Ultrasound/visible light-mediated synthesis of N-heterocycles using g-C3N4/Cu3TiO4 as sonophotocatalyst

Article abstract of DOI:10.1007/s11164-021-04461-3

In this investigation, novel g-C₃N₄/Cu₃TiO₄ (CNCT) nanocomposite was synthesized by using a simple thermal condensation method. The synthesized CNCT nanocomposite was characterized by X-ray Diffraction, Transmission electron microscopy, Atomic force microscopy, Energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectroscopy, Photoluminescence, Brunauer–Emmett–Telle, Zeta Potential, and Thermogravimetric analysis. The study revealed that the catalysts prepared have high crystalline nature, optical light-absorbing property, high surface area, and stability. The CNCT- nanocomposite was found to be an extraordinary visible light absorbing catalyst for the synthesis of quinoxaline and quinazolinone derivatives, which have important benefits in a variety of drug applications. Quinoxaline and quinazolinones were prepared from anthranilamide, diamines, benzil, and corresponding aldehydes under Ultrasonic/visible light-medium with a notable amount of g-C₃N₄/Cu₃TiO₄. The results exhibit good and excellent yields of product derivatives at mild conditions under Ultrasonic/visible light-medium. Ultrasounds always clean the active site catalyst, promoting activity and reusability. Most notably, with preserved reactivities, this heterogeneous g-C₃N₄/Cu₃TiO₄ composite can be used atleast 5 times. Furthermore, we examined the reusability of the catalyst under Ultrasonication coupled with Visible light and in the absence of an Ultrasonication medium. Finally, advantages of the method are non-conventional approach, green solvent, reduced reaction duration, mild condition, and reusable catalyst.

Full text of DOI:10.1007/s11164-021-04461-3

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-021-04461-3
Ultrasound/visible light‑mediated synthesis
of N‑heterocycles using g‑C3N4/Cu3TiO4
as sonophotocatalyst
Murugan Arunachalapandi1 · Selvaraj Mohana Roopan1
Received: 18 January 2021 / Accepted: 29 March 2021
© The Author(s), under exclusive licence to Springer Nature B.V. 2021
Abstract
In this investigation, novel g-C3N4/Cu3TiO4 (CNCT) nanocomposite was syn-
thesized by using a simple thermal condensation method. The synthesized CNCT
nanocomposite was characterized by X-ray Difraction, Transmission electron
microscopy, Atomic force microscopy, Energy-dispersive X-ray spectroscopy, X-ray
photoelectron spectroscopy, UV–vis difuse refectance spectroscopy, Photolumines-
cence, Brunauer–Emmett–Telle, Zeta Potential, and Thermogravimetric analysis.
The study revealed that the catalysts prepared have high crystalline nature, optical
light-absorbing property, high surface area, and stability. The CNCT- nanocompos-
ite was found to be an extraordinary visible light absorbing catalyst for the synthesis
of quinoxaline and quinazolinone derivatives, which have important benefts in a
variety of drug applications. Quinoxaline and quinazolinones were prepared from
anthranilamide, diamines, benzil, and corresponding aldehydes under Ultrasonic/
visible light-medium with a notable amount of g-C3N4/Cu3TiO4. The results exhibit
good and excellent yields of product derivatives at mild conditions under Ultrasonic/
visible light-medium. Ultrasounds always clean the active site catalyst, promoting
activity and reusability. Most notably, with preserved reactivities, this heterogeneous
g-C3N4/Cu3TiO4 composite can be used atleast 5 times. Furthermore, we examined
the reusability of the catalyst under Ultrasonication coupled with Visible light and
in the absence of an Ultrasonication medium. Finally, advantages of the method are
non-conventional approach, green solvent, reduced reaction duration, mild condi-
tion, and reusable catalyst.
Keywords G-C3N4 · Cu3TiO4 · Visible light · Quinoxaline · Quinazolinone
* Selvaraj Mohana Roopan
mohanaroopan.s@vit.ac.in
1
Chemistry of Heterocycles and Natural Product Research Laboratory, Department of Chemistry,
School of Advanced Sciences, Vellore Institute of Technology, Vellore, Tamil Nadu 632 014,
India
Vol.:(0123456789)
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M. Arunachalapandi, S. M. Roopan
Introdction
Heterocycles are mostly used in the feld of medicinal chemistry. Heterocycles
motifs of quinazolinones and quinoxalines are present in drugs such as luoto-
nine, Rutaecarpin, Tryptanthrin, Chloroqualone, and alloqualone [1, 2]. The core
structure of quinazolin-4(3H)-ones and quinoxaline makes them interconvertible
in heterocycles family. Quinoxalines have enormous applications in antibacterial,
antidiabetic, antimalarial, and antifungal properties [3–5]. Hence quinoxaline
and quinazolinone were used as a template for the development of many drugs
[6]. Biological applications of quinazolinone show remarkable properties such as
high molar extinction coefcient, absorption, fuorescence emission, and fuores-
cence quantum yield [7]. An additional property of quinazolinones was an optical
character in light-emitting diodes, cell imaging, and sensors [8]. Already plenty
of preparation techniques were published for the synthesis of quinoxaline and
quinazolinones. We have the challenge to produce a new method to prepare these
compounds which is an easy and better method to compare with others. Here we
introduce a new nonconventional approach for the preparation of quinazolinone
with the use of ultrasonication/visible light with a 20% CNCT catalyst.
In this decade, nanoparticles gained more attention to scientists to do more
attractive innovations (Sensors, semiconductors, nanobots, photocatalysts, etc.).
Homogeneous and Heterogeneous catalysts are mostly used in organic reactions
to enhance the reaction [9]. Some of the drawbacks present in homogeneous cata-
lysts such as reusability, removal from the reaction mixture, and stability in the
reaction medium are difcult. On the other hand, heterogeneous catalysts can eas-
ily overcome all these problems and produce excellent lower activation energy for
the reaction. Here, heterogeneous catalyst was used to carry out the condensation
reaction in presence of light and sound [10].
Graphitic carbon nitride (g-C3N4) a polymer material is rich in carbon and
nitrogen atoms. Recently, g-C3N4 has gained more attention and it is mostly used
to bind with metal nanoparticles which are used for the photocatalytic degradation
of pollutants, CO production, biosensors, semiconductors, etc. [11]. In organic
synthesis, the g-C3N4 assisted CNCT material showed great promise in photoca-
talysis, with excellent visible light properties (eV = 2.7), high stability, efcient
reusability, ease of removal from the reaction mixture, and good semiconduc-
tor properties [12]. In the past fve decades, photocatalytic titanium dioxide was
invented by Honda and Fujishima for splitting water [13]. After that TiO2 has
applied for many organic reactions such as degradation of organic dyes, cycload-
ditions, oxidation, reduction, and cross-coupling reactions [14]. Titania (TiO2) is
a UV light active material (3.1 eV) that is easily available and costless material.
Normally, CuO and TiO2 are not much active in the visible region. By coating the
semiconducting material Cu3TiO4, on the polymeric surface of g-C3N4 made it
active in visible light. In this study, heterocycles were synthesized in the presence
of CNCT using ultrasonication and visible light.
1 3

Ultrasound/visible light‑mediated synthesis of…
Materials and methods
Chemicals utilized
The Citrus Lemons were collected from Vellore local market shop, Vellore, Tamil
Nadu, India. All chemicals were purchased from AVRA, chemical Pvt. Ltd, and
Hyderabad. Throughout the experiment process, we utilized double distilled water
without any further purifcation.1H NMR and 13C NMR spectra were taken by using
500 MHz Bruker DRX-500 and TMS as an internal standard.
Preparation of extract
The lemon extract was prepared using the conventional method [15]. 50 mL of liquid
lemon juice was centrifuged at 10,000 rpm. The aqueous solution was collected and
stored for future usage. The pulp and other impurities were separated.
Synthesis of g‑C3N4
g-C3N4 was prepared by a simple condensation method [16]. The parent compound
melamine monomer was used to prepare g-C3N4 polymer. About 5 g of melamine pow-
der was heated at 550 °C for 4 h. The formation of the polymer was confrmed by a
change of color white to yellow. The collected yellow precipitate was crushed in mortar
pestle and made into fne crystals.
Synthesis of Cu3TiO4
1 M copper acetate was dissolved in 50 mL of deionized water and added 1 M of
titanium butoxide dropwise into the solution with constant stirring. The solution was
stirred with 5 mL of lemon extract for 2 h. Here bluish-white color precipitate was
obtained after 1 h. Then the precipitate was kept in a water bath. The precipitate was
washed with deionized water followed by ethanol and then calcinated for 4 h at 500 °C.
Synthesis of CNCT
About 0.1 g of prepared Cu3TiO4 and 0.9 g of g-C3N4 were mixed in diferent ratios
(Table. S1), with 5 mL of water and this mixture was kept in stirring for 2 h. The
obtained suspension was sonicated for 20 min via ultrasonication. Then, the solution
was kept for drying on a hot-air oven 50 °C. Finally, obtained light blackish yellow pre-
cipitate was calcinated at 300 °C for 2 h.
1 3

M. Arunachalapandi, S. M. Roopan
General procedure for the synthesis of quinoxalines (1.3a–1.3l)
Method A
Benzil 1.1 (1 mmol), O-phenylinediame 1.1 and (2 mmol) 40 mol% of 20% CNCT
in ethanol (5 mL) was taken in a boiling tube. The reactants were stirred at 45 °C
in an oil bath. Thin Layer Chromatography (TLC) is a tool to fnd out the reaction
completion. After completion of the reaction from TLC hot ethanol was added to the
reaction mixture. The solution was fltered which leads to separate the catalyst. Then
the remaining fltrate was poured into cool water to get solid. The precipitate was
separated and recrystallized from hot ethanol to obtain the fnal compound.
Method B
As per method A, the same quantity of the reactants were taken and placed in an
ultrasound/visible light for 10 min (Table 1, entry 10). Reaction workup and purif-
cation were done as per method A.
General procedure for the synthesis of dihydro quinazolinone
(2.3a–2.3h)
For the preparation of quinazolinone, a similar procedure optimized for the quinoxa-
line 2.3 was followed. The reactants used for this preparation were anthranilamide
2.1 (1 mmol), benzaldehyde 2.2 (1 mmol), 20% CNCT (40 mol%), solvent (5 mL)
for 10 min.
Characterization
X-ray difraction (XRD) patterns were obtained from The Bruker, D8 advance PC
system with Cu Kα (λ=1.544) as X-ray source. The range to carry out the output
was 10°–90° (2θ). The morphology of the prepared samples were characterized by
Transmission electron microscope (TEM) Tecnai G2-20 instrument. Bruker EDX
with LN2 free detector was employed to conduct EDAX analyses. On using Quanta
chrome analyser, the surface area assessment of the acquired nanocomposite was
established at 77.35 K by N2 adsorption/desorption isotherm. Samples of 0.1262 g
analyzed fx fnal gas temperature at 200 °C. The BET surface area was calculated
by a multi-point BET isotherm, whereas the BJH method was used to measure the
Table 1 Stability comparison of
Entry
Compound
Zeta value (mV)
Nature
prepared nanocomposite
1
2
3
g-C3N4
Cu3TiO4
20% CNCT
−33.6
−33.9
−34.7
Good stable
Good stable
Good stable
1 3

Ultrasound/visible light‑mediated synthesis of…
pore size distribution. Zeta potential (HORIBA SZ-100) was used to record the sta-
bility and surface charge of the constructed nanocomposite. PHI 5000 Versa Probe
III instrument was employed to record X-ray photoelectron spectroscopy (XPS) with
reference to the C 1s peak (282.8 eV). The thermogravimetric and diferential scan-
ning calorimetry (TG-DSC) were analysed at 20 °C min−1 to 800 °C in the air by
using an SDT Q600 analyzer. Jasco V-670 spectrometer was employed to record the
difuse refectance absorption spectra (DRS). FLSP920 (Edinburgh, UK) spectro-
scope was used to record the photoluminescence (PL) spectra. The F-7000 FL spec-
trophotometer with an equipped excitation wavelength of 280 nm was used to collect
the photo-luminescence spectrum.The excitation wavelength was 447 nm.
Results and discussion
Among all the catalysts, 20% CNCT showed better yield than others (Cu3TiO4,
5% CNCT, 10% CNCT, 30% CNCT). Therefore, 20% CNCT was used for further
characterisation. The phase purity and crystalline nature of synthesized CNCT
nanocomposite were analysed using X-Ray Difraction (XRD) analysis. XRD pat-
tern for the prepared g-C3N4, Cu3TiO4 and CNCT nanocomposites is shown in
Fig. 1a. XRD pattern of Cu3TiO4 was indexed as (004) (101) (102) (106) and (110)
o
found at θ=86.4, 54, 69.1, and 32.5 for Cu3TiO4 nanocomposite (JCPDS Card
no. 83–1285). Cu3TiO4 nanospheres were used for the further binding with g-C3N4
like 5%, 10%, 20%, and 30% (Fig. 1b). In 5% CNCT XRD shows the same mirror
image of g-C3N4. Slightly Cu3TiO4 peaks appears in 10% CNCT and then increase
the intensity in 20% & 30% CNCT. The crystalline size and strain were calculated
using Scherer formula, which is 47.4 nm. Two peaks absorbed at the region of 13.2°,
27.4° were indexed as (110) and (002) for g-C3N4 (JCPDS, 87-1526). The XRD of
the combined 20% CNCT nanocomposite perfectly match with its individual XRD
of g-C3N4, TiO2, CuO, and Cu3TiO4 (Fig. 1).
Fig. 1 a XRD of Cu3TiO4, g-C3N4, and 20% CNCT b XRD of CNCT composites synthesized at diferent
concentrations
1 3

M. Arunachalapandi, S. M. Roopan
To check the stability nature of 20% CNCT nanocomposite zeta potential analysis
was used. In the present study, 20% of CNCT nanocomposites were having a good
surface charge as shown in Table 1. The zeta potential value for 20% CNCT and
Cu3TiO4 nanospheres was − 34.7 mV and − 33.9 mV (Table 1, Entry 2, 3) which
indicated that the prepared nanocomposite possesses high stability.
Transmittance Electron Microscope (TEM) study has shown the surface mor-
phology of 20% CNCT (Fig. 2). Here, TEM images of 1% Cu3TiO4 nanospheres
are given in Fig. 2a. This image showed sphere-like morphology of Cu3TiO4. After
binding, the spheres of Cu3TiO4 were deposited on the sheets of g-C3N4, (Fig. 2c).
Particle size for Cu3TiO4 was observed at around 47 nm from XRD results which
was confrmed in TEM images. Figure 2b shows the clear sheets of g-C3N4 with-
out support. After binding Fig. 2c indicates the layered g-C3N4 was decorated by
nanospheres of Cu3TiO4. Sheets were decorated with Cu3TiO4 nanospheres that are
clearly shown in Fig. 2c. The selected area electron difraction (SAED) is shown
in Fig. 2d. SAED belongs to the plane (111) of hexagonal Cu3TiO4 in the nano-
composite, the high crystalline structure of the sample was shown by bright spots.
The SAED results were very consistent with the XRD results. Determination of
the elements present in 20% CNCT nanocomposite was done by Energy dispersive
X-ray (EDX). EDX spectrum of 20% CNCT nanocomposite is shown in Fig. 2f.
EDX spectrum indicates that the presence of target alone in the material. Moreover,
it was proved that the compound is pure and no other elements were formed. 20%
CNCT has copper, titanium, oxygen, carbon, and nitrogen (Table 2). To explain the
topological appearance of 20% CNCT nanocomposite, AFM analysis is shown in
Fig. 2e. CNCT nanocomposites revealed that Cu3TiO4 crystals were partly sprayed
on g-C3N4 surface. Crown and smooth-like pictures of g-C3N4 and CNCT are
depicted in Fig. 2e. For photocatalytic reaction, the specifc surface area of cata-
lyst can be detected from the above nitrogen adsorption–desorption isotherm values
(Table 3) of g-C3N4 and 20% CNCT sample.The minor improvement after the assis-
tance of Cu3TiO4 on the g-C3N4 surface is shown in both values (Table 3, Entry 1,
3). There is a small increase in CNCT surface area and pore volume, which means
an increase in catalyst reactant adsorption potential relative to g-C3N4.
To test the oxidation state of elements by X-ray photoelectron spectra (XPS) were
used. A survey graph of 20% CNCT nanocomposite is shown in Fig. 3a, it repre-
sents the major elements of C1s, N1s, Cu2p, Ti2p, and O1s. As stated in Fig. 3b,
the asymmetrical and large characteristics of C1s XPS peaks observed indicates that
distinguishable versions co-exist. Sp2-hybridized carbons (C–C) produced a sharp
peak at the range of 284.6 eV [17]. 398.8 eV-centered peak is for sp2 N involved in
triazine rings (Fig. 3c), while 399.6 eV peak corresponded to C bridged nitrogen
atoms. Cu(I) bonded with oxygen atoms is executing a sharp peak at 133,1 eV.Cu(II)
peaks presence (Fig. 3d) was confrmed at 941.8 eV, 953.3 eV, 964.7 eV. Here the
confrmation of Cu(I) and Cu(II) atoms were present in 20% of CNCT. As seen from
Fig. 3e, we fnd that XPS peaks of Ti2p exhibit two signal peaks at 458.2 that were
attributed towards the Ti4+ species. Figure 3f attributed to O1s corresponds to two
sharp peaks at 529.6 and 531.4 eV, which shows the presence of O atoms.
Ultraviolet (UV) visible spectroscopy is a tool to identify the absorption region
of synthesized nanocomposites. In the present study, 20% CNCT, g-C3N4, Cu3TiO4
1 3

Ultrasound/visible light‑mediated synthesis of…
Fig. 2 TEM images of a 1% Cu3TiO4 nanospheres, b g-C3N4, c 20% CNCT, d SAED patterns of 20%
CNCT, e EDX spectrum of 20% CNCT, f AFM analysis of 20% CNCT nanocomposites
1 3

M. Arunachalapandi, S. M. Roopan
Table 2 The amount of
Entry
Element
Serious
wt%
elements in 20% CNCT
1
2
3
4
5
Carbon
Nitrogen
Copper
Titanium
Oxygen
K-serious
K-serious
K-serious
K-serious
K-serious
43.01
15.22
1.45
23.71
16.61
Table 3 Surface studies of 20%
CNCT nanocomposite wit BET
analysis
Entry Compound Surface area Pore
Pore diameter (Å)
volume
(cc/g)
1
2
3
g-C3N4
Cu3TiO4
20% CNCT 15.238
14.209
2.739
0.075
0.016
0.085
18.991
6.922
18.968
were analyzed using the UV-DRS spectrum as shown in Fig. 4a. The UV spectrum
shows no absorption peak maximum for Cu3TiO4. After binding with g-C3N4, it has
a strong peak at 384 nm. From Tauc’s plot (Fig. 4b) we can calculate the energy gap
(bandgap) value 2.68 eV corresponding to 20% CNCT. This shows the 20% CNCT
have high activity in the visible region.
An indicator of electron–hole recombination rate for 20% CNCT nanocompos-
ite with photoluminescence (PL) spectrum. 20% CNCT shows widespread emission
peak at 430–470 nm, transition indicates the oxygen vacancies in the nanocompos-
ite. Here absorbance intensities are directly related to the recombination rate of the
catalyst. Figure 5 spectra show 20% CNCT has less intense peaks when compared
to the g-C3N4 and Cu3TiO4 peaks. That is evidence for the suppression of elec-
tron–hole pair recombination and charge carriers separation in 20% CNCT [17–19].
Thermogravimetric analysis (TGA) is an analytical tool used to assess the ther-
mal stability of a substance. TGA analysis of the prepared nanocomposite is shown
in Fig. 6. 20% CNCT and g-C3N4 are having a lower difusion temperature than
Cu3TiO4 nanospheres. Figure 6 shows a strong evidence that our catalyst doesn’t
have any impurities (hydrocarbon, water, hydroxyls, etc.). Because 20% CNCT,
g-C3N4, and Cu3TiO4 are don’t have any difusion point upto 600 °C. In Fig. 6 a
straight line indicates no difusion point for the Cu3TiO4 nanospheres. For g-C3N4,
after 600 °C has strong difusion and produce 0.6 wt% residue of carbon. In the case
of 20% CNCT the same difusion begins after 600 °C but 20 wt% residue remains. It
informs the formation of CNCT.
Benzil 1.1 and diamines 1.2, as a model reaction (Scheme 1) we have done 18
trials conducted to determine the conditions for the reaction. We attempted to refne
the model process (method A) to describe the efciency of several classic condi-
tions for comparison. In each case of ultrasonic irradiation (40 kHz) conditions,
ethanol was used as a solvent and tipping the ultrasonic rod was dipped into the
reaction mixture. The formation of product 1.3 was easier among the solvents tested
1 3

Ultrasound/visible light‑mediated synthesis of…
Fig. 3 XPS survey spectrum of a prepared 20% CNCT and the corresponding high-resolution XPS spec-
tra of b C1s, c N1s, d Cu 2p, e Ti 2p, f O 1s
such as ethanol, H2O, tetrahydrofuran (THF), dichloromethane (DCM), and solvent-
free condition. Scheme 1 also produces a moderate yield in water (Table 4, Entry
11). But ethanol produced more yield than water. Therefore, ethanol was taken as
a primary solvent for Schemes 1 and 2. Scheme 1 was performed in acetonitrile,
THF, and DCM the target product was separated at 50%, 50%, and 63%, respectively
(Table 4, Entries 12, 13, 14). The products 1.3 and 2.3 were not obtained without the
catalyst conditions (Table 4, Entry 15). To check the efciency of ultrasound/vis-
ible light irradiation, Scheme 1 was also carried out by the conventional method of
1 3

M. Arunachalapandi, S. M. Roopan
Fig. 4 a UV visible spectrum of Cu3TiO4, g-C3N4, and 20% CNCT, b bandgap image of 20% CNCT
nanocomposite
Fig. 5 Photoluminescence spec-
trum of 20% CNCT at diferent
concentration
heating at 45 °C in with ethanol (Table 4, Entries 1, 2, 3, 4). Ultrasound and visible
light conditions give more yields at a minimum time of 3–5 min (Table 4, Entry 10).
A comparatively minimum yield is absorbed in light-free reaction condi-
tions, as shown in Table 4, Entry 7. We found that the presence of visible light,
as shown in Table 4—Entry, 6, 8, and 11 could increase the reaction produc-
tion and shorten the reaction time. The above studies revealed that this reaction
had a remarkable ultrasonic temperature efect. Scheme 1 was also carried out
at 30, 40, and 50 kHz to validate the efect of frequency in the reaction. With
an increase in the level of irradiation from 40 to 50 kHz, the reaction yield did
not change substantially (98% in a similar time, Table 4, Entry 10). The perfor-
mance of CNCT was carried out under ultrasound/visible light irradiation. For
1 3

Ultrasound/visible light‑mediated synthesis of…
Fig. 6 Termogravimetric analy-
sis of 20% CNCT
Scheme 1 Synthesis of quinoxalines
5% CNCT produced 56% of 1.3. 10% CNCT has increased the yield of 1.3 upto
76%. Further, 20% CNCT with ultrasound/visible light irradiation shown a 98%
yield. Photoluminencence spectra of 20% CNCT have an excellent electron–hole
recombination rate. Then 30% CNCT also produced the same activity like 20%
CNCT to yield 98% of the product. 20% CNCT was investigated in Schemes 1
and 2 for many substituted aryl or heteroaryl aldehydes, benzil, and diamines
with ethanol (Table 4, Entry 15). When the reaction was conducted using con-
ventional methods, the product was good but the reaction time was longer. There-
fore, it was observed that ultrasonic irradiation had a benefcial impact on the
synthesis of quinoxaline derivatives. Once we got the best reaction condition to
carry out Scheme 1 with 98% of yields with 11 derivatives (Table 5). In Fig. 7
the reaction begins on the surface of g-C3N4. 1.1 has two active O2 sites where
the reaction is initiated. 1.2 which has a lone pair of electron in N-atom reacts
with the active sites to form a hydroxyl radical, releasing a water molecule and
fnally forming the fnal product 1.3. The same condition was used to carry out
Scheme 2 for the preparation of di-hydroquinazolinones in visible light/ultrasoni-
cation. This reaction was taken by carrying out in the absence of (Light/sound) at
70 °C for 45 min where 77% of yields were obtained. Then we proceed to carry
1 3

M. Arunachalapandi, S. M. Roopan
Table 4 Optimization for the synthesis of quinoxalines under ultrasonic and visible light irradiation
Entry
Catalyst
Solvent
Reaction condition
Time
Yield
1
2
3
4
5
6
7
8
CuO
TiO2
Cu(OAc)2
Zn(OAc)2
g-C3N4
ETOH
ETOH
ETOH
ETOH
ETOH
ETOH
ETOH
ETOH
ETOH
ETOH
H2O
DCM
Acetonitrile
THF
ETOH
ETOH
ETOH
ETOH
Δ
Δ
Δ
Δ
8 h
8 h
8 h
8 h
90 min
90 min
8 h
90 min
30 min
10 min
90 min
8 h
8 h
8 h
8 h
10 min
10 min
10 min
63
32.5
27.5
26
No reaction
72
80
92
88
98
79
63
50
50
Visible light
Visible light
Δ
Visible light
Ultrasonication
Ultrasonication/visible light
Visible light
Δ
Δ
Δ
Δ
Cu3TiO4
20% CNCT
20% CNCT
20% CNCT
20% CNCT
20% CNCT
20% CNCT
20% CNCT
20% CNCT
Without
9
10
11
12
13
14
15
16
17
18
No reaction
5% CNCT
10% CNCT
30% CNCT
Ultrasonication/visible light
Ultrasonication/visible light
Ultrasonication/visible light
56
76
98
Scheme 2 Synthesis of quinazolinones
out in the presence of visible light where within~ 10 min products were obtained
with 97% of yields. Sonication was introduced to increase the efciency of cata-
lysts in recyclability. Without sonication, the frst reaction gave excellent yields
in 10 min. But a slight decrease in efciency of the catalyst was seen in the next
runs. This happened when the reactants attacked g-C3N4 active sites to reduce the
activity. But in presence of sonication, g-C3N4 surface was refreshed to reduce
the reactants blocking the active sites. Sonication plays a vital role in this reac-
tion to increase the reusability of CNCT. The reaction occurred on the surface
of 20% CNCT nanocomposites in ~ 5 min. Eight diferent derivatives including
electron-donating, electron-withdrawing, and halogen compound were prepared
in visible light and the ultrasonication method is shown in Table 6.
Because of its excellent photocatalytic behavior, nanocomposites supported
with g-C3N4 were used as photocatalysts for the synthesis of quinazolinone and
1 3

Ultrasound/visible light‑mediated synthesis of…
Table 5 CNCT catalysed synthesis of Quinoxalines under ultrasonic and visible light irradiationa
Product
R1
R2
Time (min)
Yieldb
Melting point
TONd
TOFd
US/visc
Δc
Found
Ref.
1.3a
1.3b
1.3c
1.3d
1.3e
1.3f
1.3g
1.3h
1.3i
1.3j
1.3k
H
H
H
H
CH3
CH3
CH3
CH3
Br
Br
Br
H
CH3
Cl
NO2
H
CH3
Cl
NO2
H
Cl
5
5
5
3
5
5
5
3
5
5
3
98
92
89
95
91
89
88
93
92
93
83
23
21
13
43
32
29
12
38
17
15
33
125–126
120–122
121–122
139–142
146–147
129–130
115–117
121–123
131–134
117–119
112–113
[20]
[20]
[20]
[20]
[20]
[20]
[20]
[20]
[20]
[20]
[20]
6.2
5.8
5.6
6.0
5.11
5.00
4.95
4.29
3.35
3.38
3.02
1.24
1.16
1.13
2.01
1.02
1.00
0.99
1.433
0.67
0.67
1.00
NO2
aReaction condition: benzil (1 mmol), diamine (2 mmol), catalyst (40 mg) were simultaneously treated
with ultrasonic and visible light irradiation
bIsolated yields
cUS ultrasonic, VS visible light, Δ conventional heat
dTON turn over number, TOF turn over frequency
Fig. 7 Possible mechanism in synthesis of Quinoxalines under ultrasonic and visible light irradiation
1 3

M. Arunachalapandi, S. M. Roopan
Table 6 CNCT catalysed synthesis of dihydroquinazolinones under ultrasonication/visible light
irradiationa
Product
R1
Time (min)
Yieldb
US/visc
Melting point
Found
TONd
TOFd
Δc
Refs.
2.3a
2.3b
2.3c
2.3d
2.3e
2.3f
2.3h
H
5
5
3
3
5
5
3
84
81
98
95
82
89
91
19
23
31
43
32
29
27
216–217
173–174
195–195
183–184
194–195
166–167
190–192
[21]
[21]
[23]
[22]
[21]
[23]
[22]
8.2
7.9
9.6
9.3
8.06
1.75
2.98
1.65
1.59
3.21
3.11
1.61
1.75
2.98
OCH3
4-Br
3-Br
4-NO2
3-NO2
4-Cl
aReaction condition: anthranilamide (1 mmol), corresponding aldehyde (1 mmol), catalyst (40 mg) were
simultaneously treated with ultrasonic and visible light irradiation
bIsolated yields
cUS ultrasonic, VS visible light, Δ conventional heat
dTON turn over number, TOF turn over frequency
quinoxaline derivatives. Here, the use of sonication was to refresh the active sites of
a g-C3N4 surface to produce more cycles. Without sonication also the reaction pro-
duces good yields up to~97% in visible light. At that time the reusability of catalyst
efciency also varied (Fig. 8). Mainly sonication activates the catalyst surface and
produces more amount of active sites in 1.1. Cavitations also reduce the activation
energy barrier and give the fnal products 1.3, 2.3.
Finally, the recovered catalyst from the reaction mixture (Schemes 1, 2) was
washed two times with ethanol and one time with water. After washing, the
CNCT nanocomposite was dried at 60 °C. This catalyst was used for the same
reaction several times without losing its catalytic activity. 20% CNCT shows good
activity for the next fve cycles as shown in Fig. 8. Compared to the reusability
Fig. 8 Reusability of with and
without sonication
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Ultrasound/visible light‑mediated synthesis of…
cycle with and without the sonication test is slightly diferent, sonication exhibit
excellent sonophotocatalytic response.
Conclusion
In conclusion, we have developed a heterogenous g-C3N4/Cu3TiO4 catalyst as a
non-toxic and accessible catalyst. A quick and clean reaction of dihydro-quina-
zolinone and quinoxaline compounds prepared from benzil, diamines, and alde-
hydes in ethanol under ultrasound with visible light irradiation was documented.
Ultrasonication cleans the active sites in the catalyst surface to enhance the reus-
ability of g-C3N4/Cu3TiO4. The process is straightforward, begins from readily
available commercial starting materials, and provides reasonable yields for bio-
logically interesting goods. The current study demonstrates the benefts of Ultra-
sound/Visible light assisted heterogeneous catalysis in the synthesis of heterocy-
cles, which are commonly appreciated in a wide range of applications, especially
medicinal chemistry and drug development. Furthermore, while heterogeneous
catalysis has been known for over a century, recent advances in material science
have resulted in a detonation of new functional solid catalysts.
Supplementary Information The online version contains supplementary material available at https://
doi.org/10.1007/s11164-021-04461-3.
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