ompg-C3N4/SO3H: an efficient and recyclable organocatalyst for the facile synthesis of 2,3-dihydroquinazolin-4(1H)-ones

Article abstract of DOI:10.1007/s11164-019-03873-6

In the present work, sulfonated highly ordered mesoporous graphitic carbon nitride (ompg-C₃N₄/SO₃H) was synthesized successfully and employed as an efficient and reusable heterogeneous solid acid catalyst for the rapid and one-pot synthesis of 2,3-dihydroquinazolin-4(1H)-ones via the condensation of anthranilamide with aldehydes or ketones in good to excellent yields. The organocatalyst was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectrometer, Brunauer–Emmett–Teller surface area, and thermal gravimetric and differential thermal analysis. The substantial advantages of this procedure involve short reaction times, high catalytic activity, easy workup, high purity of the products, and easy recovery and reusability of the catalyst.

Full text of DOI:10.1007/s11164-019-03873-6

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-03873-6
ompg‑C N /SO H: an efcient and recyclable
3
4
3
organocatalyst ꢀor the ꢀacile synthesis
oꢀ 2,3‑dihydroquinazolin‑4(1H)‑ones
1
1
1
Hossein Ghafuri · Nahal Goodarzi · Afsaneh Rashidizadeh ·
Mohammad Ali Douzandegi Fard1
Received: 8 February 2019 / Accepted: 3 June 2019
©
Springer Nature B.V. 2019
Abstract
In the present work, sulfonated highly ordered mesoporous graphitic carbon nitride
(
ompg-C N /SO H) was synthesized successfully and employed as an eꢀcient
3 4 3
and reusable heterogeneous solid acid catalyst for the rapid and one-pot synthesis
of 2,3-dihydroquinazolin-4(1H)-ones via the condensation of anthranilamide with
aldehydes or ketones in good to excellent yields. The organocatalyst was charac-
terized by Fourier transform infrared spectroscopy, X-ray diꢁraction, ꢂeld emission
scanning electron microscopy, energy-dispersive X-ray spectrometer, Brunauer–
Emmett–Teller surface area, and thermal gravimetric and diꢁerential thermal analy-
sis. The substantial advantages of this procedure involve short reaction times, high
catalytic activity, easy workup, high purity of the products, and easy recovery and
reusability of the catalyst.
Keywords Sulfonated highly ordered mesoporous graphitic carbon nitride (ompg-
C N /SO H) · 2,3-dihydroquinazolin-4(1H)-ones · Organocatalyst · Green procedure
3
4
3
Introduction
Nowadays, solid acid catalysts are receiving considerable attention in organic synthe-
sis and transformation because of their various beneꢂts including: chemical stability,
high activity, non-toxicity, non-corrosiveness, high selectivity, easy separation and
reusability without losing activity, simplicity of operation and carrying out reactions
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4
-019-03873-6) contains supplementary material, which is available to authorized users.
*
Hossein Ghafuri
ghafuri@iust.ac.ir
1
Catalysts and Organic Synthesis Research Laboratory, Department of Chemistry, Iran University
of Science and Technology, Tehran 16846-13114, Iran
Vol.:(012
1
3456789)
3

H. Ghafuri et al.
in an economic and green route [1]. There are several factors that inꢃuence the prop-
erties and performance of the solid acid catalysts such as: type of acidity (Bronsted
or Lewis), strength of the acidic sites, availability of these sites, and morphology of
the support in terms of surface area, porosity and stability (thermal and chemical).
Hence, applying a suitable support can improve the function of these catalysts [2].
Among the organic polymeric compounds, graphite carbon nitride (g-C N ) has
3
4
attracted tremendous attention in various ꢂelds as photocatalysis, solar cells, sens-
ing, solar fuel production, and catalysis due to its special structure and fascinating
electronic properties [3–7]. g-C N with an environmentally friendly nature and
3
4
extreme thermal and chemical stability can be easily synthesized at a low price with
abundant nitrogen-rich carbon materials such as cyanamide, dicyanamide, mela-
mine, urea, and thiourea through thermal condensation [8]. Metal-free g-C N as
3
4
a π-conjugated polymer with an electron-rich surface is a promising support mate-
rial due to the incorporation of nitrogen atoms into a carbon architecture. The pres-
ence of amino functional groups with abundant basic sites in the g-C N leads to
3
4
loading high amounts of active chemical sites on the g-C N . Basically, strong Van
3
4
der Waals interactions between the layers in the two-dimensional g-C N framework
3
4
convert this material to the most chemically stable allotrope against various organic
solvents, and several acids and bases. Also, the existence of aromatic C–N hetero-
cycles, leads to thermal stability up to 600 °C. Given the mentioned advantages and
with the aim to broaden the potential of g-C N with reasonable physical and chemi-
3
4
cal properties, non-toxicity, high speciꢂc surface area, easy recyclability, abundant
anchor sites for active species and environmentally friendly nature, g-C N is appro-
3
4
priate for the design of high-performance catalysts or catalyst support. [9].
Creation of porosity in the structure of g-C N and producing a hexagonally
3
4
ordered mesoporous structure improves its properties and applications as a catalyst
support. As compared to bulk g-C N , ordered mesoporous g-C N (ompg-C N )
3
4
3
4
3
4
exhibits more excellent properties such as high speciꢂc surface area, more surface
active sites, large pore volume, and strong adsorption capacity [10, 11].
Recently, the template-directed synthesis methods, including the use of mesoporous
silica materials (SBA-15, KIT-6, and FDU-12) have been widely applied to prepare
mesoporous g-C N which can control the morphology and the pore structure of the tar-
3
4
get mesoporous g-C N [11]. SBA-15 is a common material for hard templating proto-
3
4
cols due to its advantages such as simple preparation using inexpensive precursor (tetra-
ethyl orthosilicate), high thermal and hydrothermal stability, and tunable pore size [12].
In the course of our investigations on developing novel heterogeneous catalysts for
the synthesis of organic compounds [13–16], we have recently reported the preparation
of sulfonated highly ordered mesoporous graphitic carbon nitride (ompg-C N /SO H)
3
4
3
and its application as a super-active solid acid catalyst for Biginelli reaction [17].
2
,3-Dihydroquinazolin-4(1H)-one derivatives are a signiꢂcant class of bicy-
clic heterocycles and useful intermediates in organic synthesis with a broad range
of medical, biological and pharmaceutical activities such as antioxidant, anticancer
[
18], antibacterial [19], anti-inꢃammatory [20], and antibiotic [21] activity. Conven-
tionally, 2,3-dihydroquinazolin-4(1H)-ones are synthesized using the condensation
reaction of 2-aminobenzamide with aldehydes or ketones in the presence of vari-
ous catalysts. In view of the importance of the 2,3-dihydroquinazolin-4(1H)-ones, a
1
3

ompg‑C N /SO H: an efcient and recyclable…
3
4
3
number of catalysts have been reported for the preparation of 2,3-dihydroquinazolin-
(1H)-one derivatives in literature, which include tetrabutylammonium bromide [22],
succinimide-N-sulfonic acid [23], [Emim] HSO [24], Sc(OTF) [25], and l-proline
4
4
3
nitrate [26]. However, some of the mentioned procedures suꢁer from one or several
limitations such as longer reaction times, harsh reaction conditions, low product
yields, the use of volatile organic solvents, and hard work-up procedure. Therefore,
the development of environmentally friendly synthetic methodologies using novel
heterogeneous catalysts for the synthesis of these compounds is still in great demand.
Herein we investigated the eꢀciency of ompg-C N /SO H as a green and recov-
3
4
3
erable heterogeneous catalyst for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones
in excellent yields (Scheme 1). The novel solid acid (ompg-C N /SO H) is expected
3
4
3
to have a broader potential in chemical processes as a heterogeneous catalyst due to
high activity, strong acidity strength, thermal stability, and reusability.
Experimental
Chemicals and instruments
All utilized chemicals and solvents such as P123, TEOS, ammonium hydrogen
diꢃuoride, cyanamide, chlorosulfonic acid, aldehydes and ketones, 2-aminobenza-
mide, solvents and other materials were purchased from Merck and Flucka chemical
companies and used without any puriꢂcation. The reaction progress was followed
by thin-layer chromatography (TLC) using aluminum plates coated with silica gel
F254. Melting points were measured using an Electrothermal 9100. The FT-IR spec-
tra were measured with a Shimadzu 800 IR 100 FT-IR spectrometer using a KBr
pellet. The morphology of the catalyst was discerned via ꢂeld-emission scanning
electron microscopy (FESEM) using a MRIA3 TESCAN-XMU model and trans-
mission electron microscopy (TEM) on a Zeiss-EM10C-100 kV. The powder X-ray
diꢁraction (XRD) patterns of the samples were obtained on a PANalytical X-PERT-
PRO MPD diꢁractometer equipped with a Cu Kα radiation source (λ=1.5406 Å)
in the 2θ=0.5° to 10° and 2θ=10° to 80° with a 2θ step size of 0.02°. Energy-
dispersive X-ray (EDX) spectra were determined using a Numerix DXP-X10P. The
C, H, N, and S elemental analyses were recorded using a Thermo Finnigan Flash EA
1
112 element analyzer. Thermogravimetric analysis (TGA) and diꢁerential thermal
analysis (DTG) were conducted under air using a STA504 analyzer with a 10 °C/
min ramp in the range of 20–800 °C. Nitrogen adsorption and desorption measure-
ments were carried out using Micromeritics ASAP 2020 device with nitrogen as the
O
CHO
O
O
O
NH
2
3 4 3
ompg-C N /SO H
NH
NH
or
or
NH
2
EtOH, reflux
N
H
N
H
R
1
2
R
3
(a-o)
Scheme 1 Synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives catalyzed by ompg-C N /SO H
3
4
3
1
3

H. Ghafuri et al.
analysis gas at −196 °C. BET analysis was conducted to investigate the speciꢂc sur-
face areas and the pore size distributions were obtained on the adsorption branches
of the isotherms using a Brunauer–Joyner–Halenda (BJH) model. The nuclear mag-
netic resonance (NMR) spectra, in order to identify products, were obtained on a
1
Bruker DRX-500 Avance spectrometer (500 MHz for H NMR) using DMSO-d as
6
a solvent and tetramethylsilane (TMS) as an internal standard.
Synthesis of the mesoporous silica (SBA‑15)
Synthesis of SBA-15 (as a hard template for the preparation of ompg-C N /SO H) was
3
4
3
carried out according to the procedure reported previously in the literature [27]. Ini-
tially, 3.5 g of Pluronic P123 was dissolved in 120.0 mL of 1.6 M HCl and stirred for
2
4 h at 38 °C. Afterward, 7.5 g of tetraethylorthosilicate (TEOS) was added dropwise
into the above mixture during stirring. After 24 h, the resulting milky liquid was trans-
ferred into the Teꢃon-lined autoclave and heated at 150 °C for 24 h. The obtained white
precipitate was ꢂltered and frequently washed with de-ionized water then dried at ambi-
−1
ent temperature and calcined at 550 °C with a heating rate of 2.3 °C min for 5 h.
Preparation of the ordered mesoporous graphite carbon nitride (ompg‑C N )
3
4
At the ꢂrst step, 1.0 g of SBA-15 (as a hard template) and 3.5 g of cyanamide were
added to 8.0 mL of de-ionized water and sonicated for 2 h. The mixture was then
stirred at ambient temperature for 6 h. The obtained white precipitate was ꢂltrated
and dried at 60 °C. Then it was calcined at 550 °C in a furnace under nitrogen
atmosphere for 5 h. Next, in order to remove the silica template, the obtained yellow
precipitate was added to 40.0 mL of NH ·HF (4.0 M) aqueous solution while stir-
4
2
ring at ambient temperature for 24 h. Eventually, the solid product was ꢂltered and
washed with de-ionized water and ethanol for several times, and dried at 60 °C.
Synthesis of mesoporous graphite carbon nitride nanocomposite functionalized
by sulfonic acid (ompg‑C N /SO H)
3
4
3
1
.0 g of ompg-C N was dispersed in 5.0 mL of dry CH Cl . After that, in order to
3 4 2 2
conduct HCl gas over the solution, the mixture was transferred into a suction ꢃask
that was equipped with a gas inlet tube. Afterward, ClSO H (2.0 mL) was added
3
dropwise into the mixture vessel for 30 min and then the mixture was stirred for 2 h.
Finally, the solvent was evaporated under reduced pressure, and the obtained product
was washed with de-ionized water and methanol for several times and dried at 60 °C.
General procedure for the preparation of 2,3‑dihydroquinazolin‑4(1H)‑ones
A mixture of 2-aminobenzamide (1.0 mmol), aldehyde (or ketone) (1.0 mmol), and
ompg-C N /SO H (20.0 mg) in 96% EtOH (3.0 mL) was stirred under reꢃux condi-
3
4
3
tion for an appropriate time (Table 3). Progression of the reaction was followed by
TLC (hexane/EtOAc 2:1). After completion of the reaction, the catalyst was separated
1
3

ompg‑C N /SO H: an efcient and recyclable…
3
4
3
by ꢂltration and washed with ethanol for reuse in subsequent reactions. After evapo-
ration of the solvent, the residue was puriꢂed by recrystallization from ethanol.
Back‑titration in aqueous solution of catalyst (ompg‑C N /SO H)
3
4
3
Back-titration procedure as a well-known method for determining the concentra-
+
tion of [H ] ion released by the ompg-C N /SO H was used. A mixture of 0.5 g
3
4
3
ompg-C N /SO H, 0.5 g NaCl, 10.0 mL of 0.1 M NaOH aqueous solution, and
3
4
3
3
5.0 mL of distilled water was added into an Erlenmeyer ꢃask and stirred at room
temperature for 24 h. Afterward, three drops of phenolphthalein, as an indicator,
were added to the above solution then titrated with 0.1 M HCl aqueous solution
until the color of the solution turns from pink to colorless. The pH value of the
ompg-C N /SO H was calculated (pH = 1.55).
3
4
3
Selected spectral data
,3‑dihydro‑2‑phenylquinazolin‑4(1H)‑one (3a)
2
−1
White solid; mp 229–232 °C; FTIR (KBr, cm ): 3299, 3184, 1506, 3062, 1658, 1612,
1
1
440, 1386, 746; HNMR (500 MHz, DMSO-d ) δ 8.30 (s,1H, –NH), 7.20–7.63 (m,
6
7
H, Ar–H), 7.15 (s, 1H, CH), 6.65–6.77 (m, 2H, Ar–H), 5.75 (s, 1H, –NH).
2,3‑dihydro‑2‑(2‑chlorophenyl)quinazolin‑4(1H)‑one (3h)
−
1
White solid; mp 207–209 °C; FTIR (KBr, cm ): 3363, 3197, 3060, 2912, 1650,
1
1
–
1
608, 1496, 1475, 1458, 1035, 746; HNMR (500 MHz, DMSO-d ) δ 8.19 (s,1H,
6
NH), 7.65–7.64 (d, 2H, Ar–H, J = 6.4 Hz), 7.23–7.50 (m, 4H, Ar–H), 7.00 (s,
H, –CH), 6.68–6.77 (m, 2H, Ar–H), 6.13 (s, 1H, –NH).
1H‑Spiro(cyclohexane‑1,2‑quinazolin)‑4(3H)‑one (3m)
−
1
White solid; mp 223–227 °C; FTIR (KBr, cm ): 3361, 3179, 2927, 2858,1645,
1
1
7
1
1
490, 1390, 1137, 756; H NMR (500 MHz, DMSO-d ) δ 7.90 (s, 1H, –NH),
6
.56 (d, J = 7.6 Hz, 1H, –CH), 7.21 (t, J = 7.6 Hz, 1H, –CH), 6.80 (d, J = 8.1 Hz,
H, –CH), 6.62 (d, J = 7.4 Hz, 1H, –CH), 6.60 (s, 1H, –NH), 1.73 (s, 2H, –CH),
.66–1.48 (m, 6H, –CH ), 1.42 (s, 1H, –CH), 1.31–1.19 (m, 1H, –CH).
2
1H‑Spiro(cyclopentane‑1,2‑quinazolin)‑4(3H)‑one (3n)
−
1
White solid; mp 256–258 °C; FTIR (KBr, cm ): 3290, 3163, 2941, 2848, 1637,
1
1
612, 1429, 1380, 754; H NMR (500 MHz, DMSO-d ) δ 8.07 (s, 1H, –NH), 7.56
6
1
3

H. Ghafuri et al.
(
(
d, J = 5.7 Hz, 1H, –CH), 7.20 (t, J = 7.2 Hz, 1H, –CH), 6.73 (s, 1H, –NH), 6.68
d, J = 8 Hz, 1H, –CH), 6.62 (t, J = 7.5 Hz, 1H, –CH), 1.78 (s, 4H, –CH), 1.65 (s,
4
H, –CH).
Results and discussion
Catalyst characterizations
The highly ordered mesoporous graphitic carbon nitride (ompg-C N ) was pre-
3
4
pared via a facile template-assisted method using SBA-15 as a mesoporous silica
template and functionalized with sulfonic acid (ompg-C N /SO H). The struc-
3
4
3
ture of ompg-C N and ompg-C N /SO H were proved by some analyses. The
3
4
3
4
3
small-angle region of the XRD patterns was analyzed to ascertain the hexago-
nal mesoporous structure of ompg-C N (Fig. 1a). A peak appeared at 2θ = 0.9°,
3
4
and the other one at 2θ = 1.6° proved the mesostructural order of the hexagonal
framework for ompg-C N [28–30]. The wide-angle regions of XRD patterns
3
4
of ompg-C N and ompg-C N /SO H demonstrate two obvious peaks at about
3
4
3
4
3
2
θ = 27.4° and 13.6° (Fig. 1b). The peak appearing at 2θ = 27.4° with higher
(
a)
(
b)
6
5
4
3
2
1
00
00
00
00
00
00
0
ompg-C3N4/SO3H
ompg-C3N4
0
20
40
60
80
100
Diffraction Angle (2θ)
Fig. 1 a Small-angle XRD pattern of ompg-C N and b wide-angle XRD patterns of ompg-C N and
3
4
3
4
ompg-C N /SO H
3
4
3
1
3

ompg‑C N /SO H: an efcient and recyclable…
3
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3
intensity indexed as the (002) planes belongs to the interlayer stacking existent
in the conjugated aromatic ring of the crystalline graphitic carbon nitride struc-
ture. Another peak with lower intensity at 2θ = 13.6° indexed as the (100) planes
corresponds to the in-plane structural repeating unit close to tris-s-triazine. The
intensity of both reꢃections decreases during the functionalization.
The FT-IR spectra of ompg-C N and ompg-C N /SO H are shown in Fig. 2.
3
4
3
4
3
−
1
The broad peaks at about 3000–3500 cm are attributed to –NH and –NH
2
stretching vibrations that conꢂrm the existence of amino groups and show hydro-
gen bonding interactions between the functional groups in the composition struc-
ture. The peaks related to stretching vibrations of heterocyclic s-triazine rings
−
1
−1
were seen in the region of 900–1700 cm . The characteristic peaks at 1307 cm
−
1
and 1602 cm can be ascribed to the C–N and C=N stretching vibration, respec-
−
1
tively. The observed peak at 806 cm is associated to tri-s-triazine units. The
−
1
spectrum of ompg-C N /SO H also shows the vibration bands at 1049 cm
3
4
3
−
1
(
S=O symmetric stretching), 1149 cm (S=O asymmetric stretching), and
−
1
1
413 cm (asymmetric SO stretching in SO H) that are related to SO H groups.
2 3 3
Of note, these peaks might be overlapped with the typical stretching bands of CN
heterocycles.
The morphologies of ompg-C N and ompg-C N /SO H were investigated by
3
4
3
4
3
ꢂeld-emission scanning electron microscopy (FESEM) and transmission elec-
tron microscopy (TEM) images. The images obtained of ompg-C N and ompg-
3
4
C N /SO H conꢂrm the uniform structures with typical rod-like morphology. The
3
4
3
images of ompg-C N /SO H obviously show that the ompg-C N is functional-
3
4
3
3
4
ized with SO H groups successfully (Fig. 3).
3
EDX spectroscopy analysis was utilized for characterization of elements in the
structure of ompg-C N /SO H (Fig. 4). This analysis conꢂrms the existence of
3
4
3
C, N, S, and O elements in the structure of ompg-C N /SO H, and proves that
3
4
3
3
the surface of the ompg-C N is functionalized with SO H groups. The absence
3
4
of an Si peak demonstrates that the silica template was removed entirely from
ompg-C N by washing with NH HF . Also, elemental analysis was applied for
3
4
4
2
the determination precise amounts of C, H, N, and S in the structure of ompg-
C N /SO H. According to this analysis, the existence of 27.83%, 2.91%, 47.06%,
3
4
3
1
1
1
1
8
6
4
2
0
60
40
20
00
0
0
0
0
ompg-C3N4
ompg-C3N4/SO3H
3
900
3400
2900
2400
1900
1400
900
400
Wave Number (1/Cm)
Fig. 2 The FT-IR spectra of the ompg-C N and ompg-C N /SO H
3
4
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4
3
1
3

H. Ghafuri et al.
Fig. 3 FESEM photographs of ompg-C N (a, b), ompg-C N /SO H (c, d), and TEM image of ompg-
3
4
3
4
3
C N /SO H (e)
3
4
3
1
3

ompg‑C N /SO H: an efcient and recyclable…
3
4
3
Fig. 4 EDX analysis of the ompg-C N /SO H
3
4
3
Table 1 Porous characteristics
SBET (m2 g−1)
a
Sample
Pore volume Pore size (nm)
of the ompg-C N and ompg-
3
−1
3
4
(
cm g
)
C N /SO H
3
4
3
ompg-C N
73.8
0.128
0.075
5.4
18.7
3
4
ompg-C N /SO H 14.2
3
4
3
a
0
Determined at p/p =0.97, where p is the equilibrium pressure and
0
p is the saturation pressure of nitrogen at −196 °C
and 2.72% of C, H, N, and S elements, respectively, in the ompg-C N /SO H was
3
4
3
proved.
BET analysis was performed to estimate the speciꢂc surface area, pore vol-
ume, and the pore size of the ompg-C N and ompg-C N /SO H (Table 1). After
3
4
3
4
3
immobilization of sulfonic groups on the ompg-C N , the total pore volume and the
3
4
3
−1
2
−1
BET surface area decreased from 0.128 cm g and 73.8 m g for ompg-C N to
3
4
3
−1
2
−1
0
.075 cm g and 14.2 m g for ompg-C N /SO H, which conꢂrms the immobili-
3 4 3
zation of sulfonic groups clearly (Fig S1).
The thermal stability of ompg-C N and ompg-C N /SO H was examined using
3
4
3
4
3
TGA and diꢁerential thermal analysis (DTA) under nitrogen atmosphere at the
range of 50 °C to 800 °C, at a heating rate of 10 °C/min (Fig. 5). The ꢂrst weight
loss (approximately 6%) appeared at 100–200 °C, resulting from the removal of
adsorbed water and other volatile impurities from the catalyst. Another weight loss
occurred at about 400–500 °C, corresponding to the elimination of a sulfonic group.
Eventually, sharp weight loss appeared at above 600 °C that belongs to the thermal
1
3

H. Ghafuri et al.
Fig. 5 TGA/DTA curves of the a ompg-C N and b ompg-C N /SO H
3
4
3
4
3
decomposition of g-C N which conꢂrms the high thermal stability of ompg-C N /
3
4
3
4
SO H.
3
The eꢀciency and catalytic performance of the ompg-C N /SO H was evalu-
3
4
3
ated for the one-pot synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives. This
process was carried out via the condensation reaction between carbonyl compounds
(
aldehydes or ketones) and 2-aminobenzamide as precursors. Our initial eꢁorts con-
centrated on designing an eco-friendly method with the best reaction conditions in
terms of time, yield, and the amount of catalyst. Thus, the condensation reaction
between benzaldehyde (1.0 mmol) and 2-aminobenzamide (1.0 mmol) was chosen
as a model reaction, and the eꢁect of several solvents, diꢁerent amount of catalyst,
and varying temperature on the reaction was investigated (Table 2).
1
3

ompg‑C N /SO H: an efcient and recyclable…
3
4
3
Table 2 Optimization of the reaction conditions for the condensation of benzaldehyde and 2-aminoben-
zamid as the model reaction for the one-pot synthesis of 2,3-dihydroquinazolin-4(1H)-ones
a
Entry
Solvent
Amount of catalyst (mg)
Temp. (°C)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
MeOH
EtOH
–
–
–
–
10
10
10
10
10
10
10
10
5
15
20
30
Reꢃux
Reꢃux
Reꢃux
120
RT
RT
RT
RT
120
Reꢃux
60
Reꢃux
Reꢃux
Reꢃux
Reꢃux
Reꢃux
Reꢃux
120
120
120
120
5
5
5
5
5
10
5
3
3
3
3
3
3
–
–
–
–
H O
2
–
MeOH
EtOH
89
89
83
86
87
84
91
94
89
94
98
98
Trace
H O
2
Ball milling
–
0
1
2
3
4
5
6
7
H O
2
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
(ompg-C N , 20 mg)
3
4
RT room temperature. Reaction conditions: benzaldehyde (1.0 mmol), 2-aminobenzamide (1.0 mmol),
catalyst: ompg-C N /SO H, solvent (3.0 mL)
3
4
3
a
Isolated yield
First, we applied a variety of solvents such as MeOH, EtOH, H O, and also
2
solvent-free condition (Table 2, entries 1–5). As shown in Table 2, no target prod-
ucts were detected when the reaction was performed in the absence of any catalysts
(
Table 2, entries 1–4), whereas using ompg-C N /SO H as a catalyst gave satisfac-
3 4 3
tory results. Among these solvents and solvent-free conditions, ethanol was found
to be most eꢀcient for producing satisfactory results (Table 2, entry 6). In order to
assess the eꢁect of temperature, the model reaction was conducted at diꢁerent tem-
peratures like room temperature, 60 °C, and reꢃux temperature (Table 2, entries 6,
1
1, 12).
It was observed that increasing the reaction temperature to 80 °C (reꢃux tem-
perature) led to the improvement of the yield of the desired product. To assess
the catalytic activity of sulfonated ordered mesoporous graphitic carbon nitride
(
(
ompg-C N /SO H), ompg-C N was examined as a catalyst in the model reaction
3 4 3 3 4
Table 2, entry 17). As shown, the catalytic activity of ompg-C N /SO H is greater
3
4
3
than ompg-C N (catalyst support) for this reaction. Finally, the optimal amount of
3
4
the catalyst was explored by varying the amount of the catalyst in the model reac-
tion (Table 2, entries 12–16). The results showed that the excellent yield (98%) of
the target product results when 20 mg of catalyst was used in the reaction (Table 2,
entry 15), and further increasing the amount of catalyst has no signiꢂcant eꢁect on
the reaction time and yield in the same reaction conditions (Table 2, entry 16).
1
3

H. Ghafuri et al.
Table 3 The ompg-C N /SO H-catalyzed reaction in the presence of various aldehydes or ketones for
3
4
3
synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives
a
Entry
Carbonyl compound
Product
Time
Yield
(%)
M.p
(
min)
(observed)
o
Ref.
(
C)
1
PhCHO
O
3
98
229 – 232 [31]
NH
N
H
(
3a)
O
2
3
4-(Cl)C
6
H
4
CHO
15
91
96
203–206 [23]
232–234 [32]
NH
N
H
Cl
(
3b)
O
4-(Me)C
6
H
4
CHO
5
NH
N
H
Me
OH
(
3c)
O
4
5
4-(OH) C
6
H
4
CHO
15
15
78
73
213–215 [33]
178–182 [34]
NH
N
H
(
3d)
4-(OMe) C
6
H
4
CHO
O
NH
N
H
OMe
(
3e)
6
7
3-(NO
2
) C
6
H
4
CHO
O
10
93
95
199 –202 [35]
193–197 [36]
NH
NO
2
N
H
(
3f)
4-(F) C
6
H
4
CHO
O
3
NH
N
H
F
(
3g)
8
2-(Cl) C
6
H
4
CHO
O
8
92
207– 209 [37]
NH Cl
N
H
(
3h)
1
3

ompg‑C N /SO H: an efcient and recyclable…
3
4
3
Table 3 (continued)
a
Entry
Carbonyl compound
Product
Time
Yield
(%)
M.p
(
min)
(observed)
o
Ref.
(
C)
9
4-(NO
2
) C
6
H
4
CHO
O
12
91
200–202 [38]
NH
N
H
NO
2
(3i)
O
1
1
0
1
4-(CN) C
6
H
4
CHO
5
7
91
87
349–351 [39]
242–246 [40]
NH
N
H
CN
(3j)
Terephthaldehyde
O
O
NH
NH
HN
HN
(3k)
1
1
2
3
4-(Br) C
6
H
4
CHO
O
3
3
96
96
196 –198 [23]
NH
N
H
Br
(3l)
Cyclohexanone
O
223–227 [41]
HN
HN
(3m)
1
1
4
5
Cyclopentanone
Acetophenone
O
7
3
94
98
256 –258 [42]
221–224 [43]
HN
HN
(3n)
H
N
NH
O
(3o)
Reaction conditions: aldehydes or Ketones (1.0 mmol), 2-aminobenzamide (1.0 mmol), catalyst
(
20.0 mg), EtOH (3.0 mL), under reꢃux condition
Isolated yield
a
1
3

H. Ghafuri et al.
O
NH
Ar
O
O
S
O
N
H
OH
Ar
H
(
3)
(1)
O
O
S
O
O
O
S
OH
O
O
O
H
Ar
H
NH2
N
H
Ar
NH
(2)
2
N
H
(IV)
O
O
OH
O
S
O
NH
2
NH
H
O
Ar
O
S
(
I)
NH
2
O
O
N
H
Ar
(
III)
O
H
NH
OH
Ar
2
transfer
HN
(II)
2
2
H O
O
O
S
ompg-C
3
N
4
O
Scheme 2 Suggested mechanism for the synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives cata-
lyzed by ompg-C N /SO H
3
4
3
With the optimized conditions, in order to evaluate the scope and generality of
this protocol, the reaction was carried out with various substituted aromatic alde-
hydes (Table 3, entries 1–13), as well as ketones such as cyclohexanone and cyclo-
pentanone (Table 3, entries 14–15). It was observed that the protocol was eꢁective
with aromatic aldehydes having either electron-donating (−OMe, −OH, Me) or
electron-withdrawing (−F, −Cl, −Br, −CN, −NO ) groups and also ketones to pro-
2
duce the desired products in high yields.
The possible mechanism for the formation of 2,3-dihydroquinazolin-4(1H)-
ones in the presence of ompg-C N /SO H as a solid acid catalyst is shown in
3
4
3
Scheme 2. At the ꢂrst step of this reaction, ompg-C N /SO H as a Bronsted acid
3
4
3
activates the carbonyl functional group of aldehyde or ketone (1) through pro-
tonation. Thereafter, the activated carbonyl group with high electrophilicity is
attacked by the amino group in 2-aminobenzamide (2) during nucleophilic addi-
tion to give an intermediate (I). Subsequently, proton transfer forms intermediate
(
II). Afterward, an iminium ion intermediate (III) is formed through dehydration
1
3

ompg‑C N /SO H: an efcient and recyclable…
3
4
3
Fig. 6 Reusability of the ompg-C N /SO H catalyst in the model reaction
3
4
3
1
1
1
1
8
6
4
2
60
40
20
00
0
0
0
0
0
5
300
4300
3300
2300
1300
300
Wave Number (1/cm)
Fresh ompg-C3N4SO3H
Used ompg-C3N4/SO3H
Fig. 7 FT-IR spectra of fresh and used ompg-C N /SO H
3
4
3
of (II) followed by a ring closure forming intermediate (IV) which undergoes
intramolecular cyclization to aꢁord target product (3).
One of the most important aspects of a heterogeneous catalyst in green chem-
istry is its stability and reusability. Hence, we evaluated the reusability of the
ompg-C N /SO H for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones. As the
3
4
3
reaction went to completion, the catalyst was separated from the reaction mixture,
washed with ethanol, and dried at 60 °C, then reused for the fresh reactions. It
was found that the ompg-C N /SO H shows negligible loss in the catalytic activ-
3
4
3
ity after ꢂve cycles (Fig. 6).
The acidity of the catalyst after the reaction was determined through the back-
titration method. The pH value of the used ompg-C N /SO H was calculated (pH
3
4
3
=
1.55) as the same pH value as the fresh ompg-C N /SO H. These results indicate
3 4 3
that the acidity of the ompg-C N /SO H did not change after the reaction. For fur-
3
4
3
ther conꢂrmation, FT-IR spectra of the fresh and used catalyst (ompg-C N /SO H)
3
4
3
1
3

H. Ghafuri et al.
Table 4 Comparison of the catalytic eꢀciency of ompg-C N /SO H with the previously reported cata-
3
4
3
lysts for the synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives
Entry Catalyst (amount of catalyst) Solvent
Temp. (°C) Time
Yield (%) Ref.
1
2
3
4
5
6
H PW O (1 mol%)
H O/CTAB 80 60 min 83
[44]
[45]
[46]
[47]
[48]
This work
3
12 40
2
Y(NO ) .6H O (10 mol%)
CH CN
–
RT
80
5 h
6 h
98
87
3
3
2
3
SiO -FeCl (5 mg)
2
3
ZnFe O (30 mol%)
H O
EtOH
MW
80
80 min 90
60 min 96
2
4
2
Boehmite-Si-DSA (30 mg)
Ompg-C N /SO H (20 mg)
EtOH
80
3 min
98
3
4
3
RT room temperature
was examined. As shown in Fig. 7, the ompg-C N /SO H had no obvious change
3
4
3
after ꢂve cycles.
ompg-C N /SO H as an eꢀcient and environmentally friendly organocatalyst for
3
4
3
the synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives has some advantages
in comparison with the other catalysts in the literature containing shorter reaction
time and high yield (Table 4).
Conclusion
In conclusion, we have illustrated that ompg-C N /SO H can be utilized as an eꢁec-
3
4
3
tive and eco-friendly organocatalyst for the one-pot synthesis of 2,3-dihydroquina-
zolin-4(1H)-one derivatives via the condensation of anthranilamide with carbonyl
compounds (aldehydes and ketones) under mild conditions. The remarkable advan-
tages of this novel protocol are mild reaction condition, short reaction times, simple
work-up procedure, good to excellent yield of the products, and reusability of the
catalyst without loss of activity.
Acknowledgements The authors gratefully acknowledge the partial support from the Research Council
of the Iran University of Science and Technology.
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