Sulfonyl-bridged (copper-immobilized nickel ferrite) with activated montmorillonite, [(NiFe2O4@Cu)SO2(MMT)]: a new class of magnetically separable clay nanocomposite systems towards Hantzsch synthesis of coumarin-based 1,4

Article abstract of DOI:10.1039/c9ra00177h

In this study, the synthesis of a new class of magnetic clay-based nanocomposites by bridging of sulfonyl groups between copper-immobilized nickel ferrite (NiFe₂O₄@Cu) and activated montmorillonite is described. Synthesis of the clay

Full text of DOI:10.1039/c9ra00177h

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Sulfonyl-bridged (copper-immobilized nickel
ferrite) with activated montmorillonite,
[(NiFe2O4@Cu)SO2(MMT)]: a new class of
magnetically separable clay nanocomposite
systems towards Hantzsch synthesis of coumarin-
based 1,4-dihydropyridines†
Cite this: RSC Adv., 2019, 9, 8002
*
Behzad Zeynizadeh
and Soleiman Rahmani
In this study, the synthesis of a new class of magnetic clay-based nanocomposites by bridging of sulfonyl
groups between copper-immobilized nickel ferrite (NiFe2O4@Cu) and activated montmorillonite is
described. Synthesis of the clay nanocatalyst was carried out via the activation of montmorillonite by
ClSO3H to afford sulfonated montmorillonite. The modified montmorillonite was then reacted with
copper-layered nickel ferrite to afford the magnetic clay nanocomposite [(NiFe2O4@Cu)SO2(MMT)]. Next,
the characterization of porous materials was carried out using scanning electron microscopy, energy-
dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer–
Emmett–Teller and vibrating sample magnetometer analyses. The obtained results showed that the clay
nanocomposite containing a sulfonyl-bridge has a large surface area and magnetic properties versus the
prepared one without the sulfonyl groups as (NiFe2O4@Cu)(MMT). The nanostructured clay had excellent
catalytic activity towards the Hantzsch synthesis of coumarin-based 1,4-dihydropyridines via one-pot
and three-component condensation of 4-hydroxycoumarin, aromatic aldehydes and ammonia. All
reactions were carried out in water as a green and economic green solvent within 10–45 min to affords
1,4-DHPs in high to excellent yields. Reusability of the clay nanocomposite was investigated for six
consecutive cycles without significant loss of catalytic activity. Based on this study, therefore, sulfonated
montmorillonite could be considered an excellent support for the immobilization of magnetic materials.
Received 8th January 2019
Accepted 1st March 2019
DOI: 10.1039/c9ra00177h
rsc.li/rsc-advances
transition-metal elements with magnetic materials to produce
new heterogeneous and magnetically reusable nanocomposite
1. Introduction
systems has been widely studied and applied towards the
promotion of organic transformations.12 The prepared nano-
composites because of the huge surface area of nanoparticles
and formation of numerous acid/base centers dramatically
accelerate the rate of reactions. This type of immobilization
makes the efficient and easy separation of the catalyst system
from the reaction mixture using an external magnetic eld. In
spite of this, occasionally, aer the immobilization of transi-
tion metals and because of their high surface energies, the
agglomeration of nanoparticles occurs leading to a decrease of
effective surface area as well catalytic activity of the prepared
nanocatalyst system. In this subject, some strategies have
been served to overcome the agglomeration and preserve the
original characteristic of nanoparticles. Stabilization of
magnetic nanoparticles (MNPs) on porous materials such as
silica,13,14 activated montmorillonite,15,16 carbon materials,17–19
zeolites20 and polymer matrix21,22 is one of the straightforward
methods.
Nowadays, the immobilization of homogeneous catalysts on
the surface of solid supports giving heterogeneous and more
stable catalyst systems has gained considerable interest from
academic and industrial points of view.1–4 Accordingly,
magnetic spinel ferrites (MFe2O4; M ¼ Fe, Co, Ni, Mn and Zn)
have widespread applications in drug delivery, ferrouids,
pigments, microwave devices, gas sensors and catalysis and
have also attracted the attention of scientists.5–8 Among the
spinel ferrites, NiFe2O4 is more desirable. This magnetic
material brings several advantages in terms of high saturation
magnetization, physical and electrical properties, excellent
chemical stability, good mechanical hardness and unique
magnetic structure.9–11 In addition, the combination system of
Faculty of Chemistry, Urmia University, Urmia 5756151818, Iran. E-mail: s.rahmani@
urmia.ac.ir
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c9ra00177h
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Montmorillonite (MMT) as aluminosilicate micro/ sulfonic acid,60 silica gel or acidic alumina/microwave61 and
mesoporous material has been widely used in a number of lactic acid62 were successfully utilized for synthesis of coumarin-
industrial settings and solid supports. This micro/mesoporous based 1,4-DHPs.
material has several advantages in terms of high surface area,
In line with the outlined strategies and continuation of our
swelling, high cation exchange capacity, Brønsted and Lewis research program towards synthesis of novel heterogeneous
acidity, ease of handling, non-corrosiveness and sheet-like and magnetically nanocomposite systems,36,37,63–65 herein, we
structure.23 Montmorillonite has been also used as a suitable wish to introduce sulfonyl-bridged (copper-immobilized nickel
matrix for encapsulation of anisotropic magnetic nanoparticles ferrite) with activated montmorillonite, [(NiFe2O4@Cu)
by their trapping in interlamellar spaces.15,16,24 The literature SO2(MMT): NFCSM] (Fig. 1) representing a new class of
review shows that through the acid activation of montmoril- magnetically clay nanocomposite systems. The synthesis was
lonite and exfoliation of adjacent sheets to small segments, the carried out with the aims of (i) increasing the catalytic activity of
surface properties of montmorillonite such as porosity and copper-layered nickel ferrite, (ii) preventing the agglomeration
specic surface area of the clay mineral could be greatly of nanoparticles as well as covalently bonding of NiFe2O4@Cu
improved.25,26 In this context, Xu prepared montmorillonite- on the surface of the clay mineral, and (iii) improving the
based magnetic nanoparticles in water using cetylpyridinium stability and shelf-life capability of the nanocatalyst. The
chloride (CPC) as intercalator.27 Galindo-Gonzalez synthesized examinations resulted that the prepared clay composite system
magnetite-supported montmorillonite clay particles via the exhibited a perfect catalytic activity towards Hantzsch synthesis
electrostatic attraction between Fe3O4 (positive charge) and of coumarin-based 1,4-dihydropyridines by one-pot and three-
MMT layer (negative charge) in collaboration with the negative component condensation reaction of 4-hydroxycoumarin,
charge repulsion of MMT layers.28 Kalantari prepared size- aromatic aldehydes and ammonia in water as a green and
controlled synthesis of Fe3O4 nanoparticles in the layers of economic solvent (Scheme 1).
montmorillonite using chemical co-precipitation method.29 In
this area, the synthesis of g-iron oxide nanoparticles in the
layers of montmorillonite has been also reported.30
2. Experimental
Recently, the application of Cu nanoparticles because of the
cheapness, electrical, antifungal, antibacterial properties as
well as catalyst for functional group transformations has been
considered as one of the most useful transition-metal
elements.31–35 A literature review shows that Cu NPs could be
used lonely in the reactions,35 however, the immobilization
form of copper nanoparticles on nickel ferrite (NiFe2O4@Cu)36
or magnetite (Fe3O4@Cu)37 was exhibited the better
performances.
2.1. Instruments and reagents
All reagents and substrates were purchased from chemical
companies in high purity and they were used without further
1
purication. H, 13C NMR and FT-IR spectra were recorded on
Bruker Avance 300 MHz and Thermo Nicolet Nexus 670 spec-
trometers, respectively. Melting points were measured in open
capillary tubes and were uncorrected. TLC was applied for the
purity determination of substrates, products and reaction
monitoring over silica gel 60 GF254 aluminum sheet. Magnetic
properties of the samples were measured by vibrating sample
magnetometer (VSM, Meghnatis Daghigh Caviar Co., Iran)
under magnetic elds up to 20 kOe. Morphology of the nano-
particles was determined by capturing SEM images using
FESEM-TESCAN MIRA3 instrument. The chemical composition
During the last decades, coumarin-based compounds have
been considered as prominent biological active materials and
therefore attracted the attention of many scientists. Among the
coumarin materials, biscoumarins also showed the signicant
pharmacological activities such as anti-HIV, anticancer, anti-
fungal, antithrombotic, anti-oxidative, anti-microbial and anti-
coagulant38–41 as well as cytotoxic, enzyme42,43 and urease
inhibitor activities.44 In this context, numerous reports repre-
sented the synthetic importance of biscoumarin materials in
the presence of various reagents/catalysts.45,46 Across the various
protocols, using MCRs (multi-components reactions) is one of
the straightforward methods for synthesis of this valuable
materials. Accordingly, 1,4-dihydropyridines (1,4-DHPs) are
also too important materials and received much attention
owing to their broad spectrum of biological activities such as
anti-cancer, vasodilator, cytotoxic, antidiabetic, antitumor,
antimicrobial, antialzheimer and hepatoprotective agents.47–54
In addition, 1,4-DHPs are also served as L-type Ca2+ channel
blockers to treat hypertension and angina diseases.55–58 Due
course, it would be very interesting that assembling of two
mentioned compartments (biscoumarin and 1,4-DHP struc-
tures) on a molecule is led to more and new properties attrib-
uting to the mentioned therapeutic activities. The literature
review shows that using Fe3O4@SiO2,59 guanidinium-based Fig. 1 Magnetic nanoparticles of (NiFe2O4@Cu)SO2(MMT).
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Scheme 1 Hantzsch synthesis of coumarin-based 1,4-DHPs catalyzed by (NiFe2O4@Cu)SO2(MMT) MNPs.
of nanoparticles was determined by EDX analysis. X-ray
diffraction (XRD) measurements were carried out on X'PertPro
Panalytical diffractometer in 40 kV and 30 mA with a CuKa
2.5. Preparation of sulfonated sodium montmorillonite
(Na+-MMT-SO3H)
In a round-bottom ask, a suspension of Na+-montmorillonite
(2.5 g) in CHCl3 (5 mL) and in an ice bath (0–5 ꢀC) was prepared.
Through a dropping funnel, ClSO3H (0.5 g, 9 mmol) was added
in a drop wise manner within 30 min. Aer that, the mixture
was stirred for additional 30 min for complete releasing of HCl.
The mixture was then ltered and the solid residue was washed
with MeOH (20 mL) and dried at room temperature to obtain
Na+-MMT-SO3H as a white powder.
˚
radiation (l ¼ 1.5418 A). The specic surface area and total pore
volume of the samples were determined using Brunauer–
Emmett–Teller method on Belsorp-Max, Japan. The pore size
distributions were calculated through the Barrett–Joyner–
Halenda method.
2.2. Synthesis of NiFe2O4 MNPs
A desire amount of Ni(OAc)2$4H2O, Fe(NO3)3$9H2O, NaOH and
NaCl in a molar ratio of 1 : 2 : 8 : 2, respectively, was grinded in
a mortar for 50 min. The reaction was exothermic and accom-
panied with the release of heat. It is notable that through the
grinding of the mixture, the synthesis of NiFe2O4 was initiated.
Aer completion of the reaction, the mixture was then washed
several times with deionized water to remove NaCl and other
contaminants. The obtained solid material was then dried at
80 ꢀC for 10 h. The resulting product was calcinated at 900 ꢀC for
2 h to obtain magnetically nanoparticles of NiFe2O4.
2.6. Synthesis of (NiFe2O4@Cu)SO2(MMT) MNPs
An individual suspension of Na+-MMT-SO3H (3 g) in deionized
water (200 mL, pH value of the resulting suspension was
adjusted to ꢁ5 by 3 wt% HCl) and NiFe2O4@Cu (1.5 g) in
deionized water (200 mL, pH value of the resulting suspension
was adjusted to ꢁ9 by 3 wt% ammonia) was irradiated by
ultrasound for 30 min. Two suspensions were combined
together followed by stirring for 2 h. The prepared nano-
composite of (NiFe2O4@Cu)SO2(MMT) were separated by
magnetic decantation and then washed with EtOH. Drying
under vacuum afforded the nal nanocomposite in a feeding
weight ratio of 2 : 1 for Na+-MMT-SO3H/NiFe2O4@Cu,
respectively.
2.3. Synthesis of NiFe2O4@Cu MNPs
In a round-bottom ask containing a solution of CuCl2$2H2O
(0.25 g) in deionized water (30 mL), magnetic nanoparticles of
NiFe2O4 (1 g) was added. The mixture was stirred for 30 min at
room temperature followed with the addition of NaBH4 (0.11 g
in 30 mL H2O) within 20 min in drop wise manner (N2 atmo-
sphere). The mixture was continued to stirring for 2 h. The
precipitated nanoparticles of NiFe2O4@Cu were magnetically
separated and then washed with deionized water. Drying under
vacuum affords NiFe2O4@Cu MNPs.36
2.7. Synthesis of (NiFe2O4@Cu)(MMT) MNPs
An individual suspension of Na+-MMT (3 g) in deionized water
(200 mL, pH value of the resulting suspension was adjusted to
ꢁ5 by 3 wt% HCl) and NiFe2O4@Cu (1.5 g) in deionized water
(200 mL, pH value of the resulting suspension was adjusted to
ꢁ9 by 3 wt% ammonia) was irradiated by ultrasound for 30 min.
Two suspensions were combined together followed by stirring
for 2 h. The prepared nanocomposite of (NiFe2O4@Cu)(MMT)
were separated by magnetic decantation and then washed with
EtOH. Drying under air atmosphere affords (NiFe2O4@-
Cu)(MMT) MNPs.
2.4. Preparation of homoionic Na+-montmorillonite (Na+-
MMT)
In a beaker (250 mL) containing a solution of NaCl (200 mL, 2
M), montmorillonite K10 (MMT-K10) (5 g) was added and the
mixture was stirred vigorously for 78 h at room temperature.
Aer that, mesoporous particles of homoionic Na+-montmoril-
lonite were separated by centrifugation. The particles were
2.8. Synthesis of (NiFe2O4@Cu)(MMT-SO3H) MNPs
washed with deionized water followed by drying in an oven at The prepared (NiFe2O4@Cu)(MMT) (3 g) was added to a solu-
50 C for 12 h.66,67
tion of ClSO3H (0.5 g, 9 mmol) in CHCl3 (5 mL) (0–5 ꢀC) within
ꢀ
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30 min. Aer that, the mixture was stirred for 30 min for d (ppm) 3.37 (s, 3H, OMe), 6.17 (s, 1H, CHbenzylic), 6.45–6.67 (m,
complete releasing of HCl. The mixture was then ltered and 3H, ArH), 7.05–7.33 (m, 5H, ArH and NH), 7.42–7.58 (m, 2H, ArH),
the solid residue was washed with MeOH and dried at room 7.81 (d, 2H, ArH), 8.51 (bs, 1H, OH); 13C NMR (75 MHz, DMSO-
temperature to obtain (NiFe2O4@Cu)(MMT-SO3H) MNPs.
d6) d (ppm) 35.9, 56.1, 104.2, 112.2, 115.2, 119.7, 120.4, 123.3,
131.2, 133.6, 144.5, 147.4, 152.9, 165, 168.1.
2.10.6. 7-(3-Methoxyphenyl)-7,14-dihydro-6H,8H-dichromeno
[4,3-b:30,40-e]pyridine-6,8-dione (4f). FT-IR (KBr, n cmꢂ1): 3421,
3073, 3066, 1645, 1603, 1523, 1417, 1268, 1205, 1043, 973, 897, 761;
1H NMR (300 MHz, DMSO-d6) d (ppm) 3.72 (s, 3H, OMe), 5.45 (s,
1H, CHbenzylic), 6.82 (s, 1H, ArH), 7.05–7.35 (m, 7H, ArH and NH),
2.9. A general procedure for Hantzsch synthesis of coumarin-
based 1,4-DHPs catalyzed by (NiFe2O4@Cu)SO2(MMT) MNPs
In a round-bottom ask (15 mL), a mixture of 4-hydrox-
ycoumarin (2 mmol), aromatic aldehyde (1 mmol) and
ammonia (2 mmol) in water (2 mL) was prepared. Magnetically
nanoparticles of (NiFe2O4@Cu)SO2(MMT) (10 mg) was then
added and the resulting mixture was stirred at 60 ꢀC for an
appropriate time (Table 6). Aer completion of the reaction
(monitored with by TLC), DMSO (2 mL) was added to the
reaction mixture: the catalyst was insoluble in DMSO and easily
separated by an external magnetic eld. Aer that, a saturated
solution of NaCl was added. In a meanwhile of the addition, 1,4-
DHP was precipitated, ltered and washed with n-hexane.
7.35–7.60 (m, 1H, ArH), 7.83 (bs, 1H, ArH), 8.32 (bs, 3H, ArH); 13
C
NMR (75 MHz, DMSO-d6) d (ppm) 35.7, 94.1, 103.7, 109.7, 113.7,
119.7, 122.4, 123, 141.9, 144.5, 152.9, 159.5, 165, 168.2.
2.10.7. 7-(p-Tolyl)-7,14-dihydro-6H,8H-dichromeno[4,3-b:30,40-
e]pyridine-6,8-dione (4h). FT-IR (KBr, n cmꢂ1): 3433, 2927, 1671,
1613, 1412, 1189, 1039, 763; 1H NMR (300 MHz, DMSO-d6) d (ppm)
2.19 (s, 3H, Me), 6.20 (s, 1H, CHbenzylic), 6.94 (s, 4H, ArH), 7.18–7.25
(m, 5H, ArH and NH), 7.41–7.55 (m, 2H, ArH), 7.78 (d, 2H, ArH); 13
C
NMR (75 MHz, DMSO-d6) d (ppm) 22.2, 36.1, 103.9, 120.4, 124.5,
128.7, 131.2, 133.9, 152.9, 165, 168.1.
2.10.8. 7-(4-Nitrophenyl)-7,14-dihydro-6H,8H-dichromeno
[4,3-b:30,40-e]pyridine-6,8-dione (4j). FT-IR (KBr, n cmꢂ1): 3463,
2.10. Selected spectral data
2.10.1. 7-Phenyl-7,14-dihydro-6H,8H-dichromeno[4,3-b:30,40-
e]pyridine-6,8-dione (4a). FT-IR (KBr, n cmꢂ1): 3435, 3196, 3049, 3202, 3067, 2912, 1667, 1608, 1534, 1513, 1339, 1341, 1181,
1659, 1610, 1540, 1406, 1266, 1185, 1108, 1039, 901, 755; 1H NMR 1109, 1043, 942, 850, 762; 1H NMR (300 MHz, DMSO-d6) d (ppm)
(300 MHz, DMSO-d6) d (ppm) 6.30 (s, 1H, CHbenzylic), 7.01–7.38 (m, 6.33 (s, 1H, CHbenzylic), 7.15–7.30 (m, 5H, ArH and NH), 7.30–
10H, ArH and NH), 7.45–7.55 (m, 2H, ArH), 7.82 (d, 2H, ArH); 13
C
7.40 (m, 2H, ArH), 7.45–7.61 (m, 2H, ArH), 7.75–7.85 (m, 2H,
NMR (75 MHz, DMSO-d6) d (ppm) 36.5, 103.7, 115.9, 120.1, 123.5, ArH), 8.01–8.13 (m, 2H, ArH); 13C NMR (75 MHz, DMSO–d6)
124.5, 125.4, 127, 128.2, 131.5, 142.5, 152.8, 165.3, 168.3.
d (ppm) 37.1, 103.2, 116, 120.1, 122.8, 124.2, 125.7, 131.6,
2.10.2. 7-(2-Chlorophenyl)-7,14-dihydro-6H,8H-dichromeno 145.7, 151.9, 153, 164.8, 168.4.
[4,3-b:30,40-e]pyridine-6,8-dione (4b). FTIR (KBr, n cmꢂ1): 3418,
2.10.9. 7-(3-Nitrophenyl)-7,14-dihydro-6H,8H-dichromeno
3182, 1769, 1604, 1489, 1406, 1188, 1041, 944, 758; 1H NMR (300 [4,3-b:30,40-e]pyridine-6,8-dione (4k). FT-IR (KBr, n cmꢂ1): 3437,
MHz, DMSO) d 6.15 (s, 1H, CHbenzylic), 7.15–7.40 (m, 8H, ArH and 3213, 3066, 1611, 1530, 1415, 1345, 1183, 1045, 850, 758; 1H
NH), 7.40–7.60 (m, 3H, ArH), 7.80 (d, 2H, ArH); 13C NMR (75 MHz, NMR (300 MHz, DMSO-d6) d (ppm) 6.34 (s, 1H, CHbenzylic), 7.21–
DMSO) d 36.5, 103.2, 115.2, 115.9, 120.3, 123.4, 124.4, 127.4, 7.82 (m, 11H, ArH and NH), 7.88 (s, 1H, ArH), 7.97 (s, 1H, ArH);
130.88, 131.2, 133.1, 140.8, 152.8, 164.3, 164.3, 168.1.
2.10.3. 7-(4-Chlorophenyl)-7,14-dihydro-6H,8H-dichromeno 123.5, 123.5, 129.8, 131.7, 145.6, 153, 164.8, 168.4.
[4,3-b:30,40-e]pyridine-6,8-dione (4c). FT-IR (KBr, n cmꢂ1): 3183,
2.10.10. 7-(4-Chloro-3-nitrophenyl)-7,14-dihydro-6H,8H-
13C NMR (75 MHz, DMSO-d6) d (ppm) 36.7, 103, 116, 120.1,
3046, 2594, 1611, 1540, 1407, 1186, 1099, 1029, 903, 757; 1H NMR dichromeno[4,3-b:30,40-e]pyridine-6,8-dione (4l). FT-IR (KBr,
(300 MHz, DMSO-d6) d (ppm) 6.23 (s, 1H, CHbenzylic), 6.93 (s, 1H, n cmꢂ1): 3429, 3100, 2900, 1664, 1608, 1537, 1406, 1352, 1188,
NH), 7.05–7.18 (m, 2H, ArH), 7.18–7.35 (m, 6H, ArH), 7.45–7.60 1042, 834, 764; 1H NMR (300 MHz, DMSO-d6) d (ppm) 6.29 (s, 1H,
(m, 2H, ArH), 7.80 (d, 2H, ArH); 13C NMR (75 MHz, DMSO-d6) CHbenzylic), 7.15–7.30 (m, 5H, ArH and NH), 7.35–7.45 (m, 1H,
d (ppm) 36.2, 103.5, 115.9, 120.2, 123.3, 124.5, 128, 128.9, ArH), 7.45–7.62 (m, 3H, ArH), 7.68 (s, 1H, ArH), 7.75–7.85 (m, 2H,
129.8, 131.4, 166.8.
ArH); 13C NMR (75 MHz, DMSO-d6) d (ppm) 36.4, 102.8, 116,
2.10.4. 7-(3-Hydroxy-4-methoxyphenyl)-7,14-dihydro-6H,8H- 120.1, 123.5, 124.5, 131.4, 132.8, 144.6, 153, 164.7, 168.4.
dichromeno[4,3-b:30,40-e]pyridine-6,8-dione (4d). FT-IR (KBr,
n cmꢂ1): 3411, 3142, 3047, 2927, 2851, 1661, 1611, 1562, 1510,
3. Results and discussion
3.1. Synthesis and characterization of (NiFe2O4@Cu)
1406, 1270, 1098, 1028, 906, 760; 1H NMR (300 MHz, DMSO-d6)
d (ppm) 3.68 (s, 3H, OMe), 6.14 (s, 1H, CHbenzylic), 6.42–6.55 (m,
1H, ArH), 6.55–6.65 (m, 1H, ArH), 6.65–6.75 (m, 1H, ArH), 7.15–
SO2(MMT) MNPs
7.27 (m, 5H, ArH and NH), 7.41–7.58 (m, 2H, ArH), 7.82 (d, 2H, Synthesis of the magnetic sulfonyl-bridged clay composite,
ArH), 8.60 (bs, 1H, OH); 13C NMR (75 MHz, DMSO-d6) d (ppm) NFCSM, was carried out through a ve-step procedure: (i)
35.1, 54.1, 104, 112.4, 114.8, 115.8, 117.6, 120.4, 131.3, 135.2, preparation of NiFe2O4 MNPs via a solid state grinding of
145.5, 152.9, 165.2, 168.2.
Ni(OAc)2$4H2O and Fe(NO3)3$9H2O in the presence of NaOH,
2.10.5. 7-(4-Hydroxy-3-methoxyphenyl)-7,14-dihydro-6H,8H- (ii) mixing of NiFe2O4 MNPs with an aqueous solution of
dichromeno[4,3-b:30,40-e]pyridine-6,8-dione (4e). FT-IR (KBr, CuCl2$2H2O, (iii) reduction of Cu2+ ions to Cu0 with NaBH4 to
n cmꢂ1): 3410, 3218, 3069, 2931, 1651, 1607, 1514, 1448, 1403, afford NiFe2O4@Cu MNPs, (iv) preparation of acid-activated
1277, 1185, 1114, 1034, 760; 1H NMR (300 MHz, DMSO-d6) sodium montmorillonite (Na+-MMT-SO3H) by stirring of
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Fig. 2 Preparing of (NiFe2O4@Cu)SO2(MMT) MNPs.
homoionic Na+-exchanged montmorillonite with ClSO3H, and
It was also reported that the yield and magnetic property of
nally (v) preparation of (NiFe2O4@Cu)SO2(MMT) via the reac- metal oxides could be inuenced effectively by pH value.26
tion of individual sonicated-suspension of NiFe2O4@Cu and Consequently, we investigated the inuence of pH on the yield
Na+-MMT-SO3H (Fig. 2).
Table 1 Dispersity of Na+-MMT, NiFe2O4@Cu and Na+-MMT-SO3H in
different solvents
It is notable that in the preparation of sulfonyl-bridged clay
composite system (NFCSM), the selection of proper solvent and
pH value of the suspensions is crucial. In this context, the
Sample
H2O
EtOH 90%
Acetone
DMF
CHCl3
examinations resulted that dispersity of Na+-MMT, NiFe2O4@-
Cu and Na+-MMT-SO3H in H2O is higher than the other solvents
and therefore it was selected as the solvent of choice to carry out
the synthetic reaction (Table 1).
Na+-MMT
Well
Well
Well
Medium
Medium
Well
Well
Weak
Well
Weak
Weak
Weak
Weak
Weak
Weak
NiFe2O4@Cu
Na+-MMT-SO3H
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Table 2 The influence of pH on the yield and magnetic property of
(NiFe2O4@Cu)SO2(MMT) MNPs
pH value of
Ms value of
(NFCSM)
Na+-MMT- pH value of
pH value of Yield of
SO3H (A)
NiFe2O4@Cu (B) mixing A + B (NFCSM)a (%) (emu gꢂ1
)
3
5
6
12
9
8
10
8
7
90
95
87
1.75
3.03
2.8
a
+
Yield ¼ [Wcomposite/(WNa -MMT-SO H + WNiFe O @Cu)] ꢃ 100.
3
2
4
and magnetic property of sulfonyl-bridged clay composite
(NFCSM). The results of this investigation are illustrated in
Table 2. The table shows that accessing high magnetic property
and yield of NFCSM required pH value of 9 and 5 for suspen-
sions of NiFe2O4@Cu and Na+-MMT-SO3H, respectively.
Adjusting of pH values was carried out by adding the proper
amounts of HCl or ammonia to the suspensions.
3.2. Characterization of the clay-based nanocomposites
3.2.1. XRD analysis. Wide-angle XRD spectra of MMT-K10,
Na+-MMT, Na+-MMT-SO3H, (NiFe2O4@Cu)SO2(MMT), (NiFe2-
O4@Cu)(MMT) and (NiFe2O4@Cu)(MMT-SO3H) are shown in
Fig. 3. In diffractogram of montmorillonite K10 (pattern a) and
along with hkl and two dimensional hk reections, a number of
sharp peaks attributing to some impurities (quartz, cristobalite
and feldspar) is observable. As well, the pattern b shows that
during the homoionization of MMT-K10 with NaCl and diffu-
sion of Na+ ions into interlamellar spaces of montmorillonite
(through ion-exchange ability), the signal-intensity of Na+-MMT
was raised.67 In contrast and in the case of Na+-MMT-SO3H
(pattern c), due covalently bonding of sulfonic acid moiety
instead of Na+ ions, the signal-intensity was downed. According
to the standard diffraction pattern of NiFe2O4 (JCPDS 44-1485),
diffractogram of (NiFe2O4@Cu) (pattern d) shows that during
the immobilization of copper on NiFe2O4, the cubic spinel
structure of NiFe2O4 was remained intact. Moreover, comparing
the XRD pattern of (NiFe2O4@Cu) (pattern d), [(NiFe2O4@-
Cu)(MMT)] (pattern e) and [(NiFe2O4@Cu)SO2(MMT)] (pattern f)
represents that both of the prepared [(NiFe2O4@Cu)(MMT)] and
[(NiFe2O4@Cu)SO2(MMT)] include the characteristic peaks of
NiFe2O4@Cu MNPs. This is showing that magnetically nano-
particle of NiFe2O4@Cu was highly dispersed on the surface of
clay matrix and missed its some crystallinity character.68,69
Similarly, the same discussion is given for montmorillonite
moiety through the graing of NiFe2O4@Cu MNPs. It is
meaning that by combining NiFe2O4@Cu moiety with mont-
morillonite, no structural change was occurred in the clay
matrix. In addition, XRD pattern of (NiFe2O4@Cu)(MMT-SO3H)
(pattern g) clearly shows the characteristic signals of NiFe2-
O4@Cu MNPs.
Fig. 3 Wide-angle XRD patterns of (a) MMT-K10, (b) Na+-MMT, (c)
Na+-MMT-SO3H, (d) NiFe2O4@Cu, (e) (NiFe2O4@Cu)SO2(MMT), (f)
(NiFe2O4@Cu)(MMT) and (g) (NiFe2O4@Cu)(MMT-SO3H).
case of (NiFe2O4@Cu)SO2(MMT), the SEM images (Fig. 4d–f)
represent that aer the sulfonation process of montmorillonite
K10 and graing of NiFe2O4@Cu MNPs, large akes of MMT-
K10 were exfoliated to small segments with semi-at
surfaces.70,71 The images also exhibit that magnetically nano-
particles of NiFe2O4@Cu MNPs with average size of 16 nm were
immobilized on the surface of clay matrix. Accordingly, EDX
analyses exhibited the presence of Ni, Fe and Cu elements in
(NiFe2O4@Cu)SO2(MMT) (Fig. 4g) as well as the elements of
MMT-K10 (Fig. 4c).
3.2.3. N2 adsorption–desorption study. The N2 adsorption–
desorption isotherm of (NiFe2O4@Cu)SO2(MMT), (NiFe2O4@-
Cu)(MMT) and (NiFe2O4@Cu)(MMT-SO3H) are illustrated in
Fig. 5. Investigation of the results shows that the shape of
isotherms in (NiFe2O4@Cu)SO2(MMT) and (NiFe2O4@-
Cu)(MMT-SO3H) MNPs are similar and according to BDDT
classication is closer to isotherm of Langmuir (isotherm type
I). This type of isotherms is a characteristic of mesoporous solid
3.2.2. SEM analysis. Scanning electron microscopy (SEM) is
a useful technique to elucidate the porosity and surface
morphology of materials. In this area, SEM images of mont-
morillonite K10 (Fig. 4a and b) show that the clay mineral is
multilayer material with parallel arrays of large akes. In the
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Fig. 4 SEM images and EDX spectra of MMT-K10 (a–c) and (NiFe2O4@Cu)SO2(MMT) (d–g).
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montmorillonite. The bands at 1054 cmꢂ1 and 800 cmꢂ1 can be
assigned to stretching vibration of Si–O. Moreover, the bands at
522 cmꢂ1 and 464 cmꢂ1 are also attributed to the vibration of
Al–O and Si–O bonds, respectively.75–77 FT-IR spectrum of MMT-
SO3H (Fig. 6b) shows that the absorption bands of OH groups in
montmorillonite and SO3H were overlapped and produced
a wide absorption signal at 3000–3333 cmꢂ1. Moreover, the
broad band at 1048 cmꢂ1 is also attributed to overlap vibrating
bonds of S–O and Si–O in the composite system. In the case of
(NiFe2O4@Cu)SO2(MMT) (Fig. 6d), it is seen that through the
immobilization of (NiFe2O4@Cu) moiety on sulfonated mont-
morillonite, the intensity of absorption band at 3400 cmꢂ1 was
downed. This is exactly demonstrated the interaction of
hydroxyl groups of MMT-SO3H and NiFe2O4@Cu moieties.
3.2.5. VSM analysis. Magnetic property of NiFe2O4, NiFe2-
O4@Cu, (NiFe2O4@Cu)SO2(MMT), (NiFe2O4@Cu)(MMT-SO3H)
and (NiFe2O4@Cu)(MMT) was investigated using vibrating
sample magnetometer analysis in an applied magnetic eld up
to 20 kOe (Fig. 7). All samples exhibited a characteristic
magnetic hysteresis loop of so magnetic materials.78 The
saturation magnetization (Ms) value of NiFe2O4 (curve a) and
NiFe2O4@Cu (curve b) was found to be 37.718 emu gꢂ1 and
34.584 emu gꢂ1, respectively. This shows that magnetic property
of NiFe2O4 and NiFe2O4@Cu MNPs is greater than (NiFe2O4@-
Cu)SO2(MMT) (curve c), (NiFe2O4@Cu)(MMT) (curve d), and
(NiFe2O4@Cu)(MMT-SO3H) (curve e). It is demonstrating that
through conjunction of the magnetic part of NiFe2O4 with
montmorillonite moiety, Ms value of the prepared clay
composite system is impressively decreased. In this context, the
saturation magnetization (Ms) value is exactly rationalized to
mass ratio of NiFe2O4 in the nanocomposite systems. As well,
the Ms value of NiFe2O4@Cu (curve b) is less than NiFe2O4
(curve a) indicating contribution of diamagnetic copper nano-
particles. As shown in Fig. 7f, the magnetic nanoparticles of
(NiFe2O4@Cu)SO2(MMT), because of high magnetization,
showed an excellent response to the applied external magnetic
eld (2 min).
Fig.
5 N2 adsorption–desorption spectra of (a) (NiFe2O4@Cu)
SO2(MMT), (b) (NiFe2O4@Cu)(MMT-SO3H) and (c) (NiFe2O4@Cu)(MMT).
materials with the extreme of tiny pores.72 It is noteworthy that
aer the immobilization of NiFe2O4@Cu MNPs, the BET surface
area and total pore volume of all samples were substantially
decreased versus to that of MMT-K10 (Table 3). This is attributed
to blocking of some of pores in montmorillonite K10 by
NiFe2O4@Cu MNPs.73 Based on BDDT classication, the shape
of isotherm in (NiFe2O4@Cu)(MMT) is adopted to isotherm type
IV with a H3 hysteresis loop indicating micro- and mesoporous
materials with an average pore diameter of 8 nm. Table 3 shows
that (NiFe2O4@Cu)SO2(MMT) MNPs has a high surface area in
comparison to other samples. This increasing may be due to
modication of Na+-MMT with ClSO3H leading to raise of
specic surface area and total pore volume.74 However, the
immobilization of NiFe2O4@Cu MNPs over sulfonated sodium
montmorillonite (Na+-MMT-SO3H) reduces the surface area and
total pore volume.
3.2.4. FT-IR analysis. Fig. 6 shows FT-IR spectra of Na+-
MMT, MMT-SO3H, NiFe2O4@Cu and (NiFe2O4@Cu)SO2(MMT)
clay composite systems. In the case of Na+-MMT (Fig. 6a), the
absorption band at 3620 cmꢂ1 is attributed to the vibration of
bonded-OH to Al or Mg ions in Na+-MMT. As well, the bands at
3433 cmꢂ1 and 1635 cmꢂ1 are also showing OH stretching and
deforming vibrations of adsorbed water in interlayers of
3.3. Synthesis of coumarin-based 1,4-dihydropyridines
catalyzed by (NiFe2O4@Cu)SO2(MMT) MNPs
At the next attempt, catalytic activity of the prepared (NiFe2-
O4@Cu)SO2(MMT) MNPs was studied towards Hantzsch
synthesis of coumarin-based 1,4-dihydropyridines by one-pot
and three-component condensation reaction of 4-hydrox-
ycoumarin, aromatic aldehydes and ammonia. This
Table 3 Surface properties of the prepared clay nanocomposite systemsa,b
Average pore
diameter (nm)
Total pore volume
Samples
SBET (m2 gꢂ1
)
Vm (cm3 gꢂ1
)
Vp (cm3 gꢂ1
)
(cm3 gꢂ1
)
MMT-K10
250.11
128.19
119.52
72.118
14.84
51.835
29.45
27.46
16.56
3.41
6.427
3.52
7.92
3.53
34.74
0.4016
0.0673
0.232
0.0381
0.128
0.4298
0.113
0.236
0.0638
0.129
(NiFe2O4@Cu)SO2(MMT)
(NiFe2O4@Cu)(MMT)
(NiFe2O4@Cu)(MMT-SO3H)
NiFe2O4@Cu
a
SBET: Brunauer–Emmett–Teller surface area. b Vp: BJH desorption cumulative volume of pores.
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DMF or solvent-free conditions resulted that H2O exhibited
a perfect rate enhancement. Therefore, H2O was selected as
a solvent of choice. As well, changing the amount of nano-
catalyst and temperature of the reaction revealed that using
10 mg of the nanocatalyst per 1 mmol of 4-chlorobenzaldehyde
at 60 ꢀC is the requirements to achieve the perfect efficiency. In
addition, examining NH3, NH4OAc and NH4Cl as the sources of
nitrogen represented that ammonia has the best ability to
progress of the title reaction. Therefore, the condition
mentioned in entry 12 (Table 4) was selected as the optimum
reaction conditions (Scheme 2).
Next, the inuence and catalytic activity of (NiFe2O4@Cu)
SO2(MMT) MNPs was highlighted by comparing the yield and
rate enhancement in condensation reaction of 4-hydrox-
ycoumarin, 4-chlorobenzaldehyde and ammonia in the pres-
ence of Cu0, NiFe2O4, NiFe2O4@Cu, (NiFe2O4@Cu)(MMT) and
(NiFe2O4@Cu)(MMT-SO3H) NPs at the optimized reaction
conditions. The results of this investigation are summarized in
Table 5. The obtained results exhibited that the clay containing
sulfonyl-bridge represents a perfect catalytic activity as well as
high yield of the product (Table 5, entry 4). Other modied clay
composites, Cu0 and NiFe2O4 NPs encountered with low or
unsatisfactory yield of 1,4-DHP at the same or prolonged reac-
tion times.
Generality and usefulness of (NiFe2O4@Cu)SO2(MMT) MNPs
towards Hantzsch synthesis of coumarin-based 1,4-DHPs was
further studied by examining the condensation reaction of
structurally diverse aromatic aldehydes, 4-hydroxycoumarin
and ammonia in the presence of NFCSM at the optimized
reaction conditions. The results of this investigation are illus-
trated in Table 6. The table shows that all reactions were carried
Fig. 6 FT-IR spectrum of (a) Na+-MMT, (b) MMT-SO3H, (c) NiFe2-
O4@Cu and (d) (NiFe2O4@Cu)SO2(MMT) NPs.
investigation was primarily carried out by optimizing the
progress of the reaction of 4-hydroxycoumarin (2 mmol), 4-
chlorobenzaldehyde (1 mmol) and ammonia (2 mmol) in the
presence of (NiFe2O4@Cu)SO2(MMT) MNPs at different reac-
tion conditions including the change of reaction-solvent,
amount of catalyst and the source of nitrogen transferring
agent. The illustrated results in Table 4 show that in the absence
of the magnetic clay nanocatalyst, the condensation reaction
did not any take place even at the prolonged reaction times
(entries 1 and 2). However, the inuence of (NiFe2O4@Cu)
SO2(MMT) MNPs on the rate of model reaction is noteworthy.
Entries 3–15 exhibited that by adding a small amount of NFCSM
to the reaction mixture, the rate of condensation reaction was
dramatically increased. The investigation for the inuence of
solvents such as H2O, H2O–EtOH, EtOH, EtOAc, CH3CN and
Fig. 7 Magnetization curves of (a) NiFe2O4, (b) NiFe2O4@Cu, (c) (NiFe2O4@Cu)SO2(MMT), (d) (NiFe2O4@Cu)(MMT-SO3H), (e) (NiFe2O4@-
Cu)(MMT) and (f) magnetic response of (NiFe2O4@Cu)SO2(MMT) MNPs.
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Table 4 Optimization experiments for condensation reaction of 4-chlorobenzaldehyde, 4-hydroxycoumarin and ammonia in the presence of
(NiFe2O4@Cu)SO2(MMT) MNPs
Entry
(NiFe2O4@Cu)SO2(MMT) (mg)
Solvent (2 mL)
Temp (ꢀC)
Amine
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
—
—
20
20
20
20
20
20
20
20
20
10
5
EtOH
H2O
EtOH
H2O
EtOH–H2O (1 : 1)
EtOAc
CH3CN
DMF
Solvent-free
Solvent-free
H2O
60
60
60
60
60
60
60
60
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH4OAc
NH4Cl
24 h
24 h
45
20
30
200
200
120
60
30
120
20
5
5
60
98
90
45
50
50
50
60
60
98
60
40
45
9
60
10
11
12
13
14
15
Microwave
25
60
60
60
60
H2O
H2O
H2O
H2O
20
50
50
10
10
Scheme 2 Hantzsch synthesis of coumarin-based 1,4-DHP (4c) catalyzed by (NiFe2O4@Cu)SO2(MMT) MNPs.
Table 5 Comparing the catalytic activity of (NiFe2O4@Cu)SO2(MMT)
Knoevenagel condensation of aldehyde and 4-hydroxycoumarin
is taken place to afford intermediate I. By the reaction of
intermediate I with ammonia, the imine intermediates II is
produced. Activation of intermediate II with the clay nano-
composite followed by the reaction with the second molecule of
4-hydroxycoumarin affords the Michael adducts III. At the next,
the imine intermediate III is tautomerized to produce enamine
IV. Finally, nucleophilic attack of amino group towards carbonyl
function make a ring closing product as 1,4-DHP.
with other potentially active species in synthesis of 1,4-DHP (4c)a
Entry
Catalysta
Time (min)
Yieldb (%)
1
2
3
4
5
6
Cu0 NPs
NiFe2O4
NiFe2O4@Cu
(NiFe2O4@Cu)SO2(MMT)
(NiFe2O4@Cu)(MMT)
(NiFe2O4@Cu)(MMT-SO3H)
120
120
120
20
20
20
60
50
75
98
80
85
The usefulness and capability of (NiFe2O4@Cu)SO2(MMT)
MNPs in one-pot synthesis of coumarin-based 1,4-DHP (4c,
derived by the reaction of 4-hydroxycoumarin, 4-chlor-
obenzaldehyde and ammonia) was also highlighted by
comparing of the obtained result for NFCSM with the previously
reported protocols (Table 7). A case study shows that in terms of
reaction time, reusability of the promoter and yield of the
product, the present work exhibits a more or comparable effi-
ciency than the previous systems.
a
All reactions were carried out in H2O (2 mL) under oil bath (60 ꢀC)
b
conditions using 10 mg of nanocatalyst. Isolated yield.
out successfully within 10–45 min to afford 1,4-DHPs in excel-
lent yields. It is notable that the inuence of substituents
(aromatic rings) on the rate of reaction is noteworthy. Electron-
withdrawing groups prolonged the reaction times and in
contrast, electron-releasing groups enhance the rate of
condensation reactions.
Although the exact mechanism of this synthetic protocol is
not clear, however, a depicted mechanism (Scheme 3) shows
a pathway for inuence of the magnetic clay nanocatalyst on the
formation of 1,4-DHPs. The scheme represents that through the
activation of carbonyl group with the clay nanocomposite, the
3.4. Recycling (NiFe2O4@Cu)SO2(MMT) MNPs
In order to examine the green and economic aspects of
(NiFe2O4@Cu)SO2(MMT) MNPs as well the stability of (NiFe2-
O4@Cu) moiety on the surface of sulfonated montmorillonite,
we also investigated reusability of the clay nanocomposite
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Table 6 One-pot synthesis of coumarin-based 1,4-DHPs catalyzed by (NiFe2O4@Cu)SO2(MMT) MNPsa
Entry
Ar–
Product
(NiFe2O4@Cu)SO2(MMT) (mg)
Time (min)
Yieldb (%)
Mp (ꢀC)
1
2
3
4
5
6
7
8
C6H5
2-ClC6H4
4-ClC6H4
3-OH, 4-MeOC6H3
4-OH, 3-MeOC6H3
3-MeOC6H4
2-MeOC6H4
4-MeC6H4
4a
4b
4c
4d
4e
4f
4g
4h
4i
10
10
10
10
10
10
10
10
10
10
10
10
20
25
20
10
10
15
10
15
20
45
30
40
95
90
98
85
90
90
85
90
85
80
75
80
185–187
215–217
220–222
208–210
210–214
179–182
196–198
190–192
172–174
210–212
208–211
202–205
9
4-OHC6H4
10
11
12
4-O2NC6H4
3-O2NC6H4
3-O2N, 4-ClC6H3
4j
4k
4l
a
All reactions were carried out in H2O (2 mL) at 60 ꢀC. b Isolated yield.
Scheme 3 A proposed mechanism for NFCSM-catalyzed synthesis of coumarin-based 1,4-DHPs.
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Table 7 Synthesis of coumarin-based 1,4-DHP (4c) by (NiFe2O4@Cu)SO2(MMT) and other reported systemsa
Entry
Catalyst
Time (min)
Yield (%)
Condition
Reusability
Ref.
b
1
2
3
4
5
6
(NiFe2O4@Cu)SO2(MMT)
Fe3O4@SiO2
Guanidinium-sulfonic acid
Silica gel
Acidic alumina
Lactic acid
20
20
120
25
14
150
98
88
86
65
75
79
H2O (60 ꢀC)
H2O (reux)
H2O (reux)
Microwave
6
4
4
—
—
—
59
60
61
61
62
Microwave
Ethyl-L-lactate (100 ꢀC)
a
1,4-DHP (4c) was obtained by the reaction of 4-hydroxycoumarin (2 mmol), 4-chlorobenzaldehyde (1 mmol) and NH3, NH4OAc or NH4Cl (2 mmol).
Present work.
b
reaction times, low catalyst loading, high yield of the products,
excellent reusability of the nanocatalyst as well as using water as
a green solvent are the advantages which make this protocol
a prominent choice for synthesis of coumarin-based 1,4-DHPs.
Conflicts of interest
The authors declare no conicts of interest.
Acknowledgements
The authors gratefully acknowledge the nancial support of this
work by the research council of Urmia University.
Fig. 8 Reusability of (NiFe2O4@Cu)SO2(MMT) MNPs.
system towards three-component condensation reaction of 4-
hydroxycoumarin, 4-chlorobenzaldehyde and ammonia at the
optimized reaction conditions. To do this, when the model
reaction was completed, the clay nanocomposite was magneti-
cally separated and washed with EtOH to remove any contam-
inants. Aer drying in an oven at 60 ꢀC for 2 h, the model
reaction was again charged with the fresh 4-hydroxycoumarin,
4-chlorobenzaldehyde and ammonia and the recycled clay
nanocatalyst. Fig. 8 shows that the clay nanocatalyst, (NiFe2-
O4@Cu)SO2(MMT), can be reused for 6 consecutive cycles
without the signicant loss of its catalytic activity.
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