In situ preparation of CeO2 nanoparticles on the MCM-41 with magnetic core as a novel and efficient catalyst for the synthesis of substituted pyran derivatives

Article abstract of DOI:10.1016/j.inoche.2018.11.010

An inexpensive, environmentally-benign, and magnetically recoverable nanocomposite consisting of magnetic core and MCM-41 mesoporous silica shell which was synthesized by using Rice Husk Ash (RHA) as the silica source was prepared. Subsequently, the CeO

Full text of DOI:10.1016/j.inoche.2018.11.010

Accepted Manuscript
In situ preparation of CeO2 nanoparticles on the MCM-41 with
magnetic core as a novel and efficient catalyst for the synthesis of
substituted pyran derivatives
Hamid Reza Saadati-Moshtaghin, Farrokhzad Mohammadi Zonoz
PII:
S1387-7003(18)30653-1
DOI:
https://doi.org/10.1016/j.inoche.2018.11.010
INOCHE 7174
Reference:
To appear in:
Inorganic Chemistry Communications
Received date:
Revised date:
Accepted date:
13 July 2018
25 October 2018
9 November 2018
Please cite this article as: Hamid Reza Saadati-Moshtaghin, Farrokhzad Mohammadi
Zonoz , In situ preparation of CeO2 nanoparticles on the MCM-41 with magnetic core
as a novel and efficient catalyst for the synthesis of substituted pyran derivatives. Inoche
(2018), https://doi.org/10.1016/j.inoche.2018.11.010
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ACCEPTED MANUSCRIPT
In situ preparation of CeO Nanoparticles on the MCM-41 with magnetic core as a novel
2
and efficient catalyst for the synthesis of substituted pyran derivatives
Hamid Reza Saadati-Moshtaghin*, Farrokhzad Mohammadi Zonoz
Department of Chemistry, School of Science, Hakim Sabzevari University, Sabzevar, 96179-
7
6487, Iran
Corresponding authors: Tel.: +98 51 44013060; fax: +98 51 44011161
*
E-mail: h_r_saadati@yahoo.com, h.r.saadati@hsu.ac.ir
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Abstract
An inexpensive, environmentally-benign, and magnetically recoverable nanocomposite
consisting of magnetic core and MCM-41 mesoporous silica shell which was synthesized by
using Rice Husk Ash (RHA) as the silica source was prepared. Subsequently, the CeO2
nanoparticles were synthesized and immobilized on the magnetically recoverable MCM-41 by
impregnation method. The synthesized nanocomposite was characterized with FT-IR, XRD, FE-
SEM, TEM, ICP and VSM. The obtained new nanocomposite demonstrated a catalytic
performance in the synthesis of tetrahydrobenzo[b]pyrans at the condensation condition under
solvent-free conditions. The nanocomposite catalyst could simply be recovered from the reaction
environment by using an external magnet field and be reused five times without a remarkable
losing in catalytic property.
Keywords: Magnetic nanoparticles, mesoporous silica, Rice Husk Ash, MCM-41, Pyrans, One-
pot synthesis
2

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1
. Introduction
Multicomponent reactions (MCRs) are highly efficient approaches in organic synthesis which
have been widely studied in current researches [1-10]. Pyran derivatives are among the most
important classes of heterocyclic compounds synthesized by Multicomponent reactions. Due to
the hallmark biological [11] and pharmacological activities of these compounds such as
anticoagulant, spasmolytic, diuretic, anticancer, antianaphylactin properties [12], Alzheimer’s
disease, AIDs associated dementia and myoclonus [13], have attracted strong considerable
attention. Pyran rings have intrinsic reactivity to present a variety of Synthetic methods for
producing a vast domain of heterocycles such as pyranopyrimidines, pyranopyridines, pyridine-
2
-ones, pyranopyrazoles and polyazanaphthalenes [14].
In last recent years, several methods and different catalysts have been reported in the literature
for the synthesis of these compounds. The easiest way involves one-pot, three component
condensation of propanedinitrile (malononitrile), aromatic aldehyde and 5,5-Dimethyl-1,3-
cyclohexanedione (dimedone) compounds in various conditions. Several catalysts such as
diammonium hydrogen phosphate [15], tetrabutylammonium bromide [16], L-proline [17],
H [NaP W O ] [18], N-methylmorpholine [19], hexadecyldimethylbenzyl ammonium
1
4
5
30 110
bromide [20], ionic liquids [21-24], magnetic core–shell titanium dioxide nanoparticles[25],
silica coated magnetite polyoxometalate nanoparticles [26], Tetra-methyl ammonium hydroxide
[
27], mixed metal nanooxides [28], magnesium oxide [29], Magnetite supported dihydrogen
phosphate (H PO /Fe O ) [30], nano ZnO [31], poly(4-vinylpyridine) [32], sodium selenite [33],
2
4
2
4
and 1-butyl-3-methyl imidazolium hydroxide ([bmim]OH) [34], and Lithium bromide have been
used in this synthesi[35]. However, in spite of their potential utility most of the aforementioned
3

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techniques show some limitations due to the use of toxic and corrosive reagents, the tedious
work-up procedure, and long reaction times which lead leading to restricted use of these catalysts
in practical applications. Consequently, research on substituted pyran derivatives and finding a
novel catalyst would be highly desirable.
Over the past decade, the usage use of magnetic nanoparticles (MNPs) presents a lot of merits
because these nanoparticles have magnetic and electrical characteristics, high specific surface
area and hallmark applications in various area areas such as drug delivery systems, targeted gene
therapy, magnetic resonance imaging (MRI), sensors, saving information, separation metal ion
environmental remediation, biomedicine particularly in the fields of pharmacology and catalysis
[
36-38]. The surface of MNPs could be functionalized and modified by various organic and
inorganic materials such as silica, polymers, biomolecules, metals, etc which have been used as
selective and efficient catalysts in a wide range of catalytic reactions [39, 40].
In this paper, we have tried to use the capabilities of three class of materials such as MNPs,
mesoporous silica MCM-41 and CeO nanoparticles simultaneously. For this reason, a new
2
nanocomposite called organic-mineral magnetization hybrid was developed and identified and its
catalytic effect was studied in the preparation of tetrahydrobenzo[b]pyrans under solvent-free
conditions (Scheme 1).
.
4

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2
. Experimental
.1. Material and Instrumentation
2
All reagents and starting materials were of analytical grade and were used as received from
commercial sources without further purification. The RH sample was obtained from a local mill
-1
in Rasht (Guilan province, Iran). FT-IR spectra were recorded in the range 400-4000 cm on
700 Shimadzu Fourier transform spectrophotometer using KBr pellet. X-ray diffraction (XRD)
patterns obtained from an a Philips PW1730 X-ray diffractometer with Cu Kα radiation at 40
8
-1
keV and 30 mA, and scanning rate was set to 3°min in the 2θ range from 10° to 80°. The
morphology and distribution of particles of the synthesized catalyst were characterized with a
field emission scanning electron microscopy (FESEM) which was carried out on a HITACHI S-
4
160 microscope with gold coating. Magnetic characteristics of compound compounds were
measured by vibrating samples magnetometer (VSM, BHV-55, Riken, Japan) at room
temperature. Elemental analysis was performed by inductivity coupled plasma on Varian
Australia, icp-oes, model vista pro. Spectrometry. Melting points were determined in open
capillary tube method with a Barnstead electrothermal type 9200 melting points apparatus. The
progress of the catalytic reaction was monitored by thin layer chromatography.
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2
2
.2. Synthesis
.2.1. Synthesis of Fe O magnetite nanoparticles (MNPs)
3
4
Magnetite nanoparticles (MNPs) were prepared using our previously reported method [30]. For
this reason, 5.41 g (20 mmol) FeCl .6H O and 1.99 g (10 mmol) FeCl .4H O was dissolved in
3
2
2
2
deionized water (100 mL) under N atmosphere. Under vigorous magnetic stirring (600 rpm), pH
2
is raising piecemeal by pouring (dropwise around 10 minute) of 25% NH3 solution (5 ml) to
approximate 10 and the mixed solution was refluxed for 60 min, and then cooled to room
temperature. Ultimate magnetic nanoparticles were aggregated by external magnetic field and
washed several times with disitlled water and 0.02 M solution of NaCl.
2
.2.2. Preparation of Fe O @MCM-41 nanoparticles
3 4
MCM-41 with magnetic core was prepared using rice husk ash as the silica source and CTAB as
the template according to the reported method with slight modification [41]. First of all, 200 ml
of sodium silicate solution extracted from RHA was added dropwise to 5 g of CTAB dissolved in
2
5 g of distillated water under vigorous stirring at room temperature. Secondly, about 1 g of
MNPs was dispersed in 50 ml of deionized water and ultrasonicated for 10 min and was then
added to the prior solution. Then Subsequently, the pH of the obtained solution was adjusted to
1
1 using 1 M acetic acid. The prepared surfactant-gel was stirred continuously for 6 h at room
temperature then the mixture transferred into an autoclave, which was sealed and heated at 100°
C for another 24 h under static conditions. Finally, the obtained solid product was magnetically
separated, washed abundantly with ethanol and deionized water, and dried at 60 ºC for 24 h. The
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synthesized mesoporous MCM-41 with magnetite core sample was calcined in air at 500 ºC for 5
h to remove the organic template.
2
4
.2.3. Synthesis of CeO incorporated mesoporous MCM-41 with magnetite core (CeO /MCM-
2 2
1@Fe O )
3
4
The CeO nanoparticles are synthesized by in-situ technique and immobilized on MCM-
2
4
1@Fe O . Accordingly, 1 g of MCM-41@Fe O was dispersed in 40 mL of deionized water
3 4 3 4
and stirred at 70 ºC for 1 h. Simultaneously, a solution of 2 g CeCl .7H O and 0.14 g of CTAB
3
2
was dissolved in 20 ml of deionized water and was slowly was added to the prior mixture.
Subsequently, the pH value of the mixture was adjusted to 10 by the addition of 25% aqueous
solution of ammonia. The obtained mixture was vigorously stirred for 5 h, transferred into an
autoclave to perform the hydrothermal reaction at 180º C for 24 h. After the completion of the
reaction, the reaction mixture was allowed to cool down to the room temperature. Finally, the
obtained product was washed several times with ethanol and deionized water, and dried at 60º C
in a vacuum oven for 8 h and labeled as CeO /MCM-41@Fe O . The schematic diagram of the
2
3
4
synthesis process is shown in Scheme 2.
2
2
.3. Catalytic reaction
.3.1. General procedure for the preparation of tetrahydrobenzo[b]pyrans
CeO /MCM-41@Fe O (0.05 g), was added to a mixture of the aromatic aldehyde (1 mmol),
2
3
4
propanedinitrile (malononitrile) (1.0 mmol), and 5,5-Dimethyl-1,3-cyclohexanedione (dimedone)
1.0 mmol). Then, the resulting mixture was stirred at 80 ºC in an oil bath under solvent-free
(
condition for the appropriate time. After the end of the reaction (monitoring monitored by TLC;
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hexane-ethyl acetate, 4:1), the nanocatalyst was separated from the reaction mixture by use of an
external magnetic field. The resulting crude product was cooled to room temperature and was
poured onto crushed ice, and the solid product which separated was isolated by filtration and
recrystallized from ethanol (3 ml) to afford pure tetrahydrobenzo[b]pyrans.
The purity of products was determined by the comparison of their physical and spectral data
(melting point, FT-IR spectra) with known compounds in articles [24, 33, 35]. FT-IR spectra can
be found in supplementary information online.
3
. Result and discussion
In continuation of our recent studies on the development of eco-friendly catalytic protocols
[
30,42] herein we were interested interest to in use using the CeO /MCM41@Fe O in synthesis
2 3 4
of highly substituted pyrans (tetrahydrobenzo[b]pyrans).
3
.1. Catalyst preparation and characterization
The preparation procedure for the magnetic nanocomposite is schematically illustrated in
Scheme 2. In the first step, chemical co-precipitation method was used employed to prepare
magnetite nanoparticles [30]. Then, the magnetite nanoparticles were surrounded with MCM-41
mesoporous silica to prevent further aggregation and avoid possible oxidation. In the final step,
the CeO nanoparticles were prepared by in-situ method and immobilized on the surface of
2
MCM-41@Fe O . The FT-IR, XRD, FE-SEM and VSM demonstrate demonstrated the
3
4
successful preparation of the CeO /MCM-41@Fe3O4.
2
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Scheme 2. Procedure for the preparation of CeO /MCM41@Fe O .
2
3
4
3
.1.1. FT-IR spectroscopy
FT-IR spectra of Fe O , MCM-41@Fe O and MCM-41@Fe O are shown in Fig. 1. As shown
3
4
3
4
3
4
-1
-1
in Fig. 1a, the pattern of Fe O reveal characteristic bands of Fe-O at 457 cm , 561 cm [43].
3
4
Moreover, as can be seen from in Fig. 1b, the existence of MCM-41 mesoporous silica nature
was indicated by vibrational bands band from at 1078 cm-1 which can be assigned to the
-1
asymmetric stretching vibrations of Si-O-Si. The band at 790 cm could be assigned to Si-O-H
stretching vibrations [44].
-1
The band at 3400 cm is attributed to the O-H stretching vibrations. The stretching band of Ce-O
cannot be seen because of its overlap with Fe-O Band.
Finally Lastly, by comparing all the spectra presented in this figure, the synthesis of
CeO /MCM-41@Fe O nanocomposite is easy to justify. Accordingly, the FT-IR spectroscopy
2
3
4
confirms the preparation of new nanocomposite with magnetic core and MCM-41 shell.
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Fig. 1. FT-IR spectra of Fe O , MCM-41@Fe O and CeO /MCM-41@Fe O .
3
4
3
4
2
3
4
3
.1.2. Chemical analysis
Table 1 shows the chemical analysis of the prepared nanomaterial. It demonstrates the loading of
CeO nanoparticles, which its loading amount is equal to Ce content of the prepared
2
nanocomposite.
Table 1. Result of Chemical analysis of the prepared nanomaterial.
Material
Ce (mmol/g)
MCM-41@Fe O
-
3
4
CeO /MCM-41@Fe O (g)
0.85
2
3
4
3
.1.3. X-ray diffraction (XRD) study
Fig. 2 represents the X-ray diffraction of Fe O , MCM-41@Fe O and CeO /MCM-41@Fe O .
3
4
3
4
2
3
4
The diffractions in Fig. 2a can be assigned to the planes of inverse cubic spinel structured Fe O
3
4
1
0

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(
JCPDS No. 19-0629). The prepared MCM-41@Fe O displays common diffractions of Fe O
3
4
3
4
nanoparticles beside the broad diffraction at 2 of ca. 23ꢀ in Fig 2b, indicates indicating the
existence of MCM-41 mesoporous silica around the magnetite core [45].
The XRD pattern of CeO /MCM-41@Fe O (Fig. 2c) displays common characteristic
2
3
4
diffractions of Fe O and CeO . The presence of additional diffractions indicates that the Ce O
3
4
2
2
nanoparticles [46] are formed and stabilized on the surface of MCM-41@Fe O . Generally, the
3
4
XRD patterns indicate the preparation of CeO /MCM-41@Fe O nanocomposite.
2
3
4
Fig. 2. XRD patterns of Fe O , MCM-41@Fe O and CeO /MCM-41@Fe O .
3
4
3
4
2
3
4
1
1

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The low-angle XRD patterns of MCM-41@Fe O and CeO /MCM-41@Fe O was were
3
4
2
3
4
illustrated in Fig. 3. The strong diffractions at 2ꢁ= 2.65ꢀ, indexed as the (100) diffraction, and
the small diffractions around 4.56ꢀand 5.23ꢀcan be indexed as (110) and (200) reflections of
MCM-41 [47]. The low-angle XRD patterns confirm the formation and preservation of ordered
mesoporous structure of MCM-41. Although, the intensity of the reflection diffractions of
CeO /MCM-41@Fe O decrease decreases with respect to those of MCM-41@Fe O , which can
2
3
4
3
4
be due to the immobilization of CeO nanoparticles onto the surface of mesoporous MCM-
2
4
1@Fe O and the decrease of the mesoscopic order.
3 4
Fig. 3. Low angle XRD patterns of MCM-41@Fe O and CeO /MCM-41@Fe O .
3
4
2
3
4
3
.1.4. FESEM and EDX studies
The FESEM analysis was employed to study the morphology, size and distribution of the
synthesized nanocomposite. It can be observed in Fig. 4a that the MNPs have a homogeneous
1
2

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morphology with high surface area and is are composed of quite similar sized spherical
nanoparticles with the average size of about 25-40 nm. The presented FESEM image of
CeO /MCM-41@Fe O (Fig. 4b) revealed that the CeO nanoparticles immobilized on the
2
3
4
2
MCM-41@Fe3O4 and the porous structure of CeO /MCM-41@Fe O nanocomposite has been
2
3
4
retained.
Fig. 4. FESEM images (a) Fe O and (b) CeO /MCM-41@Fe O
4
3
4
2
3
The EDX analysis was used to confirm the chemical identity of CeO /MCM-41@Fe O (Fig.5).
2
3
4
The EDX analysis indicates the coexistence of Fe, O and Si and the presence of Ce reveals that
CeO supported on the surface of MCM-41@Fe O . This These results support the successfully
2
3
4
synthesize of CeO /MCM-41@Fe O .
2
3
4
1
3

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Fig. 5. EDX analysis of CeO /MCM-41@Fe O
4
2
3
3
.1.5. The study of magnetic property
The magnetic characteristic characteristics of Fe O and CeO /MCM-41@Fe O were
3
4
2
3
4
investigated by VSM at room temperature and presented in Fig. 6. As can be seen, the hysteresis
loop loops for the samples was were entirely reversible and S-like curves, showing that the
nanoparticles exhibit superparamagnetic properties. Magnetic evaluation displays that pure
Fe O and CeO /MCM-41@Fe O have saturation magnetization amounts of 72 and 37 emu/g,
3
4
2
3
4
respectively. As expected, the magnetic properties property of obtained nanocomposite is lower
than pure Fe O which and this mass saturation magnetization reduction could be attributed to
3
4
the presence of the mesoporous silica shell and CeO nanoparticles around the magnetite core.
2
The result reveals that the nanocomposite exhibit exhibits good acceptable magnetic responsible
characteristic, which suggests a potential application for targeting and separation.
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4

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Fig. 6. Magnetization curves of Fe O and CeO /MCM-41@Fe O
4
3
4
2
3
3
.1.6. The study of thermal reliability
Thermal gravimetric analysis (TGA) was used to confirm the high thermal stability of the
CeO2/MCM-41@Fe3O4. As can be seen in Fig. 7, the TGA curves only shows one main weight
loss. The weight loss starts at 50º C with slight slope and continues with tense slope up to 150º C
(14 %) which is allocated to physically and hydrogen bonded water and it could also be due to
decomposition of the remaining surfactant functional groups. Based on the TGA analysis result,
the prepared nanocomposite demonstrates high thermal stability.
1
5

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Fig. 7. TGA analysis of CeO2/MCM-41@Fe3O4
3
.1.7. Nitrogen physisorption study
The N adsorption/desorption isotherms and the corresponding pore size distribution (PSD) were
2
determined for MCM-41@Fe O and CeO /MCM-41@Fe O and the results are listed in Table
3
4
2
3
4
2
. The decrease in the surface area and pore diameter of CeO /MCM-41@Fe O is are another
2 3 4
evidence for the formation and incorporation of CeO in the MCM-41@Fe O framework. It is
2
3
4
believed that the immobilization of CeO in the channels of MCM-41@Fe O lead to an increase
2
3
4
in the particle size and decrease of surface area. increases the particle size and decreases the
surface area.
Table 2. Nitrogen physisorption parameters for MCM-41@Fe O and CeO /MCM-41@Fe O
3
4
2
3
4
Characteristic
MCM-41@Fe O
CeO /MCM-41@Fe O
3
4
2
3
4
2
-1
Surface area (m g )
826
1.04
6.7
364
3
-1
Pore volume (cm g )
0.42
7.2
Average pore diameter (nm)
1
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3
.2. Catalytic activity of CeO /MCM-41@Fe O in tetrahydrobenzo[b]pyrans synthesis
2
3
4
After the preparation and characterization of CeO /MCM-41@Fe O , the catalytic activity of the
2
3
4
prepared nanocomposite was evaluated in the synthesis of tetrahydrobenzo[b]pyrans. For this
reason, appropriate amount of the nanocatalyst was added to a mixture of benzaldehyde (1
mmol), malononitrile (1 mmol), and dimedone (1 mmol) under various conditions. The effect of
solvent (Table 3), catalyst amount (Table 4) and reaction temperature (Table 5) on the reaction
yield was systematically investigated.
At first, reaction mixture of benzaldehyde (1 mmol), malononitrile (1 mmol), and dimedone (1
mmol) in the presence of 0.05 g of catalyst at 80º C was chosen as a model reaction and was
carried out in the different solvent solvents. It was revealed that under solvent-free conditions
much better results were obtained (Table 3).
Table 3. Effect of different solvents on the synthesis of tetrahydobenzo[b]pyarans.
Entry
Solvent
Toluene
Acetonitrile
Ethanol
Time (min)
Yield %
76
1
2
3
4
5
10
10
5
5
5
81
85
88
93
H O
2
solvent-free
Reaction conditions: benzaldehyde, malononitrile and dimedone (1:1:1 mmol) were mixed in the presence of 0.05 g
of CeO /MCM-41@Fe O and the reaction mixture was heated to 80 ºC.
2
3
4
In order to optimize the amount of the catalyst, 0-0.1 g of catalyst was added to the model
reaction under solvent-free conditions. The obtained results indicated that the reaction did not
occur in the absence of catalyst (Table 4 entry 1), whereas in the presence of nanocatalyst (0.01
g) yield% of the reaction was improved to 23% which shows showing the significant role of
catalyst in the reaction progress. With comparison of Comparing obtained results, 0.03 g of
catalyst was chosen as the optimum amount.
1
7

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Table 4. Effect of catalyst amount on the synthesis of tetrahydobenzo[b]pyarans.
Entry CeO /MCM-41@Fe O (g) Time (min) Yield %
2
3
4
1
2
3
4
5
0
30
5
5
5
5
0
0.01
0.02
0.03
0.05
23
59
91
93
Reaction conditions: benzaldehyde, malononitrile and dimedone (1:1:1 mmol) were mixed in 80 ºC water.
Finally, the effect of temperature on the yield of reaction was also investigated by using model
reaction with 0.03 g of catalyst under solvent-free conditions and the results are presented in
table 5. It was found that with increasing the reaction temperature to 80 °C, the yield of reaction
improved to 91%, but further increases in temperature lead to decrease in the yield, possibly due
to the disturbance in product formation. Therefore, the temperature 80 ꢂ was considered as
optimal temperature. After the comparison of the results, it was found that the best results have
been obtained under solvent-free condition in the presence of 0.03 g of catalyst at 80 C after 5
min.
Table 5. Effect of reaction temperature on the synthesis of tetrahydobenzo[b]pyarans.
Entry
Temperature (°C)
Yield %
17
1
2
3
4
5
25
40
60
80
100
43
76
91
83
Reaction conditions: benzaldehyde, malononitrile and dimedone (1:1:1 mmol) were mixed in the presence of 0.03 g
of CeO /MCM-41@Fe O for 5 min under solvent-free conditions.
2
3
4
Table 6 shows the total superiority of the present catalyst in terms of reaction time, and yield %
compared to the previously reported methods. Furthermore, operation simplicity, eco-friendly
nature of the catalyst, reusability and ease of catalyst separation, mild reaction conditions,
1
8

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avoidance of toxic organic solvents and economical aspects are other remarkable advantages of
present procedure.
Table 6. Comparison of the catalytic activity of CeO /MCM-41@Fe O with some reported
2
3
4
catalysts used for the synthesis of tetrahydobenzo[b]pyarans.
Catalyst
Entry
time(min)
360-420
20
yield %
84-95
93
ref.
[20]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
Hexadecyldimethyl benzyl ammonium bromide
magnetic core–shell titanium dioxide NPs
1
2
3
4
5
6
7
8
9
Fe O -SiO -H PW O
3
4
2
3
12 40
40
90
Tetra methyl ammonium hydroxide
Ce Mg Zr O
30-120
35-45
22-37
15
30
150-210
10
79-92
84-95
85-95
88
90
90-98
21
1
x
1-x
2
Magnesium oxide
H PO @SiO @Fe O
4
2
4
2
3
ZnO (Nano)
Sodium selenate
Fe O
[33]
1
1
1
0
1
2
This work
This work
This work
3
4
MCM-41@Fe O
10
-
3
4
CeO /MCM-41@Fe O
4
5
91
2
3
In order to determine the generality of the present procedure, various aromatic aldehydes bearing
electronwithdrawing and electrondonating groups can be utilized in this protocol under the
obtained optimal conditions (Table 7). As can be seen, in all cases the expected products
successfully synthesized with acceptable yields. Although, it seems that the use of aromatic
aldehydes with electron withdrawing groups give rise to supreme yield of the products.
Table 7. Synthesis of tetrahydrobenzo[b]pyran derivatives.
M.P. (ꢂ)
Entry
Ar
Yield %
TOF
Ref
5
Observed Reported
3
1
2
3
4
5
6
7
C H -
2-ClC H -
3-ClC H -
4-ClC H -
2,4-(Cl) C H -
3-BrC H -
4-BrC H -
91
92
93
92
93
94
91
428
433
230-232
213-215
232-234
215-216
230-232
239-241
180-182
227-229
207-209
6
5
3
5
6
4
3
3
3
2
3
3
5
3
4
3
438 231-233
433 237-238
438 181-183
443 228-230
428 206-208
6
4
6
4
2
6
3
6
4
6
4
1
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3
2
3
3
3
3
3
2
5
4
5
5
5
5
3
4
8
9
1
1
1
1
1
1
4-(OMe) C H -
92
83
76
94
96
95
72
69
433 201-203
391 161-163
358 217-219
443 181-183
451 211-213
447 181-183
339 228-230
325 200-202
196-198
158-160
220-222
180-182
213-214
176-178
231-233
197-199
6
4
3,4-(OMe) C H -
2
6
3
0
1
2
3
4
5
4-CH C H -
3
6
4
2-NO C H -
2
6
4
3-NO C H -
2
6
4
4-NO C H -
2
6
4
3-OHC H -
6
4
4-N(CH ) C H -
3
2
6
4
The ease of separation and reusability of catalyst is are key factor factors for its sustainable value
and economical points of view in heterogeneous catalysis. In this regards regard, after the end of
reaction, the catalyst was recovered by an external magnetic field. After washing with ethanol
and drying at 70°C for 2h, the recovered catalyst was reused four times in the condensation
reaction for preparation of tetrahydrobenzo[b]pyrans, to afford 89%, 88%, 85% and 82% yields,
respectively (Fig. 8). It seems that, the decrease in catalytic activity of catalyst could be due to
the degradation of catalyst.
Fig. 8. The reusability of CeO /MCM-41@Fe O .
2
3
4
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4
. Conclusion
In summary, CeO /MCM-41@Fe3O4 magnetic nanocomposite was successfully synthesized and
2
characterized by FT-IR, XRD, FESEM, EDX, BET and VSM. The catalytic activity of this
hetrogenous nanocatalyst was examined through the one-pot synthesis of biologically and
pharmacologically active tetrahydrobenzo[b]pyran derivatives by three-component reactions of
aromatic aldehydes, malononitrile and dimedone. Some advantages obtained by this method
versus previously reported methods can be summarized as; the catalyst is heterogeneous,
magnetically separable and reusable. Additionally, the environmentally benign nature of this
method and the excellent yields of products (61-95%) along with short reaction time is are
among other advantages (15 min). We believe that this methodology is superior to the existing
methodologies for the preparation of tetrahydrobenzo[b]pyrans.
Acknowledgment
I dedicate this research to the soul of my late aunt who contributed significantly to my personal
and academic life. I would like to extend sincere thanks to my dear friends Hamid Reza Hashemi
Moghadam and Cyrus Ahmadi Toussi for their help and English correction.
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Graphical abstract
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ACCEPTED MANUSCRIPT
Highlights

CeO immobilized magnetically recoverable MCM-41 was synthesized and
2
characterized.



The obtained nanocomposite was used for the synthesis of substituted pyran derivatives.
The catalyst was magnetically recovered and reused for four times.
The prepared nanocomposite is more efficient than previously reported catalysts.
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