Selective and efficient oxidation of sulfides to sulfoxides using Ceric Ammonium Nitrate (CAN)/bronsted acidic ionic liquid

Article abstract of DOI:10.1080/10426500802266233

A selective and efficient procedure for the oxidation of sulfides to the corresponding sulfoxides is reported using ceric ammonium nitrate in the presence of methylimidazolium hydrogensulfate as Bronsted acidic ionic liquid ([Hmim]HSO4) as the solvent under mild conditions. The use of nontoxic and inexpensive materials, straightforward procedure, short reaction times, and good yields of the products are the major advantages of this method.

Full text of DOI:10.1080/10426500802266233

This article was downloaded by: [UNIVERSITY OF ADELAIDE LIBRARIES]
On: 09 December 2014, At: 15:20
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Phosphorus, Sulfur, and Silicon
and the Related Elements
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/gpss20
Selective and Efficient
Oxidation of Sulfides to
Sulfoxides Using Ceric
Ammonium Nitrate (CAN)/
Brönsted Acidic Ionic Liquid
Abdol R. Hajipour a b , Leila Khazdooz b & Arnold E.
Ruoho a
a Dept. of Pharmacology , University of Wisconsin,
Medical School , Madison, Wisconsin, USA
b Pharmaceutical Research Laboratory , College
of Chemistry, Isfahan University of Technology ,
Isfahan, Iran
Published online: 19 Feb 2009.
To cite this article: Abdol R. Hajipour , Leila Khazdooz & Arnold E. Ruoho (2009)
Selective and Efficient Oxidation of Sulfides to Sulfoxides Using Ceric Ammonium
Nitrate (CAN)/Brönsted Acidic Ionic Liquid, Phosphorus, Sulfur, and Silicon and the
Related Elements, 184:3, 705-711, DOI: 10.1080/10426500802266233
To link to this article: http://dx.doi.org/10.1080/10426500802266233
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and

are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or
indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Phosphorus, Sulfur, and Silicon, 184:705–711, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802266233
Selective and Efficient Oxidation of Sulfides to Sulfoxides
Using Ceric Ammonium Nitrate (CAN)/Bro¨ nsted Acidic
Ionic Liquid
Abdol R. Hajipour,1,2 Leila Khazdooz,2
and Arnold E. Ruoho1
1Dept. of Pharmacology, University of Wisconsin, Medical School,
Madison, Wisconsin, USA
2Pharmaceutical Research Laboratory, College of Chemistry, Isfahan
University of Technology, Isfahan, Iran
A selective and efficient procedure for the oxidation of sulfides to the corresponding
sulfoxides is reported using ceric ammonium nitrate in the presence of methylimi-
dazolium hydrogensulfate as Bro¨nsted acidic ionic liquid ([Hmim]HSO ) as the
4
solvent under mild conditions. The use of nontoxic and inexpensive materials,
straightforward procedure, short reaction times, and good yields of the products
are the major advantages of this method.
Keywords Bro¨nsted acidic ionic liquid; ceric ammonium nitrate; methylimidazolium
hydrogen sulfate; sulfide; sulfoxide
INTRODUCTION
Ionic liquids (IL) have frequently been used as an alternative for
classical organic solvents in modern synthetic chemistry.1–5 Ionic liq-
uids are superior to conventional organic solvents due to their ex-
tremely low vapor pressure, excellent thermal stability, reusability,
and ability to dissolve many organic and inorganic substrates.6 The
application of ionic liquids as solvents and catalysts has been re-
ported for a variety of functional group transformations, but their
use as acid catalysts under solvent-free conditions requires more
Received 14 May 2008; accepted 11 June 2008.
We gratefully acknowledge the funding support received for this project from the
Isfahan University of Technology (IUT), IR Iran. Further financial support from the
Center of Excellence in Sensor Research (IUT) is gratefully acknowledged.
Address correspondence to Abdol R. Hajipour, Dept. of Pharmacology, University of
Wisconsin, Medical School, 1300 University Avenue, Madison, WI 53706-1532, USA.
E-mail: arhajipour@wisc.edu
705

706
A. R. Hajipour et al.
7
¨
attention. Bronsted acidic ionic liquids combining the advantageous
characteristics of solid acids and mineral acids are designed to re-
place traditional mineral liquid acids, such as sulfuric acid and hy-
drochloric acid, in chemical processes.8 Ionic liquids with Bronsted
¨
acidic counter ions such as 1-hexyl-3-methylimidazolium bisulfate
([hmim][HSO4]),9 1-butyl-3-methylimidazolium dihyrogen phosphate
([bmim][H2PO4]),9 1-[2-(2-hydroxy-ethoxy)ethyl]-3-methylmidazolium
bisulfate ([heemim][HSO4]),9 1-butyl-3-methylimidazolium chloroa-
luminate ([bmim]Cl.2AlCl3),10 1-butyl-3-methylimidazolium bisul-
fate ([bmim][HSO4]),11 and methylimidazolium hydrogensulfate
[Hmim]HSO142 have been used as acid catalysts and provide a useful
medium under solvent-free conditions because of their polar nature.
The selective oxidation of sulfides to sulfoxides is an attractive and
important method, because sulfoxides have been utilized extensively
in carbon–carbon bond formation reactions and as versatile building
blocks in organic synthesis.13 Oxidation of sulfides is a very useful route
for preparation of sulfoxides. Several methods are available for conver-
sion of sulfides to sulfoxides.14–22 However, some of the existing meth-
ods use expensive, toxic, or rare oxidizing reagents that are difficult
to prepare. Many of these procedures also suffer from poor selectivity
and also often suffer from lack of generality and economic applicability.
Therefore, there is a need for a simple, less expensive, general, and
safer method for conversion of sulfides to sulfoxides. In continuation of
our ongoing program to develop efficient reagents for oxidizing organic
compounds,23–27 we now wish to report a facile and selective method for
oxidation of sulfides to their corresponding sulfoxides with ammonium
¨
cerium (IV) nitrate in the presence of ([Hmim]HSO4) as a Bronsted
acidic ionic liquid under solvent-free conditions (Scheme 1).
SCHEME 1
RESULTS AND DISCUSSION
With thioanisole as the model compound, the effects of reaction condi-
tions on the sulfoxidation with other metal nitrates and various non-
¨
nitrates oxidants using Bronsted acidic ionic liquid ([Hmim]HSO4) at
80◦C have been investigated; the results are listed in Table I. The

Oxidation of Sulfides to Sulfoxides Using CAN
707
TABLE I Sulfoxidation of Thioanisole Using Various
Metal Nitrates and Oxidants in the Presence of Bro¨nsted
Acidic Ionic Liquid ([Hmim]HSO4) at 80◦Ca
Entry
Metal nitrate
Yield (%)
Time (min)
1
2
8
NaNO3
NH4NO3
Ca(OCl)2
KIO4
KBrO3
K2S2O8
CAN
70
10
Trace
0
5
40
240
105
60
60
60
45
5
9
10
11
12
94
aReaction conditions: metal nitrates or oxidants (1 mmol),
[Hmim]HSO4 (2 mmol) and thioanisole (1 mmol) were mixed and
stirred at 80◦C.
results show that most of these metal nitrates are not effective oxi-
dants for this transformation under the mentioned conditions, and ceric
ammonium nitrate (CAN) is the best oxidant under these conditions.
The generality of the method was examined using alkyl aryl, di-
alkyl, diaryl, and cyclic sulfides, and also aryl disulfides. It was dis-
covered that a wide variety of sulfides can be selectively oxidized by
this inexpensive reagent under mild conditions (Table II). The rate of
the reactions of arylalkyl and diaryl sulfides is not dependent on the
substituents of the aromatic ring.
The oxidation of various sulfides gave the corresponding sulfoxides
in high yields and short to moderate reaction times. The products were
obtained by simple extraction with ethylacetate. By using this method,
we did not observe any by-products such as over-oxidation to sulfon or
nitration of aromatic rings.
In conclusion, we have introduced a straightforward and efficient
method for selective oxidation of sulfides to their sulfoxides using
¨
ceric ammonium nitrate in the presence of Bronsted acidic ionic liquid
–
([Hmim]HSO4 ) at 80◦C. The use of non-toxic and inexpensive mate-
rials, stability of the oxidation system, simple method, short reaction
times, good yields of the products, mild reaction conditions, and the
straightforward method of the isolation of the product are the advan-
tages of this method.
EXPERIMENTAL
Products were characterized by comparison of authentic samples (IR,
1HNMR spectrum, melting point, mixed melting point, and co-TLC

708
A. R. Hajipour et al.
TABLE II Oxidation of Sulfide to Sulfoxide Using
CAN/[Hmim]HSO4 at 80◦Ca,b
Time
(Min)
Yield
(%)
Entry
Substrate
Product
1
5
7
94
94
2
3
4
5
6
7
10
10
3
93
89
93
92
92
6
10
8
8
88
(Continued on next page)

Oxidation of Sulfides to Sulfoxides Using CAN
709
TABLE II Oxidation of Sulfide to Sulfoxide Using CAN/[Hmim]HSO4
at 80◦Ca,b (Continued)
Time
(Min)
Yield
(%)
Entry
9
Substrate
Product
7
81
10
20
75
aThe yields refer to the isolated products after purification.
analysis) with those obtained by literature methods15 or alternative
methods of synthesis. All melting points were taken on a Gallenkamp
melting apparatus and are uncorrected. 1H NMR spectra were recorded
on a Varian 250 NMR Spectrometer operating at 250 MHz. The spectra
were measured in CCl4 and CDCl3 relative to TMS (0.00 ppm). GC
analysis was run with Shimadzu GC-14A. IR spectra were recorded on
a Shimadzu 435 IR spectrophotometer. Spectra of solids were performed
using KBr pellets. [Hmim]HSO4 was prepared according to a previously
reported method.28
General Procedure for the Sulfoxidation of Thioanisole Using
Various Metal Nitrates or Oxidants/[Hmim]HSO4
In a round-bottomed flask, thioanisole (1 mmol), metal nitrates
or oxidants (1 mmol), and methylimidazolium hydrogensulfate
[Hmim]HSO4(2 mmol) were mixed. The reaction mixture was warmed
to 80◦C in an oil bath and stirred for the time specified in (Table I). The
reaction progress was followed by TLC (EtOAc–cyclohexane, 20:80),
and the product was extracted with ethylacetate (2 × 5 mL) and washed
with water. The ethylacetate mixture was dried with magnesium sul-
fate. The solvent was evaporated under reduced pressure to give the
corresponding products. Purification of the residue using flash column
chromatography (silica gel, EtOAc–cyclohexane, 20:80) provided the
pure methyl phenyl sulfoxide.

710
A. R. Hajipour et al.
General Procedure for the Oxidation of Sulfide Using
CAN/[Hmim]HSO4
Sulfide (1 mmol), ceric ammonium nitrate (1 mmol), and methylimida-
zolium hydrogensulfate [Hmim]HSO4(2 mmol) were added to a round-
bottomed flask. The reaction mixture was placed in an oil bath at 80◦C
and stirred for the time specified in Table II. The reaction was followed
by TLC (EtOAc–cyclohexane, 20:80). After completion of the reaction,
the product was extracted with ethylacetate (2 × 5 mL) and washed
with water. The ethylacetate mixture was dried with magnesium sul-
fate. The solvent was evaporated under reduced pressure to give the
corresponding products. Purification of the residue using flash column
chromatography (silica gel, EtOAc–cyclohexane, 20:80) provided the
pure sulfoxide.
Methyl Phenyl Sulfoxide (1)
1H NMR (CDCl3), δ ppm 2.72 (s, 3H), 7.50–7.55 (m, 3H), 7.64–7.68
(m, 2H). IR (KBr) 3055, 2996, 2911, 1476, 1443, 1089, 1048, 956, 750
cm−1
.
4-Bromophenyl Methyl Sulfoxide (3)
1H NMR (CDCl3), δ ppm 2.70 (s, 3H). 7.52 (d, J = 9 Hz, 2H), 7.65 (d,
J = 9 Hz, 2H). IR (KBr) 3010, 2989, 2910, 1420, 1384, 1042, 1005, 816
cm−1
.
Ethyl Phenyl Sulfoxide (5)
1H NMR (CDCl3), δ ppm 1.25 (t, J = 8.0 Hz, 3H), 2.09–3.18 (q, J =
8.0 Hz, 2H), 7.55–7.7 (m, 3H), 7.9–7.95 (m, 2H). IR (KBr) 3107, 3056,
2978, 2934, 1478, 1443, 1086, 1044, 749 cm−1
.
Diphenyl Sulfoxide (7)
1H NMR (CDCl3), δ ppm 7.2–7.35 (m, 6H), 7.45–7.55 (m, 4H). IR
(KBr): 3047, 1475, 1440, 1087, 1036, 736 cm−1
.
REFERENCES
[1] T. Welton, Chem. Rev., 99, 2071 (1999).
[2] R. Sheldon, Chem. Commun., 2399, (2001).
[3] J. D. Holbrey and K. R. Seddon, Clean Prod. Process., 1, 223 (1999).
[4] A. C. Cole, J. L. Jensen, I. Ntai, K. L. T. Tran, K. J. Weaver, D. C. Forbes, and J. H.
Davis Jr., J. Am. Chem. Soc., 124, 5962 (2002).
[5] D. W. Morrison, D. C. Forbes, and J. H. Davis Jr., Tetrahedron Lett., 42, 6053 (2001).
[6] J. Kwan and M.-J. Kim, J. Org. Chem., 67, 6845 (2002).
[7] T.-S. Li, Z.-H. Zhang, F. Yang, and C.-G. Fu, J. Chem. Res., 1, 38 (1998).

Oxidation of Sulfides to Sulfoxides Using CAN
711
[8] (a) J. S. Wilkes, J. Mo1. Catal. A: Chem., 214, 11 (2004); (b) D. Fang, X. L. Zhou, Z.
W. Ye, and Z. L. Liu, Ind. Eng. Chem. Res., 45, 7982 (2006).
[9] J. Fraga-Dubreuil, K. Bourahla, M. Rahmouni, J. P. Bazureau, and J. Hamelin,
Catal. Commun., 3, 185 (2002).
[10] M. K. Potdar, S. S. Mohile, and M. M. Salunkhe, Tetrahedron Lett., 42, 9285 (2001).
[11] V. Singh, S. Kaur, V. Sapehiyia, J. Singh, and G. L. Kad, Catal. Commun., 6, 57
(2005).
[12] A. R. Hajipour, L. Khazdooz, and A. E. Ruoho,Catal. Commun., 9, 89 (2008).
[13] (a) G. H. Posner, M. Weitzberg, T. G. Hamill, E. Asirvatham, H. Cun-Heng, and J.
Clardy, Tetrahedron, 42, 2919 (1986); (b) M. Zahouily, M. Journet, and M. Malacria,
Synlett, 366 (1994); (c) S. G. Pyne and A. R. Hajipour, Tetrahedron, 48, 9385 (1992);
(d) J. M. Khurana, A. K. Pand, and A. Gogia, Org. Prep. Proc. Int., 28, 234 (1996);
(e) A. R. Hajipour, Synthetic Comm., 26, 3627 (1996).
[14] M. Tajbakhsh, R. Hosseinzadeh, and A. Shakoori, Tetrahedron Lett., 45, 1889 (2004).
[15] S. E. Martin and L. I. Rossi, Tetrahedron Lett., 42, 7147 (2001).
[16] Y. J. Chen and Y. P. Huang, Tetrahedron Lett., 41, 5233 (2000).
[17] Y. J. Chen and J. Y. Shen, Tetrahedron Lett., 46, 4205 (2005).
[18] X. T. Zhou, H. B. Ji, Z. Cheng, J. C. Xu, L. X. Pei, and L. F. Wang, Bioorg. Med. Chem.
Lett., 17, 4650 (2007).
[19] K. Surendra, N. S. Krishnaveni, V. P. Kumar, R. Sridhar, and K. R. Rao, Tetrahedron
Lett., 46, 4581 (2005).
[20] A. O. Beaudenon and S. Quideau, Tetrahedron Lett., 47, 5869 (2006).
[21] Y. Peng, X. Feng, X. Cui, Y.Jiang, M. C. K. Choi, and A. S. C. Chan, Synthetic Comm.,
33, 2793 (2003).
[22] A. Shaabani, A. Bazgir, K. Soleimani, and P. Salehi, Synthetic Comm., 33, 2935
(2003).
[23] A. R. Hajipour, B. Kooshki, and A. E. Ruoho, Tetrahedron Lett., 46, 5503 (2005).
[24] A. R. Hajipour, H. Bagheri, and A. E.Ruoho, Phosphorus, Sulfur, and Silicon, 178,
2441 (2003).
[25] A. R. Hajipour and A. E. Ruoho, Phosphorus Sulfur, and Silicon, 26, 83 (2003).
[26] A. R. Hajipour, S. Mallakpour, and H. Adibi, Sulfur Letters, 25, 155 (2002).
[27] A. R. Hajipour and N. Mahboubghah, Indian J. Chem. B, 37, 1041 (1998).
[28] A. R. Hajipour, F. Rafiee, and A. E. Ruoho, Synlett, 1118 (2007).