Efficient preparation of Zr(IV)-salen grafted mesoporous MCM-41 catalyst for chemoselective oxidation of sulfides to sulfoxides and Knoevenagel condensation reactions

Article abstract of DOI:10.1016/S1872-2067(15)60968-8

Zr(IV)-salen-MCM-41 was prepared by reaction of NH₂-MCM-41 with salicylaldehyde to afford Schiff base ligands. Thereafter, ZrOCl₂·8H₂O was reacted with the Schiff base ligands for complex formation. The structural properti

Full text of DOI:10.1016/S1872-2067(15)60968-8

Chinese Journal of Catalysis 36 (2015) 1852–1860
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Efficient preparation of Zr(IV)‐salen grafted mesoporous MCM‐41
catalyst for chemoselective oxidation of sulfides to sulfoxides and
Knoevenagel condensation reactions
Maryam Hajjamia,*, Farshid Ghorbanib, Sedighe Rahimipanaha, Safoora Roshania
a Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
b Department of Environment, Faculty of Natural Resource, University of Kurdistan, 66177‐15177 Sanandaj, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Zr(IV)‐salen‐MCM‐41 was prepared by reaction of NH2‐MCM‐41 with salicylaldehyde to afford
Schiff base ligands. Thereafter, ZrOCl2·8H2O was reacted with the Schiff base ligands for complex
formation. The structural properties of the synthesized materials were investigated by a number of
analytical techniques including X‐ray diffraction, N2 sorption‐desorption, thermogravimetric analy‐
sis, Fourier transform infrared spectroscopy, inductively coupled plasma atomic emission spec‐
troscpopy, and energy dispersive X‐ray spectroscopy. Catalytic studies of the mesoporous materials
functionalized with Zr(IV)‐Schiff base complexes were investigated and extended to selective oxida‐
tion of sulfides to sulfoxides and the Knoevenagel condensation reactions of aldehydes with malo‐
nonitriles and ethyl cyanoacetate. Additionally, catalyst recycling of the Zr‐salen‐MCM‐41 materials
was also studied.
Received 19 June 2015
Accepted 6 September 2015
Published 20 November 2015
Keywords:
Zr(IV)‐salen‐MCM‐41
Mesoporous material
Sulfoxide
Knoveonagel condensation
Sulfide
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
post‐synthetic modification of the pore surface of a purely in‐
organic silica material (grafting); (2) in situ addition of a func‐
M41S family mesoporous materials [1] have attracted con‐
siderable attention across a wide application sector as sorbents
[2–5], heterogeneous catalysts [6–8], drug delivery vehicles
[9,10], and separators [11]. Among the M41S derivatives,
tional organosiloxane to the corresponding silica material
(co‐condensation); and (3) functionalization by organic groups
bridging into the pore walls by bissilylated organosilica pre‐
cursors (periodic mesoporous organosilicas). Functionalizing
with amine‐containing groups is one of many ways to graft
useful functionality into the mesoporous silica to afford meso‐
porous catalysts [13].
Selective oxidation of sulfides to sulfoxides is an important
transformation in synthetic organic chemistry because sulfox‐
ides are useful functional groups in numerous pharmaceutical‐
ly and biologically active compounds. In addition, sulfoxides are
important synthetic intermediates for the production of mole‐
cules, especially by C–C bond formation [14,15].
MCM‐41 possessing
a two‐dimensional (2D) hexagonal
mesostructure has attracted significant attention because of
high surface areas, efficient surface functionalization, and large
pore volumes. The catalytic efficiency of this material depends
on the nature of the functionalization by grafting of organic
compounds via Si–C bond formation. The abundance of surface
hydroxyl groups on MCM‐41 permits reactions with desired
organic compounds, leading to organic‐inorganic mesoporous
hybrid materials [12]. Typically, the functionalization of meso‐
porous materials is performed in one of three ways: (1)
Numerous reports highlight synthetic methods for the oxi‐
* Corresponding author. Tel/Fax: +98‐8412227022; E‐mail: mhajjami@yahoo.com, m.hajjami@ilam.ac.ir
DOI: 10.1016/S1872‐2067(15)60968‐8 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 11, November 2015

Maryam Hajjami et al. / Chinese Journal of Catalysis 36 (2015) 1852–1860
1853
dation of sulfides to sulfoxides, based on metal intermediate
catalysts, such as Fe [16], Au [17], Ti [18], Cu [19], Co [20], Mn
[21], Zr [22], Mo [23], Zn [24], V [25], Ru [26], Ta [27], and W
[28]. These works represent considerable progress; however,
all suffer from one or more disadvantages including long reac‐
tion time, low product yield, tedious acidic work‐up, generation
of environmentally unfavorable by‐products, additional syn‐
thetic steps to remove or recover the expensive catalyst, and
difficulties in preventing over‐oxidation. Hence, a new method‐
ology is required to design suitable catalysts that can overcome
such drawbacks.
The Knoevenagel condensation reaction, discovered by
Knoevenagel [29] in 1896, involves the condensation of alde‐
hydes with a C–H acidic methylene activated group. The
Knoevenagel condensation is widely employed in the synthesis
of important chemical intermediates, such as coumarin deriva‐
tives because of their biological activities [30]. Furthermore,
the Knoevenagel condensation reaction has been used for the
preparation of cosmetics, perfumes, and substituted alkenes.
Generally, the reaction requires both a solvent and a catalyst.
Examples of acidic and basic catalysts, such as ionic liquids
[31], porous calcium hydroxyapatite [32], silica‐coated Fe3O4
nanoparticles bearing 3‐aminopropyl functional groups [33],
Fe3O4 nanoparticle‐supported amino acids [34], carbamic acid
ammonium salts [35], zinc chloride [36], cation‐exchanged
zeolites [37], montmorillonite KSF [38], and magnesium fluo‐
ride [39], have been reported. In the presence of acid catalysts
the Knoevenagel condensation reaction can accelerate because
of increasing aldehyde electrophilicity. To accomplish a cleaner
Knoevenagel synthesis, great effort has been made to prepare
heterogeneous catalysts.
Cd complexes on MCM‐41 as heterogeneous catalysts [45].
Furthermore, [Ru(salen)(NO)] complex‐modified SBA‐15 used
in the hydrogenation of ketones to the corresponding alcohols
has been reported [46]. Co(II)‐Schiff base functionalized
MCM‐41 was synthesized and used as a catalyst for styrene
oxidation with H2O2 [47]. Additionally, Cr(III) alanine‐salicylal‐
dehyde Schiff base complex immobilized on mesoporous silica
gels, MCM‐41, and SBA‐15 were promising catalysts for the
epoxidation of styrene [48].
This investigation reports the synthesis, characterization,
and catalytic properties of a MCM‐41 mesoporous silica‐sup‐
ported Zr(IV) complex applied to efficient Knoevenagel con‐
densation reactions and the chemoselective oxidation of sul‐
fides to sulfoxides.
2. Experimental
2.1. Chemicals
Analytical grade hexadecyltrimethylammonium bromide
(CTAB), HCl (37%), NaOH, tetraethyl orthosilicate (TEOS), al‐
dehydes, sulfides, H2O2 (30%), malononitrile, and ethyl cyano‐
acetate were all purchased from Aldrich and Merck and used
without further purification. De‐ionized distilled water was
used in the preparation of all solutions. The known products
were characterized by physical data with those of authentic
samples. Unknown compounds were identified by their 1H
NMR and 13CNMR spectra (Bruker NMR‐Spectrometer FX
400Q).
2.2. Synthesis of Zr(IV)‐salen‐MCM‐41
Designing suitable supports to immobilize metal‐Schiff base
complexes remains an important and relevant topic in the field
of heterogeneous catalysis. A number of solid material sup‐
ports, such as polymers, carbon nanotubes, ionic liquids, zeo‐
lites, and mesoporous silicas, including SBA‐15, have widely
been investigated. Among them, mesoporous materials have
attracted extensive attention for the immobilization of met‐
al‐salen complexes owing to their high surface area, large pore
size together, and facile functionalization of the silica walls. The
mesoporous material‐supported metal‐salen complexes have
proven to be highly efficient catalysts for the synthesis of a
variety of valuable organic compounds. Briefly, among the
mesoporous material‐supported metal‐salen complex cata‐
lyzed systems, zirconium Schiff base complex‐modified SBA‐15
was applied as a heterogeneous catalyst for the synthesis of a
library of N‐containing pyrazine‐based heterocycles [40]. Other
works have shown that pyrazine‐based heterocycles synthe‐
sized in the presence of SBA‐15‐supported Fe(III)‐Schiff base
[41] and Mn(salen)/C3N2‐Schiff‐SBA‐15 and Mn(salen)/C4N2‐
Schiff‐SBA‐15 were reported as useful for the epoxidation of
alkenes [42]. Additionally, the Sizuki C–C cross‐coupling reac‐
tion over Pd‐salen MCM‐41 has been reported [43]. In another
work, the Pd(II)‐Schiff base complex‐functionalized MCM‐41
behaved as a highly active catalyst toward the Suzuki‐Miyaura
cross‐coupling reaction [44]. Oxidation of sulfides and oxida‐
tive coupling of thiols were performed using immobilized Ni or
MCM‐41 was synthesized according to a previous literature
method [49–51]. Briefly, MCM‐41 was prepared by the reaction
of TEOS (1 mmol) as the silica source and CTAB (0.1 mmol) in a
basic solution of NaOH (0.3 mmol) and H2O (60 mL). The gel
mixture was then crystallized under hydrothermal treatment at
110 °C for 60 h in a Teflon‐lined autoclave. The resultant solid
was recovered by filtration, washed with de‐ionized water and
dried in air. The collected product was calcined at 550 °C for 7
h to remove the polymeric surfactant, CTAB.
Modification of mesoporous MCM‐41 to n‐propylamine‐
MCM‐41 was conducted according to Ref. [52]. In a typical pro‐
cedure, 27 mmol of 3‐aminopropyl triethoxysilane (APTES)
was stirred with MCM‐41 (4.8 g) in n‐hexane (96 mL) at 80 °C
for 24 h under a N2 atmosphere. The resulting solid
NH2‐(CH2)3‐MCM‐41 was filtered, washed several times with
n‐hexane and dried in vacuum. Thereafter, NH2‐(CH2)3‐MCM‐41
(1 g) was added to salicylaldehyde (1 mmol) in absolute etha‐
nol (20 mL) and stirred for 5 h under reflux conditions under a
N2 atmosphere. The solution slowly became yellow, indicating
the formation of the Schiff base. The yellow solid imine product
was isolated after ethanol removal.
Further modification was required to form the Zr(IV)‐imine
complex of MCM‐41. ZrOCl2·8H2O (2 mmol) was added to a
suspension of imine‐MCM‐41 (1 g) in acetonitrile (30 mL) at
room temperature under a N2 atmosphere. The mixture was

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Maryam Hajjami et al. / Chinese Journal of Catalysis 36 (2015) 1852–1860
stirred for 6 h. The solid product was filtered, washed with
water and then dried in an oven, obtaining a peach‐colored
Zr(IV)‐salen‐MCM‐41 (Scheme 1).
by TLC. Upon completion of the reaction, the mixture was de‐
canted and extracted with CH2Cl2. The organic layer was dried
over anhydrous Na2SO4. The solvent was evaporated under
reduced pressure. Recrystallized absolute ethanol and water
further purified the product.
2.3. Catalyst characterization
The crystalline structures of the synthesized samples were
examined by X‐ray diffraction (XRD) using a GBC‐Difftech MMA
diffractometer. The Ni‐filtered Cu Kα (λ = 0.154 nm) radiation
was used at an acceleration voltage of 35 kV and a current of
34.2 mA. The diffraction angle was scanned from 1° to 10°, 2θ
at a rate of 1°/min. To determine the textural properties, Fou‐
rier transform infrared (FT‐IR) analyses were performed using
an FT‐IR spectrophotometer Vertex 70 (Bruker, Germany) in
the range of 400–4000 cm−1. Thermogravimetric analysis (TGA,
PerkinElmer Pyris Diamond, UK) was determined from ambi‐
ent temperature to 800 °C using a ramp rate of 10 °C/min. To
determine the textural properties, N2 adsorption‐desorption
isotherms were measured using a BEL sorp‐mini II volumetric
adsorption analyzer. All of the samples were degassed at 100 °C
under an Ar gas flow for 3 h prior to analysis. The specific sur‐
face area of the synthesized materials was evaluated using the
BET model and the pore size distribution was calculated by the
BJH model. Energy dispersive X‐ray spectroscopy(EDX, FESEM‐
TESCAN MIRA3) studies of Zr(IV)‐salen‐MCM‐41 confirm the
presence of zirconium in the catalyst.
2.6. Characterization data of selected compounds
Tetrahydrothiopheneoxide (2b, Table 4). IR (ATR) cm−1:
1
1034 (S=O). H NMR (CDCl3, 400 MHz) δ: 2.21–2.3 (m, 4H),
3.02–3.11 (m, 4H).
Diethyl sulfoxide (2f, Table 4). IR (ATR) cm−1: 1066 (S=O).
1H NMR (CDCl3, 400 MHz) δ: 1.39–1.43 (q, J = 3.2, 3H), 2.98–
3.01 (q, J = 3.2, 2H). 13C NMR (CDCl3, 100 MHz) δ: 7.75, 47.30.
2‐(4‐Bromo‐benzylidene)‐malononitrile (3e, Table 7). IR
(ATR) cm−1: 3050–2900, 2226, 1576, 1487, 614. H NMR
1
(CDCl3, 400 MHz) δ: 7.27 (s, 1H), 7.68–7.72 (d, 2H), 7.77–7.79
(d, 2H). 13C NMR (CDCl3, 100 MHz) δ: 159.6, 134.2, 132.9, 131.1,
130.8, 114.6, 113.5, 84.6.
2‐(4‐Methyl‐benzylidene)‐malononitrile (3g, Table 7). IR
(ATR) cm−1: 3037–2927, 2223, 1587, 1451.1H NMR (CDCl3, 400
MHz) δ: 2.48 (s, 3H), 7.35 (d, 2H), 7.73 (s, 1H), 7.82 (d, 2H, J =
7.2).
Ethyl‐2‐cyano‐3‐(4‐methylphenyl)acrylate (3h, Table 7). IR
(ATR) cm−1: 3030–2904, 2216, 1722, 1473, 1593, 1092, 1264.
1H NMR (CDCl3, 400 MHz) δ: 1.41 (t, 3H), 2.44 (s, 3H), 4.39 (q,
2H, J = 7.06), 7.32 (d, 2H), 7.91 (d, 2H, J = 8.4), 8.22 (s, 1H).
Ethyl‐2‐cyano‐3‐(3‐hydroxyphenyl)acrylate (3j, Table 7). IR
(ATR) cm−1: 3372, 2984, 2222, 1698, 1491, 1595, 1179, 1239.
1H NMR (CDCl3, 400 MHz) δ: 1.41 (t, 3H, J = 7.2), 4.4 (q, 2H),
6.17 (s, 1H), 7.10 (d, 1H, J = 6.8), 7.37 (d, 1H), 7.44 (s, 1H), 7.60
(m, 1H), 8.22 (s, 1H). 13C NMR (CDCl3, 100 MHz) δ: 157.6, 156.4,
133.7, 131.7, 125.7, 122.2, 117.4, 104, 64, 15.3.
2.4. General procedure for the oxidation of sulfides to sulfoxides
H2O2 (30%, 0.4 mL) was added to a mixture containing sul‐
fide (1 mmol) and catalyst (Zr(IV)‐Schiff base‐MCM‐41, 0.03 g)
at 35 °C under solvent‐free conditions. The reaction mixture
was stirred until completion of the reaction as monitored by
thin‐layer chromatography (TLC). After complete conversion of
the reactant, the product was extracted with CH2Cl2 and
washed with water. The organic layer was dried over anhy‐
drous Na2SO4. The solvent was removed under vacuum and the
residue purified by chromatography (eluting with 4:1 hex‐
ane/acetone).
2‐(3‐Nitro‐benzylidene)‐malononitrile (3k, Table 7). IR
(ATR) cm−1: 3108–2867, 2226, 1611, 1595, 1524, 1353. H
NMR (CDCl3, 400 MHz) δ: 7.80 (m, 1H), 7.90 (d, 1H, J = 2.4), 8.35
(s, 1H), 8.49 (d, 1H), 8.67 (s, 1H).
2‐(4‐Ethoxy‐benzylidene)‐malononitrile (3p, Table 7). IR
(ATR) cm−1: 3000–2900, 2219, 1587, 1473, 1174, 1263. H
1
1
NMR (CDCl3, 400 MHz) δ: 1.48 (t, 3H, J = 12.66), 4.16 (q, 2H),
7.00 (d, 2H), 7.65 (s, 1H), 7.90 (d, 2H, J = 8.4).13C NMR (CDCl3,
100 MHz) δ: 160, 134.6, 124.9, 116.6, 115.6, 114.5, 79.3, 65.44,
15.7.
2.5. General procedure for the synthesis of arylidene
malononitriles and arylidene ethylcyanoacrylates
A mixture of malononitrile (2 mmol) or ethyl cyanoacetate
(2 mmol), an aromatic aldehyde (1 mmol), and catalyst
(Zr(IV)‐Schiff base‐MCM‐41, 0.05 g) in water (3 mL) was
stirred at 35 °C for a desired time. The reaction was monitored
2‐(4‐Methoxy‐benzylidene)‐malononitrile (3o, Table 7). IR
(ATR) cm−1: 3050–2900, 2220, 1603, 1568, 1276, 1179. H
NMR (CDCl3, 400 MHz) δ: 3.94 (s, 3H), 7.02 (d, 2H), 7.67 (s, 1H),
7.92 (d, 2H, J = 8). 13C NMR (CDCl3, 100 MHz) δ: 166.8, 160,
134.6, 125.1, 116.3, 115.6, 114.5, 79.6, 57, 30.
1
O
Zr
3. Results and discussion
O
O
CH
N
CH
N
3.1. Structural features of the synthesized catalyst
Si
O
Si
O O O
O
O
OH OH
OHOH
OH
OH
1)
H2N
Si(OEt)3
The low‐angle XRD patterns of the synthesized and func‐
tionalized MCM‐41 materials are presented in Fig. 1. The dif‐
fractograms reveals that a one‐dimensional hexagonal meso‐
porous p6mm structure of MCM‐41 was synthesized. In the
n-hexane, N2, 80 o
C
MCM-41
MCM-41
2) Salicylaldehyde, ethanol, reflux
.
3) ZrOCl2 8H2O, acetonitrile, N2, r.t.
Scheme 1. Synthesis of the Zr(IV)‐salen‐MCM‐41 catalyst.

Maryam Hajjami et al. / Chinese Journal of Catalysis 36 (2015) 1852–1860
1855
2500
2000
1500
1000
500
Table 1
(100)
Textural properties of synthesized materials obtained by N2 adsorp‐
tion‐desorption analysis.
Sample Name
MCM‐41
Amine‐MCM‐41
Imine‐MCM‐41
Zr‐imine‐MCM‐41
SBET (m2/g)
986.16
810.68
201.36
57.82
DBJH (nm)
3.65
2.46
1.41
1.67
Vtotal (cm3/g)
0.711
MCM-41
Amine-MCM-41
Imine-MCM-41
Zr-imine-MCM-41
Zr-imine-MCM-41 after oxidation reaction
0.758
0.177
0.081
alized MCM‐41 possessing a uniform pore size distribution.
These results are in agreement with those previously reported
[8,55]. Textural properties of the samples obtained by N2 iso‐
therms are summarized in Table 1. MCM‐41 and amine‐
MCM‐41 show high surface areas and pore volumes, which are
typical of mesoporous materials. However, a decrease in the
(110) (200)
0
2
4
6
8
10
12
2/(o )
SBET and DBJH average pore diameter is observed with function‐
Fig. 1. Low‐angle XRD patterns of the synthesized materials.
alization in imine‐MCM‐41 and Zr‐imine‐MCM‐41. This result
can be easily interpreted because of the presence of pendant
functional groups on the surface that partially block the ad‐
sorption of nitrogen molecules. Such a significant decrease of
textural properties of porous materials on grafting has already
been reported [56,57]. A wall thickness of MCM‐41, 2.14 Å, was
calculated by the following equation [54]:
MCM‐41 diffractogram it is clearly discernible that a very sharp
diffraction peak (100) at 2θ = 2.64° and two additional
high‐order reflections (110, 200) with lower intensities at 4.60°
and 5.47°, respectively, are observed [53]. The d‐spacing values
for these peaks are 33.46, 19.21, and 16.16 Å, respectively. The
unit cell parameter (a0) of 38.64 Å was calculated using the
following equation [54]:
Wall thickness = a0 – DBJH
(2)
FT‐IR spectroscopy was employed to detect the presence of
the functional binding groups in the amine‐functionalized
MCM‐41 material, the imine analog, and the Zr(IV)‐imine‐
MCM‐41 catalyst together with the recovered catalysts after
oxidation of sulfides and the Knoevenagel condensation reac‐
tion (Fig. 3). The vibration signals at ~1040 and 800 cm–1 are
typical Si–O–Si bands attributed to the asymmetric and sym‐
metric stretching, respectively [58,59]. The presence of the
peak close to 1630 cm–1, mainly from the NH2 symmetric
bending vibration, indicates the successful grafting of the or‐
a0 = 2d100/√3
(1)
A significant difference was observed in the intensity of the
peaks in the XRD diffractogram through each functionalization
of MCM‐41. These results provide further evidence that func‐
tionalization occurred mainly inside the mesopore channels.
They also confirm that the integrity of the hexagonal symmetry
long‐range order was retained after several stages of function‐
alization and oxidation reactions.
N2 adsorption‐desorption isotherm data revealed that all
samples exhibited type IV isotherms typical of mesoporous
porosity (Fig. 2) possessing hysteresis loops with parallel and
almost horizontal branches, classified as H4‐type according to
the IUPAC nomenclature.
(1)
(2)
(3)
Furthermore, a distinct inflection in the p/p0 range from
0.25 to 0.35 represents the characteristic capillary condensa‐
tion of nitrogen inside the parent MCM‐41 and amine‐function‐
500
400
MCM-41
Amine-MCM-41
Imine-MCM-41
Zr-imine-MCM-41
(4)
(5)
300
200
100
3500 3000 2500 2000 1500 1000
Wavenumber (cm1)
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
Fig. 3. FT‐IR spectra of (1) amine‐MCM‐41, (2) imine‐MCM‐41, (3)
Zr(IV)‐MCM‐41, (4) Zr(IV)‐MCM‐41 after oxidation reaction, and (5)
Zr(IV)‐MCM‐41 after Knoevenagel reaction.
Fig. 2. Nitrogen adsorption (solid symbols)‐desorption (open symbols)
isotherms of synthesized materials.

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Maryam Hajjami et al. / Chinese Journal of Catalysis 36 (2015) 1852–1860
ganic amine onto the surface [60,61]. The absorbance of the
C–N stretching vibration is normally observed around
1000–1300 cm–1. However, this peak cannot be resolved be‐
cause of its overlap with the absorbance of the Si–O–Si stretch
in the 970–1350 cm–1. A band residing at 1640 cm–1 (MCM‐41)
could be assigned to the C=N bond of imine in the Schiff base
mesoporous silica. After the complex preparation, FT‐IR spec‐
troscopy displays an imine bond shift to 1616 cm–1, confirming
complex formation. The spectrum of the recovered Zr(IV)‐
imine‐MCM‐41 shows that the catalyst is stable during the re‐
action (Fig. 3(d) and (e)).
Based on inductively coupled plasma atomic emission spec‐
troscopy (ICP‐AES), the concentration of Zr(IV) in the complex
Schiff base MCM‐41 catalyst was 0.318 mmol/g. To investigate
leaching of the Zr species, a leaching experiment was per‐
formed via oxidation of methylphenyl sulfide. In a representa‐
tive test, the solid catalyst Zr(IV)‐salen‐MCM‐41 was recovered
by filtration, and the filtrate was analyzed for Zr(IV) content
using ICP‐AES. The concentration of Zr(IV) obtained was de‐
termined to be 0.275 mmol/g, resulting in a decrease of 13%.
EDX of the Zr(IV)‐salen‐MCM‐41 showed that the mass per‐
cents of C, N, Si, O, and Zr are 12.59%, 1.88%, 38.47%, 42.96%,
and 4.10%, respectively (Fig. 4). These peaks suggest successful
complexation of zirconium with the Schiff base of MCM‐41
mesoporous support.
The TGA curves of the synthesized materials are presented
in Fig. 5. The thermogram of the calcined MCM‐41 shows three
individual steps of weight loss. The first distinct weight loss is
1.76% in the region of 25–120 °C associated with desorption of
water. Thereafter, a second (120–600 °C) weight loss of 3.52%
is observed, which is likely to be attributed to the decomposi‐
tion of trace amounts of the residual template. The final weight
loss (600–800 °C) of 1.32% results from water loss via further
condensation of silanol groups. The thermogram of the
amine‐functionalized MCM‐41 material shows a gradual weight
loss up to 800 °C. The TGA curve of amine‐MCM‐41 shows four
distinct weight loss regions (25–120, 120–300, 300–600, and
600–800 °C). The weight loss at the lower temperature, at‐
tributed to the desorption of physisorbed water held in the
pores, is 7.18%. The weight losses in the second and third steps
(13.85%) are associated with oxidative decomposition of the
organic functional groups. At the higher temperature, the
weight loss (1.37%) relates to the dehydroxylation of the sili‐
100
95
90
85
80
75
MCM-41
Amine-MCM-41
Imine-MCM-41
Zr-imine-MCM-41
100
200
300
400
500
600
700
800
Temperature (oC)
Fig. 5. TGA curves of the synthesized materials.
cate networks. On the basis of elemental analysis, the amount
of loaded functional amine groups was calculated to be 0.465
mmol/g of MCM‐41. The TGA curve of the imine‐MCM‐41 ma‐
terial shows four steps of weight loss (25–120, 120–300,
300–600, and 600–800 °C). A weight loss of 2.16% is observed
in the first step. Upon increasing the temperature, a weight loss
equal to 19.87% for the second and third steps is observed.
Water loss from additional condensation of the silanol groups
finally results in the fourth step recording a weight loss of
1.61%. Hence, the amount of loaded imine as a functional group
was calculated to be 0.501 mmol/g of MCM‐41. Finally, The
TGA curve of the Zr‐imine‐MCM‐41 material shows four indi‐
vidual steps of weight loss (25–120, 120–280, 280–700, and
700–800 °C). A weight loss of 3.05% relates to the first step and
a weight loss equal to 20.85% corresponds to the second and
third steps. Finally, a 0.89% weight loss results at the high‐
er‐temperature fourth step.
3.2. Catalytic activity
3.2.1. Selective oxidation of sulfides to sulfoxides
In the present work various sulfides were oxidized to sul‐
foxides by H2O2 (30%) in the presence of Zr(IV)‐salen‐MCM‐41
as a catalyst under solvent‐free conditions. The amount of the
catalyst is a major factor affecting the oxidation yield. Thus,
after screening catalyst loading levels (Table 2), the results
show that 0.03 g of Zr(IV)‐salen‐MCM‐41 gave the optimal
loading of catalyst (Table 2, entry 6).
SiK
5000
Table 2
4000
3000
Optimization of Zr(IV)‐salen‐MCM‐41 as a catalyst for selective oxida‐
tion of methyl phenyl sulfide under solvent‐free conditions.
Entry
Catalyst (g)
—
Time (h)
Yielda (%)
1
2
3
4
5
6
7
5
2
2
2
2
2
3.5
60
70
78
80
85
93 b
75
0.01
0.015
0.02
0.025
0.03
0.04
AlK
2000
O K
N K
1000
ZrL ClK
ClK
ZrL
C K
keV
0
0
5
10
Reaction conditions: methyl phenyl sulfide 1 mmol, H2O2 0.4 mL.
a Purification by preparative TLC. b Isolated yield.
Fig. 4. EDX spectrum of the Zr(IV)‐salen‐MCM‐41 catalyst.

Maryam Hajjami et al. / Chinese Journal of Catalysis 36 (2015) 1852–1860
1857
Table 3
Table 4
Oxidation of methyl phenyl sulfide under varying solvents.
Oxidation of sulfides to sulfoxides with H2O2 catalyzed by Zr(IV)‐salen‐
MCM‐41 under solvent‐free conditions.
Entry
Solvent
Acetone
Dichloromethane
H2O
n‐Hexane
Ethanol
Acetonitrile
Solvent‐free
Yielda (%)
O
1
2
3
4
5
6
7
15
20
35
40
70
70
93b
Cat. (0.03 g), H O (0.4 mL)
2
2
S
S
R
R
2
R , R = alkyl or aryl
1
R
R
2
o
1
2
1
35 C, solvent-free
1a-i
2a-i
Time
Isolated
Entry
1
Substrate
Product
(min)
yield(%)
2a
120
240 a
135
120
93
Reaction conditions: methylphenyl sulfide 1 mmol, H2O2 0.4 mL, Zr(IV)‐
salen‐MCM‐41 0.03 g, 35 °C.
2
3
4
2a
2a
2a
60 b
63 b,c
51 b,d
a Purification by preparative TLC. b Isolated yield.
Furthermore, during the optimization of the reaction condi‐
tions in choosing an appropriate solvent, the methylphenyl
sulfide was subjected to oxidation by H2O2 in the presence of
the synthesized catalyst in varying solvents. As is evident from
Table 3, the optimum condition is under solvent‐free condi‐
tions, which was then applied throughout the remainder of this
investigation.
According to the obtained results, the optimized reaction
conditions were selected to determine the scope of the func‐
tionalized MCM‐41 catalyzed by the oxidation reaction. In this
light a wide range of aliphatic and aromatic sulfides were sub‐
jected to oxidation to their corresponding sulfoxides in the
presence of 0.03 g of Zr(IV)‐salen‐MCM‐41. The results are
summarized in Table 4.
5
6
7
8
2b
2c
2d
2e
30
20
45
10
89
99
86
77
O
S
O
O
S
S
9
2f
2g
2h
2j
40
30
98
95
90
98
S
S
10
11
12
160
10
S
As shown in Table 4 in all cases, the reaction proceeded ef‐
fectively to give the corresponding sulfoxides in satisfactory
yields. In this report, aromatic and aliphatic sulfides oxidize
successfully in the presence of Zr(IV)‐salen‐MCM‐41 as a cata‐
lyst. To investigate the reaction mechanism, the oxidation reac‐
tion of methylphenyl sulfide by H2O2 in the presence of the
Schiff base of MCM‐41 and without interference of Zr(IV) was
examined (Table 4, entry 2). The reaction did not proceed to
completion and therefore the presence of the metal is obviously
necessary. In another study, the reaction of methylphenyl sul‐
fide was performed in the presence of the Zr(IV)‐salen com‐
plex. The over‐oxidation to sulfone occurred at the beginning of
the reaction (Table 4, entry 3). Additionally, a catalyst was
synthesized on the surface of a non‐porous silica. After catalyst
preparation, the catalytic properties were examined in the oxi‐
dation of methyl phenyl sulfide under the same conditions but
in the presence of the new catalyst. The progress of the reaction
was monitored by TLC. The reaction failed to complete after
120 min and furthermore, sulfone was formed. The yield of
methylphenyl sulfoxide was 51% (Table 4, entry 4). Interest‐
ingly, this reaction, which performed in the presence of modi‐
fied MCM‐41 (Table 4, entry 1) at the same time on stream
(120 min), gave a yield of 93%. Therefore a significant differ‐
Reaction condition: sulfide 1 mmol, H2O2 0.4 mL, Zr(IV)‐salen‐MCM‐41
0.03 g, 35 °C. a Blank run using Schiff base‐MCM‐41 as the catalyst
without Zr. b Purification by preparative TLC. c Zr(IV)‐salen was used as
a catalyst. d Zr(IV)‐salen‐silica was used as a catalyst.
ence in yields is observed.
A plausible oxidation reaction mechanism is shown in
Scheme 2 [62]. The role of Zr(IV) in the modified MCM‐41 cat‐
alyst is to form the active oxidant‐sulfide complex. Finally,
transfer of oxygen to sulfur leads to the formation of the sul‐
foxide.
3.2.2. Knoevenagel condensation reaction
First, to optimize the reaction conditions, the reaction of
2‐nitrobenzaldehyde (1 mmol) and malononitrile (2 mmol) in
the presence of varying loadings of catalyst was selected as a
model reaction. The results are summarized in Table 5. As
shown, a higher yield and shorter reaction time were obtained
using 0.05 g of Zr(IV)‐salen‐MCM‐41. No improvement in the
reaction efficiency was observed upon increasing the Zr(IV)‐
salen‐MCM‐41 loading to 0.08 g.
In a separate study, the condensation of 2‐nitrobenzalde‐
hyde and malononitrile in the presence of Zr(IV)‐salen‐MCM‐
Scheme 2. Proposed mechanism for the oxidation of sulfides to sulfoxides.

1858
Maryam Hajjami et al. / Chinese Journal of Catalysis 36 (2015) 1852–1860
Table 5
Table 6
Optimization of the Zr(IV)‐salen‐MCM‐41 catalyst for the synthesis of
2‐(2‐nitro‐benzylidene)‐malononitrile in water at 35 °C.
Knoevenagel condensation reaction of 2‐nitrobenzaldehyde and malo‐
nonitrile under varying solvents.
Entry
Catalyst (g)
—
Time (min)
Isolated yield (%)
Solvent
Solvent‐free
H2O
Ethanol
H2O/PEG (1:1)
Time (min)
Isolated yield (%)
1
2
3
4
200
50
30
98
88
99
91
180
30
150
40
88
99
83
86
0.03
0.05
0.08
15
Reaction conditions: 2‐nitrobenzaldehyde 1 mmol, malononitrile 2
mmol, H2O 3 mL, 35 °C.
Reaction conditions: 2‐nitrobenzaldehyde 1 mmol, malononitrile 2
mmol, solvent 3 mL, 35 °C.
41 was examined under varying solvents at 35 °C. As Table 6
indicates, the optimum results were obtained when the reac‐
tion was performed in water.
To assess the efficiency and scope of the functionalized
mesoporous silica catalyst in the preparation of arylidene
malononitriles and arylidene ethylcyanoacrylate, the conden‐
sation of various aldehydes with malononitrile and ethyl cy‐
anoacetate was examined in the presence of Zr(IV)‐salen‐
MCM‐41 in water at 35 °C. The corresponding results are pre‐
sented in Table 7. It was observed that the desired products
were produced in excellent yields (90%–99%) and the
Zr(IV)‐salen‐MCM‐41 is a highly efficient, general and mild
modified mesoporous catalyst for the Knoevenagel condensa‐
tion. Malononitrile was more reactive than ethyl cyanoacetate.
Table 7
Knoevenagel condensation reaction of active methylene compounds with functionalized aromatic aldehydes.
X
CN
CN
X
Cat. (0.05 g)
H2O, 35 o
CHO
+
+
H2O
C
R
R
X = CN, COOEt
3a-p
Entry
1
Aldehyde
X
Product
Time (min)
60
Isolated yield (%)
M.P. a (°C)
CN
CN
CN
3a
3a
3a
3b
96
70–75 (83 [63])
71–75 (83 [63])
73–76 (83 [63])
47–50 (52 [63])
130
120
330
45 b
60 c
98
COOEt
CN
COOEt
3c
3d
60
300
95
99
156–160 (164 [63])
83–87 (87 [63])
2
3
4
CN
COOEt
3e
3f
70
400
97
99
156–158 (153–156 [63])
88–94
CN
COOEt
3g
3h
80
360
97
99
132–134 (132–133 [64])
87–92 (88–91 [64])
CN
COOEt
3i
3j
5
5
95
99
150–153
79–84
5
6
7
CN
COOEt
3k
3l
35
130
99
99
100–103 (104–105 [63])
121–126 (128–132 [63])
CN
COOEt
3m
3n
30
90
99
98
136–140 (141–142 [63])
89–94 (96 [63])
8
9
CN
CN
3o
3p
250
150
96
99
107–110 (115 [63])
127–132
Reaction conditions: aldehydes 1 mmol, malononitrile or ethyl cyanoacetate 2 mmol, Zr(IV)‐salen‐MCM‐41 0.05 g, water 3 mL, 35 °C.
a The data in parentheses are reported in the literature. b Zr(IV)‐salen was used as a catalyst. c Zr(IV)‐salen‐silica was used as a catalyst.

Maryam Hajjami et al. / Chinese Journal of Catalysis 36 (2015) 1852–1860
1859
Additionally, to show the important role of MCM‐41 as a
Table 8
support, Zr(IV)‐salen was prepared without any support and
immobilized on non‐porous silica. The catalytic activity of these
prepared catalysts was tested in the synthesis of benzylidene
malononitrile (Table 7, entry 1). As mentioned, in the presence
of Zr(IV)‐salen, a yield of only 45% was attained, whereas in
the presence of Zr(IV)‐salen supported on non‐porous silica the
product yield increased to 60% even with a shorter reaction
time. These results show that MCM‐41, as a mesoporous com‐
pound that offers inherent textural properties such as high
surface area and large pore volume, has great potential as a
support for the Knoevenagel condensation reaction.
For any heterogeneous system, an additional important
factor is to determine the recycling and reusability properties.
The experimental design further encompassed the reusability
of Zr(IV)‐salen‐MCM‐41 for the oxidation of sulfides and the
Knoevenagel condensation reaction (Table 8). In both cases,
the catalyst could be easily separated and recovered by simple
filtration. The recovered catalyst, after washing with CH2Cl2
and H2O followed by drying, was used in a subsequent run. A
minimal decrease in activity was observed. As expected, the
reactions proceeded with similar yields to the first run.
Reusability of Zr(IV)‐salene‐MCM‐41 in the sulfide oxidation and
Knoevenagel condensation.
Isolated yield (%)
Run
Tetrahydothiophen
2‐(3‐Nitro‐benzylidene)‐
oxide a
89
malononitrile b
1
2
3
4
99
98
90
88
83
97
95
a Reaction conditions: tetrahydrothiophene 1 mmol, H2O2 0.4 mL, cata‐
lyst 0.03 g, 30 min, 35 °C, solvent‐free.
b Reaction conditions: 3‐nitrobenzaldehyde 1 mmol, malononitrile 2
mmol, catalyst 0.05 g, 35 min, water 3 mL, 35 °C.
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Graphical Abstract
Chin. J. Catal., 2015, 36: 1852–1860 doi: 10.1016/S1872‐2067(15)60968‐8
O
S
Efficient preparation of Zr(IV)‐salen grafted mesoporous MCM‐41
catalyst for chemoselective oxidation of sulfides to sulfoxides and
Knoevenagel condensation reactions
Cat. (0.03 g), H O (0.4 mL)
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R , R = alkyl or aryl
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Cat. (0.05 g)
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Maryam Hajjami *, Farshid Ghorbani, Sedighe Rahimipanah, Safoora Roshani
Ilam University, Iran; University of Kurdistan, Iran
R
H O, 35
2
C
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X = CN, COOEt
O
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Zirconium‐imine‐MCM‐41 catalyst was prepared by reaction of NH2‐MCM‐41
with salicylaldehyde to afford the Schiff base ligands. Then zirconyl chloride
octahydate was added to Schiff base ligands for complex formation. This
Zr(IV)‐Schiff base mesoporous material can be used as a solid acid catalyst for
the selective oxidation of sulfides to sulfoxides and Knoveonagel condensation
reaction of aldehydes.
CH
CH
Zr
N
N
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Si
Cat:
O
O
O O O
MCM-41

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