Synthesis and characterization of sodium polyaspartate-functionalized silica-coated magnetite nanoparticles: A heterogeneous, reusable and magnetically separable catalyst for the solvent-free synthesis of 2-amino-4H-chromene derivatives

Article abstract of DOI:10.1002/aoc.4108

An efficient and facile method was used for the synthesis of sodium polyaspartate-functionalized silica-coated magnetite nanoparticles. The structure of this nanoparticle was characterized by scanning electron microscopies, X-ray diffraction, energy-dispe

Full text of DOI:10.1002/aoc.4108

Received: 4 July 2017
DOI: 10.1002/aoc.4108
Revised: 17 August 2017
Accepted: 17 August 2017
F U L L P A P E R
Synthesis and characterization of sodium polyaspartate‐
functionalized silica‐coated magnetite nanoparticles: A
heterogeneous, reusable and magnetically separable catalyst
for the solvent‐free synthesis of 2‐amino‐4H‐chromene
derivatives
1
2
1
Akbar Mobinikhaledi
| Hassan Moghanian | Masoumeh Ghanbari
1
Department of Chemistry, Faculty of
An efficient and facile method was used for the synthesis of sodium
polyaspartate‐functionalized silica‐coated magnetite nanoparticles. The
structure of this nanoparticle was characterized by scanning electron micros-
copies, X‐ray diffraction, energy‐dispersive X‐ray, Fourier transform infrared
spectroscopies and vibrating sample magnetometry. Then, this compound was
used as a reusable heterogeneous catalyst for green synthesis of 2‐amino‐4H‐
chromene derivatives via one‐pot three‐component reactions. This novel
material showed great catalytic performance and the reactions which were
carried out by this catalyst showed good to excellent yields. Besides, the catalyst
could easily be separated from the reaction mixture by using an external
magnetic field and it was stable enough to reuse several times without any
significant reduction in the yield of reactions. Eco‐friendliness, high purity of
the desired products, short reaction time and easy workup procedure can be
mentioned as the other advantages of this method.
Science, Arak University, Arak 38156‐8‐
8349, Iran
2
Department of Chemistry, Dezful
Branch, Islamic Azad University, Dezful,
Iran
Correspondence
Akbar Mobinikhaledi, Department of
Chemistry, Faculty of Science, Arak
University, Arak 38156‐8‐8349, Iran.
Email: akbar_mobini@yahoo.com
KEYWORDS
2‐amino‐ 4H‐chromenes, green chemistry, magnetic nanoparticles, multicomponent reactions
[
10]
[11]
1
| INTRODUCTION
Recently, catalysts like lipase,
Et N,
Zn(L‐pro-
iodine,
3
[
12]
[13]
[14]
line)2,
p‐toluenesulfonic acid (p‐TSA),
[
15]
One‐pot multicomponent reactions are very useful tools
for the synthesis of organic compounds because of their
low costs, least waste production, simple approach, short
times, and environmentally friendliness. For this reason,
medicinal and organic chemists have widely applied these
Meglumine,
Silica functionalized propyl sulfonic
[
16]
[17,18]
acid, and ionic liquids
have been used for the syn-
thesis of chromene derivatives. However, these methods
have some disadvantages including long reaction times,
harsh reaction conditions and toxic catalysts. In order to
avoid these limitations, scientists have intensely focused
on developing efficient, reusable catalysts which shorten
[
1]
reactions to synthesize biologically active compounds.
Among biologically active compounds, 2‐amino‐ 4H‐
chromenes have attracted a lot of attention due to their
wide range of medicinal properties, such as spasmolytic,
diuretic, anticoagulant, anticancer and anti‐anaphylactic
[
1–3]
the reaction times.
On the other hand, nanoparticles do not have any of
disadvantages mentioned above and they can be useful
heterogeneous catalysts for synthesis of 2‐amino‐4H‐
[2–9]
activity.
Appl Organometal Chem. 2017;e4108.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 13
https://doi.org/10.1002/aoc.4108

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MOBINIKHALEDI ET AL.
chromenes because they have high surface areas. How-
ever, the application of these compounds as catalysts has
been limited due to their tedious recovery procedures
which resulted from their small sizes. Also, remarkable
amounts of these solid catalysts are lost during the separa-
tion process. Therefore, scientists have used magnetic
nanoparticles (MNPs), like Fe O , as catalysts for the syn-
transformation due to the high surface area, easy prepara-
tion and functionalization and facile removing with aid of
external magnet from the reaction mixture. As shown in
Scheme 2, the MNPs‐SPAsp magnetic nanoparticle was
synthesized in five steps from commercially available
materials. Magnetite Fe O nanoparticles were prepared
3
4
by the simple co‐precipitation of iron (II) and iron (III)
3
4
thesis of biologically active compounds to solve this prob-
lem because not only they have high surface areas but
also they can be easily separated by using an external
ions in basic solution, according to the reported litera-
[
22,24]
ture.
Considering the aggregation tendency of the
Fe O nanoparticles and acid corrosion problem, the syn-
3
4
[19]
magnetic field.
thesized MNPs were coated by silica using a sol–gel pro-
cess. The Fe O @SiO core‐shell structures were then
Besides, using magnetic nanoparticles as catalysts is
associated with other advantages including easy synthesis
and functionalization, low toxicity and low cost. However,
magnetic nanoparticles can easily aggregate into larger
clusters because of their anisotropic dipolar attraction.
In addition, they have other deficiencies such as leaching
under acidic conditions and being susceptible to autoxida-
tion and toxicity. Therefore, it is necessary to protect the
surface of MNPs in order to reduce these undesirable fea-
tures. For this purpose, MNPs are usually coated with a
3
4
2
sequentially treated with 3‐aminopropyltrimethoxysilane
(APTS) to obtain 3‐aminopropyl magnetic nanoparticles
(Fe O @SiO ‐NH ) substrate. Next, poly(succinimide)‐
3
4
2
2
functionalized magnetic silica nanoparticles (MNPs‐PSI)
were obtained from thermal polymerization of pre‐formed
Fe O @SiO ‐NH with L‐aspartic acid using o‐phosphoric
3
4
2
2
acid as a dehydration agent. The amino groups in
Fe O @SiO ‐NH can act as nucleophilic groups and
3
4
2
2
attack the carbonyl group of L‐aspartic acid to build a
stable and compact coating on the magnetic core. Finally,
hydrolysis of surface MNPs‐PSI nanoparticles with NaOH
solution gives biodegradable sodium polyaspartate‐func-
tionalized magnetic silica nanoparticles (MNPs‐SPAsp).
The structure of MNPs‐SPAsp was characterized by
Fourier transform infrared spectroscopy (FT‐IR), scan-
ning electronmicroscopy (SEM), energy dispersive spec-
trometry (EDS), X‐ray powder diffraction (XRD), N2
adsorption and desorption, vibrating sample magnetome-
try (VSM) and thermogravimetry (TG). Figure 1 shows
the FT‐IR spectra of Fe O , Fe O @SiO , Fe O @SiO ‐
[20]
polymeric or inorganic matrix.
Among inorganic com-
pounds, SiO can be a suitable candidate for protecting
2
the surface of MNPs due to its high chemical and thermal
stability and most importantly its easy modification by a
wide range of functional groups, which increase chemical
[21–23]
and colloidal stability of these compounds.
The objective of the present work was to develop a
more efficient synthetic process for the synthesis of 2‐
amino‐4H‐chromene derivatives (Scheme 1). Herein,
sodium polyaspartate‐functionalized silica‐coated magne-
tite nanoparticles were prepared and its catalytic perfor-
mance for synthesis of 2‐amino‐4H‐chromenes was
investigated. The method was very useful because of the
considerable efficiency of the catalyst and its environmen-
tal compatibility. Also, the catalyst was inexpensive and
highly efficient and it could easily be recovered and reused.
3
4
3
4
2
3
4
2
NH , MNPs‐PSI and MNPs‐SPAsp nanoparticles. The
2
characteristic absorption of Fe‐O from magnetic nanopar-
−
1
ticle cores was observed at about 579 cm (Figure 1a).
Compared with Fe O , Figure 1b presented an intense
3
4
−
1
adsorption peak at 1088 cm and three weak peaks at
62, 808 and 455 cm , which could be ascribed to the
−
1
9
asymmetric stretching, symmetric stretching, in plane
bending and rocking mode of the Si‐O‐Si group respec-
2
2
| RESULTS AND DISCUSSION
.1 | Synthesis and structural
tively, in the SiO shell. Moreover, the O‐H stretching
2
−
1
vibration modes (Si‐OH) near 3400 cm and H‐O‐H twist-
characterization of MNPs‐SPAsp as catalyst
−
1
ing vibration mode near 1620 cm were observed for
both (Figure 1a and Figure 1b). Figure 1c shows the FT‐
IR spectrum of Fe O @SiO ‐NH nanoparticles. In com-
Magnetic nanoparticles (MNPs) are considered to be
attractive as heterogeneous supports in catalytic
3
4
2
2
parison with Fe O @SiO characteristic absorption bonds
3
4
2
are the same, demonstrating the existence of SiO compo-
2
nents. In addition, the new bands are observed at 2949
−
1
and 2872 cm (CH ), indicating the definite graft of 3‐
2
aminopropyl group. According to FT‐IR spectra of
MNPs‐PSI nanoparticles (Figure 1d), the symmetric
stretching bond of imide group at 1722 cm demon-
SCHEME
1
Multicomponent synthesis of 2‐amino‐4H‐
−
1
chromenes using sodium polyaspartate‐functionalized silica‐coated
magnetite nanoparticles
strated that the poly(succinimide) (PSI) was successfully

MOBINIKHALEDI ET AL.
3 of 13
3 4
SCHEME 2 Preparation of sodium polyaspartate‐functionalized silica‐coated nano‐Fe O particles
3 4 3 4 2 3 4 2 2
FIGURE 1 FT‐IR spectra of (a) Fe O , (b) Fe O @SiO , (c) Fe O @SiO ‐NH , (d) MNPs‐PSI and (e) MNPs‐SPAsp
conjugated to the surface of the magnetic nanoparticles.
indicating the formation of polyaspartatelayers on mag-
netic nanoparticles.
Next, the morphology and nanoparticle size of the syn-
thesized magnetic MNPs‐SPAsp catalyst was characterized
The FT‐IR of MNPs‐SPAsp illustrates characteristic peaks
−
1
at 1651 cm (C = O stretching), which is derived from
hydrolysis of surface MNPs‐PSI nanoparticles, clearly
FIGURE 2 Low‐magnification (right) and high‐magnification (left) FE‐SEM images of MNPs‐SPAsp nanoparticles

4
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MOBINIKHALEDI ET AL.
by field emission scanning electron microscopy (FE‐SEM)
Figure 2). As shown in Figure 2, the catalyst particles pos-
nanoparticles were pure with a cubic spinel structure
and they are perfectly matched with the standard Fe O
(
3
4
sess near spherical morphology with average diameter of
about 30–50 nm. Furthermore, SEM images show some
aggregation, which was illustrated the successful grafting
of the polymer on to magnetic nanoparticles. The compo-
nent of MNPs‐SPAsp was analyzed by using an energy dis-
persive spectrometer (EDS) (Figure 3). Figure 3 confirms
the presence of Na in the structure of the catalyst. More-
over, Si, O, and Fe signals can be seen in EDS analysis indi-
cating that the iron oxide particles were loaded into silica.
Also, the signal related to Si is more intense than those
sample (JCPDS card no. 85–1436). The broad peak from
2θ = 20 to 27 (Figure 5B) is related to an amorphous silica
phase in the shell of the silica‐coated Fe O nanoparticles
3
4
[
17]
(Fe O @SiO ).
The average crystallite size of the mag-
3
4
2
netic nanoparticles can be estimated by the (311) XRD
peak and Scherrer's formula (D = 0.9λ/β cos θ). In this
formula, D is defined as the average crystalline size, λ is
the X‐ray wave‐length (0.154 nm), β is the full width in
radians subtended by the half maximum intensity width
of the (311) powder peak, and θ belongs to the Bragg
[
18]
related to Fe showing that SiO2 trapped the Fe O4
angle of the (311) peak in degrees.
According to the
3
nanoparticles.
data, the crystallite size of the magnetic nanoparticle
was obtained 13.3 nm by using Scherrer's equation. The
crystallite size obtained by XRD was smaller than that
obtained by FE‐SEM analysis (Figure 2). This difference
can be explained by the fact that crystallite sizes are con-
sidered as the sizes of ‘coherently diffracting domains’ of
crystals in XRD measurements while grains may contain
several types of these domains.
The thermal stability of the MNPs‐SPAsp catalyst was
determined using TGA analysis and the results were
shown in Figure 4. Two steps of decomposition were
observed in TGA curve of the MNPs‐SPAsp catalyst. In
the first step, the weight loss of 6.30% below 140 °C was
assigned to the removal of physically trapped solvents
and surface hydroxyl groups. The second step involves
the decomposition of 13.35% over the range of 140–
Also, the magnetic properties of the nanoparticles were
studied by using the vibrating sample magnetometer
(VSM). Figure 6 illustrates the magnetization curves of
Fe O and MNPs–SPAsp nanoparticles. The magnetization
5
50 °C which is due to the decomposition of the coating
organic moiety in the nanocomposite. Based on this mass
loss, it was calculated that 0.82 mmol of SPAsp was loaded
on 1 g of the MNPs‐SPAsp catalyst.
3
4
of samples was completely saturated at high fields of up to
XRD measurements were used to investigate the pres-
ence as well as the degree of crystallinity of both magnetic
Fe O and the MNPs–SPAsp catalyst (Figure 5). Both of
these compounds showed the same patterns, indicating
that the crystalline spinel ferrite core remained intact dur-
ing the silica‐coating process. The XRD data of the synthe-
sized magnetic nanoparticles appeared diffraction peaks
at 2θ = 30.4, 35.8, 43.3, 53.9, 57.3, 63.0, and 74.5 which
can be assigned to the (220), (311), (400), (422), (511),
8000.0 Oe and the M of MNPs–SPAsp nanoparticles
s
−
1
decreased from 43.3 to 17.6 emu g upon coating Fe O
3
4
core with silica and functionalizing with polyaspartate.
Also, the hysteresis loops indicate the super‐paramagnetic
behavior of the Fe O and MNPs–SPAsp particles in which
3
4
3
4
the M and the H are close to zero (M = 0.85 and 0.49 emu
r
c
r
−
1
[19]
g , and H = 4.9 and 8.71 Oe, respectively). The strong
c
magnetization of the nanoparticles was also proved by
using an external magnet.
(
440) and (533) planes of Fe O , respectively. This pattern
The surface characteristics of the MNPs–SPAsp nano-
particles were investigated by nitrogen adsorption at 77 K.
3
4
proves that the Fe O4 particles of the MNPs–SPAsp
3
FIGURE 3 The EDS spectrum of
MNPs‐SPAsp nanoparticles

MOBINIKHALEDI ET AL.
5 of 13
FIGURE 4 Thermal gravimetric
analysis (TGA) of MNPs‐SPAsp
FIGURE 5 The XRD diffraction pattern
of Fe O (a) and MNPs‐SPAsp (b)
3 4
FIGURE 6 Magnetization curves for
the prepared Fe MNPs (a) and MNPs‐
SPAsp nanoparticles at room temperature
b) left inset: The magnified field from −15
3 4
O
(
to 15 Oe
Figure 7 illustrates BJH plot and adsorption–desorption
isotherm of the catalyst. This isotherm was type IV indi-
cating mesoporous nature of the material. Furthermore,
the narrow hysteresis loop observed in the isotherm of
the MNPs–SPAsp nanoparticles proves the porous nature
[
20]
of this material.
According to results of these analyses,

6
of 13
MOBINIKHALEDI ET AL.
FIGURE 7 Nitrogen adsorption
isotherms and BJH plot for MNPs‐SPAsp
nanoparticles
BET‐surface area (S ) and total pore volume (V ) were
results were summarized in Tables 2 and 3. These reac-
tions were very efficient and the desired products were
obtained in good to excellent yields (85–97%) in relatively
short reaction times, without formation of byproducts.
Also, since a wide range of inorganic or organic cata-
lysts were used for the synthesis of 2‐amino‐4H‐
chromenes, we decided to gather the results obtained by
these catalysts for the synthesis of both 3‐amino‐1‐phe-
nyl‐1H‐benzo[f]chromene‐2‐carbonitrile and 2‐amino‐
7,7‐dimethyl‐5‐oxo‐4‐phenyl‐5,6,7,8‐tetrahydro‐4H‐
chromene‐3‐carbonitrile under optimized conditions in
order to compare the catalytic performance of our catalyst
with the reported inorganic or organic ones. Tables 4 and
5 compare catalytic performance of different catalysts in
the synthesis of these two compounds. It can be concluded
from these Tables that the MNPs–SPAsp catalyst can be
considered as one of the best catalysts for these reaction
because of their short reaction times, simple conditions
and environmentally friendliness. Most importantly, the
advantages related to the inherent magnetic properties
have distinguished the efficiency of this catalyst.
BET
p
2
−1
3
−1
5
5.11 m g and 0.199 cm g , respectively. Moreover,
the BJH plot showed an average pore diameter of
.1 nm for this material.
2
2.2 | Catalytic studies
The catalytic performance of this novel basic organo‐cata-
lyst has been studied for the synthesis of 2‐amino‐4H‐
chromenes (Scheme 3 and Scheme 4). To find the
optimized conditions, the reaction of 2‐naphthol 2
(1 mmol), benzaldehyde 3 (1 mmol) and malononitrile 4
(1.2 mmol) was used as a model, and variables affecting
on the reaction yields such as the type of solvent, the
amount of catalyst, different temperatures, and solvent‐
free conditions were studied (Table 1). As shown in
Table 1, conventional heating at 120 °C under solvent‐free
conditions is more efficient (Table 1, entry 7) over the
organic solvents, because of its considerable efficiency
and environmental compatibility.
In order to prove the generality and efficacy of the cat-
alyst, malononitrile and different kinds of aldehyde,
containing either electron‐donating or electron‐withdraw-
ing groups, were reacted with one of these reagents: β‐
naphthol, α‐naphthol, dimedone or ethyl acetate. The
Scheme 5 illustrates the possible mechanism for the
reactions catalyzed by MNPs–SPAsp. The formation of
the products can be rationalized by initial Knoevenagel
condensation reaction between an aldehyde and
malononitrile anion; then, the first intermediate reacted
SCHEME 3 The one‐pot three component reaction of aldehyde,
malononitrile and α‐ or β‐naphthol catalyzed by MNPs‐SPAsp
nanoparticles
SCHEME 4 The one‐pot three component reaction of aldehyde,
malononitrile and dimedone or ethyl acetoacetate catalyzed by
MNPs‐SPAsp nanoparticles

MOBINIKHALEDI ET AL.
7 of 13
a
TABLE 1 Optimization of reaction conditions for the synthesis of 2‐amino‐4‐phenyl‐4H‐benzo[f]chromene‐3‐carbonitrile (Table 2, entry 1)
b
Entry
1
Catalyst (mg)
Solvent
EtOH
Condition
R.T.
Time (h)
24
Yield (%)
<10
MNPs‐SPAsp(50)
2
3
4
5
6
7
8
9
MNPs‐SPAsp(50)
MNPs‐SPAsp(50)
MNPs‐SPAsp(50)
MNPs‐SPAsp(50)
MNPs‐SPAsp(50)
MNPs‐SPAsp(50)
MNPs‐SPAsp(20)
MNPs‐SPAsp(100)
‐
EtOH
Reflux
Reflux
Reflux
Reflux
85 °C
12
12
12
12
2
60
EtOH‐H
2
O (1:1)
48
CH
3
CN
58
CHCl
3
56
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
38
120 °C
120 °C
120 °C
120 °C
120 °C
120 °C
120 °C
120 °C
0.5
1.5
0.5
4
93
62
93
10
11
12
13
14
Trace
30
Fe
Fe
3
3
O
4
4
(50)
3
O
@SiO
2
(50)
(50)
MNps‐PSI (50)
3
28
MNPs‐NH
2
3
65
3
20
a
Benzaldehyde (1 mmol), 2‐naphthol (1 mmol), malononitrile(1.2 mmol).
b
Isolated yields.
with the compounds containing hydroxyl group (β‐naph-
thol, α‐naphthol, dimedone or ethyl acetate) through
Michael addition reaction to produce the second
intermediate. Then, an intramolecular cyclization
followed by the elimination of H gives the final
products.
+
TABLE 2 MNPs‐SPAsp mediated synthesis of 2‐amino‐4H‐chromene derivatives with aldehydes, malononitrile and β‐naphthol or α‐
naphthol
M.P. (°C)
Time
(min)
Yield
(%)
a
Lit.
Entry
Ar
Naphthol
Product
5a
Found
Reported
[
[
[
25]
1
C
6
H
5
β‐naphthol
30
25
40
45
50
30
60
50
75
30
15
45
30
15
93
96
87
91
90
85
89
86
85
95
96
92
89
97
295–296
297–299
187–189
233–234
255–256
185–187
257–259
225–228
252–253
‐
26]
27]
2
3
4
5
6
7
8
9
4‐NO
4‐FC
4‐MeC
4‐MeOC
2‐ClC
4‐N(me)
4‐OH‐3‐MeOC
4‐(iso‐Pr) C
2
C
6
H
4
β‐naphthol
β‐naphthol
β‐naphthol
β‐naphthol
β‐naphthol
β‐naphthol
β‐naphthol
β‐naphthol
α‐naphthol
α‐naphthol
α‐naphthol
α‐naphthol
α‐naphthol
5b
5c
188–189
234–236
253–254
187–188
255–256
226–228
250–251
209–211
211–212
188–190
235–237
241–243
210–212
6
H
4
[
[
[
15]
6
H
4
5d
5e
28]
29]
6
H
4
6
H
4
5f
[
30]
2
C
6
H
4
5 g
5 h
5i
[
31]
6
H
3
6
H
4
[
[
[
[
[
26]
26]
32]
15]
33]
10
11
12
13
14
C
6
H
5
6j
213–215
190–192
239–241
245–246
214–215
4‐OHC
4‐BrC
4‐ClC
3‐NO
6
H
4
6 k
6 l
6 m
6n
6
H
4
6
H
4
2 6 4
C H
a
Isolated yields.

8
of 13
MOBINIKHALEDI ET AL.
TABLE 3 MNPs‐SPAsp mediated synthesis of 2‐amino‐4H‐chromene derivatives with aldehydes, malononitrile and dimedone or ethyl
acetoacetate
M.P. (°C)
Time
(min)
Yield
(%)
a
Lit.
Entry
Ar
β‐Dicarbonyl
Product
9o
Found
Reported
[
[
[
[
[
34]
1
C
6
H
5
Dimedone
30
25
30
45
30
60
60
75
90
92
97
88
86
82
84
75
72
70
227–228
228–230
196–198
201–205
230–232
191–194
‐
35]
2
3
4
5
6
7
8
9
4‐BrC
2‐ClC
4‐OH‐3‐MeOC
6
H
4
Dimedone
9p
197–199
198–200
228–229
193–195
198–200
172–173
171–173
130–133
36]
37]
38]
6
H
4
Dimedone
9q
6
H
3
Dimedone
9r
Thiophene‐2‐carbaldehyde
3‐Pyridyl
Dimedone
9 s
9 t
Dimedone
[
[
39]
40]
3‐NO
4‐ClC
4‐MeOC
2
C
6
H
4
Ethyl acetoacetate
Ethyl acetoacetate
Ethyl acetoacetate
10u
10v
10w
174–176
170–172
6
H
4
[41]
6
H
4
135
a
Isolated yields
TABLE 4 Comparison of MNPs‐SPAsp with some reported catalysts for synthesis of 3‐amino‐1‐phenyl‐1H‐benzo[f]chromene‐2‐
a
carbonitrile
b
Entry
Catalyst (amount)
Nano‐Bi WO (5 mol%)
Condition
O, R.T.
Time
Yield(%)
Ref.
[30]
1
2
6
H
2
20 min
86
[
25]
2
3
4
5
6
7
8
9
Imidazole (0.2 mmol)
EtOH, reflux
1 h
86
82
95
97
93
90
93
91
90
100
87
95
95
93
c
[42]
[29]
[26]
TBAC (10 mol%)
Solvent‐free, 100 °C
35 min
20 min
13 min
3 h
d
Nano CP (0.01 g)
H
2
O, reflux
e
POPI (5 mol%)
Ball milling, ambient
[
[
[
[
[
[
[
[
[
43]
44]
45]
46]
33]
47]
48]
49]
50]
ZnFe
2
O
4
NPs (40 mg)
CO (10 ml)
H
H
2
2
O, R.T.
O, mw
Saturated K
2
3
3.2 min
10 min
30 min
60 min
40 min
25 min
5 min
40 min
30 min
Gel entrapped DABCO (1 g)
CAN (5 mol%)
EtOH, ambient
Solvent‐free, 120 °C
1
1
1
1
1
1
0
1
2
3
4
5
[bmim]OH (0.5 mmol)
H
2
O, reflux
Solvent‐free, 125 °C
O, 80 °C
2 3
Na CO (0.1 mmol)
SBA‐DABCO (0.125 g)
5‐Å MS (0.5 g)
H
2
Solvent‐free, MW
Solvent‐free, 120 °C
Solvent‐free, 120 °C
Fe
3 4 2
O /SiO /propyl‐pip (0.05 g)
MNPs‐SPAsp (50 mg)
This work
a
Reaction conditions: Benzaldehyde (1 mmol), β‐naphthol (1 mmol), malononitrile (1.2 mmol).
b
c
d
e
Isolated yields; tetrabutylammonium chloride; Nanozeolite clinoptilolite; potassium phthalimide
2.3 | Catalytic recyclability
catalysts was confirmed by FT‐IR spectroscopy
Figure 8). The FT‐IR spectrum of the recycled catalyst
(
Because the recovery and reusability of the catalyst are
very important for commercial and industrial purposes
as well as green process considerations, the recovery and
reusability of MNPs–SPAsp was investigated in the
sequential reaction of 3‐nitrobenzaldehdye (1 mmol), α‐
naphthol (1 mmol), malononitrile (1.2 mmol) and the cat-
alyst (0.05 g) under solvent‐free conditions at 120 °C. The
results were shown in Table 6. The catalyst could be
reused at least six times without any significant loss in
the yield of reactions. The stability of the recovered
after six runs was very identical to that of fresh catalyst,
confirming that the catalyst indicates excellent perfor-
mance for the synthesis of 2‐amino‐4H‐chromenes.
3
| EXPERIMENTAL
.1 | General
3
All reagents were used without further purification and
were procured from commercial sources. Melting points

MOBINIKHALEDI ET AL.
9 of 13
TABLE 5 Comparison of MNPs‐SPAsp with some reported catalysts for synthesis of 2‐amino‐7,7‐dimethyl‐5‐oxo‐4‐phenyl‐5,6,7,8‐
a
tetrahydro‐4H‐chromene‐3‐carbonitrile
b
Entry
Catalyst (amount)
Ni(NO .6H O (10 mol%)
Condition
O, reflux
EtOH‐H O (1:1), R.T.
EtOH, 60 °C
EtOH‐H O, (1:1), R.T.
Time
Yield(%)
Ref.
[51]
1
3
)
2
2
H
2
20 min
95
[39]
2
3
4
5
6
7
8
9
Urea (10 mol%)
2
3 h
90
94
97
95
90
80
90
90
86
90
99
95
92
c
[36]
15]
[52]
MSNs (10 mg)
15 min
5 min
[
Meglumine (5 mol%)
2
d
POPINO (5 mol %)
H
H
H
H
2
2
2
2
O, reflux
O, 80 °C
O, reflux
O, reflux
15 min
25 min
10 min
40 min
25 min
15 min
5 min
[
[
53]
38]
Fe
3
O
4
@SiO
2
/DABCO (0.05 g)
γ‐Fe
2
O
3
2 3
@hap‐Si‐(CH ) ‐AMP (1.5 mol%)
e
[54]
[40]
TBAB (10 mol%)
f
SBPPSP (0.05 g)
2
EtOH‐H O, (1:1), reflux
[
[
[
34]
37]
35]
1
1
1
1
1
0
1
2
3
4
Nano‐NH
4
H
2
PO
4
/Al
2
O
3
(0.03 g)
EtOH, reflux
[cmmim]Br (10 mol%)
Solvent‐free, 110 °C
Ball milling, R.T.
Na
2
CO
3
(10 mol%)
25 min
15 min
30 min
g
[55]
Nano CP (0.01 g)
H
2
O, reflux
MNPs‐SPAsp (50 mg)
Solvent‐free, 120 °C
This work
a
Reaction conditions: Benzaldehyde (1 mmol), dimedone (1 mmol), malononitrile (1.2 mmol).
b
c
Isolated yields;
Mesoporous Silica Nanoparticles;
d
Potassium phthalimide‐N‐oxyl;
e
Tetrabutylammonium Bromide;
f
Silica‐bonded N‐propylpiperazine sodium n‐propionate;
g
Nanozeolite clinoptilolite
SCHEME 5 The possible mechanism
for one‐pot synthesis of 2‐amino‐4H‐
chromenes using MNPs‐SPAsp
nanoparticles
were determined on Electrothermal 9200 apparatus.
Elemental analysis was performed on a Vario EL III ele-
mental analyzer. Analytical thin layer chromatography
λ = 0.15405 nm) in the range of 2θ = 20–80° using 0.04° as
the step length. The specific surface area and the pore size
distribution were calculated by the Brunauer–Emmett–
Teller (BET) method and Barrett–Joyner–Halenda (BJH)
model, respectively. The particle size and external
morphology of the particles were carried out on a Hitachi
S‐4700 field emission‐scanning electron microscope (FE‐
SEM). The magnetization and hysteresis loop were mea-
sured at room temperature using a Vibrating Sample
Magnetometer (Model 7300 VSM system, Lake Shore
Cryotronic, Inc., Westerville, OH, USA). The thermogra-
vimetric analysis (TGA) and differential thermal
(
TLC) was performed using Merck 0.2 mm silica gel
0 F‐254 Al‐plates. The FTIR spectrum of the sample
was recorded on a Unicom Galaxy Series FT‐IR 5000 spec-
6
−
1
trophotometer at region of 4000–400 cm using pressed
1
13
KBr discs. The H and C NMR spectra were recorded
on a Brucker Avance spectrometer operating at 400 and
1
13
1
00 MHz for H and carbon, respectively in DMSO‐d6
with TMS as an internal standard. The X‐ray diffraction
XRD) was performed on Philips X‐Pert (Cu‐Ka radiation,
(

10 of 13
MOBINIKHALEDI ET AL.
TABLE 6 Recyclability of MNPs‐SPAsp in reaction of 3‐
nitrobenzaldehdye (1 mmol), α‐naphthol (1 mmol),
3
.3 | Synthesis of silica‐coated MNPs
(Fe O @SiO MNPs)
3
4
2
malononitrile(1.2 mmol) and catalyst (0.05 g) under solvent‐free
a
conditions
The Fe O @SiO core‐shell nanoparticles were prepared
according to the Stober method.
3
4
2
[
56]
Typically, 500 mg of
Run Yield(%)
the synthesized magnetitena noparticles were dispersed
by ultrasonic vibration in a mixture of ethanol (20 ml),
deionized water (3 ml) and 1 ml of 25 wt% concentrated
aqueous ammonia solution for 20 min. Subsequently,
0.7 ml of tetraethylorthosilicate (TEOS) was added
dropwise. After stirring for 12 h at room temperature
1
2
3
4
5
6
97
95
95
94
93
91
under N atmosphere, the products was collected from
2
the solution using a magnet, and then washed several
times with water and ethanol and dried at 25 °C under
vacuum.
a
Time of reaction was 15 min.
3
.4 | Synthesis of 3‐aminopropyl‐
gravimetric (DTG) data for MNPs‐SPAsp were done using
a Mettler TA4000 System. About 10 mg of samples was
heated from room temperature to 800 °C with a heating
functionalized magnetic silica
nanoparticles (Fe O @SiO ‐NH MNPs)
3
4
2
2
−
1
5
5
00 mg Fe O @SiO nanoparticles were dispersed into
3 4 2
0 ml toluene and sonicated for 20 min, followed by the
rate of 10 °C min in nitrogen atmosphere.
addition of 0.5 mL (3‐aminopropyl) trimethoxysilane
APTES). Then, the mixture was refluxed at 110 °C with
3
.2 | Preparation of the magnetic Fe O4
3
(
nanoparticles (MNPs)
continuous stirring for 12 h under a nitrogen flow. The
resulting functionalized Fe O @SiO was collected by
Fe O4 nanoparticles are prepared by chemical co‐
precipitationof Fe and Fe described in the litera-
ture.
3
4
2
3
3+
2+
magnetic separation followed by washing with toluene
and ethanol several times and drying at 60 °C for 6 h.
[22,24]
Briefly, FeCl .4H O (0.9941 g, 5 mmol) and
2 2
FeCl .6H O (2.7029 g, 10 mmol) were dissolved in 100 ml
3
2
of deionized water in a three‐necked round bottomed flask
250 mL). The resulting solution is heated for 1 h at 80 °C
3
.5 | Synthesis of poly(succinimide)‐
(
functionalized magnetic silica
nanoparticles (MNPs‐PSI)
under N atmosphere. Consequently, 10 mL of concen-
2
trated ammonia (25%) were added quickly. After 1 h, the
mixture was cooled to room temperature and magnetic
nanoparticles were isolated by magnetic decantation, first
washed with distilled water, then ethanol, and finally dried
under vacuum at room temperature.
The MNPs‐PSI magnetic nanoparticles were prepared
according to the procedure described in the literature.
for synthesis of poly (succinimide) with some modifica-
tions as follows: 500 mg of MNPs‐PSI is dispersed in 85%
[57]
FIGURE 8 FT‐IR spectra of the fresh
catalyst and the six‐times reused catalyst

MOBINIKHALEDI ET AL.
11 of 13
o‐phosphoric acid (2 g) in an ultrasonic bath for 20 min,
followed by the addition of L‐aspartic acid (ASP) (1.5 g,
temperature and the crude products which precipitated
were collected and recrystallized from ethanol if necessary.
1
1.3 mmol). The reaction mixture was then stirred for
8
h, under nitrogen atmosphere at 200 °C. The product
3
.9 | Characterization data for new
was dispersed several times in water by ultrasonic vibra-
tion and collected by magnetic separation until it was
neutral. It was subsequently washed with hot DMSO
and with methanol and then was dried at 85 °C under
vacuum to yield MNPs‐PSI.
compounds
3
.6 | Synthesis of sodium polyaspartate‐
functionalized magnetic silica
Compound 5i (Table 2, Entry 9):
nanoparticles (MNPs‐SPAsp)
IR (KBr): υmax = 3427, 3335, 3209, 2958, 2191, 1649,
411, 1234, 1082, 1037, 812, 750 cm ; H NMR
−
1
1
1
(
The hydrolysis of MNPs‐PSI was carried out as follows:
400 MHz, DMSO‐d ): δ = 7.89–7.98 (m, 2H), 7.87 (d,
6
5
00 mg of MNPs‐PSI nanoparticles were added to 10 ml
J = 7.2 Hz, 1H), 7.40–7.49 (m, 2H), 7.34 (d, J = 8.8 Hz,
of NaOH 5% solution and then ultrasonically dispersed
for 20 min. After stirring for 1 h at room temperature
1
2
(
1
H), 7.15–7.06 (m, 4H), 6.96 (br, 2H), 5.26 (s, 1H), 2.84–
13
.74 (m, 1H), 1.13 (d, J = 5.2 Hz, 6H). C NMR
under N atmosphere, the resulting product was collected
2
100 MHz, DMSO‐d ): δ = 159.7, 146.7, 146.5, 143.1,
6
by magnetic separation followed by washing with water
and ethanol several times and drying at 40 °C for 6 h
under reduced pressure.
30.8, 130.1, 129.3, 128.4, 127.1, 126.8, 126.6, 124.9,
23.6, 120.6, 116.8, 115.9, 58.0, 37.6, 32.9, 23.7. Analytical
1
calculation for C H N O: C, 81.15; H, 5.92; N, 8.23.
23
20 2
Found: C, 81.22; H, 5.95, N, 8.19.
3.7 | Acid–base titrations of MNPs‐SPAsp
The concentration of carboxyl groups was quantitatively
estimated by back titration using NaOH (0.01 N). 5 ml
of 0.01 M HCl solution was added to 0.05 g of the mag-
netic nanoparticles and the mixture was stirred for
3
0 min. The catalysts were magnetically separated and
Compound 9 t (Table 3, Entry 6):
washed with deionized water. The sample was back‐
titrated with the 0.01 M NaOH solution in the presence
of phenolphthalein as indicator. Averages of three sepa-
rate titrations were performed to obtain an average value
for the concentration of dissociable COOH groups. The
acid–base titration results revealed 0.02 mmol/g carboxyl
groups amount.
IR (KBr): υmax = 3394, 3323, 3211, 2958, 2204, 1660,
1
425, 1369, 1249, 1215, 1140, 1028, 711, 628, 561, 489 cm
−
1 1
;
H NMR (400 MHz, DMSO‐d ): δ = 8.42–8.37 (m,
6
2H), 7.55 (d, J = 8.0 Hz, 1H), 7.36–7.30 (m, 1H), 7.13
(
br, 2H), 4.26 (s, 1H), 2.54 (d, J = 5.2 Hz, 2H), 2.26 and
2
3
1
.12 (AB system, J = 16.0 Hz, 2H), 1.04 (s, 3H), 0.96 (s,
H). C NMR (100 MHz, DMSO‐d ): δ = 195.7, 162.9,
58.6, 148.6, 147.8, 140.0, 134.7, 123.6, 199.5, 111.8, 57.3,
13
6
3
.8 | General procedure for the synthesis
49.9, 39.6, 33.4, 31.8, 28.2, 26.9. Analytical calculation
for C17 : C, 69.14; H, 5.80; N, 14.23. Found: C,
9.20; H, 5.86, N, 14.17.
of 2‐amino‐4H‐chromene derivatives
H N O
17 3 2
6
To a mixture of aromatic aldehyde (1 mmol), malonitrile
(
(
1.2 mmol), and enolizable C‐H activated compound
1 mmol), MNPs‐SPAsp (0.05 g) was added as a catalyst,
4 | CONCLUSIONS
and the mixture was magnetically stirred under thermal
solvent‐free condition on a preheated oil bath at 120 °C
for the appropriate time. After completion of the reaction
as indicated by TLC (using n‐hexane‐ethylacetate as elu-
ent), the resulting mixture was diluted with hot ethanol
In conclusion, the synthesis of polyaspartate‐functional-
ized silica‐coated magnetite nanoparticles was performed
by using a very simple, efficient and inexpensive method.
The structure of this nanoparticle was characterized by
using the following techniques: FT‐IR, XRD, TG/DTG,
FE‐ESM, EDS, VSM and acid–base titration. Then, syn-
thesis of 2‐amino‐ 4H‐chromenes was carried out by using
(
10 ml) and the catalyst separated by an external magnet
and washed with hot distilled water (5 ml) and ethanol
3 ml) two times. The filtrate was cooled down to room
(

12 of 13
MOBINIKHALEDI ET AL.
a facile, versatile, one‐pot multicomponent reaction and
the new synthesized material was used as an efficient,
magnetically separable and reusable heterogeneous cata-
lyst for these reactions. This method has some advantages
over the previous methods. High catalytic activity, gener-
ality, high yields, short reaction times, simple experimen-
tal procedure and easy work‐up procedure are among
these advantages.
[20] S. H. Araghi, M. H. Entezari, Appl. Surf. Sci. 2015, 333, 68.
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How to cite this article: Mobinikhaledi A,
Moghanian H, Ghanbari M. Synthesis and
characterization of sodium polyaspartate‐
functionalized silica‐coated magnetite
nanoparticles: A heterogeneous, reusable and
magnetically separable catalyst for the solvent‐free
synthesis of 2‐amino‐4H‐chromene derivatives.
Appl Organometal Chem. 2017;e4108. https://doi.
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2