An efficiently and quickly synthesized NiO@g-C3N4 nanocomposite-catalyzed green synthesis of spirooxindole derivatives

Article abstract of DOI:10.1007/s11164-019-03951-9

NiO@g-C₃N₄ as an efficient catalyst for the synthesis of spirooxindole derivatives was prepared by impregnation of g-C₃N₄ with NiO nanoparticles and characterized by various techniques including thermogravimetri

Full text of DOI:10.1007/s11164-019-03951-9

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-03951-9
An efciently and quickly synthesized NiO@g‑C3N4
nanocomposite‑catalyzed green synthesis of spirooxindole
derivatives
Zahra Amini Moqadam1 · Ali Allahresani2 · Hassan Hassani1
Received: 15 February 2019 / Accepted: 8 August 2019
© Springer Nature B.V. 2019
Abstract
NiO@g-C3N4 as an efcient catalyst for the synthesis of spirooxindole derivatives
was prepared by impregnation of g-C3N4 with NiO nanoparticles and characterized
by various techniques including thermogravimetric analysis, transmission electron
microscopy, X-ray difraction and Fourier transform infrared spectroscopy. The one-
pot synthesis of spirooxindole derivatives using 1 mmol isatin, 1 mmol dimedone
(or 4-hydroxycoumarin or ethyl acetoacetate) and 1 mmol malononitrile was car-
ried out in the presence of 50 mg NiO@g-C3N4 in EtOH media at refux condi-
tions. The results showed that both series of reactions had short reaction times (less
than 7 min) and high reaction efciency (greater than 87%). Some advantages can
be cited for this method, including short reaction time, excellent yields, easy workup
and a reusable and inexpensive nanocatalyst.
Keywords 4-Hydroxycoumarin · Dimedone · Isatin · Malononitrile · NiO@g-C3N4 ·
Spirooxindole derivatives
Introduction
The signifcance of indole and its derivatives is well recognized by synthetic
organic chemists and biologists [1]. The indole ring system is the most ubiqui-
tous heterocycle in many biological systems usually found in nature [2] as well
as in many compounds with pharmaceutical and biological activity [3]. There-
fore, remarkable eforts have been made to synthesize analogs of di-indolyloxin-
doles as a variety of indole derivatives. Di-indolyloxindoles are naturally found
* Hassan Hassani
Hassaniir@yahoo.com
1
Department of Chemistry, Payam Noor University, Mashhad, Iran
2
Department of Chemistry, Faculty of Sciences, University of Birjand, P.O. Box 97175-615,
Birjand, Iran
Vol.:(0123456789)
1 3

Z. Amini Moqadam et al.
in medicinal plants and possess biological properties such as anti-infammatory,
anti-bacterial, anti-protozoal and laxative efects [4]. These compounds were pre-
pared by the reaction of indoles with isatin or its derivatives [5], pyrazolones [6],
aromatics in trific acid [7] and other ways [8]. Despite various methods reported
for the synthesis of oxindole derivatives (using a broad range of catalysts such
as TfOH, Bi(OTf)3, silica sulfuric acid, montmorillonite-K10 clay, KSF, Amber-
lyst-15, FeCl3, I2, ceric ammonium nitrate, phosphotungstic acid, ionic liquids
and boron trifuoride supported on nano-SiO2 [9]), there are still limitations for
this purpose including the use of toxic solvents and heavy metals.
With the development of nanoscience and nanotechnology, nanoparticulate
catalysts like metal oxides have attracted signifcant attention in organic trans-
formations [10]. One possibility to expand the application of metal oxides as
catalysts is to tailor their sizes in nanodimensions and consequently their sur-
face chemistry and catalytic properties. As one of the metal oxides, nickel oxide
nanoparticles have attracted much attention as inexpensive and nonhazardous
catalysts or benefcial promoters that can increase the reactivity and selectivity
of diferent organic reactions [11, 12]. A number of examples are available in the
literature where nickel-based nanoparticles have been employed as catalysts dur-
ing organic transformations [13, 14]. These nanoparticles may be considered as
promising, safe and reusable catalysts compared to traditional catalysts because
they are often recovered easily by simple workup which prevents the contamina-
tion of products [15].
A considerable challenge in handling the nanoparticles in polar solvent is the
propensity of nanoparticles to aggregate rapidly into micrometer-sized particles
due to van der Waal forces. The mentioned problem can be greatly resolved by
decoration of nanoparticles onto the surface of supporting materials. This method
signifcantly reduces the nanoparticles accumulation and leads to the larger sur-
face area and superior properties for the obtained composites compared to the
bare nanoparticles. In recent years, graphitic carbon nitride (g-C3N4) nanosheets
have been known as a good candidate for supporting nanoparticles and the prepa-
ration of composite materials [16–20]. These 2D nanosheets possess advantages
such as high stability in acid to alkali aqueous solutions, large surface areas, non-
toxicity, easy functionalization, high thermal stability, specifc physical features,
simple recycling and acceptable biocompatibility [21, 22]. It is worth consider-
ing that the immobilization of metal oxide nanoparticles onto g-C3N4 improves
the catalytic activity by advancing the charge separation at the interface of metal
oxide nanoparticles’ heterojunction and also by limiting the aggregation of nano-
particles [23, 24]. Recently, Allahresani et al. [25, 26] have reported a three-com-
ponent synthesis of cyclic 1,3-diketones, isatin and malononitrile catalyzed by
GN/SO3H and SiO2@g-C3N4.
Regarding all of the matters discussed up to now, we predicted a great catalytic
performance for NiO@g-C3N4 nanocomposite. Thus, in this work, we report the
synthesis of spirooxindole derivatives by coupling of isatin and malononitrile with
cyclic-1,3-diketone or 1,3-diketoesters or 4-hydroxycoumarin using a NiO@g-C3N4
nanocomposite as a heterogeneous efcient catalyst via a multicomponent reaction
in an aqueous medium (Scheme 1).
1 3

An efciently and quickly synthesized NiO@g‑C3N4…
Scheme 1 Synthesis of spirooxindole derivatives in the presence of NiO@g-C3N4 nanocomposite
Experimental
Materials
All reagents were commercial reagent grade and were purchased from Merck
Company and used without further purifcation. FT-IR spectra were recorded in
the range 400–4000 cm−1 on a Bruker Vector-22 FT-IR spectrometer (AVATR-
370) in a KBr pellet. All NMR spectra (13C and 1H) were measured at room tem-
perature, at 250 MHz and 62.9 MHz in DMSO-d6 using tetramethylsilane (TMS)
as an internal standard, using a Bruker DPX-250 Advance instrument. X-ray dif-
fraction (XRD) patterns are obtained from a Bruker D8-advance X-ray difrac-
tometer with Cu Ka radiation (k = 1.5406 Å). The transmission electron micros-
copy (TEM) images of the heterogeneous catalyst were recorded using a Philips
CM10 instrument. TGA patterns of the samples were recorded using PerkinElmer
Diamond TG/DTA thermal analyzer by heating the samples in an argon fow at a
rate of 100 mL min−1 with a heating rate of 10 °C min−1, and a Mira 3TEScan-
XMU scanning electron microscope was used for the scanning electron micros-
copy (SEM) images.
Catalyst preparation
To synthesize the NiO@g-C3N4 nanocomposite, in a typical procedure, fne
powdered NiO (0.2 g) was well dispersed in 80 mL of deionized water for 1 h
(mixture 1). Melamine (4.5 g) was also dissolved in a mixture of 5 mL of EtOH
and 15 mL deionized water (mixture 2). Then, mixture 2 was added to mixture
1 and the fnal mixture was stirred at room temperature for 20 h. The mixture
was heated at 60 °C to dryness. Finally, the prepared nanocomposite was heated
in an alumina crucible with a cover in a mufe furnace at a rate of 2 °C min−1
under air conditions until reaching 550 °C and held at this temperature for 4 h.
The resulting black powder was ground into fne powder and stored for further
use.
1 3

Z. Amini Moqadam et al.
General procedure for one‑pot synthesis of di‑indolyloxindole derivatives
The NiO@g-C3N4 nanocomposite (0.05 mmol) was dispersed in ethanol (3 mL)
for 30 min. 1 mmol dimedone (or ethyl acetoacetate or 4-hydroxycoumarin),
1 mmol malononitrile and 1 mmol isatin were added to the mixture which was
stirred at refux condition for the appropriate time, and the progress of the reac-
tion was monitored by thin-layer chromatography. After the completion of the
reaction, the crude product was extracted with ethyl acetate and dried over anhy-
drous Na2SO4. The pure products were recrystallized in hot ethanol and were
1
identifed by IR, H and 13C NMR spectral data. NiO@g-C3N4 nanocomposite
was separated by centrifuging, washed several times with ethanol, dried and
reused for the next run.
Spectral data for selected products
2‑Amino‑2′,5‑dioxo‑5,6,7,8‑tetrahydrospiro‑[chromene‑4,30‑indoline]‑3‑carbonitr
ile White solid; mp>250 °C; IR (KBr, cm−1): 33,537 (N–H), 3291 (N–H), 3171
(C–H, sp2), 2956 (C–H, sp3), 2209 (CN), 1710 (C=O), 1650 (N–C=O), 1477 (C–H,
1
Ar); H NMR (250 MHz, DMSO-d6), ppm: 1.95 (2H, t, CH2), 2.15 (2H, m, CH2),
2.66 (2H, t, CH2), 6.68 (1H, d, ArH), 6.87 (1H, t, ArH), 7.10 (1H, d, ArH), 7.22 (1H,
t, ArH), 7.30 (2H, s, NH2), 10.67 (1H, s, NH); 13C NMR (62.4 MHz, DMSO-d6),
ppm: 19.84, 26.82, 36.46, 46.90, 57.69, 109.204, 111.91, 117.46, 121.82, 123.30,
128.59, 134.66, 141.7, 158.75, 166.15, 178.20, 195.19.
2‑Amino‑7,7‑dimethyl‑2′,5‑dioxo‑5,6,7,8‑tetrahydrospiro‑[chromene‑4,30‑indoline]‑
3‑carbonitrile White solid; mp>250 °C; IR (KBr, cm−1): 3370 (N–H), 3317 (NH),
3141 (C–H, sp2), 2923 (C–H, sp3), 2196 (CN), 1728 (C=O), 1650 (N–C=O), 1605
1
(C–H, Ar), 1478 (C–H, Ar); H NMR (250 MHz, DMSO-d6) ppm: 0.99 (6H, s,
2CH3), 2.15 (2H, s, CH2), 2.47 (2H, s, CH2), 6.75–7/25 (4H, ArH, 2H, NH2, m),
10.31 (1H, s, NH); 13C NMR (62.9 MHz, DMSO-d6), ppm: 27.49, 28.05, 32.30,
47.28, 50.463, 57.91, 109.80, 111.31, 117.71, 122.40, 123.47, 128.55, 134.86,
142.43, 152, 159.38, 164.48, 178.428, 195.27.
2‑Amino‑1′‑benzyl‑7,7‑dimethyl‑2,5‑dioxo‑5,6,7,8‑tetrahydrospiro‑[chromene‑4,30‑
indoline]‑3‑carbonitrile White solid; mp>250 °C; IR (KBr, cm−1): 3317 (N–H),
3303 (NH), 3145 (C–H, sp2), 2917 (C–H, sp3), 2199 (CN), 1710 (C=O), 1661 (N–
1
C=O), 1602 (C–H, Ar), 1466 (C–H, Ar); H NMR (250 MHz, DMSOd6) ppm:
1.01 (3H, s, CH3), 1.09 (3H, s, CH3) 2.16–2.297 (2H, m, CH2), 2.49 (2H, s, CH2),
4.90 (2H, s, CH2-Ar), 6.69 (1H, d, ArH), 6.80(1H, t, ArH), 7.08–7.14 (2H, m,
ArH), 7.17–7.330 (3H, m, ArH), 7.30 (2H, s, NH2), 7.53 (2H, d, ArH); 13C NMR
(62.9 MHz, DMSO-d6) ppm: 27.35, 28.10, 32.40, 43.65, 47.07, 50.322, 57.2, 109.3,
111.2, 117.94, 123, 123.2, 127.56, 127.6, 127.72, 128.92, 133.7, 135.6, 144.5,
159.22, 165.65, 177.15, 194.95.
1 3

An efciently and quickly synthesized NiO@g‑C3N4…
2‑Amino‑2′0,5‑dioxo‑5,6‑dihydro‑spiro[pyrano[3,2‑c]quinoline‑4,3′‑indoline]‑3‑ car‑
bonitrile White solid; mp>250 °C; IR (KBr, cm−1): 3418 (NH), 3260 (N–H), 3140
(C–H, sp2), 2942 (C–H, sp3), 2208 (CN), 1711 (C=O), 1674 (N–C=O), 1600 (C–H,
1
Ar), 1477 (C–H, Ar); H NMR (250 MHz, DMSO-d6), ppm: 6.75 (1H, d, ArH),
6.83 (1H, t, ArH), 7.25 (1H, d, ArH), 7.44 (1H, d, ArH), 7.49 (1H, t, ArH), 7.36
(1H, t, ArH), 7.63 (1H, d, ArH), 7.72 (2H, s, NH2), 7.64 (1H, d, ArH), 10.85 (1H, s,
NH); 13C NMR (62.9 MHz, DMSO-d6), ppm: 57.24, 70.56, 101.85, 109.78, 112.76,
117.37, 117.76, 122.63, 123.10, 124.48, 125.53, 129.58, 133.63, 134.23, 142.53,
152.63, 155.58, 155.75, 158.63, 177.63.
Results and discussion
Characterizations of catalyst
The NiO@g-C3N4 nanocomposite was characterized by diferent techniques such as
TGA, TEM, XRD and FT-IR.
In the case of the TGA images of g-C3N4, the result which is shown in Fig. 1a
indicates that g-C3N4 is stable up to 550 °C, and after this temperature up to about
650 °C, decomposition or concentration of g-C3N4 nanoparticles was occurred and
then stopped. Figure 1b depicts the signifcant decrease in the decomposition range of
NiO@g-C3N4 toward g-C3N4 (occurs at 450 °C up to about 600 °C), which could be
due to the presence of g-C3N4 stenosis connected to NiO.
As can be seen in Fig. 2a, TEM image of pure g-C3N4 nanosheets showed the
agglomeration of the lamellar structure. According to Fig. 2b, c, NiO nanoparticles are
well dispersed on the surface of g-C3N4 nanosheets.
The XRD patterns of g-C3N4 and the NiO@g-C3N4 nanocomposite are shown in
Fig. 3a, b, respectively. The peaks at 13.1° (100) and 27.4° (002) can be related to
the hexagonal phase of g-C3N4, according to JCPDS 087-1526, indicating in-plane
repeated units and interlayer stacking peak of g-C3N4, respectively (Fig. 3a). Weaken-
ing of peaks at 13.1° and 27.4° in Fig. 3b refects the reduction in the g-C3N4 crystallin-
ity by the introduction of NiO nanoparticles.
As shown in Fig. 4a, the N–H bond is detected by the broad peak ranging from 3000
to 3500 cm−1. The peak at 1645 cm−1 belongs to heterocyclic C=N stretching vibration
bond, while the C–N stretching bond of tri-s-triazine assigned by the peaks centered
at 1238, 1317, 1405 and 1543 cm−1. Eventually, the sharp peak at 806 cm−1 is corre-
sponding to the out-of-plane bending vibration of triazine cycle. In Fig. 4b, the peaks
centered at 806, 1238, 1317, 1405 and 1543 cm−1 are the peaks related to g-C3N4 and
the peaks in the 450–550 cm−1 are related to NiO.
1 3

Z. Amini Moqadam et al.
Fig. 1 TGA image of g-C3N4 (a) and NiO@g-C3N4 nanocomposite (b)
Fig. 2 TEM images of g-C3N4 (a) and NiO@g-C3N4 (b 100 nm and c 50 nm)
Catalytic activity studies
Synthesis of spirooxindole
To investigate the catalytic activity of NiO@g-C3N4 nanocomposite, the synthesis
1 3

An efciently and quickly synthesized NiO@g‑C3N4…
Fig. 3 XRD images of g-C3N4
(a) and NiO@g-C3N4 (b)
Fig. 4 FT-IR spectra of g-C3N4
(a) and NiO@g-C3N4 (b)
Scheme 2 Synthesis of spirooxindoles in the presence of a catalytic amount of SiO2@g-C3N4 nanocom-
posite
of spirooxindole derivatives using 1 mmol of any initial compound (isatin, dime-
done and malononitrile) was carried out in the presence of nanocomposite (0.05 g)
as a catalyst in refux conditions (Scheme 2).
To determine the optimal amount of the catalyst, the reaction was initially per-
formed in the absence of catalyst, which did not produce any product after an
hour (Table 1, entry 1). The control reaction in the presence of g-C3N4 (50 mg)
1 3

Z. Amini Moqadam et al.
Table 1 Efect of diferent
amounts of NiO@g-C3N4
nanocomposite as a catalyst on
yield (%) of spirooxindole
Entry
NiO@g-C3N4 (g)
Time (min)
Yielda (%)
1
0
60
60
10
10
8
7
7
5
2
Trace
Trace
42
47
50
58
80
83
93
2b
3
0.05
0.005
0.01
0.02
0.03
0.04
0.045
0.05
0.055
4
5
6
7
8
9
10
2
93
Reaction conditions: isatin (1 mmol), dimedone (1 mmol) and malo-
nonitrile (1 mmol) in the presence or the absence of catalyst in etha-
nol under refux
aIsolated yield
bg-C3N4 as catalyst
as a catalyst was also carried out, and the same results were observed after an
hour (Table 1, entry 2). By increasing the amount of catalyst from 5 to 50 mg,
an increasing trend was observed in the percentage of the product along with the
reduction in the reaction time (Table 1, entries 3–9). A further increase in catalyst
content did not result in a signifcant change in the amount of product or reaction
time (Table 1, entry 10). Therefore, 50 mg of catalyst was selected as the best
value for subsequent reactions.
The reaction was performed using an optimal amount of catalyst in the pres-
ence of diferent solvents (Table 2). The best results were obtained in terms of
product percentage and reaction time in the presence of ethanol as a solvent
(Table 2, entry 1).
Table 2 Efect of diferent
Entry
Solvent
Time (min)
Yielda (%)
solvents on the yield (%) of
spirooxindole in the present
of (0.05 g) NiO@g-C3N4
nanocomposite as catalyst
1
2
3
4
5
6
7
EtOH
H2O
2
2
2
2
2
2
2
93
88
90
55
70
50
40
EtOH/H2O
CHCl3
MeOH
n-Hexane
THF
Reaction conditions: isatin (1 mmol), dimedone (1 mmol) and malo-
nonitrile (1 mmol) in the presence of NiO@g-C3N4 nanocomposite
(0.05 gr) as catalyst in various solvents
aIsolated yield
1 3

An efciently and quickly synthesized NiO@g‑C3N4…
Table 3 Comparison of the efciency of NiO@g-C3N4 with diferent catalysts
Entry
Catalyst
Solvent/T (°C)
Time (min)
Yield (%)
References
1
2
3
4
5
6
7
8
[CHOSO3H]3W12PO40
TBA acetate
(SB-DBU)Cl
Carbon–SO3H
Piperidine
Sodium citrate
NaOAc
Urea: ChCl
a-amilase
EtOH/r.t.
Solvent-free/100 °C
EtOH/r.t
EtOH/refux
EtOH/r.t
H2O/60 °C
40
10
150
180
60
180
15
60
92
92
97
81
92
95
95
95
98
90
95
[12]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
Grinding
Deep eutectic solvent
EtOH/H2O/r.t.
H2O/60 °C
9
10
11
180
180
2
[36]
[37]
This work
TEBA
NiO@g-C3N4
EtOH/refux
Reaction conditions: isatin (1 mmol), malononitrile (1 mmol) and dimedone (1 mmol)
Diferent methods have been reported for the synthesis of spirooxindole deriva-
tives under diferent conditions [11, 27–35]. The method presented in this article
has advantages over previous studies, including easy synthesis, short reaction time,
workup and no side products (Table 3).
To show the generality of NiO@g-C3N4 in organic reactions, the synthesis of
various spirooxindole derivatives using isatins and cyclic-1,3-diketone or 1,3-dike-
toesters or 4-hydroxycoumarin derivatives (Scheme 1) was investigated using the
described reaction conditions (Table 4). Changing of substitutions on isatin caused
the change in reaction time or yield (%), electron donating group on the R1 or R2
position reduce the reaction’s progress (Table 4, entries 4, 5, 9, 17, 19 and 20), and
electron withdrawing group (EWG) in the R2 position increase the reaction speed
and yield (%) (Table 4, entries 2, 3, 15 and 16). Studies have also shown that the
dimedone can produce better results than 1,3-cyclohexadione (Table 4, entries
10–13). Also, studies have shown that the methyl and ethyl acetoacetate can pro-
duce various spirooxindole derivatives with less reactivity to dimidon (Table 4,
entries 14–17). When 4-hydroxycoumarin was used, the synthesis of corresponding
spirooxindole was less reactive compared to when 1,3-diketones was used (Table 4,
entries 18–26); this may be due to less reactivity of 4-hydroxycoumarin than
1,3-diketones. Of course, it should be considered in these reactions the presence of
EWG on isatins also led to less time and more product percentages (Table 4, entries
19 and 20). Generally, the best efciencies were obtained with dimedone and isatin
bearing EWG on R2 position (Table 4, entry 12).
In all reactions, the products could easily be separated by recrystallizing in hot
ethanol. As can be deduced from Table 4, no side products were produced in these
reactions. Also, according to Table 4, NiO@g-C3N4 exhibited high catalytic activ-
ity, which could be due to the uniform distribution of NiO nanoparticles, which is
stabilized by p-conjugated graphitic carbon nitrides as well as readily accessible
surface-exposed NiO nanoparticles, which obviously favors the C–C bond formation
reactions.
1 3

Z. Amini Moqadam et al.
Table 4 Preparation of oxindole
Entry Isatin
1,3-dik-
Time (min) Yield (%)
derivatives
etone or
1,3-dike-
toesters or
4-hydroxy-
coumarin
R1
R2
R3
R4
1
2
3
4
5
6
7
8
H
H
H
H
H
Cl
H
H
H
H
H
H
H
H
H
Me
Me
Me
Me
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2
2
2
3
3
2
2
2
4
4
2
2
2
6
8
6
8
6
5
5
7
6
8
8
7
7
93
95
95
90
90
93
93
95
91
93
95
97
95
92
90
90
90
90
91
93
88
89
87
88
90
80
NO2
OMe
Me
NO2
Br
Br
H
H
NO2
Cl
H
H
Me
H
Me
H
Cl
NO2
H
H
C2H5
C2H5
Me
CH2Ph
CH2Ph
C2H5
H
H
H
H
H
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
–
Me
Me
Et
Et
–
–
–
–
–
–
–
H
H
H
H
CH2Ph
CH2Ph NO2
H
H
Me
C2H5
OMe
Me
Br
–
–
–
–
–
–
Br
Reaction conditions: isatin derivatives (1.0 mmol), 1,3-diketone or
1,3-diketoesters or 4-hydroxycoumarin (1 mmol), malononitrile
(1 mmol), catalyst (50 mg) and EtOH (3 mL); reactions conducted
in refux conditions
A plausible mechanism for one-pot reaction of isatin, dimedone and malo-
nonitrile is given in Scheme 3. As can be seen, the product of the frst step is
caused by the addition of NiO@g-C3N4 to the carbonyl group of isatin. Adding
malononitrile to mentioned carbon, followed by the release of NiO along with
the oxygen of the carbonyl group, produces 4. With the addition of dimedone, the
NiO@g-C3N4 catalyst again enters to the mechanism to create 6 (spirooxindole
derivatives).
1 3

An efciently and quickly synthesized NiO@g‑C3N4…
Scheme 3 Proposed mechanism for the synthesis of spirooxindole derivatives
100
90
80
70
60
50
40
30
20
10
0
Fig. 5 Reusability of the NiO@g-C3N4 nanocomposite for the synthesis of spirooxindole derivatives
Since the reusability of the catalyst in the industry is important, repetitive experi-
ments were conducted under similar conditions to investigate the stability of NiO@g-
C3N4. So, after the end of each reaction, the catalyst was separated, washed and dried
for subsequent use. After 6 times of catalyst reuse, the reaction efciency was still
above 80% which confrmed the catalyst recovery capability (Fig. 5).
1 3

Z. Amini Moqadam et al.
Conclusion
We presented a rapid and green hydrothermal method for the immobilization of
the NiO nanoparticles on the g-C3N4 nanosheets. Prepared nanocomposite was
characterized by diferent techniques including TEM, XRD, TGA and FT-IR
spectra. The one-pot synthesis of spirooxindole derivatives using 1 mmol isatin,
1 mmol dimedone and 1 mmol malononitrile was carried out in the presence of
50 mg NiO@g-C3N4 in EtOH media at refux conditions. High percentage of
products (90–97%) were produced in short reaction times (2–4 min). 4-Hydrox-
ycoumarin was reacted instead of dimedone, and again acceptable results were
obtained in terms of reaction times (5–8 min) with good reaction efciency
(87–93%). In addition, the catalyst stability was investigated for 8 cycles with-
out a signifcant reduction in catalytic efciency. Therefore, this study introduces
a facile and green method for the synthesis of the NiO@g-C3N4 nanocomposite
which can be efective for the synthesis of spirooxindole derivatives.
Acknowledgements The authors are grateful to the University of Birjand and Payam Noor University of
Mashhad for fnancial support.
References
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