Synthesis and applications of CoFe2O4 nanoparticles for multicomponent reactions

Article abstract of DOI:10.1039/c3cy00594a

An efficient, simple, green protocol is developed for the synthesis of 2-amino-4-(phenyl)-5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-3- carbonitrile derivatives and 2,2′-arylmethylene bis(3-hydroxy-5,5- dimethyl-2-cyclohexene-1-one) derivatives in the presence of CoFe ₂O₄ nanoparticles in aqueous ethanol medium. CoFe ₂O₄ nanoparticles have been synthesised by a co-precipitation method followed by ultrasonication. The synthesised CoFe ₂O₄ nanoparticles have high surface area (140.9 m ² g^-1) and small size (2-8 nm). The present catalytic process provides sustainability as aqueous medium is used, the reaction proceeded in short reaction times by providing high yields of products and is economical as the catalyst is inexpensive and can be recovered from the reaction mixture. The recovered catalyst can be used for multiple cycles without much loss of its activity. The protocol is green as no chromatographic technique is used, thus eliminating the use of hazardous organic solvents. CoFe ₂O₄ emerged as an efficient, sustainable, stable and recyclable catalyst.

Full text of DOI:10.1039/c3cy00594a

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Synthesis and applications of CoFe2O4
nanoparticles for multicomponent reactions
Cite this: Catal. Sci. Technol., 2014,
4, 142
*
Jaspreet Kaur Rajput and Gagandeep Kaur
An efficient, simple, green protocol is developed for the synthesis of 2-amino-4-(phenyl)-5,6,7,8-tetrahydro-
7,7-dimethyl-5-oxo-4H-chromene-3-carbonitrile derivatives and 2,2′-arylmethylene bis(3-hydroxy-5,5-
dimethyl-2-cyclohexene-1-one) derivatives in the presence of CoFe2O4 nanoparticles in aqueous ethanol
medium. CoFe2O4 nanoparticles have been synthesised by a co-precipitation method followed by
ultrasonication. The synthesised CoFe2O4 nanoparticles have high surface area (140.9 m2 g−1) and small size
(2–8 nm). The present catalytic process provides sustainability as aqueous medium is used, the reaction
proceeded in short reaction times by providing high yields of products and is economical as the catalyst
is inexpensive and can be recovered from the reaction mixture. The recovered catalyst can be used for
multiple cycles without much loss of its activity. The protocol is green as no chromatographic technique is
used, thus eliminating the use of hazardous organic solvents. CoFe2O4 emerged as an efficient, sustainable,
stable and recyclable catalyst.
Received 14th August 2013,
Accepted 28th September 2013
DOI: 10.1039/c3cy00594a
www.rsc.org/catalysis
benign and low impact protocols.13 Thus water is chosen as a
green solvent, which addresses several features of green
Introduction
In recent years, use of sustainable catalysts and benign solvents
are considered as key points from a green chemistry point of
view for the development of sustainable protocols.1 From this
aspect, nanocatalysts have emerged with good catalytic activity
due to their small size, large surface area, selectivity, recovery
from reaction mixtures and reusability.2,3 Moreover, the
magnetic nanoparticles (MNPs) have gained a significant place
among nanocatalysts because of their applications in a variety
of disciplines such as biotechnology/biomedicine,4 magnetic
resonance imaging,5 data storage6 and especially in catalysis as
a magnetically separable catalyst.7 The separation of magnetic
nanoparticles from reaction mixtures is driven by an external
magnet, which make the recovery and reusability of the catalyst
easier and avoids loss of catalyst associated with traditional
filtration and centrifugation methods, therefore supporting the
green chemistry principles in terms of eco-benign and econom-
ical needs for sustainability.8 In addition to these points, the
magnetic properties of nanoparticles are stable and can toler-
ate the chemical environment except those that are acidic/
corrosive.9 Among the various MNPs, Fe3O4 is used widely as a
catalyst,10 but is reactive to acidic and oxidative environments
as Fe2+ present in Fe3O4 is oxidised easily and the magnetic
properties of Fe3O4 are vulnerable to loss of magnetism,11
while Fe2O3 nanoparticles are not thermally stable.12
chemistry such as being cheap, easily available, non-toxic and
non-flammable.14 Further, the hydrophobic nature of water
enhances the rate of reaction and influences the selectivity
of reaction.15
In organic chemistry the synthesis of biologically and
pharmaceutically active heterocycles are considered as a
pivotal theme. Among various heterocycles, 2-amino-4-
(phenyl)-5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-3-
carbonitrile derivatives have gained a strong place in drug
research due to their pharmaceutical, biological and medici-
nal properties such as antifungal, antioxidant, antiviral, hypo-
tensive and antitumor activities.16 Further these derivatives
have applications in various fields such as pigments, cos-
metics,17 agrochemicals,18 optical brighteners,19 laser dyes,20
and fluorescence makers.21 The 2,2′-arylmethylene bis(3-
hydroxy-5,5-dimethyl-2-cyclohexene-1-one) derivatives are also
considered as important biologically active compounds
possessing tyrosinase inhibitor properties.22 These compounds
are used as key intermediates for the preparation of hetero-
cyclic compounds such as xanthenediones which show a wide
range of biological, therapeutic23 and spectroscopic properties
as used in laser technology,24 and acridindione derivatives,25
which have been used as electron donors,26 electron acceptors
and in the photoinitiated polymerisation of acrylates and
methacrylates.27 2,2′-Arylmethylene bis(3-hydroxy-5,5-dimethyl-
2-cyclohexene-1-one) derivatives have a phenolic functionality
so they can couple with diazonium compounds to afford dye-
stuffs.28 The synthesis of 2-amino-4-(phenyl)-5,6,7,8-tetrahydro-
7,7-dimethyl-5-oxo-4H-chromene-3-carbonitrile derivatives has
The aqueous mediated reactions have gained intensive
attention in organic synthesis for the design of environmentally
Department of Chemistry, Dr. B. R. Ambedkar National Institute of Technology,
Jalandhar, Punjab 144011, India. E-mail: rajputj@nitj.ac.in
142 | Catal. Sci. Technol., 2014, 4, 142–151
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been carried out by the reaction of aldehydes, active
methylene compounds and enolizable C–H activated com-
pounds with the variety of reagents. On the other hand
2,2′-arylmethylene
bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-
1-one) derivatives can be prepared by condensation of aro-
matic aldehydes with 1,3-cyclic diketones using catalyst and
catalyst free conditions. However, many of the reported
methods are not effective for the synthesis of the desired
compounds and suffer from drawbacks such as toxic sol-
vents, long reaction times, use of excessive catalysts, low
yields, tedious workup procedures, complex reaction path-
ways, harsh reaction conditions, cost effective reagents/
catalysts, unrecyclable catalyst and formation of side products.
So in continuation of our work on green catalysis,29 we
synthesised CoFe2O4 nanoparticles and applied them as a
catalyst for the preparation of 2-amino-4-(phenyl)-5,6,7,8-
tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-3-carbonitrile deri-
vatives and 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-
cyclohexene-1-one) derivatives. CoFe2O4 nanoparticles have a
spinel structure with high thermal stability, moderate mag-
netisation, chemical stability, high surface area and mechani-
cal hardness.30,31
Fig. 2 TEM image of CoFe2O4 nanoparticles.
The CoFe2O4 nanoparticles were recovered from the reac-
tion product using an external magnet due to their magnetic
character, which was established by a vibrating sample mag-
netometer (VSM) showing saturation magnetization to be
1.77 emu g−1 (Fig. 3).
To establish the scope of catalytic activity of CoFe2O4
nanoparticles, we synthesised different products using
CoFe2O4 nanoparticles.
Results and discussion
In this paper we present the synthesis of 2-amino-4-(phenyl)-
5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-3-carbonitrile
derivatives and 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-
cyclohexene-1-one) derivatives using CoFe2O4 nanoparticles as a
catalyst. The CoFe2O4 nanoparticles were prepared by a previ-
ously reported method29b involving co-precipitation along with
ultrasonication under basic conditions resulting in small sized
(2–8 nm) nanoparticles with high surface area (140.9 m2 g−1)
and good thermal stability. The formation of CoFe2O4 nano-
particles was confirmed from XRD data. The synthesised
CoFe2O4 nanoparticles have a cubic structure. Fig. 1 represents
the XRD diffraction pattern. The size of particles was deter-
mined by transmission electron microscopy (TEM). TEM
images showed the spherical shaped nanoparticles (Fig. 2).
Synthesis of 2-amino-4-(phenyl)-5,6,7,8-tetrahydro-7,7-dimethyl-
5-oxo-4H-chromene-3-carbonitrile derivatives using CoFe2O4
nanoparticles as catalyst
Firstly the study was carried out by choosing the reaction of 4-Cl
benzaldehyde (1a), 1,3-cyclohexanedione (2a) and malononitrile
Fig. 1 XRD pattern of CoFe2O4 nanoparticles.
Fig. 3 VSM plot of CoFe2O4 nanoparticles.
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(3a) in equimolar ratio as the model reaction (Scheme 1) with-
out using catalyst providing low yield of product 58% after
60 min of reaction (Table 1, entry 1) but the addition of
CoFe2O4 (0.05 mmol) to the reaction mixture increased the
yield of product to 68% by decreasing the reaction time to
15 min (Table 1, entry 2), which showed the role of catalyst in
the present protocol. Encouraged by these results we studied
the various parameters such as different reaction tempera-
tures, various solvents and amount of catalyst to find the
optimised reaction conditions. The investigation was started
by carrying out the reaction of 1a, 2a and 3a at different tem-
peratures starting from stirring at room temperature to 80 °C
in EtOH using CoFe2O4 (0.05 mmol) (Table 1, entries 3–6). The
reaction at 60 °C was chosen as the best temperature in terms
of yield and time. After this, the effect of different solvents
was examined at 60 °C (Table 1, entries 7–15). The H2O : EtOH
(1 : 3) system was considered as the optimum solvent. It is
mentioned here that polar solvents gave better results as com-
pared to non-polar solvents. However the yield of product in
water was lower in comparison to other polar solvents because
of lesser solubility of reactants. Generally the choice of solvent
is explained on the basis of the fact that the solvent affects the
transition state in the synthesis, as the transition state is bet-
ter solvated by polar solvents and increases the reaction rate,
which increases the product yield.32 The reaction in H2O : EtOH
(1: 3) gave the best yield of product (89%) in a shorter time,
which was further explained as higher dispersability of the
magnetic nanoparticles in the water–ethanol mixture making
the system quasi-homogenous, which increases the interaction
of the nanoparticles with the reactants, resulting in increased
reaction rate.33 0.025 mmol of catalyst CoFe2O4 was taken as
standard from various amounts of catalyst (Table 1, entries
16–19). The reaction was also carried out using bulk CoFe2O4
but the yield and reaction time were not impressive as
compared to our synthesised CoFe2O4 nanoparticles (Table 1,
entry 20). This can be attributed to the higher surface area
and smaller size of CoFe2O4 nanoparticles, which increases the
catalytic activity and interaction with the reacting species.
All the results are shown in Table 1. The CoFe2O4 (0.025 mmol)
with H2O : EtOH (1 : 3) mixture at 60 °C was considered as the
optimum reaction conditions (Table 1, entry 17) for the
preparation of the desired product to obtain the best yield in
shorter reaction time. We also investigated the reaction with
synthesised Fe3O4, ZnO nanoparticles, but the yield was very
low as compared to CoFe2O4 nanocatalyst, which showed the
superiority of present catalytic system (Table 1, entries 20, 21).
The efficiency of these optimised parameters were examined
for the synthesis of 2-amino-4-(phenyl)-5,6,7,8-tetrahydro-7,7-
dimethyl-5-oxo-4H-chromene-3-carbonitrile derivatives, which
were prepared by carrying out a one pot three component
reaction of 1,3-cyclic diketones (2a and 2b), active methylene
compounds (3a and 3b) and a wide range of aldehydes in
the presence of CoFe2O4 (0.025 mmol) in H2O–EtOH (1 : 3)
mixture at 60 °C (Scheme 2 and Table 2, entries 1–28). All
the aldehydes including aromatic, heterocyclic and unsatu-
rated were employed for the present synthesis and reacted
smoothly. The reactions of aldehydes bearing electron
withdrawing groups (–Cl, –NO2) and electron releasing
Scheme 1
Table 1 Optimization of various reaction conditions for the synthesis of 4b
Entry
Catalyst (mmol)
Solvents
Time (min)
Temperature (°C)
Yielda (%)
1
2
3
4
5
6
7
8
—
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
H2O
MeOH
60
15
5
7
6
4
7
8
20
23
25
6
6
5
5
7
4
5
RT (35 °C)
RT (35 °C)
Stirring (35 °C)
58
68
69
70
83
75
76
82
80
79
70
84
86
87
85
85
89
87
84
65
65
71
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.01)
CoFe2O4 (0.025)
CoFe2O4 (0.07)
CoFe2O4b(0.1)
CoFe2O4 (0.025)
Fe3O4 (0.025)
ZnO (0.025)
45
60
80
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
9
CH3CN
EtOAc
Toluene
10
11
12
13
14
15
16
17
18
19
20
21
23
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 2)
H2O : EtOH (1 : 3)
H2O : EtOH (1 : 4)
H2O : EtOH (1 : 3)
H2O : EtOH (1 : 3)
H2O : EtOH (1 : 3)
H2O : EtOH (1 : 3)
H2O : EtOH (1 : 3)
H2O : EtOH (1 : 3)
H2O : EtOH (1 : 3)
5
20
18
16
a
Isolated yield. b Bulk CoFe2O4.
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products, such as hydrolysis of cyano group35 and formation
of polymerised product36 in the case of cinnamaldehyde,
which is an acid sensitive aldehyde.
The catalyst played the role of base to afford the product
by the Knoevenagel condensation followed by a Michael addi-
tion. The Lewis basic sites originate from electrons trapped
in the intrinsic defects or from surface hydroxyl groups41 or
from co-ordinatively unsaturated oxide ion associated with
neighbouring hydroxyl groups.42
Scheme 2
groups (–OH, –OCH3) proceeded well in the given time under
optimised reaction conditions. The results are tabulated in
Table 2. It was demonstrated that a variety of 2-amino-4-
(phenyl)-5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-3-
carbonitrile derivatives were synthesised in good to high
yields (60–96%). The reactions were clean and completion of
reaction was identified by precipitation of product along with
TLC. The catalyst was separated out from reaction product
without any tedious work-up by just attaching the external
magnet to the walls of reaction flask and reused after drying.
It was found that the reaction proceeded with ethyl cyano-
acetate (Table 2, entries 23–28) took longer time as compared
to malononitrile (Table 2, entries 11–14, 16, 17). The reason
may be because the cyanide group attached to malononitrile,
which has a greater capability to stabilize the intermediate as
compared to the ester group of ethyl cyanoacetate.34 All the
products were formed with good chemoselectivities without
the formation of any previously reported unwanted side
Synthesis of 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-
cyclohexene-1-one) derivatives using CoFe2O4 nanoparticles
as catalyst
Encouraged from the above results we also tried to synthesise
2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-
1-one) derivatives by the reaction of aromatic aldehydes and
1,3-cyclic diketones (dimedone and 1,3-cyclohexanedione) in
a 1 : 2 molar ratio to investigate the scope of our catalytic sys-
tem. The initial study started with the reaction of 4-methoxy
benzaldehyde (1d) with dimedone (2a) in the presence of
CoFe2O4 (0.025 mmol) in H2O : EtOH (1 : 1) mixture at room
temperature to afford the desired product, which is obtained
in 72% yield (Table 3, entry 1). To check further the role of
catalyst, a blank reaction was studied under similar reaction
conditions and gave the product with 48% yield after 48 min
(Table 1, entry 2). From these observations we carried out fur-
ther work to obtain the standardised reaction conditions for
Table 2 Scope of catalytic activity of CoFe2O4 nanoparticles for synthesis 2-amino-4-(phenyl)-5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-
3-carbonitrile derivativesa
Entry
Ar
X
R
Product
Time (min)
Yieldb (%)
M.P. obs.
M.P. lit.
1
2
3
4
5
6
7
8
4-Cl C6H4
C6H5
2-Cl C6H4
3-NO2 C6H4
4-Br C6H4
4-OCH3 C6H4
4-OH C6H4
3,4-OCH3 C6H3
C6H5CHCH
-N(CH3)2 C6H4
4-Cl C6H4
C6H5
2-Cl C6H4
3-NO2 C6H4
3-Cl C6H4
-N(CH3)2 C6H4
4-OCH3 C6H4
4-OH C6H4
3,4-OCH3 C6H3
C6H5CHCH
4-OH-3,5-OCH3 C6H2
Furyl
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
COOEt
COOEt
COOEt
COOEt
COOEt
COOEt
H
H
H
H
H
H
H
H
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4
6
9
6
3
10
12
20
15
10
4
7
12
7
89
85
83
86
91
80
87
84
88
89
96
93
90
94
93
91
85
87
89
86
80
84
80
71
69
60
70
77
230–232
228–230
200–202
200–202
235–238
188–190
240–242
192–194
195–198
171–174
210–212
224–226
198–200
210–212
210–212
206–208
190–192
212–215
170–172
185–188
190–192
200–204
150–152
148–150
170–172
200–202
140–141
130–133
226–22937
234–23537
213–21537
198–20037
—
186–18938
—
—
—
—
9
H
H
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
215–21734
234–23534
215–21634
213–21434
224–22537
210–21234
196–19834
224–22634
171–17339
182–18434
—
5
10
9
15
18
12
14
6
10
15
18
16
20
14
4s
4t
4u
4v
5a
5b
5c
5d
5e
5f
220–22334
151–15340
154–15640
—
C6H5
3-NO2 C6H4
-N(CH3)2 C6H4
2-Cl C6H4
4-OCH3 C6H4
4-Cl C6H4
209–21240
131–13440
139–14240
a
Reaction conditions: aldehyde (2.5 mmol), dimedone (or 1,3-cyclohexanedione) (2.5 mmol), malononitrile (or ethylcyanoacetate) (2.5 mmol),
CoFe2O4 (0.025 mmol), H2O : EtOH (1 : 3) 3 ml. b Isolated yield.
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Table 3 Optimisation of different reaction conditions for the synthesis of 6d
Entry
Catalyst (mmol)
Different optimization conditions
Solvents
Yielda (%)
1
2
3
4
5
6
7
8
CoFe2O4 (0.025)
—
RT (35–40 °C)
RT (35–40 °C)
Stirring at RT (35–40 °C)
50 °C
60 °C
70 °C
Refluxing
60 °C
60 °C
60 °C
60 °C
60 °C
60 °C
60 °C
60 °C
60 °C
60 °C
60 °C
60 °C
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 2)
H2O : EtOH (1 : 3)
H2O : EtOH (1 : 4)
EtOH
H2O
MeOH
CH3CN
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
H2O : EtOH (1 : 1)
72
48
76
85
93
89
90
87
95
88
86
90
88
83
80
70
75
78
68
62
80
CoFe2O4 (0.025)
CoFe2O4 (0.025)
CoFe2O4 (0.025)
CoFe2O4 (0.025)
CoFe2O4 (0.025)
CoFe2O4 (0.01)
CoFe2O4 (0.05)
CoFe2O4 (0.07)
CoFe2O4 (0.1)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
CoFe2O4 (0.05)
9
10
11
12
13
14
15
16
17
18
19
20
21
b
CoFe2O4 (0.05)
Fe3O4 (0.05)
ZnO (0.05)
60 °C
60 °C
a
Isolated yield. b Bulk CoFe2O4.
the synthetic protocol. Various parameters were studied,
such as temperature, catalyst loading and effect of solvents
(Scheme 3). First the effect of temperature was investigated
(Table 3, entries 3–7). The reactions were studied at differ-
ent temperatures, refluxing and stirring conditions using
CoFe2O4 (0.025 mmol) in H2O : EtOH (1 : 1) mixture. Of
various temperature conditions, reaction at 60 °C provided
the best results. Next we moved our consideration towards
the influence of the amount of catalyst on the synthesis of
the desired compounds. The reactions were carried out with
model reactants (1d) and (2a) in the presence of H2O : EtOH
(1 : 1) mixture at 60 °C, starting from 0.01 mmol to 0.1 mmol
(Table 3 entries 5, 8–10). We observed that the reaction
proceeded smoothly with 0.05 mmol of catalyst providing an
excellent yield. Last, to evaluate the effect of solvent on the
synthesis of desired products, various solvents were studied,
including H2O, EtOH, MeOH, CH3CN, H2O : EtOH (1 : 1),
H2O : EtOH (1 : 2), H2O : EtOH (1 : 3) and H2O : EtOH (1 : 4)
using CoFe2O4 (0.05 mmol) nanoparticles at 60 °C (Table 3,
entries 9, 12–18). The H2O : EtOH (1 : 1) solvent system gave
a good result (Table 3, entry 4). Hence the standardised
reaction conditions were found to be 0.05 mmol of catalyst
at 60 °C using H2O : EtOH (1 : 1) mixture as solvent (Table 3,
entry 9).
To explore the versatility of the present protocol, different
substituted aldehydes were taken to react with dimedone
(2b)/1,3-cyclohexanedione (2a) using CoFe2O4 (0.05 mmol) at
60 °C to give the corresponding desired products in good
to excellent yields (76–95%) in H2O : EtOH (1 : 1) (Table 4,
Scheme 4).
The reactions proceeded smoothly with aldehydes hav-
ing electron donating groups like –OH, –OCH3, –3,4-OCH3,
–N(CH3)2 and electron withdrawing groups like –Cl, –NO2.
The reactions were simple, clean and completion of the
reaction was monitored by TLC. After that, the catalyst was
separated out from the reaction mixture using an external
magnet. The products were purified during the separation
of catalyst from reaction product and characterized by
FT-IR, 1H-NMR and 13C-NMR spectroscopy. The aldehydes
such as heteroatomic aldehydes and unsaturated aldehydes
were well reacted to afford the corresponding products. All the
products have good chemoselectivity.
To present the merits and capability of our protocols,
they were compared with other reported methods/catalysts.
Pd nanoparticles46 (0.04 mmol) and potassium phthalimide-
N-oxyl (POPINO)34 (0.5 mmol) afforded 4k in 88% yield after
4.2 h in CH3CN and 95% after 15 min in H2O under refluxing
conditions, respectively. Amberlyst A2147 (30 mg mmol−1) gave
84% yield in H2O after 1 h at room temperature. But CoFe2O4
(0.025 mmol) nanoparticles afforded 96% yield of com-
pound 4k after 4 min in H2O : EtOH (1 : 3) at 60 °C. On the
other hand compound 6d was obtained in 95% yield after
5 min in H2O : EtOH (1 : 1) at 60 °C using CoFe2O4 (11.7 mg)
nanoparticles, while Fe3O4@SiO2–SO3H44 (10 mg), CaCl2
43
(22 mg) and urea48 (15 mg) afforded 95% yield after 90 min
at room temperature in H2O, 85% yield after 15 h at room
Scheme 3
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Table 4 Synthesis of 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) derivatives via condensation of various substituted
aldehydes and dimedone or 1,3-cyclohexanedione in the presence of CoFe2O4 nanoparticlesa
M.P.
Obs.
M.P.
Lit.
Time
(min.)
Yield
(%)b
Entry
Ar
R
Product
1
2
3
4
5
6
7
8
C6H5
4-Cl C6H4
2-Cl C6H4
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
H
H
H
H
H
H
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
6r
3
4
2
5
8
5
3
4
9
3
5
5
5
4
7
9
10
4
91
89
86
95
94
89
76
79
92
91
92
87
84
80
85
90
89
92
188–190
143–144
200–202
142–145
194–196
190–192
210–212
140–142
178–181
189–191
192–194
207–209
204–206
229–231
193–195
192–194
170–172
205–207
192–19443
145–14743
202–20443
146–14843
201–20343
194–19544
215–21643
142–14443
187–18943
197–19843
—
4-OCH3 C6H4
4-OH C6H4
4-(CH3)2N C6H4
C6H5CHCH
Furyl
3,4-(OCH3) C6H4
3-NO2 C6H4
4-OH-3,5-(OCH3) C6H3
C6H5
4-Cl C6H4
2-Cl C6H4
4-OCH3C6H4
4-OH C6H4
3,4-(OCH3) C6H4
3-NO2 C6H4
9
10
11
12
13
14
15
16
17
18
208–21045
202–20445
—
195–19745
197–19945
—
6s
207–20945
a
Reaction conditions: aldehyde (1.25 mmol), dimedone (or 1,3-cyclohexanedione) (2.5 mmol), CoFe2O4 (0.05 mmol), H2O : EtOH (1 : 1) 3 ml.
Isolated yield.
b
Further the morphology of reused catalyst was checked by
TEM analysis (Fig. 5 (a) and (b)) which showed not much
change in morphology and size but showed agglomeration,
which can be the reason for slight decrease in yield of the
products 4k and 6d.
Scheme 4
Experimental
All the solvents and reagents were obtained from local sup-
temperature in CH3CN and 93% yield after 100 min using
ultrasound at 50 °C in H2O, respectively. The results are tabu-
lated in Table 5 and Table 6, from which it is clear that both
the present protocols are superior to other reported protocols
and the catalyst is an excellent catalyst as it is required in
smaller quantity, it is cheap and efficient, no loading/coating/
functionalisation is needed and moreover it is recyclable.
pliers. Products were analyzed and characterized by using
BRUKER AVANCE II 400 NMR spectrometer using CDCl3 as a
solvent and tetramethyl silane (TMS) as an internal standard
1
for H-NMR and 13C-NMR measurements. FT-IR spectra were
recorded on a Perkin Elmer spectrometer. Melting points were
determined by Gallenkamp apparatus and were uncorrected.
Thin layer chromatography (TLC) was carried out on silica gel
60 precoated on aluminium sheets with layer thickness 0.2 mm
(SD-fine chemicals). The visualization of spots was performed
in an I2 chamber.
Reusability of CoFe2O4 nanoparticles
Finally recyclability and reusability of CoFe2O4 nanoparticles
was investigated for the synthesis of desired products 4k and
6d. The investigation was carried out in following steps.
1) After completion of reaction, solvent EtOH (3 ml) was
added to the reaction flask and flask was stirred to
completely dissolve the product.
2) The catalyst was recovered by attaching the external
magnet to the walls of reaction flask, providing the clear
solution which was extracted by micro syringe to another
flask. The whole process was repeated twice and combined
layers of product were concentrated under vacuum to obtain
the pure form of product. The recovered catalyst was dried in
same reaction flask at 70 °C for 1 h and reused for up to
seven cycles. The recycled CoFe2O4 nanoparticles can be
reused without much loss of activity. The results are
summarised in Fig. 4.
General procedure for the synthesis of 2-amino-4-(phenyl)-
5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-3-
carbonitrile derivatives (4a–4v and 5a–5f)
The dimedone (2.5 mmol) (or 1,3-cyclohexanedione), an aro-
matic aldehyde (2.5 mmol), malononitrile (2.5 mmol) (or ethyl
cyanoacetate) was dissolved in H2O : EtOH (1 : 3) mixture (3 ml)
followed by addition of CoFe2O4 (0.025 mmol, 0.0058 g). The
reaction mixture was heated for the appropriate time (Table 2).
The completion of reaction was identified by precipitation of
product formed and along with TLC. The solid product formed
was dissolved in EtOH. The catalyst was separated from the
resulting clear solution of product by the use of an exter-
nal magnet, washed with ethanol, dried and reused. The
solution of product was concentrated under vacuum to
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Table 5 Comparison of synthesis of 2-amino-4-(phenyl)-5,6,7,8-tetrahydro-7,7-dimethyl-5-oxo-4H-chromene-3-carbonitrile derivatives with
reported protocols for compound 4k
S. no.
Catalyst
Reaction conditions (temp./solvent/time)
Yield (%)
Catalyst loading
1
2
3
4
5
6
7
8
Ni(NO3)2·6H2O49
N-Methylimidazole50
DMAP40
Refluxing/H2O/20 min
RT/H2O/90 min
Refluxing/EtOH/15 min
RT/Neat/25 min
Refluxing/H2O/15 min
RT/EtOH/25 min
80–90 °C/H2O/7.5 h
RT/EtOH/1 h
88
90
94
86
95
95
90
84
93
88
96
0.1 mmol
0.2 mmol
0.2 mmol
0.5 mmol
0.5 mmol
MgO51
POPINO34
SB-DABCO52
HDMBAB37
0.06 mmol
0.12 mmol
30 mg mmol−1
0.05 mmol
0.04 mmol
0.025 mmol
Amberlyst A2147
53
9
10
12
PPA-SiO2
Refluxing/H2O/10 min
Refluxing/CH3CN/4.2 h
60 °C/H2O : EtOH (1 : 3)/4 min
Pd nanoparticles46
CoFe2O4 [present work]
Table
6 Comparative study of synthesis of 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) derivatives with reported
protocols for compound 6d
S. no.
Catalyst
Reaction conditions (temp./solvent/time)
Yield (%)
Catalyst amount
1
2
3
4
5
6
7
8
Ni nanoparticles54
RT/E.G./10 min
RT/H2O/90 min
Grinding/neat/2 min
RT/CHCl3/15 h
Ultrasound at 50 °C/H2O/100 min
100 °C/H2O/48 min
Refluxing/THF/4 h
Stirring at RT/H2O/4 h
MW/neat/8 min
60 °C/ionic liquid/45 min
60 °C/H2O : EtOH(1 : 1)/5 min
90
95
83
85
93
74.2
94
93
81
85
95
100 mg
10 mg
300 mg
22 mg
15 mg
16 mg
54 mg
—
Fe3O4@SiO2–SO3H44
45
Yb(OTf)3-SiO2
43
CaCl2
Urea48
55
HClO4·SiO2
EDDA56
Catalyst free57
Neutral alumina58
L-Histidine59
9
10
14
—
31 mg
11.7 mg
CoFe2O4 [present work]
give the product. The product obtained was pure without
recrystallisation. The products were characterised based on
their melting point and FT-IR, 1H-NMR and 13C-NMR spectra.
Spectral data. Table 2, entry 2: m.p 228–230 °C; 1H-NMR
(400 Hz, CDCl3) δ (ppm):1.90–2.05 (m, 2H, CH2), 2.25–2.36
(m, 2H, CH2), 2.53–2.66 (m, 2H, CH2), 4.22 (s, 1H, CH), 6.79
(s, 2H, NH2), 7.14–7.28 (m, 5H, Ar–H).
Table 2, entry 19: m.p 170–172 °C; FT-IR(KBr) (νmax, cm−1):
3390, 1602, 1415, 1245; H-NMR (400 Hz, CDCl3) δ (ppm): 1.05
(s, 3H, CH3), 1.11 (s, 3H, CH3), 2.23 (d, 2H, J = 3.72 Hz, CH2),
2.44 (s, 2H, CH2), 3.83 (s, 3H, CH3), 3.86 (s, 3H, CH3), 4.35 (s,
1H, CH), 4.56 (s, 2H, NH2), 6.73–6.80 (m, 3H, Ar–H); 13C-NMR
(400 Hz, CDCl3) δ (ppm): 27.5, 29.0, 32.1, 35.0, 50.6, 55.8, 63.6,
111, 111.2, 114.1, 119.4, 135.9, 148.0, 148.8, 157.3, 161.3, 196.0.
1
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Fig. 4 Reusability of CoFe2O4 nanoparticles for synthesis of 4k and 6d up to seven cycles.
Fig. 5 TEM images of reused CoFe2O4 nanoparticles: (a) after catalytic reaction of 4k (b) after catalytic reaction of 6d after 5th run.
Table 2, entry 21: m.p. 190–192 °C; 1H-NMR (400 Hz,
CDCl3) δ (ppm):1.06 (s, 3H, CH3), 1.12 (s, 3H, CH3), 2.24 (d, 2H,
J = 2.88 Hz, CH2), 2.45 (d, 2H, J = 3.48 Hz, CH2), 3.85 (s, 6H,
OCH3), 4.32 (s, 1H, CH), 4.64 (s, 2H, NH2), 5.47 (s, 1H, OH),
6.44 (s, 2H, Ar–H).
mixture. The mixture was heated at 60 °C until the com-
pletion of the reaction, monitored by TLC. The completion
of the reaction resulted in the separation of solid product.
The product was dissolved in EtOH and catalyst was sepa-
rated from reaction product using an external magnet,
washed with ethanol, dried and reused. The organic layer
was concentrated under vacuum to give the product,
which was characterized by its melting point and FT-IR and
1H-NMR spectra.
General procedure for the synthesis of 2,2′-arylmethylene
bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) derivatives
(6a–6s)
Spectral data. Table 4, entry 1: m.p 188–190 °C; 1H-NMR
(400 Hz, CDCl3) δ (ppm): 1.09 (s, 6H, CH3), 1.23 (s, 6H, CH3),
2.28–2.48 (m, 8H, CH2), 5.54 (s, 1H, CH), 7.09 (d, 2H, J = 7.6 Hz,
Ar-H), 7.16 (t, 1H, J = 7.1 Hz, Ar–H), 7.26 (d, 2H, J = 7.4 Hz,
Ar–H), 11.44 (s, 1H, OH), 11.90 (s, 1H, OH).
The dimedone (2.5 mmol) (or 1,3-cyclohexanedione) was
dissolved in H2O : EtOH (1 : 1) mixture (3 ml) followed by
addition of an aromatic aldehyde (1.25 mmol). The catalyst
CoFe2O4 (0.05 mmol, 0.0117 g) was added to the reaction
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Table 4, entry 11: m.p 192–194 °C; 1H-NMR (400 Hz, CDCl3)
δ (ppm): 1.11 (s, 6H, CH3), 1.24 (s, 6H, CH3), 2.35–2.47 (m, 8H,
CH2), 3.77 (s, 6H, CH3), 5.43 (s, 1H, OH), 5.49 (s, 1H, CH), 6.34
(s, 2H, Ar–H), 11.5(s, 1H, OH), 12.0(s, 1H, OH).
7 (a) M. B. Gawande, P. S. Branco, I. D. Nogueira,
C. A. A. Ghumman, N. Bundaleski, A. Santos,
O. M. N. D. Teodoro and R. Luqued, Green Chem., 2013, 15,
682–689; (b) M. B. Gawande, A. K. Rathi, I. D. Nogueira,
R. S. Varma and P. S. Branco, Green Chem., 2013, 15,
1895–1899; (c) R. Cano, D. J. Ramón and M. Yus, J. Org. Chem.,
2010, 75, 3458–3460; (d) V. Polshettiwar and R. S. Varma,
Tetrahedron, 2010, 66, 1091–1097; (e) M. B. Gawande,
A. K. Rathi, I. D. Nogueira, C. A. A. Ghumman, N. Bundaleski,
O. M. N. D. Teodoro and P. S. Branco, ChemPlusChem,
2012, 77, 865–871; (f) J. Feng, L. Sua, Y. Maa, C. Ren, Q. Guo
and X. Chen, Chem. Eng. J., 2013, 221, 16–24; (g) J. Mondal,
T. Sen and A. Bhaumik, Dalton Trans., 2012, 41, 6173–6181; (h)
F. Shi, M. K. Tse, M. M. Pohl, A. Bruckner, S. Zhang and
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S. R. Kale, S. S. Kahandal, M. B. Gawande and R. V. Jayaram,
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Conclusion
In conclusion, we developed an efficient, simple, green method
for the synthesis of 2-amino-4-(phenyl)-5,6,7,8-tetrahydro-7,7-
dimethyl-5-oxo-4H-chromene-3-carbonitrile derivatives and
2,2′-arylmethylene
bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-
1-one) derivatives using CoFe2O4 nanoparticles as a catalyst.
The merits of the present work are as follows: 1) high
efficiency, clean reaction, simplicity, short reaction time,
versatility, high yields, chemoselectivity, non-chromatography
technique. 2) Separation and recrystallisation of product
occurs simultaneously, which reduces the use of organic sol-
vents. 3) The catalyst is efficient, sustainable, stable and recy-
clable. 4) The catalyst is cheap and formed in single step, no
coating/loading material or functionalisation is used. 5) The
catalyst has small size, high surface area and magnetic proper-
ties. These features make the present work useful from indus-
trial, economical and environmental points of view.
8 (a) A. H. Lu, E. L. Salabas and F. Schuth, Angew. Chem., Int.
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W. R. Thiel, Angew. Chem., Int. Ed., 2010, 49, 3428–3459; (c)
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9 A. Rostami, B. Atashkar and H. Gholami, Catal. Commun.,
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Commun., 2005, 4435–4437; (b) H. Yoon, S. Ko and J. Jang,
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Acknowledgements
We are thankful to SAIF, Panjab University Chandigarh for
1
FT-IR, TEM, H-NMR, 13C-NMR, XRD for IIT Ropar and CIL,
IIT Roorkee for VSM. One of the authors (G. K.) is thankful to
MHRD and NIT Jalandhar for providing the research
fellowship.
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