Synthesis and characterization of Al2O3-SiO2-MgO nanocomposite prepared by sol-gel process as an efficient catalyst for the Knoevenagel condensation of aldehydes with malononitrile

Article abstract of DOI:10.1007/s11164-014-1765-8

Abstract The composite of Al₂O₃-SiO₂ and Al₂O₃-SiO₂-MgO nanocomposite were synthesized by sol-gel method and FT-IR, XRD, FE-SEM, EDAX, TEM, and BET surface area analysis were used to charac

Full text of DOI:10.1007/s11164-014-1765-8

Res Chem Intermed
DOI 10.1007/s11164-014-1765-8
Synthesis and characterization of Al2O3–SiO2–MgO
nanocomposite prepared by sol–gel process
as an efficient catalyst for the Knoevenagel
condensation of aldehydes with malononitrile
•
Mahmood Iranpour Mobarakeh Ali Saffar-Teluri
S. A. Hassanzadeh Tabrizi
•
Received: 30 May 2014 / Accepted: 7 July 2014
Ó Springer Science+Business Media Dordrecht 2014
Abstract The composite of Al2O3–SiO2 and Al2O3–SiO2–MgO nanocomposite
were synthesized by sol–gel method and FT-IR, XRD, FE-SEM, EDAX, TEM, and
BET surface area analysis were used to characterize the as-prepared samples. XRD
results show the formation of MgO phase in the nanocomposite. FE-SEM images
indicate uniform distribution of MgO nanoparticles in the Al2O3–SiO2 matrix and
also amorphous and spherical-like structures for Al2O3–SiO2 and Al2O3–SiO2–MgO
nanocomposite, respectively. An increase in the surface area of the nanocomposite
compared to Al2O3–SiO2 composite is observed with adding MgO. The catalytic
activity of Al2O3–SiO2–MgO nanocomposite was tested by using them as an effi-
cient base catalyst for the Knoevenagel condensation of different aromatic alde-
hydes with malononitrile at room temperature. The nanocomposite can be easily
separated and reused for several cycles.
Keywords Nanocomposite Á Sol–gel method Á Knoevenagel condensation
Introduction
The formation of C = C bonds in the organic compounds is one of the most useful
reactions in the synthesis of therapeutic drugs [1], natural products [2], herbicides,
insecticides, functional polymers [3], and fine chemicals [4]. This bond can be
formed by the Knoevenagel condensation. The Knoevenagel reaction is the
M. I. Mobarakeh Á A. Saffar-Teluri (&) Á S. A. H. Tabrizi
Faculty of Material Science & Engineering, Najafabad Branch, Islamic Azad University,
PO Box 85141-43131, Najafabad, Iran
e-mail: a.saffar.t@iaun.ac.ir
A. Saffar-Teluri
Department of Chemistry, Faculty of Science, Najafabad Branch, Islamic Azad University,
PO Box 85141-43131, Najafabad, Iran
123

M. I. Mobarakeh et al.
condensation of an aromatic aldehyde and a compound containing an active
methylene group, which proceeds in the presence of a catalyst. The catalysts are
ammonia, organic amines and their salts [5], some Lewis acids, and bases such as
ZnCl2, CdI2, zeolites, hydrotalcite in ionic liquid media, amino-functionalized
mesoporous silica, and metal–organic frameworks have also been used as catalysts
[6–17]. However, some of these methods are limited by harsh conditions, low
yields, long reaction times, and use of toxic solvents.
Al2O3–SiO2 mixed oxides, or composites of them, as an inorganic support are
widely used as catalysts and ceramic materials [18–25]. Clay minerals [18], zeolites
[19, 23], mullite [21], and SiO2–Al2O3 catalysts are examples of materials where the
existence of Al–O–Si bond structures or SiO2–Al2O3 interfaces controls their final
performance for the desired application. The reason for choosing these particular
mixed oxides was the properties such as low thermal expansion and conductivity,
low dielectric constant, excellent creep resistance, robust chemical and thermal
stability, good high temperature strength, and oxidation resistance [24].
Metal oxides have potential applications in water treatment due to their high
surface area added to low production and regeneration costs. Among the large
family of metal oxides, magnesium oxide (MgO) is an interesting multifunctional
and an exceptionally important material used in catalysis [26], toxic-waste
remediation, or as an additive in refractory, paint, and superconducting products
as well as for fundamental and application studies [27]. It has also been used as
bactericides and adsorbents. MgO in particular has shown great promise as a
destructive adsorbent for toxic chemical agents [28]. MgO is mainly obtained by the
thermal decomposition of magnesium hydroxide or carbonate, sol–gel process,
spray pyrolysis, sonochemical synthesis, and hydrothermal reaction [28–31]. The
MgO morphology and particle size were found to depend on the preparation
conditions such as pH, gelling agent, calcination rate, and temperature.
In the past few years, the synthesis of solid base catalysts has played a prominent
role in the field of heterogeneous catalysis. Solid base catalysts have several
advantages over homogeneous base catalysts, such as easy recovery of the catalyst,
simple product isolation, and recyclability. Thus, the heterogeneous solid base
catalysts have been recognized as potential alternatives to homogeneous base
catalysts. In an effort to design various solid base catalysts for the synthesis of a,b-
unsaturated dicyanide derivatives and in continuation of our interest in the use of
heterogeneous catalyst in organic reactions [32–35], herein we report a novel and
mild condensation of various aromatic aldehydes with malononitrile reaction for the
synthesis of a,b-unsaturated dicyanides using reusable Al2O3–SiO2–MgO catalyst at
room temperature (Scheme 1).
Experimental
All reagents were purchased from Merck and Aldrich and used without further
purification. All products obtained are known compounds and were identified by
1
comparing their physical and spectral data with those reported in the literature. H
NMR spectra were recorded on an Ultra Shied spectrometer (400 MHz) using TMS as
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Synthesis and characterization of Al2O3–SiO2–MgO
Al2O3-SiO2-MgO
Ethanol
ArCH=C(CN)2
NCCH2CN
ArCHO
+
Ar = C6H5, 2-Cl-C6H4, 4-Cl-C6H4, 2,4-Cl2-C6H4, 2-NO2-C6H4, 3-NO2-C6H4,
4-NO2-C6H4, 2-OH-C6H4,4-OH-C6H4, 4-(CH3)2N-C6H4, 4-OH-3-OCH3-C6H3
Scheme 1 Knoevenagel condensation aromatic aldehydes with malononitrile
internal standard. Fourier transform infrared (FT-IR) spectroscopy was performed
using a Jasco FT/IR-3600 FT-IR spectrometer. The phase and crystallinity were
characterized by using a Philips x’pert X-ray diffractometer with Cu-Ka radiation in
the 2h range of 10–70°. FE-SEM and EDAX were taken by a SIGMA VP field
emission scanning electron microscopy. Specific surface area was carried out using
Micrometrics adsorption equipment (BELSORP Instrument, Japan).
Synthesis of Al2O3–SiO2–MgO nanocomposite
Al2O3–SiO2–MgO nanocomposite with 50 wt% of MgO was synthesized using the
sol–gel approach. Firstly, tetraethyl orthosilicate (TEOS) was diluted in ethanol and
water. Then the necessary amount of HCl (37 %) was added to the mixture and
refluxed at 75 °C for 2 h (TEOS: C2H5OH: H2O: HCl molar ratio was 1:22:13:
7.9 9 10-4). Afterwards, magnesium nitrate (Mg(NO3)2Á6H2O) and aluminum
nitrate (Al(NO3)3Á9H2O) dissolved in ethanol was added to the mixture and refluxed
at 75 °C for another 2 h. The resulting mixture was aged at room temperature for
24 h and dried in an oven for 24 h at 120 °C. It was then calcined to 500 °C at a
heating rate of 8 °C/min and once 500 °C was reached, it was kept at this
temperature for 12 h. The nominal content of MgO was 50 wt%, and the
corresponding nanocomposite was denoted as ASM50. Also, Al2O3–SiO2 composite
was synthesized under similar conditions.
Synthesis of a,b-unsaturated dicyanides from the condensation reaction
of different aromatic aldehydes with malononitrile
In a typical procedure, 1 mmol aromatic aldehyde was mixed with the 1 mmol
malononitrilein5 ml ofethanol taken in a round-bottomflask. Then 20 mgASM50 was
added to it and the reaction mixture was stirred at room temperature for the presented
time in Table 1. The progress of the reaction was monitored by TLC. After this reaction
mixture was filtered, the solid was washed with the ethanol and dried. The solvent was
removed and the obtained solid product residue was crystallized from ethanol.
Results and discussion
Figure 1 presents the FTIR spectrum of ASM50 sample after calcining at 500 °C.
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M. I. Mobarakeh et al.
Table 1 ASM50 nanocomposite catalyzed Knoevenagel condensation
Entry
1
1
a
Substrate
Time (min) Yield (%)a m.p. (°C) Lit. m.p. (°C) [ref.]
90
70
91
90
81–84
82–85 [36]
CHO
2
3
4
5
b
c
d
e
81–83
80–82 [36]
CHO
Cl
60
50
40
94
93
95
160–162 160 [36]
CHO
Cl
Cl
141–142
136–138
141–143 [37]
CHO
Cl
137–138 [37]
CHO
NO2
6
7
f
50
20
93
96
98–101
100–102 [37]
160–162 [39]
O2N
CHO
CHO
g
160–163
O2N
H3C
8
h
i
100
120
140
180
89
90
88
90
131–133
84–86
132–133 [36]
84–86 [38]
CHO
9
CHO
OCH3
10
11
j
110–112
163–165
111–115 [36]
163–164 [40]
CHO
H3CO
k
CHO
OH
123

Synthesis and characterization of Al2O3–SiO2–MgO
Table 1 continued
Entry
1
Substrate
Time
(min)
Yield
(%)a
m.p.
(°C)
Lit. m.p. (°C)
[ref.]
12
l
200
150
205
87
90
91
186–188
187–188 [38]
CHO
HO
13
14
a
m
n
179–182
180–181 [40]
CHO
(H3C)2N
H3CO
135–138 136.5–139 [40]
CHO
HO
Isolated yields
In Fig. 1, the absorption peaks 427 and 517 cm-1 are attributed to Mg–O
vibration, whereas the peaks obtained at 619 and 712 cm-1 indicate Al–O bond
vibrations. There is also a band at 898 and 1,023 cm-1 duo to the Al–O–Al and Si–
O–Si bond stretching vibration. The stretching vibration and bending vibration of
the O–H group for water appeared at 3,444 and 1,634 cm-1, respectively.
The room-temperature X-ray diffraction (XRD) patterns of Al2O3–SiO2 and
ASM50 are presented in Fig. 2a, b, respectively.
The solid Al2O3–SiO2 displays the characteristic spectral profile of an amorphous
structure in the 2h = 23° for Al2O3–SiO2 (Fig. 2a). Comparison with the spectrum
of Al2O3–SiO2, With adding the MgO content to 50 wt%, two peaks appear in
2h = 43.22° and 62.98° (Fig. 2b), which can be indexed to the structure of MgO
(JCPDS card No: 78-0430). In order to obtain detailed structure information of the
composite, a low-angle XRD pattern of ASM50 is presented in Fig. 3. The
composites do not diffract in the 2h range of 1–10°, which indicates that ASM50 has
an amorphous matrix.
Figure 4a, b shows the FE-SEM images and EDAX analysis of samples Al2O3–
SiO2 and ASM50.
Two types of morphology, uniform (a) and spherical-like (b), can be seen in the
FE-SEM images. Surface morphology of the ASM50 sample is different from the
Al2O3–SiO2 as would expected due to formation of MgO in nanocomposite. The
Al2O3–SiO2 composite has a uniform structure, while adding MgO to the composite
causes the formation of homogeneous spherical-like particles. In the FE-SEM image
of ASM50, the MgO nanoparticles exist in the nanocomposites with almost uniform
distribution.
The EDAX patterns are performed to identify the elemental composition of the
nanocomposite. From the corresponding EDAX spectra, Al2O3–SiO2 composite and
ASM50 nanocomposite are composed of Al, Si, and O elements (Fig. 4a) and of Al,
Si, O, and Mg elements (Fig. 4b), respectively. These results are in good agreement
123

M. I. Mobarakeh et al.
Fig. 1 The FTIR spectrum of ASM50
Fig. 2 XRD patterns of Al2O3–SiO2 (a) and ASM50 (b)
Fig. 3 Low-angle XRD pattern
of ASM50
with the XRD analysis and strongly prove that the MgO is successfully mixed with
Al2O3–SiO2 matrix.
In order to obtain the crystallite size of nanocomposite, the TEM image of
ASM50 is shown in Fig. 5. Based on Fig. 5, nanoparticle size distribution is
123

Synthesis and characterization of Al2O3–SiO2–MgO
Fig. 4 FE-SEM images and EDAX analysis of Al2O3–SiO2 (a) and ASM50 (b)
continuous between the minimal diameter (about 5 nm) and the maximal diameter
(about 90 nm).
The results of BET measurements are presented in Table 2. The Al2O3–SiO2
composite has a low BET surface area (63 m2/g). With adding MgO, the surface
area of the ASM50 nanocomposite was increased (141 m2/g).
In order to investigate the catalytic activity of ASM50 nanocomposites, the
Knoevenagel condensation between different aromatic aldehydes with malononitrile
as active methylene compound was carried out and the results are presented in
Table 1. All reactions were completed in 20–205 min duration to produce the
corresponding alkenes with 87–96 % yield. Aromatic aldehydes with electron-
withdrawing groups (–NO2) provided very good yields and the reaction were
completed in short times. Also, in the case of electron-donating groups (–OH,
–OCH3, –CH3), reasonably good yields were observed but demanded little more
reaction time. In the case of ortho and para substitutions, the latter gave more yield
than the former due to steric hindrance.
Reusability of the catalyst was investigated by carrying out repeated runs on the
same batch of the used catalyst. After the completion of the reaction, the catalyst
was washed with dichloromethane and acetone, and then dried and recycled. No
appreciable change in the activity was observed for five runs (Fig. 6).
123

M. I. Mobarakeh et al.
Fig. 5 TEM image of ASM50
Table 2 BET measurement results for different nanocomposites
Sample
Surface area (m2/g)
Al2O3–SiO2
ASM50
63
141
Fig. 6 Recyclability of ASM50 after fifth cycle
Conclusions
Based on the above-obtained results, (1) adding MgO to Al2O3–SiO2 composite
causes an increase in the surface area of the Al2O3–SiO2–MgO nanocomposite, (2)
uniform structure of Al2O3–SiO2 composite was converted to spherical-like
structure by adding MgO in the Al2O3–SiO2–MgO nanocomposite, (3) the reusable
Al2O3–SiO2–MgO nanocomposite synthesized through the sol–gel process is an
123

Synthesis and characterization of Al2O3–SiO2–MgO
efficient base catalyst in the Knoevenagel condensation of different aromatic
aldehydes with malononitrile for the synthesis of dicyanides with very good yields.
Acknowledgments We gratefully acknowledge the financial support from the Research Council of
Islamic Azad University of Najafabad Branch.
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