Organic base grafted on magnetic nanoparticles as a recoverable catalyst for the green synthesis of hydropyridine rings

Article abstract of DOI:10.1007/s13738-019-01788-y

Synthesis of 4-aminiquinaldine grafted on silica-coated nano-Fe₃O₄ particles (MNPs-AQ) and their performance as a retrievable heterogeneous basic catalyst are disclosed. The catalytic performance of this novel material was studied fo

Full text of DOI:10.1007/s13738-019-01788-y

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-019-01788-y
ORIGINAL PAPER
Organic base grafted on magnetic nanoparticles as a recoverable
catalyst for the green synthesis of hydropyridine rings
Mohammad Ali Bodaghifard1,2
Received: 9 August 2018 / Accepted: 24 September 2019
© Iranian Chemical Society 2019
Abstract
Synthesis of 4-aminiquinaldine grafted on silica-coated nano-Fe3O4 particles (MNPs-AQ) and their performance as a retriev-
able heterogeneous basic catalyst are disclosed. The catalytic performance of this novel material was studied for the green
synthesis of substituted 1,4-dihydropyridine and polyhydroquinoline derivatives via one-pot multicomponent reactions.
Eco-friendly method, high yield and purity of the desired products, and short reaction time along with the ease of the work-
up procedure outline the advantages of these new methodologies over the earlier ones. The surface and magnetic properties
of the core/shell hybrid nanoparticles were characterized via TEM, SEM, XRD, EDS, and FT-IR analysis techniques. This
nanocatalyst is recyclable without any deterioration in its catalytic activity.
Keywords 1,4-Dihydropyridines · Polyhydroquinoline · Green chemistry · Hybrid nanoparticles
Introduction
[9]. In recent years, several modifed synthesis methods to
access 1,4-DHPs have been developed [10] like FeF3 [11],
organocatalysts [12], microwave assisted [13], cellulose sul-
furic acid [14], nano-ZnO [15], CAN [16], I2 [17, 18], metal
trifates [19], heteropolyacid catalyst [20], ionic liquids [21,
22], 3,4,5-trifuorobenzeneboronic acid [23], iodotrimethyl-
silane (TMSI) generated in situ in CH3CN [24], thiamine
hydrochloride [25], bismuth nitrate [26], triphenylphosphine
[27], and sulfated polyborate [28]. Although some reactions
are satisfactory in terms of yield, the use of high tempera-
tures, expensive metal precursors, catalysts that are harmful
to the environment, and long reaction times are some draw-
backs of these methods.
1,4-Dihydropyridines (1,4-DHPs) are valuable heterocyclic
compounds in view of pharmaceuticals and drugs devel-
opment [1, 2]. 1,4-DHPs possess a wide range of biologi-
cal activities such as anti-atherosclerotic [3], vasodilator
[4], anti-diabetic [5], geroprotective and hepatoprotective
[6], and group of calcium modulators for the treatment
of cardiovascular diseases [7]. Realizing the importance
of 1,4-dihydropyridine derivatives, increasing interest by
1,4-DHPs as synthetic targets is ongoing. Hantzsch reac-
tion is commonly used for the preparation of 1,4-DHPs [8].
This method involves cyclocondensation of an aldehyde,
1,3-dicarbonyl compounds or CH-acids, and ammonia (or
primary amine) either in acetic acid or in refuxing ethanol
for long reaction times which typically leads to low yields
Organic–inorganic hybrid materials are of great interest
as heterogeneous catalysts in organic synthesis, due to the
functional diversity merged with thermal and mechanical
stability of inorganic solids [29–31]. Their large surface area
per unit volume makes them interesting in the heterogene-
ous catalysis area; Heterogeneous catalysis in the nano-scale
takes advantage of a high exposure of the active species
leading to a higher efciency of the catalyst [32, 33]. Nev-
ertheless, the application of heterogeneous nano-catalysts
is usually limited by the inevitable loss of catalyst during
the tedious separation processes, i.e., fltration or centrifu-
gation. In this vein, easily separable magnetic nanoparti-
cles (MNPs), e.g., Fe3O4, have demonstrated high stability,
easy synthesis, and functionalization alongside with high
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s13738-019-01788-y) contains
supplementary material, which is available to authorized users.
* Mohammad Ali Bodaghifard
mbodaghi2007@yahoo.com; m-bodaghifard@araku.ac.ir
1
Department of Chemistry, Faculty of Science, Arak
University, Arak 38156-88138, Iran
2
Institute of Nanosciences and Nanotechnology, Arak
University, Arak, Iran
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
surface area, low toxicity, and cost. These superb properties
set magnetic nanoparticles as a target for extensive investiga-
tion as inorganic supports in the synthesis of semi-hetero-
geneous catalysts [34–38]. These metallic nanoparticles can
be coated with silica shell to introduce numerous surface
Si–OH groups for further modifcation and higher chemical
and colloidal stability since the magnetically agglomeration
will be diminished [29–31, 39, 40].
as shown in Scheme 2. Magnetite (Fe3O4) nanoparticles
were prepared easily via the chemical co-precipitation of
Fe2+ and Fe3+ ions in basic solution [29–31, 44]. These
were subsequently coated with silica layer (Fe3O4@SiO2)
through the well-known Stober method [45]. The Fe3O4@
SiO2 core–shell structures were treated with 3-chloropro-
pyltrimethoxysilane (CPTMS), which can bind covalently
to the free-OH groups at the particles surface and aforded
the Fe3O4@SiO2-PrCl. 4-aminoquinaldine grafted on silica-
coated magnetite nanoparticles (MNPs-AQ) prepared with
the reaction of the 3-chloropropyl-functionalized silica-
coated magnetic nanoparticles (Fe3O4@SiO2-PrCl) and
4-aminoquinaldine.
As part of our continuous efort to develop efcient het-
erogeneous magnetic nano-catalysts and green organic reac-
tions [29–31, 41–43], and for the above reasons, herein we
describe the synthesis and characterization of 4-aminoqui-
naldine-grafted magnetite nanoparticles (MNPs-AQ) to give
access to biologically interesting 1,4-dihydropyridines as a
new eco-friendly method (Scheme 1). This newly design cat-
alyst fulflled our endeavor toward a heterogeneous system
with a green synthetic aspects by avoiding the use of hazard-
ous conditions for accessing target heterocyclic compounds.
The FT-IR spectrum of Fe3O4, Fe3O4@SiO2, Fe3O4@
SiO2-PrCl, and Fe3O4@SiO2-AQ nanoparticles in the
wavenumber range of 4000–400 cm−1 is shown in Fig. 1.
The magnetic Fe3O4 nanoparticles’ FT-IR spectra (Fig. 1a)
showed the characteristic Fe–O absorption near 578 cm−1.
FT-IR spectrum of Fe3O4@SiO2 displays bands at about
1087 (asymmetric stretching), 955 (symmetric stretching),
781 (in plane bending), and 461 cm−1 (rocking mode) of the
Si–O–Si group and confrm the formation of SiO2 shell. The
broad peaks in the range 3200–3500 cm−1 (Si–OH stretching
vibration mode) and the weak peak at 1639 cm−1 (twisting
vibration mode of H–O–H adsorbed in the silica shell) are
obvious in the spectrum. The weak aliphatic vibrations at
Results and discussion
Preparation and characterization of the catalyst
The magnetic nanoparticle supported 4-aminoquinaldine
catalyst (MNPs-AQ) was prepared via sequential reactions
Scheme 1 Synthesis of
1,4-dihydropyridine deriva-
tives using novel MNPs-AQ as
catalyst
O
O
Ar
O
4
EtO2C
O
+
O
N
H
OEt
O
6a-n
14 example
2
Reflux
Ar
H
EtOH/H2O
Ar
1
NH4OAc
EtO2C
CN
3
5
N
N
N
H
NH2
7a-o
16 example
H
N
O
O
Si
SiO2
Fe3O4
N
O
CH3
(MNPs-AQ)
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Journal of the Iranian Chemical Society
Cl
NH2
N
Fe2+
NH3
SiO2
Si
O
O
CPTMS
H3C
TEOS
Fe3O4
O
+
Fe3O4
SiO2
EtOH/H2O
H2O
Tuluene
Fe3+
NEt3
Tuluene
Reflux
r.t.
)))
80 °C
Fe3O4
Re
flu
x
O
O
O
SiO2
Si
N
H
N
Fe3O4
CH3
Scheme 2 Preparation of 4-aminoquinaldine grafted on silica-coated nano-Fe3O4 particles
Fig. 1 Comparative FT-IR spectra for (a) Fe3O4, (b) Fe3O4@SiO2, (c)
Fe3O4@SiO2-PrCl, (d) Fe3O4@SiO2-AQ
Fig. 2 The FE-SEM images of MNPs–AQ nanoparticles
2933 and 2940 cm−1 (Fig. 1c, d) are related to C–H symmet-
ric and asymmetric stretching and confrmed the presence of
the attached alkyl groups. The peaks correspond to C=N and
C=C in heterocyclic rings are appeared at 1400–1600 cm−1
(Fig. 1d). N–H bending appeared at 1647 cm−1 (Fig. 1d)
[46]. Therefore, the above results prove that the functional
groups were successfully grafted onto the surface of the
magnetic Fe3O4@SiO2 nanoparticles.
The nanoparticle size and morphology of MNPs-AQ
catalyst were surveyed by feld emission scanning electron
microscopy (FE-SEM) (Fig. 2). As can be seen from Fig. 2,
MNPs-AQ particles have a mean diameter of 25–35 nm and
a nearly spherical shape.
The energy dispersive X-ray spectroscopy (EDS) results,
obtained from SEM analysis of MNPs-AQ, are shown in
Fig. 3, and clearly show the presence of Si, O, N, and Fe
signals in MNPs-AQ, and the higher intensity of the Si peak
Fig. 3 The EDS spectrum of MNPs-AQ nanoparticles
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Journal of the Iranian Chemical Society
compared with the Fe peaks indicates that the Fe3O4 nano-
particles were trapped by SiO2 layer. According to the above
analysis, it can be concluded that the MNPs-AQ have been
successfully synthesized.
The presence and degree of crystallinity of magnetic
Fe3O4 and the MNPs-AQ catalyst was considered from XRD
measurements (Fig. 4). The same peaks were observed in
the both of the magnetic Fe3O4 and MNPs-AQ XRD pat-
terns, indicating retention of the crystalline spinel ferrite
core structure during the silica-coating and functionalization
processes. The XRD data of the synthesized magnetic nano-
particles show difraction peaks at 2θ=30.4°,35.8°, 43.3°,
53.9°, 57.3°, 63°, and 74.5° which can be assigned to the
(220), (311), (400), (422), (511), (440), and (533) planes of
Fe3O4, respectively, indicating that the Fe3O4 particles in the
nanoparticles were pure Fe3O4 with a cubic spinel structure;
these matches well with the standard Fe3O4 sample (JCPDS
Card No. 85-1436). The broad peak from 2θ= 20° to 27°
(Fig. 5b) is consistent with an amorphous silica phase in the
shell of the silica-coated Fe3O4 nanoparticles (Fe3O4@SiO2)
[47]. The (311) XRD peak was used to estimate the average
crystallite size of the magnetic nanoparticles by Scherrer’s
equation (D=0.9λ/β cos θ), where D is the average crystal-
line size, λ is the X-ray wavelength (0.154 nm), β denotes
the full width in radians subtended by the half maximum
intensity width of the (311) powder peak, and θ corresponds
to the Bragg angle of the (311) peak in degrees [48]. From
the width of the peak at 2θ=35.7 (311), the crystallite size
of the magnetic nanoparticle is calculated to be 20.1 nm
using Scherrer’s equation, which is in near range of the size
determined by FE-SEM analysis (Fig. 2).
Fig. 5 TG-DTG analyses for MNPs-AQ nanoparticles
physically adsorbed solvent and surface hydroxyl groups, the
second stage at about 250 °C to nearly 620 °C is attributed
to the decomposition of the organic moiety in the nanocom-
posite. Therefore, the weight loss between 250 and 620 °C
gives the organic grafting ratios of the magnetic catalyst.
The grafted organic moiety on the magnetic Fe3O4@SiO2
nanoparticles was approximately 22 wt%. In accordance
with this mass loss, it was calculated that 0.8 mmol of 4-AQ
was loaded on 1 g of MNPs-AQ catalyst and are accessible
for catalytic reaction processes. Therefore, the MNPs-AQ is
stable around or below 250 °C.
The magnetic properties of nanoparticles were measured
by VSM (magnetic vibration measurement). Figure 6 illus-
trates the magnetic nanoparticle curve at the room tempera-
ture, which contains the magnetization (M) against magnetic
feld (H) (hysteresis loops) of Fe3O4, MNPs-AQ. The hyster-
esis curve provides important information about magnetic
properties such as the saturation magnetization (Ms), rema-
nent magnetization (Mr), and coercivity (Hc). It is obvious
that by increasing the magnetic feld, the magnetization
increases rapidly and it fxed in the 10,000 Os feld and the
sample is saturated completely. As shown in the Fig. 6, the
Ms of MNPs-AQ is altered from 64 to 42 emu g−1 because
the silica shell is formed around the Fe3O4. The hysteresis
The stability of the MNPs-AQ catalyst was determined
by thermogravimetric analysis (TGA) and derivative ther-
mogravimetry (DTG) (Fig. 5). The magnetic catalyst shows
two-step weight loss steps over the temperature range of TG
analysis (Fig. 6). The frst stage, including a low amount
of weight loss (2%) at T<250 °C, is due to the removal of
Fig. 4 XRD difraction pattern of Fe3O4 MNPs (a), and MNPs-AQ
(b)
Fig. 6 Magnetic hysteresis loops of a Fe3O4 MNPs and b MNPs-AQ
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Journal of the Iranian Chemical Society
curve indicates the super paramagnetic properties for Fe3O4,
MNPs-AQ which the Mr and Hc are near the zero [48, 49].
After the characterization of the MNPs-AQ hybrid nano-
material, its catalytic activity was evaluated for the synthesis
of 1,4-dihydropyridine derivatives (Scheme 1). An impor-
tant feature of these nano-catalysts is simple separation of
them using an external magnet, thereby removing the neces-
sity for fltration or centrifugation. In order to optimize the
reaction conditions and obtain the best catalytic activity, the
reaction of benzaldehyde (1 mmol), malononitrile, ethylace-
toacetate, and ammonium acetate was used as a model and
was conducted under diferent reaction parameters (Table 1).
As shown in Table 1 (entry 7), the best result was found in
H2O/EtOH (1:1) at refux condition using 30 mg of the cata-
lyst. Moreover, the catalyst is essential and in the absence
of the catalyst, only 17% of the corresponding 1,4-dihydro-
pyridine was produced even after prolonged reaction times
(Table 1, entry 13). The efciencies of Fe3O4, Fe3O4@SiO2
and MNPs-PrCl and MNPs-AQ as the catalyst toward the
model reaction were compared and the results are depicted
in Table 1. It was observed that the MNPs-AQ was more
efcient than the other ones (entries 7 and 14–16).
reacted under the optimized reaction condition (Scheme 1,
Table 2). All reactions proceeded efciently in the presence
of catalytic amounts of MNPs-AQ in refux condition, and
the desired products were obtained in good to excellent
yields (83–96%) at relatively short reaction times, without
formation of side products.
A plausible mechanism for the formation of 1,4-dihy-
dropyridine derivatives catalyzed by MNPs-AQ is shown in
Scheme 3. The MNPs-AQ catalyst deprotonates the malon-
onitrile and facilitates the Knoevenagel condensation to pro-
duce the arylidene malononitrile intermediate. The Michael
addition of activated ethylacetoacetate in the presence of
MNPs-AQ to arylidene malononitrile resulted in the inter-
mediate. The condensation of intermediate with ammonium
acetate and subsequent tautomerization produce the corre-
sponding 1,4-dihydropyridine.
The results of this study are compared with some existing
methods for the preparation of 1,4-dihydropyridine and pol-
yhydroquinoline derivatives in the literature. The results of
these catalysts in the condensation reaction of benzaldehyde,
ethylacetoacetate, dimedone, and ammonium acetate under
optimized conditions have been indicated in Table 3. As
can be seen, the catalytic system reported in this paper has
benefts in terms of simple conditions, short reaction times,
and excellent yields and is superior to many other methods.
In order to determine the generality and efcacy of the
catalyst, diferent kinds of aromatic aldehyde carrying either
electron-donating or electron-withdrawing groups were
Table 1 Optimization of reaction conditions for preparation of 1,4-dihydropyridine derivatives
OEt
O
H2N
HN
Me
CN
CN
O
conditions
H
NH4OAc
+
+
+
CN
O
CO2Et
No.
Catalyst (mg)
Solvent
Temp. (°C)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
MNPs-AQ (20)
MNPs-AQ (20)
MNPs-AQ (20)
MNPs-AQ (20)
MNPs-AQ (30)
MNPs-AQ (20)
MNPs-AQ (30)
MNPs-AQ (50)
MNPs-AQ (30)
MNPs-AQ (30)
MNPs-AQ (30)
MNPs-AQ (30)
–
THF
Refux
Refux
Refux
Refux
Refux
Refux
Refux
Refux
60
40
r.t.
100
Refux
Refux
Refux
45
45
45
30
30
45
30
30
30
30
30
30
90
30
30
63
53
41
81
93
47
95
94
76
56
43
87
17
49
48
CH3CN
CH2Cl2
EtOH
EtOH
H2O
EtOH:H2O
EtOH:H2O
EtOH:H2O
EtOH:H2O
EtOH:H2O
–
9
10
11
12
13
14
15
EtOH:H2O
EtOH:H2O
EtOH:H2O
Fe3O4 (30)
Fe3O4@SiO2 (30)
aIsolated yields
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Journal of the Iranian Chemical Society
Table 2 Multicomponent
one-pot synthesis of
Product
Ar
Time (min)
Yield (%)a
MP (°C)b
1,4-dihydropyridine derivatives
Found
Reported
6a
6b
6c
6d
6e
6f
6g
6h
6i
C6H5
30
35
30
30
35
35
40
40
35
35
30
30
35
35
30
30
35
30
35
30
30
40
35
35
30
35
35
30
35
35
96
93
95
93
93
92
93
90
92
91
90
95
91
87
95
96
93
90
91
93
95
90
87
90
90
90
93
83
83
86
204–205
179–181
240–242
242–244
252–253
260–262
232–233
253–255
259–261
230–232
204–205
240–241
202–203
199–201
185–187
217–219
201–203
229–230
126–128
161–163
177–178
191–193
187–188
207–209
161–162
172–174
225–227
201–202
211–214
222–225
202–204 [16]
178–179 [17]
243–244 [17]
245–246 [17]
253–255 [16]
260–261 [16]
230–231 [17]
255–257 [17]
262–263 [17]
236–238 [16]
207–208 [17]
241–243 [15]
198–199 [17]
204–206 [16]
188–190 [50]
221–223 [50]
197–199 [51]
223–225 [52]
123–125 [52]
158–159 [53]
173–175 [50]
188–190 [52]
192–194 [51]
209–211 [52]
166–168 [54]
176–177 [55]
221–223 [50]
204–205 [55]
208–209 [50]
226–228 [54]
3-NO2–C6H4
4-NO2–C6H4
4-Cl–C6H4
4-Br–C6H4
4-CH3–C6H4
4-OH–C6H4
4-OMe–C6H4
4-N(Me)2–C6H4
3-OH–C6H4
2-Cl–C6H4
2,4-Cl2–C6H3
3,4-(OCH3)–C6H3
C6H5–CH=CH-
C6H5
6j
6k
6l
6m
6n
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
7l
4-Cl–C6H4
4-Br–C6H4
4-F–C6H4
2-NO2–C6H4
3-NO2–C6H4
4-NO2–C6H4
4-OMe–C6H4
3-OMe–C6H4
2-OMe–C6H4
3,4-(OCH3)–C6H3
3-CH3–C6H4
4-CH3–C6H4
2-Furyl
7m
7n
7p
7o
2-Thienyl
3-Pyridyl
aIsolated yields
bMelting points were not corrected
in catalytic activity. The recovered catalyst after fve runs
had no obvious change in structure, as shown by compari-
son of the FT-IR spectra to that of fresh catalyst (Fig. 8).
The consistent structure and activity of recovered and
reused MNPs-AQ catalyst indicate that the reused MNPs-
AQ also shows excellent performance for the synthesis of
1,4-dihydropyridines.
Catalyst recovery and reuse
The recovery and reusability of the catalyst are very impor-
tant for commercial and industrial applications as well as
green process considerations. Thus, the recovery and reus-
ability of MNPs-AQ were investigated in the sequential
reaction of benzaldehdye (1 mmol) with other reactants and
MNPs-AQ (30 mg) as catalyst in refuxing H2O/EtOH (1:1)
for 30 min. After completion of the reaction, the resulting
solidifed mixture was diluted with hot EtOH (15 mL). Then,
the catalyst was easily separated using an external magnet,
washed with hot EtOH, dried under vacuum, and reused in
a subsequent reaction. Nearly quantitative recovery of cata-
lyst (up to 97%) could be obtained from each run. As seen
in Fig. 7, the recycled catalyst could be reused fve times
without any additional treatment or appreciable reduction
Experimental
All chemicals were purchased from Merck or Acros chem-
ical companies and used without further purification.
Melting points were measured by using capillary tubes
on an electro thermal digital apparatus and are uncor-
rected. Known products were identified by comparison of
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Journal of the Iranian Chemical Society
H N
H3C
R1
R1
OH
H
N
O
H
N
N
N
CH3
N
N
H2O
N
N
CH3
H
O
H
H
O
N
R1
H
R1
R1
N
EtO2C
R1
N
CO2Et
N
O
N
CH3
N
H
N
CH3
H
EtO2C
R1
EtO2C
R1
N
NH
H
O
H
N
N
N
N
H3C
NH OAc
N
N
4
EtO2C
R1
H
N
NH
NH
EtO2C
R1
NH
+
H
N
H3C
NH2
N
CH3
N
Scheme 3 The proposed mechanism for 1,4-dihydropyridine synthesis using MNPs-AQ catalyst
Table 3 Comparison of
MNPs-AQ with some other
catalysts described in the
literature for the synthesis of
polyhydroquinolines
Entry
Catalyst
Condition
Time (min)
Yield (%)a
References
1
2
3
4
5
6
7
8
[hmim]BF4
l-proline
I2
Solvent-free, 90 °C
EtOH, rt
Solvent-free, rt
Solvent-free, rt
EtOH, rt
EtOH, refux
C10F18, 60 °C
EtOH:H2O, refux
10
120
90
95
85
93
92
90
90
95
96
[21]
[12]
[17]
[16]
[19]
[56]
[57]
Present work
CAN
60
Yb(OTf)3
MNPs@GSA
Hf(NPf2)4
MNPs-AQ
300
240
180
30
Reaction conditions: benzaldehyde (1 mmol), ethylacetoacetate (1 mmol), dimedone (1 mmol), ammonium
acetate (1.2 mmol)
aIsolated yields
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Journal of the Iranian Chemical Society
Preparation of the magnetic Fe3O4 nanoparticles
Fe3O4-MNPs were prepared using simple chemical co-
precipitation described in the literature [44]. Briefly,
FeCl2·4H2O (0.9941 g, 5 mmol) and FeCl3·6H2O (2.729 g,
10 mmol) were dissolved in 100 mL of deionized water in a
three-necked round bottomed fask (250 mL). The mixture
was heated under N2 at 80 °C for 1 h, and then 10 mL of
concentrated ammonia (25%) were added quickly. The solu-
tion was stirred under N2 for another 1 h and then cooled to
room temperature. The black precipitate formed was isolated
by magnetic decantation, exhaustively washed with double-
distilled water until neutrality, and further washed twice with
ethanol and dried at 60 °C under vacuum.
Fig. 7 Recyclability of MNPs-AQ in the preparation of 1,4-dihydro-
pyridines
Synthesis of silica‑coated MNPs (Fe3O4@SiO2 MNPs)
The Fe3O4@SiO2 core–shell nanoparticles were prepared
according to the Stober method [45]. The details are as fol-
lows: Magnetic nanoparticles MNPs (1.0 g) were homoge-
neously dispersed by ultrasonic vibration in a mixture of
40 mL of ethanol, 6 mL of deionised water, and 1.5 mL
of 25 wt% concentrated aqueous ammonia solution, fol-
lowed by the addition of 1.4 mL of tetraethylorthosilicate
(TEOS). After stirring for 12 h at room temperature under
an N2 atmosphere, the black precipitate (Fe3O4@SiO2)
was collected from the solution using a magnet, and then
washed several times with water and ethanol and dried at
25 °C under vacuum.
Fig. 8 FT-IR spectra of the fresh catalyst and the fve times reused
catalyst
Synthesis of 3‑chloropropyl‑functionalized
silica‑coated magnetite nanoparticles (Fe3O4@
SiO2‑PrCl MNPs)
their spectral data and melting points with those reported
in the literature. Thin-layer chromatography (TLC) was
performed on UV active aluminum backed plates of silica
In a typical procedure, 1.0 g of Fe3O4@SiO2 MNPs were
dispersed in 50 mL of dry toluene using an ultrasonic bath
to produce a uniform suspension, to which 2.0 g of 3-chlo-
ropropyltrimethoxysilane (CPTMS) was added using a
syringe. The resulting mixture was stirred for 24 h at 60 °C
under an N2 atmosphere. Finally, the chloropropyl-function-
alized solid Fe3O4@SiO2-PrCl MNPs were separated using
a magnet, washed with toluene, and dried under vacuum.
1
gel (TLC Silica gel 60 F254). H and 13C NMR spectra
were recorded on a Bruker Avance 300 MHz spectrom-
eter at 300 MHz and 75 MHz, respectively. Coupling
constants, J, were reported in hertz unit (Hz). IR spectra
were recorded on a Unicom Galaxy Series FT-IR 5030
spectrophotometer using KBr pellets and are expressed
in cm−1. Elemental analyses were performed by Vario
EL equipment at Arak University. X-ray diffraction
(XRD) was performed on Philips XPert (Cu–Kα radia-
tion, λ = 0.15405 nm) over the range 2θ = 20°–80° using
0.04° as the step length. Thermalgravimetric analysis
(TGA) and differential thermal gravimetric (DTG) data
for MNPs-AQ were recorded on a Mettler TA4000 System
4‑Aminoquinaldine grafted on silica‑coated
magnetic nanoparticles (MNPs‑AQ)
In a 100 mL round-bottomed fask, MNPs-AQ nanoparticles
(1.0 g) were dispersed in 50 mL toluene using an ultrasonic
bath. 1.9 g 4-aminoquinaldine (12 mmol) and 1.7 g triethyl-
amine (12 mmol) were added to the suspension. The reac-
tion mixture was refuxed at 100 °C for 24 h. The Fe3O4@
SiO2-AQ MNPs were washed with hot toluene an ethanol,
separated using a magnet, and dried under vacuum at 60 °C.
under an N2 atmosphere at a heating rate of 10 °C min−1
.
The scanning electron microscope measurement was car-
ried out on a Hitachi S-4700 field emission scanning elec-
tron microscope (FE-SEM).
1 3

Journal of the Iranian Chemical Society
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(1:1) for appropriate time. After completion of the reaction
as followed by TLC, the resulting solidifed mixture was
diluted with hot EtOH (15 mL). Then, the catalyst was sepa-
rated using an external magnet, the solvent was evaporated,
and the product was recrystallized with EtOH, and dried in
an oven at 80 °C (Table 2).
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A mixture of dimedone (1 mmol), ethylacetoacetate
(1 mmol), aldehyde (1 mmol), ammonium acetate
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(15 mL). Then, the catalyst was separated using an external
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In this work, the 4-aminoquinaldine-functionalized silica
coated magnetic nanoparticles (MNPs-AQ) successfully
have been prepared and used as heterogeneous basic hybrid
organocatalyst for one-pot synthesis of substituted 1,4-dihy-
dropyridine and polyhydroquinoline derivatives under green
conditions. Moreover, the catalyst can be easily separated
and recovered from the reaction system by a magnet, and
can be reused for several times without signifcant miss of its
activity. In addition, the method presents various advantages
including high yields, operational simplicity, clean reaction
conditions, and minimum pollution of the environment,
which makes it an efective and attractive procedure for the
synthesis of these hydropyridine derivatives.
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