Synthesis, characterization, and application of CoFe2O4@TRIS@sulfated boric acid nanocatalyst for the synthesis of 2-amino-3-cyanopyridine derivatives

Article abstract of DOI:10.1007/s11164-020-04369-4

Abstract: The aim of this research is the synthesis of a novel acidic nanocatalyst using the layer-by-layer assembly technique. The CoFe₂O₄@TRIS@sulfated boric acid nanoparticles were easily synthesized and studied as a highly beneficial, recyclable, and magnetite nanocatalyst for the synthesis of 2-amino-3-cyanopyridine derivatives. The chemical structure of CoFe₂O₄@TRIS @sulfated boric acid nanocatalyst was completely confirmed with different techniques like FESEM, Map, EDS, XRD, TGA/DTG, VSM, and FT-IR analyses. Briefly, the newly synthesized nanocatalyst offers some advantages such as simplicity of work-up, highly stable, environmental friendliness, reusability, excellent yields, and short reaction time. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11164-020-04369-4

Research on Chemical Intermediates (2021) 47:1315–1330
https://doi.org/10.1007/s11164-020-04369-4
Synthesis, characterization, and application of CoFe2O4@
TRIS@sulfated boric acid nanocatalyst for the synthesis
of 2‑amino‑3‑cyanopyridine derivatives
Homayoun Faroughi Niya1 · Nourallah Hazeri1 · Malek Taher Maghsoodlou1 ·
Maryam Fatahpour1
Received: 24 July 2020 / Accepted: 11 December 2020 / Published online: 3 February 2021
© The Author(s), under exclusive licence to Springer Nature B.V. part of Springer Nature 2021
Abstract
The aim of this research is the synthesis of a novel acidic nanocatalyst using the
layer-by-layer assembly technique. The CoFe2O4@TRIS@sulfated boric acid nano-
particles were easily synthesized and studied as a highly benefcial, recyclable, and
magnetite nanocatalyst for the synthesis of 2-amino-3-cyanopyridine derivatives.
The chemical structure of CoFe2O4@TRIS @sulfated boric acid nanocatalyst was
completely confrmed with diferent techniques like FESEM, Map, EDS, XRD,
TGA/DTG, VSM, and FT-IR analyses. Briefy, the newly synthesized nanocatalyst
ofers some advantages such as simplicity of work-up, highly stable, environmental
friendliness, reusability, excellent yields, and short reaction time.
Supplementary Information The online version contains supplementary material available at (https
://doi.org/10.1007/s11164-020-04369-4).
*
Nourallah Hazeri
n_hazeri@yahoo.com; nhazeri@chem.usb.ac.ir
1
Department of Chemistry, Faculty of Science, University of Sistan and Baluchestan, P.O.
Box 98135-674, Zahedan, Iran
Vol.:(0123456789)
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H. Faroughi Niya et al.
Graphic abstract
Keywords CoFe2O4@TRIS@sulfated boric acid · 2-Amino-3-cyanopyridine
derivatives · Magnetite nanocatalyst · Reusable catalyst
Introduction
The progress of the research on magnetic nanomaterials (MNPs) has opened a novel
perspective in the development of various areas of science such as biomedicine,
magnetic resonance imaging, environmental remediation, catalysis, and high-density
magnetic storage [1–4]. Magnetically separation of materials is a rapid and easy path
for separation and recovery of catalysts from the reaction system. Over the past sev-
eral decades, iron oxide (Fe3O4) MNPs have been widely reported as attractive can-
didates for the manufacture of supported solid catalysts. In this regard, bimetal oxide
magnetic MNPs MFe2O4 (M: Co, Fe, Ni, Zn, Cu, and Mn) have been extremely
studied owing to their meaningful applications. They allow a better tuning of the
nanomaterials’ properties (morphology, size, and monodispersion). Cobalt ferrites
(CoFe2O4) MNPs have been demonstrated to be one of the most versatile magnetic
systems due to their high saturation magnetization, large surface area-to-volume
ratio, strong anisotropy, high coercivity and high mechanical hardness, chemical,
and thermal stability [5, 6]. Nowadays, various magnetic nanocatalysts were pre-
pared for the use in modern synthetic organic chemistry including 6-APA/γ-Fe2O3@
SiO2 [7], DDBSA@MNP [8], CoFe2O4@Pr [9], CoFe2O4@HT@Imine‐CuII [10],
Fe3O4@SiO2‐EDTA‐Pd [11].
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Synthesis, characterization, and application of…
1317
On the other hand, a growing interest has been shown on the production of func-
tionalized magnetic nanoparticles for widespread applications as catalysis over con-
ventional materials especially for the binding of homogeneous organocatalysts. The
coated homogeneous catalysts on solid supports can be used to design the novel het-
erogeneous catalyst systems which have high catalytic activity and high surface area
to increase catalyst coating along with simple separation from the reaction mixture
[12].
Cyanopyridine derivatives are very well known for their wide range of biological
properties such as antitumor [13], antibacterial [14], anti-cardiovascular [15], anti-
infammatory, analgesic, antipyretic [16], IKK-β inhibitors [17], potent inhibitor of
HIV-1 integrase [18], and A2A adenosine receptor antagonists [19].
Considering all the aforementioned points and in continuation of our research to
develop the synthesis of new solid acid catalyst systems for the important organic
conversions [20–23], herein, we have been successfully immobilized TRIS@sul-
fated boric acid onto CoFe2O4 nanostructured and further applied as a novel ef-
cient, and reusable nanocatalyst with excellent catalytic activity for a one-pot four-
component synthesis of 2-amino-3-cyanopyridine from the reaction between aryl
aldehydes 1, malononitrile 2, ketones 3, and ammonium acetate 4 (Scheme 1). It is
noteworthy that this is the frst report on the synthesis of CoFe2O4@TRIS@sulfated
boric acid magnetic nanoparticles that can be reused up to fve times without notable
reduction in its catalytic activity.
Experimental
General
Melting points of pure products were obtained using an Electrothermal melting point
apparatus (type 9100). All applied chemicals were prepared from Merck and Aldrich
companies in high purity. BRUKER DRX 300 MHz in DMSO at 300 Hz and FT-IR-
1
JASCO-460 plus spectrometer were applied to record H NMR and FT-IR spectras
related to known compounds, respectively.
Scheme 1 The synthesis of 2-amino-3-cyanopyridine derivatives in the presence of novel acidic nano-
catalyst
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H. Faroughi Niya et al.
Synthesis of the magnetic CoFe2O4 nanoparticles
The KOH solution (1.0 M) was slowly added to 100 mL of an aqueous solution
containing 1.0 mmol of CoCl2·6H2O and 2.0 mmol of FeCl3·6H2O until the pH
of 11–12 was reached. Thereafter, the prepared solution was refuxed for 3 h at
140 °C under N2 atmosphere and vigorous stirring at 1000 rpm. Lastly, the syn-
thesized CoFe2O4 nanoparticles (black precipitate) were magnetically collected
and purifed several times using ethanol and water and dried at 60 °C.
Synthesis of the magnetic CoFe2O4@TRIS nanoparticles
CoFe2O4@TRIS nanoparticles were synthesized by a simple method. Initially, a
known amount (0.2 g) of the CoFe2O4 MNPs was dispersed in 20 mL of ethanol
using an ultrasonic bath for 15 min. Then, 0.4 g of tris (hydroxymethyl) ami-
nomethane (TRIS, trisamine) was added to the magnetic solution and the result-
ing mixture was refuxed under N2 atmosphere for 24 h at 100 °C. Finally, the
obtained CoFe2O4@TRIS MNPs were separated, washed, and dried at 60 °C for
8 h.
Synthesis of the magnetic CoFe2O4@TRIS–CH2CH2–Cl nanoparticles
0.05 mL of triethylamine and 0.5 mL of dichloroethane were added dropwise to
the mixture of the dispersed CoFe2O4@TRIS nanoparticles (0.2 g) in acetonitrile
(20 mL). Then, the resulting mixture was refuxed under N2 atmosphere for 24 h
at 90 °C. Finally, the obtained CoFe2O4@TRIS–CH2CH2–Cl MNPs were sepa-
rated, washed, and dried at 60 °C for 8 h.
Synthesis of magnetite CoFe2O4@TRIS@boric acid nanoparticles
Initially, 0.5 g of boric acid was added to the mixture of the dispersed CoFe2O4@
TRIS–CH2CH2–Cl (0.2 g) in dry toluene (5 mL). Thereafter, the resulting mix-
ture was refuxed for 1 day under N2 atmosphere. Lastly, the achieved CoFe2O4@
TRIS@boric acid nanoparticles were magnetically collected and purifed several
times using ethanol and water and dried at 60 °C.
Synthesis of magnetite CoFe2O4@TRIS@sulfated boric acid nanoparticles
Firstly, 0.2 g of CoFe2O4@TRIS@boric acid nanoparticles were ultrasonically
dispersed in 5 mL of dry toluene. Next, chlorosulfonic acid (0.5 mL) was added
dropwise and stirred at room temperature for 3 h. Afterward, the synthesized
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Synthesis, characterization, and application of…
1319
CoFe2O4@TRIS@sulfated boric acid MNPs were magnetically collected and
purifed several times using ethanol and water, lastly dried at 80 °C.
General procedure for the four‑component synthesis of 2‑amino‑3‑cyanopyridine
derivatives
CoFe2O4@TRIS@sulfated boric acid nanocatalyst (0.01 g) was entered into a
vial containing a mixture of acetophenone derivatives (1.0 mmol), malononitrile
(1.0 mmol), ammonium acetate (1.5 mmol) as a nitrogen source, and aromatic alde-
hydes (1.0 mmol). The fnal mixture was placed at 90 °C in an oil bath for a cer-
tain time and the reaction was followed by TLC. After completing the reaction, the
mixture was cooled to room temperature. The resulting solid product was dissolved
in hot ethanol, and then the CoFe2O4@TRIS@sulfated boric acid nanocatalyst was
conveniently removed from the solution by an external magnet. Finally, the resulting
solution was cooled to room temperature to the crude product was crystallized to
aford the pure products.
Selected spectra for fve Known products are given below
2‑Amino‑4,6‑bis(4‑chlorophenyl)nicotinonitrile (5a))
FT-IR (KBr): ν 822, (C–H), 1581, 1609 (C=C), 2206 (CN), 2922 (CHaliphatic),
1
3461, 3501 (NH2). H-NMR (300 MHz, DMSO-d6): (δ, ppm): 8.18 (d, 2H, Ar–H)
7.56–7.74 (m, 6H, Ar–H), 7.33 (s, 1H, Ar–H), 7.12 (s, 2H, NH2).
2‑Amino‑4,6‑diphenylnicotinonitrile (5b)
FT-IR (KBr): ν 685, 753, (C–H), 1592, 1516 (C=C), 2198 (CN), 2956, 2919
1
(CHaliphatic), 3063 (CHaromatic), 3471, 3324 (NH). H-NMR (300 MHz, DMSO-d6):
(δ, ppm): 7.50–8.17 (m, 10H, Ar–H), 7.30 (s, 1H, Ar–H), 7.05 (s, 2H, NH2).
2‑Amino‑6‑(4‑chlorophenyl)‑4‑(3,4‑dimethoxyphenyl)nicotinonitrile (5c)
FT-IR (KBr): ν 762, 808 (C–H), 1554, 1516 (C=C), 2205 (CN), 2956, 2997
1
(CHaliphatic), 3225 (CHaromatic), 3369, 3496 (NH). H-NMR (300 MHz, DMSO-d6):
(δ, ppm): 8.19 (d, J=8.1, 2H, Ar–H), 7.58(d, J=8.4, 2H, Ar–H), 7.13–7.34 (m, 4H,
Ar–H), 7.02 (s, 2H, NH2), 3.87 (s, 3H, OCH3), 3.86 (s, 3H, OCH3).
2‑Amino‑6‑(4‑chlorophenyl)‑4‑(3‑nitrophenyl)nicotinonitrile (5d)
FT-IR (KBr): ν 811, 826, 743 (C–H), 1533, 1622 (C=C), 2204 (CN), 3090
(C–Haromatic), 3398, 3498 (NH). 1H-NMR (300 MHz, DMSO-d6): (δ, ppm): 8.54 (s,
1H, Ar–H), 8.41 (d, J=7.2, 1H, Ar–H), 8.20 (m, 3H, Ar–H), 7.88 (t, J=7.2, 1H,
Ar–H), 7.59 (d, J=7.5, 2H, Ar–H), 7.47 (s, 1H, Ar–H), 7.22 (s, 2H, NH2).
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H. Faroughi Niya et al.
2‑Amino‑4‑(4‑chlorophenyl)‑6‑phenyl nicotinonitrile (5e)
FT-IR (KBr): ν 687, 770, 826 (C–H), 1546, 1574 (C=C), 2216 (CN), 3361, 3484
1
(NH). H-NMR (300 MHz, DMSO-d6): (δ, ppm): 8.15 (dd, 2H, Ar–H), 7.49–7.75
(m, 7H, Ar–H), 7.31 (s, 1H, Ar–H), 7.09 (s, 2H, NH2).
Results and discussion
Synthesis and characterization of catalyst
The novel nanocatalyst (CoFe2O4@TRIS@sulfated boric acid) was synthesized
based on the stages shown in Scheme 2. As can be seen, the chlorosulfonic acid
was immobilized on the surface of CoFe2O4 magnetic nanoparticles using trisamine,
dichloroethane, and boric acid.
The synthesized CoFe2O4@TRIS@sulfated boric acid nanocatalyst was charac-
terized by scanning electron microscopy (SEM), X‐ray mapping, energy‐dispersive
X‐ray spectroscopy (EDS), Fourier transform infrared (FT‐IR), diferential thermal
analysis (DTA), thermal gravimetric analysis (TGA), X‐ray Difraction (XRD), and
vibrating sample magnetometer (VSM) techniques.
To confrm the structure of CoFe2O4@TRIS@sulfated boric acid nanoparticles,
FT-IR spectroscopy was initially studied. The typical FT-IR spectra of CoFe2O4 (a),
and CoFe2O4@TRIS@sulfated boric acid (b) are shown in Fig. 1. The adsorption
peak at 618 cm−1 can be assigned to the Fe–O and Co–O in CoFe2O4 MNPs which
shifts to 593 cm−1 after coating with the organic layer (Fig. 1a, b). Also, an intense
absorption band at 3373 cm−1 is related to Co–OH stretching vibration. Furthermore,
the peaks which appeared at 1044–1215 cm−1 correspond to the O=S=O symmetric
Scheme 2 Synthetic pathway for construction of CoFe2O4@TRIS@sulfated boric acid nanocatalyst
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Synthesis, characterization, and application of…
1321
Fig. 1 FT-IR spectra of CoFe2O4 (a) and CoFe2O4@TRIS@sulfated boric acid (b) MNPs
and asymmetric stretching modes of ‐SO3H groups on the CoFe2O4@TRIS@sul-
fated boric acid surface (Fig. 1b). Additionally, the FT‐IR spectrum of CoFe2O4@
TRIS@sulfated boric acid MNPs (Fig. 1b) indicates two bands at 1626 cm−1 and
2923 cm−1 that are clear evidence for existing of the surface-adsorbed water and the
C–H stretching vibrations in the aliphatic groups, respectively.
To earn further data about the synthesized nanoparticles, the morphology, and
size of CoFe2O4, and CoFe2O4@TRIS@sulfated boric acid MNPs were investi-
gated by the FESEM method. As depicted in Fig. 2, both images (Fig. a, a1, b, b1)
show that the prepared nanoparticles have a nearly spherical shape. Moreover, the
CoFe2O4@TRIS@sulfated boric acid MNPs (Fig. 3) have the same sizes (19.20 nm)
in comparison with CoFe2O4 (19.46 nm). Therefore, it can be concluded that the
organic layer coating onto the CoFe2O4 MNPs (TRIS@sulfated boric acid) has no
efect on the morphology and the size of CoFe2O4 MNPs.
EDS and X‐ray mapping techniques were also applied as two practical methods
for generating qualitative data on the distribution of various elemental compositions
in the nanocatalyst (Figs. 4, 5). The EDS spectrum of the CoFe2O4@TRIS@sulfated
boric acid MNPs showed the content of nitrogen (N, 2.74%), carbon (C, 7.71%),
boron (B, 11.84%), oxygen (O, 37.44%), and sulfur (S, 1.38%) signal peaks, which
confrms CoFe2O4@TRIS@sulfated boric acid MNPs were successfully synthesized
(Fig. 4). Furthermore, Fig. 5 shows the elemental map of the nanocatalyst. As can be
seen, the elements of C, N, B, and S are homogeneously distributed and they are dis-
tinguishable in the prepared sample. These results confrm the EDS results (Fig. 5).
TGA technique was used to evaluate the thermal stability of CoFe2O4@
TRIS@sulfated boric acid nanoparticles. As shown in Fig. 6, the TGA curve of
CoFe2O4@TRIS@sulfated boric acid showed three steps of mass loss following
the rise in temperature. The frst one, in the regions 25–150 °C (about 2.54%)
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H. Faroughi Niya et al.
Fig. 2 FESEM images of CoFe2O4 (a, a1) and CoFe2O4@TRIS@sulfated boric acid (b, b1) MNPs
Fig. 3 The size histogram of CoFe2O4 (a) and CoFe2O4@TRIS@sulfated boric acid (b) MNPs
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Synthesis, characterization, and application of…
1323
Fig. 4 EDS spectrum of CoFe2O4 (a) and CoFe2O4@TRIS@sulfated boric acid (b) MNPs
Fig. 5 The X‐ray mapping of CoFe2O4@TRIS@sulfated boric acid MNPs
mainly related to the evaporation of the adsorbed solvent and water from the sur-
face of CoFe2O4@TRIS@sulfated boric acid nanoparticles. The second mass
loss, in the regions 150–330 °C (about 4.21%), is due to the decomposition of
sulfuric acid functional groups (SO3H). According to this mass loss, 42.12 mg
(0.52 mmol) of the SO3H group was loaded on 1 g of CoFe2O4 nanoparticles.
The fnal mass loss, at higher 330 °C (5.25%), is attributed to the decomposition
of other organic moieties on the surface of CoFe2O4@TRIS@sulfated boric acid
nanoparticles, which confrmed the grafting of organic moieties on the surface
of CoFe2O4 MNPs. According to these results, 0.26 mmol of the organic layer
(TRIS@boric acid) was loaded on 1 g of CoFe2O4 nanoparticles. Moreover, the
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H. Faroughi Niya et al.
Fig. 6 TGA and DTG curves of CoFe2O4@TRIS@sulfated boric acid MNPs
DTG curve showed that CoFe2O4@TRIS@sulfated boric acid nanoparticles are
stable below 277.9 °C.
The XRD patterns of CoFe2O4@TRIS@sulfated boric acid nanoparticles are
illustrated in Fig. 7. As depicted in Fig. 7, there were seven difraction peaks at
62.73°, 57.17°, 53.89°, 43.47°, 35.45°, 30.06°, and 18.23° for CoFe2O4 MNPs that
Fig. 7 XRD pattern of CoFe2O4@TRIS@sulfated boric acid MNPs
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Synthesis, characterization, and application of…
1325
were indicated by the respective indicators (4 4 0), (5 1 1), (4 2 2), (4 0 0), (3 1 1), (2
2 0), and (1 1 1) (JCPDS Card No. 03–0864). This pattern is in good agreement with
the standard CoFe2O4 XRD pattern [24, 25]. Furthermore, this pattern shows that
the structure of cobalt ferrite nanoparticles was maintained after modifcation with
the organic layer (TRIS@sulfated boric acid).
Figure 8 shows the magnetization curves for the CoFe2O4 (curve a) and
CoFe2O4@TRIS@sulfated boric acid (curve b) nanoparticles. The saturation mag-
netization (Ms) values of pure CoFe2O4 and CoFe2O4@TRIS@sulfated boric acid
nanoparticles are 28.4, and 23.0 emu/g, respectively. Due to immobilization and
loading of the organic layer on the surface of cobalt ferrite nanoparticles, the Ms
value of CoFe2O4@TRIS@sulfated boric acid nanoparticles is smaller than that
of the CoFe2O4 nanoparticles. The area of the hysteresis loop for the CoFe2O4@
TRIS@sulfated boric acid nanoparticles is bigger than for the CoFe2O4 nanoparti-
cles, so the CoFe2O4@TRIS@sulfated boric acid nanoparticles are the harder mag-
netic material with larger coercivity. These materials are difcult to magnetize and
demagnetize.
Catalytic study
After the characterization of the new nanocatalyst, its catalytic activity for the
synthesis of 2-amino-3-cyanopyridine derivatives was explored (Scheme 1). As
can be seen in Table 1, the optimal reaction conditions were investigated on the
condensation of 4-chloroacetophenone (1.0 mmol), malononitrile (1.0 mmol),
ammonium acetate (1.5 mmol), and 4-chlorobenzaldehyd (1.0 mmol). At frst,
the model reaction was performed in various solvents such as ethanol, water, and
ethanol:water (1:1), as well as solvent-free condition at 70 °C. Results showed
that the kind of solvent had a strong efect on yield and time of reaction in the
present 0.01 g of CoFe2O4@TRIS@sulfated boric acid nanoparticles as a het-
erogeneous catalyst and the best result was obtained in solvent-free condition
(Table1, Entry 4). Then, the diferent amounts of CoFe2O4@TRIS@sulfated
boric acid nanoparticles examined to investigate the efect of them in the model
reaction. As can be seen in Table 1, in the absence of CoFe2O4@TRIS@sulfated
Fig. 8 VSM spectra of CoFe2O4 (a) and CoFe2O4@TRIS@sulfated boric acid (b) MNPs
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H. Faroughi Niya et al.
Table 1 Optimization of reaction conditions for the synthesis of 2-amino-3-cyanopyridines
Entry
Catalyst (g)
Solvent
Temperature
(°C)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
0.01
0.01
0.01
0.01
0.005
0.01
0.015
0.005
0.005
0.005
0.005
No catalyst
EtOH
H2O:EtOH (1:1)
H2O
70
70
70
80
85
95
20
10
10
10
10
5
46
41
34
54
80
62
64
82
73
69
68
45
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
70
100
100
100
90
120
80
10
15
10
70
120
Bold indicates appropriate reaction condition to produce high amount of product
boric acid nanoparticles, the reaction was performed in the lowest yield and high-
est time. The best result showed in 0.005 g of CoFe2O4@TRIS@sulfated boric
acid nanoparticles (Table 1, Entry 5). Finally, the catalytic activity of CoFe2O4@
TRIS@sulfated boric acid nanoparticles was investigated in the diferent reaction
temperatures (from r.t to 120 °C). At the results, the highest yield and the lowest
time were obtained in the reaction at 90 °C (Table 1, Entry 8).
On the basis of optimal condition, the efciency of CoFe2O4@TRIS@sulfated
boric acid nanoparticles as a heterogeneous nanocatalyst was evaluated in the
synthesis of 2-amino-3-cyanopyridine derivatives with a diverse range of elec-
tron-withdrawing and electron-donating aldehydes and the various derivatives of
acetophenone. Based on the summarized results in Table 2, all the synthesized
products were obtained in the highest yield and the lowest time that confrmed the
very high catalytic activity of CoFe2O4@TRIS@sulfated boric acid nanoparticles
for the synthesis of 2-amino-3-cyanopyridine derivatives.
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Synthesis, characterization, and application of…
1327
Table 2 Synthesis of 2-amino-3-cyanopyridine derivatives in the presence of CoFe2O4@THAM@sul-
fated boric acid (0.005 g) as catalyst under solvent-free condition at 90 °C
Entry R1
R2
Product Time (min) Isolated
Yield (%)
M.p (°C) M.p (°C) [Lit.] references
1
2
3
4
5
6
7
8
4-Cl
H
4-Cl
H
5a
5b
5c
5d
5e
5f
10
35
15
10
25
20
15
20
15
15
25
82
73
89
82
80
95
83
63
82
77
67
277–279 280–282 [26]
184–186 183–185 [27]
205–207 207–208 [27]
276–278 277–279 [27]
187–189 186–188 [27]
196–198 198–200 [27]
167–170 170–173 [28]
203–206 205–207 [29]
174–176 173–175 [30]
198–200 201–203 [31]
158–161 160–163 [30]
3.4-diOMe 4-Cl
3-NO2
4-Cl
3-NO2
4-NO2
4-OMe
4-Cl
4-Cl
H
H
H
4-Cl
4-Me 5i
4-Me 5j
4-Me 5k
5g
5h
9
10
11
4-NO2
H
The proposed mechanism for the synthesis of 2-amino-3-cyanopyridines is shown
in Scheme 3. First, CoFe2O4@TRIS@sulfated boric acid nanoparticles as catalyst
via protonation of the carbonyl group of aldehydes and ketones generate conveni-
ent electrophiles. The Knoevenagel condensation between active aldehydes 1 and
malononitrile 3 produces the arylidene malononitrile A. In the other hand, active
acetophenones 2 reacts with ammonium acetate 4 to give enamine B. In the next
step, Michael addition of arylidene malononitrile A to enamine B was formed the
intermediate C. Finally, corresponding products (5a–k) will be generated via subse-
quent stages intramolecular cyclization/isomerization/aromatization.
Recyclability study
Figure 9 displays the results from reusability tests of CoFe2O4@TRIS@sulfated
boric acid nanocatalyst in the model reaction under optimal conditions. For this pur-
pose, the nanocatalyst was magnetically separated from the reaction solution after
every cycle and washed several times with ethanol, dried at 60 °C in an oven, and
reused in the next cycle. As shown in Fig. 9, the nanocatalyst could be stable for fve
cycles and reused without any signifcant loss in its catalytic activity. As a result, the
synthesized nanocatalyst has highly recyclability and stability that make it valuable
in the organic synthesis.
Comparison
Compared with the reported protocols for the synthesis of the 2-amino-3-cyano-
pyridines, as shown in Table 3, the present procedure for the synthesis of 2-amino-
3-cyanopyridine derivatives possesses the advantages of high yield of product, short
reaction time that afrmed the high catalytic activity of the CoFe2O4@TRIS@
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H. Faroughi Niya et al.
Scheme 3 The proposed mechanism for the synthesis of 2-amino-3-cyanopyridines
Fig. 9 Reusability tests of CoFe2O4@TRIS@sulfated boric acid nanocatalyst in the synthesis of model
reaction (5a)
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Synthesis, characterization, and application of…
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Table 3 Comparison of the efciency of CoFe2O4@TRIS@sulfated boric acid nanocatalyst with other
catalysts in literature
Entry Catalyst
Amount of
catalyst
Condition
Time
Yield (%) References
1
2
Nanomagnetic
(10 mg)
Solvent-free,
80 °C
10–25 min 81–95
50–80 min 68–91
[25]
[31]
catalyst bearing
morpholine tags
Nano-Fe3O4
(30 mg)
Solvent-free,
80 °C
3
4
Yb (PFO)3
Iron (III) phos-
phate
(2.5 mol%)
(10 mol%)
EtOH, refux
ETOH, refux
1.5 h
2–4.5 h
68–93
65–93
[32]
[33]
5
6
7
PDMAF-MNPs
Graphene oxide
(40 mg)
(10 mol%)
EtOH, refux
H2O, 80 °C
1–3.5 h
5 h
10–35 min 63–95
74–93
75–97
[34]
[35]
This work
CoFe2O4@TRIS@ (5 mg)
Solvent-free,
sulfated boric
90 °C
acid
sulfated boric acid nanocatalyst as a novel, green, and heterogeneous magnetically
reusable nanocatalyst.
Conclusions
In conclusion, this study presents a new and highly profcient CoFe2O4@TRIS@sul-
fated boric acid nanoparticle catalysed procedure for easy access to 2-amino-3-cyan-
opyridines from the one-pot four-component reaction between aryl aldehydes, malo-
nonitrile, ketones, and ammonium acetate in a green solvent. FT-IR, XRD, MAP,
EDS, SEM, VSM, and TG/DTG analysis results can be fully shown immobilization
of TRIS@sulfated boric acid onto CoFe2O4 nanostructured. Easy handling of the
catalyst, high recyclability, environmental acceptability, and use of commercially
available cheap starting materials are the other privilege features of this research.
Acknowledgements The authors would like to thank the Research Council of University of Sistan and
Baluchestan because of its fnancial supporting.
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