Ag–TiO2 nanocomposite as an efficient and recyclable catalyst for the synthesis of imidazole-pyrimidine derivatives in solvent-free conditions

Article abstract of DOI:10.1007/s00706-020-02624-3

Abstract: The one-pot three-component synthesis of 2-amino-4-substituted-1,4-dihydrobenzo[4,5]imidazolo[1,2-a]pyrimidine-3-carbonitrile derivatives by the reaction between various aldehydes with 2-aminobenzimidazole and malononitrile with an excellent out

Full text of DOI:10.1007/s00706-020-02624-3

Monatshefte für Chemie - Chemical Monthly
https://doi.org/10.1007/s00706-020-02624-3
ORIGINAL PAPER
Ag–TiO2 nanocomposite as an efcient and recyclable catalyst
for the synthesis of imidazole‑pyrimidine derivatives in solvent‑free
conditions
Seyed Erfan Mirmoeeni1 · Mozhdeh Liyaghati‑Delshad1 · Azize Abdolmaleki1
Received: 22 July 2019 / Accepted: 25 May 2020
© Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract
The one-pot three-component synthesis of 2-amino-4-substituted-1,4-dihydrobenzo[4,5]imidazolo[1,2-a]pyrimidine-3-car-
bonitrile derivatives by the reaction between various aldehydes with 2-aminobenzimidazole and malononitrile with an excel-
lent output and in low-response period was studied in the presence of Ag–TiO2 nanocomposite as an efcient and recyclable
catalyst under solvent-free conditions at 60 °C. The results indicated that the isolation of the desired products could be
attained via simple fltration, and the Ag–TiO2 nanocomposite could be reusable and reused continuously.
Graphic abstract
Keywords Ag–TiO2 nanocomposite · 2-Amino-4-substituted-1,4-dihydrobenzo[4,5]imidazolo[1,2-a]pyrimidine-3-
carbonitrile · Solvent-free conditions
Introduction
semiconductor or metal produces the core materials which
appear more stable at extreme conditions. Ag reinforced
with titania is of applied signifcance, since Ag–TiO2 nano-
composites are favorable photocatalysts not only for disin-
fecting, self-cleaning, and water splitting but also for water
and air purifcation. Meanwhile, the other noble metals, such
as Au, Rh, Pt, and Pd, are very expensive, and Ag nanopar-
ticles may serve as a much more cost-efcient solutions.
Furthermore, Ag nanoparticles dispersed on metal-oxide
supports are of interest, because they can serve as true cat-
alysts for the oxidative dehydrogenation of formaldehyde
from methanol [3] and are afective epoxidation catalysts
[4–7]. As for the Ag–TiO2 nanocomposite, due to its interac-
tion between the dielectric matrix and metal nanoparticle,
Metal–semiconductor nanocomposites, in comparison
to pure semiconductors, show better luminescent [1], gas
sensing, nonlinear optical [2], and catalytic properties.
The coating of the metal or semiconductor with a suitable
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s00706-020-02624-3) contains
supplementary material, which is available to authorized users.
* Mozhdeh Liyaghati-Delshad
mo.liyaghatidelshad@gmail.com
1
Department of Chemistry, Tuyserkan Branch, Islamic Azad
University, Tuyserkan, Iran
Vol.:(0123456789)
1 3

S. Mirmoeeni et al.
the quantum size efect, or surface efect, it has a unique
photoelectric transforming, electric, and optical properties.
Stimulated with a femtosecond laser pulse, the Ag–TiO2
nanocomposite shows large nonlinear optical properties
resulting from its temporary rapid and slow optical reply
to time [8–11].
on rice husk ash (RHA-[pmim]HSO4) [26], [PVPH]ClO4
[27], S-Chit-HAp@Fe3O4 [28], and the using of microwave
[29–31] have been employed to catalyze the synthesis of
imidazole-pyrimidines.
Herein, we report application of the Ag–TiO2 nanocom-
posite for the synthesis of 2-amino-4-substituted-1,4-dihy-
drobenzo[4,5]imidazolo[1,2-a]pyrimidine-3-carbonitrile
derivatives (ADIPs) in solvent-free conditions at 60 °C
(Scheme 1).
The one-pot multi-component reactions (MCRs) for the
synthesis of biologically active scafolds has attracted much
attention in the recent years [12]. Designing eco-friendly and
simple mild reactions for the synthesis of medicinal struc-
tures is among attractive aspects of chemical studies. Multi-
component reaction (MCR), which is mainly carried out
under environmentally friendly circumstances, is one of the
most suitable routes which can help chemists to adapt their
reaction processes to the requirements of “green chemistry”
as well as to develop libraries of medicinal scafolds [13].
MCRs have appeared as infuential and efcient media in
current synthetic biological chemistry agreeing with the sim-
plistic formation of many new bonds in a one-pot reaction.
Consequently, in recent years, investigations in academia
and industry have gradually corroborated the use of MCRs
in addition to domino reaction sequences for a wide range
of products [14]. Therefore, approaches can be used for
diversity-oriented synthesis and drug design of heterocycles
owing to their simplicity, high choosiness, and efcacy [15,
16]. One such MCR is the synthesis of imidazole-pyrimidine
derivatives. Nitrogen-including heterocycles are diverse in
nature, and they are of crucial importance because of their
uses in agrochemicals, biologically active pharmaceuticals,
and medicinal chemistry [17, 18].
Results and discussion
Several synthetic processes for ADIPs preparation have been
reported, among which we describe a rapid preparation of
a series of ADIPs with good-to-excellent overall yields
(88–98%) based on the use of 2 mg of Ag–TiO2 nanocom-
posite by an improved procedure using commercially avail-
able numerous aldehydes, 2-aminobenzimidazole, and malo-
nonitrile under solvent-free conditions at 60 °C (Scheme 1).
Figure 1 displays the two- and three-dimensional AFM
images of Ag–TiO2 nanocomposite as a catalyst. No con-
siderable partition area in size is observed in the illustra-
tions. Through the three-dimensional 2.1 µm2 × 2.1 µm2
frameworks, we were able to identify that the attained
Ag–TiO2 nanocomposite confrms a broken-up structure
with desirable exterior planarity. The surface of the coat on
the Ag–TiO2 nanocomposite was clearly exposed to be less
than 25 nm [25, 32, 33].
To determine the optimized amount of Ag–TiO2 nano-
composite, the reaction of 4-chlorobenzaldehyde (3d,
1 mmol) with 2-aminobenzimidazole (1, 1 mmol) and
malononitrile (2, 1 mmol) was chosen as a model and dif-
ferent amounts of Ag–TiO2 in a range of 25–90 °C were
tested in solvent-free conditions (Table 1). As presented
in Table 1, the best results were attained when the reac-
tion was done using 2 mg of Ag–TiO2 at 60 °C (Table 1,
entry 6). No improvement was observed in the yield of
Due to their therapeutic and pharmacological proper-
ties, the synthesis of imidazole-pyrimidine derivatives such
as TIE-2 and VEGFR2 inhibitory activities [19], T cell
activation [20], protein kinase inhibitor [21], and antineo-
plastic [22] has attracted the attention of organic chemists.
Numerous reagents such as sulfamic acid [23], p-toluene-
sulfonic acid [24], tetramethylguanidinium trifluoroac-
etate (TMGT) [25], Brönsted acidic ionic liquid supported
Scheme 1
1 3

Ag–TiO2 nanocomposite as an efcient and recyclable catalyst for the synthesis of…
Fig. 1 Two-dimensional (a and b), topography (c), and three-dimensional (d) of AFM images of the Ag–TiO2 nanocomposite
the reaction by increasing the amount of the Ag–TiO2 and
temperature. Table 1 clearly displays that in the absence
of a catalyst, derivatives with low yields are produced
(Table 1, entries 1 and 2). Data of optimized conditions
with bold symbols are shown inside the tables.
Table 1 Efect of the amount of the catalyst and temperature on the
synthesis of ADIPs in solvent-free conditions
Entry
Amount of
catalyst/mg
Temperature/°C
Response
time/min
Yield/%
To examine the efcacy and the scope of the catalyst,
2 mg of Ag–TiO2 was used in polar and non-polar solvents
such as H2O, C2H5OH, CH3CN, CH3CO2Et, CH2Cl2, and
toluene at 60 °C. The results are summarized in Table 2.
As shown in Table 2, solvent-free condition is obviously
the most suitable choice for these reactions. An additional
reason for selecting solvent-free conditions for this reac-
tion would be safe, kind, cheap, and “green” reaction con-
dition in comparison with organic solvents.
1
2
3
4
5
6
7
8
9
10
11
12
–
–
1
1
2
2
2
4
4
4
10
10
r.t.
90
r.t.
90
r.t.
60
90
r.t.
60
90
r.t.
60
60
60
10
10
10
8
10
15
65
70
70
98
98
70
98
98
98
98
8
8
8
8
8
As a next step, we compared the performance of
Ag–TiO2 nanocomposite with the ones reported in the
previous articles, listed in Table 3, showing that the
utilization of Ag–TiO2 would improve reaction time,
8
1 3

S. Mirmoeeni et al.
Table 2 The efect of numerous solvents on the synthesis of ADIPs
The recyclability, reusability, and efficiency of the
Ag–TiO2 nanocomposite were also investigated. To do this
at the end of the reaction, 15 cm3 hot ethyl acetate was added
to the reaction mixture and it was centrifuged to separate
Ag–TiO2 nanocomposite. Then, the reused catalytic agent
was employed for the other reaction. The results showed that
Ag–TiO2 nanocomposite could be reused six times without
a signifcant loss of catalytic activity (Fig. 2).
at 60 °C
Entry
Solvent
Response time/
min
Yield/%
1
2
3
4
5
6
7
H2O
10
8
10
15
15
45
60
94
98
94
80
80
30
15
Solvent-free
C2H5OH
CH3CN
CH3CO2Et
CH2Cl2
A plausible mechanism for the synthesis of the ADIPs 4
is well defned in Scheme 2. As it can be seen, frst, Ag–TiO2
nanocomposite activates the carbonyl group of the aromatic
aldehyde 3 to provide intermediate 5, and malononitrile
(2) is tautomerized to 6. The Knoevenagel condensation of
intermediate 5 and 6 happens to form the arylidene malo-
nonitrile 7. Consequently, 2-aminobenzimidazole (1) tol-
erates a nucleophilic attack to 7 and afords the Michael
adduct 8. The Michael adduct 8 cyclizes to provide the fully
aromatized 2-amino-4-substituted-1,4-dihydrobenzo[4,5]-
imidazolo[1,2-a]pyrimidine-3-carbonitrile 4.
Toluene
temperature, efciency, and amount of catalyst needed for
the synthesis of ADIPs.
Stimulated by such fndings as described above, a variety
of ADIPs were produced from the one-pot three-component
reaction. The results are summarized in Table 4. As indi-
cated in the table, the reaction times of aromatic aldehydes
possessing electron-withdrawing groups were somewhat
shorter than those in electron-donating groups. Though
meta- and para-substituted aromatic aldehydes produced
superb results, perhaps because of the steric efects ortho-
substituted aromatic aldehydes produced relatively lower
yields.
Conclusion
In conclusion, we have defned a practical and straight-
forward procedure for the synthesis of the one-pot three-
component synthesis of ADIPs in the presence of catalytic
Table 3 Comparing the
Entry
Catalyst
Catalyst loading
Temperature/°C
Time/min
Yield/% [Lit]
efciency of Ag–TiO2
nanocomposite with other
catalysts used in previous
articles for synthesis of ADIPs
1
2
3
4
5
6
Ag–TiO2
2 mg
Solvent free/60 °C
H2O/refux
Solvent free/100 °C
Solvent free/100 °C
H2O/100 °C
8
10
15
3
540
30
98
S-Chit-HAp@Fe3O4
[PVPH]ClO4
RHA-[pmim]HSO4
–
10 mol%
30 mg
10 mg
–
88 [31]
96 [30]
93 [29]
70 [34]
93 [35]
p-TSA
10 mol%
Solvent free/80 °C
Table 4 Synthesis of ADIPs
Entry
Comp.
R
Response
time/min
Yield/%
M.p./C
Lit. m.p./°C
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4e
4f
4g
4h
4i
4-OHC-C6H4–
4-Br-C6H4–
3-Cl-C6H4–
4-Cl-C6H4–
2,4-Cl2-C6H3–
3-HO-C6H4–
2-Me-C6H4–
2,6-Cl2-C6H3–
4-F-C6H4–
12
10
12
8
10
10
14
8
90
98
96
98
92
95
90
93
97
95
98
96
235–236
242–243
221–222
232–233
236–237
219–220
230–231
249–250
267–268
238–239
225–226
226–227
–
242–244 [26]
–
234–236 [35]
–
–
233–235 [35]
248 [34]
266–268 [35]
236–238 [35]
–
9
8
10
8
10
11
12
4j
4k
4l
2-Cl-C6H4–
4-O2N-C6H4–
3-O2N-C6H4–
8
226–228 [35]
1 3

Ag–TiO2 nanocomposite as an efcient and recyclable catalyst for the synthesis of…
could be attained via a simple centrifuge and the Ag–TiO2
nanocomposite could be reused continually.
Experimental
All of the chemical materials applied in this study were
bought from Merck and Fluka and used without additional
purifcation. Melting points were determined with an elec-
trothermal 9100 apparatus and remained uncorrected. FT-IR
1
spectra were attained on a Perkin-Elmer spectrometer. H
NMR and 13C NMR spectra were recorded on a Bruker
DRX-400 AVANCE at 400 and 100 MHz, respectively,
using TMS as an internal standard and DMSO-d6 as a sol-
vent. Mass spectra data were obtained using an MS Model
5975C VL MSD with Tripe-Axis Detector.
Fig. 2 Recycling of the Ag–TiO2 nanocomposite synthesis of ADIPs
after 10 min
amount of Ag–TiO2 nanocomposite as a recyclable and
reusable catalytic agent from the reaction between various
aldehydes, 2-aminobenzimidazole, and malononitrile with
excellent output and in a low-response period in solvent-free
conditions at 60 °C. The vital advantage of this procedure is
the ease of the work-up, and a possibility to separate with-
out chromatography. While the reaction was being accom-
plished in the heterogeneous model, isolation of the desired
products, as well as Ag–TiO2 nanocomposite as a catalyst,
Procedure for the synthesis of Ag–TiO2
nanocomposite
Ag–TiO2 nanocomposite was produced by the sol–gel
method according to prior works [25, 32, 33]. TiCl4 was
used as the initial material to synthesize unadulterated TiO2.
AgNO3 was used as an Ag source. The immobilization of Ag
molecules by tethering them to the TiO2 surface has been
established by the previous investigation [25, 32, 33].
Scheme 2
1 3

S. Mirmoeeni et al.
141.7, 143.5, 149.2, 151.5 ppm; MS (70 eV): m/z=356.21,
General procedure for the preparation
of imidazole‑pyrimidine derivatives 4a–4l
found 355 (M+).
2‑Amino‑4‑(3‑hydroxyphenyl)‑1,4‑dihydrobenzo[4,5]‑
i m i d a z o [ 1 , 2 ‑ a] p y r i m i d i n e ‑ 3 ‑ c a r b o n i t r i l e ( 4 f ,
C17H13N5O) White powder; m.p.: 219–220 °C; yield: 95%;
IR (KBr): v̄ = 3472, 3376, 2884, 2187, 1666, 1632, 1597,
To 0.134 g 2-aminobenzimidazole (1, 1 mmol), 0.066 g
malononitrile (2, 1 mmol) and the corresponding aldehyde
(3, 1 mmol) were added. The mixture was heated in the pres-
ence of 2 mg of the Ag–TiO2 nanocomposite under solvent-
free condition. After completion of the reaction [proper time
given in Table 4, TLC (n-hexane/ethyl acetate: 8/2) monitor-
ing] for the recycling of Ag–TiO2 nanocomposite, 15 cm3
hot ethyl acetate was added to the reaction vessel and then
centrifuged to get the catalyst separated from the product.
The organic solvent layer was removed and recrystallization
was performed with an ethanol solvent.
1
1472 cm−1; H NMR (400 MHz, DMSO-d6): δ = 5.10 (s,
1H, –CH aliphatic), 6.68 (t, 3H, J=8 Hz, ArH), 6.82 (brs,
2H, –NH2), 7.00 (t, 1H, J=8 Hz, ArH), 7.10–7.15 (m, 2H,
J = 8 Hz, ArH), 7.22 (d, 1H, J = 8 Hz, ArH), 7.38 (d, 1H,
J=8 Hz, ArH), 7.61 (d, 1H, J=8 Hz, ArH), 8.57 (brs, 1H,
–NH), 9.50 (brs, 1H, –OH) ppm; 13C NMR (100 MHz,
DMSO-d6): δ=53.1, 61.9, 112.3, 112.4, 114.7, 116, 116.3,
119.2, 119.7, 123.2, 129.2, 129.6, 143.6, 144.5, 148.94,
148.99, 151.7, 157.5 ppm; MS (70 eV): m/z=303.33, found
303 (M+).
4,4′‑(1,4‑Phenylene)bis(2‑amino‑1,4‑dihydrobenzo[4,5]‑
i m i d a zo [ 1 , 2 ‑ a] py r i m i d i n e ‑ 3 ‑ c a r b o n i t r i l e ) ( 4 a ,
C28H20N10) White powder; m.p.: 235–236 °C; yield: 90%; IR
(KBr): v̄ =3321, 3060, 2878, 2190, 1682, 1634, 1470 cm−1;
1H NMR (400 MHz, DMSO-d6): δ=5.22 (s, 2H, –CH ali-
phatic), 6.86 (s, 4H, –NH2), 7.02 (t, 2H, J = 8 Hz, ArH),
7.12 (t, 2H, J = 6 Hz, ArH), 7.22 (d, 2H, J = 8 Hz, ArH),
7.24–7.29 (m, 2H, J = 8 Hz, ArH), 7.34 (t, 2H, J = 6 Hz,
ArH), 7.62 (d, 2H, J = 8 Hz, ArH), 8.64 (brs, 2H, –NH)
ppm; 13C NMR (100 MHz, DMSO-d6): δ=53.1, 61.8, 112.4,
116, 119.8, 123.2, 125.8, 127.8, 128.6, 142.9, 143.5, 149.1,
151.7 ppm; MS (70 eV): m/z=496.54, found 496 (M+).
2‑Amino‑4‑(4‑nitrophenyl)‑1,4‑dihydrobenzo[4,5]‑
i m i d a z o [ 1 , 2 ‑ a] p y r i m i d i n e ‑ 3 ‑ c a r b o n i t r i l e ( 4 k ,
C17H12N6O2) White powder; m.p.: 225–226 °C; yield:
98%; IR (KBr): v̄ = 3326, 3220, 2189, 1679, 1639, 1600,
1519 cm−1; 1H NMR (400 MHz, DMSO-d6): δ=5.52 (s, 1H,
–CH aliphatic), 6.99 (s, 2H, –NH2), 7.02 (t, 1H, J =8 Hz,
ArH), 7.13 (t, 1H, J = 8 Hz, ArH), 7.25 (d, 1H, J = 8 Hz,
ArH), 7.55 (d, 2H, J = 8 Hz, ArH), 7.62 (d, 1H, J = 8 Hz,
ArH), 8.24 (d, 2H, J = 8 Hz, ArH), 8.78 (brs, 1H, –NH)
ppm; 13C NMR (100 MHz, DMSO-d6): δ = 52.4, 60.5,
112.5, 116.2, 115.5, 118.9, 120, 123.4, 124, 127.2, 129.2,
130.1, 143.4, 147, 149.4, 150.1, 151.4 ppm; MS (70 eV):
m/z=332.32, found 332 (M+).
2‑Amino‑4‑(3‑chlorophenyl)‑1,4‑dihydrobenzo[4,5]‑
i m i d a z o [ 1 , 2 ‑ a] p y r i m i d i n e ‑ 3 ‑ c a r b o n i t r i l e ( 4 c ,
C17H12ClN5) White powder; m.p.: 221–222 °C; yield: 96%;
IR (KBr): v̄ = 3449, 3318, 3058, 2927, 2195, 1603, 1575,
1
1472 cm−1; H NMR (400 MHz, DMSO-d6): δ = 5.29 (s,
Acknowledgements This study was fnancially supported by Islamic
1H, –CH aliphatic), 6.91 (s, 2H, –NH2), 7.01–7.03 (td, 1H,
J=6 Hz, ArH), 7.11–7.14 (td, 1H, J=6 Hz, ArH), 7.25 (t,
2H, J=6 Hz, ArH), 7.35–7.40 (m, 2H, J=8 Hz, ArH), 7.54
(t, 1H, J=8 Hz, ArH), 7.63 (d, 1H, J=8 Hz, ArH), 8.70 (brs,
1H, –NH) ppm; 13C NMR (100 MHz, DMSO-d6): δ=52.5,
61.08, 112.4, 116.1, 119.0, 119.9, 123.4, 124.6, 125.9,
127.8, 129.2, 130.7, 133.1, 143.4, 145.3, 149.3, 151.4 ppm;
MS (70 eV): m/z=321.77, found 321 (M+).
Azad University, Tuyserkan Branch, Iran.
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