β-Enaminones over recyclable nano-CoFe2O4: a highly efficient solvent-free green protocol

Article abstract of DOI:10.1007/s11164-018-3454-5

Abstract: β-Enaminone and its derivatives have emerged among the finest bioactive intermediates. High yields of several β-enaminones (86–97%) are achieved through treatment of substituted aromatic and aliphatic amines with cyclic/acyclic 1,3-diketones, over the magnetically separable cobalt ferrite nanoparticles (CoFe₂O₄ NPs). The latter was prepared upon co-precipitation. Its purity, fine crystallinity, elemental distributions, morphology, magnetic features, and thermal stability were confirmed by Fourier transform infrared, X-ray diffraction, energy dispersive X-ray spectrometry, scanning electron microscopy, vibrating sample magnetometry, and thermal gravimetric analysis analyses. Thus, CoFe₂O₄ NPs acted as an excellent green heterogeneous nanocatalyst for synthesis of β-enaminones and gave good recyclability, while showing insignificant loss of their activity. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11164-018-3454-5

Res Chem Intermed
https://doi.org/10.1007/s11164-018-3454-5
b-Enaminones over recyclable nano-CoFe2O4: a highly
efficient solvent-free green protocol
Esmaiel Eidi1 Mohamad Z. Kassaee1,2 Peter T. Cummings2
•
•
Received: 6 February 2018 / Accepted: 24 April 2018
Ó Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract b-Enaminone and its derivatives have emerged among the finest bioactive
intermediates. High yields of several b-enaminones (86–97%) are achieved through
treatment of substituted aromatic and aliphatic amines with cyclic/acyclic 1,3-diketones,
over the magnetically separable cobalt ferrite nanoparticles (CoFe2O4 NPs). The latter
was prepared upon co-precipitation. Its purity, fine crystallinity, elemental distributions,
morphology, magnetic features, and thermal stability were confirmed by Fourier trans-
form infrared, X-ray diffraction, energy dispersive X-ray spectrometry, scanning elec-
tron microscopy, vibrating sample magnetometry, and thermal gravimetric analysis
analyses. Thus, CoFe2O4 NPs acted as an excellent green heterogeneous nanocatalyst for
synthesis of b-enaminones and gave good recyclability, while showing insignificant loss
of their activity.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11164-
018-3454-5) contains supplementary material, which is available to authorized users.
Mohamad Z. Kassaee: Visiting scholar (sabbatical).
&
Mohamad Z. Kassaee
mohamad.z.kassaee@vanderbilt.edu; kassaeem@modares.ac.ir
1
2
Department of Chemistry, Tarbiat Modares University, P.O. Box 14155-175, Tehran, Iran
Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN 37211, USA
123

E. Eidi et al.
Graphical Abstract
O
O
R
HN
O
R NH2
Solvent-free
80 o
C
Keywords Magnetic nanocatalyst Á Cobalt ferrite Á Bimetallic oxide Á Synthons Á b-
Enaminones
Introduction
Bimetallic oxide nanoparticles (NPs) often show synergistic effects in catalyzing
modern organic reactions [1–3]. They are involved in heterogeneous catalysis,
improving the yield, simplification of reaction conditions, economic efficiency,
providing high catalytic surface area, easy separation and workup, etc. In addition,
the nanosize and magnetic properties of spinel ferrites have made them crucial in
science and technology [4]. Nano-cobalt ferrite has attracted much attention because
of its large surface-to-volume ratio, high magnetization, and magnetic behavior
dependence on its size and shape [5–7]. Applications of CoFe2O4 nanocrystals
involve environmental remediation, biomedical diagnosis, therapy, high-density
magnetic storage, and catalytic innovative synthesis [8–10]. b-Enaminones are one
of the finest bioactive intermediates. They are used for the synthesis of many
important compounds including a,b-amino acids [11, 12], c-amino alcohol [13],
heterocycles [14], alkaloids [15, 16], quinolines [17], azocompounds [18], etc. b-
Enaminones are employed as basic synthons for various drugs used as antitumor
[19], antiepileptic [20], antibacterial [21, 22], anticonvulsant [23], antitussive [24],
anti-inflammatory [25], etc. (Scheme 1).
Numerous procedures have been developed for synthesis of enaminones using
different catalysts such as ZrOCl2Á8H2O [26], NaAuClO4 [27], Ag NPs [28], Cu
NPs [29], Zn(ClO4)2Á6H2O [30], Zn(OAc)2Á2H2O [31], CeCl3Á7H2O [32], ZrCl4
[33], SiO2-sulphuric acid [34], silica-supported Fe(HSO4)3 [35], bimetallic Ag–Cu
alloy NPs [36], industrial-quality graphene oxide (IQGO) [37]. Here in continuation
of our investigation [38, 39], we describe an economically sound, simple, and
efficient protocol for the synthesis of pure b-enaminones, with minimal side-
products, through the reaction of 1,3-dicarbonyl compounds and amines, using
cobalt ferrite NPs as a reusable heterogeneous catalyst under solvent-free conditions
(Scheme 2).
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b-Enaminones over recyclable nano-CoFe2O4: a highly…
O
N
O
O
NH2
Me
OH
N
H
3CO2S
F3C
O
N
N
H
N
H2N
Hap90
N
H
Anti-mitotic
inhibitor
N
Anti-anginal
F3C
Cl
CB1 ANTAGONIST
O
R
N
H
O
R
R
O
R
F
N
R
N
H
R
N
H
OH
N
OH
COOH
O
NH
O
O
Atrovastatin
OH
O
N
H
Me
C11H23
H
F
N
O
OH
N
COOH
N
H
NH
N
Me
O
mPGES-1 inhibitor
Anti-i
nflammat
ory
Antiangiogenic
Anti-proliferative
N
O2
NH
2HCl
OH
H
OPri
HN
O
N
O
NH
O
O
O
O
N
H3C
OH
OH OH
O
O
CH3
O
OCH3
O
Antieukemia
Antmicrobial
Antibacterial
O
Herbicide
O
O
OMe
O
O
O
N
H
N
N
H
O
O
N
N
H
O
O
O
Flavipucine
Antitumors
Antihypertensive
Scheme 1 Examples of bioactive b-enaminones
Scheme 2 Synthesis of b-enaminones catalyzed by CoFe2O4 NPs
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E. Eidi et al.
Experimental
Materials and physical techniques
All chemical reagents used in our experiments were purchased from Merck or
Aldrich Chemical Company with high purity. All solvents were distilled, dried, and
purified using standard procedures. Melting points were measured on an
1
Electrothermal 9100 apparatus. H NMR and 13C NMR spectra were recorded on
a Bruker Avance instrument (DPX 300 MHz and DPX 75 MHz) in pure deuterated
dimethylsulfoxide (DMSO-d6) using tetramethylsilane (TMS) as an internal
reference. Fourier transform infrared (FT-IR) spectra were recorded using KBr
pellets on a Nicolet IR-100 infrared spectrometer. The powder X-ray diffraction
(XRD) spectrum was recorded at room temperature using a Philips X-Pert 1710
˚
diffractometer. The latter appeared with Co Ka (a = 1.79285 A) with a voltage of
40 kV, a current of 40 mA, and was in the range of 20–80° (2h) with a scan speed of
0.02 °/s. The particle morphology was examined by scanning electron microscopy
(SEM) using a HITACHI S-4160 scanning electron microscope on gold-coated
samples. Magnetic properties were obtained by a vibrating sample magnetometer/
alternating gradient force magnetometer (VSM/AGFM, MDK Co., Iran).
Preparation of magnetic CoFe2O4 NPs
Initially, magnetic CoFe2O4 NPs were prepared by chemical co-precipitation of
chloride salt of Fe3? and Co2? ions with a molar ratio of 2:1. Typically, FeCl3Á6H2O
(5.8 g, 0.02 mol) and CoCl2 (1.3 g, 0.01 mol) were dissolved in 100 mL of
deionized water at 80 °C under N2 atmosphere and vigorous stirring. Then, 10 mL
of 25% NH4OH was quickly injected into the reaction mixture in one portion. The
addition of the base to the Co2?/Fe3? salt solution results in immediate formation of
a black precipitate of magnetic NPs (MNPs). The reaction was continued for
another 60 min and the mixture was cooled to room temperature. The black
precipitate was washed with doubly warm distilled water and dried in vacuum
overnight.
General procedure for synthesis of b-enaminones
CoFe2O4 MNPs (0.01 g) were added to a mixture of 1,3-diketone (1 mmol) and
amine (1 mmol) at 80 °C and stirred in an oil bath for an appropriate time under
solvent-free conditions. After the completion of the reaction (monitored by thin-
layer chromatography), the product was extracted with hot ethanol (3 mL), catalyst
was separated by an external magnet, washed several times with water and ethanol,
and dried under vacuum at room temperature, to prepare for a later run.
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b-Enaminones over recyclable nano-CoFe2O4: a highly…
Results and discussion
Characterization of the catalyst
In continuation of our previous work [38, 39], we report the use of CoFe2O4 as a
heterogeneous nanocatalyst, with high efficiency for the synthesis of b-enaminones.
Cobalt ferrite is prepared and characterized via FT-IR, VSM, energy-dispersive
X-ray spectrometry (EDX), SEM, thermal gravimetric analysis (TGA), and XRD
analyses.
FT-IR spectroscopy
Among FT-IR peaks of CoFe2O4, the strong absorption at 597.54 cm-1 corresponds
to the M–O tetrahedral site of the spinel structure and shows the basic nature of the
NPs (Fig. 1). The broad bands at 3405.11 and 1628.29 cm-1 are attributed to the
hydroxyl groups stretching and bending vibrations of water, respectively.
X-ray diffraction
According to International Center for Diffraction Data PDF cards 3-864 and
22-1086, CoFe2O4 NPs have a cubic structure (Fig. 2) [40, 41]. The powder XRD
pattern in the high-angle region of 5 B 2h B 80 for the sample of CoFe2O4 shows
six different peaks at 2h about 35.1°, 41.4°, 50.9°, 63.5°, 67.5°, and 74.4° marked by
their indices (220), (311), (400), (422), (511), and (440), respectively. The sharp
peaks and the lack of additional peaks confirm the purity and the good crystallinity
of the prepared nanocatalyst.
EDX analyses
The chemical composition of the product is further examined using EDX, which
reveals Co and Fe elemental distributions in CoFe2O4 (Fig. 3).
Fig. 1 FT-IR spectrum of CoFe2O4 NPs
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E. Eidi et al.
Fig. 2 XRD pattern of the catalyst CoFe2O4 NPs
Fig. 3 Energy-dispersive spectrometry (EDX) results of CoFe2O4 NPs
SEM
The size and morphology of CoFe2O4 NPs are estimated via SEM (Fig. 4).
Uniformly dispersed spherical particles are observed, along with weak agglomer-
ations. The obtained histogram of the SEM image shows a narrow maximum
particle size distribution in the range of 10–30 nm.
VSM
The magnetic features of the catalyst, which accounts for its easy recovery, is
confirmed using a VSM in the range from ?1 to -1 T. Room temperature-specific
magnetization (M) versus applied magnetic field (H) curve measurements of the
sample indicate a saturation magnetization value (Ms) of 17 emu g-1 (Fig. 5).
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b-Enaminones over recyclable nano-CoFe2O4: a highly…
Fig. 4 SEM analysis of the CoFe2O4 NP catalyst
Fig. 5 Vibrating sample magnetometer curve for CoFe2O4 NPs
Thermal analyses
TGA/differential thermal analyses (TGA/DTA) of CoFe2O4 NPs are recorded over a
temperature range of room temperature to 900 °C at rate of 10 °C min-1 (Fig. 6).
The thermogram shows an initial weight loss at 100 °C due to water desorption. The
slight weight loss below 350 °C may be due to dehydration of water or loss of
hydroxyl groups present on the surface of the spinel structure; no further mass loss
is detected up to 800 °C, which indicates the thermal stability of the catalyst
[42, 43].
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E. Eidi et al.
Fig. 6 TGA/DTA/differential thermogravimetry analysis of CoFe2O4 NPs
Catalytic activity
After characterization of CoFe2O4, its activity was probed as a heterogeneous
catalyst in the preparation of b-enaminones. To access the optimum conditions, we
employed model reaction of acetyl acetone (1 mmol), and benzylamine (1 mmol)
over various amounts of the nanocatalyst under solvent-free conditions at various
temperatures (Table 1). Firstly, the effect of temperature was examined with
Table 1 Optimization of the
reaction conditions
Entry Catalyst (mg) Temperature (°C) Time (h) Yield (%)a
1
10
10
10
10
10
10
15
10
5
25
40
60
70
80
80
80
90
80
80
100
80
80
80
3
3
3
3
3
2
3
3
3
4
6
3
3
3
15
37
60
88
96
84
96
97
82
96
43
27
77
86
2
3
4
5
Reaction conditions: acetyl
acetone (1 mmol), benzylamine
(1 mmol), solvent-free
aIsolated yield
bReaction conditions: CoCl2,
acetyl acetone (1 mmol),
benzylamine (1 mmol), solvent-
free
6
7
8
9
10
11
12
13b
14c
10
–
cReaction conditions:
–
FeCl3Á6H2O, acetyl acetone
(1 mmol), benzylamine
(1 mmol), solvent-free
10
10
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b-Enaminones over recyclable nano-CoFe2O4: a highly…
Table 2 Synthesis of b-enaminones in the presence of CoFe2O4 NPs under solvent-free condition
Reaction conditions: 1,3-diketone (1 mmol), amine (1 mmol), solvent-free, 80 °C, 3 h
Isolated yield
aReaction conditions: 1,3-diketone (2 mmol), amine (1 mmol), solvent-free, 80 °C, 3 h
constant amounts of the catalyst. The yield of the desired enaminones rose at higher
temperatures, requiring shorter reaction times. It is noticed that the temperature
plays a crucial role in the present system. A decrease in temperature results in
reduced yield with traces of the product at room temperature. In order to find the
effectiveness of the catalyst, the model reaction is studied with different amounts of
the catalyst (5, 10, 15 mg) at various times in solvent-free conditions. The best
result is obtained when the reaction reaches 96% conversion in 3 h with 10 mg of
the catalyst. Increasing the amount of the catalyst from 10 to 15 mg does not
significantly affect the yield of the product formed. In the absence of the catalyst, no
improvement of the product yield is observed at temperatures [ 80 °C. Also, to
distinguish between the roles of homogeneous versus that of heterogeneous
catalysts, the reactions were run under similar conditions with comparable amounts
of Co2?, Fe3?, and CoFe2O4 NPs, giving product yields of 77, 86, and 96%,
respectively (Table 1).
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E. Eidi et al.
Scheme 3 A plausible mechanism for catalytic synthesis of b-enaminones over CoFe2O4 NPs
Fig. 7 Recyclability of CoFe2O4 NPs in catalytic synthesis of b-enaminones
Using these optimized reaction conditions, we extended the scope and efficiency
of this protocol by reaction of substituted aromatic and aliphatic amines, with
cyclic/acyclic 1,3-diketone (Table 2). Substituents present (electron withdrawing or
electron donating) on the aromatic rings of the amines do not significantly affect the
yield of the desired products. As the results indicate, this procedure is uniformly
effective for both aliphatic and aromatic amines. For practical applications,
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b-Enaminones over recyclable nano-CoFe2O4: a highly…
Table 3 Activity of CoFe2O4
Entry Catalyst
Condition
Yield (%)b Ref.
NPs versus those of other
catalysts in catalytic synthesis of
1
2
3
4
5
6
Ag NPs
CH3OH/60 °C/8 h
CH3OH/60 °C/48 h 86
90
[28]
[31]
[44]
[45]
[37]
–
b-enaminones
Zn(OAc)2ÁH2O
Fe(NO3)3Á9H2O CHCl3/r.t./90 min
88
83
85
92
CuO NPs
60 °C/9 h
60 °C/3 h
80 °C/3 h
IQGO
CoFe2O4 NPs
bIsolated yield
diamines are used as nucleophiles to obtain bis-(b-enaminones) and bis-(b-enamino
esters; Table 2q, y, z).
Following our plausible mechanism, CoFe2O4 NPs appears to act as a Lewis acid
by increasing the electrophilicity of the carbonyl groups of diketones, giving I. The
amine’s nucleophilic attack on the activated carbonyl group of I leads to
intermediate II. Subsequent loss of water from III affords imine IV, which may
render V through tautomerisation (Scheme 3).
Upon completion of the reactions, potential catalyst recycling was probed using
the model reaction under described reaction conditions. After completion of the
reaction, the catalyst was readily separated by an external magnet and washed with
ethanol. It was dried under vacuum and reused directly in the next cycle where no
significant loss of its activity was observed (Fig. 7).
In order to investigate the efficiency of this procedure in comparison with known
methods reported in the literature, the activity of CoFe2O4 NPs was probed against
others in catalytic synthesis of (Z)-4-(phenylamino)pent-3-en-2-one (Table 3).
Conclusion
In continuation of our attempts to make important synthons for biological
compounds, a heterogeneous nanocatalyst, CoFe2O4 NPs, was fabricated and fully
characterized. Subsequently, it was employed in an efficient, one-pot, solvent-free
preparation of a number b-enaminone derivatives with minimal side-products
(86–97%). Specifically, this achievement was reached through treatment of
substituted aromatic and aliphatic amines with cyclic/acyclic 1,3-diketones over
the magnetically separable CoFe2O4 NPs. Other than high yields, the nanocatalyst
offers several promising advantages, including short reaction time, easy handling,
simple work up procedure, product purity, ease of separation, and recyclability of
the catalyst. A control test involving comparable amounts of Co2?, Fe3?, and
CoFe2O4 NPs under similar conditions clearly indicated higher efficiency of the
latter heterogeneous nanocatalyst over the former homogeneous ions. The magnetic
properties of CoFe2O4 NPs help easy separation from the reaction mixture. The
introduced magnetically stable nanocatalyst could be reused in five successive runs
with no significant structural change or loss of activity.
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E. Eidi et al.
Compliance with ethical standards
Conflict of interest The authors declare no conflict of interest.
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