F. Koohestani and S. Sadjadi
Journal of Molecular Liquids 334 (2021) 115754
(AIBN), 1-bromobutane, 3-(trimethoxysilane) propyl methacrylate
(3-TMSPMA) and diethyl ether. The reagents used for the evaluation
of the activity of the as-prepared catalyst included aldehyde, dimedone,
malononitrile, barbituric acid, NaOH, MeOH and EtOH. All of the
chemicals applied for this research were purchased from Sigma-Aldrich.
thin-layer chromatography (TLC). After the reaction was completed,
the solvent was removed and the product was recrystallized in EtOH,
Fig. 2.
2.4.2. Synthesis of tetrahydrobenzo[b]pyran derivatives
A mixture of malononitrile (1 mmol), dimedone (1 mmol), aldehyde
(1 mmol) and Bead-PIL as catalyst (20 mg) was stirred at 25 °C in H2O
(15 mL) as solvent for 40 min. The reaction progress was followed
using TLC, Fig. 2. Afterward, Bead-PIL was separated, washed with
MeOH (3 × 10 mL) and dried for further use. The products were recrys-
tallized in EtOH and purified via column chromatography.
2.2. Apparatus and equipment
The techniques used for the validation of the catalyst structure in-
cluded, Fourier transform infrared (FTIR), X-ray diffraction (XRD),
Thermo gravimetric analysis (TGA), scanning electron microscope
(SEM) and Energy dispersive spectroscopy (EDS). Chemical structure
of the samples were identified using FTIR spectroscopy with PERKIN-
ELMER-Spectrum 65. Siemens, D5000 apparatus via Cu Kα source was
utilized for analysis of the structure of the catalyst. The thermal features
of the samples were determined by TGA on METTLER TOLEDO at a
heating rate of 10 °C.min−1 under N2 flow. The morphology and compo-
sition of Bead-PIL were explored via JMIRA 3 TESCAN-XMU.
2.4.3. Synthesis of pyrano[2,3-d]pyrimidine derivatives
A mixture of aldehyde (1 mmol), barbituric acid (1 mmol) and
malononitrile (1 mmol) were added to a round-bottomed flask contain-
ing Bead-PIL (20 mg) and H2O (15 mL). The resulting mixture was
stirred at room temperature for 20 min, Fig. 2. After completion of
the reaction (as monitored by TLC), Bead-PIL was removed, washed
with MeOH and derided for further use. The pure products were ob-
tained after recrystallization in EtOH and purification via column
chromatography.
2.3. Preparation of bead-PIL
2.3.1. Synthesis of IL
IL monomer was prepared via a solvent-free procedure [39]. In this
respect, VIM (5 mL) and excess amount of 1-bromobutane were
charged in a reaction vessel and stirred at 70 °C for 1 day under inert at-
mosphere. Afterward, the resulting mixture was cooled. Then, diethyl
ether was added to obtain viscous IL. At the end, diethyl ether was re-
moved under vacuum and the resultant IL was washed with MeOH
and dried at 40 °C overnight.
3. Result and discussion
3.1. Bead-PIL characterization
According to visual observation, Bead exhibited spherical morphol-
ogy. To further analyze the morphology and surface characterization
of Bead, it was subjected to SEM analysis. As depicted in Fig. 3, the as-
prepared Bead showed a smooth surface. The study of the morphology
of Bead-PIL, Fig. 3, on the other hand, confirmed that upon introduction
of PIL on Bead, it preserved its spherical morphology. However, the sur-
face of Bead-PIL is rough and porous. This observation approved that
conjugation of PIL caused morphological change.
To further evaluate Bead-PIL, EDS and elemental mapping analyses
were also accomplished. The result of EDS analysis, presented in Fig. 4,
indicated the presence of C, O, N, Br and Si atoms in Bead-PIL. C, N and
O atoms can be attributed to Bead. On the other hand, C, N and Br
atoms can approve conjugation of PIL. Moreover, attachment of 3-
TMSPMA can be confirmed by observing Si atom in the composition of
Bead-PIL.
2.3.2. Synthesis of CS bead
Preparation of CS bead was achieved through conventional method
[40]. Briefly, a solution of CS (2 g) in acetic acid solution (2%, 100 mL)
was gently dropped via burette into aqueous solution of NaOH (0.5
M) to generate CS beads. Then, the generated beads were kept for 1
day in NaOH solution and washed with distilled water.
2.3.3. Synthesis of cross-linked bead
Cross linking of the formed beads was performed by treating them
with GA solution in EtOH (5 wt%) under stirring condition. The reaction
was continued at 70 °C for 12 h. Subsequently, the obtained beads,
Bead-GAs, were separated, washed with EtOH and dried under vacuum.
FTIR spectroscopy was carried out for Bead, Bead-GA, Bead-GA-V,
Bead-PIL samples, Fig. 5. The FTIR spectrum of the synthesized Bead is
in good accordance with the literature [41] and exhibited the absor-
bance bands at 1058 cm−1 (stretching of C\\O group), 2921 cm−1
(-C-H functionality), 3433 cm−1 (amino and hydroxyl groups), and
1636 cm−1 (N\\H bending vibration and stretching for primary
amine). Next, Bead-GA has been analyzed by FTIR spectroscopy. The
FTIR spectrum of Bead-GA, shown in Fig. 5, possessed all of the above-
mentioned absorbance bands related to Bead. This issue confirms the
stability of Bead in the course of cross linking. In this spectrum, the
sharp absorbance band in 1562–1702 cm−1 can be indicative of forma-
tion of\\C_N bonds. In the case of Bead-GA-V, the distinguishing ab-
sorbance band appeared at 1720 cm−1. This sharp band can be
assigned to the \\C_O functionality in 3-TMSPMA. Moreover, the
broad band at 1041–1190 cm−1 can be attributed not only to the
stretching of C\\O group, but also to the –Si-O functionality of 3-
TMSPMA. In the FTIR spectrum of the catalyst, the absorbance bands
of Bead-GA-V can be observed. Noteworthy, the characteristic bands
of PIL, i.e.\\C_N bonds of the imidazolium rings overlap with imine
bands resulted from cross linking with GA.
2.3.4. Synthesis of bead-GA-V
In order to vinyl-functionalize Bead-GA, a mixture of Bead-GA (1.5
g) and 3-TMSPMA (1 mL) in EtOH (50 mL) was prepared and heated
at 110 °C. Then, the reaction mixture was refluxed for 1 day under
inert atmosphere. At the end, the obtained Bead-GA-V was separated,
washed with MeOH and dried at ambient temperature overnight.
2.3.5. Synthesis of bead-PIL
Bead-PIL was synthesized via free-radical polymerization of the IL
monomer and Bead-GA-V. Typically, Bead-GA-V (1 g) was suspended
in EtOH and stirred for 30 min. In the following, a solution of IL mono-
mer (1.5 g) and AIBN (0.1 g) was injected into above-mentioned mix-
ture. The polymerization reaction was carried out at 70 °C for 1 day
under inert atmosphere. At the end, Bead-PIL was collected, washed
with MeOH and dried at ambient temperature. The procedure for the
preparation of Bead-PIL is depicted in Fig. 1.
2.4. Evaluation of the catalyst activity
Thermograms of Bead, Bead-GA, Bead-GA-V and Bead-PIL are
depicted in Fig. 6. As can be observed, Bead thermal stability is low
and degradation of Bead was discerned at 250 °C. Bead-GA-V thermo-
gram showed that the thermal stability of this sample is higher than
that of Bead. This issue is expectable, as the cross-linked network in
2.4.1. Knoevenagel condensation reaction
Aldehyde (1 mmol) and malononitrile (1.2 mmol) were mixed in
H2O (10 mL). Then, Bead-PIL (10 mg) was added and the mixture was
stirred at 25 °C for 30 min. The reaction progress was monitored by
2