Synthesis of polymer-supported Fe3O4 nanoparticles and their application as a novel route for the synthesis of imidazole derivatives

Article abstract of DOI:10.1007/s11164-018-3536-4

Abstract: Cross-linked poly(4-vinylpyridine) supported Fe₃O₄ nanoparticles, abbreviated as [P₄-VP]-Fe₃O₄NPs, were easily prepared as a new magnetic polymeric catalyst and efficiently used for the synthesis of imidazole derivatives. The polymeric catalyst was characterized by using of?various techniques including field emission scanning electron microscopy, X-ray diffraction, vibrating sample magnetometry and Fourier transform infrared spectroscopy (FT-IR) techniques. According to the obtained results, good dispersion of Fe₃O₄ nanoparticles on the polymer-support and excellent magnetic property of the catalyst were achieved. Various methods have been reported for the synthesis of multi-substituted imidazoles by the reaction of benzil, aldehydes and amines or ammonium acetate in the presence of various catalysts. These methods have some disadvantages including long reaction times, non-reusability of the catalyst, polluted reaction conditions, effluent pollution, and low yields; therefore, we wish to report an efficient, fast, clean and green method for the synthesis of imidazole derivatives that has been developed by one-pot condensation reaction of benzil, ammonium acetate and aldehydes in the presence of [P₄-VP]-Fe₃O₄ nanoparticles. The catalyst displayed good catalytic activity when applied for the synthesis of imidazole derivatives. Various imidazole derivatives were prepared in high to excellent yields (68–99%) with short reaction time and high purity. The present procedure offers advantages such as short reaction time, simple reaction work-up, and the polymeric catalyst can be regenerated and reused several times without significant loss of its activity. Graphical abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11164-018-3536-4

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Synthesis of polymer-supported Fe3O4 nanoparticles
and their application as a novel route for the synthesis
of imidazole derivatives
Zeinab Hamidi1
Mohammad Ali Karimi Zarchi1
•
Received: 26 May 2018 / Accepted: 12 July 2018
Ó Springer Nature B.V. 2018
Abstract
Cross-linked poly(4-vinylpyridine) supported Fe3O4 nanoparticles, abbreviated as
[P4-VP]-Fe3O4NPs, were easily prepared as a new magnetic polymeric catalyst and
efficiently used for the synthesis of imidazole derivatives. The polymeric catalyst
was characterized by using of various techniques including field emission scanning
electron microscopy, X-ray diffraction, vibrating sample magnetometry and Fourier
transform infrared spectroscopy (FT-IR) techniques. According to the obtained
results, good dispersion of Fe3O4 nanoparticles on the polymer-support and excel-
lent magnetic property of the catalyst were achieved. Various methods have been
reported for the synthesis of multi-substituted imidazoles by the reaction of benzil,
aldehydes and amines or ammonium acetate in the presence of various catalysts.
These methods have some disadvantages including long reaction times, non-
reusability of the catalyst, polluted reaction conditions, effluent pollution, and low
yields; therefore, we wish to report an efficient, fast, clean and green method for the
synthesis of imidazole derivatives that has been developed by one-pot condensation
reaction of benzil, ammonium acetate and aldehydes in the presence of [P4-VP]-
Fe3O4 nanoparticles. The catalyst displayed good catalytic activity when applied for
the synthesis of imidazole derivatives. Various imidazole derivatives were prepared
in high to excellent yields (68–99%) with short reaction time and high purity. The
present procedure offers advantages such as short reaction time, simple reaction
work-up, and the polymeric catalyst can be regenerated and reused several times
without significant loss of its activity.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11164-
018-3536-4) contains supplementary material, which is available to authorized users.
Extended author information available on the last page of the article
123

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Z. Hamidi, M. A. Karimi Zarchi
Graphical abstract
Ph
Ph
HN
H
O
R
N
R
NH4OAc
O
[P4-VP]-Fe3O4
Ph
O
Ph
Solvent-free, 100 °C
S
N
Keywords Imidazole synthesis Á Magnetic nanoparticle Á One-pot condensation
reaction Á Benzil Á Polymeric catalyst
Introduction
There are many studies that lately have reported on the preparation of nanoparticles
because of their unrivaled physical and chemical properties compared to bulk
materials. Recently, magnetic iron oxide nanoparticles (MNPs) have attracted much
attention compared to other nanoparticles because of their unique physicochemical
properties, great potential biomedical applications, large surface area, and fast
response under applied external magnetic field, high coercively and low Curie
temperature [1–3]. Additionally, magnetically recyclable catalysts have the
potential to approach catalysts benefiting from high activity, high selectivity, high
stability, and easy separation, because MNP-immobilized catalysts combine the
advantages of nanocatalysts with their inherent properties including non-toxicity,
biocompatibility, facile assembling, and high accessibility of reusability through
magnetic attraction [4, 5]. Fe3O4 have been applied in some new types of
biomedical fields such as dynamic sealing [6], biosensors [7], contrast agents in
magnetic resonance imaging [8], localizers in therapeutic hyperthermia [9] and
magnetic targeted drug delivery systems [10]. Sun and Zeng reported, for the first
time, simple organic-phase synthesis of magnetite nanoparticles with sizes variable
from 3 to 20 nm in diameter [11]. Liz et al. employed water-in-oil microemulsion to
obtain magnetic iron-oxide nanoparticles with size less than 10 nm [12–16].
However, these methods use organic solvents, which are not only higher cost, but
also non-friendly to the environment, and is a major problem. Therefore, co-
precipitation method, as an economic, biocompatible, and environmentally friend
method, is usually used to synthesize MNPs [17, 18].
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Synthesis of polymer-supported Fe3O4 nanoparticles and their…
Polymeric reagents [19–22] and catalysts [23–25] have been extensively used in
organic reactions for several years. The importance of these compounds compared
to monomeric reagents result from their good properties such as insolubility in the
reaction mixture, and thus their rapid and simple work-up, efficient reduction of the
leaching of chemicals to reaction, solvent or environment at work-up procedures
such as extraction or chromatography [26], safe handling, reusability of the reagents
and reduction of environmental pollution in their presence because of their easy
isolation by simple filtration. Therefore, by combining the positive properties of
magnetic nanoparticles and polymeric reagents, we have a class of polymeric
reagents and catalysts that show excellent magnetic properties.
Recently, imidazole derivatives have attracted considerable attention due to their
biological properties including anti-allergenic, anti-inammatory, analgesic, antifun-
gal, antimycotic, antibiotic, antiulcerative, antibacterial and antitumor activities
[27, 28]. They are also known as inhibitors of p38 MAP kinases and therapeutic
agents [29]. Furthermore, substituted imidazole derivatives, especially tri- and tetra-
substituted, act as plant growth regulators, glucagon receptors, photosensitive
compounds in photography, and building blocks for the synthesis of other classes of
compounds [30–32]. They have an important role in green chemistry as ionic liquids
[33] and have optical absorption and bright luminescence [34]. Generally, in terms
of physiological and pharmacological aspects, imidazoles are used to treat a variety
of diseases [35]. According to these mentioned properties, synthesis of substituted
imidazoles is still in demand. Debus reported for the first time in 1858 synthesized
imidazole derivatives [36]. Over the years various methods have been reported for
the synthesis of multi-substituted imidazoles by the reaction of benzil, aldehydes
and amines or ammonium acetate in the presence of various catalysts such as
ZnFe2O4 [37], silica chloride [38], silica coated magnetic NiFe2O4 nanoparticle-
supported phosphomolybdic acid [39], copper nanoparticles [40], nano-copper and
cobalt ferrites [41], FHS/SiO2 [42], Fe3O4 nanoparticles [43] and ZrCl4 [44].
These methods have some disadvantages including long reaction time, non-
reusability of the catalyst, polluted reaction condition, effluent pollution, and low
yields; therefore, herein we aim to report an efficient, fast, clean and green method
for the synthesis of trisubstituted imidazoles by one-pot three-component reaction of
benzil, aldehydes and ammonium acetate in the presence of [P4-VP]-Fe3O4 as a
novel magnetic polymeric catalyst under solvent-free conditions (Scheme 1).
Scheme 1 Synthesis of tri-substituted imidazoles by the one pot three-component reaction in the
presence of [P4-VP]-Fe3O4
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Z. Hamidi, M. A. Karimi Zarchi
Experimental
Materials and instruments
All chemical materials and reagents were purchased from Fluka (Buchs, Switzer-
land), Aldrich (Milwaukee, WI, USA) and Merck (Germany) chemical companies
with a purity of 99%. Polymeric reagent poly(4-vinylpyridine) cross-linked with 2%
divinyl benzene, [P4-VP] 2% DVB, (white powder, 100–200 mesh, purity of 99%)
and thin-layer chromatography (TLC) with silica gel PolyGram SIL G/UV 254
plates were purchased from Fluka. Characterization of all products was done by
comparison of their melting points, Fourier transform infrared (FTIR) spectroscopy,
1
and H and 13C-NMR spectral data with those of known products, and all yields
refer to the isolated pure products. The melting points were determined with a Buchi
melting point B-540 B. V.CHI apparatus. The FTIR spectra were obtained with a
Bruker Equinox (model 55), Germany, and the NMR spectra were recorded on a
1
Bruker AC 400 Avance DPX spectrophotometer, Germany at 400 MHz for H and
at 100 MHz for 13C NMR in DMSO solution.
Preparation of magnetic Fe3O4 nano particles (MNPs)
In a typical procedure, 2 mmol FeCl3Á6H2O (1.6 g) and 1 mmol FeCl2Á4H2O (0.8 g)
were dissolved in deionized water (0.9 mL) under ultrasound treatment and under
N2 atmosphere for 15 min. Thereafter, under rapid mechanical stirring, 15 mL of
dilute aqueous ammonia (NH4OH) was added drop-wise into this solution within
30 min. The resulting black precipitate was isolated with external magnet and then
washed with distilled water (4 9 5 mL) and finally dried at 80 °C in a vacuum
oven.
Preparation of [P4-VP]-Fe3O4
The synthesized Fe3O4 nanoparticles (2 g) were dispersed in EtOH/H2O (1/1,
20 mL) under ultrasonification for 15 min. Then (3-chloropropyl) trimethoxysilane
(3.4 g, 16 mmol) was added to this mixture and stirred overnight at 80 °C.
Thereafter, [P4-VP] 2%DVB (1 g) was added to the resulted mixture and stirred at
80 °C for 20 h. The resulting [P4-VP]-Fe3O4 were collected by external magnet,
washed three times with ethanol (5 mL) and finally dried at 50 °C in a vacuum oven
(Scheme 2).
General procedure for the synthesis of 4,5-diphenyl-2aryl imidazoles
To the mixture of benzil (1 mmol), aldehydes (1.3 mmol) and ammonium acetate
(3.5 mmol), [P4-VP]-Fe3O4 (0.1 g) was added and the mixture was stirred at 100 °C
under solvent-free conditions for 20–80 min. Progress of the reaction was
monitored by TLC (n-hexane/EtOAc, 80/20). After completion, the reaction
mixture was dissolved in EtOH (1 mL), and then [P4-VP]-Fe3O4 was separated from
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