Magnetic nanoparticle immobilized N-propylsulfamic acid: The chemoselective, efficient, green and reusable nanocatalyst for oxidation of sulfides to sulfoxides using H2O2 under solvent-free conditions

Article abstract of DOI:10.1016/j.molcata.2013.06.004

An efficient and eco-friendly method is reported for the chemoselective oxidation of sulfides to sulfoxides in good to high yields using 30% H ₂O₂ in the presence of catalytic amounts of N-Propylsulfamic acid supported onto magnetic Fe₃O₄ nanoparticles (MNPs-PSA) under solvent-free conditions at room temperature. Various types of aromatic and aliphatic sulfides possessing functional groups such as alcohol, ester, and aldehyde are successfully and selectively oxidized without affecting sensitive functionalities. The magnetic nanocatalyst can be readily recovered easily by applying an external magnet device and reused for at least 10 reaction runs without considerable loss of reactivity.

Full text of DOI:10.1016/j.molcata.2013.06.004

Journal of Molecular Catalysis A: Chemical 378 (2013) 200–205
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Magnetic nanoparticle immobilized N-propylsulfamic acid: The
chemoselective, efficient, green and reusable nanocatalyst for
oxidation of sulfides to sulfoxides using H O under solvent-free
2
2
conditions
a,∗
a
b
a
Amin Rostami , Bahman Tahmasbi , Fatemeh Abedi , Zahra Shokri
a
Department of Chemistry, Faculty of Science, University of Kurdistan, Zip Code 66177-15175, Sanandaj, Iran
Department of Chemistry, Payame Noor University, Hamedan, Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient and eco-friendly method is reported for the chemoselective oxidation of sulfides to sulfox-
ides in good to high yields using 30% H2O2 in the presence of catalytic amounts of N-Propylsulfamic acid
supported onto magnetic Fe3O4 nanoparticles (MNPs-PSA) under solvent-free conditions at room tem-
perature. Various types of aromatic and aliphatic sulfides possessing functional groups such as alcohol,
ester, and aldehyde are successfully and selectively oxidized without affecting sensitive functionalities.
The magnetic nanocatalyst can be readily recovered easily by applying an external magnet device and
reused for at least 10 reaction runs without considerable loss of reactivity.
Received 12 January 2013
Received in revised form 30 May 2013
Accepted 9 June 2013
Available online xxx
Keywords:
Magnetic nanoparticle
Nanocatalyst
©
2013 Elsevier B.V. All rights reserved.
N-Propylsulfamic acid
H2O2, Sulfide
Sulfoxide
1
. Introduction
oxidizable functional groups, such as alcohols, alkenes and alde-
hydes, sometimes react as well producing undesirable compounds
[11–14]. Concerning the green oxidant, hydrogen peroxide is one of
the most powerful candidates besides molecular oxygen, because
it is inexpensive, readily available, high atom efficiency, and water
is expected as the only by-product to be generated from the reac-
tion [15]. This feature has stimulated the development of useful
Environmentally benign, economical, practical and efficient pro-
cesses for the catalyst separation and reuse have been increasingly
important goals in the chemical community [1]. Magnetic nanopar-
ticles are efficient, readily available, high-surface-area resulting in
high catalyst loading capacity and outstanding stability heteroge-
neous supports for catalysts. They show identical and sometimes
even higher activity than their corresponding homogeneous ana-
logues [2–4]. More important, magnetic separation of the magnetic
nanoparticles is more effective than filtration or centrifugation [5],
simple, economical and promising for industrial applications [6].
Among the various magnetic nanoparticles as the core magnetic
procedures for H O2 oxidation in the presence of various catalyst
2
systems including transition metal complexes [16–19], polymer
supported catalysts [20,21], protic acid [22,23], and organocatalysts
[24–26]. Although these protocols represent considerable progress,
however recover and reuse of catalysts are difficult.
support, Fe O nanoparticles are arguably the most extensively
3
4
studied [7–9].
2. Experimental
Sulfoxides are fine chemicals, pharmaceuticals and valuable
intermediates in the synthesis of chemically useful and biologically
active molecules [10]. Oxidation of sulfides is the most straight-
forward method for the synthesis of sulfoxides, however, the
most common problems encountered during the reaction is over-
oxidation of sulfoxides to their corresponding sulfones, and other
2.1. Preparation of large-scale the magnetic Fe O nanoparticles
(MNPs)
3
4
FeCl ·6H O (4.865 g, 0.018 mol) and FeCl ·4H O (1.789 g,
3
2
2
2
0.0089 mol) were added to 100 mL deionized water and sonicated
until the salts dissolved completely. Then, 10 mL of 25% NH OH
4
(10 mL) was added quickly into the reaction mixture in one portion
∗ Corresponding author. Tel.: +98 9183730910; fax: +98 8716624004.
E-mail address: a rostami372@yahoo.com (A. Rostami).
under N2 atmosphere at room temperature followed by stirring
about 30 min with mechanical stirrer. The black precipitate was
1
381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.06.004

A. Rostami et al. / Journal of Molecular Catalysis A: Chemical 378 (2013) 200–205
201
Fig. 1. The XRD pattern of MNPs-PSA.
washed with doubly distilled water (five times).
loading of 1.9 mmol/g of sulfamic acid group. This result confirmed
by back-titration of the catalyst.
2.5. General procedure for the oxidation of sulfides to sulfoxides
2.2. Preparation of MNPs coated by
To a mixture of sulfide (1 mmol) and 30% H2O2 (0.5 g, 1.2 equiv.),
(
3-aminopropyl)-trimethoxysilane (MNPs-APTMS)
MNPs-PSA (5 mg, 0.95 mol%) was added and the mixture was stirred
at room temperature for the time specified. Completion of the
reaction was indicated by TLC (n-hexane/ethylacetate 2:1). After
completion of the reaction, Et2O (2× 5 mL) was added and the cat-
alyst was separated by an external magnet. The combined organics
were washed with brine (5 mL) and dried over anhydrous Na2SO4.
The resulting solution was concentrated under reduced pressure to
afford the essentially pure products in most cases. Further purifi-
cation was achieved by short-column chromatography on silica gel
with EtOAc/n-hexane as eluent. All the products are known and
The obtained MNPs powder (1.5 g) was dispersed in 250 mL
ethanol/water (volume ratio, 1:1) solution by sonication for
0 min, and then APTMS (99%, 2.5 mL) was added to the mixture.
3
◦
After mechanical stirring under N2 atmosphere at 33–38 C for
h, the suspended substance was separated with centrifugation
8
(
RCF = 13,200 × g for 30 min). The settled product was re-dispersed
in ethanol by sonication. The final sample was separated by an
external magnet and washed five times with ethanol. The prod-
uct stored in a refrigerator to use.
2
.3. Preparation of N-propylsulfamic acid-functionalized
were characterized by IR, 1H NMR, 13C NMR and by melting point
comparisons with those of authentic samples [12–14,25,27].
magnetic Fe O4 nanoparticles (MNPs-PSA)
3
The MNPs-APTMS (1 g) were dispersed in dry CH Cl2 (6–8 mL)
2
by ultrasonic bath for 10 min. Subsequently, chlorosulfuric acid
3. Results and discussions
(
0.8 mL) was added drop wise over a period of 20 min and the
mixture was stirred for 2 h at room temperature. Hydrogen chlo-
ride gas evolved from the reaction vessel immediately. Then, the
final product was separated by magnetic decantation and washed
twice by dry CH Cl , EtOH and CH Cl respectively to remove the
3
.1. Characterization of MNPs-PSA
The catalyst has been characterized by scanning electron
2
2
2
2
microscopy (SEM), X-ray diffraction (XRD), Fourier transform
unattached substrates. The product stored in a refrigerator to use.
2.4. PH analysis of MNPs-PSA
infrared (FT-IR) spectroscopy and by their comparisons with that
of authentic sample [28].
To determine the acid amount on the surface, the prepared cat-
The XRD spectrum of MNPs-PSA is shown in Fig. 1. A weak broad
band (2ꢀ = 18–22 ) appeared in MNPs-PSA pattern which could be
assigned to the amorphous silane shell formed around the magnetic
cores [29]. The position and relative intensities of all peaks confirm
well.
◦
alyst (100 mg) was added to an aqueous NaCl solution (1 M, 10 mL)
with an initial pH = 5.93. The mixture stirred for 0.5 h after which
the pH of solution decreased to 1.72, indicating an ion exchange
between sulfamic acid protons and sodium ions, this is equal to a

2
02
A. Rostami et al. / Journal of Molecular Catalysis A: Chemical 378 (2013) 200–205
Table 1
Optimization of the reaction conditions for the selective oxidation of methyl phenyl
sulfide (1 mmol) to methyl phenyl sulfoxide using H2O2 (1.2 equiv.) in terms of time
and product yield.
◦
Entry Catalyst
Solvent
Temp. ( C) Time (min) Yield (%)
1
2
1
2
3
4
5
Catalyst-Free
Fe3O4 NP (5 mg)
MNPs-PSA (5 mg) Solvent-free r.t.
MNPs-PSA (5 mg) CH3CN
MNPs-PSA (5 mg) CH2Cl2
MNPs-PSA (5 mg) EtOH
MNPs-PSA (5 mg) n-Hexane
Solvent-free r.t.
Solvent-free r.t.
24 h
24 h
80
30
120
30
50
50
100
100
100
100
50
70
40
70
60
2.5 h
a
Conversions determined by GC.
Fig. 2. FT-IR spectra of (a) magnetic nanoparticles Fe3O4, (b) amino-functionalized
nanomagnets (MNPs-APTMS), and (c) magnetic nanoparticles supported PSA
(
MNPs-PSA).
The IR spectrum of MNPs-PSA shows peaks that are charac-
teristic of a functionalized SA group, which clearly differs from
that of the unfunctionalized Fe O nanomagnets and aminopropyl-
3
4
functionalized magnetic nanoparticles (Fig. 2). The FT-IR spectrum
−
1
for the MNPs alone shows a stretching vibration at 3420 cm
which incorporates the contributions from both symmetrical and
asymmetrical modes of the O H bonds which are attached to the
−
1
surface iron atoms. The bands at low wavenumbers (≤700 cm
come from vibrations of Fe O bonds of iron oxide, in which for
)
−
1
the bulk Fe O samples appear at 570 and 375 cm but for Fe O4
Fig. 3. Image showing MNPs-PSA can be separated by applied magnetic field. A
reaction mixture in the absence (left) or presence of a magnetic field (right).
3
4
3
−1
nanoparticles at 611 and 577 cm as a blue shift, due to the size
reduction [30,31]. The FT-IR spectra of MNPs-APTMS and MNPs-
PSA Fe O vibrations in the same vicinity, the introduction of APTMS
to the surface of MNPs is confirmed by the band at 1000 cm
assigned to the Fe Si stretching vibrations. Reaction of MNPs-
APTMS with chlorosufonic acid produces MNPs-PSA in which the
times and in high yields. To show the chemoselectivity of the
presented protocol, the sulfides containing oxidation-prone and
−
1
O
acid-sensitive functional groups such as OH, CHO and COOCH were
3
subjected to the sulfoxidation reaction. These functional groups
remained intact during the conversion of sulfide to sulfoxides
(Table 2, entries 12–14).
−
1
presence of SO H moiety is asserted with 1221 and 1125 cm
3
bands in FT-IR spectra.
For practical purposes, the ability to easily recycle the catalyst
is highly desirable. To investigate this issue, the recyclability of the
catalyst was examined for the oxidation of methyl phenyl sulfide.
We found that this catalyst demonstrated remarkably excellent
reusability; after the completion of the reaction, the reaction mix-
ture was diluted with diethyl ether and the catalyst was easily and
rapidly separated from the product by exposure to an external
3
.2. Application of MNPs-PSA for the oxidation of sulfides to
sulfoxides
In continuation of our studies on environmentally benign chem-
ical processes [32–34], in the present work we disclose that
MNPs-PSA can be used as an interphase catalyst for the chemos-
elective oxidation of structurally diverse sulfides to sulfoxides
using 30% H O under solvent-free conditions at room temperature
2
2
(
Scheme 1).
In order to optimize the reaction conditions, we examined the
oxidation reaction of methyl phenyl sulfide as a model compound
using 30% H O under various reaction conditions in terms of time
2
2
and product yield (Table 1). As shown in Table 1, the reaction was
incomplete in the absence of MNPs-PSA even after 24 h (entries
1
and 2). H O (1.2 equiv.) in the presence of catalytic amount of
2 2
MNPs-PSA (5 mg, 0.95 mol%) under solvent-free conditions at room
temperature was found to be ideal the reaction conditions for the
complete conversion of methyl phenyl sulfide to methyl phenyl
sulfoxide.
The generality of this approach has been demonstrated by a
facile oxidation of aryl, benzylic, linear, cyclic and heterocyclic sul-
fides as shown in Table 2. The sulfoxides were obtained in short
Fig. 4. The recycling experiment of MNPs-PSA (5 mg, 0.95 mol%) in oxidation of
methyl phenyl sulfide using H2O2 (1.2 equiv.) at room temperature for 80 min.

A. Rostami et al. / Journal of Molecular Catalysis A: Chemical 378 (2013) 200–205
203
Scheme 1. MNPs-SA catalyzed the selective oxidation of sulfides to sulfoxides with H2O2.
Fig. 5. SEM images of MNPs-PSA: (left) before reaction and (right) after reaction.
magnet and decantation of the reaction solution (Fig. 3). The
remaining magnetic nanocatalyst was further washed with diethyl
ether to remove residual product. Then, the reaction vessel
catalyst system is the rapid (within 5 s) and efficient separa-
tion of the catalyst (100%) by using an appropriate external
magnet, which minimizes the loss of catalyst during separa-
tion.
was charged with fresh substrate and 30% H O and sub-
2
2
jected to the next. As shown in Fig. 4, the catalyst can be
recycled up to 10 runs without any significant loss of activ-
ity. In addition, one of the attractive features of this novel
The SEM images of both the fresh and reused catalyst (Fig. 5)
also indicated that no detectable changes of the catalyst occurred
during the reaction and the recycling stages.
Scheme 2. Proposed mechanisms for the oxidation of sulfides using H2O2 catalyzed by MNPs-PSA.

2
04
A. Rostami et al. / Journal of Molecular Catalysis A: Chemical 378 (2013) 200–205
Table 2
MNPs-PSA (5 mg, 0.95 mol%) catalyzed selective oxidation of sulfides (1 mmol) to sulfoxides using 30% H2O2 (1.2 equiv.) under solvent-free conditions at room temperature.
Entry
1
Substrate
Product
Time (min)
Isolated yield (%)
2
3
O
S
S
CH CH
2
3
4
5
CH CH
85
85
2
3
O
S
S
10
95
85
S
6
7
5
S
O
O
O
S
S
S
5
95
86
O
S
8
9
45
O
O
S
50
45
87
90
S
O
1
0
1
CH3(CH2)11S(CH2)11CH3
CH (CH ) S(CH ) CH3
3
2 11
2 11
1
S
8
90
90
S
O
O
S
S
1
1
2
3
OH
20
OH
O
O
S
S
H
H
20
87
85
O
O
O
O
S
S
OMe
OMe
1
4
8
O
On the basis of the previously reported mechanism for the oxida-
peroxide, followed by the oxygen transfer to the organic substrate
(Scheme 2a). Another explanation is that SA might act as protic
acid, which polarizes the O O bond in H O to produce the reactive
tion of sulfides using hydrogen peroxide in the presence of an acid
catalyst [22,23], one explanation for this process is the in situ for-
mation of peroxyacid by the reaction of MNPs-PSA with hydrogen
2
2
oxygen transfer agent (Scheme 2b).

A. Rostami et al. / Journal of Molecular Catalysis A: Chemical 378 (2013) 200–205
205
Table 4
Comparison of the activity of various catalysts in the oxidation of benzyl methyl sulfide using H2O2.
Entry
Catalyst
Conditions
Time (min)
Yield (%)
Ref.
1
2
3
4
5
6
7
8
MNPs-PSA
SSA
NBS
Solvet-free, rt
CH3CN, rt
10
40
15
20 h
150
330
240
360
95
96
90
52
96
92
83
53
This work
[22]
[24]
[18]
[19]
[16]
[17]
[23]
◦
CH3CN, 35–40
C
◦
Copper(II) complex, TEMPO
TaCl5
CH3CN, 20
MeOH, 45
C
◦
C
ꢀ
Cp Mo(CO)3Cl
Acetone:MeOH
CH2Cl2:MeOH, rt
MeOH, rt
Silica-based ammonium tungstate
ZnBr2, pyridine-2,3-carboxylic acid
The efficiency of this method is demonstrated by comparison
our result on the oxidation of benzyl phenyl sulfide with data from
the literature (Table 4). As shown in Table 4, the previously reported
procedures suffer from one or more disadvantages such as longer
reaction times [16–19,23,24], low yield [18,23], using a transition
metal [16–19,23], and the need for volatile and toxic organic sol-
vents [16–19,22–24].
[6] S. Laurent, D. Forge, M. Port, A. Roch, C. Robic, L.V. Elst, Chem. Rev. 108 (2008)
064–2110.
2
[
7] C.T. Yavuz, J.T. Mayo, W.W. Yu, A. Prakash, J.C. Falkner, S. Yean, L.L. Cong,
H.J. Shipley, A. Kan, M. Tomson, D. Natelson, V.L. Colvin, Science 314 (2006)
964–967.
[
[
8] B. Karimi, E. Farhangi, Chem. Eur. J. 17 (2011) 6056–6060.
9] V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara, J.-M. Basset, Chem. Rev.
111 (2011) 3036–3075.
[10] S. Patai, Z. Rappoport, The Synthesis of Sulfones, Sulfoxides and Cyclic Sulfides,
J. Wiley, Chichester, 1994.
[
[
11] I. Frenanez, N. Khiar, Chem. Rev. 103 (2003) 3651–3706.
12] K. Orito, T. Hatakeyama, M. Takeo, H. Suginome, Synthesis (1995)
4
. Conclusion
1357–1358.
In summary, we have demonstrated that MNPs-PSA can be used
[13] D. Habibi, M.A. Zolfigol, M. Safaiee, A. Shamsian, A. Ghorbani-Choghamarani,
Catal. Commun. 10 (2009) 1257–1260.
as a green, efficient and reusable nanocatalyst for the selective oxi-
dation of a wide range of sulfides to sulfoxides using H O under
[
14] B.M. Choudary, B. Bharathi, C.V. Reddy, M.L. Kantam, J. Chem. Soc. Perkin Trans.
1 (2002) 2069–2074.
2
2
solvent-free conditions at room temperature. The advantages of
this protocol are the use of a commercially available, eco-friendly,
cheap and chemically stabile oxidant, the mild reaction conditions,
operational simplicity, practicability, short reaction times, good to
high yields and excellent chemoselectivity. Besides that, the sys-
tem couples the advantages of heterogeneous (easy separation, and
excellent reusability of up to 10 runs) and homogeneous SA-based
[15] B.S. Lane, K. Burgess, Chem. Rev. 103 (2003) 2457–2573.
[
16] C.A. Gamelas, T. Louren c¸ o, A.P. Costa, A.L. Simplício, B. Royo, C.C. Romão, Tetra-
hedron Lett. 49 (2008) 4708–4712.
[
17] B. Karimi, M. Ghoreishi-Nezhad, J.H. Clark, Org. Lett. 7 (2005) 625–628.
[18] S. Velusamy, V.A. Kumar, R. Saini, T. Punniyamurthy, Tetrahedron Lett. 46
2005) 3819–3822.
19] M. Kirihara, J. Yamamoto, T. Noguchi, Y. Hirai, Tetrahedron Lett. 50 (2009)
180–1183.
(
[
1
[20] S.M. Islam, A.S. Roy, P. Mondal, K. Tuhina, M. Mobarak, J. Mondal, Tetrahedron
Lett. 53 (2012) 127–131.
(
high activity and reproducibility), which make it as a promising
material for practical and large-scale applications.
[
21] S.P. Das, J.J. Boruah, N. Sharma, N.S. Islam, J. Mol. Catal. A: Chem. 356 (2012)
6–45.
3
[
[
[
[
22] A. Shaabani, A.H. Rezayan, Catal. Commun. 8 (2007) 1112–1116.
23] X.-F. Wu, Teterahedron Lett. 53 (2012) 4328–4331.
24] B. Karimi, D. Zareyee, J. Iran. Chem. Soc. 5 (2008) 103–107.
25] K. Bahrami, M.M. Khodaei, M. Sheikh-Arabi, J. Org. Chem. 75 (2010) 6208–6213.
Acknowledgment
We are grateful to the University of Kurdistan Research Councils
for partial support of this work.
[26] P.C.B. Page, D. Bethell, P.A. Stocks, J.P. Heer, A.E. Graham, H. Vahedi, M. Healy,
E.W. Collington, D.M. Andrews, Synlett (1997) 1355–1358.
[
27] C.J. Pouchert, J. Behnke, The Aldrich Library of C and 1H FT NMR Spectra, vol.
1
3
1
, 1st ed., Aldrich Chemical Company, Inc., Milwaukee, WI, 1993.
[28] M.Z. Kassaee, H. Masrouri, F. Movahedi, Appl. Catal. A: Gen. 395 (2011)
8–33.
29] Y. Jiang, J. Jiang, Q. Gao, M. Ruan, H. Yu, L. Qi, Nanotechnology 19 (2008)
5714–75719.
References
2
[
[
[
[
1] P.T. Anastas, J.C. Warner, Green Chemistry: Theory and Practice, Oxford Uni-
versity, Oxford, 1998.
2] C.O. Dalaigh, S.A. Corr, Y.G. Ko, S.J. Connon, Angew. Chem. Int. Ed. 46 (2007)
7
[
[
[
[
[
30] Z.M. Rao, T.H. Wu, S.Y. Peng, Acta Phys. Chim. Sin. 11 (1995) 395–399.
31] R.D. Waldron, Phys. Rev. 99 (1955) 1727–1735.
32] A. Rostami, J. Akradi, Tetrahedron Lett. 51 (2010) 3501–3503.
33] A. Rostami, A. Yari, J. Iran. Chem. Soc. 9 (2012) 489–493.
34] A. Rostami, F. Ahmad-Jangi, M.R. Zarehbin, J. Akradi, Synth. Commun. 40 (2010)
4
329–4332.
3] F. Shi, M.K. Tse, M.M. Pohl, A. Bruckner, S. Zhang, M. Beller, Angew. Chem. Int.
Ed. 46 (2007) 8866–8868.
4] D.H. Zhang, G.D. Li, J.X. Li, J.S. Chen, Chem. Commun. (2008) 3414–3416.
5] D. Guin, B. Baruwati, S.V. Manorama, Org. Lett. 9 (2007) 1419–1421.
[
[
1500–1507.