CeO2/CuO@N-GQDs@NH2 nanocomposite as a high-performance catalyst for the synthesis of benzo[g]chromenes

Article abstract of DOI:10.1002/aoc.5657

A three-component reaction of aromatic aldehydes, malononitrile or ethyl cyanoacetate and 2-hydroxy-1,4-naphthaquinone has been achieved in the presence of an amino-functionalized CeO₂/CuO@ nitrogen graphene quantum dot nanocomposite as a highl

Full text of DOI:10.1002/aoc.5657

Received: 18 December 2019
DOI: 10.1002/aoc.5657
Revised: 22 February 2020
Accepted: 23 February 2020
F U L L P A P E R
CeO2/CuO@N-GQDs@NH2 nanocomposite as a high-
performance catalyst for the synthesis of benzo[g]
chromenes
Javad Safaei-Ghomi
| Fatemeh-Sadat Bateni | Pouria Babaei
Department of Organic Chemistry,
Faculty of Chemistry, University of
Kashan, Kashan, 51167, I. R, Iran
A three-component reaction of aromatic aldehydes, malononitrile or ethyl
cyanoacetate and 2-hydroxy-1,4-naphthaquinone has been achieved in the
presence of an amino-functionalized CeO2/CuO@ nitrogen graphene quantum
dot nanocomposite as a highly effective heterogeneous catalyst to produce
Correspondence
Javad Safaei-Ghomi, Department of
Organic Chemistry, Faculty of Chemistry,
University of Kashan, Kashan, 51167, I. R.
Iran.
benzo[g]chromenes. The catalyst has been characterized by X-ray diffraction,
scanning electron microscopy, transmission electron microscopy, Fourier
transform infrared, energy-dispersive X-ray spectroscopy, thermogravimetric
analysis, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller (BET)
and vibrating sample magnetometry. This new catalyst has been demonstrated
to be highly effective in the preparation of benzo[g]chromenes.
Email: safaei@kashanu.ac.ir
K E Y W O R D S
chromenes, graphene quantum dots, nanocatalyst, nanocomposite
1 | INTRODUCTION
regarding biological,[19] biomedical,[20] drug delivery,[21]
photocatalyst,[22]
surfactant,[23]
bioelectronic,[24]
Chromenes have biological properties including
anticancer,[1] antimicrobial,[2] antivirus,[3] anti-inflamma-
tory[4] and antidiabetes,[5] and are used in the treatment of
Alzheimer's disease.[6] Some other examples of chromenes
are prominent drug molecules such as vitamin E,
acronycine, uvafzlelin and cromakalim, which have high
bioavailability, slow onset and prolonged effect.[7] Chro-
menes are regarded as notable targets of organic synthesis.
Therefore, searching for efficient methods for the prepara-
tion of chromenes is an attractive challenge. A number of
methods have been developed for the preparation of chro-
menes using diverse catalysts containing lipase,[8] p-TSA,[9]
Et3N,[10] Zn[L-proline]2,[11] [Et3NH][HSO4],[12] DBU,[13]
Cu (OTf)2,[14] TEBA (triethylbenzylammonium chlo-
ride)[15] and [bmim]OH.[16] Metal oxides are a broad class
of materials that have been researched extensively owing
to their unique attributes and potential applications in var-
ious fields.[17, 18] Graphene quantum dots (GQDs) have
received much attention owing to their significant features
electrocatalytic,[25] Li-ion battery,[26] solar cell,[27] photo-
luminescence[28,29] and bioimaging properties,[30] and cata-
lytic activity.[31] Potential applications of N-GQDs have
been reviewed on the basis of theoretical and experimental
studies.[32–35] Herein, we report on the use of a CeO2/
CuO@N-GQDs@NH2 nanocomposite as a new and effi-
cient catalyst for the preparation of benzo[g]chromenes
through a three-component reaction of aromatic alde-
hydes, malononitrile or ethyl cyanoacetate and 2-hydroxy-
1,4-naphthaquinone (Scheme 1).
2 | EXPERIMENTAL SECTION
2.1 | Preparation of CeO2/CuO
nanoparticles
.
.
Ce (SO4)2 4H2O and CuCl2 2H2O with 1:1 molar ratio
were dissolved in deionized water. Afterwards, the
Appl Organometal Chem. 2020;e5657.
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https://doi.org/10.1002/aoc.5657

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SAFAEI-GHOMI ET AL.
GQDs@NH2 nanocomposite was stirred in 5 ml ethanol
under reflux conditions. The reaction was monitored by
TLC. After completion of the reaction, hot ethyl acetate
was added. The catalyst was insoluble in ethyl acetate
and it could therefore be recycled by simple filtration.
Water was added, and the precipitate was collected by fil-
tration and washed with water. The crude product was
recrystallized or washed with ethanol to give the pure
product. The structures of the products were confirmed
SCHEME 1 Synthesis of benzo[g]chromenes using CeO2/
CuO@N-GQDs@NH2 nanocomposite
1
appropriate amount of aqueous sodium hydroxide solu-
tion (0.70 M) was added to the solution until the pH value
reached 10. Then, the transparent solution was placed in
an autoclave at 120ꢀC for 6 h. The obtained precipitate
was washed twice with methanol and dried at 60ꢀC for
5 h. Finally, the product was calcined at 500ꢀC for 2 h.
using H NMR and Fourier transform infrared (FT-IR)
spectroscopy (see Supporting Information).
2.4.1 | 2-Amino-4-(4-chlorophenyl)-
5,10-dihydro-5,10-dioxo-4H-benzo[g]
chromene-3-carbonitrile (4a)
2.2 | Preparation of CeO2/CuO@N-GQDs
nanocomposite
Orange powder; m.p. 249–252ꢀC. IR (KBr) (νmax/cm−1):
3406, 3419, 3336, 2199, 1666, 1529, 1355. 1H NMR
(400 MHz, DMSO-d6): δ (ppm), 4.63 (1H, s, CH),
7.34–8.03 (10H, m, Ar and NH2). 13C NMR (100 MHz,
DMSO-d6): δ (ppm), 36.3, 57.6, 119.8, 121.7, 126.2, 126.4,
128.9, 130.2, 131.3, 131.5, 132.2, 134.6, 134.8, 143.1, 149.6,
158.8, 177.3, 182.6. Anal. calcd for C20H11ClN2O3: C,
66.22; H, 3.06; N, 7.72. Found: C, 66.12; H, 3.11; N, 7.79.
A 1 g aliquot of citric acid was dissolved into 20 ml
deionized water, and stirred to form a clear solution. After
that, 0.3 ml ethylenediamine was added to the above solu-
tion and mixed to obtain a clear solution. Then, 0.1 g
CeO2/CuO nanoparticles were added to mixture. The mix-
ture was stirred at room temperature for 5 min. Then the
solution was transferred into a 50 ml Teflon-lined stain-
less autoclave. The sealed autoclave was heated to 180ꢀC
for 9 h in an electric oven. Finally, as-prepared nanostruc-
tured CeO2/CuO@N-GQDs were obtained, washed sev-
eral times with deionized water and ethanol, and then
dried in an oven until a constant weight was achieved.
2.4.2 | 2-amino-4-(4-bromophenyl)-
5,10-dihydro-5,10-dioxo-4H–benzo[g]
chromene-3-carbonitrile (4b)
Orange powder; m.p. 253–255ꢀC. IR (KBr) (νmax/cm−1):
1
3410, 3195, 2200, 1664, 1596, 1347. H NMR (400 MHz,
DMSO-d6): δ (ppm), 4.62 (1H, s, CH), 7.28–8.04 (10H, m,
Ar and NH2). 13C NMR (100 MHz, DMSO-d6): δ (ppm),
36.6, 57.5, 119.7, 120.6, 121.7, 126.3, 126.4, 130.2, 131.4,
131.6, 131.8, 134.5, 134.9, 143.5, 149.4, 158.6, 177.3, 183.1.
Anal. calcd for C20H11BrN2O3: C, 58.99; H, 2.72; N, 6.88.
Found: C, 58.92; H, 2.78; N, 6.78.
2.3 | Preparation of CeO2/CuO@N-
GQDs@NH2 nanocomposite
A 1 g aliquot of CeO2/CuO@N-GQDs nanocomposite was
added to a solution of 3-aminopropyltriethoxysilane
(2 mmol, 0.44 g) in dry toluene (20 ml) and refluxed for
24 h under N2 atmosphere. After the reaction had fin-
ished, the aminated CeO2/CuO@N-GQDs were separated
using a centrifuge, washed with double-distilled water and
anhydrous ethanol, and dried at 80ꢀC for 8 h to give the
surface-bound amino group CeO2/CuO@N-GQDs@NH2.
2.4.3 | 2-amino-4-(4-nitrophenyl)-5,10 -
dihydro-5,10–dioxo-4H-benzo[g]chromene-
3-carbonitrile (4c)
Orange powder; m.p. 240–242ꢀC. IR (KBr) (νmax/cm−1):
1
3418, 3332, 2199, 1666, 1595, 1529. H NMR (400 MHz,
2.4 | General procedure for the
preparation of benzo[g]chromenes
DMSO-d6): δ (ppm), 4.75 (1H, s, CH), 7.45–8.15 (10H, m,
Ar and NH2). 13C NMR (100 MHz, DMSO-d6): δ (ppm),
36.5, 56.9, 119.4, 121.2, 124.3, 126.3, 126.6, 129.7, 131.3,
131.5, 134.8, 135.2, 147.3, 149.8, 151.8, 158.7, 177.2, 182.7.
Anal. calcd for C20H11N3O5: C, 64.35; H, 2.97; N, 11.26.
Found: C, 64.25; H, 2.92; N, 11.20.
A mixture of aldehyde (1 mmol), malononitrile (1 mmol),
ethyl
cyanoacetate
(1
mmol),
2-hydroxy-1,-
4-naphthaquinone (1 mmol) and 6 mg CeO2/CuO@N-

SAFAEI-GHOMI ET AL.
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2.4.4 | 2-amino-5,10-dihydro-5,10-dioxo-
4-phenyl-4H–benzo[g]chromene-
3-carbonitrile (4d)
(100 MHz,CDCl3): δ (ppm), 14.3, 36.7, 61.8, 75.4, 120.7,
120.8, 121.3, 121.7, 126.4, 130.3, 131.4, 134.6, 135.1,
145.8, 147.4, 160.7, 162.9, 167.4, 178.1, 183.2. Anal. calcd
for C22H16N2O7: C, 62.86; H, 3.84; N, 6.66. Found: C,
62.95; H, 3.93; N, 6.52%.
Orange powder; m.p. 261–262ꢀC. IR (KBr) (νmax/cm−1):
1
3457, 3392, 2213, 1662, 1592, 1406. H NMR (400 MHz,
DMSO-d6): δ (ppm), 4.61 (1H, s, CH), 7.29–7.84 (11H, m,
Ar and NH2). 13C NMR (100 MHz, DMSO- d6): δ (ppm),
36.8, 57.6, 119.8, 122.5, 126.2, 126.5, 127.5, 128.3, 129.2,
131.1, 131.5, 134.7, 134.9, 144.0, 149.3, 158.7, 177.2, 183.3.
Anal. calcd for C20H12N2O3: C, 73.16; H, 3.68; N, 8.53.
Found: C, 73.09; H, 3.61; N, 8.59.
2.4.8 | Ethyl 2-amino- 4-(2-chlorophenyl)-
5,10-dihydro-5,10-dioxo-4H-benzo [g]
chromene-3-carboxylate (4h)
Orange solid; m.p. 208–210ꢀC. IR (KBr) cm−1: 3432,
1
1681. H NMR (400 MHz, DMSO- d6): δ (ppm), 1.12 (t,
3H, J = 7.6 Hz), 3.92 (q, 2H, J = 7.6 Hz), 5.34 (s, 1H),
7.10 (s, 2H, NH2), 7.14 (m, 1H),7.23 (m, 1H), 7.80–7.88
(m, 5H), 8.02 (m, 1H). 13C NMR (100 MHz, DMSO-d6): δ
(ppm), 14.7, 32.2, 61.6, 75.3, 120.6, 126.3, 126.7, 126.7,
127.8, 128.4, 130.4, 131.5, 131.8, 135.3, 143.1, 160.4,
162.7, 167.4, 178.9, 183.8. Anal. calcd for
C22H16ClNO5: C, 64.48; H, 3.94; N, 3.42. Found: C,
64.46; H, 4.05; N, 3.54%.
2.4.5 | 2-amino-4-(2-chlorophenyl)-
5,10-dihydro-5,10-dioxo-4H-benzo[g]
chromene-3-carbonitrile (4e)
Orange powder, m.p. 237–239ꢀC. IR (KBr) (νmax/cm−1):
1
3428, 2216, 1643, 1595. H NMR (400 MHz, DMSO-d6): δ
(ppm), 4.81 (1H, s, CH), 7.23–8.06 (10H, m, Ar and NH2).
13C NMR (100 MHz, DMSO-d6): δ (ppm), 33.8, 56.5,
119.3, 121.7, 126.3, 126.6, 128.4, 129.0, 129.7, 130.8, 131.1,
131.2, 132.6, 134.5, 135.5, 141.3, 149.7, 158.9, 177.4, 182.7.
Anal. calcd for C20H11ClN2O3: C, 66.22; H, 3.06; N, 7.22.
Found: C, 66.21; H, 3.02; N, 7.28.
2.4.9 | Ethyl2-amino-4-(4-bromophenyl)-
5,10-dioxo-5,10-dihydro-4H-benzo[g]
chromene-3-carboxylate (4i)
Orange solid; m.p. 190–192ꢀC. IR (KBr) cm−1: 3425.10,
1
2.4.6 | Ethyl 2-amino-4-(4-nitrophenyl)-5,
10-dioxo-5, 10-dihydro-4H-benzo [g]
chromene-3-carboxylate (4f)
1681.16. H NMR (400 MHz, CDCl3): δ (ppm), 1.22 (t,
3H, J = 7.6 Hz), 4.15 (q, 2H, J = 7.6 Hz), 5.12 (s,1H), 6.64
(s, 2H, NH2), 7.24 (d, J = 7.6 Hz, 2H), 7.38 (d, J = 7.4 Hz,
2H), 7.72 (d, J = 8.2 Hz, 2H), 8.02 (d, J = 8.2 Hz, 1H),
8.15 (d, J = 7.4 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ
(ppm), 14.4, 37.8, 61.3, 75.7, 120.8, 120.8, 126.3, 130.5,
131.4, 131.7,131.8, 135.7, 143.4, 160.5, 162.4, 167.6, 178.5,
183.7. Anal. calcd for C22H16BrNO5: C, 58.17; H, 3.55; N,
3.08. Found: C, 58.23; H, 3.60; N, 3.18%.
Orange solid; m.p.197–199ꢀC. IR (KBr) cm−1: 3408.14,
1
1681.02. H NMR (400 MHz, CDCl3): δ (ppm), 1.22 (t,
3H, J = 8.0 Hz), 4.08 (q, 2H, J = 8.0 Hz), 5.12 (s, 1H), 6.52
(s, 2H, NH2), 7.53 (d, J = 7.2 Hz, 2H), 7.73–7.85 (d,
J = 7.2 Hz, 2H), 8.14 (d, J = 8.0 Hz, 2H), 8.33 (d,
J = 8.0 Hz, 2H). 13C NMR (100 MHz,CDCl3): δ (ppm),
14.4, 37.3, 61.9, 75.3, 120.8, 123.4, 126.3, 126.6, 130.5,
131.7, 135.9, 144.3, 150.8, 160.2, 162.3, 167.4, 178.5, 183.2.
Anal. calcd for C22H16N2O7: C, 62.86; H, 3.84; N, 6.66.
Found: C, 62.97; H, 3.94; N, 6.55%.
2.4.10 | Ethyl 2-amino-4-(4-chlorophenyl)-
5,10-dihydro-5,10-dioxo-4H-benzo[g]
chromene-3-carboxylate (4j)
Orange solid; m.p. 198–200ꢀC. IR (KBr) cm−1: 3461.46,
1
2.4.7 | Ethyl2-amino-4-(3-nitrophenyl)-
5,10-dioxo-5,10-dihydro-4H-benzo[g]
chromene-3-carboxylate (4g)
1681.56. H NMR (400 MHz, CDCl3): δ (ppm), 1.32 (t,
3H, J = 7.6 Hz), 4.22 (q, 2H, J = 7.6 Hz), 5.12 (s, 1H), 6.48
(s, 2H, NH2), 7.20 (d, J = 7 Hz, 2H), 7.26 (d, J = 7 Hz,
3H), 7.65 (d, J = 8 Hz, 2H), 8.10–8.14 (d, J = 8 Hz, 1 H).
13C NMR (100 MHz, CDCl3): δ (ppm), 14.5, 37.4, 61.0,
75.9, 125.2, 126.2, 128.9, 130.7, 130.9, 131.5, 131.8, 135.4,
142.1, 160.1, 162.2, 167.3, 178.5, 183.9. Anal. calcd for
C22H16ClNO5: C, 64.48; H, 3.94; N, 3.42. Found: C,
64.40; H, 4.06; N, 3.58%.
Orange solid; m.p. 198–200ꢀC. IR (KBr) cm−1: 3432.80,
1681.72. 1H NMR (400 MHz,CDCl3): δ (ppm), 1.27 (t,
3H, J = 8.0 Hz), 4.15 (q, 2H, J = 8.0 Hz), 5.11 (s, 1H),
6.63 (s, 2H, NH2), 7.48 (m, 1H), 7.76 (m, 3H), 8.03 (m,
2H), 8.14 (m, 1H), 8.29 (s, 1H). 13C NMR

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SAFAEI-GHOMI ET AL.
2.4.11 | Ethyl2-amino-
4-(4-methoxyphenyl)-5,10-dioxo-5,10-dihydro-
4H-benzo[g]chromene-3-carboxylate (4k)
(400 MHz, DMSO-d6): δ (ppm), 4.32 (1H, s, CH),
6.12–7.98 (9H, m, Ar and NH2). 13C NMR (100 MHz,
DMSO-d6): δ (ppm), 35.2, 57.4, 105.3, 111.4, 118.2, 126.3,
126.5, 130.6, 131.4, 132.2, 134.5, 134.8, 142.7, 149.2, 151.7,
158.2, 177.1, 181.5. Anal. calcd for C18H10N2O4: C,
67.92; H, 3.17; N, 8.80. Found: C, 67.82; H, 3.12; N, 8.72%.
Orange solid; m.p. 223–225ꢀC. IR (KBr) cm−1: 3423.89,
1683.93. 1H NMR (400 MHz,CDCl3): δ (ppm), 1.25 (t, 3H,
J = 7.2 Hz), 3.73 (s, 3H), 4.04 (q, 2H, J = 7.2 Hz), 5.26 (s,
1H), 6.34 (s, 2H, NH2), 6.82 (d, J = 8.2 Hz, 1H), 6.92 (t,
J = 8.0 Hz, 1H), 7.15 (t, 1H), 7.43 (d, J = 7.2 Hz, 1H),7.72
(m, 2H), 7.92 (m, 1H), 8.12 (m, 1H). 13C NMR (100 MHz,
CDCl3): δ (ppm), 14.9, 31.4, 56.7, 61.4, 75.5, 112.8, 120.9,
121.7, 126.9, 127.1, 130.8, 131.6, 135.8, 158.5, 160.8, 162.7,
167.4, 178.5, 183.3. Anal. calcd for C23H19NO6: C,
68.14; H, 4.72; N, 3.46. Found: C, 68.22; H, 4.74; N, 3.45%.
2.4.14 | 2-amino-5,10-dihydro-5,10-dioxo-
4-(thiophen-2-yl)-4H-benzo[g]chromene-
3-carbonitrile (4n)
Orange powder; m.p. 186–188ꢀC. IR (KBr) (νmax/cm−1):
3402, 3421, 3332, 2195, 1667, 1528, 1359. 1H NMR
(400 MHz, DMSO-d6): δ (ppm), 4.12 (1H, s, CH),
6.70–7.24 (9H, m, Ar and NH2). 13C NMR (100 MHz,
DMSO-d6): δ (ppm), 36.1, 57.2, 118.5, 122.8, 126.4, 126.6,
126.8, 127.9, 130.2, 131.4, 132.5, 134.1, 134.4, 142.5,
151.8, 158.3, 176.2, 182.1. Anal. calcd for
C18H10N2O3S: C, 64.66; H, 3.01; N, 8.38. Found: C,
64.62; H, 3.08; N, 8.31%.
2.4.12 | Ethyl 2-amino-
4-(4-methylphenyl)-5,10-dihydro-5,10-dioxo-
4H-benzo[g]chromene-3-carboxylate (4l)
Yellow solid; m.p.212–214ꢀC. IR (KBr) cm−1: 3463.85,
1
1679.5. H NMR (400 MHz, CDCl3): δ (ppm), 1.25 (t, 3H,
J = 8.2 Hz), 2.25 (s, 3H), 4.12 (q, 2H, J = 8.2 Hz), 5.16 (s,
1H), 6.43 (s, 2H, NH2), 7.03 (d, J = 7 Hz, 2H), 7.23 (d,
J = 7 Hz, 2H), 7.72 (d, J = 8 Hz, 2H), 8 (d, J = 8 Hz, 1H),
8.12 (d, J = 8 Hz, 1H). 13C NMR (100 MHz,CDCl3): δ
(ppm), 14.9, 21.7, 37.2, 61.3, 75.8, 120.3, 126.4,
128.7,130.8, 131.5, 135.8, 135.8, 141.6, 160.5, 162.4, 167.8,
178.2, 183.7. Anal. calcd for C23H19NO5: C, 70.94; H, 4.92,
N; 3.60. Found: C, 70.90; H, 5.01; N, 3.68%.
3 | RESULTS AND DISCUSSION
We prepared CeO2/CuO nanoparticles by easy tech-
niques. A hydrothermal way was used for the preparation
of N-GQDs.[36] Amino-functionalized GQDs were pre-
pared using 3-aminopropyltriethoxysilane. The X-ray dif-
fraction (XRD) patterns of CeO2/CuO and CeO2/
CuO@N-GQDs@NH2 nanocomposite are shown in
Figure 1. The XRD patterns confirm the presence of both
CuO (JCPDS no. 89-2529) and CeO2 (JCPDS
no. 34-0394).
In order to investigate the morphology and particle
size of nanocatalyst, scanning electron microscopy (SEM)
images of CeO2/CuO and CeO2/CuO@N-GQDs@NH2
nanocomposite are shown in Figure 2(a, b). Figure 2(c)
2.4.13 | 2-amino-4-(furan-2-yl)-
5,10-dihydro-5,10-dioxo-4H-benzo[g]
chromene-3-carbonitrile (4m)
Orange powder; m.p. 192–194ꢀC. IR (KBr) (νmax/cm−1):
3409, 3425, 3334, 2198, 1660, 1525, 1354. 1H NMR
FIGURE 1 X-ray diffraction pattern of
(a) CeO2/CuO and (b) CeO2/CuO@N-
GQDs@NH2

SAFAEI-GHOMI ET AL.
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FIGURE 2 (a) Scanning electron
microscopy (SEM) of CeO2/CuO;
(b) SEM of CeO2/CuO@N-GQDs@NH2;
and (c) transmission electron
microscopy of CeO2/CuO@N-
GQDs@NH2
indicates the TEM (transmission electron microscope)
image of nanocatalyst. The TEM and SEM images of the
CeO2/CuO@N-GQDs@NH2 nanocomposite show the
formation of uniform particles, and the energy-dispersive
X-ray spectrum (EDS) confirms the presence of Ce,
Cu, O, N and C species in the structure of the
nanocomposite (Figure 3).
The magnetic properties of CeO2/CuO, CeO2/
CuO@N-GQDs
and
CeO2/CuO@N-GQDs@NH2
nanocomposites were determined with the help of a
FIGURE 3 Energy-dispersive X-ray spectrum of (a) CeO2/CuO and (b) CeO2/CuO@-GQDs@NH2

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SAFAEI-GHOMI ET AL.
vibrating sample magnetometer (Figure 4). These results
demonstrate that the magnetization property decreases
with coating and functionalization.
9.82 m2/g after modification with GQDs and
3-aminopropyltriethoxysilane; therefore, more active sites
were introduced to the CeO2/CuO@N-GQDs@NH2 sur-
face. The results for N2 adsorption–desorption containing
the BET surface area (SBET) and the total pore volumes
(Vtotal) of the CeO2/CuO, CeO2/CuO@N-GQDs and
CeO2/CuO@N-GQDs@NH2 nanocomposites are summa-
rized in Table 1.
Thermogravimetric analysis was used to examine the
thermal stability of the CeO2/CuO@N-GQDs@NH2
nanocomposites (Figure 7). These nanoparticles show
suitable thermal stability without a significant decrease
in weight. The weight loss (2.14%) at temperatures below
200ꢀC is due to the removal of physically adsorbed sol-
vent and surface hydroxyl groups. The curve displays a
weight loss of about 12.98% from 200 to 600ꢀC, attributed
to the oxidation and degradation of N-GQD and decom-
position of the organic spacer grafting to the N-GQD
surface.
The FT-IR spectra of CeO2/CuO, CeO2/CuO@N-
GQDs and CeO2/CuO@N-GQDs@NH2 nanocomposites
are shown in Figure 5. The absorption peak at 3300 cm−1
is related to the stretching vibrational absorptions of
OH. The peaks at 509 and 663 cm−1 correspond to Cu–O
and Ce–O respectively. The characteristic peaks at
3435 cm−1 (O-H stretching vibration), 1660 cm−1 (C=O
stretching vibration) and 1101 cm−1 (C–O–C stretching
vibration) appear in the spectrum shown in Figure 5b.
The peak at approximately 1475–1580 cm−1 is attributed
to C=C bonds. The peaks at 1560, 3438 and 3350 cm−1
are related to the bending and stretching vibrational
absorptions of N–H (Figure 5c).
The BET specific surface areas of CeO2/CuO and
CeO2/CuO@N-GQDs@NH2 nanocomposites were mea-
sured using nitrogen gas adsorption–desorption iso-
therms (Figure 6). The results showed that the BET
specific surface area of CeO2/CuO improved from 1.72 to
X-ray photoelectron spectroscopy (XPS) analysis of
CeO2/CuO@N-GQDs@NH2 nanocomposite is shown in
FIGURE 4 Vibrating sample
magnetometer of (a) CeO2/CuO, (b) CeO2/
CuO@GQDs and (c) CeO2/CuO@GQDs@NH2
FIGURE 5 Fourier transform infrared
spectrum of (a) CeO2/CuO, (b) CeO2/CuO@N-
GQDs and (c) CeO2/CuO@N-GQDs@NH2

SAFAEI-GHOMI ET AL.
7 of 15
FIGURE 6 The BET specific surface area of (a) CeO2/CuO and (b) CeO2/CuO@N-GQDs@NH2
TABLE 1
BET surface area (SBET) and the total pore volumes
(Vtotal) of the nanostructures
Materials
SBET (m2/g)
1.72
Vtotal (cm3/g)
CeO2/CuO
0.04
0.09
0.12
CeO2/CuO@N-GQDs
CeO2/CuO@N-GQDs@NH2
7.89
9.82
Figure 8. In the wide-scan spectrum of the nanocatalyst,
the predominant components are Cu 2p (940–970 eV), Ce
3d (883.8 eV), O 1 s (530.6 eV), N 1 s (400 eV) and C 1 s
(286.3 eV).
Initially, we investigated the three-component reac-
tion of benzaldehyde, malononitrile and 2-hydroxy-1,-
4-naphthaquinone as a model reaction. The model
reactions were performed using p-TSA, NaHSO4, ZrO2,
Et3N, CeO2/CuO, CeO2/CuO@N-GQDs and CeO2/
CuO@N-GQDs@NH2 nanocomposites. The reactions
were tested using various solvents including ethanol, ace-
tonitrile, water and dimethylformamide. The best results
were obtained in EtOH and the reaction gave convincing
FIGURE 8 X-ray photoelectron spectroscopy (XPS) analysis of
CeO2/CuO@GQDs@NH2 nanocomposite
results in the presence of CeO2/CuO@N-GQDs@NH2
nanocomposite (6 mg) under reflux conditions (Table 2).
In further studies on the catalyst loading, we recognized
that the yield of compound 4d remained almost the same
when
7
mg
of
CeO2/CuO@N-GQDs@NH2
FIGURE 7 Thermogravimetric analysis of
CeO2/CuO@N-GQDs@NH2

8 of 15
SAFAEI-GHOMI ET AL.
TABLE 2
Optimization of reaction conditions using different catalystsaa
Entry
Catalyst (amount)
Solvent (reflux)
EtOH
Time (min)
Yieldab (%)
1
None
400
400
350
350
400
250
150
75
NR
10
21
32
60
48
70
86
90
90
70
75
80
2
p-TSA (5 mol%)
EtOH
3
NaHSO4 (6 mol%)
EtOH
4
ZrO2 (5 mol%)
EtOH
5
Et3N (5 mol%)
EtOH
6
CeO2/CuO nanocomposite
EtOH
7
CeO2/CuO@N-GQDs nanocomposite
CeO2/CuO@N-GQDs@NH2 nanocomposite (5 mg)
CeO2/CuO@N-GQDs@NH2 nanocomposite (6 mg)
CeO2/CuO@N-GQDs@NH2 nanocomposite (7 mg)
CeO2/CuO@N-GQDs@NH2 nanocomposite (6 mg)
CeO2/CuO@N-GQDs@NH2 nanocomposite (6 mg)
CeO2/CuO@N-GQDs@NH2 nanocomposite (6 mg)
EtOH
8
EtOH
9
EtOH
75
10
11
12
14
EtOH
75
H2O
120
100
80
DMF
CH3CN
aBenzaldehyde (1 mmol), malononitrile (1 mmol) and 2-hydroxy-1,4-naphthaquinone (1 mmol).
bIsolated yield.
nanocomposite was used. The use of lower catalyst load-
ing (5 mg) afforded 4d in 86% yield.
for the synthesis of benzo[g]chromenes, the results are
tabulated in Table 4. As the table shows, CeO2/CuO@N-
GQDs@NH2 nanocomposite is superior with respect to
the reported catalysts in terms of reaction time, yield and
conditions.
We considered recycling of CeO2/CuO@N-
GQDs@NH2 nanocomposite as a catalyst for the model
reaction. The results showed that nanocomposite can be
reused several times without remarkable loss of catalytic
activity (yields 90–88%; Figure 9).
The morphology of CeO2/CuO@N-GQDs@NH2
nanocomposite was investigated by scanning electron
microscopy (SEM) before use and after reuse five times
(Figure 10). The shape and size of the nanoparticles
remained unchanged before and after reaction. We sup-
pose that this is also a possible reason for the extreme sta-
bility of the nanocatalyst presented herein.
To complete the reusability studies, we have used the
hot filtration test.[37] For this purpose, we studied the
model reaction three-component reaction of benzalde-
hyde, malononitrile and 2-hydroxy-1,4-naphthaquinone
under optimized conditions. The reaction mixture was fil-
tered after 50% conversion to remove the catalyst. Contin-
uation of the reaction under the same conditions showed
54% conversion after 2.5 h. This result shows that the
The influence of electron-withdrawing and electron-
donating substituents on the aromatic ring of aldehydes
upon the reaction yields was investigated. The results
showed excellent in yields from aromatic aldehydes,
either bearing electron-withdrawing or electron-donating
substituents (Table 3). Aromatic aldehydes having NO2
and halogen groups reacted at a faster rate compared
with aromatic aldehydes substituted with other groups.
Generalization of the reaction was carried out by
employing various aldehydes, malononitrile or ethyl
cyanoacetate, and the results are summarized in Table 3.
The structures of the prepared benzo[g]chromenes were
1
fully characterized by H and 13C NMR spectra, IR spec-
1
tra and elemental analysis. For example, in the H NMR
spectrum of 4d, the proton at 4.61 ppm displays CH ali-
phatic. The protons at 7.29–7.84 ppm indicate CH aro-
matic and NH2. In the FT-IR spectrum of 4d, the peaks at
3457 and 3392 cm−1 are related to the stretching vibra-
tional absorptions of N–H; the peaks at 2213 and
1662 cm−1 are related to the stretching vibrational
absorptions of C ≡ N and C=O respectively.
To compare the efficiency of CeO2/CuO@N-
GQDs@NH2 nanocomposite with the reported catalysts

SAFAEI-GHOMI ET AL.
9 of 15
TABLE 3
Synthesis of benzo[g]chromenes using CeO2/CuO@N-GQDs@NH2 nanocomposite (6 mg) under reflux conditionsaa
Aldehyde
Entry (1a–1l)
Malononitrile or
ethyl cyanoacetate (4a–4l)
Product
Time
(min)
Yieldb
(%)
m.p.
(ꢀC)(reference)
m.p. (ꢀC)
(reported)
1
65
65
65
75
93
92
94
90
249–252[10]
253–255[10]
234–235[10]
261–262[10]
249–252
253–255
240–242
261–262
2
3
4
(Continues)

10 of 15
SAFAEI-GHOMI ET AL.
TABLE 3 (Continued)
Aldehyde
Entry (1a–1l)
Malononitrile or
ethyl cyanoacetate (4a–4l)
Product
Time
(min)
Yieldb
(%)
m.p.
(ꢀC)(reference)
m.p. (ꢀC)
(reported)
5
65
92
236–239[10]
237–239
6
80
91
197–199[39]
197–199
7
90
85
198–200[40]
198–200
8
100
87
208–210[40]
208–210
(Continues)

SAFAEI-GHOMI ET AL.
11 of 15
TABLE 3 (Continued)
Aldehyde
Entry (1a–1l)
Malononitrile or
ethyl cyanoacetate (4a–4l)
Product
Time
(min)
Yieldb
(%)
m.p.
(ꢀC)(reference)
m.p. (ꢀC)
(reported)
9
90
87
88
80
83
190–192[40]
189–191[16]
224–226[39]
211–214[16]
190–192
198–200
223–225
212–24
10
11
12
90
120
120
(Continues)

12 of 15
SAFAEI-GHOMI ET AL.
TABLE 3 (Continued)
Aldehyde
Entry (1a–1l)
Malononitrile or
ethyl cyanoacetate (4a–4l)
Product
Time
(min)
Yieldb
(%)
m.p.
(ꢀC)(reference)
m.p. (ꢀC)
(reported)
13
90
84
—
192–194
14
100
84
—
186–188
aAromatic aldehydes (1 mmol), malononitrile or ethyl cyanoacetate (1 mmol) and 2-hydroxy-1,4-naphthaquinone (1 mmol).
bIsolated yield.
TABLE 4
Comparison of catalytic activity of CeO2/CuO@N-GQDs@NH2 nanocomposite with other reported catalysts for the synthesis
of 4d
Entry
Catalyst (condition)
Time (min)
Yieldaa (%)
Reference
[8]
1
2
3
4
5
Lipase (20 mg, 55ꢀC, EtOH)
Et3N (10 mol%,CH3CN)
DBU (10 mol%, H2O, reflux)
TEBA (10 mol%, 85ꢀC)
800
900
90
85
82
87
90
90
[10]
[13]
[15]
240
75
CeO2/CuO@N-GQDs@NH2
This work
nanocomposite (6 mg, EtOH, reflux)
aIsolated yield
amount of leaching of the catalyst into the reaction mix-
ture should be low and confirms that the catalyst acts
heterogeneously in the reaction.
To determine the degree of leaching of the metal from
the heterogeneous catalyst, the catalyst was removed by
filtration and the Ce and Cu amounts in the reaction
medium after each reaction cycle were measured through
spectroscopy. The analysis of the reaction mixture by the
inductively coupled plasma technique showed that the
leaching of Ce and Cu was negligible (the leaching of Ce
and Cu in five continuous runs was found to be
≤0.6 ppm).
A plausible mechanism for the preparation of
benzo[g]chromenes using CeO2/CuO@N-GQDs@NH2
nanocomposites is indicated in Scheme 2. Firstly, we
inductively
coupled
plasma–atomic
emission

SAFAEI-GHOMI ET AL.
13 of 15
GQDs@NH2
nanocatalyst.
Then,
2-hydroxy-1,-
4-naphthaquinone was added to intermediate I to give
the intermediate II. The intermediate III formed by
intramolecular cyclization reaction. The migration of the
hydrogen atom provided the final product (Scheme 2).
The amino groups distributed on the surface of CeO2/
CuO@N-GQDs activated the C=O and C ≡ N groups
through hydrogen bonding.[38–41] The activity of catalysts
was influenced by the acid–base properties and many
other factors such as surface area, geometric structure
(particularly pore structure), the distribution of sites and
the polarity of the surface sites.[38, 42] This mechanism is
supported by the literature.[8, 11, 16]
FIGURE 9 Recycling of CeO2/CuO@N-GQDs@NH2
nanocomposite as the catalyst for the model reaction
A structure for the catalyst based on the results and
some authoritative references43–45 is presented in
Figure 11. Herein, we reported the use of CeO2/CuO@N-
GQDs@NH2 nanocomposite as a new efficient catalyst
for the preparation of benzo[g]chromenes.
assumed that the reaction occurred via condensation
between malononitrile and aldehyde, to form the inter-
mediate I on the active sites of the CeO2/CuO@N-
FIGURE 10 SEM images of CeO2/
CuO@N-GQDs@NH2 nanocomposite
(a) before use and (b) after reuse five
times
SCHEME 2 Proposed mechanism for the three-
component reaction

14 of 15
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In conclusion, we have reported an efficient method for
the synthesis of benzo[g]chromenes using CeO2/
CuO@N-GQDs@NH2 nanocomposite as a superior cata-
lyst under reflux conditions. The new catalyst is charac-
terized by SEM, TEM, FT-IR XRD, EDS,
thermogravimetric analysis, XPS, BET and vibrating sam-
ple magnetometry. The current method provides obvious
positive points including environmental friendliness,
reusability of the catalyst, low catalyst loading and simple
workup procedure.
ACKNOWLEDGMENTS
The authors are grateful to the University of Kashan for
supporting this work.
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ORCID
Javad Safaei-Ghomi https://orcid.org/0000-0002-9837-
4478
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How to cite this article: Safaei-Ghomi J,
Bateni F-S, Babaei P. CeO2/CuO@N-GQDs@NH2
nanocomposite as a high-performance catalyst for
the synthesis of benzo[g]chromenes. Appl
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