Selective and efficient oxidation of sulfides to sulfoxides using ammonium cerium (IV) nitrate in the presence of a catalytic amount of KBr or NaBr

Article abstract of DOI:10.1007/s00706-008-0868-6

A wide range of aliphatic or aromatic sulfides are selectively oxidized to the corresponding sulfoxides using ammonium cerium (IV) nitrate (CAN) and a catalytic amount of KBr or NaBr in the presence of wet SiO₂ in CH₂Cl₂ u

Full text of DOI:10.1007/s00706-008-0868-6

Monatsh Chem 139, 895–899 (2008)
DOI 10.1007/s00706-008-0868-6
Printed in The Netherlands
Selective and efficient oxidation of sulfides to sulfoxides using ammonium
cerium (IV) nitrate in the presence of a catalytic amount of KBr or NaBr
Mohammad Ali Zolfigol1, Kamal Amani2, Maryam Hajjami2, Arash Ghorbani-Choghamarani3
1
Faculty of Chemistry, Bu-Ali Sina University, Hamadan, Iran
2
Department of Chemistry, Faculty of Science, University of Kurdistan, Sanandaj, Iran
3
Department of Chemistry, Faculty of Science, Ilam University, Ilam, Iran
Received 5 December 2007; Accepted 10 December 2007; Published online 21 April 2008
# Springer-Verlag 2008
Abstract A wide range of aliphatic or aromatic sul-
fides are selectively oxidized to the corresponding
sulfoxides using ammonium cerium (IV) nitrate (CAN)
and a catalytic amount of KBr or NaBr in the pres-
ence of wet SiO2 in CH2Cl2 under heterogeneous
conditions in moderate to high yields.
have become increasingly important. Also it is usu-
ally observed that sulfoxidation is sufferes by at least
one of the following disadvantages: long reaction
times, low selectivity, low yields of products, toxi-
city, expensive reagents and catalysts, etc. Fur-
thermore, sulfoxides can undergo overoxidation to
sulfones and therefore it is important that the catalyst
has low reactivity towards the sulfoxides [31].
Keywords Sulfides; Sulfoxides; Ammonium cerium (IV)
nitrate (CAN); Monoselectivity.
Results and discussion
Introduction
To overcome the above mentioned disadvantages
and in continuation of our studies on the application
of oxidizing agents in organic transformations [32–
38] we became interested in the use of a new oxidiz-
ing system, based on in situ generation of Xþ for the
selective oxidation of sulfides to sulfoxides.
To find the best catalytic conditions for the oxi-
dation of sulfides, a combination of different oxi-
dants and catalytic amounts of KBr, NaBr, or NaCl,
in the presence of wet SiO2 (50% w=w) in dichlor-
omethane at room temperature was examined, and
the results are summarized in Table 1. As it can
be seen in Table 1, the best choice is referred to
ammonium cerium (IV) nitrate (CAN)=KBr or NaBr.
Subsequently we screened different solvents for the
oxidation of dibenzyl sulfide and found that dichlor-
omethane is the best solvent in term of activity and
selectivity (Table 2).
The chemistry of sulfoxides has been attractive to
organic chemists. The interest to the chemistry of
sulfoxides is due to the fact that sulfoxides are im-
portant synthetic intermediates in the preparation of
biologically and medicinally compounds [1–3].
Sulfoxides have been also used extensively in C–C
bond-forming, molecular rearrangements, and func-
tional group transformations [4–8].
Although many reagents are available for the oxi-
dation of sulfides to the sulfoxides [9–30], the cata-
lytic process with environmentally benign oxidants
Correspondence: Mohammad Ali Zolfigol, Faculty of Chem-
istry, Bu-Ali Sina University, P.O. Box 6517838683,
Hamadan, Iran. E-mail: Zolfi@basu. ac.ir; Kamal Amani,
Department of Chemistry, Faculty of Science, University of
Kurdistan, P.O. Box 6617715175, Sanandaj, Iran. E-mail:
amani_71454@yahoo.com

896
M. A. Zolfigol et al.
Table 1 Comparison of different oxidants in oxidation of sulfides using catalytic amounts of a metal halide, in the presence of
wet SiO2 (50% w=w) in CH2Cl2 at room temperature
Entry
Substrate
Oxidizing system
Substrate=
oxidant=MXa
Time=h
Yield=%b
c
1
2
3
4
5
6
7
8
benzyl phenyl sulfide
benzyl phenyl sulfide
benzyl phenyl sulfide
benzyl phenyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
benzyl phenyl sulfide
benzyl phenyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
dibenzyl sulfide
(NH4)2Ce(NO3)6 ꢀ 2H2O=KBr
(NH4)2Ce(NO3)6 ꢀ 2H2O=KBr
(NH4)2Ce(NO3)6 ꢀ 2H2O=KBr
(NH4)2Ce(NO3)6 ꢀ 2H2O=NaCl
(NH4)2Ce(NO3)6 ꢀ 2H2O=KBr
(NH4)2Ce(NO3)6 ꢀ 2H2O=NaBr
(NH4)2Ce(NO3)6 ꢀ 2H2O=NaCl
Oxone+=KBr
1:1.5:0.3
1:1.1:0.15
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.3:0.2
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
1:1.1:0.3
0.75
1.5
0.5
2
0.3
0.3
15
5
2.5
2.5
5
5
5
2
3.5
2
2
3
4
3
3
3
–
d
–
83
e
–
96
89
c
–
–
–
e
9
Oxone+=KBr
d
10
11
12
13
14
15
16
17
18
19
20
21
22
Oxone+/KBr
51f
e
(NH4)4Ce(SO4)4 ꢀ 2H2O=KBr
–
–
–
–
–
–
–
–
–
–
–
–
g
KClO3=KBr
HIO4=KBr
e
g
NH4VO2=KBr
NaBO2H2O2 ꢀ 3H2O=KBr
g
g
Na2WO4=KBr
g
DABCO-DNODP=KBr
UHP=KBr
HIO3=KBr
(NH4)2S2O8=KBr
K2S2O8=KBr
Na2O2=KBr
g
d
g
g
g
c
a
b
Substrate: wet SiO2 ¼ 1 mmol: 0.3 g; Isolated yield; Reaction was completed but impurity of sulfone was observed;
g
was observed on the TLC; GC yield; No reaction
Reaction did not complete and a mixture of sulfoxide and sulfone was observed; e Reaction did not complete and a few spots
d
f
Table 2 Oxidation of dibenzil sulfide using ammonium
cerium(IV) nitrate CAN and catalytic amounts of KBr in
the presence of wet SiO2 (50% w=w)a in different solvents
To show the catalytic role of KBr and NaBr in the
described system, benzyl-phenyl-sulfide was sub-
jected to the oxidation without any KBr and NaBr.
However, the reaction did not complete after 15 h
and an impurity of sulfone was observed (Table 3,
entry 2). Also we considered the role of wet SiO2 in
our system and found that sulfoxidation was not per-
formed without this agent (Table 3, entry 3).
It is of interest that this oxidizing system was
monoselectively oxidized thianthrene to thianth-
rene monosulfoxide (Table 3, entries 19, 20 and
Scheme 2).
To consider the chemoselectivity of the described
system, two sulfides containing an alcoholic group
were subjected to the sulfoxidation reaction, but
alcohol oxidation did not occur under these condi-
tions, and primary hydroxyl groups remained intact
during the reaction (Table 3, entries 13,14, 21, and
22, and Scheme 3).
Entry
Solvent
Time=min
Yield=%b
c
1
2
3
4
5
acetonitrile
acetone
chloroform
dichloromethane
n-hexane
105
120
105
20
–
–
d
98
96
d
120
–
a
Sub.:CAN:KBr:wet SiO2 ¼ 1 mmol:1.1 mmol:0.3 mmol:
b
c
0.3 g; Isolated yield; Reaction was completed but a few
spots was observed on the TLC; d Reaction did not complete
and a few spots was observed on the TLC
Eventually, we wish to report here the selective
oxidation of different types of sulfides 1 to the corre-
sponding sulfoxides 2 using CAN (I) and catalytic
amounts of KBr (II) or NaBr (III) in the presence
of wet SiO2 (50% w=w) in dichloromethane at room
temperature with good to excellent yields (Scheme 1
and Table 3).
A plausible mechanism of this oxidation is shown
in Scheme 4 based on reported pathway in Refs. [34,
39], our observations and obtained results.

Selective and efficient oxidation of sulfides
897
Scheme 1
Table 3 Oxidation of sulfides 1 to the corresponding sulfoxides 2 using CAN (I) and catalytic amounts of KBr (II) or NaBr (III)
in the presence of wet SiO2 (50% w=w) in dichloromethane at room temperature
Entry
Substrate
Product
Substrate=reagent=catalystsa
Time=min
Yield=%b
I
II
III
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1b
1b
1c
1c
1d
1d
1e
1e
1f
2a
2a
2a
2a
2b
2b
2c
2c
2d
2d
2e
2e
2f
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
0.4
–
0.3
–
0.3
–
0.3
–
–
–
–
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
0.3
–
35
83
–
–
c,d
15 h
24 h
35
6 h
6.5 h
20
20
30
15
25
e,f
93
96
88
96
89
98
98
98
85
97
98
98
89
46g
68g
92
91
81
77
67
74
79
81
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
20
25
80
15
1f
2f
1g
1g
1h
1h
1i
1i
1j
1j
2g
2g
2h
2h
2i
2i
2j
2j
20
5 h
4.75 h
80
95
10
25
20
20
15
1k
1k
1l
2k
2k
2l
0.3
–
1l
2l
0.3
30
a
b
c
Substrate: wet SiO2 ¼ 1 mmol: 0.3 g; Isolated yield; Reaction did not complete and impurity of sulfone was observed;
d
e
f
Without KBr and NaBr; Without wet SiO2; No reaction; GC yield
g

898
M. A. Zolfigol et al.
Scheme 2
Scheme 3
In conclusion, we report here an efficient method
for the selective oxidation of sulfides to sulfoxides
under very mild heterogeneous conditions with good
to high yields. Also chemoselectivity, the cheapness
and availability of the reagents, easy and clean work-
up, and high yields make this method attractive. We
believe that the present methodology could be an
important addition to the existing methodologies.
Experimental
Chemicals were purchased from Fluka, Merck and Aldrich
chemical companies. The oxidation products were character-
Scheme 4
1
ized by comparison of their spectral (IR, H NMR, and 13C
NMR) and physical data with authentic samples [14, 40–44].
Reaction of ammonium cerium nitrate CAN with
H2O might in situ generates HNO3. Subsequently,
Brþ can be produced via oxidation of bromide ion
by nitric acid. The final step of oxidation involves a
nucleophilic attack of sulfur on the Brþ followed by
concerted oxygen transfer from water to give sulf-
oxides (Scheme 5).
Oxidation of dibenzyl sulfides to dibenzyl sulfoxide
Potassium bromide (0.0357 g, 0.3 mmol) was added to a solu-
tion of 0.214 g dibenzyl sulfides (1mmol) and 0.3 g wet SiO2
in 10cm3 CH2Cl2 followed by addition of 0.603 g CAN I
(1.1mmol). The resulting reaction mixture was stirred at room
temperature for 20min (the reaction progress was monitored
by TLC) and then filtered. The residue was washed with
20cm3 CH2Cl2. Anhydrous Na2SO4 (1.5g) was added to the
filtrate and filtered off after 20 min. Finally, CH2Cl2 was re-
moved and the yield was 0.222 g (96%).
Acknowledgements
Financial support for this work by the Center of Excellence of
Development of Chemical Methods (CEDCM) of Bu-Ali Sina
University, Hamedan, Iran is gratefully acknowledged.
Scheme 5

Selective and efficient oxidation of sulfides
899
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