Bentonite with high loading of ionic liquid: A potent non-metallic catalyst for the synthesis of dihydropyrimidinones

Article abstract of DOI:10.1016/j.molliq.2020.114393

In attempt to devise an environmentally-benign metal-free catalyst, ionic liquid was supported on bentonite that is a natural clay. To enhance the loading of ionic liquid, bentonite was first functionalized with a dendritic moiety through successive react

Full text of DOI:10.1016/j.molliq.2020.114393

Journal of Molecular Liquids 319 (2020) 114393
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Bentonite with high loading of ionic liquid: A potent non-metallic
catalyst for the synthesis of dihydropyrimidinones
⁎
Samahe Sadjadi , Fatemeh Koohestani
Gas Conversion Department, Faculty of Petrochemicals, Iran Polymer and Petrochemical Institute, PO Box 14975-112, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2020
Received in revised form 17 September 2020
Accepted 20 September 2020
Available online xxxx
In attempt to devise an environmentally-benign metal-free catalyst, ionic liquid was supported on bentonite that
is a natural clay. To enhance the loading of ionic liquid, bentonite was first functionalized with a dendritic moiety
through successive reactions with 2,4,6-trichloro-1,3,5-triazine and 1,3-diaminopropane. Then, the terminal
functionalities of dendron were adorned with ionic liquids via reaction with 1-methyl imidazole. The study of
the catalytic activity of the resultant catalyst for promoting Biginelli reaction in aqueous media under mild reac-
tion condition approved high activity of the designed composite, superior to that of bentonite. To investigate the
role of ionic liquid content in the activity of the catalyst, two model catalysts were prepared through immobili-
zation of ionic liquid on bentonite and bentonite decorated with dendron of lower generation. It was found
that the presence of the dendritic moiety could increase grafting of ionic liquid on bentonite and consequently
improve the catalytic activity of final catalyst. Notably, the catalyst was highly recyclable. Moreover, analysis of
the recycled catalyst indicated the stability of the catalyst.
Keywords:
Bentonite
Catalyst
Ionic liquid
Dihydropyrimidinones
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
studies confirmed that ligands with di or multi amino groups are prom-
ising functionalization agents [16–21] and can provide effective interac-
Ionic liquid, IL, is referred to a class of salts with low pressure, in
which the cationic moiety is organic [1–3]. Considering the diversity
of both anions and cations that can be employed for the formation of
ILs, numerous ILs with controllable physiochemical properties can be
coined [1,4,5]. As ILs benefit from outstanding properties such as low
toxicity, high electric conductivity and thermal stability, their uses in
various sciences have blossomed rapidly [6–8]. One of the most
flourishing utility of ILs is catalysis. In fact, ILs can be utilized as reaction
media and catalysts. To improve the catalytic performance of ILs, they
are mostly immobilized on supports to furnish heterogeneous catalysts.
Taking the increasing importance of green chemistry into account, ILs
have been considered as alternatives for metallic catalysts.
Clay materials are extensively utilized in diverse fields, such as catal-
ysis, oil and gas, food, agriculture, ceramics, pharmaceutical and cos-
metics. Bentonite, Bent, is one of the most applicable clay that has an
aluminum phyllosilicate structure and is of category of silicates with
three layers [9–12]. Bent benefits from notable features such as high
chemical and thermal stability, good surface area, high adsorption-
absorption properties, low-cost and environment benign nature
[13–15]. One of the major utility of Bent is supporting the catalytic spe-
cies. Mostly, supporting materials are surface functionalized prior to the
stabilization of the catalysts. Both experimental and computational
tions with the supported catalytic species. In this regard, we have
recently studied a library of diamines to disclose the most suitable li-
gand that can furnish the most efficient interactions with Pd nanoparti-
cles [21]. In some cases, to increase the number of surface functional
groups, the supporting materials are first decorated with other organic
moieties that possess multiple active sites such as 2,4,6-trichloro-
1,3,5-triazine or melamine and then reacted with other heteroatom
containing moieties such as diamines, ILs, etc. [4,22,23]. Moreover, in-
troduction of dendritic moieties with multi nitrogen atoms is a promis-
ing strategy for surface modification [24–28]. As an example, it was
proved that dendrimer decorated halloysite clay is an efficient support
for Pd immobilization [28]. This method provides multiple functional
groups on the supporting materials.
Biginelli reaction is a well-established multicomponent one-pot re-
action that has been widely used for the synthesis of 4-aryl-3,4-
dihydropyrimidin-2(1H)-one derivatives (DHPMs) [29–34]. As DHPMs
are key biologically active chemicals with extensive pharmacological
properties [35–38], development of efficient protocols for promoting
Biginelli reaction is of great importance. In this regard, disclosing effi-
cient catalysts has been targeted.
The focus of our research team is on the heterogeneous catalysis
[39]. In this regard, we tried to use natural clays as catalyst supports
[39]. On the other hand, we are interested in developing IL containing
catalytic systems for promoting various chemical transformations
[8,40]. Recently, we have reported efficient catalysts based on natural
⁎
Corresponding author.
E-mail address: s.sadjadi@ippi.ac.ir (S. Sadjadi).
https://doi.org/10.1016/j.molliq.2020.114393
0167-7322/© 2020 Elsevier B.V. All rights reserved.

S. Sadjadi and F. Koohestani
Journal of Molecular Liquids 319 (2020) 114393
clay supported ILs [41]. In this topic, one of the challenging issue was
low loading of IL on the clay. In attempt to load high content of IL on
the clay, in this article Bent clay was selected as a natural support and
then adorned with a dendritic moiety, prepared through reaction of
2,4,6-trichloro-1,3,5-triazine and 1,3-diaminopropane. Subsequently,
the periphery of the formed dendritic moiety was functionalized with
ILs. The resultant composite, Bent-D-IL, was then applied as a metal-
free catalyst for promoting Biginelli reaction in aqueous media under
mild reaction condition. Investigation of the effective parameters on
the reaction, study of the substrate scope and recyclability of the catalyst
were also performed.
In the final step, to embellish the amino terminal groups of the den-
dritic moiety with ILs, suspension of Bent-D (1 g) in THF (50 mL) was
treated with 1-methylimidazole (1.5 g) under continuous stirring at
65 °C for 24 h under inert atmosphere. Upon completion of the reaction,
Bent-D-IL was gathered, washed with MeOH and dried in vacuum oven.
The schematic illustration of the synthesis steps for fabrication of Bent-
D-IL is depicted in Fig. 1.
2.4. General procedure for the synthesis of dihydropyrimidinones
In a particular procedure, all of the reagents, i.e. benzaldehyde
(1 mmol), ethyl acetoacetate (1 mmol), urea (1.2 mmol) were dissolved
in EtOH/H2O (1:1, 10 mL). Then, Bent-D-IL (50 mg) was introduced and
the reaction mixture was stirred at 50 °C. Using TLC technique, the reac-
tion was monitored and after completion, the reaction mixture was di-
luted with EtOH to dissolve DHPM. Then, Bent-D-IL was simply filtered,
washed with EtOH several times and dried in oven overnight. On the
other hand, the solvent in the reaction vessel was evaporated and the
solid organic product was washed with distilled water to remove the
unreacted urea. Further purification was accomplished with column
chromatography, using ethyl acetate/hexane mixture.
2. Materials and apparatus
2.1. Materials
The chemicals that have been applied for the synthesis of the catalyst in-
cluded, 2,4,6-trichloro-1,3,5-triazine (TCT), 3-aminopropyltriethoxysilane
(APTES), 1,3-diaminopropane (DAP), 1-methylimidazol, tetrahydrofuran
(THF), toluene and MeOH. Biginelli reaction was performed by employing
the following reagents: benzaldehydes, ethyl acetoacetate, urea, EtOH
and distilled water. All the chemicals and solvents used for the catalyst
preparation and Biginelli reaction were provided from Sigma-Aldrich
and used without further purification. The applied Bent was purchased
from Madan Kavan Co., Iran and used as received.
3. Result and discussion
3.1. Verification of Bent-D-IL formation
FTIR spectroscopy was carried out after each synthetic step. In Fig. 2
the recorded FTIR spectra of Bent, Bent-N, Bent-TCT, Bent-DAP and
Bent-D-IL are presented. According to the literature, the bands in the
range of 3631–3425 cm−1 in the FTIR spectrum of Bent are ascribed to
the hydroxyl groups [42–44]. The band at 795 cm−1 is assigned to the
typical stretching modes of Si\\O for silica, while the bands at
1032 cm−1 and 526 cm−1 are related to the absorption band of
Si\\O\\Si and Al\\O\\Si deformation respectively. Moreover, the
band at 1636 cm−1 is attributed to the stretching vibration of water
molecules [42–44]. In the FTIR spectrum of Bnet-N, similar characteristic
bands are discerned, indicating that reaction with APTES did not lead to
the collapse of Bent structure. Notably, the observed band at 2927 cm−1
is assigned to –CH2 functionality in APTES. Other characteristic bands of
APTES, i.e. Si\\O\\Si and Si\\O stretching, overlapped with the bands of
Bent. Similarly, for three other samples, Bent-TCT, Bent-DAP and Bent-
D-IL, the characteristic bands of Bent are discerned. This observation
confirms the stability of Bent structure upon decoration with IL-
terminated dendritic moiety. The distinguishing point in the FTIR spec-
tra of the mentioned spectra is the appearance of an additional band at
1720 cm−1 that is corresponded to the\\C_N functionality in the TCT
and IL structure. In fact, this characteristic band can demonstrate conju-
gation of D-IL.
Next, the XRD pattern of Bent-D-IL was obtained to appraise
whether incorporation of IL terminated dendritic moiety can affect the
structure of Bent. As illustrated in Fig. 3, in the recorded XRD pattern
of Bent-D-IL the characteristic bands of Bent at 2θ = 7°, 20.8°, 21.9°,
26.6°, 27.7°, 31.7°, 36°, 50°, 62°, 73.5° and 76° can be discerned
[45,46]. This result corroborated that functionalization of Bent with D-
IL did not alter Bent structure.
Using SEM technique, the morphologies of both Bent and Bent-D-IL
were analyzed (Fig. 4). As depicted, Bent exhibited a flake-like morphol-
ogy, while Bent-D-IL showed a distinguished morphology from Bent.
The change of morphology upon introduction of IL-containing function-
ality is quite expectable. In fact, the non-covalent interactions of IL moi-
eties of the backbone of Bent-D-IL could affect the morphology. To
further approve conjugation of the organic moiety on the clay, EDS anal-
ysis was exploited. As shown, in EDS analysis of Bent, Al, Ca, K, Cu, Mg,
Fe, O and Si atoms can be observed. In the EDS analysis of Bent-D-IL,
these atoms can also be discerned. Additionally, C, N and Cl atoms can
be observed in the EDS analysis of the catalyst, indicating conjugation
2.2. Instrumentation and analysis
Formation of Bent-D-IL was verified by analyzing the catalyst by
XRD, BET, TGA, FTIR, FE-SEM, EDS and elemental mapping analysis. X-
ray diffraction (XRD) pattern of Bent-D-IL was collected on Siemens,
D5000 apparatus using graphite monochromatic Cu-Kα. Field emission
scanning electron microscope (FE-SEM) images and energy dispersive
spectroscopy (EDS) were obtained by MIRA 3 TESCAN-XMU. Fourier
transform infrared (FT-IR) spectra were recorded via PERKIN-ELMER-
Spectrum 65. Thermo gravimetric analysis (TGA) was accomplished
by a METTLER TOLEDO under N2 atmosphere at heating rate of10 °C
min−1
.
2.3. Synthesis of the catalyst
2.3.1. Amino-functionalization of Bent: synthesis of Bent-N
In the first step, Bent was functionalized with APTES. In this regard,
Bent (3 g) was dispersed in dry toluene and ultrasounded for 10 min. Af-
terwards, APTES (3 mL) was gradually mixed with the aforementioned
suspension. To allow successful functionalization, the mixture was
refluxed under N2 atmosphere at 110 °C overnight. At the end, the pre-
cipitate was collected via conventional filtration, washed with toluene
repeatedly, and dried in oven at 70 °C.
2.3.2. Introduction of IL-terminated dendritic moiety on Bent-N: synthesis
of Bent-D-IL
In order to adorn Bent-N with IL-terminated dendritic moiety, a well
dispersed suspension of Bent-N (2 g) in THF (60 mL) was prepared
using ultrasonic irradiation. Then, TCT (2 g) was separately dissolved
in THF and the resultant solution was slowly added to the Bent-N sus-
pension at 0 °C. To allow the amino functionalities on Bent to react
with Cl-functionalities of TCT, the reaction mixture was stirred for
24 h. At the end of the reaction, the precipitate, Bent-TCT, was filtered
and after washing with THF dried in oven at 70 °C. In the next step, a
suspension of Bent-TCT (1.5 g) in THF (40 mL) was prepared and then
reacted with DAP (1.5 g). The reaction was completed after stirring for
24 h at 60 °C to furnish Bent-DAP. The latter was filtered, washed and
dried in oven at 80 °C and subsequently treated with TCT using similar
procedure explained for the formation of Bent-TCT to furnish Bent-D.
2

S. Sadjadi and F. Koohestani
Journal of Molecular Liquids 319 (2020) 114393
Fig. 1. Synthetic procedure of Bent-D-IL.
of the organic functionality (D-IL) on the backbone of the catalyst. Nota-
bly, some of the Cl functionalities on TCT can not find an opportunity to
participate in the reaction with diamine due to the steric effect. This
issue is in good accordance with the literature [47].
weight loss step is observed at 280 °C (~1.5 wt%) that is corresponded to
the decomposition of APTES and another weight loss is appeared in the
range of 450–560 °C that is related to the decomposition of Bent. Simi-
larly, in TG curve of Bent-TCT, weight losses due to the loss of water
and decomposition of Bent are observed. Moreover, the weight loss ap-
peared in the range of 300–370 °C (6 wt%) confirmed conjugation of
TCT. Thermogram of Bent-DAP was similar to that of Bent-TCT, except,
the weight loss in the range of 280–350 °C was ~8.8 wt%, approving
grafting of DAP. In TG curve of Bent-D-IL, apart from loss of structure
of water and Bent decomposition, a weight loss was observed in the
range of 240–350 °C (11.7 wt%). These results established successful
grafting of organic moieties in each synthetic step.
In the following, both Bent and Bent-D-IL were analyzed by BET
technique, Fig. 7. The results signified that the specific surface area of
the used Bent was 40.62 m2 g−1. This value for Bent-D-IL dramatically
reduced and reached to 5.19 m2 g−1, approving grafting of IL-
terminated dendritic moiety.
Elemental mapping analysis of the Bent-D-IL (Fig. 5) was also carried
out to disclose the dispersion of the organic functionality on Bent. As il-
lustrated, C, N and Cl atoms showed high dispersion, implying that IL-
containing dendritic moiety was grafted on Bent almost uniformly.
A potent analysis that can approve grafting of the organic functional-
ities is TG analysis. In this regard, TG curves of Bent-N, Bent-TCT, Bent-
DAP and Bent-DIL were obtained and compared, Fig. 6. The comparison
of all four curves implied that the thermal stability of the samples de-
creased as Bent-N > Bent-TCT > Bent-DAP > Bent-D-IL. This is a logical
result, as by addition of more organic moieties, it is expected that the
thermal stability decreases. In fact, the degradation of the organic func-
tionalities can justify the observed decrement of the thermal stability. In
more detail, in Bent-N, apart from weight loss due to loss of water, one
3

S. Sadjadi and F. Koohestani
Journal of Molecular Liquids 319 (2020) 114393
Bent-D-IL
Bent-DAP
Bent-TCT
Bent-N
Bent
3800
3300
2800
2300
1800
1300
800
300
Wavenumber (cm¯¹)
Fig. 2. FTIR spectra of Bent, Bent-N, Bent-TCT, Bent-DAP and Bent-D-IL.
3.2. Catalyst activity
Table 1, approved that in the absence of the catalyst only low yield of
the desired product was furnished (10%). This result emphasized the
necessity of use of the catalyst for this reaction.
In this article, it was intended to design a heterogeneous metal-free
catalyst by supporting ILs on a low-cost and readily available clay, Bent.
According to our experiences on functionalization of clays and other re-
ports, direct grafting of ILs on clay surface resulted in low loading of IL
[41]. To cope with this challenging issue, a dendritic moiety that
contained several reactive sites for conjugation of IL was first grown
on Bent and then, IL was introduced. After confirmation of the formation
of Bent-D-IL, its activity was assessed. In this regard, one of the most
conventional chemical transformation, Biginelli reaction, was selected.
The importance of this reaction is formation DHPMs that are precious
heterocycles with potential biological activities. To commence the
study, a model reaction, reaction of benzaldehyde, ethyl acetoacetate
and urea, was targeted. First, to elucidate the necessity of the presence
of the catalyst for this reaction, the model reaction was performed in
the absence of the catalyst at 50 °C in H2O/EtOH (1:1). The results,
Confirming the importance of the use of the catalyst, the reaction
condition was optimized. First, the model reaction was performed by
loading 30 mg Bent-D-IL in water at 50 °C, Table 1. Under this condition,
low yield of the product was obtained after relatively long reaction time.
To increase the reaction yield, the reaction solvent was changed to H2O/
EtOH (1:1). The result indicated significant improvement of the reaction
yield. Taking the important effect of solvent into account, the effects of
other solvents were also investigated. The results implied that H2O/
EtOH (1:1) led to the best results. Next, the loading of the catalyst was
optimized. As shown, increment of the catalyst loading to 50 mg effec-
tively improved the yield of the reaction. Hence, for further investiga-
tion, this value was considered as the optimum catalyst loading.
Reaction temperature effect was also appraised. To this purpose, the re-
action was performed at two additional temperatures, 25 and 60 °C. The
Fig. 3. XRD pattern of Bent-D-IL.
4

S. Sadjadi and F. Koohestani
Journal of Molecular Liquids 319 (2020) 114393
Fig. 4. A) FESEM image of Bent, B: SEM image of Bent-D-IL, C and D) EDS analyses of Bent and Bent-D-IL.
results implied that at lower temperature, the reaction yield decreased,
while increment of the temperature from 50 to 60 °C had no effect on
the reaction yield. Hence, the best temperature was selected as 50 °C.
APTES, (3-chloropropyl)triethoxysilane was applied), followed by reac-
tion with 1-methylimidazol. The second control catalyst, referred as
Bent-TCT-IL, was fabricated through reaction of Bent-TCT with 1-
methylimidazol. The results of the comparison of the activities of
these two control catalysts with that of the catalyst, Table 2, indicated
that the content of IL in the structure of the catalyst significantly affected
the activity of the catalyst and higher content of IL resulted in superior
catalytic activity. Another point that can be inferred from the tabulated
results is that the content of IL on the structure of the catalyst is influ-
enced by the presence of the dendritic moiety. In more detail, in Bent-
IL, the loading of IL is very low. This observation is expectable because
TG analysis confirmed that loading of (3-chloropropyl)triethoxysilane
on Bent was very low (~1 wt%). Hence, just a few molecules of 1-
methylimidazol have the chance of grafting on Bent. The TG analysis
of Bent-TCT-IL showed that introduction of TCT prior to conjugation of
IL led to the increase of IL content. This is a rational result as each at-
tached TCT molecule on Bent can provide two opportunities for IL
grafting. Comparing the IL content of Bent-IL and Bent-TCT-IL, it can
be seen that the loading of IL in the latter is slightly lower than two
fold. This can be due to the fact that some of Cl functionalities on
Bent-TCT had no chance to react with 1-methylimidazol as a result of
steric hindrance. Similarly, in Bent-D-IL sample, IL content increased
by introduction of another generation of dendritic moiety and more
possible grafting sites. These results corroborated that introduction of
3.3. Investigation of roles of IL and Bent in the catalysis
High catalytic activity of Bent-D-IL motivated us to study the roles of
Bent and IL in catalysis more precisely. To fulfill this issue, it was first ex-
amined whether bare Bent has any catalytic activity. In this regard, the
model Biginelli reaction was performed in the presence of Bent as a cat-
alyst under the optimum reaction condition. It was found that only low
yield of the desired product (25%) was furnished by using Bent as a cat-
alyst. This result confirmed that IL is the main catalytic species and its
presence is essential for obtaining high yield of the reaction.
3.4. Study of the role of IL content in the catalysis
Confirming the main role of IL in the catalysis, it was appraised
whether the content of IL on the structure of Bent-D-IL can affect the
catalytic activity. In this regard, some model catalysts with different
loading of ILs were prepared and their activities for the model Biginelli
reaction were compared. One of the control catalyst, denoted as Bent-
IL, was prepared through\\Cl functionalization of Bent (the procedure
was similar to that used for the synthesis of Bent-N, except instead of
5

S. Sadjadi and F. Koohestani
Journal of Molecular Liquids 319 (2020) 114393
Fig. 5. Elemental mapping analysis of Bent-D-IL.
Bent-D-IL
Bent-DAP
Bent-TCT
Bent-N
100
95
90
85
80
75
70
20
120
220
320
420
520
620
720
Temperature (°C)
Fig. 6. Thermograms of Bent-N, Bent-TCT, Bent-DAP and Bent-D-IL.
6

S. Sadjadi and F. Koohestani
Journal of Molecular Liquids 319 (2020) 114393
Table 2
Study of the effect of IL content on the catalytic activity.
Entry
Catalyst
IL content (wt%)
Yielda (%)
1
2
3
Bent-IL
Bent-TCT-IL
Bent-D-IL
1
1.8
3
68
78
98
a
Reaction condition: aldehyde (1 mmol), ethyl acetoacetate (1 mmol), urea
(1.2 mmol), catalyst (50 mg), H2O/EtOH (10 mL) at 50 °C in 3 h.
have been developed to furnishe DHPMs efficiently. Although exact
comparison of the reported methods is not possible, in this section,
some reported reaction conditions and yields of the model DHPMs are
tabulated in Table 4 to disclose whether the present protocol by using
Bent-D-IL can be placed among the efficient methodologies. The results
summarized in Table 4 indicated that both metallic and metal free cata-
lysts have been utilized for catalyzing Biginelli reaction. On the other
hand, use of clays and ILs has also been considered. Considering the eco-
nomic and environmental issues, applications of natural compounds as
catalysts or catalyst supports is of great interest. In fact, although syn-
thetic supports such as MCM-41 benefit from some advantageous
such as tunable properties, their syntheses are mostly carried out in sev-
eral steps that rendered them time consuming, tedious and expensive.
On the other hand, metal free catalysts and use of aqueous media as re-
action media are in agreement with the principles of Green chemistry.
Considering the fact that the yield of all tabulated protocols are almost
comparable, it can be inferred that Bent-D-IL that is a metal free catalyst
is an efficient catalyst that can promote Biginelli reaction in aqueous
media to furnish the corresponding products in high yields.
Fig. 7. N2-adsorption desorption isotherm of the a) Bent and b) Bent-D-IL.
a dendritic moiety is an efficient strategy to improve loading of IL on
Bent clay.
3.5. Generality of the present protocol
3.7. Catalyst recyclability
Next, it was appraised whether the observed results for the model
reagents can be generalized to other substrates. In this regard, the reac-
tions of a variety of aromatic aldehydes with electron-donating and
electron-withdrawing functionalities were performed under Bent-D-IL
catalysis. Gratifyingly, aromatic aldehydes with different electronic den-
sities could tolerate Biginelli reaction to give raise to the corresponding
DHPMs, Table 3. Noteworthy, even the heterocyclic aldehyde could un-
dergo the reaction to furnish the product in high yield.
To evaluate the recyclability of Bent-D-IL, the catalyst was recovered
from first run of Biginelli model reaction and then utilized for the next
run of the same reaction. Measurement of the yield of the reaction
established that use of Bent-D-IL for the second run of Biginelli model
reaction caused no decrement of the catalytic activity and the corre-
sponding DHPMs derivative was formed in high yield. Recovery and
use of the catalyst for the third run, however, resulted in slight decrease
of the initial activity. This trend continued and the yield of the reaction
decreased from 100 to 82% after using Ben-D-IL for five runs. Notably,
after sixth run, 7% loss of the activity was observed, Fig. 8.
3.6. Comparison of the catalytic activity
As mentioned, Biginelli reaction is an important organic reaction
that has been focus of many researchers and till now many protocols
To shed light to the impact of reusing Bent-D-IL on the morphology,
the reused catalyst after sixth run was characterized by SEM. As
Table 1
Optimization of Biginelli reaction condition.
Entry
Catalyst
(mg)
Temp.
(°C)
Solventa
Time
(h:min)
Yieldb
(%)
1
2
3
4
5
6
7
8
9
10
30
30
30
30
30
40
50
50
50
–
50
50
50
50
50
50
50
60
25
50
H2O
H2O/EtOH
CH3CN
DMF
THF
H2O/EtOH
H2O/EtOH
H2O/EtOH
H2O/EtOH
H2O/EtOH
5:30
4:00
4:00
5:00
5:00
4:00
3:00
2:40
4:00
6:00
20
60
40
20
30
85
98
98
65
10
a
Reaction condition: benzaldehyde (1 mmol), ethyl acetoacetate (1 mmol), urea (1.2 mmol).
Isolated yields.
b
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S. Sadjadi and F. Koohestani
Journal of Molecular Liquids 319 (2020) 114393
Table 3
Synthesis of DHPMs by using Bent-D-IL as the catalyst.
No.
1
Substrate
Producta
Yieldb (%)
98
2
3
4
100
90
95
5
6
90
85
a
Reaction condition: aldehyde (1 mmol), ethyl acetoacetate (1 mmol), urea (1.2 mmol), catalyst (50 mg), H2O/EtOH (10 mL) at 50 °C in 3 h.
Isolated yield.
b
illustrates in Fig. 8, the reused catalyst exhibited more aggregated mor-
phology compared to fresh Bent-D-IL. FTIR spectrum of reused Bent-D-
IL after sixth run was also obtained and compared with that of fresh
Bent-D-IL. As shown, FTIR spectrum of the reused catalyst exhibits all
of the characteristic absorbance bands of fresh Bent-D-IL, approving
the stability of Bent-D-IL in the course of reusing.
terminal functionalities of dendron were adorned with ILs via reaction
with 1-methyl imidazole. Notably, some of the Cl functionalities on
TCT can not find an opportunity to participate in the reaction with di-
amine due to the steric effect. The resulting catalyst, Bent-D-IL, exhib-
ited high catalytic activity for catalyzing Biginelli reaction in aqueous
media under mild reaction condition. This protocol can be generalized
to various substrates for the formation of broad range of DHPMs in
high yields. Investigation of the role of the dendritic moiety in the in-
crease of IL content on the structure of the catalyst indicated that the
dendritic moiety could effectively improve IL loading and consequently
the observed catalytic activity. It is worth mentioning that the catalyst
was recyclable up to six runs and analysis of the recycled catalyst indi-
cated the stability of catalyst.
4. Conclusion
In summary, a novel heterogeneous catalyst was devised by
adorning Bent with a dendritic moiety and introduction of ILs. In this re-
gard, bentonite was first functionalized with a dendritic moiety through
successive reactions with TCT and 1,3-diaminopropane. Then, the
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S. Sadjadi and F. Koohestani
Journal of Molecular Liquids 319 (2020) 114393
Table 4
Comparison of the catalytic activity of the present catalyst with other reported catalysts for Biginelli reaction.
Entry
Catalyst
Catalyst amount
Condition
Solvent
Time (h:min)
Yield (%)
Ref
1a
2b
3c
4d
5e
6
PANI-FeCl3
HBF4
AT-Mont
(0.5)ILHSO4@MCM-41@Cu(15)
30% TPA/bent
Silica sulfuric acid
Fe(III)/Al-MCM-41
β-CD-SO3H
0.2 g
Reflux
45 °C
Reflux
80 °C
80 °C
Reflux
Reflux
100 °C
50 °C
CH3CN
Solvent-free
EtOH
EtOH
EtOH
EtOH
CH3CN
Solvent-free
H2O/EtOH
24:00
00:35
2:00
2:00
5:00
6:00
4:00
2:00
3:00
83
95
98
90
95
91
85
89
95
[48]
[49]
[50]
[51]
[52]
[53]
[54]
[55]
10 mol%
0.02 g
0.5 g
0.09 g
0.23 g
0.03 g
0.04 g
0.05 g
7f
8g
9
Bent-DIL
This study
a
Polyaniline supported FeCl3.
b
c
d
e
f
Fluoroboric acid.
Acid activated montmorillonite clay.
Copper-doped mesoporous silica supported dual acidic ionic liquid.
Heteropolyacid 12-tungstophosphoric acid H3[PW12O40] immobilized over natural bentonite.
FeCl3 immobilized on Al-MCM-41.
g
β-Cyclodextrin–SO3H.
100%
80%
60%
40%
20%
100
1
87
82
100
2
75
95
0%
3
4
5
6
A
B
Fresh Catalyst
Reused Catalyst
3850
3350
2850
2350
1850
1350
850
350
Wavenumber (cm¯¹)
C
Fig. 8. A: The results of the recyclability of Bent-DIL and B: SEM image and C: FTIR spectrum of the recycled catalyst.
CRediT authorship contribution statement
Declaration of competing interest
Samahe Sadjadi: Conceptualization, Funding acquisition, Investiga-
tion, Methodology, Project administration, Supervision. Fatemeh
Koohestani: Formal analysis, Methodology, Visualization.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
9

S. Sadjadi and F. Koohestani
Journal of Molecular Liquids 319 (2020) 114393
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Acknowledgements
The authors appreciate the partial support of Iran Polymer and Pet-
rochemical Institute.
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