1 mmol), 30% H
2
O
O
2
(1.2 equiv), sulfamic acid (5 mol %), rt.
(3.6 equiv), sulfamic acid (10 mol %), rt.
2
2
The disulfoxide=disulfone was formed.
d
ꢀ
(3.6 equiv), sulfamic acid (40 mol %), 80 C.
Reaction conditions: sulfide (1 mmol), 30% H
2
O
2
entries 9–12). It is notable that these functional groups remained intact during the
conversion of sulfides to sulfoxides or sulfones.
To illustrate the catalytic activity of SA, we compared our results for the oxi-
dation of diphenyl sulfide with the best of the well-known data from the literature
(Table 2). As shown in Table 2, the advantages or the characteristic aspects of the
described method in this communication in comparison with other previously
reported catalysts are (1) the use of a commercially available, cheap, metal-free,
Table 2. Comparison of various protocols in the oxidation of diphenyl sulfide using hydrogen peroxide
Sulfoxide
Sulfone
Time Yield Time Yield
(min) (%) Conditions (min) (%) Ref.
Entry
Catalyst
Conditions
1
2
3
Sulfamic acid
MoO Cl
Neat, rt
Acetone, rt
12
21
94 Neat, rt
55
33
92
91
95
—
2
2
89 CH
3
CN, rt
CN,
[15]
[16]
H
5
PMo11Al0.5
V
0.5
O
3
40 CH CN, reflux
120
100 CH
3
240
reflux
4
5
Silica sulfuric acid
Carbon-based solid
acid
CH
3
CN, rt
Cl , reflux
360
95 CH
C
3
CN, rt
Cl
45
10.2
95
95
[17]
[18]
C
2
H
4
2
10.2
98
2
H
4
2
,
reflux
90 CH OH,
reflux
6
7
TaCl
5
CH
t-BuOH, rt
Neat, rt
3
CN or i-PrOH or 120
3
210
16
90
97
[19]
[22]
TAPC
2
91 Neat, rt

SULFAMIC ACID–CATALYZED OXIDATION OF SULFIDES
3153
2 2
Scheme 2. Proposed mechanism for oxidation of sulfides using H O in the presence of SA as catalyst.
ecofriendly, and chemically stable catalyst, and (2) the oxidation reaction under neat
conditions (no need for volatile and toxic organic solvents) at room temperature.
The actual role of SA is not clear. However, on the basis of the previously
reported mechanism for the oxidation of sulfides using hydrogen peroxide in the
[12,13]
presence of an acid catalyst,
one explanation for this process is the in situ for-
mation of persulfamic acid by the reaction of SA with hydrogen peroxide, followed
by the oxygen transfer to the organic substrate (Scheme 2, a). Another explanation is
that SA might act as protic acid, which polarizes the O-O bond in H O to produce
2
2
the reactive oxygen transfer agent (Scheme 2, b). However, at this time the precise
role of SA is not clear.
EXPERIMENTAL
General Procedure for the Oxidation of Sulfides to Sulfoxides
The sulfide (1 mmol) was added to a solution of 30% H O (1.2 equiv, 0.5 g)
2
2
and SA (0.05 mmol), and the mixture was stirred at room temperature for the time
specified in Table 1. The progress was monitored by thin-layer chromatography
(TLC) or gas chromatography (GC). After completion of the reaction, the product
was extracted with diethyl ether (3 Â 10 mL), and the combined organics was washed
with brine (15 mL) and dried over anhydrous Na SO . The solvent was removed
2
4
under reduced pressure to give the corresponding pure sulfoxide in most cases.
Further purification was achieved by short-column chromatography on silica gel
with EtOAc=n-hexane (1=10) as eluent. All the products are known and were char-
1
13
acterized by infrared (IR), H NMR, C NMR, and melting-point comparisons
with authentic samples.
[3,6,14,22,30]
General Procedure for the Oxidation of Sulfides to Sulfones
The sulfide (1 mmol) was added to a solution of 30% H O (3.6 equiv) and SA
2
2
(0.1 mmol), and the mixture was stirred at room temperature for the time specified in
Table 1. The progress was monitored by TLC or GC. After completion of the reac-
tion, the product was extracted with diethyl ether (3 Â 10 mL), and the combined

3154
H. JAFARI ET AL.
organics was washed with brine (15 mL) and dried over anhydrous Na SO . The sol-
2
4
vent was removed under reduced pressure to give the corresponding pure sulfone in
most cases. Further purification was achieved by recrystallization from EtOH. All
1
the products are known and were characterized by IR, H NMR, C NMR, and
13
[
13,14,22,30]
melting-point comparisons with authentic samples.
CONCLUSIONS
In conclusion, we have developed an efficient method for oxidation of sulfides
to sulfoxides and sulfones under mild condition. The notable special features of this
methodology are (i) the use of a commercially available, cost-effective, and green
catalyst and reagent, (ii) simple reaction procedure, easy workup, and good to excel-
lent yield of products, (iii) control over the degree of oxidation offers access to sulf-
oxides or sulfones, (iv) the SA=H O system can be applied to the oxidation of
2
2
sulfides in the presence of oxidation-prone functional groups such as –CHO, –
COOCH , and –OH, and (v) the method conforms to several of the guiding princi-
3
ples of green chemistry. These advantages make this method attractive both for
laboratory and industry.
ACKNOWLEDGMENT
We are thankful to the Islamic Azad University–Sanandaj Branch for partial
support of this work.
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