Salen copper(II) complex heterogenized on mesoporous MCM-41 as nano-reactor catalyst for the selective oxidation of sulfides using urea hydrogen peroxide (UHP)

Article abstract of DOI:10.1007/s11164-014-1690-x

MCM-41 silica spheres were synthesized and functionalized with 3-aminopropyltriethoxysilane (3-APTES). The Schiff base has been derived from amino groups and 5-boromo salicylaldehyde, then a tetra dentate Cu(II)-Schiff base complex was prepared. This comp

Full text of DOI:10.1007/s11164-014-1690-x

Res Chem Intermed
DOI 10.1007/s11164-014-1690-x
Salen copper(II) complex heterogenized on mesoporous
MCM-41 as nano-reactor catalyst for the selective
oxidation of sulfides using urea hydrogen peroxide
(
UHP)
Arida Jabbari
Mohsen Nikoorazm
•
Houri Mahdavi
•
•
Arash Ghorbani-Choghamarani
Received: 22 January 2014 / Accepted: 26 April 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract MCM-41 silica spheres were synthesized and functionalized with 3-ami-
nopropyltriethoxysilane (3-APTES). The Schiff base has been derived from amino
groups and 5-boromo salicylaldehyde, then a tetra dentate Cu(II)–Schiff base complex
was prepared. This compound was characterized by X-ray diffraction, nitrogen physi-
sorption, UV–Vis spectrometer, transmission electron micrographys (TEM), IR-spectra,
and TGA/DTA technique. The prepared grafting Cu-salen-MCM-41 over a mesoporous
surface was found to be an efficient and selective catalyst for the oxidation of different
sulfides into sulfoxides with urea hydrogen peroxide (UHP) giving excellent yields at
room temperature. The results showed that Cu-salen-MCM-41 is an effective catalyst for
the oxidation of sulfides and can be repeatedly used and regenerated with no significant
decrease in its catalytic ability. They also showed that the prepared material retained a
good mesoporous structure and the best catalytic properties.
Keywords UHP Á Meso structure Á Catalyst Á Sulfoxides Á Cu(II)–Salen
complex
Introduction
Encapsulation of suitable molecular species in MCM-41 prepares new types of
functional materials which have been a popular field of study [1–4]. The discovery of
2
mesoporous materials with extremely high surface area (ca. 1,000 m /g), large channels
3
from 1.5 to 10 nm ordered in a hexagonal array, and large pore volume ([1.0 cm /g),
have opened up new opportunities for designing novel heterogeneous catalysts [5, 6].
A. Jabbari (&)
Islamic Azad University, Qeshm Branch, Tehran, Iran
e-mail: arida_jabbari@yahoo.com
H. Mahdavi Á M. Nikoorazm Á A. Ghorbani-Choghamarani
Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
123

A. Jabbari et al.
Inner surfaces of MCM-41contain Si–OH groupsthat can be developed basic properties
by functionalization with organic components (as amino groups) [7]. Recently, metal
complexes of porphyrins, Schiff-bases, phthalocyanines, etc. have been encapsulated
into MCM-41 for the development of efficient oxidation catalytic phenomena [8–10].
Schiff base compounds are usually formed by the condensation of amine group
with active carbonyl group, which usually linked to the aldehyde. Salicylidene
Schiff base (salen) as bidentate ligand can be easily prepared by the condensation of
amine derivatives and salicylaldehyde derivatives. Salen ligand is known to easily
form stable complexes with transition metals [11]. Because of their high activity and
selectivity of salen complexes with most transition metals (Cu(II), Co(II), Ni(II),
Fe(III), and Zn(II)), they show wide applicability in biological, medicinal,
industrial, and catalyst fields [12–22]. Among them, copper modifications are of
considerable importance, and widely applied as oxidant catalyst in many processes
because of their high stability potential and environmental importance.
In the other hand, sulfoxides are very useful compounds in organic synthesis [23]
and the formation of biological active molecules [24]. They play a vital role as
antihypertensive drugs [25] and cardiotonic agents [26], as well as vasodilators [27].
Various efforts have been made to develop new synthetic methods for sulfoxide
synthesis [28]. For this reason, oxidation of sulfides is a simple, straight and widely
accepted method for the preparation of sulfoxides, various oxidizing reagents which
are now available such as PhIO, t-butylhydroperoxide (TBHP), NaOCl, H O , UHP,
2
2
etc. [29–32]. Anhydrous urea–hydrogen peroxide complex (UHP, H NCONH ÁÁÁ
2
2
H O ) [33] is a green oxidant for sulfide oxidation. Its stability at room temperature
2
2
and the potential for releasing it in a controlled manner, as well as its solubility in
organic solvents, make it a good and safe substitute as a ‘‘dry carrier’’ of the unstable
and hazardous hydrogen peroxide in most oxidation reactions.
The reactions between urea–hydrogen peroxide and sulfides are slow, hence,
extensive studies have been made for the discovery of new and efficient catalysts.
Efficient systems for such reactions can be accomplished by supporting active phase
on various materials, such as polymers [34] or inorganic solids such as zeolites [35],
clays [36], alumina [37], and silica [38]. A solid catalyst capable of working under
heterogeneous conditions is required to the sustainability of the process.
In this paper, we report the synthesis of eco-friendly oxidation system and
characterization of Cu (Salen) complex grafted over the modified surface MCM-41
using 3-aminopropyltriethyoxysilane. The mentioned hetereogenized complex was
applied as catalyst in the oxidation of sulfide using anhydrous urea hydrogen
peroxide (UHP) as oxidizing agent. The results showed good catalytic activity and
stability as well as the ability to be recycled for repeated use.
Experimental
General
Fourier transform infrared (FTIR) spectra of KBr disks were measured on a VRTEX
7
0 model Bruker FTIR spectrometer. The powder X-ray diffraction (XRD) patterns
1
23

Salen copper(II) complex heterogenized on mesoporous MCM-41
of the samples were recorded on an X Pert MPD diffractometer using Cu radiation
under the conditions of 40 kV and 30 mA. The UV–Vis diffused reflectance spectra
(
TGA/DTA was carried out by a Shimadzu DTG-60 instrument. N adsorption–
UV–Vis DRS) were recorded on a UV–Vis Ava Spec 2048 Tec spectrometer.
2
desorption isotherms were measured at -196 °C with a Micromeritics ASAP 2020.
The transmission electron micrographys (TEM) were recorded with a Philips CM10
microscope, working at 200 kV accelerating voltage.
The cationic surfactant cetyltrimethylammoniumbromide (CTAB, 98 %), tetra-
ethylorthosilicate (TEOS, 98 %), sodium hydroxide, organic sulfides, solvents, and
urea hydrogen peroxide) were purchased from Merck, Aldrich, and Fluka, and were
used as received.
Synthesis of MCM-41 material
The MCM-41 material was prepared using the modified synthesis recipe of Chen
et al. [46]. We used cetyltrimethylammoniumbromide (CTAB) as a surfactant
template and tetraethylorthosilicate (TEOS) as a source of silicon for the preparation
of the mesoporous material. The molar composition rate of the reactant mixture
(
TEOS:CTAB:NaOH:H O) was: 60:3/0:1/0:1. TEOS was added to an aqueous
2
solution containing CTAB, NaOH, and deionized water. After stirring for about 1 h
at room temperature, the resulting homogeneous mixture was crystallized under
static hydrothermal conditions at 100 °C in a teflon-lined autoclave for 96 h. After
cooling at room temperature, the solid product was separated by filtration, washed
with deionized water, and dried in air at 70 °C. The material was finally calcined at
5
50 °C for 5 h with a ramp of 2 °C/min.
Preparation of 3-APTES functionalized mesoporous silica (MCM-41-nPr-NH2)
To a suspension of calcined Si-MCM-41 (4.8 g, 80 °C) in n-hexane under nitrogen
atmosphere, 4.8 g of 3-aminopropyltriethoxysilane (3-APTES) was added slowly
and then refluxed for 24 h (Scheme 2). The separated white solid MCM-41-
(
SiCH CH CH NH ) was washed with n-hexane and dried under vacuum.
2 2 2 2 x
Elemental analysis shows that that 3-APTES was functionalized on mesoporous
silica.
Preparation of Cu-salen-MCM-41
5-Boromo salicylaldehyde (1 mmol) was added to a suspended solution of white
solid MCM-41-(SiCH CH CH NH ) in ethanol and refluxed under N atmosphere
2
2
2
2 x
2
at 80 °C for 3 h to prepare a Schiff base on the surface of MCM-41 (a bi-dentate
ligand; Scheme 1).The yellow solid was filtered, Soxhlet-extracted with ethanol,
and dried under vacuum. The Soxhleted Cu-salen-MCM-41 was obtained by stirring
0
.5 g of the hybrid material, MCM-41–Schiff base ligand (salen-MCM-41), with
Cu(NO ) Á3H O (1 mmol) in 30 mL of ethanol at room temperature for 12 h. Then,
3
2
2
the resulting catalyst (green powder) was filtered off, and extracted with ethanol in
Soxhlet and dried in a vacuum (Soxhlet-extracted with ethanol and dried in a
123

A. Jabbari et al.
O
S
S
UHB, r.t
Solvent, Cat.
Scheme 1 Optimizing of oxidation of dibenzyl sulfide
Scheme 2 Synthesis steps of Cu-salen-MCM-41
vacuum) to obtain the heterogenized complexes (Cu-salen-MCM-41) in almost
quantitative yields (Scheme 2).
General procedure for the oxidation of sulfides to sulfoxide
To the mixture of sulfide (1 mmol) and catalyst (20 mg) in ethanol (4 mL), UHP
was added (7 mmol).The reaction mixture was stirred at room temperature for the
appropriate time until TLC indicated the reaction was complete. The product was
extracted with ethanol (10 mL), dried over anhydrous Na SO , and then concen-
2
3
trated to get an analytically pure product.
Results and discussion
Characterization of parent supports and heterogeneous catalyst
Mesoporous materials are characterized by a variety of techniques, such as X-ray
diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission
1
23

Salen copper(II) complex heterogenized on mesoporous MCM-41
2
Fig. 1 Low angle XRD patterns of MCM-41, MCM-41-nPr-NH , salen-MCM-41, Cu-salen-MCM-41,
and recovered Cu-salen-MCM-41
electron microscopy (TEM), N sorption measurements, TGA/DTA analysis, and
2
UV–Vis-spectroscopy. The main characteristics of the mesoporous silica that has
been used in this survey are presented as follows.
Figure 1 illustrates the XRD patterns of pure MCM-41, MCM-41-nPr-NH2,
salen, Cu-salen-MCM-41 materials, and the recovered catalyst. MCM-41 is a
hexagonal structured material with long-range ordered pores (Fig. 1a). The XRD
pattern shows three peaks assigned to 1 0 0, 1 1 0, and 2 0 0 reflections. In fact, these
peaks reflect the hexagonal unit of the structure. The ordered mesoporous structure
is basically preserved after functionalizing amine (MCM-41-nPr-NH ), salen, and
2
Cu-salen-MCM-41 that exhibited well-defined reflections of the MCM-41 meso
phase. However, compared to the parent material, some broadening and decreased
intensity of the 1 0 0 diffraction peak is observed, as well as the disappearance of the
1
1 0 and 1 0 0 peaks. Similar changes, which reveal some loss of order upon
functionalization of MCM-41, were reported [39]. Furthermore, Fig. 1e is the
recovered Cu-salen-MCM-41 and the curve clearly indicated the structural stability
of catalyst after 5 reused.
The prepared heterogeneous catalysts were characterized by FT-IR. The IR
spectra of MCM-41, MCM-41-nPr-NH , salen-MCM-41, Cu-salen-MCM-41, and
2
the recovered catalyst are exhibited in Fig. 2. The characteristic absorption bands of
silica are presented as follows: bending vibration (O–Si–O) of valence angle of
-
tetrahedral SiO located at 463 cm , symmetric and asymmetric stretching (Si–O)
1
4
-
of tetrahedral SiO located at 800 and 800–1,300 cm range, and stretching (O–H)
1
4
-
1
of H O of silanol groups in the surface of silica located at 3,000–3,600 cm range.
2
-
The transmissions around 2,900 cm of the prepared catalysts were due to C–H
1
123

A. Jabbari et al.
Fig. 2 FT-IR spectra of a MCM-41, b MCM-41-nPr-NH
e recovered Cu-salen-MCM-41
2
, c salen-MCM-41, d Cu-salen-MCM-41, and
bond stretching vibrations of the alkyl groups. The MCM-41-nPr-NH sample has
2
-
1
typical (NH ) bending at 1,542 cm
2
that conformed to the MCM-41 to be
-
1
functionalized. The adsorption bands around 1,655 cm , assigned to stretching
vibrations of azomethine groups (H–C=N) bending, is the characteristic band of
1
salen ligand that shifts this band to 1,632 cm when C=N is coordinated to the
-
-
1
metal (Cu).The peaks at 2,375 and 1,468 cm
can be assigned to the C=C
stretching vibration of the phenyl group. The curve of the recovered complex is
quite similar to that of Cu-salen-MCM-41
N sorption measurements have been used to determine the physical textural
2
properties including surface area, pore size distribution, and pore volume per gram.
The textural properties (surface area and pore size) of MCM-41, MCM-41-nPr-NH2,
and Cu-salen-MCM-41 were determined from the N -sorption studies carried out at
2
liquid nitrogen temperature (Table 1). On modifying Si-MCM-41 with 3-APTES,
2
the surface area of Si-MCM-41 decreased from 986.16 to 694.98 m /g and the pore
1
23

Salen copper(II) complex heterogenized on mesoporous MCM-41
Table 1 Textural properties of the functionalized MCM-41
Sample
SBET
(
Pore diam by BJH
method (nm)
Pore vol
3
(cm /g)
wall diam
(nm)
2
m /g)
MCM-41
986.16
694.98
32.84
3.65
3.3
0.711
0.340
0.150
0.902
0.906
3.067
MCM-41-nPr-NH
2
Cu-salen-MCM-41
1.19
Fig. 3 Nitrogen adsorption–desorption isotherms of MCM-41, MCM-41-nPr-NH
2
, Cu-salen-MCM-41
size reduced from 3.56 to 3.3 nm. On Cu-salen-MCM-41, a further reduction in the
2
surface area from 694.98 to 32.84 m /g and pore size from 3.3 to 1.19 nm was
observed. The reduction in the surface area and pore size is due to the lining of the
walls of the Si-MCM-41 with the organic moieties. A similar trend has also been
previously observed [40].
Furthermore, adsorption–desorption isotherms of calcined MCM-41, MCM-41-
nPr-NH , and Cu-salen-MCM-41 are depicted in Fig. 3. IUPAC classification and
2
its steep condensation behavior indicate the existence of uniformly sized mesopor-
ous [41]. In detail, region 0.05 \ P/P0 \ 0.3 corresponds to the multi-layer
adsorption of liquid N on the walls of the mesoporous compound. When the amino
2
group was functionalized on MCM-41, the curve shows a lower value of 0.05 \ P/
P0 \ 0.25, while after formation of the complex, the P/Po value changed to a lower
value of *0.05 and the other adsorption takes place at 0.95 \ P/P0 \ 1 which we
think it is due to the N adsorption between the grains of solid.
2
Thermo-gravimetric analyses (TGA) of MCM-41, MCM-41-nPr-NH , and the
2
Cu-salen-MCM-41 complex are shown in Fig. 4. TGA of MCM-41 indicated no
123

A. Jabbari et al.
2
Fig. 4 TGA curves for bulk MCM-41 (a), MCM-41-nPr-NH (b), and Cu-salen-MCM-41 (c)
alteration in weight loss by increasing the temperature after an initial weight loss of
% that was observed with regard to the loss of moisture inside the MCM-41
4
channels. The TG/DTG spectrum of MCM-41-nPr-NH2 displays two steps of
weight loss, one below *100 °C and the other in the region of 200 to *300 °C. As
mentioned, the former weight loss is due to desorption of physisorbed water, while
the second weight loss is attributed to the loss of organo propyl amino fragments
[
42]. The thermal decomposition of the Cu-salen-MCM-41 complex is increased in
two steps of weight loss, one at *100 °C and the other between 350 and 600 °C,
when heated under airflow. The former weight loss (\100 °C) is usually attributed
to the desorption of physisorbed water, while the latter loss is due to the
decomposition/combustion of organic ligand present in the complex. A complete
decomposition of the Cu-salen takes place in a temperature range of 350–600 °C
which indicates that the calcination procedure used for the removal of structured
directors was optimum.
The TEM micrographs and size distributions (Fig. 5) of MCM-41 demonstrated
that MCM-41 possesses clear well-order channels and confirms the 2D hexagonal
pore arrangement and long-range mesoporous architecture (50 and 20 nm).
Anchoring of ligands on the solid surface coordinated to transition metals was
appropriately followed by diffuse reflectance of spectroscopy of the resulting
catalysts [43, 44]. The UV–Vis DRS spectra of 3-APTES-modified mesoporous
(
MCM-41-nPr-NH ), salen-MCM-41, Cu(II)-salen mesoporous (Cu-salen-MCM-
2
4
1), and the reused complex are presented in Fig. 6. No peak appears for the MCM-
1-nPr-NH . In the UV–Vis DR spectrum of salen, two bands around 255 and 312
4
2
and a band near to 420 nm are due to the p–p* and n-p* transitions, respectively. In
1
23

Salen copper(II) complex heterogenized on mesoporous MCM-41
Fig. 5 TEM micrographs of MCM-41
2
Fig. 6 UV–Vis diffuse reflectance spectra of a MCM-41-nPr-NH , b Salen-MCM-41, c Cu-salen-MCM-
41, and d recovered Cu-salen-MCM-41
the spectrum of Cu-salen-MCM-41, a broadening of the absorption bands at
65–785 nm when compared to the absorption bands for the salen-MCM-41 shows
5
that this peak can be attributed to several d ? d transitions. Also, the Cu-salen
complex shows a red shift (p–p*) at 264 and a blue shift (n–p*) transition at 392 due
to coordination of salen to copper(II). The charge transfer transition is not observed
because of overlapping with p–p* and n–p* transitions. The CT and d ? d tran-
sition provide evidence for complexation of Schiff base ligand with the Cu(II) ions.
Moreover, Fig. 6 shows that the structure of the recovered supported catalyst is not
damaged with respect to the starting complex.
123

A. Jabbari et al.
Catalytic and chemoselective oxidation of sulfides into sulfoxides
In continuation of our interest in sulfur chemistry [45], we were searching for a
high-yielding, catalytic, cheap, and environmentally benign reagent for sulfide
oxidation and considered Cu-salen-MCM-41 with UHP as a reagent of choice. We
report an exceptionally mild, general, and efficient Cu- salen-MCM-41 catalyzed for
the oxidation of sulfide to sulfoxide using UHP as oxidant. In order to find the
optimum reaction conditions, the influence of different factors affecting the
conversion and selectivity of the oxidation reaction. such as solvent nature, catalyst
concentration, and the molar ratio of UHP, were investigated. For this purpose,
Fig. 7 Effect of solvents on oxidation of dibenzyl sulfide
Table 2 Oxidation of dibenzyl
Entry
Cu-salen-MCM-41
mg)
UHP
(mmol)
Time
(h)
Yield
a
(%)
sulfide to dibenyl sulfoxide
employing various amounts of
Cu-salen-MCM-41 as catalyst
and urea hydrogen peroxide as
oxidant
(
1
2
3
4
5
6
7
8
–
7
7
7
7
8
7
6
5
12
3.75
3
90
92
15
20
25
20
20
20
20
96
2.75
4
93
85
3.5
3
89
969
95
3
a
Isolated yield
1
23

Salen copper(II) complex heterogenized on mesoporous MCM-41
Table 3 Oxidation of sulfides to the sulfoxides with catalyzed by Cu-salen-MCM-41 in ethanol
Entry
Substrate
Product
UHP
eqiuv.)
Yield
a
(%)
Time
(min)
(
1
S
O
S
7
97
140
OH
OH
2
3
4
5
7
7
7
96
95
94
91
170
O
S
S
b
9 h
O
S
S
c
10.5 h
O
S
S
S
O
S
12
7
13 days
36 h
6
7
95
92
O
S
S
7
15 h
O
S
S
C12H25
C12H25
C
12
H
25
12 25
C H
8
9
7
7
93
98
45
S
S
O
O
O
O
S
285
S
O
O
1
1
0
1
O
7
7
96
97
35
O
S
O
S
2.05
S
S
O
123

A. Jabbari et al.
Table 3 continued
Entry Substrate
Product
UHP
eqiuv.)
Yield
a
(%)
Time
(min)
(
12
S
O
S
7
92
16
Reaction conditions: substrate (1 mmol) UHP (7 equiv.) and catalyst (0.02 g) in EtOH (4 mL) at room
temperature
a
Isolated yield
b
Reaction proceeded in the presence of MCM-41 as catalyst
c
2
Reaction proceeded in the presence of MCM-41-nPr-NH as catalyst
dibenzyle sulfide was considered as the model substrate and was subjected to
different reaction conditions (Scheme 1). In the first step, the oxidation was
investigated in various solvents such as ethyl acetate, ethanol, acetone, dichloro-
methane, acetonitrile, water, and chloroform as shown in Fig. 7.
It was found that the reaction in the eco-friendly ethanol proceeded smoothly
with the high conversion and good chemo-selectivity (96 %). To study the effect
of catalyst concentration on the conservation and selectivity of the dibenzyl
sulfide oxidation, Cu-salen-MCM-41 catalyst loading were used in the reaction.
The results are shown in Table 2. It was observed that the highest conversion and
selectivity to sulfoxide were achieved in the presence of 20 mg of catalyst within
2
.5 h (Table 2, entry 3). For dibenzyl sulfide, a separate experiment showed the
presence of catalyst is necessary, since oxidation with UHP alone occurs rather
slowly (12 h).
The various molar ratios of UHP were performed in ethanol (Table 2). As
outlined in Fig. 4, the conversion of dibenzyl sulfide oxidation improved from 80
to 96 % as the molar ratio increases from 5 to 7. Thus, the reaction gave the high
yield and selectivity of sulfoxide at 7 mmol of UHP. However, according to
Table 2, the employment of an excess amount of UHP considerably promoted the
overoxidation of sulfoxide. Based on the above observation, we come to the
conclusion that 20 mg of salen catalyst and 7 mmol of UHP in ethanol as solvent
is the best combination.
Based on the mentioned optimal conditions, a wide range of structurally
divergent aryl alkyl sulfides was subjected to oxidation with very high selectivity
and excellent yield being observed in all cases (Table 3). The high yields of
oxidation products (91–96 %) obtained by this catalytic system indicate the high
efficiency of Cu-salen-MCM-41 with UHP.
One of the outstanding advantages of these oxidizing systems is selectivity and
chemoselectivity of the oxidation reaction, which is outlined in Scheme 3.
As is evident from Scheme 3, no side reaction such as overoxidation to sulfone or
oxidation of the hydroxyl group was observed.
Due to the need to obtain catalysts for green processes, the use of recycled
catalysts is required for reducing the catalytic cost. When the reaction was
1
23

Salen copper(II) complex heterogenized on mesoporous MCM-41
O
O
O
S
S
S
UHB, r.t
+
Solvent, Cat.
91-98 %
0%
O
S
S
UHB, r.t
Solvent, Cat.
S
OH
OH
O
+
97 %
0%
Scheme 3 Selectivity in the oxidation of sulfides by present procedure
Fig. 8 Influence of the number of uses on the catalytic activity of Cu-salen-MCM-41 for the oxidation of
dibenzyl sulfide
completed, the catalyst (insoluble) was filtered, dried, and reused. The catalyst was
used and reused for five cycles with similar activity (Fig. 8)
Conclusion
The internal pore surface of the meso- structure sieve MCM-41, grafted ligands
were used for the preparation of the copper(II) complex. These materials were
characterized by UV–Vis, FT-IR, BET, TEM, N adsorption, and XRD. These
2
materials show that the Cu complex is attached to the surface of MCM-41.
Especially, UV–Vis diffuse reflectance of spectroscopy is an extremely sensitive
probe for the presence of the Cu-salen complex in molecular sieves. An efficient and
heterogeneous complex is active in catalyzing the oxidation of different sulfides
with excellent yield, 100 % selectivity, and mild conditions using UHP as oxidant.
123

A. Jabbari et al.
The advantages of the use of UHP in the oxidation of sulfides are non-corrosive,
high thermal stability, and easy work.
Acknowledgment Financial support for this work by the research affairs of Ilam University, Ilam, Iran,
is gratefully acknowledged.
References
1
2
3
4
5
6
7
8
9
. J. Drabowicz, P. Kielbasinski, M. Mikolaiczyk, Synthesis of sulfoxides (Wiley, New York, 1994)
. H.L. Holland, Chem. Rev. 473, 88 (1988)
. M.C. Carreno, Chem. Rev. 1717, 95 (1995)
. S. Patai, Z. Rappoport, Synthesis of sulfones, sulfoxides and cyclic sulfides (Wiley, Chichester, 1994)
. B. Kotelanski, R.J. Grozmann, J.N. Cohn, Clin. Pharmacol. Ther. 427, 14 (1973)
. W.J. Parsons, V. Ramkumar, G.L. Stiles, Mol. Pharmacol. 37, 34 (1988)
. S. Padmanabhan, R.C. Lavin, G.J. Durant, Tetrahedron Asymmetr. 11, 3455 (2000)
. N.N. Mahamuni, P.R. Gogate, A.B. Pandit, Ultrason. Sonochem. 14, 135 (2007)
. R.E. Del Rio, B. Wang, S. Achab, L. Bohe, Org. Lett. 9, 2265 (2007)
10. G. Maayan, R. Popovitz-Biro, R. Neumann, J. Am. Chem. Soc. 128, 4968 (2006)
11. C.S. Lu, E.W. Hughes, P.A. Giguere, J. Am. Chem. Soc. 63, 1507 (1941)
12. Ch.E. Song, E.J. Roh, B.M. Yu, D.Y. Chi, S.Ch. Kim, K.J. Lee (2000) J. Chem. Soc. Chem.
Commun. 615
13. L. Canali, E. Cowan, H. Deleuze, C.L. Gibson, D.C. Sherrington, J. Chem. Soc. Chem. Commun.
2561 (1998)
1
1
4. L. Canali, E. Cowan, H. Deleuze, C.L. Gibson, D.C. Sherrington, J. Chem. Soc. Perkin Trans. I 2055 (2000)
5. E.F. Murphy, L. Schmid, T. Burgi, M. Maciejewski, A. Baiker, D. Gunther, M. Schneider, Chem.
Mater. 13, 1296 (2001)
16. S.K. Kim, K.H. Kim, S.K. Ihm, Chemosphere 68, 287 (2007)
17. M. Kurian, S. Sugunan, Chem. Eng. J. 115, 139 (2006)
18. X.G. Zhou, X.Q. Yu, J.S. Huang, S.G. Li, L.S. Li, C.M. Che, J. Chem. Soc. Chem. Commun. 1789
(1999)
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
9. E. Mollmann, P. Tomlinson, W.F.J. Holderich, Mol. Cat. 206, 137 (2003)
0. S. Ernst, E. Fuchs, X. Yang, Microporous Mesoporous Mater. 35–36, 137 (2000)
1. J. Guzman, B.C. Gates, J. Chem. Soc. Dalton Trans. 3303 (2003)
2. R. Ganesan, B. Viswanathan, J. Phys. Chem. B 108, 1702 (2004)
3. S. Ray, S. Vasudevan, Inorg. Chem. 42, 1711 (2003)
4. J. Deutsch, H.A. Prescott, D. Muller, E. Kemnitz, J. Catal. 231, 269 (2005)
5. A. Galarneau, D. Desplantier-Giscard, F. Di Renzo, F. Fajula, Catal. Today 68, 191 (2001)
6. D. Trong On, D. Desplantier-Giscard1, C. Danumah, S. Kaliaguine. Appl. Catal. A 253, 545 (2003)
7. J.A. Incavo, P.K. Dutta, J. Phys. Chem. 94, 3075 (1990)
8. H. Chen, Y. Wang, Ceram. Int. 28, 541 (2002)
9. A.S. Al-Shiri, Spectrochim. Acta (A) 60, 118 (2004)
0. T. Chinnusamy, O. Reiser, ChemSusChem 2010, 3 (1040)
1. B. Yu, A.H. Liu, L.N. He, B. Li, Z.F. Diaoa, Y.N. Lia, Green Chem. 14, 957 (2012)
2. B. Yu, C.X. Guo, C.L. Zhong, Z.F. Diao, L.N. He, Tetrahedron Lett. 2014, 55 (1818)
3. H.A. El-Borae, Therm. J. Anal. Calorim. 81, 339 (2005)
4. Z.M. Zaki, S.S. Haggag, A.A. Sayed, Spectrosc. Lett. 31, 757 (1998)
5. G. Kumar, D. Kumar, C.P. Singh, A. Kumar, V.B. Rana, J. Serbian Chem. Soc. 75, 629 (2010)
6. V.K. Aghera, P.H. Parsania, J. Sci. Ind. Res. 2008, 67 (1083)
7. N. Raman, V. Muthuraj, S. Ravichandran, A. Kulandaisamy, J. Chem. Sci. 115, 161 (2003)
8. V.P. Lozitsky, V.E. Kuzmin, A.G. Artemenko, R.N. Lozitska, A.S. Fedtchouk, E.N. Muratov, A.K.
Mescheriakov, SAR QSAR Environ. Res. 16, 219 (2005)
39. M.A. Villar, M.D. Failla, R. Quijada, R.S. Mauler, E.M. Valles, G.B. Galland, L.M. Quinzani,
Polymer 42, 9269 (2001)
4
0. T. Joseph, M. Hartmannb, S. Ernst, S.B. Halligudi, J. Mol. Catal. A 207, 131 (2004)
1. K.S.W. Sing, D.H. Everett, R.A.W. Haul, L.A. Moscou, R. Pierotti, J. Rouquerol, T. Siemieniewska,
Pure Appl. Chem. 57, 603 (1985)
4
1
23

Salen copper(II) complex heterogenized on mesoporous MCM-41
42. P. Karandikar, K.C. Dhanya, S. Deshpande, A.J. Chandwadkar, S. Sivasanker, M. Agashe, Catal.
Commun. 5, 69 (2004)
43. S. Shylesh, S. Sharma, S.P. Mirajkar, A.P.J. Singh, Mol. Catal. A. 212, 219 (2004)
44. H. Yang, L. Zhang, W. Su, Q. Yang, C. Li, J. Catal. 248, 204 (2007)
45. A. Ghorbani-Choghamarani, M. Nikoorazm, H. Goudarziafshar, L. Shiri, Z. Chenani, Bull. Korean
Chem. Soc. 30, 972 (2009)
46. H. Chen, Y. Wang, Ceram. Int. 28, 541 (2002)
123