Synthesis and characterization of the immobilized Ni-Zn-Fe layered double hydroxide (LDH) on silica-coated magnetite as a mesoporous and magnetically reusable catalyst for the preparation of benzylidenemalononitriles and bisdimedones (tetraketones) under

Article abstract of DOI:10.1039/c8nj00788h

Herein, novel magnetic Fe₃O₄@SiO₂@Ni-Zn-Fe layered double hydroxide (LDH) intercalated with water molecules and carbonate anions as interlayer contents was prepared as a new heterogeneous and separable nanocatalyst. The me

Full text of DOI:10.1039/c8nj00788h

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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ARTICLE
Synthesis and Characterization of the Immobilized Ni-Zn-Fe
Layered Double Hydroxide (LDH) on Silica Coated Magnetite as a
Mesoporous and Magnetically Reusable Catalyst for the
Preparation of Benzylidenemalononitriles and Bisdimedones
(Tetraketones) under Green Conditions
Received 00th February 2018,
Accepted 00th March 2018
DOI: 10.1039/x0xx00000x
www.rsc.org/
Masumeh Gilanizadeh,*a and Behzad Zeynizadeha
Novel magnetic Fe3O4@SiO2@Ni-Zn-Fe layered double hydroxide (LDH) intercalated with water molecules and carbonate
anions as interlayer contents was prepared as a new heterogeneous and separable nanocatalyst. The mesoporous catalyst
was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron
microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), Brunauer-Emmett-Teller (BET), vibration sample
magnetometer (VSM), thermogravimetric analysis (TGA), differential thermal gravity (DTG) and transmission electron
microscopy (TEM). The Knoevenagel and tandem Knoevenagel-Michael reactions have been carried out between aromatic
aldehydes, malononitrile and dimedone by the magnetically reusable nanocatalyst in water as a green and eco-friendly
solvent, to afford benzylidenemalononitrile and bisdimedone derivatives (tetraketones), respectively. Reusability and
recoverability of the core-shell hydrotalcite was examined six times without considerable loss of its catalytic activity. This
magnetic LDH catalyst in the promotion of titled transformations provides high yields, mild reaction conditions,
satisfactory reaction times and high purity of the obtained products without utilizing any hazardous organic solvents.
morphology; as well the surface area is not capable to avoid
aggregation of powder samples. Recently, the combination of
magnetic nanoparticles (MNPs) and LDH as magnetite-LDH has
Introduction
In recent decades, heterogeneous catalysts are accepted as
important part of reaction in the large variety of organic
transformations.1-6 There are some of heterogeneous catalysts
to facilitate many organic reactions such as hydrotalcites,7
Zeolites,8 metal oxides,9 solid supports10 and ion-exchange
resins.11 Layered double hydroxides (LDHs) also known as
hydrotalcite-like compounds (HT) are great group of anionic
clay minerals which consist of brucite-like layers with positive
charge and interlayers with negative charge containing anions
and water molecules.12,13 The positive charge of the layers is
been developed to be applied in many processes since the
nanoparticles possess a high surface to volume ratio, which
increases their activity and selectivity. In addition, they can be
simply separated by a magnetic field at the end of reaction.20-
28
The Knoevenagel condensation is an important reaction for
development of C=C bond in organic compounds. It takes place
through the nucleophilic addition of an active methylene
group to an aldehyde followed by a dehydration reaction.29
This process is appropriate for the preparation of various
alkenes, and they can be used as intermediates for a lot of
reactions.30 In general, benzylidenemalononitrile (BMN)
derivatives are synthesized by the Knoevenagel condensation
of various aromatic aldehydes with malononitrile. BMN
derivatives have various applications in pharmaceutical and
balanced by intercalating anions such as CO32-, NO3 , SO42- and
-
Cl-. LDHs can be applied as environmentally friendly materials
in many fields such as adsorption,14 anion exchange,15
catalysis,16 precursors to magnetic materials17 and drug
carriers.18 Nowadays, hydrotalcite-like compounds has
attracted considerable attention.19 LDHs exist as naturally
occurring minerals and also synthesized by simple and
economic procedures. Furthermore, preparation of LDHs by
usual methods provides poor control over the particle size and
biological purposes. They have exhibited
a variety of
behaviours including antioxidant, anti-inflammatory,
anticonvulsant and anticancer.31,32 In this context, many
practical procedures have been reported for the synthesis of
BMN derivatives.33-50 Domino Knoevenagel-Michael reaction
was carried out through the addition of aldehydes with 1,3-
cyclic diketones.51 This multicomponent reaction between
aromatic aldehydes and dimedone has been used as
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intermediates maker for the synthesis of numerous types of
heterocyclic and spirocyclic compounds like acridine diones,
xanthene and thioxanthenes diones.52 Tetraketones are
important species of oxygen-containing compounds that have
showed biological, antibacterial, antiviral and anti-
inflammatory properties.53-56 Also several methods were
introduced for the synthesis of tetraketones because of their
significant properties.57-65 Although most of the reported
methods have practical synthetic procedures, however they
endure some disadvantages such as using expensive organic
solvents, harsh and hazardous reaction conditions, long
reaction times, unacceptable yields, costly reagents and
tedious work-up procedure. Therefore, a simple method which
utilizes mild and effective catalysts under green conditions is
still a favorite topic.
Scheme 3 Synthesis of Fe3O4@SiO2@Ni-Zn-Fe LDH
Catalyst characterization
Fourier transform infrared spectroscopy (FTIR)
The structure of catalyst was initially characterized by FTIR
spectra (Figure 1). The FTIR spectrum of nano magnetite
(Figure 1a) shows a strong peak for the vibration of the Fe-O
bonds of iron oxide at 575 cm-1. The absorption peaks at 3400
cm-1 and 1625 cm-1 are assigned to the O-H stretching and
deforming vibrations of adsorbed water, respectively. The
spectrum of Fe3O4@SiO2 nanoparticles are presented at Figure
1b. Additional peaks could be seen in this spectrum compared
to the Fe3O4. The peaks around 1094 cm−1 and 796 cm−1 are
assigned to the asymmetrical and symmetrical Si-O-Si
stretching vibrations. These results show that SiO2 is
immobilized on the surfaces of magnetite. The FTIR spectrum
of Fe3O4@SiO2@Ni-Zn-Fe LDH (Figure 1c) indicates a broad and
strong absorption band among 3600 cm-1 and 3200 cm-1,
which is related with a superposition of hydroxyl stretching
band arising from metal hydroxyl groups in the layers and
hydrogen-bonded interlayer water molecules. An additional
absorption band around 1600 cm−1 represents the water
deformation. The peak observed around 1300 cm−1 is the
In this work, we wish to develop a new type of magnetic
hydrotalcite (Fe3O4@SiO2@Ni-Zn-Fe LDH) that can be effective
for Knoevenagel and tandem Knoevenagel-Michael reactions.
Therefore, the Ni-Zn-Fe layered double hydroxide supported
Fe3O4@SiO2 nanoparticles was used as a novel and reusable
nanocatalyst
for
the
one-pot
synthesis
of
benzylidenemalononitrile and tetraketone derivatives in water
as a green solvent (Scheme 1).
CN
NC
CN
R
CN
CHO
R
Fe3O4@SiO2@Ni-Zn-Fe LDH
H2O, Reflux
O
O
R
O
OH
2-
R = H, Me, OMe, NO2, OH, Cl, CHO
asymmetric stretching of the CO3 ion. This shows that the
HO
carbonate anion presents between layers. Additionally, the
absorption peaks between 1000 cm-1 and 500 cm-1 have been
allocated to the lattice vibration modes of M-OH and M-O
vibrations.
O
Scheme 1 Green synthesis of benzylidenemalononitriles and
tetraketones by nano-Fe3O4@SiO2@Ni-Zn-Fe LDH/H2O system
Results and discussion
Synthesis and characterizations of catalyst
Fe3O4@SiO2@Ni-Zn-Fe LDH was synthesized through a three-
step procedure: i) preparation of magnetite nanoparticles by a
chemical co-precipitation of FeCl2·4H2O and FeCl3·6H2O in
aqueous ammonia, ii) covering silica on the surface of Fe3O4 by
TEOS at room temperature (Scheme 2), and iii) in situ growth
procedure with an aqueous solution of Ni2+, Zn2+ and Fe3+ salts
to prepare Ni-Zn-Fe LDH nano-shell on the surface of
Fe3O4@SiO2 (Scheme 3).
Fig. 1 FTIR spectra of (a) Fe3O4, (b) Fe3O4@SiO2, and (c)
Fe3O4@SiO2@Ni-Zn-Fe LDH
Scheme 2 Synthesis of Fe3O4@SiO2 magnetic nanoparticles
X-ray diffraction (XRD)
2 | New J. Chem., 2018, 00, 1-3
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ARTICLE
To further confirmation of crystalline structure of Fe3O4, 3b) and 17 to 36 nm (Figure 3c), respectively. The SEM
Fe3O4@SiO2 and Fe3O4@SiO2@Ni-Zn-Fe LDH, X-ray diffraction confirmed the mesoporous structure of the catalyst.
(XRD) was measured (Figure 2). Figure 2a represents the
diffraction peaks at 2θ values of 30.2°, 35.5°, 43.3°, 53.7°, 57.2°
and 62.9° correspond to (220), (311), (400), (422), (511) and
a
(440) crystal planes of nano magnetite. Fe3O4 has crystalline
cubic spinel structure which agrees with the standard Fe3O4
XRD spectrum (JCPDS No. 65-3107).68,69 The same patterns of
characteristic peaks were observed for Fe3O4@SiO2,
demonstrating that the embedded magnetite cores keep their
crystalline phase after SiO2 covering without induce a phase
change because of the existence of amorphous state. In the
case of the XRD pattern of Fe3O4@SiO2@Ni-Zn-Fe LDH, all the
peaks of magnetite are observed. The peaks at 11.2°, 23.1°,
34.4°, 36.6°, 39.1°, 42.2°, 46.6°, 48.9°, 50.1°, 60.1° and 61.2°
correspond to (003), (006), (102), (104), (105), (0011), (0012),
(109), (0013), (110) and (113) crystal planes in green rust. The
hydrotalcite has hexagonal crystal system, which is in good
agreement with the ICSD reference pattern: 00-049-0722 (iron
nickel chloride hydroxide hydrate), with sharp and symmetric
reflections for (003), (006), (110) and (113) as characteristic
planes of layered double hydroxide-like materials.70
b
c
Fig. 2 XRD patterns of (a) Fe3O4, (b) Fe3O4@SiO2 and (c)
Fe3O4@SiO2@Ni-Zn-Fe LDH
Scanning electron microscopy (SEM)
The size distribution and morphology of the synthesized
materials was examined by SEM. The SEM images of Fe3O4,
Fe3O4@SiO2 and Fe3O4@SiO2@Ni-Zn-Fe LDH are illustrated in
Figure 3. The SEM images represent that the catalyst is as
roughly spherical and granule nano particles. The size
distribution of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2@Ni-Zn-Fe
LDH ranged from 23 to 43 nm (Figure 3a), 22 to 30 nm (Figure
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Fig. 3 FE-SEM images of (a) Fe3O4, (b) Fe3O4@SiO2, and (c)
New Journal of Chemistry
double hydroxid. BET and BJH methods were used to
examining the surface area and pore size distribution of the
Fe3O4@SiO2@Ni-Zn-Fe LDH
nanocatalyst. The calculated BET specific surface area (SBET
)
Energy-dispersive x-ray spectroscopy (EDS)
was 90.716m2.g-1. The pore volume (Vp) was 0.3187cm3.g-1. It
shows a high surface to volume ratio, which increases its
activity and selectivity. The average pore size of the catalyst
was determined to be 14.054 nm using the Barrett-Joyner-
Halenda (BJH), which fits the size range of mesoporous
materials.
Electron dispersive analysis (EDS-SEM) is a practical technique
for the determination of elements exists in the material. In this
analysis, the corresponding elemental contents and the EDX
spectrums of Fe3O4 (Figure 4a), Fe3O4@SiO2 (Figure 4b) and
Fe3O4@SiO2@Ni-Zn-Fe LDH (Figure 4c) are observed. These
analyses indicated that the Fe3O4@SiO2 was synthesized by
coating silica on the magnetite and the Ni-Zn-Fe LDH has been
covered the surface of the Fe3O4@SiO2 via the in situ growth
method.
O Kα
Weight
percent
(%)
Atom
percent
(%)
3000
2500
2000
1500
1000
500
FeKα
Element
FeLα
O
33.83
66.17
64.09
35.91
Fe
FeKβ
a
a
keV
15
0
0
5
10
SiKα
4000
3500
3000
2500
2000
1500
1000
500
O Kα
FeLα
Weight
percent
(%)
Atom
percent
(%)
Fig. 5 Nitrogen adsorption-desorption isotherm of the
Element
Fe3O4@SiO2@Ni-Zn-Fe LDH
O
Si
50.94
21.35
27.71
71.70
17.12
11.17
Vibration sample magnetometer (VSM)
Figure 6 represents magnetic characterization with a vibrating
sample magnetometer. The curves appear reversible and
nonlinear; they show paramagnetic behavior of the particles.
The saturation magnetization (Ms) values of Fe3O4 (Figure 6a),
Fe3O4@SiO2 (Figure 6b) and Fe3O4@SiO2@Ni-Zn-Fe LDH (Figure
6c) were found to be 70 emu.g-1, 30 emu.g-1 and 7 emu.g-1,
respectively. In addition, the decrease of saturation
magnetization (Ms) was occured when one shell was covered
on the surface of the other.
Fe
FeKα
b
FeKβ
keV
15
0
0
5
10
Weight
percent
(%)
Atom
percent
(%)
Element
c
O Kα
2000
1500
1000
500
0
O
Si
38.91
11.71
20.91
20.28
8.19
65.83
11.29
10.14
9.35
80
FeLα
a
60
ZnLα
NiLα
Fe
Ni
Zn
40
b
c
FeKα
20
NiKα
SiKα
Applied Field (oe)
3.39
0
ZnKα
NiKβ
FeKβ
ZnKβ
-10000
-5000
0
5000
10000
keV
15
-20
-40
-60
-80
0
5
10
Fig. 4 EDS and the corresponding elemental contents of (a)
Fe3O4, (b) Fe3O4@SiO2 and (c) Fe3O4@SiO2@Ni-Zn-Fe LDH
Magnetization (emu/g)
Brunauer-Emmett-Teller (BET)
Fig. 6 Hysteresis loops of (a) Fe3O4, (b) Fe3O4@SiO2, and (c)
Figure 5 represents the Nitrogen adsorption and desorption
isotherms of the synthesized Fe3O4@SiO2@Ni-Zn-Fe layered
Fe3O4@SiO2@Ni-Zn-Fe LDH
4 | New J. Chem., 2018, 00, 1-3
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ARTICLE
Thermogravimetric analysis (TGA)
Thermogravimetric analysis (TGA) was used to explain the
thermal behavior, possible thermal stability and degradation
processes of the synthesized catalyst (Figures 7, 8). The
content of the organic moiety loaded on the surface of
magnetic nanoparticles also can be specified from the TGA
data. Figure 7a shows the TGA-thermogram of magnetite and
it is clearly referring to the high thermal stability of the Fe3O4.
Just one thermal degradation step was determined at
b
°
temperature lower than 45 C and this corresponds to the
starting mass to demonstrate a 1.71% loss. Figures 7b, 8a
illustrate the TGA and DTG thermogram of Fe3O4@SiO2 with
two thermal degradation steps. The first decomposition step
Fig. 8 TGA and DTG of (a) Fe3O4@SiO2 and (b) Fe3O4@SiO2@Ni-
Zn-Fe LDH
°
was recognized at a temperature range of 30-158 C and this
Transmission electron microscopy (TEM)
corresponds to a loss of 2.18% from the starting Fe3O4@SiO2
and it is attributed to the adsorbed solvent or water. The
weight loss in the second degradation step of this material
The transmission electron microscope (TEM) images show that
the Fe3O4@SiO2@Ni-Zn-Fe LDH has the core-shell magnetic
layered double hydroxide structure. The TEM images of
Fe3O4@SiO2@Ni-Zn-Fe LDH are illustrated in Figure 9.
°
corresponds to 3.28% at a temperature range of 474-616 C.
The sum of these two degradation steps gives a straight
evidence for the loading of SiO2 on the surface of nano
magnetite. Figures 7c, 8b characterize the TGA and DTG
thermogram of Fe3O4@SiO2@Ni-Zn-Fe LDH with two thermal
degradation steps. The first weight loss was identified at a
°
temperature range of 117-194 C (6.12%), corresponding to
the elimination of water from the interlayer and surface area.
The second weight loss was at a temperature range of 194-387
°C (15.35%), which includes the de-hydroxylation of layers and
2-
.
the loss of interlayer CO3
Fig. 7 TGA patterns of (a) Fe3O4, (b) Fe3O4@SiO2 and (c)
Fe3O4@SiO2@Ni-Zn-Fe LDH
a
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benzylidenemalononitrile derivatives in water as a green
solvent.
For further investigation, the tandem Knoevenagel-Michael
condensation was examined. In order to optimize the reaction
conditions, reaction of benzaldehyde and dimedone was
studied as a model reaction (Table 3). As can be seen from
Table 3, the reaction did not progress in the absence of
catalyst and a number of solvents were tested to obtain the
best conditions. The observations revealed that the reaction of
benzaldehyde (0.5 mmol) with dimedone (1 mmol), using 20
mg of nanocatalyst in refluxing water gave the best result.
The condensation was investigated using diverse aromatic
aldehydes containing electron-withdrawing and electron-
donating groups; the expected products were produced in
good to high yields. The outcome of this study is summarized
in Table 4. The reactions of terephthalaldehyde and
isophthalaldehyde were examined by two various amounts of
dimedone (Table 4, entries 13-16), the bis-dimedone
derivatives were produced by 1 mmol of dimedone and the
tetra-dimedone derivatives were obtained by 2 mmol of
dimedone. Accordingly, this method can be valuable for the
synthesis of tetraketones in water as an eco-friendly solvent.
The suitability of this method was shown by comparison of the
modal reactions by Fe3O4@SiO2@Ni-Zn-Fe LDH with a number
of reported reagents (Table 5). The present research
represents advantages of reusability combined with
satisfactory yields and reaction times.
A possible mechanism for the Fe3O4@SiO2@Ni-Zn-Fe LDH-
catalyzed reactions are shown in Scheme 4. As can be seen,
catalyst makes active the aldehyde and then the nucleophilic
attacks of activated methylene group in malononitrile can take
place as the Knoevenagel condensation. Accordingly, the C-C
bond formation and dehydration are occurred. Also, activated
β-dicarbonyl attacks the catalyst-activated aldehyde and then
elimination of water happens by the Knoevenagel reaction. For
the second time, the Michael addition of dimedone to the α,β-
unsaturated carbonyl compound be occurred and tetraketones
can be produced.
Fig. 9 TEM images of Fe3O4@SiO2@Ni-Zn-Fe LDH
Synthesis of benzylidenemalononitrile and tetraketone derivatives
We investigated catalytic activity of Fe3O4@SiO2@Ni-Zn-Fe
LDH as a heterogeneous mesoporous catalyst for the
Knoevenagel and tandem Knoevenagel-Michael reactions by
condensation of aromatic aldehyde with malononitrile and
dimedone in water as a green solvent. In order to optimize the
reaction conditions, the Knoevenagel condensation of
benzaldehyde and malononitrile was examined as a model
reaction (Table 1). In this condensation, the presence of
catalyst is necessary and the reaction did not proceed in the
absence of catalyst. The observations revealed that the
reaction of benzaldehyde (1 mmol) with malononitrile (1.1
mmol), using 20 mg of nanocatalyst in refluxing water was
obtained the greatest consequence.
O
OH
Ar
Fe3O4@SiO2@Ni-Zn-Fe LDH
O
HO
O
Ar
H
CN
CN
H2O
Ar
H
H
Fe3O4@SiO2@Ni-Zn-Fe LDH
NC
CN
H
Fe3O4@SiO2@Ni-Zn-Fe LDH
H
O
O
OH
O
H
CN
Ar
Ar
H
O
O
Ar
H
CN
Encouraged by the observations, the condensation was
studied using various aromatic aldehydes and in all cases, the
products were obtained in good to high yields. The results of
this examination are summarized in Table 2. The reactions of
terephthalaldehyde and isophthalaldehyde with two
substituted formyl groups were reacted by higher amount of
malononitrile (2.2 mmol) and the bis-substituted derivatives
were produced (Table 2, entries 12 and 13). Consequently, this
process can be helpful for the synthesis of
HO
O
Fe3O4@SiO2@Ni-Zn-Fe LDH
OH
O
Fe3O4@SiO2@Ni-Zn-Fe LDH
Ar
H
O
O
O
H
Ar
H
H2O
O
O
Scheme 4 Possible mechanism for the formation of
benzylidenemalononitrile and bisdimedone derivatives in the
presence of Fe3O4@SiO2@Ni-Zn-Fe LDH
6 | New J. Chem., 2018, 00, 1-3
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ARTICLE
Table 1. Determination of reaction conditions for the Knoevenagel reaction of benzaldehyde and malononitrile
by nano Fe3O4@SiO2@Ni-Zn-Fe LDHa
CN
CN
CHO
Fe3O4@SiO2@Ni-Zn-Fe LDH
NC
CN
+
Fe3O4@SiO2@Ni-Zn-Fe
LDH (g)
Time
(min)
Entry
Solvent
Condition
Conversion (%)
1
2
3
4
5
6
7
8
9
-
-
Solvent-free
H2O
EtOH
MeOH
THF
80 °C
Reflux
90
60
40
60
40
20
60
4
Trace
Trace
85
30
Trace
80
20
100
95
0.02
0.02
0.02
0.02
0.02
0.02
0.01
60-70 °C
60-70 °C
60-70 °C
60-70 °C
RT
H2O
H2O
H2O
H2O
Reflux
Reflux
40
aAll reactions were carried out with 1 mmol of benzaldehyde and 1.1 mmol of malononitrile in 2 mL of solvent.
Table 2. The Knoevenagel reaction of aldehydes and malononitrile by nano Fe3O4@SiO2@Ni-Zn-Fe LDH/H2O systema
Mp (°C)
Reported [Ref.]
Time
(min)
Yield
(%)b
Entry
1
Substrate
Product
Found
81-83
CHO
CN
CN
4
3
91
90
82-84 [34]
CHO
CN
2
3
137-139
113-115
137-138 [38]
CN
Me
Me
CHO
CN
15
97
112-114 [37]
CN
MeO
MeO
OMe
OMe
CHO
CN
4
5
6
5
1
3
90
93
89
77-79
160-162
89-91
80 [38]
CN
CN
CN
CHO
161-162 [48]
93-94 [48]
Cl
Cl
Cl
Cl
CN
CN
CHO
CN
CHO
CHO
7
8
15
10
93
96
155-157
102-104
157-160 [37]
103-105 [48]
CN
CN
O2N
O2N
O2N
O2N
CN
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New Journal of Chemistry
O2N
Cl
CN
O2N
Cl
CHO
9
70
3
96
91
137-139
141-143
-
CN
Cl
Cl
CHO
CHO
CN
CN
10
-
Cl
Cl
MeO
CN
CN
MeO
11
12
70
3
98
90
135-137
260-262
134-136 [41]
295-297 [33]
HO
HO
CN
CHO
CHO
CN
CN
CN
NC
NC
OHC
OHC
CN
13
5
96
175-177
-
CN
aAll reactions were carried out with aromatic aldehyde (1 mmol), malononitrile (1.1 mmol), Fe3O4@SiO2@ Ni-Zn-Fe LDH (20 mg) and
H2O (2 mL) under reflux conditions. In entries (12 and 13): 2.2 mmol of malononitrile was used. bYields refer to isolated pure products.
Table 3. Optimization experiments for synthesis of tetraketones by nano Fe3O4@SiO2@Ni-Zn-Fe LDH under different conditionsa
O
OH
O
O
CHO
Fe3O4@SiO2@Ni-Zn-Fe LDH
+
HO
O
Fe3O4@SiO2@Ni-Zn-Fe
LDH (g)
Time
(min)
Entry
Solvent
Condition
Conversion (%)
1
2
3
4
5
6
7
8
9
-
Solvent-free
Solvent-free
Solvent-free
EtOH/H2O
EtOH
MeOH
THF
H2O
70-80 °C
70-80 °C
RT
70-80 °C
60-70 °C
60-70 °C
60-70 °C
70-80 °C
Reflux
100
60
60
60
60
60
60
30
9
Trace
80
70
70
60
50
60
60
100
95
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.01
0.03
H2O
H2O
H2O
10
11
Reflux
Reflux
30
7
100
aAll reactions were carried out with 1 mmol of dimedone and 0.5 mmol of benzaldehyde in 3 mL of solvent.
Table 4. Synthesis of tetraketones by nano Fe3O4@SiO2@Ni-Zn-Fe LDH/H2O systema
Mp (°C)
Reported [Ref.]
Time
(min)
Yield
(%)b
Entry
Substrate
Product
Found
8 | New J. Chem., 2018, 00, 1-3
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ARTICLE
CHO
O
OH
1
9
93
180-182
185 [60]
HO
Me
O
CHO
O
OH
2
10
96
134-136
132 [63]
Me
HO
O
OMe
CHO
O
O
OH
OH
3
4
5
6
7
15
40
5
90
93
93
96
93
143-145
180-182
137-139
195-197
186-188
146-148 [58]
184-186 [64]
138-141 [60]
199-200 [64]
188-190 [64]
MeO
HO
O
O
CHO
OMe
OMe
HO
Cl
CHO
O
O
OH
OH
Cl
HO
HO
O
O
CHO
Cl
Cl
5
NO2
CHO
O
OH
15
O2N
HO
O
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NO2
CHO
O
OH
OH
OH
OH
OH
OH
8
15
91
95
196-198
197-199 [59]
NO2
HO
Cl
O
O
O
O
O
O
NO2
O
CHO
9
10
149-151
173-175
92-94
-
Cl
NO2
HO
Cl
CHO
Cl
O
10
11
12
13
3
90
95
89
91
-
-
-
-
Cl
Cl
HO
OMe
OH
O
CHO
50
40
2
MeO
OH
HO
OH
OMe
O
CHO
187-189
HO
OMe
HO
CHO
CHO
O
177-179
OHC
HO
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ARTICLE
O
OH
CHO
OH
O
O
14
5
90
239-241
225 [60]
OHC
OH
HO
HO
O
CHO
O
CHO
OH
15
40
93
187-189
-
CHO
O
O
OH
O
CHO
16
40
91
184-186
-
HO
O
OH
CHO
HO
O
a All reactions were carried out with dimedone (1 mmol), aromatic aldehyde (0.5 mmol), Fe3O4@SiO2@ Ni-Zn-Fe LDH (20 mg) and
H2O (3 mL) unde reflux conditions. In entries (14 and 16): 2 mmol of dimedone was used.
bYields refer to isolated pure products.
Table 5. Comparison of the Fe3O4@SiO2@Ni-Zn-Fe LDH-catalyzed reactions and existing literature reports
CN
CN
CHO
Catalyst
NC
CN
+
Time
(min)
Yield
(%)
Reusability
(times)
Entry Catalyst
Condition/Solvent
Ref.
1
2
3
4
5
6
7
Fe3O4@SiO2@Ni-Zn-Fe LDH (20 mg)
Taurine (25 mg)
Reflux/H2O
Reflux/H2O
RT/H2O
4
14
120
90
80
1
91
86
6
6
-
[33]
[37]
[36]
[39]
[44]
[46]
CSC-Star-Glu-IL2 (200 mg)
PANTTF (81 mg)
94
5
20˚C/H2O
RT/Solvent-free
RT/H2O
99
21
-
ZnO (100 mg)
92
[C4dabco][BF4] (19 mg)
MP(DNP) (14 mg)
100
96
7
RT/EtOH
3
5
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New Journal of Chemistry
O
OH
O
O
CHO
Catalyst
+
HO
O
Time
(min)
Yield
(%)
Reusability
Ref.
Entry Catalyst
Condition/Solvent
(times)
1
Fe3O4@SiO2@Ni-Zn-Fe LDH (20 mg)
Taurine (30 mg)
Reflux/H2O
Reflux/H2O
RT/H2O
9
93
95
91
97
92
88
98
6
6
-
-
2
3
4
5
6
7
10
[33]
[58]
[59]
[60]
[61]
[64]
SmCl3 (25 mg)
20
Fe3O4@SiO2-SO3H (10 mg)
choline chloride-urea (1 mL)
EDDA (54 mg)
RT/H2O
80
5
-
20˚C
240
240
105
Reflux/THF
Reflux/EtOH
-
Fe/NaY (2.5 mg)
5
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ARTICLE
Recycling of Fe3O4@SiO2@Ni-Zn-Fe LDH
The reusability of Fe3O4@SiO2@Ni-Zn-Fe LDH was examined
for Knoevenagel and tandem Knoevenagel-Michael reactions
by modal reactions. Recoverability of catalyst was studied by
reactions of benzaldehyde with malononitrile and dimedone
under optimized conditions. After completion of the
condensations, the catalyst was separated by a permanent
magnetic field, washed with Et2O, dried and reused for six
consecutive runs without considerable loss of activity (Figure
10).
Fig. 12 XRD pattern of recovered Fe3O4@SiO2@Ni-Zn-Fe LDH
Benzylidenemalononitrile %
Tetraketone %
93
91
after 2nd run
93
91
91
89
87
87
89
89
87
87
6
5
4
3
2
1
Fig. 10 Reusability of Fe3O4@SiO2@Ni-Zn-Fe LDH in the model
reactions
For further investigation, the FTIR spectrum (Figure 11), XRD
spectrum (Figure 12), SEM image (Figure 13) and TEM images
(Figure 14) of the recycled catalyst were examined after 2nd
run. A review of the analysis showed that the recovered nano
magnetic LDH has not changed after the second run and its
structure is almost constant.
Fig. 13 FE-SEM image of recovered Fe3O4@SiO2@Ni-Zn-Fe LDH
after 2nd run
Fig. 11 FTIR spectrum of recovered Fe3O4@SiO2@Ni-Zn-Fe LDH
after 2nd run
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New Journal of Chemistry
was determined by EDS done in SEM. The N2 adsorption-
desorption isotherms was tested on Belsorp-mini, BET Japan.
The specific surface area of sample was measured by the
Brunauer-Emmett-Teller (BET) technique. The pore volume
and pore size distribution were resulted from the desorption
profiles of the isotherms using the Barrett-Joyner-Halanda
(BJH) method. Magnetic properties of the samples were
obtained by a vibration sample magnetometer (VSM, model
MDKFT) under magnetic fields. Thermo gravimetric analyses
(TGA) were conducted on STA of Rheometric Scientific Inc.
Transmission electron microscope (TEM) images were
obtained using an accelerating voltage of 100 kV on a Zeiss-
EM10C Transmission Electron Microscope.
Fig. 14 TEM images of recovered Fe3O4@SiO2@Ni-Zn-Fe LDH
after 2nd run
Preparation of magnetic Fe3O4 NPs
Fe3O4 nanoparticles were prepared by chemical co-
precipitation of chloride salts of Fe3+ and Fe2+.66 Generally,
FeCl3·6H2O (5.838 g, 0.0216 mol) and FeCl2·4H2O (2.147 g,
0.0108 mol) were dissolved in 100 mL of distilled water. The
solution was stirred at 85˚C under N2 atmosphere for 10 min.
Next, aqueous ammonia (25 wt%, 10 mL) was added to the
prepared solution and a black precipitate was instantly
formed. The resulting mixture was heated for 30 min at 85˚C
with stirring under N2 atmosphere followed by cooling to the
room temperature. The nanoparticles were magnetically
separated from the reaction mixture and washed doubly with
distilled water and solution of NaCl (0.02 M).
Conclusions
In summary, we have developed a novel, efficient and green
method for synthesis of benzylidenemalononitrile and
tetraketone derivatives in water by mesoporous magnetic
Fe3O4@SiO2@Ni-Zn-Fe LDH which is confirmed with FTIR, XRD,
SEM, EDS, BET, VSM, TGA, DTG and TEM. The nanocatalyst was
synthesized by the three-step process. In the first step, Fe3O4
nanoparticles were prepared. The magnetite core can give
magnetic feature to the catalyst and it can be easily separated
at the end of reaction. In the second step, the Fe3O4 core was
covered by SiO2 to increase the surface area and be an
efficient layer for loading hydrotalcite. In the third step, Ni-Zn-
Fe layered double hydroxide as a nano-shell was prepared on
the surface of Fe3O4@SiO2 and the green catalyst was
synthesized. This procedure has several advantages such as
mild reaction conditions, high yield, short reaction time, simple
workup process, easy separation and reusability of the
magnetic nanocatalyst. The catalyst can be used at least six
times without considerable decrease in activity. Therefore, the
Fe3O4@SiO2@Ni-Zn-Fe LDH can make this procedure a useful
addition to the available synthetically methods.
Preparation of Fe3O4@SiO2 NPs
Magnetite core was covered by silica according to the reported
process.67 Fe3O4 (1.5 g) was dissolved in 20 mL of distilled
water; magnetite suspension was added to 2-propanol (200
mL) and homogenized by ultrasonic (30 min). Under
continuous stirring, PEG (5.36 g), distilled water (20 mL),
aqueous ammonia (28 wt%, 10 ml) and TEOS (2 mL) were
added into the suspension, respectively. The mixture was
reacted for 28 h under stirring at room temperature. After
completion of the reaction, the product was collected by an
external magnetic field and washed two times with ethanol
and distilled water.
Experimental
Preparation of Fe3O4@SiO2@Ni-Zn-Fe LDH
Material and physical measurements
The Fe3O4@SiO2 NPs were covered with Ni-Zn-Fe LDH by in situ
growth of the metal cations. Typically, Fe3O4@SiO2 (0.25 g),
Na2CO3 (1.060 g, 0.01 mol) and NaOH (0.160 g, 0.004 mol)
were dissolved in 30 mL of distilled water. Another solution of
FeCl3·6H2O (1.352 g, 0.005 mol), Ni(NO3)2·6H2O (2.617 g, 0.009
mol) and Zn(NO3)2·6H2O (1.785 g, 0.006 mol) was prepared in
distilled water (30 mL). These two solutions were sonicated for
30 min and they were added drop-wise to 30 mL of distilled
water with continuous stirring. During the reaction process, its
pH was kept at 11 by addition of appropriate amounts of
NaOH and HCl solutions. The resulting slurry was stirred at
room temperature for additional 30 min and then it was aged
for 20 h at 80˚C. Next, the acquired sample was cooled to
room temperature and filtered. Afterward, the product was
All the chemicals were purchased from Merck Chemical
1
Companies and were used without further purification. H, 13C
NMR and FT-IR spectra were acquired by Bruker Avance
spectrometers (300 MHz) and Thermo Nicolet Nexus 670,
respectively. Melting points were taken in open capillary tubes
with a melting point apparatus (Electrothermal) and were
uncorrected. Thin layer chromatography (TLC) was used for
the purity determination of the substrates, products and
reaction monitoring over silica gel 60 F254 aluminum sheet. X-
ray diffraction (XRD) measurements were made with a
X'PertPro. The X-ray wavelength was 1.54 A˚ and the
diffraction patterns were recorded in the 2θ range (5-80˚). The
particle morphology was examined by measuring SEM using
FESEM-TESCAN. The chemical composition of the nanocatalyst
14 | New J. Chem., 2018, 00, 1-3
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ARTICLE
9
M. B. Gawande, R. K. Pandey and R. V. Jayaram, Catal.
Sci. Technol., 2012, , 1113.
dried at 150˚C and the mesoporous Fe3O4@SiO2@Ni-Zn-Fe
LDH was obtained.
2
10 K. Smith, Solid supports and catalysts in organic
synthesis, Ellis Horwood, New York, 1992.
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692.
General procedure for the Knoevenagel condensation of
benzaldehyde and malononitrile
In a round-bottom flask (10 mL) equipped with a magnetic
stirrer,
a mixture of benzaldehyde (0.106g, 1 mmol),
,
,
malononitrile (0.072 g, 1.1 mmol) and H2O (2 mL) was well
mixed at room temperature. Fe3O4@SiO2@Ni-Zn-Fe LDH (20
mg) was then added and the resulting mixture was stirred for 4
min at reflux temperature. TLC monitored the progress of the
reaction (eluent, n-hexane/ethyl acetate: 4/2). After
completion of the reaction, the catalyst was separated by an
external magnet and the reaction mixture was extracted with
,
19 G. R. Williams and D. O. Hare, J. Mater. Chem., 2006,
16, 3065.
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EtOAc (2
×5 mL). The organic layer was dried over anhydrous
Na2SO4 and followed by evaporation of the solvent to give the
pure product in 91% yield (Table 2, entry 1).
21 V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara
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Chem. Soc., 2006, 128, 5279.
General procedure for the tandem Knoevenagel-Michael reaction
of benzaldehyde and dimedone
A mixture containing benzaldehyde (0.053 g, 0.5 mmol) and
dimedone (0.140 g, 1 mmol) in water (3 ml) was well mixed at
room temperature. Fe3O4@SiO2@Ni-Zn-Fe LDH (20 mg) was
then added and the reaction mixture was stirred for 9 min at
reflux temperature. After completion of the reaction
(monitored by TLC, n-hexane/ethyl acetate: 4/2), the mixture
was cooled to room temperature. Then, EtOAc (5 mL) was
added to the reaction mixture followed by stirring for 10 min.
In order to separate the magnetic nano catalyst, an external
magnet was used. The product was extracted and the organic
layer was dried over anhydrous Na2SO4. Finally, evaporation of
the solvent gave the pure product in 93% yield (Table 4, entry
1).
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28 S. M. Baghbanian and M. Farhang, Syn. Commun.,
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29 L. F. Tietze and U. Beifuss, Comprehensive Organic
Synthesis, Oxford, UK, 1991, ch. 1, pp. 341-394.
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Conflicts of interest
There are no conflicts to declare.
35 J. Zhang, T. Jiang, B. Han, A. Zhu and X. Ma, Synth.
Commun., 2006, 36, 3305.
Acknowledgments
36 G. Li, J. Xiao and W. Zhang, Green Chem., 2012, 14
2234.
,
The authors gratefully acknowledged the financial support of
this work by the research council of Urmia University.
37 P. Gupta, M. Kour, S. Paul and J. H. Clark, RSC Adv.,
2014, , 7461.
4
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New Journal of Chemistry
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Synthesis and characterization of the immobilized Ni-Zn-Fe layered double hydroxide
(LDH) on silica coated magnetite as a mesoporous and magnetically reusable catalyst for
the preparation of benzylidenemalononitriles and bisdimedones (tetraketones) under
green conditions
Masumeh Gilanizadeh* and Behzad Zeynizadeh
Faculty of Chemistry, Urmia University, Urmia 5756151818, Iran
E-mail: masumehgilanizadeh@gmail.com
New Journal of Chemistry
Magnetically Fe3O4@SiO2@Ni-Zn-Fe LDH was prepared as an efficient nanocatalyst for the
Knoevenagel and tandem Knoevenagel-Michael reactions to afford products in water.
1