Preparation of choline sulfate ionic liquid supported on porous graphitic carbon nitride nanosheets by simple surface modification for enhanced catalytic properties

Article abstract of DOI:10.1016/j.molliq.2019.112263

Supported ionic liquids (SILs) have attracted rising interest and the subject of active research in the last decades due to the diversified range of applications and yet reports on ILs is still rapidly increasing. This work reports a choline sulfate ionic liquid supported on fascinating and highly stable porous graphitic carbon nitride (g-C₃N₄) nanosheets as an inexpensive and an environmentally friendly reusable ionic catalyst in organic synthesis typically requiring a harmful organic solvent and highly toxic acids. g-C₃N₄?SO₃Ch was prepared by mixing sulfonic acid functionalized graphitic carbon nitride nanosheets (g-C₃N₄?SO₃H) with choline hydroxide or via a novel approach. The introduction of a choline sulfate could significantly enlarge specific surface areas with rich reaction sites and suppressed the recombination of sheets. This work provides a new way to improve the chemical property of g-C₃N₄ along with the recyclability of the ionic liquid. g-C₃N₄?SO₃Ch (IL/g-C₃N₄) offers an effective, reusable, inexpensive, environmentally friendly and low-cost catalyst for the synthesis of 3,4-dihydropyrimidin-2 (1H)-ones, 2,3-dihydroquinazolin-4 (1H)-ones and bisindolylmethanes in good to excellent yields. The prepared catalyst synthesized compounds were well characterized by different techniques such as FT-IR, XRD, SEM, EDX and TGA.

Full text of DOI:10.1016/j.molliq.2019.112263

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Preparation of choline sulfate ionic liquid supported on porous
graphitic carbon nitride nanosheets by simple surface
modification for enhanced catalytic properties
Najmedin Azizi, Mahtab Edrisi
PII:
S0167-7322(19)34646-X
DOI:
https://doi.org/10.1016/j.molliq.2019.112263
MOLLIQ 112263
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
19 August 2019
1 December 2019
4 December 2019
Please cite this article as: N. Azizi and M. Edrisi, Preparation of choline sulfate ionic liquid
supported on porous graphitic carbon nitride nanosheets by simple surface modification
for enhanced catalytic properties, Journal of Molecular Liquids(2018), https://doi.org/
10.1016/j.molliq.2019.112263
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Preparation of choline sulfate ionic liquid supported on
porous graphitic carbon nitride nanosheets by simple
surface modification for enhanced catalytic properties
Najmedin Azizi* and Mahtab Edrisi
Department of green chemistry, Chemistry and Chemical Engineering Research Center of Iran,
P.O. Box 14335-186, Tehran, Iran
E-mail: azizi@ccerci.ac.ir
Abstract
Supported ionic liquids (SILs) have attracted rising interest and the subject of active research in
the last decades due to the diversified range of applications and yet reports on ILs is still rapidly
increasing. This work reports a choline sulfate ionic liquid supported on fascinating and highly
stable porous graphitic carbon nitride (g-C3N4) nanosheets as an inexpensive and an
environmentally friendly reusable ionic catalyst in organic synthesis typically requiring a
harmful organic solvent and highly toxic acids. g-C3N4@SO3Ch was prepared by mixing
sulfonic acid functionalized graphitic carbon nitride nanosheets (g-C3N4@SO3H) with choline
hydroxide or via a novel approach. The introduction of a choline sulfate could significantly
enlarge specific surface areas with rich reaction sites and suppressed the recombination of sheets.
This work provides a new way to improve the chemical property of g-C3N4 along with the
recyclability of the ionic liquid. g-C3N4@SO3Ch (IL/g-C3N4) offers an effective, reusable,
inexpensive, environmentally friendly and low-cost catalyst for the synthesis of 3,4-
dihydropyrimidin-2 (1H) -ones, 2,3-dihydroquinazolin-4 (1H) -ones and bisindolylmethanes in
good to excellent yields. The prepared catalyst synthesized compounds were well characterized
by different techniques such as FT-IR, XRD, SEM, EDX and TGA.
Keywords: porous graphitic carbon nitride, ionic nanosheets, choline sulfate ionic liquid,
heterocycle chemistry
Introduction
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As fascinating novel support, mesoporous materials with large specific surface area, high
porosity, and large conductivity for charge and mass transport, has become a new research
hotspot and an important challenge to widen the feasible range of application [1,2]. In most
cases, mesoporous materials used as supports for catalysts or directly in some catalysis reactions.
Graphitic carbon nitride (g-C3N4) has attracted broad interdisciplinary attention as a low-cost and
robust nanoporous structure due to its outstanding visible light activity, high chemical stability
and environment purification [3-5]. As a novel and promising supported catalytic material, g-
C3N4 and their composites can be easily prepared by thermal polycondensation of nitrogen-based
precursors like cyanamide, guanidine, melamine, and urea [6]. However, the practical application
of pure g-C3N4 is limited because of the small specific surface area, low photocatalytic efficiency
and limited catalytic activity. Considerable efforts have been directed towards the development
of active components anchored on g-C3N4 using chemical functionalization or van der Waals
interactions that can affect the electronic structure and catalytic activity [7-9]. To our knowledge,
the preparation and applications of IL/g-C3N4 in the organic synthesis has not been reported.
Here, we demonstrate the simple assembly of g-C3N4 with ionic liquids to design of a highly
ionic functional tailored g-C3N4, which leads to a good catalytic activity.
Ionic liquids (ILs) have attracted enormous attention as promising green alternatives to
conventional volatile organic solvents, electrolytes, and advanced materials during the past
decade [9-14]. ILs are an emerging class of green materials due to their unique properties such as
wide liquid range, nonflammable, thermally stable properties and excellent solubility [15-18].
The unusual properties of ILs have made truly interesting applications such as solvent, thermal
fluids for the solar thermal device, treatment of high-level nuclear waste, high ionic conductivity
and a suitable catalyst used in organic synthesis in recent years [19-27]. The reason for the
increase in a number of publications can be attributed to the diversity of applications of these
tunable and multipurpose materials [28,29]. However, the significant disadvantages of ionic
liquids become obvious for large scale applications that some of them are expensive and
extremely viscous and recycling of pure ionic liquid energy-intensive. Therefore, a large
proportion of research effort has been focused on the eco-compatible synthesis of pure ILs or use
alternative media such as deep eutectic solvents to overcome the major drawback of ILs such as
the availability and cost issues [30-32].
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Experimental section
Material and methods
All chemical and solvents were analytical pure and were obtained from commercially available
sources and used without further purifications. All products were known and confirmed by
1
Fourier transform infrared spectroscopy (FTIR) and H nuclear magnetic resonance (NMR)
spectra. Melting points were recorded on Buchi 535 melting point apparatus and are uncorrected.
The morphological and EDX studies were performed using Scanning Electron Microscope
TESCAN Vega Model.
Preparation of g-C3N4@SO3Ch (IL/g-C3N4) catalyst
Bulk graphitic carbon nitride (g-C3N4) was synthesized via the thermal condensation reaction
from melamine precursors [23]. 5 g of melamine were placed in a ceramic crucible covered with
◦
◦
a lid and followed by thermal polycondensation process under 550 C at a heating 2.5 C min−1
under static air and then left for 2 h at the reached temperature and a light yellow powder g-C3N4
was collected after cooling down. In a typical procedure, in three-neck round-bottom flask, g-
C3N4 (2 g) was dispersed in 200 mL of dry CH2Cl2 and ultrasonicated for 2 h at ambient
temperature. The flask was equipped with a constant-pressure dropping funnel under the steady
stream of inert gas (N2) and chlorosulfonic acid (3.0 mL) in dry CH2Cl2 (30 mL) was added in an
ice bath under vigorous stirring for 25 min. After completion of the addition, the reaction system
was stirred for 8 h at room temperature. The resultant solid was washed with ethyl acetate,
methanol and dried under vacuum at 50 °C. The g-C3N4@SO3Ch ionic catalyst were prepared as
follows. g-C3N4@SO3H (2.0 g) was dispersed in 100 mL ethanol by ultrasonic treatment and 4.0
g choline hydroxide (ChOH) was added and the mixture was stirred at room temperature for 24
h. The reaction suspension was diluted with 50 mL of water and then centrifuged at about 4000
rmp and was washed by ethanol many times to obtain the g-C3N4@SO3Ch porous nanosheets as
a white powder.
General procedure
The one-pot experiment was conducted in a 5.0 mL flask under stirring with magnet. A mixture
of aldehyde (1.0 mmol), β-keto ester (1.0 mmol) and urea (1.0 mmol) in the presence of IL/g-
C3N4 (80 mg) was heated at 80 oC for a period of 120-240 min (Table 1). After completion of the
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reaction, the reaction mixture was allowed to cool to room temperature and was extracted with
hot ethyl acetate. After completion of the reaction, the reaction mixture was gradually cooled to
room temperature. The solid crude product was collected by simple filtration and extract with hot
ethyl acetate and recrystallized from ethanol or ethyl acetate to afford the pure products.
Results and discussion
With these precedents in mind and in continuation to our green chemistry endeavors using ionic
liquids and deep eutectic solvents [33-36], in the present article, the preparation, characterization
and applications of inexpensive and biodegradable IL/g-C3N4 is explained. The synthetic
approach used to prepare the supported ILs was so simple and green. The starting materials
(melamine, choline chloride and chlorosulfuric acid) are the cheapest and most abundant
substance in the world and it is easier to prepare by a simple and direct assembly of g-C3N4 with
choline sulfate at room temperature without requiring a reaction step. Pure g-C3N4 was obtained
by direct pyrolysis of melamine as the single raw material in a semi-closed system. the sulfonic
acid groups, which function as the active sites, were grafted using the reaction of chlorosulfonic
acid with C3N4 at room temperature. Acid-base neutralization reaction are used to make IL, that
stoichiometric amounts of C3N4-SO3H and choline hydroxide are mixed together in an ice bath to
form the IL supported C3N4 (Scheme 1).
Scheme 1
After simple preparation of ionic C3N4, it was thoroughly characterized by X-ray diffraction
(XRD), FT-IR spectroscopy, thermogravimetric analysis (TGA), and scanning electron
microscopy (SEM).
The structures of g-C3N4@SO3Ch were confirmed by powder X-ray Diffraction (XRD) and are
shown in Figure 1. It can been seen that two diffraction characteristic peak is observed that
reveals the crystalline nature of g-C3N4@SO3Ch. The main peak at around 2θ = 27.6° which can
be indexed as the graphitic interlayer (002) and the peak at 2θ = 13.3° is attributed to the (100)
planes of g-C3N4. In addition, no apparent diffraction peaks of SO3CH appear in the patterns of
g-C3N4@SO3Ch.
Figure 1.
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The distribution of the elements of the prepared catalyst was analyzed using the energy-
dispersive X-ray (EDX) spectrum (Fig. 2) shows the presence of elements C, N, O and S, in the
ionic catalyst, which further revealed the grafting of the SO3Ch on the surface of g-C3N4.
Figure 2. EDX spectra of g-C3N4@SO3Ch.
Scanning electron microscopy (SEM) chemical microanalysis technique used to confirm the
chemical structure and the morphology of the ionic functionalized g-C3N4 nanocomposite as
shown in Fig. 3. The SEM image of the pure g-C3N4 appeared as aggregated morphology
containing a nanosheet like structure. When the bulk g-C3N4 was functionalized with IL, it shows
porous exfoliated nanosheet type morphology forming loose and soft agglomerates which can be
confirmed from the SEM image. In addition, the volume of the g-C3N4@SO3Ch with same
weight is much higher than the pure g-C3N4 sample indicating its fluffy nature and larger
porosity.
Figure 3.
FTIR spectroscopy of g-C3N4@SO3Ch clearly confirmed the presence of essential functionality
differences and electronic nature of choline sulfate ionic liquid on the carbon nitride (Fig. 4.).
The presence of strong peaks in the range of 1241-1635 cm−1 have been observed in pure g-C3N4
(a) and g-C3N4SO3Ch, which are the typical vibrations of hepatizine-based molecular units and a
-1
strong intense peak at 806 cm is related to the characteristic breathing mode of triazine units.
The sulfonic acid groups have been successively incorporated on the graphitic carbon nitride as
evidenced by the peak at 1236 cm−1 a characteristic signal due to the stretching vibrations of –
SO3 groups.
Figure 4
To investigate the thermal stability and the loading of choline sulfate in the ionic catalyst,
◦
thermal gravimetric (TG) and DTG analysis has been performed from rt to 600 C under the
conditions of air atmosphere at a heating rate of 10 ◦C min−1, and the results are shown in Fig. 5.
The DSC and TG graph indicated that (Fig. 5) various phase transformations and transforming
°
reactions occur under this process. The first mass loss process from the rt to 120 C due to the
removal of the absorbed water. Meanwhile, the strongest endothermal peak appears in the range
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°
of 150-400 C shows that the decomposition of the choline sulfate groups mainly occurred,
which is related to the main weight loss of 23% against the total ionic support.
Figure 5
To ascertain the activity of the novel ionic C3N4 based catalyst in organic synthesis, and gauge
their performance relative to an unsupported ionic liquid, some important organic reactions have
been successfully conducted in C3N4SO3Ch to evaluate the catalytic activity as well as
selectivity.
Biginelli reaction
Validation of the hypothesis started by evaluating the ability of C3N4SO3Ch to catalyze the
Biginelli reaction [37]. The Biginelli reaction is one of the important acid-catalyzed three-
components reaction for the synthesis of multifunctionalized 3,4-dihydropyrimidin-2-(1H)- ones
derivatives. Dihydropyrimidine scaffold shows a wide range of pharmaceutical and biological
activity, as calcium channel blockers due to the connection with purine and pteridine systems
[38]. One-pot, three-components condensation reaction of β-keto ester, an aryl aldehyde, and
urea under acidic conditions is the simple and straightforward procedure and various reaction
conditions have been developed in the literature [39]. Consequently, the development of a more
amenable and sustainable approach for Biginelli reaction is significant contemporary interest in
green chemistry.
In order to evaluate the catalytic activity of C3N4SO3Ch, the one-pot three component Biginelli
reaction between benzaldehyde (1.0 mmol), urea (1.0 mmol) and ethyl acetoacetate (1.0 mmol)
at room temperature (rt) under solvent free was examined. Initially, we used 50 mg of catalyst
under solvent-free conditions, no desired product was obtained after reacting at rt for 6 h (Table
1, entry 1). In our endeavor to further improve the yield, the reaction temperature increased from
°
°
rt to 120 C, a tremendous and rapid reaction rate was observed at 80 C and resulting the sole
formation of dihydropyrimidinone product 4a. Water is added to a reaction mixture and the solid
product was separated and recrystallized from ethanol in 62% isolated yield. Finally, the effect of
the amount of C3N4SO3Ch on the Biginelli reaction was explored. Increasing the catalyst loading
from 50 mg to 150 mg led to a significant increase in the yields of reaction and decrease in the
time of the reaction completion. (Table 1, entries 5-7). However, no obvious increase of the yield
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was observed when the reaction carried out in organic solvents like ethanol and water (Table 1,
entries 9, 10).
In order to underline the importance of the C3N4SO3Ch for Biginelli reaction, we also
investigated the behaviors of the other choline sulfate ionic liquid supported system to promote
the multicomponent reaction under the same experimental conditions. (Table 1, entries 11-14). It
is interesting to observe that only g-C3N4-SO3-1-butyl-3-methylimidazolium catalyzed the
dihydropyrimidinone product 4a, while silica based ionic liquid such as SiO2-SO3Ch, SBA-15-
SO3Ch and MCM-41-SO3Ch exhibited moderate isolated yields. In additions, 1-butyl-3-
methylimidazolium based ionic catalyst showed higher reaction rate along with the formation of
bisamide byproducts.
Table 1 optimization of reaction conditions
With the aforementioned optimized conditions, we then explored the generality and synthetic
scope of this three-components coupling protocol by treating several aromatic aldehydes and
ethylacetoactate with urea using ionic catalyst (Table 2). To our satisfaction, there was no
apparent difference in the product yield regardless of the structural variations of aldehydes.
Aromatic aldehydes with electron-neutral or -donating groups as well as electron-withdrawing
groups on aryl rings, such as methyl, methoxyl, chloro, bromo and nitro are subjected under this
green procedure to produce the corresponding dihydropyrimidinones in good to excellent yields
(Table 2).
Table 2 choline sulfate supported g-C3N4-catalyzed one-pot synthesis of dihydropyrimidinones
Synthesis of bis(indolyl)methane
Among the various bioactive nitrogen-containing heterocycles, indole derivatives constitute a
unique class of compounds with a wide range of biological activities and important intermediates
in organic synthesis [40]. Synthetic as well as both marine and terrestrial sources of
bis(indolyl)alkane derivatives are known to promote estrogen metabolism and have great
potential to become breast anticancer drugs in both women and men [41]. Due to the unique
biological profiles of bisindolylmethanes, methods for the synthesis of this heterocycles is of
particular interest and have gained much attention in the past decades. The most general method
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involves the direct coupling of indoles with carbonyl compounds and a considerable number of
milder catalytic systems have been developed over the past few years [42-44].
An initial screening was done in the model reaction between indole (1.0 mmol) 1 and
benzaldehyde (0.5 mmol) to obtain maximum conversion to the product in the presence of IL
supported catalyst in water (Table 3). An initial reaction was conducted using 80 mg of IL
supported catalyst under solvent-free condition. We were quite satisfied to see that our reaction
o
proceeded smoothly at 50 C and showed the highest activity and up to 95 % product was
isolated after a reaction time of 40 min in polyethylene glycol 200 (PEG 200). When the reaction
was also carried out in organic solvents, water and solvent-free conditions, moderate to good
conversions were observed. Furthermore, due to the additional purification steps for organic
solvent, a decrease in the yield of the isolated products was observed. Because of water-soluble
property of C3N4SO3Ch, C3N4SO3Ch removed easily and completely from the water-insoluble
product 6a and afforded the highly pure product just by simple filtration and washing with hot
water. After optimization of reaction parameters such as reaction time, temperature, solvent and
C3N4SO3Ch loading, we then expended the scope and generality of this strategy to various
aldehyde and substituted indoles (Table 3). The reaction of various aldehydes and cyclic ketones
with indole, 2-methyl indoles, 5-bromoindole and N-methyl indole proceed smoothly to furnish
the bis(indolyl)alkane derivatives in good to excellent yields. Electronic and steric effect of
substituents on the aromatic aldehydes has not considerable difference in yields and reaction
time. A variety of electron-rich and electron-poor aromatic aldehydes was found to react
smoothly with most of the indoles to give the corresponding products in good to excellent yields.
The reaction gave lower yields with heterocyclic and aliphatic aldehydes. Cyclic ketones are
poor reaction partners for indole so the reaction was sluggish and gave somewhat lower product
yield and required longer reaction times.
Synthesis of 2,3-dihydroquinazolin-4(1H)-ones
The quinazolineones scaffold is a central part of biologically active compounds with multiple
pharmacophores, that's responsible for a wide range of bioactivities such as thymidylate synthase
inhibition, antibiotic, antidefibrillatory effects and sedative effects [45]. Furthermore, 2,3-
dihydroquinazolinones as well as the oxidized form, have been identified as synthetic building
blocks and structural scaffolds in various natural products [46]. Based on this wide range of
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applications, a large numerous protocols for preparation of 2,3-dihydroquinazolin-4(1H)-ones
have been developed in the literatures [47-51].
The effectiveness of the protocol was further showcased by the synthesis of 2,3-
dihydroquinazolin-4(1H)-ones from and carbonyl compounds (aldehydes and ketones) in the
presence of IL supported C3N4. It was very interesting to find that when the reaction of 2-
aminobenzamide (1.0 mmol) and benzaldehyde (1.0 mmol) was carried out in the presence of 80
mg of IL/C3N4 in PEG 200 (0.5 mL) under constant stirring at room temperature for 120 min.,
the analytically pure product 8a was obtained by re-crystallization from ethanol. With optimized
conditions in hand (PEG 200, rt, IL-C3N4 80 mg), the scope and limitations of this green protocol
was subsequently determined (Table 4). A wide range of commercially available aliphatic and
aromatic aldehydes and ketones underwent condensations with a 2-aminobenzamide by this
procedure to provide the corresponding 2,3-dihydroquinazolin-4(1H)-ones derivatives. The
protocol allows to prepare dihydroquinazolin-4 (1H)-ones with a wide range of aryl aldehydes
(o-, m- and p-substituted) bearing electron donating and withdrawing substituents, irrespective of
the nature of the substituted and afforded the products in good to excellent yields.
Heteroaromatic aldehydes such as thiophenyl and pyridinyl aldehydes as well as aliphatic
aldehydes also underwent smooth reactions with moderate yields. To further expand the scope of
the green method, when cyclic ketones like cyclohexanone and tetrahydro-4H-pyran-4-one were
used as starting materials under the optimized reaction conditions, the reaction proceeded
smoothly to give good yields of the desired products.
Recycling studies
For practical applications of such novel heterogeneous ionic catalyst, the reusability is one of the
important properties which has a great potential for applications in industry. To test the
possibility of recovery and reusability of IL/C3N4, the one-pot reaction between benzaldehyde
(1.0 mmol), urea (1.0 mmol) and ethyl acetoacetate (1.0 mmol) in the presence of IL/C3N4 (80
mg) as a model reaction under solvent free condition were heated at 80 ºC for 150 min. After
completion of the model reaction, the product was dissolved in ethyl acetate and the catalyst was
recovered from the reaction mixture by centrifugal separation. The recovered catalyst was
washed with ethyl acetate and dried for two hours before its reuse in subsequent catalytic runs.
The result reveals that the catalyst worked well at least 5 times without a noticeable drop in the
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product yield and its catalytic activity. In addition, the composition and structure of the fresh and
recycled samples were further characterized by XRD, EDS and FT-IR, which indicates no
significant change is observed in the physical properties and structure of the recycled samples
due to the high stability of ionic support.
Figure 6
Conclusions
In summary, we have demonstrated a rapid and facile synthesis of porous graphitic carbon
nitride nanosheets functionalized with choline sulfate based ionic liquid through an efficient
exfoliation approach of bulk g-C3N4. The incorporation of ionic liquid provides not only an
attractive strategy to enhance the surface area, charge separation efficiency, and the overall
catalytic activity, but also simple exfoliation with facile operation free of long-time
ultrasonication or stirring, filtration and repeated washing process to remove the residual acid or
base. The obtained IL-C3N4 show excellent catalytic performance at room temperature for the
construction of various biologically active heterocyclic compounds with convenient and
excellent reusability without any loss in mass and activity.
Acknowledgements
We gratefully acknowledge the financial support of the Iran National Science Foundation (INSF)
and the Chemistry and Chemical Engineering Research Center of Iran.
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Table 1 optimization of reaction conditions
Entry
Catalyst (mg)
Times (min.)
Yielda (%)
Temp oC
rt
1
2
3
4
5
6
7
8
50
50
50
50
80
100
150
-
80
80
80
80
80
80
600
200
200
200
150
150
150
150
150
150
150
150
150
100
10
45
62
88
94
96
96
28
45
28
42
64
53
73
50
80
120
80
80
80
80
80
80
80
80
80
80
9b
10c
11d
12e
13f
14g
a isolated yields. b water as solvent. c ethanol as solvent. d SiO2-SO3Ch as catalyst. e SBA-15-SO3Ch as
catalyst. f MCM-41-SO3Ch as catalyst g g-C3N4-SO3-1-butyl-3-methylimidazolium
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Table 2 choline sulfate supported g-C3N4-catalyzed one-pot synthesis of dihydropyrimidinones
entry
1
R
Ph
Yielda %
94
M.P( °C) Found
209
M.P( °C) Report
208-210[35]
2
3
4
5
6
7
4-MeC6H4
4-OMeC6H4
4-ClC6H4
88
76
82
89
91
78
216-217
207-208
212-214
196-198
206-208
210-212
216-217[35]
206-208[34]
213-215[34]
197-199[33]
208-210[33]
206-208 [35]
4-BrC6H4
4-NO2C6H4
2-NO2C6H4
a
isolated yields
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Table 3 choline sulfate supported g-C3N4-catalyzed synthesis of bis(indolyl) methanes
o
entry
1
R-CHO
Ph
Yield (%)a
84
M.P C
245-247
M.P oC (Reported)[Ref]
246-247 [58]
5a-5d
5a
2
3
4-Cl-Ph
88
82
254-256
225-226
258-260 [59]
217-218 [60]
5a
5a
4-Me-Ph
4
5
4-OMe-Ph
Ph
76
92
74
89
81
83
88
80
213-215
178-181
227-229
140-142
74-76
213-215 [61]
180-183[39]
230-232[40]
140-142[40]
75-77[29]
5a
5b
5c
5d
5d
5d
5b
5b
6
Ph
7
Ph
8
4-Cl-Ph
4-Me-Ph
4-Me-Ph
4-Cl-Ph
9
96-98
94-96[[29]
10
11
178-180
208-211
182-183[39]
212-213[29]
a isolated yields.
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Table 4 IL/C3N4 catalyzed synthesis of the 2,3-dihydroquinazolinones derivatives in PEG
Entry
RCHO or RR’CO
Products
Time
(min)
Yield a
(%)
m.p. (оC)
(8)
Found Reported[ref.]
1
2
C6H5
4-CH3-C6H4
4-Cl-C6H4
2-Cl-C6H4
4-OCH3-C6H4
3-NO2-C6H4
4-pyridyl
120
140
120
180
180
120
120
180
150
150
180
95
82
78
79
75
86
81
77
89
80
68
219-220
225-227
208-211
203-206
188-191
211-213
166-168
166-168
198-200
218-220
183-185
208-209[41]
229-231[41]
207-209[46]
206-208[46]
190-192[46]
210-212[44]
170-172[42]
165-167[42]
197-199[45]
216-218[46]
180-182[46]
8a
8b
8c
8d
8e
8f
3
4
5
6
7
8g
8h
8i
8
2-furyl
9
4-Br-C6H4
4-CO2Me-C6H4
10
11
8g
8k
O
12
180
70
266-268
263-265[42]
8l
O
O
a isolated yields.
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NH2
H2N
N
N
N
N
N
N
N
N
N
NH2
N
N
N
N
N
N
N
N
N
H2N
N
N
NH2
H2N
N
NH2
550 oC, 2h
N
N
N
N
N
N
N
N
N
N
N
NH2
N
N
Melamine
g-C3N4 nanosheets
Cl.SO3H, r.t., 8 h
CH2Cl2, r.t. 2h
N
OH
N
OH
N
HO
N
O3S
N
NH
SO3
HO3S
O3S
N
N
N
N
N
N
N
NH
NH
N
SO3H
NH
HO
HO3S
N
N
N
N
N
N
OH
N
N
N
N
N
N
N
N
N
N
SO3
SO3
N
N
N
N
N
N
N
N
ChOH, r.t., 24 h
HN
N
N
N
N
NH
SO3H
SO3H
NH
HN
N
N
N
N
N
N
N
N
N
N
O3S
N
SO3
N
N
N
N
N
N
N
O3S
N
SO3
N
N
N
N
N
N
O3S
SO3
N
N
N
N
N
NH
HN
SO3
O3S
SO3
SO3
HN
HN
SO3H
SO3H
N
N
OH
OH
g-C3N4@SO3Ch
g-C3N4-SO3H
Scheme 1. The synthesis procedure for the preparation of g-C3N4@SO3Ch
Figure 1. XRD pattern of g-C3N4@SO3Ch.
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Figure 2. EDS image of g-C3N4@SO3Ch.
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Figure 3 SEM image of g-C3N4@SO3Ch.
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Figure 4. FT-IR of g-C3N4 (a) and g-C3N4@SO3Ch (b)
Figure 5 DSC and TG thermograms
1
2
3
4
5
Number of Cycles
Figure 6 Recyclability study of the g-C3N4@SO3Ch
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CRediT author statement
NajmedinAzizi: Writing- Original draft preparation, Supervision, Writing- Reviewing and
Editing.
Mahtab Edrisi: Methodology, Data curation.
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Declaration of Interest
☒ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests:
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Graphical abstract
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Highlights





Highly active ionic mesoporous graphitic carbon nitrides were prepared.
Enhancement of surface properties of carbon nitride by the choline sulfate ionic liquid.
This approach appears as a promising route to prepare highly ionic g-C3N4.
Superior catalytic activities to other mesoporous materials.
The IL-C3N4 composite was recycled several times without loss in its activity.
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