A magnetically retrievable copper ionic liquid nanocatalyst for cyclooxidative synthesis of 2-phenylquinazolin-4(3: H)-ones

Article abstract of DOI:10.1039/d0dt03634j

In the present work, we report the design and fabrication of a copper-containing ionic liquid supported magnetic nanocatalyst via a convenient and straightforward synthetic approach for the formation of 2-phenylquinazolin-4(3H)-ones using o-aminobenzamide and benzaldehydes as the reaction partners. The successful formation and properties of the as-prepared catalyst have been thoroughly investigated using diverse physico-chemical techniques including FT-IR, XRD, FE-SEM, TEM, ICP, VSM, BET and TGA. Using this nanocatalytic system, a variety of 2-phenylquinazolin-4(3H)-ones are synthesized in excellent yields with operational ease and short reaction times in an environmentally preferable solvent under open air and without using any external oxidizing agent. Besides, the catalyst possessed facile magnetic recoverability and remarkable reusability for six consecutive runs without any appreciable decrease in the catalytic efficiency.

Full text of DOI:10.1039/d0dt03634j

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A magnetically retrievable copper ionic liquid
nanocatalyst for cyclooxidative synthesis of
Cite this: DOI: 10.1039/d0dt03634j
2-phenylquinazolin-4(3H)-ones†
Radhika Gupta, a Gunjan Arora, a Priya Yadav, a,b Ranjana Dixit,a
a
Anju Srivastavab and Rakesh Kumar Sharma
*
In the present work, we report the design and fabrication of a copper-containing ionic liquid supported
magnetic nanocatalyst via a convenient and straightforward synthetic approach for the formation of
2-phenylquinazolin-4(3H)-ones using o-aminobenzamide and benzaldehydes as the reaction partners.
The successful formation and properties of the as-prepared catalyst have been thoroughly investigated
using diverse physico-chemical techniques including FT-IR, XRD, FE-SEM, TEM, ICP, VSM, BET and TGA.
Using this nanocatalytic system, a variety of 2-phenylquinazolin-4(3H)-ones are synthesized in excellent
yields with operational ease and short reaction times in an environmentally preferable solvent under open
air and without using any external oxidizing agent. Besides, the catalyst possessed facile magnetic reco-
verability and remarkable reusability for six consecutive runs without any appreciable decrease in the cata-
lytic efficiency.
Received 20th October 2020,
Accepted 6th December 2020
DOI: 10.1039/d0dt03634j
rsc.li/dalton
utility in large-scale industrial applications, such as large IL
requirements, high costs, limited metal reservoirs, product
Introduction
Since the 1980s, ionic liquids (ILs) have increasingly fascinated contamination and tedious recycling protocols that often lead
a wide domain of researchers due to their remarkable physical to the decomposition of the ILs.14 Besides, their high viscosity
and chemical properties, particularly low volatility, wide tun- also impedes the substrate diffusion which slows down the
ability, high thermal stability, good conductivity and overall reaction rate.
reusability.1–4 They are being used as green and sustainable
To overcome these limitations, the concept of heterogeniza-
alternatives to traditional volatile solvents and as potential tion of ILs came into picture, which aims to transfer the
catalytic entities in organic synthesis. Over the past few years, desired properties of ILs onto a solid support material.15–19
transition metal-containing ionic liquids (MetILs) have gar- Numerous promising immobilized MetILs have been prepared
nered substantial interest in the field of basic and applied in the past few years for catalyzing the synthesis of significant
sciences owing to their advantages over conventional ILs, such organic molecules with easier operation and better perform-
as enhanced solubility and chemical availability of metal salts, ance. Previously, Iwasawa and co-workers immobilized a series
strong magnetic response and an appealing color rendering of first row transition metal-containing alkylimidazolium salts
characteristic, which originate from the incorporation of metal onto hydrophilic silica and evaluated their catalytic efficacy in
species into the intrinsic structure of the ILs.5–7 Several groups the Kharasch addition reaction.20 Later, Bhanage et al.
have explored the catalytic competency of homogeneous designed immobilized palladium- and iron-containing IL cata-
MetILs in a variety of organic transformations, C–C bond for- lysts for conducting various carbonylation reactions21 and
mation,8 hydroformylation,9 debromination,10 allylic oxi- chemoselective
hydrogenation,22
respectively.
Another
dation,11 cycloaddition12 and depolymerization,13 to mention polymer-supported metal-containing imidazolium salt catalyst
a few. In spite of the outstanding performances of these cata- (PS-(Im)2MX2) was also prepared for the synthesis of glycerol
lytic MetILs, certain constraints have limited their practical carbonate.23 These successive works encourage the design and
development of other heterogeneous MetILs with improved re-
cycling ability and practical relevance. In recent years, silica-
coated magnetic nanoparticles (SMNPs) have emerged as an
excellent support material due to some of their exceptional fea-
tures including large surface area to volume ratios, ease of
functionalization, high thermal and chemical stability and
aGreen Chemistry Network Centre, Department of Chemistry, University of Delhi,
Delhi-110007, India. E-mail: rksharmagreenchem@hotmail.com
bDepartment of Chemistry, Hindu College, University of Delhi, Delhi-110007, India
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
D0DT03634J
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effortless magnetic recoverability.24,25 Taking these advantages modified rare earth oxide,60 iron porphyrin-based porous
into account and in continuation of our efforts for the develop- organic polymers,61 zeolite-supported platinum metal nano-
ment of sustainable magnetic nanocatalysts,26–35 we herein clusters,62 Cu3(BTC)2 MOF63 and so forth. Although many of
report the fabrication of a copper-containing IL supported these demonstrated superior product yields, wide substrate
magnetic nanocatalyst using a convenient and straightforward scope and reusability for multiple runs, their recovery still
approach. The catalytic application of the as-synthesized remains challenging due to tedious and time-consuming cen-
material is investigated in the formation of 2-phenylquinazo- trifugation and filtration procedures. In this regard, a few mag-
lin-4(3H)-ones.
netically supported catalysts have been prepared and success-
Quinazolin-4(3H)-ones represent a ubiquitous class of aza- fully utilized including magnetic nanoparticle immobilized Cu
heterocyclic moieties. They are found in a wide array of natural (I)64 and 1,4-diazabicyclo[2.2.2]octane tribromide,65 graphene
products and biologically active compounds (Fig. 1). They are oxide/Fe3O4-CuI66 and Fe3O4-carbon dot nanocomposites.67
also used as a pharmacophore in drug designing due to their However, apart from the benefits they offer, most of the pre-
remarkable performance in anticancer, antibacterial, antitu- viously reported methods suffer from one or more drawbacks
berculosis,
anti-inflammatory
and
antihypertensive such as use of non-green reaction media, need for ligands or
activities.36–40 In recent years, 2-aryl substituted quinazolin-4 additives or bases, large excess of oxidizing agents, high reac-
(3H)-ones’ activities are being evaluated in treating numerous tion temperatures and long reaction time. Hence, the develop-
disorders; Apabetalone or RVX-208 is under clinical trials for ment of other sustainable and green catalysts with high activity
the treatment of atherosclerosis and other cardiovascular and easy and efficient recyclability is extremely important. The
diseases,41,42 Bouchardatine has been found to act as an present work describes the use of a magnetically recoverable
inhibitor of adipogenesis/lipogenesis,43 and 2-(4-nitrophenyl) copper-containing IL for the one-pot cyclooxidative synthesis
quinazolin-4(3H)-one is being investigated as a potential of 2-phenylquinazolin-4(3H)-ones under mild reaction con-
NLRP3 inflammasome inhibitor,44 to name a few. Considering ditions with excellent product yields and multiple recyclable
their wide utility, a variety of approaches have been reported in runs. To the best of our knowledge, this is the first report
the past towards the construction of quinazolinone skeletons. wherein
a magnetically immobilized metal-containing IL
One such conventional method involves an Ullmann-type nanocatalyst has been utilized for the synthesis of 2-phenylqui-
N-arylation for the preparation of heterocyclic compounds nazolin-4(3H)-ones.
using copper salts or complexes.45–48 Another most frequently
used protocol includes the cascade reaction of alcohols/alde-
hydes with o-aminobenzamides using complexes of various
precious and base metals such as Ir,49,50 Ru,51 Pd,52 Ni,53 Cu,54
Fe,55 Co,56 Zn57 and V.58
Results and discussion
Design and synthesis of the nanocatalyst (CuIL@SMNP)
Although each of the above-mentioned catalytic routes and
reaction protocols holds its own merits, nearly all of them are
associated with the use of metals under homogeneous con-
ditions. However, due to their limited reserves, difficulty in
recovery and probability towards product contamination, their
use is considered neither safe nor sustainable from the view-
point of environmental safety and human health. Hence, in
order to combat these issues, numerous heterogeneous
systems have been reported to date such as α-MnO2,59 ZnO
The design and synthesis of the catalyst is shown in Scheme 1.
It involves the discrete synthesis of a magnetic support
(SMNPs) and functionalized IL (FIL) followed by its immobiliz-
ation on the prepared support (IL@SMNPs) and further com-
Fig. 1 Structures of some of the biologically active 2-arylquinazolin-4
(3H)-ones.
Scheme 1 Schematic illustration of the fabrication of CuIL@SMNPs.
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plexation with the metal salt to obtain the final immobilized
MetIL (CuIL@SMNPs).
Characterization of CuIL@SMNP
Functional group analysis. In order to ascertain the success-
ful formation of nanomaterials and attachment of various
groups on the support, FT-IR analysis was conducted. Fig. 2a
shows a split intense peak at wavenumbers 632 and 585 cm−1
which emerged due to the Fe–O vibration present in the Fe3O4
nanoparticles.68 Besides, a broad band at 3436 cm−1 rep-
resents the large number of surface hydroxyl groups.
Furthermore, silica coating on these magnetite spheres was
confirmed by the appearance of new and strong peaks at 1090,
957, 808 and 462 cm−1 that are ascribed to Si–O–Si stretching,
Si–OH stretching, Si–O bending and Si–O–Si bending, respect-
ively (Fig. 2b).69 Fig. 2c shows the FT-IR spectrum of the final
CuIL@SMNP whose formation is confirmed by the peaks at
2928 and 2852 cm−1, which corresponds to the C–H antisym-
metric and symmetric stretching bands of the methylene
group.70 Additional bands appear at 1632 and 1570 cm−1
which arise due to the –CvC– and –CN stretching vibrations,
respectively, present in the imidazolium ring.71,72
Phase and structural characterization. For the determination
of the crystallinity, structural integrity and size of the syn-
thesized nanomaterials, XRD studies were carried out. Fig. 3a
reveals the presence of six diffraction peaks at 2θ = 30.19°,
35.63°, 43.29°, 53.60°, 57.37° and 62.92°. It was observed that
the position of all the peaks in the concerned XRD spectrum
are in good agreement with the standard XRD pattern of the
cubic inverse spinel structure of Fe3O4 (Joint Committee on
Powder Diffraction Standards (JCPDS) card no. 19-0629) and
correspond to the (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4
0) crystalline planes of the magnetite phase, respectively.67
Fig. 3b and c also show the presence of the above-mentioned
peaks, with no extra peaks, which proves that the structural
integrity of the magnetic core is retained even after silica
coating or functionalization with the copper–containing IL.
Nevertheless, the signals pertaining to copper metal and silica
coating were not observed in the XRD spectra of the SMNPs
Fig. 3 XRD spectra of (a) MNPs, (b) SMNPs and (c) CuIL@SMNPs.
and CuIL@SMNPs, which implies their high dispersity over
the nanoparticles.73 Apart from evaluating the crystallinity, the
XRD spectrum was also used for the determination of the size
of the magnetite nanoparticles. For this, the Scherrer equation
was used according to which Dhkl = kλ/β cos θ, where Dhkl is the
mean size of the crystalline domains in a direction perpen-
dicular to the lattice plane, hkl are the Miller indices of the
plane under consideration, k is a dimensionless shape factor
(0.89 for spherical particles), λ is the wavelength of the X-ray
used (0.15418 nm for Cu K-alpha), β is the full line width at
half maximum intensity (FWHM; in radians) and θ is the
Bragg angle (in degrees). After taking into account the diffrac-
tion peak with maximum intensity, the size of the MNPs was
found to be 11 nm in diameter.
Shape, size, morphology and surface area determination.
The shape and morphological studies were conducted using
electron microscopic techniques. Fig. 4 shows the FE-SEM
images of the MNPs, SMNPs and CuIL@SMNPs. The micro-
graph of the MNPs clearly depicts their uniform spherical
nature whose surface becomes spongy and rough after coating
a silica layer over it. A similar surface nature was observed in
the case of the CuIL@SMNPs as well which suggests that no
substantial morphological changes occurred even after the
immobilization of the MetIL over the SMNPs.
Furthermore, to gain valuable information about the inner
structure of the nanoparticles, TEM images were recorded.
Fig. 5a shows uniform spherical MNPs with a diameter of
around 10.5 nm, which is in good agreement with the XRD
Fig. 2 FT-IR spectra of (a) MNPs, (b) SMNPs and (c) CuIL@SMNPs.
Fig. 4 FE-SEM images of (a) MNPs, (b) SMNPs and (c) CuIL@SMNPs.
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magnetic support utilized throughout the study. To reinforce
the above statement, TGA analysis of the MNPs and SMNPs
was also carried out (Fig. S3†) and the results authenticate
that no substantial weight loss occurs even at high
temperatures.
Elemental analysis. To illustrate the elemental composition
of the synthesized nanocatalyst, SEM-coupled EDAX analysis
was performed. Fig. 7 clearly depicts the presence of Fe, Si, C,
N, O, Cl and Cu in the final IL immobilized nanoparticles.
Furthermore, the copper metal loading in the catalyst was esti-
mated using ICP-MS and was found to be 0.83 mmol g−1. The
existence and semi-quantitative estimation of copper in the
catalyst were also confirmed using a standalone benchtop
EDXRF elemental analyzer (Fig. S2†).
Fig. 5 TEM images of (a) MNPs, (b) SMNPs and (c) CuIL@SMNPs.
results. Fig. 5b illustrates the internal core–shell structure of
the SMNPs with a dense magnetic core at the centre and a
uniform silica shell at the outer surface which is approximately
4–5 nm in thickness. Besides, a similar internal structure was
observed for the CuIL@SMNP nanocatalyst justifying that
modification with the MetIL does not disrupt the internal
structure of the SMNPs (Fig. 5c). For the determination of the
size of the nanoparticles, discrete particles were analyzed and
size distribution histograms were plotted according to which
the MNPs, SMNPs and CuIL@SMNPs were of sizes between
9–10, 18–20 and 20–22 nm (Fig. S1†). Besides, the specific
surface area of the as-synthesized MNPs and CuIL@SMNPs
was also evaluated using BET analysis and was found to be
Magnetic property analysis. The evaluation of the magnetic
properties of the material becomes highly significant when it
comes to the fabrication of a magnetic nanocatalyst. Due to
this, the nanocomposites were subjected to VSM analysis at
room temperature at a magnetic field varying from −10 000 Oe
to +10 000 Oe. Fig. 8a depicts that the synthesized MNPs have
a saturation magnetization value (Ms) of 73.2 emu g−1
.
However, upon the coating of these MNPs with diamagnetic
silica, the Ms value decreases to 40.7 emu g−1 (Fig. 8b). This
value further goes down to 28.6 emu g−1 upon the immobiliz-
69.27 and 16.15 m2 −1, respectively. There was an expected
g
decrease in the specific surface area of the catalyst which
implies the effective immobilization of CuIL over the magnetic
support.
Thermal stability analysis. TGA analysis was performed in
order to assess the thermal stability of the prepared nano-
catalyst (Fig. 6). For this, the sample was heated from 37 °C to
950 °C and its corresponding weight was recorded. The curve
represents that a weight loss of approximately 4.5% takes place
upon initial heating to 237 °C, which is attributed to the
removal of the adsorbed water and other organic solvents that
were utilized during the preparation of the catalyst. With the
subsequent increase in the temperature, further weight loss is
observed from 237 to 410 °C and from 410 to738 °C, which
could be due to the decomposition of the organic species used
for the formation of the CuIL. Afterwards, no significant loss
was observed which indicates the high thermal stability of the
Fig. 7 SEM-coupled EDAX spectrum of CuIL@SMNPs.
Fig. 8 Magnetization curves of (a) MNPs, (b) SMNPs and (c)
Fig. 6 TGA curve of CuIL@SMNPs.
CuIL@SMNPs.
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ation of the CuIL over the SMNPs (Fig. 8c); nevertheless, it was ging results in hand, experiments were performed to know if
sufficiently magnetic to be recovered from the reaction mixture the reaction conditions could be further refined. Hence,
with the application of a simple external magnet. In addition, various solvents and solvent systems were also screened, such
all of the synthesized nanomaterials possess superpara- as water, acetonitrile and ethanol–water mixture, but the best
magnetic nature as no hysteresis loop, remanence or coercivity results were obtained in ethanol as a solvent (Table 1, entries
was observed in any of the cases.
3–5). Furthermore, the temperature was brought down to 60 °C
(Table 1, entry 6), but unfortunately, the yield decreased by
>44%. Afterwards, the effect of time was studied and it was
found that 4 h is the optimum time for obtaining the
maximum yield of the desired product (Table 1, entries 7–10).
Now, with the optimized parameter obtained so far, the cata-
lytic amount was varied from 75 mg to 40 mg and >99% of qui-
nazolinone was obtained with just 50 mg of the catalyst, i.e.
CuIL@SMNPs (Table 1, entries 11–12). The catalytic aptitude
of various precursors formed during catalyst fabrication was
also evaluated; however, no significant product yield was
observed in any of the cases, justifying the exclusive utility of
the CuIL@SMNPs for the efficient synthesis of quinazolinones
(Table 1, entries 13–15).
Substrate scope. Having these optimized conditions in
hand, a variety of benzaldehydes were reacted with o-amino-
benzamide in ethanol as the solvent system and 50 mg of
CuIL@SMNPs as the catalyst under reflux conditions for the
required time. The results are summarized in Fig. 9. A wide
range of benzaldehydes were obtained in good to excellent
yields in short reaction times, i.e. from just 30 min to 4 h. The
unsubstituted benzaldehyde however took longer time than
the substituted ones. Many electron donating groups bearing
benzaldehydes, such as –OH, –Me, –OMe, and halo groups
containing benzaldehydes, such as –Cl and –Br, were obtained
in excellent yields; nevertheless, those with electron withdraw-
Catalytic activity test
With an aim to develop an environmentally friendly catalyst
which gives excellent yields of the desired compounds with
efficient recovery and recyclability, the catalytic activity of the
prepared SMNP immobilized CuIL nanocatalyst was investi-
gated in the synthesis of 2-phenylquinazolin-4(3H)-ones using
o-aminobenzamide and benzaldehydes as the reaction
partners.
Optimization of reaction conditions. In order to maximize
the yield of 2-phenylquinazolin-4(3H)-ones with the use of a
safe and benign solvent under improved reaction conditions,
various reaction parameters were optimized. For this, o-amino-
benzamide and benzaldehyde were chosen as the model sub-
strates. After careful study of the previously reported methods
and reaction conditions, initially, the two of these precursors
were allowed to react in the absence of any catalyst in ethanolic
solution under reflux conditions for 12 h under an air atmo-
sphere (Table 1, entry 1). However, poor conversion was
observed with dihydroquinazolinone (1) as the dominant
product over the desired quinazolinone (2). This prompted the
application of the CuIL@SMNPs as catalytic species. To our
delight, high conversion and >99% of quinazolinone were per-
ceived under identical conditions and in the absence of any
external oxidizing agent (Table 1, entry 2). With these encoura-
Table 1 Optimization of the reaction parameters for the synthesis of 2-phenylquinazolin-4(3H)-onea
% Yieldb
% 1
S. no.
Catalyst (amount)
Solvent
Temp. (°C)
Time (h)
% 2
1
2
3
4
5
6
7
8
—
Ethanol
Ethanol
H2O
Reflux
Reflux
Reflux
Reflux
Reflux
60 °C
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
12
12
12
12
12
12
8
6
4
3
4
35
—
60
42
55
15
—
—
—
12
—
5
5
>99
5
7
8
55
>99
>99
>99
85
>99
81
15
8
CuIL@SMNP (75 mg)
CuIL@SMNP (75 mg)
CuIL@SMNP (75 mg)
CuIL@SMNP (75 mg)
CuIL@SMNP (75 mg)
CuIL@SMNP (75 mg)
CuIL@SMNP (75 mg)
CuIL@SMNP (75 mg)
CuIL@SMNP (75 mg)
CuIL@SMNP (50 mg)
CuIL@SMNP (40 mg)
FIL@SMNP (75 mg)
SMNP (75 mg)
CH3CN
EtOH : H2O (1 : 1)
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
9
10
11
12
13
14
15
4
12
12
12
55
40
40
MNP (75 mg)
8
a Reaction conditions: o-aminobenzamide (0.5 mmol), benzaldehyde (0.5 mmol), solvent 3.0 mL. b GC-MS yield.
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Fig. 10 Recyclability test for the synthesis of 2-phenylquinazolin-4
(3H)-one using CuIL@SMNPs. Reaction conditions: o-aminobenzamide
(0.5 mmol), benzaldehyde (0.5 mmol), recovered catalyst, ethanol
(3.0 mL), reflux, 4 h, under air.
Fig. 9 Catalytic efficacy of CuIL@SMNPs in the synthesis of various
2-phenylquinazolin-4(3H)-ones with the data representing the isolated
product yield, time taken and product code. Reaction conditions: o-ami-
nobenzamide (0.5 mmol), benzaldehyde (0.5 mmol), ethanol 3.0 mL,
CuIL@SMNPs (50 mg), reflux, under air.
runs without any appreciable loss in the catalytic activity. Any
morphological or structural changes in the recycled catalyst
were analyzed by various characterization techniques. Fig. S4
and S5† illustrate the FT-IR, VSM, FE-SEM, TEM and XRD
results of the fresh and recovered catalyst after the sixth run
which authenticate that the functionalities, magnetism, mor-
phology and structural integrity of the catalyst remain intact
even after six runs. Table S1† shows the comparison of our pre-
pared catalyst with many other previously reported ones and it
depicts that the present CuIL immobilized SMNPs remain
ing groups such as –NO2 and –NHCOCH3 gave comparatively
lesser yields, irrespective of their substitution position.
Catalytic stability test
In order to check the stability of the catalyst and to assess any superior amongst many others in terms of product yields, mild
possible leaching of the catalytic species from the magnetic reaction conditions and better recyclability.
support, a split test was conducted. For this, o-aminobenza-
mide and benzaldehyde were allowed to react under the opti-
Plausible reaction mechanism
mized conditions. After 2 h, the catalyst was removed from the
A plausible reaction mechanism has been proposed based on
reaction mixture using an external magnet and the leftover
the optimization studies and relevant literature investigation,
mixture was divided into two equal halves. One of the parts
according to which initially benzaldehyde in the presence of
was kept aside and the other was heated at the same tempera-
o-aminobenzamide and the catalyst, i.e. CuIL@SMNPs, forms
an aminal intermediate called 2,3-dihydroquinazolin-4(1H)-
one (a) via intermolecular cyclization, which is also detected
ture for 3 h, but now, in the absence of catalyst. Afterwards,
both of the parts were subjected to GC-MS analysis and it was
observed that both of them yielded nearly the same amount of
by GC-MS when the reaction mixture is analyzed at shorter
quinazolinone. This illustrates that no substantial leaching
reaction times (Scheme 2, step 1). This intermediate is then
occurred during the reaction. To validate this point, after the
dehydrogenated in the presence of CuIL and aerial oxygen to
removal of the catalyst from the reaction mixture, the recovered
form the desired product 2-phenylquinazolin-4(3H)-one
catalyst was analyzed via ICP-MS to estimate the amount of
(Scheme 2, step 2).59,67,74 This step is also validated when no
desired product was obtained under a nitrogen atmosphere.
copper present in it. To our delight, only a negligible decrease
in the copper loading was observed, i.e. 0.008 mmol g−1
,
which again proved the truly heterogeneous nature of the
catalyst.
Catalytic reusability test
With the fabrication of the heterogeneous catalyst, the responsi-
bility of assessing its reusability becomes highly imperative. To
evaluate this, the model reaction was chosen. After the catalyst
was removed from the reaction mixture using a simple external
magnet, it was washed thoroughly with acetone and water and
subsequently dried in a vacuum oven for an hour at 60 °C. Later
on, the same reaction was conducted again using this recycled
catalyst and the results were recorded. Fig. 10 shows that the
Scheme 2 Reaction mechanism for the formation of 2-phenylquinazo-
immobilized CuIL can be effectively utilized for six consecutive lin-4(3H)-one.
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thermogravimetric curve was obtained using a Linseis TGA
under a nitrogen atmosphere with a gas flow of 2 L h−1 and in
Conclusions
In summary, a copper metal-containing IL immobilized silica- the temperature range from 37 °C to 950 °C with a heating rate
coated magnetic nanocatalyst was designed, prepared and of 10 °C min−1. The copper content present in the nanocatalyst
characterized, and was further utilized for the tandem cycliza- was determined using a PerkinElmer Optima 2100 DV induc-
tion and oxidative synthesis of 2-phenylquinazolin-4(3H)-ones tively coupled plasma-mass spectrometer. Furthermore, the
using o-aminobenzamide and benzaldehydes in an environ- Brunauer–Emmett–Teller (BET) surface areas were measured
mentally benign solvent under mild reaction conditions and using an ASI-CT-11 Quantachrome instrument at a degassing
in short reaction times. The catalyst transforms a wide variety temperature of 150 °C. The optimization of the reaction con-
of substrates in good to excellent yields without any additional ditions was carried out using an Agilent gas chromatograph
purification that conventionally requires column chromato- (6850 GC) having a HP-5MS capillary column (stationary
graphy. The quasi-homogeneous nature of the IL on the phase: 5% phenyl methyl siloxane; column length: 30 m;
SMNPs and better chemical availability of the metallic species internal diameter: 0.25 mm; film thickness: 0.25 µm) and a
in the form of the MetIL account for the exceptional catalytic quadrupole mass filter equipped 5975C mass selective detector
activity of the system. Besides, the magnetic feature of the cata- (MSD) using helium as a carrier gas. Operation conditions:
lyst imparted facile catalytic recovery and outstanding re- injection temperature: 250 °C, detector temperature: 250 °C,
usability for six successive runs with negligible loss of catalytic helium gas flow: 1.0 mL min−1. Temperature programming:
activity. All of the above-mentioned features imply the effective initial column temperature = 60 °C, hold time = 5 min; next
use of MetIL@SMNPs in various significant heterogeneous temperature = 150 °C, rate of temperature ramp 1 = 10 °C
organic transformations.
min−1, hold time = 0 min; final temperature = 250 °C, rate of
temperature ramp 2 = 15 °C min−1, hold time = 2 min. Finally,
the organic compounds were characterized using 1H
(400 MHz) and 13C (100 MHz) JEOL JNM-EXCP-400 nuclear
magnetic resonance spectrophotometers. The spectra were
recorded in either CDCl3 or DMSO-d6. Chemical shifts (δ) for
Experimental section
Chemicals and instruments
All of the reagents were procured from commercial sources proton and carbon are reported in parts per million (ppm)
and used without further purification. Ferric sulfate hydrate units downfield from tetramethylsilane (internal standard).
and ferrous sulfate heptahydrate were purchased from Fischer
Synthesis of the magnetic support
Scientific. Tetraethyl orthosilicate (TEOS) and (3-chloropropyl)
trimethoxysilane (CPTMS) were obtained from Sigma Aldrich. The first step included the synthesis of SMNPs which were
N-Methylimidazole and copper chloride were purchased from chosen as a support for immobilizing the MetIL. Initially, mag-
Spectrochem. All other chemical reagents, organic compounds netite nanoparticles (MNPs) were prepared according to a co-
and solvents used were of high purity and were procured from precipitation method. In a typical procedure, 6.0 g of ferric
Alfa Aesar and Merck. Besides, double distilled water was used sulfate hydrate and 4.2 g of ferrous sulfate heptahydrate were
throughout the study and was prepared in our laboratory.
dissolved in 250 mL of double distilled water followed by stir-
The developed catalyst was characterized using various ring at 60 °C till the solution became yellowish-orange in
analytical techniques. Fourier-transform infrared spectra were color. Later, 15 mL of 25% ammonium hydroxide was added
obtained on a PerkinElmer Spectrum 2000 using the KBr to set the pH around 10. After 30 minutes of continuous stir-
pellet method in the range of 4000 to 400 cm−1. X-ray diffracto- ring at the same temperature, the black colored nanoparticles
grams were obtained using a Rigaku MiniFlex diffractometer were separated magnetically, washed with water and further
in the 2θ range of 20–70° with a scan rate of 2° min−1. Field- with ethanol till the solution became neutral and finally dried
emission scanning electron micrographs were acquired using in a vacuum oven. The MNPs were coated with a layer of silica
a Hitachi SU8010 FE-SEM. Prior to imaging, finely crushed using a sol–gel approach. For this, 0.5 g of MNPs was activated
and dried powdered nanoparticles were mounted on carbon- by adding 2.2 mL of 0.1 M HCl. Furthermore, the solution was
taped clean metal stubs followed by coating with gold using a kept under sonication for 30 minutes after the addition of
sputter coater. Transmission electron microscopic images were 200 mL of ethanol and 50 mL of water. Afterwards, 5 mL of
obtained on a FEI TECNAI G2 T20 TEM instrument. The ammonium hydroxide and 1 mL of TEOS were added in a
samples were prepared by first dispersing the nanoparticles in dropwise fashion. The solution was then stirred for 6 h at
ethanol and then casting a drop of it on carbon-coated copper 60 °C. Finally, the as-obtained brown colored SMNPs were sep-
grids. The size of the nanoparticles was determined using arated magnetically, washed with ethanol until neutral pH and
ImageJ software. An SEM-coupled EDAX system was used to dried in a vacuum oven.
analyze the elemental composition of the supported MetIL. A
MicroSense ADE-EV9 vibrating sample magnetometer was
Synthesis of the functionalized IL
used to measure the magnetization values of the nano- Initially, a silyl-functionalized methylimidazolium chloride
materials. The analyses were carried out at room temperature homogeneous IL was synthesized. For this, equal moles of
in the magnetic field range of −10 000 Oe to +10 000 Oe. The N-methylimidazole and CPTMS were heated at 80 °C for 48 h
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under solvent-free conditions. Later, the as-synthesized color-
less and viscous IL was washed with diethyl ether to remove
any unreacted materials. It was further dried in a vacuum oven
to obtain a pure functionalized IL.
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