Synthesis and characterization of nano acid catalyst derived from rice husk silica and its application for the synthesis of 3,4-dihydropyrimidinones/thiones compounds

Article abstract of DOI:10.1016/j.molstruc.2018.12.113

In the present work, the extraction of silica nanoparticles from the rice husk followed by the modification using an acidic ionic liquid containing imidazolium butyl sulfonic acid through a sol-gel method (RH@[SiPrImBuSO₃H]Cl) has been investig

Full text of DOI:10.1016/j.molstruc.2018.12.113

Accepted Manuscript
Synthesis and characterization of nano acid catalyst derived from rice husk silica and
its application for the synthesis of 3,4-dihydropyrimidinones/thiones compounds
Jamal Davarpanah, Mohammad Hosein Sayahi, Mahboubeh Ghahremani, Sahar
Karkhoei
PII:
S0022-2860(18)31546-1
DOI:
https://doi.org/10.1016/j.molstruc.2018.12.113
MOLSTR 26050
Reference:
To appear in: Journal of Molecular Structure
Received Date: 31 October 2018
Revised Date: 29 December 2018
Accepted Date: 31 December 2018
Please cite this article as: J. Davarpanah, M.H. Sayahi, M. Ghahremani, S. Karkhoei, Synthesis and
characterization of nano acid catalyst derived from rice husk silica and its application for the synthesis
of 3,4-dihydropyrimidinones/thiones compounds, Journal of Molecular Structure (2019), doi: https://
doi.org/10.1016/j.molstruc.2018.12.113.
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ACCEPTED MANUSCRIPT
Graphical abstract
R
O
O
X
O
O
Cat. (0.1 g)
+
+
R1
R2
H2N
NH2
H
R1
NH
EtOH, Reflux
25-40 min
R2= OEt, Me
R1= Me
X= O, S
R2
N
X
R
H
X-
R= PrImBuSO3H
OH
O
X-= Cl-
O
RH@[SiPrImBuSO3H]Cl :
Si
Si
O
Si
O
Si
O
O
O
Si
O
O
O
Si
O
OH
O
Si
O
Si
HO
Si
O
O
O
O
X-
O
Si
O
X-
Si
O
OH
HO

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Synthesis and characterization of nano acid catalyst derived from rice husk silica and its
application for the synthesis of 3,4-Dihydropyrimidinones/thiones compounds
Jamal Davarpanaha*, Mohammad Hosein Sayahib, Mahboubeh Ghahremanic, Sahar
Karkhoeib
aChemistry Department, Production Technology Research Institute-ACECR, Ahvaz, Iran.
Email: jamaldavarpanah@gmail.com
b Department of Chemistry, Payame Noor University (PNU), Tehran, Iran
cYoung Researchers and Elites club, Science and Research Branch, Islamic Azad University, Tehran, Iran

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Abstract
In the present work, the extraction of silica nanoparticles from the rice husk followed by
the modification using an acidic ionic liquid containing imidazolium butyl sulfonic acid
through a sol-gel method (RH@[SiPrImBuSO3H]Cl) has been investigated. The composition,
morphology and structural properties of the synthesized solid acid were analyzed by fourier
transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron
microscopy (SEM), thermal gravimetric analysis-derivative thermogravimetric (TGA-DTG),
and nitrogen adsorption-desorption. The catalytic activity of the nanocomposite was
examined through the one-pot condensation of aromatic aldehyde, β-diketone, urea or
thiourea under reflux condition. Diverse 3,4-dihydropyrimidinones/thiones derivatives were
produced up to excellent yields in a short period of time. This nanocatalyst could be easily
recovered, and reused without considerable loss of catalytic activity. This method seems to be
a promising method for synthesizing organic chemicals. In addition to the conducted
1
experiments, the H and 13C chemical shift and X-ray spectra values together with the
structural parameters of 3,4-dihydropyrimidinones/thiones were computed and compared to
1
13
the corresponding experimental values. As a result, the calculated H and C chemical shift
and X-ray spectra show a good agreement with the experimental results.
Keywords: Three component reaction; 3,4-dihydropyrimidinones/thiones; Solid acid; Rice
husk ash; Theoretical NMR and X-ray simulation.

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1. Introduction
Ever growing demands of acidic ionic liquid catalysts (AILCs) in a variety of organic
transformations, separation problems, reactor corrosion, waste neutralization, and
incapability to reuse still remains a great challenge [1-3]. Immobilization of the AILC on the
solid supports like silica shows the synergetic effects along with the advantages of
immobilizations such as ability to design, great solubility of the catalytic site, ease of
handling, separation, and recycling. AILCs are dissolved in both water and an organic solvent
making them appropriate catalysts for industrial application [4-6]. Surface functionalized rice
husk silica nanoparticles are unprecedented functional materials that can be used in
biotechnology and catalysis industry [7-9]. The silane agents, especially 3-
chloropropyltriethyloxysilane (CPTES) and 3-aminopropyltriethyloxysilane (APTES), are
mainly used for modifying the surface of silica nanopatricles. The presence of hydroxyl
groups on the surface of silica leads to the reaction with alkoxysilane reagents and formation
of Si-O bonds, which supports the availability of terminal functional groups to immobilize
other substances [10-12]. Ring opening reaction of 1,3 and 1,4-propanesultone, and oxidation
of immobilized thiols to sulfonic acids are the most common approaches for covalently
bonded sulfonic acid sites on the solid supports [13-15].
Since the synthetic procedure should be facile, fast, and efficient [16-18], multicomponent
condensation reactions (MCRs) could be a good candidate for molecular diversity per step
with reduction of the steps for synthesis of bioactive and complex molecules. In addition, 3,4-
dihydropyrimidinones and their derivatives are very well known for their wide range of
biological activities, such as calcium channel blockers, antihypertensive agents, and
neuropeptide Y antagonists [19-21]. Herein, several methods have been reported for the

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promoting preparation 3,4-dihydropyrimidinones /thiones derivatives. Most of the reported
processes offer unique advantages while suffer from low yields production, extended reaction
times, harsh reaction conditions, tedious work up procedures, toxic solvents, and using
expensive or unavailable catalysts. Moreover, the catalysts lose their activities and cannot be
reused [22-24]. In this work, synthesis of 3,4-dihydropyrimidinones/thiones derivatives by
inorganic-organic hybrid containing imidazolium chloride-butyl sulfonic acid supported on
the rice husk silica, RH@[SiPrImBuSO3H]Cl, as a proficient, mild, eco-friendly, recyclable,
and non-toxic solid Brönsted acid catalyst was investigated.
2. Experimental Section
2.1. Chemicals and Equipment
All Chemical were purchased from Fluka and Merck companies and used without further
1
purification. Products were characterized by comparison of their physical data, IR and H
NMR and 13C NMR spectra with known samples.
2.2. Synthesis of RHA@[SiPrImBuSO3H]Cl
Amorphous silica nanoparticles were extracted from rice husk (RH-SiO2)[7]. About 3.0 g
of the nanosilica (obtained from RH) was stirred in 350 mL of the NaOH solution (1.0 M) at
the room temperature. The solution was filtered to remove the undissolved particles, and
about 1.0 mL of CPTMS was added to the resulting sodium silicate. The solution was then
titrated slowly (1.0 mL min-1) with nitric acid (3.0 M) with constant stirring. The acid
solution was added at a slow rate of ca. 1.0 mL min-1 with constant stirring. The silica gels
started to precipitate when the pH decreased to the values less than 11. The titration was
continued until the pH of solution reached 5.0 and aged for 24 h. The filtered silica gel

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washed thoroughly with distilled water and dried at 100 ºC for 18 h (RH-PrCl). RH-PrCl (3.0
g) was added to a flask containing 30 mL of ethanol and an excess of imidazole (6 mmol).
The reaction mixture was refluxed with stirring for 24 h. Then, the reaction mixture was
cooled down to the room temperature, transferred to a vacuum glass filter, and washed with
water and acetone. The rice husk which is chemically bonded to imidazole (RH@SiPrIm) was
dried at 50 oC for 8 h. For target catalyst preparation, 1,4-Butanesultone (6 mmol) was slowly
added into the mixture of RH@SiPrIm (3.0 g) and toluene (100 mL). The mixture was stirred
o
at 100 C for 12 h and toluene was removed by rotary evaporation under reduced pressure.
The formed RH@[SiPrImBuSO3H]Cl then was washed with ether for 3 times and dried in
vacuum at 50 oC for 3 h.
2.3. pH-analysis of RHA@[SiPrImBuSO3H]Cl
To an aqueous solution of NaCl (1 M, 25 mL) with an initial pH 5.9, the
RHA@[SiPrImBuSO3H]Cl (100 mg) was added and the resulting mixture stirred for 24 h
after which the pH of solution decreased to 2.2. This is equal to a loading of 1.58 mmol
SO3H/g of acidic catalyst. Additionally, this result confirmed by back-titration analysis of the
catalyst.
2.4. Typical procedure for the preparation of 3,4-dihydropyrimidin-2(1H)-ones/thiones
A mixture of aromatic aldehyde (1.0 mmol), β-diketone (1.0 mmol), urea or thiourea (2
mmol) and 0.1 g of RHA@[SiPrImBuSO3H]Cl was refluxed in ethanol for the time shown in
Table 3. After complete consumption of aromatic aldehyde as judged by TLC (using n-
hexane-ethylacetate as eluent), the mixture was washed with distilled water to separate the
excess of urea or thiourea. The crude product was dissolved in hot ethanol and the catalyst

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was filtered. The crude product was purified by recrystallization in aqueous ethanol to afford
the pure product.
3. Results and Discussion
3.1. Investigation around the approach of RH@[SiPrImBuSO3H]Cl preparation and its
structural and morphological analysis
Inorganic-organic hybrid which contains imidazolium chloride-butyl sulfonic acid
supported on rice husk silica, RH@[SiPrImBuSO3H]Cl, with high surface area was prepared
by the direct incorporation of chloropropyl groups through co-condensation of RH-SiO2 and
CPTMS (Scheme 1). Thereafter, a simple nucleophilic substitution reaction of imidazole with
propyl chloride groups (RH@SiPrIm) takes place, and the last step exhibits the ring opening
of 1,4-butanesultone with imidazole (Scheme 1). The catalyst has been characterized by
SEM, FT-IR, TGA, XRD and BET methods (Figs 1-5). Additionally, characterization shows
the promising results revealing the advantages of the RH@[SiPrImBuSO3H]Cl as a
heterogeneous catalyst. We have examined the catalytic activity in the preparation of 3,4-
dihydropyrimidinones/thiones derivatives.
Scheme 1 Synthesis of RH@[SiPrImBuSO3H]Cl

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The FT-IR spectra of RH@[SiPrImBuSO3H]Cl and RH-SiO2 are shown in Fig. 1. In two
materials, the typical bands around 990-1220, 801 and 473 cm-1 were attributed to the
presence of Si-O group. The band around 1635 cm-1 is also due to the bending vibration of
water molecules bound to the silica matrix. The presence of peaks at 1200-1500 and 2870-
3040 cm-1 in the RH@[SiPrImBuSO3H]Cl were most probably due to the C-H bonds and also
a band around 1465 cm-1 is characteristic for the tertiary amine group.
120
100
80
60
40
20
0
RH@[SiPrImBuSO3H]Cl
RH-SiO2
3900
3400
2900
2400
1900
1400
900
400
Wavenumber (Cm-1)
Figure 1 FT-IR spectra of RH@[SiPrImBuSO3H]Cl and RH-SiO2
The thermal stability of catalyst was investigated by TGA and DTG. The TGA and DTG
thermograms of RH-SiO2 and RH@[SiPrImBuSO3H]Cl in N2 atmosphere is shown in Fig. 2.
The 0-4% weight loss below 200 oC might be due to the loss of the adsorbed water as well as
dehydration of the surface OH groups. Curve (a) indicates that the nanosilica particles are
thermally stable, and no obvious weight loss was observed, while in curve (b), the mass loss
of RH@[SiPrImBuSO3H]Cl at 300-600 oC is attributed to the organic groups. DTG was also
o
shown in Fig. 2 and no transition was observed up to 300 C for both of them. A sharp
o
endotherm transition in around 300 C might be due to the breakdown and decomposition of

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organic moieties observed for RH@[SiPrImBuSO3H]Cl. Thus, the TGA and DTG curves also
reveal that the nanosilica particles are successfully coated by imidazolium butyl sulfonic acid
groups.
Figure 2 Thermal gravimetric analysis (TGA) of RH@[SiPrImBuSO3H]Cl

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Fig. 3 shows the XRD spectra of RH@[SiPrImBuSO3H]Cl. Lack of any sharp peaks in the
X-ray diffraction pattern indicates the amorphous nature of the samples in which only a broad
diffraction band at 2θ angle of ca. 22 can be observed.
Figure 3 The X-ray diffraction pattern for RH@[SiPrImBuSO3H]Cl
The BET adsorption isotherm obtained for RH@[SiPrImBuSO3H]Cl is shown in Fig. 4.
The hysteresis loop was observed in the range of 0.4 < P /P0 < 1.0, which is associated with
capillary condensation taking place within the mesopores. The isotherms present a sharp
adsorption step in the P/P0, which implied that the materials possess large pore size with
narrow distributions. The BET surface area of RH@[SiPrImBuSO3H]Cl was found to be 134
m2 g-1, while that of RH-SiO2 was reported as 347 m2 g-1 [25]. This was further confirmed by
the pore size distributions calculated by BJH method from the adsorption branches. The
average pore diameter of 10.58 nm (BJH model) was obtained for RH@[SiPrImBuSO3H]Cl.
The characteristic data on the sample are summarized in Table 1.

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Table 1 Specific surface area (SBET), diameter pore and total pore volume of
RH@[SiPrImBuSO3H]Cl
Sample
BET surface area
(m2 g-1)
diameter
(nm)
pore volume
(cm3 g-1)
0.744
RH@[SiPrImBuSO3H]Cl
134
10.58

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Figure 4 (a) Pore size distributions and (b) nitrogen adsorption-desorption isotherm of
RH@[SiPrImBuSO3H]Cl
SEM is a useful tool for determining the size distribution, particle shape and porosity. It
has been a primary tool for characterizing the surface morphology and fundamental physical
properties of the surface [26]. According to Fig. 5, both kinds of RH@[SiPrCl] and
RH@[SiPrImBuSO3H]Cl nanoparticles apparently are similar in size and shape and have
nano dimension ranging from 90 to 170 nm. Particles are rather uniform in morphology.

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Figure 5 SEM images of (a) RH@[SiPrCl](b) RH@[SiPrImBuSO3H]Cl
3.2. Application of RH@[SiPrImBuSO3H]Cl as heterogeneous solid acid catalyst for one-pot
synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones

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To evaluate the catalytic activity of RH@[SiPrImBuSO3H]Cl as heterogeneous solid acid
catalyst in the synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones through multicomponent
condensation reaction (Scheme 2), a model three-component coupling reaction of
benzaldehyde (1 mmol), ethylacetoacetate (1 mmol) and urea (2 mmol) was examined to
determine whether the use of RH@[SiPrImBuSO3H]Cl was efficient and to investigate the
optimized conditions (Table 2).
R
O
O
X
O
O
Cat. (0.1 g)
+
+
R1
R2
H2N
NH2
H
R1
NH
EtOH, Reflux
25-40 min
R2= OEt, Me
R1= Me
X= O, S
R2
N
X
R
H
X-
R= PrImBuSO3H
OH
X-= Cl-
O
RH@[SiPrImBuSO3H]Cl :
Si
Si
O
Si
O
Si
O
O
O
O
O
Si
O
O
O
Si
O
OH
Si
O
Si
HO
X-
Si
O
O
O
O
O
O
Si
O
X-
Si
OH
HO
Scheme 2 Synthesis of 3,4 -dihydropyrimidin-2(1H)-ones/thiones through
multicomponent reaction promoted by RHA@[SiPrImBuSO3H]Cl
Table 2 Reaction of benzaldehyde, ethylacetoacetate, and urea under different
conditions
Yielda (%)
Entry
Solvent
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Water
T(oC) Catayst (g) Time (min)
1
2
3
4
5
6
7
8
9
50
80
80
80
Reflux
0.1
0.1
0.2
-
0.1
0.1
0.1
0.05
0.1
180
180
180
180
180
180
90
62
65
65
15
40
52
80
78
95
Acetonitrile Reflux
Ethanol
Ethanol
Ethanol
50
Reflux
Reflux
60
30

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10
11
Toluene
CH2Cl2
Reflux
Reflux
0.1
0.1
180
180
53
50
Subsequently, with optimal conditions in hand, 1:1:2 molar ratios of aldehyde,
ethylacetoacetate and urea and 0.1 g of RHA@[SiPrImBuSO3H]Cl under reflux condition,
the generality and synthetic scope of this coupling protocol were demonstrated by
synthesizing a series of 3,4-dihydropyrimidin-2(1H)-ones (Table 3).
Table 3 Synthesis of 3,4 -dihydropyrimidin-2(1H)-ones/thiones in presence of
RHA@[SiPrImBuSO3H]Cl
Time
Entry
R
X
R2
Yielda (%)
(min)
30
40
20
25
30
30
40
20
40
40
40
40
40
40
30
30
25
25
30
30
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
H
H
4-N
4-O2N
4-Cl
4-Cl
4-CH3O
4-CN
2-HO
2-HO
4-H3C
4-H3C
4-CH3O
2-HO
H
O
S
O
S
O
S
O
O
O
S
O
S
O
O
O
S
O
S
O
S
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
Me
Me
Me
Me
Me
Me
Me
Me
95
88
95
88
92
87
88
95
85
82
82
81
88
85
95
90
95
90
92
87
H
4-O2N
4-O2N
4-Cl
4-Cl
As it is shown in Table 3, aromatic aldehydes having electron-releasing as well as
electron-withdrawing groups were uniformly transformed into the corresponding 3,4-
dihydropyrimidin-2(1H)-ones in high yields within 20-40 min. Substituents on the aromatic
ring had no obvious effect on yield or reaction time under the above optimal conditions.

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The reusability of the catalyst in the reaction of benzaldehyde, ethylacetoacetate and
urea, under reflux condition was evaluated. In this procedure, after completion of each
reaction, hot ethanol was added to the system and then the catalyst was filtered. The
recovered catalyst was washed with ethanol, dried and reused for four times (Fig.6). The pH
change during reaction process was also considered for fresh and recovered catalyst, and the
pH decrease was not observed after reaction process. Based on titration of the proton-
exchanged brine solutions, fresh and recovered catalysts were shown the loading of 1.58
mmol SO3H/g.
95
93
93
90
90
1
2
3
4
5
No of runs
Figure 6 Recyclability of RHA@[SiPrImBuSO3H]Cl
To evaluate the generality and synthetic scope of this coupling protocol this three
component condensation reaction also proceeded with acetyl acetone and thiourea (Table 3).
In order to show the merit of the presented protocol in DHPMs synthesis, we have compared
the results of RHA@[SiPrImBuSO3H]Cl catalyst with some of those reported in the
literatures. The model reaction of benzaldehyde, ethyl acetoacetate and urea was considered
as a representative example (Table 4).

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Table 4 Comparison of the efficacy of RHA@[SiPrImBuSO3H]Cl catalyst with some of
those reported in the literature
Catalyst loading
(g or wt. %)
0.1 g
Time
(h)
0.5
48
4
10
2
6
Yield
(%)
95
77
94
80
56
91
80
Entry
Catalyst
Ref
1
2
3
4
5
6
7
RHA@[SiPrImBuSO3H]Cl
Montmorillonite KSF
Sulfated zirconia
PS-PEG-SO3H
This work
[27]
15%
15.15%
0.3 g
10 mol%
35%
[28]
[21]
[29]
[19]
ZrOCl2.8H2O
Silica-sulfuric acid
H3PMo12O40
11%
5
[30]
Zeolite [HY(Si/Al = 2.43,
H56(SiO2)136(AlO2)56]
8
15%
12
80
[31]
9
10
Bentonite/PS-SO3H
O4@Silica sulfuric acid
0.1
0.05
g
0.5
0.6
89
92
[32]
[33]
Fe3
4. Theoretical Section
4.1. 1H and 13C NMR Study
1
In this section, the H and 13C NMR chemical shifts of the considered compound is
simulated and compared with the experimental results. For this purpose, the product of the
reaction between 4-chlorobenzaldehyde (1 mmol), acetyl acetone (1 mmol) and urea (2
mmol) (entry19 in Table 3) is chosen to assign each peak to the corresponding atom. The full
geometry optimization of the corresponding product is carried out at B3LYP/6-311++G(d,p)
level of theory [34]. The obtained optimized structure is displayed in Fig. 7. The minimum
nature is examined by frequency analysis at the same computational level. Since the
experimental chemical shifts are achieved in DMSO solvent, the chemical shielding of the
titled compound, and tetramethylsilane (TMS) are calculated through the GIAO formalism
[35], in DMSO solvent using IEFPCM model at B3LYP /6-311++G(d,p) level of theory. All
calculations are accomplished using Gaussian 03 program revision A.02 [36]. The values of

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1
31.882 (1H) and 182.465 (13C) ppm in DMSO solvent are applied to scale the H and 13C
NMR chemical shifts to the TMS. Both experimental and theoretical 1H and 13C NMR spectra
are depicted in Fig. 8 for the studied compounds. The calculated chemical shifts are also
listed in Table 5, which reveals that all of the calculated 1H/13C chemical shifts with respect to
TMS are in the range of 1.63-7.90/22-200.20 ppm; whereas the experimental values are
observed at 2.13-7.40/19.43-194.62 ppm. The result shows a significant correlation (R2 =
1
0.98) between the experimental and calculated H/13C chemical shifts (Fig. 9). Note that the
1
13
estimated slopes for both graphs are close to unity (0.937 and 0.924 for H and C spectra,
respectively) showing the similarity between the experimental and the corresponding
theoretical spectra. It is noteworthy that the hydrogen atoms positions in NH group (24-H and
23-H in Fig. 7) are sensitive and influenced by different experimental conditions [37, 38].

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Figure 7 The optimized geometry of entry 19 in Table 3.
Table 5 The calculated ( Calc. ) and experimental ( Exp.) chemical shift values of 1H NMR
δ
δ
and13C NMR for the entry 19 in Table 3 (all in ppm).
Atom
δ
Calc.
δ
Exp.
Atom
δ
Calc.
δ Exp.
21-H
7.90
7.242-7.409(7.32)
13-C
7-C
200.20 194.62
185.08 152.53
157.16 148.98
150.85 143.64
146.12 132.30
134.30 128.94
133.41 128.77
132.98 128.77
130.82 128.94
118.52 109.96
20-H
31-H
22-H
25-H
29-H
27-H
30-H
28-H
26-H
7.37
7.34
5.67
2.58
2.56
2.49
2.31
2.04
1.63
10-C
16-C
1-C
5.26
2.13
2.50
2.13
2.50
2.50
2.13
4-C
2-C
3-C
17-C
6-C
5-C
57.09
33.06
22.00
53.49
30.91
19.43
15-C
12-C

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Figure 8 The obtained experimental (a) 1H NMR and (b) 13C NMR spectra together with theoretical (c) 1H NMR and (d) 13C
NMR spectra simulated at B3LYP/6-311++G** in DMSO for the entry 19 in Table 3(see Fig. 7).

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Figure 9 The correlations between the experimental and calculated (a) 1H NMR together with (b) 13C NMR chemical shifts
of the entry 19 in Table 3.
4.2. Structural Study
The optimized geometry of the product of the reaction between 4-chlorobenzaldehyde (1
mmol), acetyl acetone (1 mmol) and thiourea (2 mmol) (entry 20 in Table3) at B3LYP/6-
311++G(d,p) level of theory is shown in Fig.10. In order to check the reliability of the
optimized structure, it is attempted to find the correlation between the obtained bond lengths
from this calculation and those which are reported in the X-ray data [39]. The calculated

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values for some selected bond lengths and the corresponding experimental data are listed in
Table 6; and the correlation between these bonds lengths are shown in Fig. 11. The closeness
of the calculated slope to unity (0.955) and the negligible intercept (0.076) verify significant
correlation between the optimized structure and the reported experimental data.
Figure 10 The optimized geometry of entry 20 in Table 3.
Table 6 Some of optimized (B3LYP/6-311++G**) and experimental bond lengths of the
entry 20 in Table 3 (see Fig.10).
Bond
RExp
.
RCalc.
Bond
RExp. RCalc.
1C-2C
1C-3C
3C-4C
4C-16C 1.386 1.400
2C-17C 1.397 1.393
16C-5C 1.525 1.533
5C-9N
5C-6C
9N-10C 1.320 1.344
1.343 1.390
1.370 1.391
1.392 1.392
10C-8N
6C-7C
1.359 1.384
1.353 1.363
1.686 1.671
1.498 1.507
1.469 1.477
1.501 1.519
1.211 1.227
10C-11S
7C-12C
6C-13C
13C-15C
13C-14O
1.461 1.468
1.515 1.530
1C-18CL 1.747 1.760
C16-C17 1.374 1.399

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8N-7C
1.395 1.388
Figure 11 The correlation between the calculated and experimental values of some selected bond
lengths in the backbone of the entry 20 in Table 3.
5. Conclusion
RH@[SiPrImBuSO3H]Cl is successfully achieved by a multiple synthetic procedure which
is confirmed with FT-IR, TGA, SEM and BET. The most interesting features of the present
work include durability as well as remarkable catalytic activity for one-pot synthesis of 3,4-
dihydropyrimidin-2(1H)-ones/thiones via three component coupling reactions under reflux
condition. This method offers several advantages including high yield, short reaction time,
simple workup procedure, ease of separation and recyclability of the catalyst, as well as the
1
ability to tolerate a wide variety of substitutions in the reagents. Moreover, the H and 13C
chemical shift and X-ray spectra values together with the structural parameters of 3,4-
dihydropyrimidinones have been also computed, and the scaled values have been compared
with the corresponding experimental NMR and X-ray spectra. Consequently, the calculated

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1H and 13C chemical shift and X-ray spectra are in good agreement with the experimental
results.
Acknowledgment
We gratefully acknowledge the support of this work by ACECR and Payame Noor
University Research Council.
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Highlights
•
•
•
•
extraction of silica nanoparticles from the rice husk followed by the modification using
an acidic ionic liquid.
Diverse 3,4-dihydropyrimidinones/thiones derivatives were produced up to excellent
yields in a short period of time.
1
The H and 13C chemical shift and X-ray spectra values together with the structural
parameters of 3,4-dihydropyrimidinones have been computed.
1
13
The calculated H and C chemical shift and X-ray spectra are in good agreement with
the experimental results.