Synthesis and characterization of nano-copper ferrite as a magnetically separable catalyst for the one-pot synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles under solvent-free condition

Article abstract of DOI:10.1080/15533174.2016.1212223

The authors report herein, synthesis and characterization of nano-copper ferrite as a recoverable, ecofriendly, inexpensive, and readily available catalyst for efficient, simple, and green synthesis of multisubstituted imidazoles. Short reaction times, high yields, easy workup, and mild condition are the advantages of this protocol. The catalyst can be reused without evident loss of the catalytic activity. Characterization of the catalyst was performed fully by Fourier transform infrared spectra, X-ray diffraction, FESEM, electron dispersive X-ray, and vibration sampling magnetometer analyses.

Full text of DOI:10.1080/15533174.2016.1212223

Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry
ISSN: 1553-3174 (Print) 1553-3182 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt20
Synthesis and Characterization of Nano-copper
ferrite as a Magnetically Separable Catalyst for
the One-pot Synthesis of 2,4,5- Trisubstituted and
1,2,4,5-Tetrasubstituted Imidazoles under Solvent-
free Condition
Firouzeh Nemati, Ali Elhampour & Mahshid Bagheri Natanzi
To cite this article: Firouzeh Nemati, Ali Elhampour & Mahshid Bagheri Natanzi (2016):
Synthesis and Characterization of Nano-copper ferrite as a Magnetically Separable Catalyst for
the One-pot Synthesis of 2,4,5- Trisubstituted and 1,2,4,5-Tetrasubstituted Imidazoles under
Solvent-free Condition, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal
Chemistry, DOI: 10.1080/15533174.2016.1212223
To link to this article: http://dx.doi.org/10.1080/15533174.2016.1212223
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Synthesis and Characterization of Nano-copper ferrite as a Magnetically Separable
Catalyst for the One-pot Synthesis of 2,4,5- Trisubstituted and 1,2,4,5-Tetrasubstituted
Imidazoles under Solvent-free Condition
Firouzeh Nemati,* Ali Elhampour, Mahshid Bagheri Natanzi
Department of Chemistry, Semnan University, Semnan, 35131-19111 Iran
*Corresponding author. E-mail: fnemati_1350@yahoo.com; fnemati@semnan.ac.ir.
Abstract
We reported here in, synthesis and characterization of nano-copper ferrite as
aمتن یا آدرس
وب سایتی را
تایپ
یا
کنید
را
سندی
ترجمه کنید.
ترجمه از:
فارسیrecoverable, eco-friendly, inexpensive and
readily available catalyst for efficient, simple and green synthesis of multi-substituted
imidazoles.. Short reaction times, high yields, easy workup and mild condition are the
advantages of this protocol. The catalyst can be reused without evident loss of the catalytic
activity. Characterization of the catalyst was performed fully by FT-IR, XRD, FESEM, EDX and
VSM analyses.
Keywords
Nano-magnet; Heterogeneous catalyst; Benzil; Copper ferrite
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Introduction
Multi-component reactions have been shown as versatile synthetic tools for the assembling of
novel and structurally complex molecules from simple starting materials in minimum of reaction
steps (1). These reactions have emerged a valuable manner for the formation and breakage of
carbon-carbon and carbon-heteroatom bonds in one-pot and simple work-up procedure. The
synthesis of highly substituted imidazoles is a very good application for multi-component
reaction, because the imidazole moiety is an important nucleus that comprises a key structure of
numerous natural and bio-active molecules (2-4). For example benzimidazole-based structures
were found in medical active compounds such as omperazole (5), pimobendan (6), histamine,
biotin and histidine (7). Moreover, imidazoles were found to possess multiple pharmacological
and biological activities such as antibacterial (8), antiplasmodium (9), anticancer (10), anti-
fungal (11), anti-inflammatory (12), analgesic (13), anti-allergy (14), anticonvulsant (15) and
anti-HIV (16). Therefore, a number of methods for the synthesis of imidazole derivatives have
been reported that mostly involve a three-component reaction of benzil/benzoin, aldehydes and
aromatic primary amines or ammonium acetate using different catalysts such as perlite-HBF4
(17), ionic liquid (18), DABCO (19), Fe3O4@chitosan (20), FeCl3-6H2O (21), BF3-SiO2 (22),
InCl3-3H2O (23), K5CoW12O40-3H2O (24), ZnO (25), Hetropolyacids (26), p-TsOH (27), MCM-
41-SO3H (28), nano-TiCl4-SiO2 (29), cellulose supported sulfuric acid (30), urea-functionalized
Fe3O4/SiO2 (31), NiCl2-6H2O (32), PEG-400 (33), 2,6-dimethylpyridinium trinitromethanide
(34), cobalt ferrites (35), potassium dihydrogen phosphate (36), molecular iodine (37), graphene
oxide-chitosane (38), Fe3O4-chitosane (39) . Hence, in view of widespread applications and the
aforementioned biological properties, the development of environmentally benign synthetic routs
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for the preparation of imidazoles derivatives is still remains a considerable interest.
Following the increasing environmental and economic concerns the search for
economical synthetic methods for organic transformations has received special attention. In this
regards, utilization of magnetic ferrites has gained much interest because of economic and
environmental considerations (40).
Among them, copper ferrite nanoparticles (CuFe2O4) have the great interest due to
stability, easy work-up, magnetic separability and recyclability which minimize the organic
waste generation as compared to the conventional catalytic systems.
Considering the above subjects and continuing our efforts on the development of
environmental benign synthetic methodology (41), herein we wish to report a facile procedure
for synthesis of highly substituted imidazoles in the presence of catalytic amount of nano-
CuFe2O4 under solvent-free condition at 90°C with short reaction time in high to good yields.
Results and Discussion
At first, nano-CuFe2O4 was synthesized using a chemical co-precipitation method
according to literature report (42) and fully characterized by X-ray diffraction (XRD), Fourier
transform infrared spectra (FT-IR), scanning electron microscopy (SEM), vibration sampling
magnetometer (VSM), electron dispersive X-ray (EDX) and DLS analysis.
The FTIR spectrum of the magnetic nanoparticles is shown in Figure 1a. The adsorption band
at 563 cm-1 is attributed to metal-O stretching mode and stretching vibration of tetrahedral sites.
The bands centred at 3400 cm-1, clearly indicated the OH on the surface of magnetic
nanoparticles. The XRD pattern of CuFe2O4 is shown in Figure 1b. The peak position and
relative intensity of all peaks clearly matches with the literature data (42) and the patterns
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demonstrate the tetragonal structure of copper ferrite CuFe2O4. Typical diffraction peaks located
approximately at 18.3, 30.3, 35.6, 42.8, 57.1 and 62.98 can be well assigned to the diffraction of
CuFe2O4 nanoparticles with spinal from the (101), (200), (211), (221), (303) and (224) planes,
respectively. The crystallite size of the nanoparticles was calculated to be around 25 nm from the
XRD results using the Debye-Scherrer equation.
Elemental analyses of the CuFe2O4 NPs were performed with EDX analysis (Figure 2).
Quantitative EDX analysis showed that, Fe, Cu and O were the main elemental components. The
analysis indicates that as-synthesized MNPs are of initial
formula CuFe2O4.
SEM was used to examine the morphology of the nanoparticles. It can be observed that the as-
prepared nano-CuFe2O4 particles are uniform and nearly spherical in shape and possess a smooth
and clean surface (Figure 3).
Room-temperature magnetization study shows that the NPs have super-paramagnetic
properties (Figure 4). The saturation magnetization of CuFe2O4 was 33.86 emu/g, that enough for
magnetic separation from the reaction.
After successful preparation and characterization of nano-CuFe2O4 particles the catalytic
performance of MNPs was examined in the synthesis of 2,4,5-triaryl-1H-imidazoles and 1,2,4,5-
tetraaryl-1H-imidazoles by one-pot condensation of benzil with a variety of arylaldehydes,
primary aromatic amines and ammonium acetate. For this purpose the reaction of benzaldehyde,
benzil and ammonium acetate was selected as a template reaction in various solvents,
temperatures and loading of magnetic NPs. The results for the optimization of the reaction
conditions are summarized in Table 1. No product was obtained in the absence of the catalyst
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indicating that the catalyst is necessary for the reaction. To improve the yield of the product the
model reaction was tested with 0.03, 0.05 and 0.075 g of the catalyst at 90°C. Further increase of
catalyst loading does not affect the yield. Also the effect of temperature was studied by carrying
out the model reaction at different temperatures under solvent free condition. The use of other
solvents such as EtOH afforded the desired product in lower yields in the model reaction. As
could be seen in Table 1, no product was obtained in presence of water. As the reaction done in
high temperature, the optimization of ammonium acetate also achieved (Table 1, entries 12 and
13). Finally, the results reveal that 0.05 g nano-magnetic catalyst, neat condition (at the begin of
the reaction few drops of EtOH was added) at 90°C in the presence of 3 mmol ammonium
acetate were the best to afford 2,4,5-triphenyl imidazole in 98% yield in short reaction time(12
min.). So this condition was chosen for all further studies.
The generality of present methodology was studied with the range of arylaldehydes as
presented in Table 2. To our delight almost all screened arylaldehydes underwent in this reaction
to afford the triarylimidazoles exclusively in 85 to 98% yields in 10-70 minutes as shown in
Table 2. The results show that the reactions are facile with both electron-donating and electro-
withdrawing substituents on arylhalides. However, aliphatic aldehydes were unable to provide
the desired product in an acceptable yield (Table 2, entry 14 and 15).
With this interesting results in our hand, we further investigated the possibility of
synthesis of 1,2,4,5-tetrasubstituted imidazoles by condensing benzil(1 mmol), arylaldehydes (1
mmol), aromatic amines (1.1 mmol) and ammonium acetate ( 1 mmol) in the same condition.
Optimization of model reaction (benzil; ammonium acetate; aniline and benzaldehyde) show that
the 1.1 mmol of aromatic amine gave the higher yield of corresponding product. The results are
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illustrated in Table 3. These show that aldehydes with electron releasing group provided better
results as compared to benzaldehyde (Table 3).
On the basis of literature survey (18, 38, 43)a plausible mechanism for the reaction is
shown in Scheme 1. At first the catalyst facilitates the formation of diamine intermediate [A] by
increasing the electrophilicity of the carbonyl group of the aldehyde. Intermediate [A], condenses
with benzil to form intermediate [B], which rearranges via a [1, 5] sigmatropic shift or
elimination of water to the corresponding tri or tetra substituted arylimidazoles.
To examine the reusability of nano-CuFe2O4, after each run, the catalyst was separated
from by an external magnet, washed with diethyl ether, then with acetone, dried and reused in
another reaction. Treatment with acetone removes the tar (the organic residue in the catalyst)
from the catalyst surface more efficiently. The template reaction was repeated with recycled
nano-magnetic catalyst and the yields were found to remain in the range of 98-90% for five runs.
Table 4 compared the efficiency of our methods with recently reported works for
synthesis of tri-substituted imidazoles. As it can be seen from Table4, CuFe2O4 was used as an
efficient catalyst in ETOH at 70ºC (Table 4, entry 12) (35). But, in this research limited
derivatives of tri-substituted imidazoles were reported. So, we believe that synthesis of various
imidazoles can be carried out under our suggested condition with respect to reaction times and
product yields.
Experimental
Chemicals were purchased from the Fluka, Merck and Aldrich chemical companies.
Melting points were determined on Electro thermal 9100 without further corrections. TLC on
commercial aluminum-backed plates of silica gel 60 F254 was used to monitor the progress of
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reactions. Infrared spectra were recorded on a Shimadzu 8400s spectrometer with KBr plates.
Only representative absorptions are given. NMR spectra were taken in DMSO on a Bruker
Avance 3–400 MHz instrument at 20–25 °C.
Preparation of nano-CuFe2O4
The nano-CuFe2O4 particles were prepared according to literature report (42).
The procedure for the synthesis of 2,4,5-triphenyl-1H-imidazoles:
A mixture of benzil (0.21 g, 1 mmol), benzaldehyde (0.106 g, 1 mmol), NH4OAc (0.23 g,
3 mmol) and nano-CuFe2O4 (0.05 g, 0.195 mmol) were placed in a round bottom flask and
stirred at 90°C for the appropriate time (indicated in Table 2) under solvent free conditions. After
completion of the reaction (monitored by TLC) the mixture was allowed to cool, dissolved in hot
ethanol and the catalyst removed magnetically. The pure products were crystallized from hot
ethanol.
The procedure for the synthesis of 2-methoxy-4-(1,4,5-triphenyl-1H-imidazol-2-yl) phenol:
Benzil (0.21g, 1 mmol), aniline (0.102 g, 1.1 mmol), 4-hydroxyl-3-methoxy
benzaldehyde (vanillin) (0.152 g, 1 mmol), ammonium acetate (0.077 g, 1 mmol) and and nano-
CuFe2O4 (0.05 g, 0.195 mmol) were placed in a round bottom flask and stirred at 90°C for 40
minutes, under solvent free condition. After completion of the reaction (monitored by TLC) the
mixture was cooled to room temperature and dissolved in ethyl acetate. The catalyst was
removed magnetically and the product was purified by a short column chromatography to afford
the pure products in 90% yield.
2-methoxy-4-(1,4,5-triphenyl-1H-imidazol-2-yl) phenol :M.P. 209-210 °C; IR (KBr): 3058 (C-H
1
aromatic), 1600, 1473 (C=C aromatic), 1539(C=N), 1473, 1120 (C-O-Ar) cm−1, H-NMR (400
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MHz, DMSO-d6): δ 3.43 (d, 3H, CH3) , 6.68 (d, 1H, ArH), 6.84–6.87 (m, 2H, ArH), 7.14–7,32
13
(m, 13H, ArH), 7.48–7.50 (d, 2H, ArH), 9.27 (s, 1H, OH) ppm; C NMR (100 MHz, DMSO-
d6): δ 31.14, 55.62, 126.81, 128.57, 128.73, 128.88, 128.99, 129.34, 129.57, 131.06, 131.59,
146.82, 147.33; Anal. Calcd. for C28H22N2O2: C 80.38, H 5.26, N 6.69; found: C 80.29, H5.39, N
6.54.
Conclusion
This research demonstrates the efficient synthesis of tri- and tetra substituted imidazole
derivatives using a catalytic amount of inexpensive, magnetically separable and recyclable
CuFe2O4 nano-magnetic particles in solvent-free condition. This method provided short reaction
times, simplicity and an economical in operation, simple workup and environmental friendliness,
with high performance and good to excellent yield.
Acknowledgements
The authors gratefully acknowledge Semnan University Research Council for financial
support of this work.
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Table 1. Reaction conditions evaluation in model reaction for synthesis trisubstituted imidazoles.
CuFe2O4 loading NH4CH3COO
Time
(min)
12
12
12
12
8h
8 h
35
35
Entry
Condition
Yield (%)
(g)
(mmol)
1
2
3
4
5
6
7
8
9
10
11
12
13
3
3
3
3
3
3
3
3
3
3
3
2
4
S.F/ 90°C
S.F/ 90°C
S.F/ 90°C
S.F/ 90°C
S.F/r.t.
-
47
98
81
Trace
-
73
42
38
30
55
77
98
0.03
0.05
0.075
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
H2O/Reflux
EtOH/Reflux
CH3CN/Reflux
THF/Reflux
S.F/70°C
35
12
12
12
S.F/80°C
S.F/ 90°C
S.F/ 90°C
12
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Table 2. Synthesis of tri-aryl imidazoles using magnetic nano-catalysta.
Ph
N
Ph
Ph
O
O
CuFe2O4
(0.05 g)
Ar
NH4OAC
R-CHO
N
H
Solvent-Free
90C
Ph
Entry
1
R
Time(min) Yield(%)b
Mp(Lit.)°C
Ph
12
40
60
12
40
73
45
32
44
45
35
48
24
120
120
98
98
94
85
95
86
80
90
90
94
88
85
98
trace
trace
276-277 (275-276) (44)
220-223 (220–223) (45)
207-209 (210–211) (45)
360-364 (>350) (46)
256-258 (258–260) (44)
191-193 (190–191) (45)
241-243 (241–242) (47)
260-261 (260-261) (48)
166 (197) (41a)
266-267 (267-268) (41a)
325-327 (>300) (49)
234-236 (236–238) (50)
305-308 (>300) (41a)
-
2
3
4
5
6
7
8
9
10
11
12
13
14
15
4-MeO_C6H4
2-MeO_C6H4
4-HOC_C6H4
4-Cl_C6H4
2-Cl_C6H4
2-naphthyl
2-thiophene
4-HO-3-EtO_C6H3
4-Br–C6H4
3-O2N–C6H4
4-O2N–C6H4
4-HO2C–C6H4
n-C4H9
(CH3)2CH
-
aReaction condition: arylaldehydes (1 mmol), benzyl (1 mmol), ammonium acetate (3 mmol),
CuFe2O4 (0.05 g), 90°C, solvent-free.
b Isolated yield.
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Table 3. Synthesis of tetra-aryl imidazoles using magnetic nano-catalysta.
Ph
Ph
N
Ph
Ph
O
O
(0.05 g)
CuFe2O4
Ar1
Ar1-CHO
NH4OAC
Ar2-NH2
N
Solvent-Free
90C
Ar2
Time
(min)
40
40
80
40
100
50
Yield
Entry
1
Ar1
Ar2
Mp (Lit.) °C
209-210
199-201 (199-201)(41a)
219-221 (218) (41a)
185-186.5 (41a)
192-194 (190–193) (41a)
170-172 (173–175) (41a)
(%)b
90
4-HO-3-MeO_C6H3
3-EtO-4-HO-C6H3
C6H5
C6H5
4-Me–C6H4
C6H5
C6H5
4-Cl–C6H4
4-Me–C6H4
92
77
90
70
3
4
5
6
4-MeO-C6H4
C6H5
C6H5
82
aReaction condition: arylaldehydes (1 mmol), benzil (1 mmol), aryl amine (1.1 mmol),
ammonium acetate (1 mmol), CuFe2O4 (0.05 g), 90°C, solvent-free.
b Isolated yields.
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Table 4. Comparison of catalytic activity of CuFe2O4 with some reported catalysts for synthesis
of 2,4,5-triphenyl-1H-imidazoles.
Time
Yield
(%)
Entry
Catalyst
Ref
Conditions
(min.)
1
2
CuFe2O4 (0.01 mol%)
Cyclic phosphoric acid
Celulose supported
sulfuric acid
perlite-HBF4
NiCl2-6H2O
MgAl2O4
S.F., 90 oC
S.F., 80 oC
12
30
98
80
This work
43b
3
S.F., MW
2
96
30
4
5
6
7
35
25
30
98
94
97
17
32
EtOH, Reflux
S.F., 120ºC
H2O, Reflux
ZnO
2.5 h 80
25
31
urea-functionalized
Fe3O4/SiO2
Fe3O4@chitosan
SiO2-Cu2O
8
EtOH, Reflux
50
95
9
EtOH, Reflux
EtOH, Reflux
EtOH, 70ºC
EtOH, 70ºC
2h
15
10
10
95
90
98
94
39
43a
35
10
11
12a
CoFe2O4
CuFe2O4
35
graphene oxide-
chitosane
13
14
S.F., 120º
10
43
95
94
38
-
Glycerol, 90º
41a
aThe nano-magnetic particles synthesized in different procedure and reported for limited
derivatives.
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Figure 1. (a) FTIR and (b) XRD of CuFe2O4 particles.
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Figure 2. The EDX analysis of nano-CuFe2O4.
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Figure 3. The FESEM analysis of the nano-CuFe2O4 magnetic
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Figure 4. VSM curve of the nano-CuFe2O4 magnetic.
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Scheme 1. A plausible mechanism.
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