Synthesis, characterization and catalytic application of a novel polyethylene-supported Fe/ionic liquid complex

Article abstract of DOI:10.1016/j.molcata.2016.11.015

A novel polyethylene-supported Fe/ionic liquid complex (PEt@Fe/IL) is prepared, characterized and its catalytic performance is investigated in the synthesis of 3,4-dihydropyrimidinones. The chemical properties and thermal stability of the PEt@Fe/IL materi

Full text of DOI:10.1016/j.molcata.2016.11.015

Accepted Manuscript
Title: Synthesis, characterization and catalytic application of a
novel polyethylene-supported Fe/ionic liquid complex
Author: Davar Elhamifar Dawood Elhamifar Frood
Shojaeipoor
PII:
S1381-1169(16)30489-7
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2016.11.015
MOLCAA 10112
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
12-5-2016
18-10-2016
8-11-2016
Please cite this article as: Davar Elhamifar, Dawood Elhamifar, Frood Shojaeipoor,
Synthesis, characterization and catalytic application of a novel polyethylene-
supported Fe/ionic liquid complex, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2016.11.015
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Synthesis, characterization and catalytic application of a novel
polyethylene-supported Fe/ionic liquid complex
a,b
c,
d
∗
Davar Elhamifar, Dawood Elhamifar and Frood Shojaeipoor
aDepartment of Chemical Engineering, Islamic Azad University, Shahreza Branch, Isfahan,
Iran
bMehr Petrochemical Company, Phase 2 of PSEEZ, Assaluyeh, Bushehr, Iran
cDepartment of Chemistry, Yasouj University, Yasouj, 7518-74831, Iran
dDepartment of Chemistry, Payame Noor University, Tehran, 19395-4697, Iran
*
To whom correspondence should be addressed. Tel&fax. (0098)-743-3233977, E-mail:
d.elhamifar@yu.ac.ir
Graphical abstract
A novel polyethylene-supported ionic liquid/iron complex is prepared, characterized and its
catalytic application is developed in the synthesis of 3,4-dihydropyrimidinones through Biginelli
reaction. The corresponding coupling products were obtained in high to excellent yield and
selectivity. Moreover, the catalyst was recovered and reused several times without decrease in
efficiency.
1

7
N
N
Br
Me
-
Xylene, reflux, stirring
Me
+
Iron acetate
1
2
3
4
. Xylene, reflux, 2 h
. MeOH, 4 o
. Washing with MeOH
. Drying
C
PEt@Fe/IL composite
Highlights



For the first time, a novel polyethylene-supported ionic liquid/iron complex (PEt@Fe/IL)
is prepared and characterized
The chemical properties and thermal stability of the PEt@Fe/IL was investigated using
DRIFTs, EDX, TGA, XPS and SEM
The PEt@Fe/IL was successfully applied in the one-pot Biginelli condensation of
aldehydes, urea and alkylacetoacetates


The coupling products were obtained in high to excellent yield and selectivity
The PEt@Fe/IL was recovered and reused several times without significant decrease in
efficiency
2

Abstract
A novel polyethylene-supported Fe/ionic liquid complex (PEt@Fe/IL) is prepared,
characterized and its catalytic performance is investigated in the synthesis of 3,4-
dihydropyrimidinones. The chemical properties and thermal stability of the PEt@Fe/IL
material were studied by diffuse reflectance infrared Fourier transform (DRIFT)
spectroscopy, thermal gravimetric analysis (TGA) and energy dispersive X-ray (EDAX)
analysis. The morphology of the material was obtained using scanning electron
microscopy (SEM). The PEt@Fe/IL material was then successfully applied in the
Biginelli condensation of aldehydes, urea and alkylacetoacetates to prepare a set of
different 3,4-dihydropyrimidinone derivatives in high to excellent yields. The
PEt@Fe/IL was recovered and reused several times without significant decrease in
efficiency. The other advantages of this novel catalytic system include excellent yield,
short reaction time and solvent-free conditions.
Keywords:
Polymer-supported
catalyst,
Fe/ionic
liquid
complex;
3,4-
dihydropyrimidinones; solvent free conditions, recoverable and reusable catalyst
1
. Introduction
One pot synthesis of 3,4-dihydropyrimidine-2-(1H)-ones through Biginelli reaction is an
important chemical process due to its key role in the preparation of biologically useful
compounds. This reaction involves three component cyclocondensation of alkyl-
acetoacetates, aldehydes and urea/thiourea under acidic conditions [1-2]. Some promising
biological effects of the 3,4-dihydropyrimidine-2-(1H)-ones include antiviral,
antibacterial, antitumor, and anti-inflammatory activities. They have also been found to
be as calcium channel modulators [3], antihypertensive agents [4] and α-1a-antagonists
[
5]. According to aforementioned advantages of the Biginelli products, to date many
synthetic protocols for preparing these compounds have been reported in the presence of
3

both Lewis and Brønsted acid catalysts under homogeneous conditions [6-10]. However,
the problems of catalyst and product separation, catalyst recovery and also environmental
pollution have restricted these catalytic systems. To overcome these limitations, the
immobilization of homogeneous catalysts onto/into solid supports has been recently
developed [11, 12]. Along this line, more recently we also have prepared a number of
ionic liquid based nano-organosilicas supported acid catalysts and studied their
application in the Biginelli condensations [13, 14].
On the other hand, metal–polymer composites exhibiting the properties of both metals
and polymers have been the subject of research interest at last two decades. Structure and
properties of these composites are very important to design new engineering materials
with desired characteristics [15]. In fact, to improve properties such as thermal and
electrical conductivity, mechanical stability, chemical reactivity, and to stiffen the matrix,
various kinds of fillers and additives such as metal or ceramic are introduced into polymer
matrix [15-18]. The properties of the composite materials depend on the volume fraction
of the fillers and additives as well as the interfacial compatibility between the additives
and the matrix [19]. Various kinds of polymers and polymer matrix composites reinforced
with metal particles have a wide range of industrial applications such as heaters and
electrodes [20]. Non-toxic and environmentally bearable metals have widely been tested
as a viable alternative to other more expensive metal-containing polymeric catalysts [21].
For example, catalysts containing metals such as scandium, molybdenum, copper, nickel,
manganese, and others have been successfully employed [22-26]. Catalysts based on one
of the earth most abundant and cheapest metal, iron, have been also tested to overcome
safety, ecological and toxicity drawbacks associated with toxic metals [27,28]. But the
search still continues for more active iron-based catalysts able to operate under more
sustainable conditions. Moreover, the incorporation and immobilization of ionic liquids
into the polymer systems has been an interesting topic because ionic liquids can be used
as solvents, processing aides and plasticizers to enhance the polymer properties [29-31].
According to these and in continuous studies in the Biginelli reaction, in the present work
a novel Fe/ionic liquid complex containing polyethylene (PEt@Fe/IL, Scheme 1) is
prepared, characterized and its catalytic performance is investigated in the synthesis of
3,4-dihydropyrimidinones through Biginelli reaction. Our study showed that the
4

PEt@Fe/IL was very effective and could be recovered and reused several times without
significant decrease in its efficiency.
2
. Experimental
2.1. Preparation of methyl-octyl-imidazolium bromide/Fe (Fe/IL) complex
Firstly, N-methyl-imidazole (5 mmol) and octyl-bromide (5 mmol) were added in toluene
and refluxed with stirring for 36 h. After cooling reaction temperature to room
temperature, a biphasic system (including ionic liquid and toluene phases) was obtained.
The supernatant toluene solution was next removed and the ionic liquid phase was
washed several times with toluene to remove impurities. After removing solvent and
drying at 70 °C, a viscous liquid called methyl-octyl-imidazolium bromide ([MOIM][Br])
was obtained. Iron acetate (5 mmol) was then added into this ionic liquid with stirring at
room temperature for 24 h to give ionic liquid/iron (Fe/IL) complex.
2
.2. Preparation of the PEt@Fe/IL composite
The immobilization of Fe/IL complex on polyethylene was achieved via coacervation
approach [32]. Firstly, the high-density polyethylene (HDPE) was dissolved in xylene at
reflux conditions in a container equipped with a condenser, mechanical stirrer and
thermometer. Then, the pre-prepared ionic liquid/Fe (Fe/IL) complex was added to the
HDPE solution and mixing process was continued for 2 hours. Then the resulting mixture
was precipitated into methanol at 4 °C. The obtained precipitate was finally washed with
methanol several times and dried for 24 h at 90 °C to give PEt@Fe/IL composite.
2
.3. General procedure for the Biginelli reaction using PEt@Fe/IL catalyst
For this, the PEt@Fe/IL catalyst (0.75 mol %) was added to a homogeneous mixture of
aldehyde (2 mmol), ethylacetoacetate (2 mmol) and urea (3 mmol). This was then
magnetically stirred at 80 °C while the reaction progress was monitored by thin layer
chromatography (TLC). After completion of the process, hot ethanol (10 mL) was added
5

to the reaction flask and the obtained solution was hotly filtered. The filtrate was then
placed in an ice bath to precipitate crude crystals. These were recrystallized in ethanol to
give pure Biginelli products in high to excellent yields. The products were characterized
1
13
by IR, H-NMR, C-NMR and via comparison of their melting points with the reported
ones. Spectroscopic data of new compounds are as following:
5
- Ethoxycarbonyl-6-methyl-4-(3-methoxyphenyl)-3,4-dihydropyrimidin-2(1H)-one:
OMe
EtO C
2
NH
H C
N
O
3
H
-
1
Mp: 217-220 °C; IR (KBr, cm ): 3245, 3118, 2933, 1726, 1704, 1577, 1646, 1222, 1086.
1H NMR (400 MHz, DMSO-d
.26 (s, 3H, CH
CH), 6.88-7.17 (m, 4H, Ar–H), 7.69 (s, 1H, NH), 9.17 (s, 1H, NH); C NMR (100.63
MHz, DMSO-d ) δ (ppm): 165.9, 158.9, 152.7, 152.6, 148.5, 148.4, 137.5, 127.9, 114.2,
00.1, 59.6, 55.5, 53.8, 18.2, 14.6.
, 25 C, TMS) δ (ppm): 1.10 (t, 3H, OCH
o
C
H
, j=7.2 Hz),
6
2
3
2
3
), 3.74 (s, 3H, OCH
3
), 3.97 (q, 2H ,OC
H
2
CH
3
, j=7.2 Hz), 5.11 (s, 1H,
1
3
6
1
5
-Ethoxycarbonyl-6-methyl-4-(4-methylphenyl)-3,4-dihydropyrimidin- 2(1H)-one:
CH3
EtO C
2
NH
H C
N
O
3
H
-
1
Mp: 213-214 ˚C; IR (KBr, cm ): 3247, 3112, 2927, 1724, 1707, 1459, 1649, 1220.
1H-NMR (400 MHz, DMSO-d
H, CH ), 2.28 (s, 3H, CH
H), 7.7 (s, 1H, NH), 9.17 (s, 1H, NH);
, 25 C, TMS) δ (ppm): 1.10 (t, 3H, OCH
o
CH
, j=6.8 Hz), 2.25 (s,
6
2
3
3
3
3
), 3.97 (q, 2H ,OCH
2
CH
3
, j=6.8 Hz), 5.11 (s, 1H, CH), 7.1 (s, 4H, Ar-
6

13C NMR (100.63 MHz, DMSO) δ (ppm): 165.8, 152.7, 148.6, 142.4, 136.9, 129.4,
26.6, 99.9, 59.6, 54.12, 21.1, 18.2, 14.6.
1
5
- Ethoxycarbonyl -6-methyl-4-(2,4-dichlorophenyl)-3,4-dihydropyrimidin-2(1H)-one :
Cl
Cl
EtO C
2
NH
H C
N
O
3
H
-
1
Mp: 246-248 ˚C; IR (KBr, cm ): 3243, 3112, 2956, 2931, 1725, 1706, 1648, 1614, 1511,
222, 1087.
1H-NMR (400 MHz, DMSO-d
.27 (s, 3H, CH ), 4.00 (q, 2H ,OC
Ar–H), 7.76 (s, 1H, NH), 9.22 (s, 1H, NH).
13C-NMR (100.63 MHz, DMSO) δ (ppm): 165.83, 160.5, 152.7, 148.8, 145.3, 136.9,
1
o
6
, 25 C, TMS) δ (ppm): 1.10 (t, 3H, OCH
2
C
H
3
, j=7 Hz),
2
3
H
2
CH , j=7 Hz), 5.16 (s, 1H, CH), 7.24-7.35 (m, 3H,
3
1
28.9, 127.8, 126.7, 99.8, 59.7, 54.4, 18.5, 14.5.
2
.4. General procedure for the recovery of the PEt@Fe/IL catalyst in the Biginelli
reaction
For this, 0.75 mol% of PEt@Fe/IL catalyst was added to a flask containing benzaldehyde,
ethylacetoacetate and urea. The obtained mixture was then magnetically stirred at 80 °C.
The reaction progress was monitored by TLC. After completion of the reaction, hot
ethanol was added and the obtained solution was hotly filtered. The recovered catalyst
was completely washed with ethanol. Then this catalyst was reused at the same conditions
as the first run for at least 7 times and delivered corresponding Biginelli product in high
to excellent yield.
3
. Results and discussion
7

The PEt@Fe/IL was prepared by immobilization of iron/ionic liquid complex onto
polyethylene via coacervation method (Scheme 1) [32]. The structural and chemical
properties of the material was investigated with several techniques such as DRIFTs, SEM,
TGA and EDX. Firstly, the DRIFT spectroscopy was used to determine the functional
groups of the material (Figure 1). The absorption peaks of organic functional groups were
−
1
−1
observed at 2915 and 2850 cm (aliphatic C-H stretching vibrations), 1629 cm (C=N
stretching vibration of imidazolium ring), 1525 cm−1 (C=C stretching vibration of
imidazolium ring) 1473 cm−1 (CH
vibrations), 1367 cm−1 (CH
bending vibration), 1461 cm (C-H deformation
−1
2
bending vibration), and 720 cm−1 (CH
rocking),
3
2
respectively. These observations successfully confirm well immobilization of alkyl
imidazolium ionic liquid groups onto polyethylene. Thermal gravimetric analysis (TGA)
of the PEt@Fe/IL was next carried out from room temperature to 800 °C (Figure 2). This
analysis demonstrated a weight loss of 1.37% below 250 °C which is attributed to the
removal of water and methanol. The second weight loss between 300 and 400 °C
corresponding to elimination of ionic liquid groups which are located onto/into polymer
material. The main weight loss of 92.55 in the range of 400–500 °C corresponding to the
decomposition and removal of polyethylene organic moieties. These data also confirm the
successful immobilization of the ionic liquid functional groups in the material network
and also verify high thermal stability of the catalyst.
The PEt@Fe/IL was also analyzed by inductively coupled plasma/optical emission spectroscopy
(
ICP-OES). According to this analysis, the amount of iron in the catalyst was 0.5 percent (0.09
mmol Fe/g) confirming that the iron species have been well immobilized on the material. The
results of energy-dispersive X-ray (EDX) spectroscopy elemental microanalysis of the
PEt@Fe/IL also confirmed the presence of C, N, and Fe in the catalyst (Figure 3). This is in good
agreement with DRIFT and TGA analyses confirming successful immobilization of IL/Fe
complex on polymer support. In the next study, X-ray photoelectron spectroscopy (XPS) of the
PEt@Fe/IL material was performed to identify true catalyst in the reaction process. The XPS
signals versus binding energy clearly showed Fe-peaks at 711.02 eV (for Fe 2p3/2) and 717.01 eV
(
for Fe 2p1/2) proving the successful immobilization of Fe-complex in the material network
Figure 4). This result is reasonably far from metallic iron (with Fe 2p3/2 of 706.75) and is very
(
close to those of FeX
3
with Fe 2p3/2 of 711 eV [33]. This means that the understudied iron is
8

strongly bound to electronegative atoms and its oxidation state is as Fe (III). Based these
observations, we conclude that the actual catalyst is ([MOIM][Fe(OAc) Br]).
3
The scanning electron microscopy (SEM) analysis was next carried out to study
morphology of the material. The SEM image of the PEt@Fe/IL before reaction (Figure
5
a) revealed the presence of regular particles with uniform morphology. The SEM image
of the PEt@Fe/IL material after reaction showed the particles with morphology different
with those of its parent (Figure 5b) confirming a change in material particles during
reaction process.
In the next stage, the activity of characterized PEt@Fe/IL was tested in the three
component Biginelli condensation of benzaldehyde, urea and ethylacetoacetate according
to Table 1. To find optimal reaction conditions, firstly the effect of solvent, temperature
and catalyst loading was studied.
As presented in Table 1, trace product was obtained in the absence of the catalyst after 90
min (entry 1) indicating that the catalyst is necessary for the reaction. This study showed
that with increasing amount of the catalyst from 0.2 to 0.75 mol%, the yield of the desired
product is remarkably increased indicating significant effect of the catalyst loading in the
reaction progress (Table 1, entries 2–4).
°
The reaction was also affected by temperature and the best result was obtained at 80 C
(Table 1, entries 4–6). Our study was also extended to observe the effect of solvent on the
reaction (Table 1, entries 7-10). As shown, the polar solvent such as ethanol, acetonitrile
and tetrahydrofuran resulted in 71%, 68% and 57% yield, respectively, while 15% yield
of the product was obtained by using toluene. This may be attributed to the better
solubility of the starting materials in the polar solvents. Interestingly, under solvent-free
media at similar conditions and time as above, the reaction was completed and a
quantitative yield of corresponding Biginelli product was obtained (Table 1, entry 4).
According to the aforementioned results, the use of 0.75 mol% of PEt@Fe/IL catalyst at
°
8
0 C under solvent-free media were selected as optimum conditions (Table 2). As shown,
various aromatic aldehydes have been successfully employed in this reaction which is a
good evidence to the large scope of this catalyst system. This condensation process was
fairly robust and several functionalities such as nitro, chloro, bromo, hydroxyl, methyl
and methoxy survived during the course of reaction in a single step. It is also clear that,
9

aromatic aldehydes containing either electron-withdrawing or electron-donating
substituents afford high yields of products with high purity. As presented in Table 2,
electronic effects were observed: benzaldehydes containing electron-donating group
required lower reaction times to deliver the corresponding products in high yield, while
those with an electron-withdrawing group gave high yield in longer reaction times.
Interestingly, ortho-substituted benzaldehydes which due to steric effects are usually less-
reactive in organic reactions, also afforded the corresponding 3,4-dihydropyrimidin-
2(1H)-ones in relatively high yields, whether they had an electron-donating or an
electron-withdrawing group (Table 2, entries 4, 5, 7, 11, 14). These observations confirm
high efficiency of the catalyst for the conversion of a broad range of aromatic aldehydes
to their corresponding Biginelli products applicable in different area of chemistry and
biochemistry. Where an aliphatic aldehyde, such as isoporopyl aldehyde, was used as
substrate, only a trace conversion was observed.
In the next study, the recycling performance of the PEt@Fe/IL catalyst was tested in the
condensation of benzaldehyde, urea and ethylacetoacetate under optimized conditions.
For this, after the reaction was completed, the mixture was filtered and thoroughly
washed with hot ethanol. The recovered catalyst was then reused in the next run under the
same conditions as the first run. The more experiments were performed as before and the
results illustrated that the catalyst could be recovered and reused for at least 7 times
without significant decrease in activity (Table 3). This observation successfully confirms
high recycling efficiency of the PEt@Fe/IL catalyst which is a noteworthy property in
economic and environmental points of view.
Although according the later test, no significant reduce in the catalyst performance was
observed, however, to verify the leaching of active iron species from the material during reaction
process, in the next study a hot filtration test was performed in the reaction of benzaldehyde, urea
and ethylacetoacetate after about 45% of the coupling reaction was completed. The catalyst free
filtrate was then transferred to another flask and the reaction progress was monitored under the
1
0

same conditions as before. Interestingly, after 2 h only 5% additional conversion was observed in
the coupling reaction. Moreover, the atomic absorption spectroscopy showed no presence of iron
species in the filtrate. These significantly confirm well immobilization and high stability of the
catalytic species onto polymer support as well as prove that the catalyst operates in a
heterogeneous manner.
In the final study, to explore the advantages of PEt@Fe/IL catalyzed synthesis of 3,4-
dihydropyrimidin-2(1H)-one, the results obtained under our optimized conditions were
compared with those reported in the literature using other catalysts (Table 4). As shown,
the most of the former catalytic systems have been performed in the organic solvents at
higher reaction times than the PEt@Fe/IL catalyst. Moreover, in the most cases of the
previous works, the recycling times of the catalyst are lower than present ones. These
significantly confirm high efficiency and recoverability of the designed catalytic system
in comparison with former systems.
4
. Conclusion
In summary, we described here an efficient method for the synthesis of 3,4-
dihydropyrimidinones in a PEt@Fe/IL catalyzed reaction of aldehydes, alkylacetoacetates
and urea under solvent free conditions. The material characterization showed high
thermal stability of the catalyst and also well immobilization of ionic liquid/Fe complex
onto PEt polymer support. The catalyst demonstrated excellent reactivity for the Biginelli
condensation of a variety of different electron-withdrawing and electron-donating
aromatic aldehydes and delivered corresponding 3,4-dihydropyrimidinone products in
high to excellent yields. The simplicity of the reaction, easy separation of catalyst and
products from the reaction mixture, high yields and short response time make this an
improved protocol than existing methods. In addition, the catalyst could be easily
recovered and reused several times without significant loss in efficiency. Therefore, the
use of PEt@Fe/IL as catalyst not only makes the reaction economical viable but also help
to reduce environmental pollution to achieve environmentally friendly processes.
1
1

Acknowledgements
The authors acknowledge the Yasouj University, Iran National Science Foundation
(INSF) and the Graduate School and Research Council of the Payame Noor University for
supporting this work.
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1
5

1
6

Figures caption:
Fig. 1. DRIFT spectrum of PEt@Fe/IL.
Fig. 2. Thermal gravimetric analysis (TGA) of the PEt@Fe/IL
Fig. 3. Energy dispersive X-ray (EDX) spectroscopy of the PEt@Fe/IL
Fig. 4. XPS analysis of PEt@FE/IL catalyst
Fig. 5. Scanning electron microscopy (SEM) image of the PEt@Fe/IL (a) before and (b)
after the reaction
Scheme 1. Preparation of the PEt@Fe/IL composite
Fig. 1.
1
7

Fig. 2.
Fig. 3.
1
8

Fig. 4
(a)
(b)
Fig. 5.
1
9

7
N
N
Br
Me
-
Xylene, reflux, stirring
Me
+
Iron acetate
1
2
3
4
. Xylene, reflux, 2 h
. MeOH, 4 o
. Washing with MeOH
. Drying
C
PEt@Fe/IL composite
Scheme 1
2
0

Table 1. The effect of catalyst loading, temperature and solvent in the Biginelli reaction of benzaldehyde with urea
and ethylacetoacetatea
Entry
Catalyst
Catalyst loading (mol %)
T (°C)
80
80
80
80
30
50
Reflux
Reflux
80
Solvent
Yield (%)b
1
2
3
4
5
6
7
8
9
No catalyst
PEt@Fe/IL
PEt@Fe/IL
PEt@Fe/IL
PEt@Fe/IL
PEt@Fe/IL
PEt@Fe/IL
PEt@Fe/IL
PEt@Fe/IL
PEt@Fe/IL
-
0.2
0.5
0.75
0.75
0.75
0.75
0.75
0.75
0.75
-
-
-
-
-
-
Trace
27
55
95
10
45
71
68
15
EtOH
CH
3
CN
Toluene
THF
1
0
Reflux
57
a
b
Reaction conditions: benzaldehyde (1 mmol), ethylacetoacetate (1 mmol), urea (1.5 mmol), 90 min. Isolated
yield.
Table 2. Preparation of dihydropyrimidinone derivatives in the presence of PEt@Fe/IL catalyst a
O
Ar
O
O
O
PEt@Fe/IL (0.75 mol%)
solvent-free, 80 °C
EtO
H C
NH
ArCHO +
H C
3
OEt
+
H N
NH2
2
N
H
O
3
Entry Ar
Time (min)
Yield (%)b
TON]c
Found M. p. (°C)
Reported M. p. (°C)
[
1
2
3
4
5
6
7
8
9
C
6
H
5
90
95 [126.7]
94 [125.3]
90 [120]
83 [110.7]
85 [113.3]
89 [118.7]
84 [112]
95 [126.7]
89 [118.7]
92 [122.7]
92 [122.7]
91 [121.3]
93 [124]
200-202
209-210
190-193
218-221
246-248
188-190
205-207
207-208
228-231
213-214
207-209
198-200
218-219
257-260
201-203 [34]
210-212 [34]
192-193 [35]
222-224 [36]
248-250 [37]
190-192 [38]
206-208 [34]
207-210 [34]
229-231 [36]
215-216 [36]
208-210 [36]
199-201 [34]
220-221 [39]
4-Cl–C
3-Cl–C
2-Cl–C
2,4-Cl–C
3-Br-C
2-Br–C H
4
4-NO
3-NO
4-CH
2-CH
6
6
6
H
H
H
H
6 4
H
4
4
4
4
110
110
120
120
110
110
100
100
120
120
120
120
120
6
6
2
–C
–C
6
H
H
H
H
4
4
4
4
2
6
1
0
1
2
3
4
3
–C
–C
6
1
1
1
1
3
6
4-MeO–C
3-MeO–C
2-MeO –C
6
H
H
4
4
6
6
H
4
85 [113.3]
257-258 [39]
a
Reaction conditions: aldehyde (1 mmol), ethylacetoacetate (1 mmol), urea (1.5 mmol). Isolated yield.c
b
TON=turnover number (defined as mmol of product/mmol of catalyst).
2
1

Table 3. Reusability of the PEt@Fe/IL catalyst in the Biginelli reaction of benzaldehyde with
ethylacetoacetate and urea
Run
1
Time (min)
Conversion
Run
5
Time (min)
110
Conversion
90
95
97
96
96
94
92
90
85
83
2
6
115
3
105
110
7
115
4
8
120
2
2

Table 4. Comparison of catalytic activity of PEt@Fe/IL with other catalysts reported in the literature for the
synthesis of 3,4-dihydropyrimidinones
Entry Catalyst
Conditions
Time (h)
2
Recovery times
-
Ref.
[40]
1
2
3
4
5
6
7
PsMimPF
PEG-SO
6
AcOH, 100 °C
3
H
Microwave oven, 100 °C
EtOH, 80 °C
0.1
7
-
5
-
[41]
[42]
[43]
[44]
[45]
Poly(SIL)
PS-PEG-SO
3
H
Dioxane/2-propanol, reflux
Solvent-free, 50 °C
EtOH, reflux
10
PEG.TUD II
10-15
6
-
PANI–HBF
4
–DHS
2
7
PEt@Fe/IL
Solvent-free, 80 °C
1.5
This
work
Abbreviations: PsMimPF
6
: polystyrene–methylimidazolium hexafluorophosphate, PEG: poly(ethyleneglycol),
Poly(SIL): poly(l-vinyl-3-(3-sulfopropyl) imidazolium hydrogen sulfate), PS-PEG: polystyrene–poly(ethylene
glycol) PEG.TUD II: polyethylene glycol and thiourea dioxide, PANI–HBF –DHS: polyaniline–fluoroboric acid–
4
dodecylhydrogensulfate
2
3