Green synthesis of TiO2 nanoparticles as an efficient heterogeneous catalyst with high reusability for synthesis of 1,2-dihydroquinoline derivatives

Article abstract of DOI:10.1002/aoc.5005

Nano materials find wide applications due to their behavior at nano scale. TiO₂ nanoparticles (TiO₂ NPs) was synthesized using Neem leaf extract. This is simple, rapid, eco-friendly, cheaper and green tools for TiO₂ NPs synthesis using agricultural waste at lower applied temperature. Characterization of the extracted TiO₂ NPs was confirmed by XRD, SEM, EDAX, TEM, HR-TEM, SAED, and FT-IR, respectively. The catalytic activity of TiO₂ NPs was investigated in synthesis of 1,2-dihydroquinoline derivatives with excellent yields and low cost. Purification of the synthesized 1,2-dihydroquinoline derivatives carried out by easy work-up of non-chromatographic methods.

Full text of DOI:10.1002/aoc.5005

Received: 27 December 2018
DOI: 10.1002/aoc.5005
Revised: 16 April 2019
Accepted: 30 April 2019
F U L L P A P E R
Green synthesis of TiO nanoparticles as an efficient
2
heterogeneous catalyst with high reusability for synthesis of
1,2‐dihydroquinoline derivatives
Mahmoud Abd El Aleem Ali Ali El‐Remaily
| Ahmed M. Abu‐Dief | O. Elhady
Department of Chemistry, Faculty of
Nano materials find wide applications due to their behavior at nano scale. TiO2
Science, Sohag University, Sohag 82524,
Egypt
nanoparticles (TiO NPs) was synthesized using Neem leaf extract. This is sim-
2
ple, rapid, eco‐friendly, cheaper and green tools for TiO NPs synthesis using
2
Correspondence
Mahmoud Abd El Aleem Ali Ali El‐
Remaily and Ahmed M. Abu‐Dief,
Department of Chemistry, Faculty of
Science, Sohag University, Sohag 82524,
Egypt.
agricultural waste at lower applied temperature. Characterization of the
extracted TiO NPs was confirmed by XRD, SEM, EDAX, TEM, HR‐TEM,
2
SAED, and FT‐IR, respectively. The catalytic activity of TiO NPs was investi-
2
gated in synthesis of 1,2‐dihydroquinoline derivatives with excellent yields and
low cost. Purification of the synthesized 1,2‐dihydroquinoline derivatives car-
ried out by easy work‐up of non‐chromatographic methods.
Email: msremaily@yahoo.com;
ahmed_benzoic@yahoo.com
KEYWORDS
1
2
,2‐dihydroquinolines, efficient catalyst, neem leaf extract, non‐chromatographic, TiO nanoparticles
1
| INTRODUCTION
research has been directed towards the utilization of TiO2
nanoparticles which have emerged as an attractive
multi‐functional material. So the catalytic potential of
Modern science highlights on one of the most effective and
applicable research which is nanoscience. Recently, nano-
technology is highly progressed technology with inter
disciplined research between different branches, e.g.
chemistry, physics, biology, material science and medi-
cine. Comparing to bulk materials, nanoparticles (NPs)
are more of interest because of their enhanced surface Ray-
leigh scattering, plasmon resonance, and enhanced surface
Raman scattering for fine materials of metal and their cor-
responding metal oxide. Consequently, medical, catalytic,
electronic, optoelectronic, and developed research of dif-
ferent chemical and biochemical sensor depend strongly
TiO nanoparticles is used in a wide range of reactions
2
[
5]
and syntheses of bioactive heterocycles.
On the other hand, substituted dihydroquinolines
are highly of interest due to their high potential
[6–9]
and applicability in biology pharmacology.
dihydroquinoline backbone is key molecular motifs to
synthesize various natural organic products, e.g. Phar-
[
10–12]
maceuticals and synthetic intermediates.
Different
synthetic routes of polysubstituted 1,2‐dihydroquinolines
[
13–20]
were progressed
within traditional gradual proce-
[21]
dures of low yielding and special synthetic precursors.
[1–3]
upon the technology of nanoparticles.
Fast expansions
Recently, synthesis of dihydroquinoline derivatives has
been developed with more progressed efficient strategies
using catalysts. One of the most effective catalysts for such
dihydroquinoline derivatives synthesis are transition
in research for metal and metal oxide synthesis with strong
surface modification as nanoparticle materials are carrying
out for many proposals, e.g. biological, medicine, and elec-
tronic applications. Owing to toxicity, using chemicals and
solvents for nanoparticles synthesis is very limited. New
methods for nanoparticle materials synthesis as green,
[
22]
[23,24]
[25]
metals, e.g. palladium,
ruthenium,
silver,
and
[
26]
gold. They catalyzed anilines reactions with various
reagents, like alkynes, scandium triflate,
[
27]
silicotungstic
[4]
[28]
[29]
[30]
[31]
non‐toxic and safe ways are rapidly developed. Recent
acid,
indium triflate,
HNO3,
and zeolite.
Appl Organometal Chem. 2019;e5005.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
1 of 10
https://doi.org/10.1002/aoc.5005

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EL‐REMAILY ET AL.
Moreover, reactivity of amines towards α‐ketoesters was
studied catalytically by using indium which mediated
allylation of quinolones as catalysts.
2.3 | Characterization techniques for the
prepared titanium dioxide nanoparticles
Progress to develop more green processes by applying
agricultural waste in order to synthesize nanoparticles is
blossoming into an effective applicable field of nanotech-
The phase of the extracted TiO was characterized by X‐
2
ray diffraction (XRD) pattern with Cu‐Kα line (λ = 1.54
A°) operating at 30 kV and 30 mA in the 2θ range 10° –
80°. Surface morphology of the as prepared s TiO2
nanopowder was studied by a JEOL SET scanning elec-
tron microscopy (SEM) with an accelerating voltage of
15.0 kV in a high vacuum mode to achieve magnification
between 100 and 10000 using the gold as a reference. The
chemical composition of the synthesized nanostructures
was also analyzed using energy dispersive analysis of X‐
ray (EDAX) unit attached to the FE‐SEM. Transmission
electron microscopy studies (TEM, HR‐TEM, SAED)
were performed on a JEOL JEM‐2100F model. The calcu-
lated histograms were performed using image J for TEM
program (Broken symmetry software). FT‐IR spectra
were recorded by FT‐IR spectrophotometer Shimadzu‐
[32–35]
nology.
Particularly, TiO2 nanoparticles are the
most of interesting in that field resulted from their
photo‐catalytic sufficiency. TiO nanoparticles have been
2
involved as an high reactive catalyst in alternative
[36,37]
organic synthetic processes.
The present work describe highly simple and very
good yielding protocol for the synthesis polysubstituted
1
,2‐dihydroquinolines synthesized by α‐ketoesters with
arylamines using natural TiO2 nanoparticles as an
eco‐friendly heterogeneous and recoverable catalyst.
2
2
| EXPERIMENTAL
8400 S (Japan) in KBr tablets.
.1 | Material and methods
The utilized plants in our investigation are Neem healthy
leaves, which were collected from India. The collected
leaves were washed several times by double distilled
water to remove any adhering dust. The leaves were dried
for 15 days at 25 °C under clean condition. After that,
dried leaves were cut into tiny pieces, grinded and sieved
to get the finest powder as soon as possible. Ten grams of
the dried leaves were mixed with 100 ml of ethanol and
refluxed for 3 hrs. Then, the obtained ethanolic leaf
extract was obtained by filtering the mixture. Now, the
obtained extract is ready for using in synthesis of tita-
nium dioxide nanoparticles. Titanium (IV) isopropoxide
2.4 | General procedure for
1,2‐dihydroquinolines (3a‐p)
In a two nick 50 ml round flask arylamines (1.0 mmol)
was mixed with ethyl or methyl pyruvate (2.0 mmol) in
the presence of the suspended TiO2 nanoparticles
(6.0 mol%). The resulted mixture solution was heated at
80 °C for the stipulated period of time (Scheme 1). The
reaction progress was followed and monitored by TLC.
After the reaction completion, the reaction mixture was
cooled to room temperature. The solid residue was dis-
solved in hot ethanol and centrifuged to remove the cata-
lyst by filtration. The product obtained was purified by
TLC and NMR spectroscopy. However, the products were
purple further purified by recrystallization from ethanol.
≥
97.0%, TiO2 commercial (CAS Number 13463‐67‐7)
and ethanol Laboratory Reagent, 96% were purchased
from Sigma‐ Aldrich.
[
23,38]
All the products reported in literature
and the data
of products were given in supporting information.
IR spectral measurements was achieved as KBr pellets
in a Shimadzu DR‐8001 spectrometer. H and CNMR
were recorded on a Bruker DRX‐300 or 400 MHz using
2
.2 | Preparing of TiO nanoparticles from
2
the extracted neem leaf
1
13
0
.5 M of titanium tetraisoproxide in ethanolic containing
TMS as an internal reference and CDCl as a solvent.
3
leaf extract was reacted under stirring at 55 °C in the
Erlenmeyer flask. Then of the under steady stirring
5
All compounds were checked for their purity on TLC
plates.
hr, the formed titanium dioxide nanoparticles was
acquired by centrifugation at 20000 rpm for 10 minutes.
Then the centrifuged particles were washed with ethanol
several times and re‐centrifuged. The obtained titanium
dioxide nanoparticles were dried and grinded to calcinate
at 500 °C in muffle furnace for about 5 hours with
heating rate 10 °C/min. The calcined titanium dioxide
nanopowder was used for further characterization
techniques.
2.5 | Diethyl
2‐methyl‐1,2‐dihydroquinoline‐2,4‐
dicarboxylate, 3a
−
1
Yellow oil; FTIR (KBr, cm ): 3127, 3051, 2930,
1
1739,1730, 1450; H NMR (CDCl ): δ 1.20 (t, 3H), 1.32
3
(t, 3H), 1.45 (s, 3H), 4.04–4.19 (m, 2H), 4.21–4.28 (m,

EL‐REMAILY ET AL.
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SCHEME 1 Synthesis of 1,2‐
dihydroquinolines 3a‐p time of reaction
(
min) and yield (%)
2
7
2
1
H), 4.45 (br, 1H), 6.55 (d, 1H), 6.58 (s, 1H), 6.65 (t, 1H),
2H), 4.57 (br, 1H), 6.50 (d, 1H), 6.72 (s, 1H), 7.14 (dd,
13
13
.01 (t, 1H), 7.72 (d, 1H); C NMR (CDCl3): δ 14.2, 14.2,
7.5, 58.4, 61.01, 61.7, 114.2, 116.4, 118.5, 126.4, 128.4,
29.5, 132.6, 142.7, 165.7, 173.8.
1H), 8.00 (d, 1H); C NMR (CDCl ): δ 14.0, 14.2, 27.3,
3
58.5, 61.1, 61.7, 110.1, 115.6, 118.1, 127.2, 129.1, 132.0,
133.9, 141.6, 165.1, 173.5.
2
6
.6 | Diethyl
‐chloro‐2‐methyl‐1,2‐dihydroquinoline‐2,4‐
2.8 | Diethyl
6‐methoxy‐2‐methyl‐1,2‐dihydroquinoline‐
2,4‐dicarboxylate, 3d
dicarboxylate, 3b
−
1
−1
Yellow oil; FTIR (KBr, cm ): 3211, 3047, 2898,
Yellow oil; FTIR (KBr, cm ): 3147, 3048, 2890,
1
1
1
741,1723, 1451; H NMR (CDCl ): δ 1.26 (t, 3H), 1.37
1742,1729, 1450; H NMR (CDCl ): δ 1.25 (t, 3H), 1.37
3
3
(t, 3H), 1.56 (s, 3H), 4.10–4.27 (m,2H), 4.31–4.38 (m,
(t, 3H), 1.55 (s, 3H), 3.76 (s, 1H), 4.10–4.25 (m, 2H),
2
1
5
1
H), 4.55 (br, 1H), 6.56 (d,1H), 6.73 (s,1H), 7.03 (dd,
4.29–4.37 (m, 2H), 4.37 (br, 1H), 6.62 (d, 1H), 6.70 (dd,
13
13
H), 7.86 (d, 1H); C NMR (CDCl ): δ 14.2, 14.1, 27.1,
1H), 6.75 (s, 1H), 7.50 (d, 1H); C NMR (CDCl ): δ
3
3
8.6, 61.1, 62.0, 115.1, 117.7,123.2, 126.2, 127.3, 129.3,
33.8, 141.0, 165.2, 173.7.
14.2, 14.3, 26.6, 55.6, 58.5, 60.9, 61.8, 111.4, 115.1, 116.2,
117.5, 128.1, 134.1, 136.7, 152.5, 165.7, 174.2.
2
6
.7 | Diethyl
‐bromo‐2‐methyl‐1,2‐dihydroquinoline‐2,4‐
2.9 | Diethyl
2,6‐dimethyl‐1,2‐dihydroquinoline‐2,4‐
dicarboxylate, 3e
dicarboxylate, 3c
−
1
−1
Yellow oil; FTIR (KBr, cm ): 3169, 3052, 2911,
Yellow oil; FTIR (KBr, cm ): 3138, 3054, 2981,
1
1
1
740,1729, 1451; H NMR (CDCl ): δ 1.25 (t, 3H), 1.37
1738,1720, 1449; H NMR (CDCl ): δ 1.25 (t, 3H), 1.38
3
3
(t, 3H), 1.55 (s, 3H), 4.11–4.26 (m,2H), 4.30–4.37 (m,
(t, 3H), 1.54 (s, 3H), 2.21 (s, 3H), 4.11–4.25 (m, 2H),

4
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EL‐REMAILY ET AL.
4
6
2
1
.28–4.37 (m, 2H), 4.44 (br, 1H), 6.56 (d, 1H), 6.65 (s, 1H),
2.14 | Dimethyl
6‐chloro‐2‐methyl‐1,2‐dihydroquinoline‐2,4‐
dicarboxylate, 3j
13
.91 (d, 1H), 7.62 (s, 1H); C NMR (CDCl ): δ 14.0, 14.3,
3
0.7, 27.0, 58.4, 61.0, 61.8, 114.2, 116.6, 126.7, 127.7, 128.5,
30.1, 132.7, 140.3, 165.9, 174.1.
−
1
Yellow oil; FTIR (KBr, cm ): 3129, 3051, 2983, 1745,
1
1
3
7
5
1
710, 1450; H NMR (CDCl ): δ 1.56 (s, 3H), 3.75 (s,
3
2
6
2
.10 | Diethyl
‐hydroxy‐2‐methyl‐1,2‐dihydroquinoline‐
,4‐dicarboxylate, 3f
H), 3.87 (s, 3H), 4.56 (br, 1H), 6.56 (d, 1H), 6.75 (s, 1H),
.00 (dd, 1H), 7.87 (d, 1H); C NMR (CDCl ): δ 27.2,
2.3, 53.0, 58.6, 115.1, 117.6, 123.3, 126.2, 127.2, 129.3,
34.1, 141.1, 165.5, 174.2.
13
3
−
1
Yellow oil; FTIR (KBr, cm ): 3437, 3127, 3048, 2911,
1
1
3
5
7
6
1
743,1733, 1450; H NMR (CDCl ): δ 1.26 (t, 3H), 1.37 (t,
H), 1.55 (s, 3H), 4.11–4.25 (m, 2H), 4.26–4.34 (m, 2H),
.68 (br, 1H), 6.55 (d, 1H), 6.64 (dd, 1H), 6.75 (s, 1H),
.45 (d, 1H); C NMR (CDCl ): δ 14.0, 14.2, 26.7, 58.5,
1.2, 61.8, 113.3, 115.2, 116.8, 117.6, 127.9, 134.4, 136.4,
48.5, 165.8, 174.3.
3
2.15 | Dimethyl
6‐bromo‐2‐methyl‐1,2‐dihydroquinoline‐2,4‐
dicarboxylate, 3 k
13
3
−
1
Yellow solid; FTIR (KBr, cm ): 3126, 3050, 2990, 1741,
1
1
3
7
5
1
717, 1450; H NMR (CDCl ): δ 1.55 (s, 3H), 3.74 (s,
3
H), 3.83 (s, 3H), 4.61 (br, 1H), 6.51 (d, 1H), 6.70 (s, 1H),
.15 (dd, 1H), 7.98 (d, 1H); C NMR (CDCl ): δ 27.2,
2.1, 52.9, 58.6, 110.3, 115.6, 118.0, 127.0, 128.9, 132.2,
34.1, 141.5, 165.5, 174.1.
2
2
.11 | Diethyl
‐methyl‐6‐nitro‐1,2‐dihydroquinoline‐2,4‐
13
3
dicarboxylate, 3 g
−
1
Yellow solid; FTIR (KBr, cm ): 3131, 3051, 2981,
1
1
3
5
8
6
1
744,1721, 1451; H NMR (CDCl ): δ 1.26 (t, 3H), 1.37 (t,
2.16 | Dimethyl
6‐methoxy‐2‐methyl‐1,2‐dihydroquinoline‐
2,4‐dicarboxylate, 3 l
3
H), 1.61 (s, 3H), 4.15–4.29 (m, 2H), 4.30–4.38 (m, 2H),
.36 (br, 1H), 6.57 (d, 1H), 6.75 (s, 1H), 7.97 (dd, 1H),
.80 (d, 1H); C NMR (CDCl ): δ 14.0, 14.2, 28.3, 59.1,
1.7, 62.4, 113.1, 114.3, 123.4, 126.0, 126.8, 133.2, 138.8,
47.9, 164.7, 172.4.
13
3
−
1
Yellow oil; FTIR (KBr, cm ): 3129, 3053, 2987, 1740,
1
1722, 1453; H NMR (CDCl ): δ 1.54 (s, 3H), 3.74 (s,
3
3
6
H), 3.75 (s, 3H), 3.87 (s, 3H), 4.35 (br, 1H), 6.57 (d, 1H),
.71 (dd, 1H), 6.75 (s, 1H), 7.52 (d, 1H); C NMR (CDCl3):
13
2
.12 | Diethyl 2‐methyl‐1,2‐dihydrobenzo
δ 26.7, 52.1, 52.7, 55.7, 58.5, 111.4, 115.1, 116.2, 117.5,
27.8, 134.3, 136.6, 152.5, 166.1, 174.5.
[h]quinoline‐2,4‐dicarboxylate, 3 h
1
−
1
Reddish brown oil; FTIR (KBr, cm ): 3126, 3047, 2980,
1
1
3
5
2
742,1727, 1449; H NMR (CDCl ): δ 1.27 (t, 3H), 1.42 (t,
2.17 | Dimethyl
2,6‐dimethyl‐1,2‐dihydroquinoline‐2,4‐
dicarboxylate, 3 m
3
H), 1.60 (s, 3H), 4.14–4.29 (m, 2H), 4.33–4.42 (m, 2H),
.36 (br, 1H), 6.69 (d, 1H), 7.23 (d, 1H), 7.43–7.48 (m,
H), 7.73–7.77 (m, 1H), 7.85–7.88 (m, 1H), 7.90 (d, 1H);
1
3
−1
C NMR (CDCl ): δ 14.1, 14.3, 27.3, 58.6, 61.2, 61.8,
Yellow oil; FTIR (KBr, cm ): 3127, 3050, 2981, 1742,
3
1
1
1
11.3, 117.7, 120.0, 122.3, 124.1, 125.1, 126.4, 128.5,
29.3, 130.1, 134.2, 137.8, 166.3, 174.0.
1720, 1450; H NMR (CDCl ): δ 1.55 (s, 3H), 2.24 (s,
3
3H), 3.72 (s, 3H), 3.86 (s, 3H), 4.44 (br, 1H), 6.56 (d, 1H),
13
6
.67 (s, 1H), 6.91 (dd, 1H), 7.61(s, 1H); C NMR (CDCl3):
δ 20.6, 27.2, 52.1, 52.7, 58.4, 114.2, 116.4, 126.8, 127.9,
28.2, 130.3, 133.0, 140.2, 166.1, 174.5.
2
2
.13 | Dimethyl
‐methyl‐1,2‐dihydroquinoline‐2,4‐
dicarboxylate, 3i
1
2
.18 | Dimethyl
−
1
Yellow oil; FTIR (KBr, cm ): 3127, 3048, 2987, 1744,
6‐hedroxy‐2‐methyl‐1,2‐dihydroquinoline‐
2,4‐dicarboxylate, 3n
1
3
1
3
6
729, 1452; H NMR (CDCl ): δ 1.54 (s, 3H), 3.71 (s,
H), 3.86 (s, 3H), 4.57 (br, 1H), 6.61 (d, 1H), 6.67 (s, 1H),
.70 (t, 1H), 7.07 (t, 1H), 7.78 (dd, 1H); C NMR (CDCl3):
δ 27.3, 52.2, 52.7, 58.5, 114.4, 116.3, 118.6, 126.4, 128.3,
29.6, 132.7, 142.6, 166.2, 174.3.
13
−1
Yellow oil; FTIR (KBr, cm ): 3417, 3123, 3050, 2987,
1740, 1723, 1450; H NMR (CDCl ): δ 1.52 (s, 3H), 3.73
(s, 3H), 3.85 (s, 3H), 4.60 (br, 1H), 5.75 (s,1H), 6.55 (d,
1
3
1

EL‐REMAILY ET AL.
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13
1
H), 6.73 (s, 1H), 6.98 (dd, 1H), 7.72(s, 1H); C NMR
(
CDCl ): δ 27.2, 52.1, 52.8, 58.3, 113.9, 116.7, 123.8,
3
1
25.9, 126.2, 130.0, 134.1, 141.1, 165.7, 174.3.
2
6
.19 | Dimethyl
‐nitro‐2‐methyl‐1,2‐dihydroquinoline‐2,4‐
dicarboxylate, 3o
−
1
Yellow solid; FTIR (KBr, cm ): 3121, 3053, 2981, 1741,
1
1
3
7
5
1
720, 1450; H NMR (CDCl ): δ 1.51 (s, 3H), 3.65 (s,
3
H), 3.84 (s, 3H), 4.61 (br, 1H), 6.54 (d, 1H), 6.72 (s, 1H),
.15 (dd, 1H), 7.93(s, 1H); C NMR (CDCl ): δ 27.1,
2.2, 52.7, 58.2, 110.5, 115.7, 118.8, 127.3, 129.2, 132.10,
34.4, 142.1, 165.0, 174.1.
13
3
FIGURE 1 Powder x‐ ray pattern for the extracted TiO
2
nanoparticles
2
2
.20 | Dimethyl
‐methyl‐1,2‐dihydrobenzo[h]quinoline‐2,4‐
The particle size distribution can be explained on the
basis of TEM image for the extracted TiO and the calcu-
lated histogram (see Figure 3(a,b)) . It is observed that the
major of the particles have the size 19 nm. HRTEM image
2
dicarboxylate, 3p
−
1
Reddish brown oil; FTIR (KBr, cm ): 31271, 3050, 2987,
displayed in Figure 4a for the extracted TiO confirms the
2
1
1
3
7
7
1
1
743, 1722, 1451; H NMR (CDCl ): δ 1.62 (s, 3H), 3.78 (s,
H), 3.91 (s, 3H), 5.37 (br, 1H), 6.72 (d, 1H), 7.25 (d, 1H),
.43–7.48 (m, 2H), 7.74–7.78 (m, 1H), 7.86–7.90 (m, 1H),
.92 (d, 1H); C NMR (CDCl ): δ 27.2, 52.1, 52.8, 58.7,
11.1, 117.8,119.8, 122.3, 124.0, 125.2, 126.4, 128.6,
29.0, 130.2, 134.2, 137.9, 166.3, 174.4.
high crystalline nature of these nanoparticles. TEM
3
micrograph of a single TiO nanoparticle (Figure 4b)
2
shows the arrangements of atoms within single nanopar-
ticle. The presence of lines also depicts the crystallites of
13
3
TiO nanoparticles, which were otherwise absent in non-
2
metallic organic molecules. Selected area electron diffrac-
tion (SAED) patterns (Figure 5) show that the as‐prepared
powder is completely crystalline and entirely consists of
anatase phase. These are in agreement with XRD results
in Figure (1).
3
| FINDINGS AND DISCUSSION
The structural evolution extracted TiO was investigated
2
by XRD was closely matched with the Joint Committee
on powder diffraction standards (JCPDS Card No. 78–
[
39]
2
486).
It is clearly obtained from the XRD results,
3.1 | FTIR of the extracted TiO2
nanoparticles
which confirm the presence of TiO in the plant extract
and this compared with extracted TiO from Jatropha
curcas L.
means grain size of TiO is rather small. The average size
d’ crystallization in nanometer has been evaluated using
Debye Scherrer formula
The images show a narrow size distribution of parti-
cles with uniformed spherical structure morphology.
The surface morphology of the extracted TiO2 are
shown in Figure 2(a). The images show a narrow size dis-
tribution of particles with uniformed spherical structure
morphology. The structural composition was investigated
by EDX (Figure 2(b)). Ti and O peaks are only observed
in the spectrum, suggesting that the product is composed
of Ti and O. A quantitative EDS analysis shows that the
atom ratio Ti: O is 24: 51, close to 1: 2, confirming the
composition of the extracted product represent TiO2.
2
2
[
40]
The TiO peaks in Figure (1) are wide, which
FTIR spectrum analysis was performed to specify the bio-
molecules responsible for capping of the bioreduced TiO2
NPs synthesized using plant extract (Figure 6). FTIR of
Neem leaf plant (see Figure S1) indicates the presence of
active functional groups in the synthesized silver nanopar-
2
2
‘
[3,41]
and found to be 20 nm.
−
1
−1
ticles. The peaks observed at 3289 cm and 2964 cm
correspond to O–H and C–H stretching frequency, respec-
−
1
tively. The assignment at 1642 cm corresponds to C=O
group. The peak at 1040 might be contributed to the pres-
ence of methoxy group. It shows that the extracted TiO
2
−
1
NPs has absorption peaks were located at 714 cm (Ti–
−
1
O–O bond), 1076 cm (C–N stretch aliphatic amines
−
1
1172 cm (C–O stretching vibrations in alcoholic groups),
−
1
−1
1642 cm
(N–H bend bond), and 3426 cm
(O–H
stretching due to alcoholic group).

6
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EL‐REMAILY ET AL.
2 2
FIGURE 2 (a) SEM image for the extracted TiO nanoparticles. (b): EDS spectrum of the as extracted TiO nanoparticles
2 2
FIGURE 3 (a) Low magnification TEM image for the extracted TiO nanoparticles. (b): Particle size distribution of extracted TiO
nanoparticles
2 2
FIGURE 4 (a) HRTEM image for the extracted TiO . (b): HR‐TEM micrograph of extracted single Ti O nanoparticle
3
.2 | Functionalization of the extracted
suitable method. Such method is easily, environmentally
friendly and not costed method for the TiO NPs syn-
TiO nanoparticles in synthesis of
2
2
1
,2‐dihydroquinolines derivatives
thesis of at lower temperature form the sources of the
agricultural wastes. Their catalytic applications were
synthesis of 1,2‐dihydroquinolines derivatives 3a‐p in
excellent yields.
The TiO2 nanoparticles biosynthesis was progressed
Neem leaf extract method as a biodegradable and

EL‐REMAILY ET AL.
7 of 10
TABLE 1 The yielding amount percentages of TiO
2
NPs in the
synthesis of 1,2‐dihydroquinolines, 3
b
Catalysts/
Entry mol%
Catalysts/
Yield % Entry mol%
a
Yield %
1
2
3
4
2
3
4
5
62
75
85
92
5
6
7
8
6
7
8
9
98
98
96
92
a
Isolated Yield.
cascade reaction was carried out 4‐chloroaniline and
ethyl pyruvate 3 as a model reaction.
b
The reaction could not be proceeded in the absence of
the TiO catalyst. Moreover, the catalytic reaction was ini-
2
tiated by using three different types of TiO catalysts, i.e.,
2
TiO commercial, TiO nanoparticles fresh (extracted)
FIGURE 5 Selected area electron diffraction (SAED) patterns for
2
2
the extracted TiO
2
and recovered TiO nanoparticles. The optimized yielding
2
amount of product was afforded using TiO nanoparticles
2
in the shortest time because of the greater diffusion of
TiO nanoparticles in the reaction media. Similarity for
2
the recovered catalyst was resulted to the fresh TiO nano-
2
particles (Table 2).
To evaluate the effect of the solvents on the catalytic
process, various solvents were applied with estimation
of the reaction scope and limitation. In particular, it was
found that the syntheses of 1,2‐dihydroquinolines 3a‐p
catalyzed by TiO NPs were not only faster in various
2
solvents, but awarded higher yields under solvent free
conditions (Table 3).
2
FIGURE 6 FTIR spectra of extracted TiO nanoparticles
TABLE 2 The effect of different types of TiO
2
in the synthesis of
1,2‐dihydroquinolines, 3
b
a
Catalysts
Time
Yield %
When reacted arylamines 1a‐h with 2.0 mmol ethyl or
methyl pyruvate 2a,b, using TiO2 nanoparticles as an
TiO
2
commercial
4 hour
40 min
40 min
72
98
98
eco‐friendly
heterogeneous
catalyst
gave
1,2‐
TiO NPs fresh (extracted)
2
dihydroquinolines derivatives 3a‐p (Scheme 1) .
2
recovered TiO NPs
This protocol offers flexibility in tuning the molecular
complexity and diversity. The reactions proceeded to
completion almost instantly, and the reaction product
was quite pure and did not need to be purified by chro-
matographic tools, which could be recrystallized only in
ethanol.
a
Isolated Yield
TABLE 3 Solvent Effect on the synthesis of 1,2‐
dihydroquinolines (3
b 2
) catalyzed by TiO NPs
Solvent
Tim (min)
Yield (%)
Optimized conditions for the reaction within different
Toluene
190
180
160
90
60
63
63
88
87
90
98
mole amounts of TiO NPs, catalyst concentration has a
2
CHCl
DCM
3
remarkable role in the product yielding percentages. It
was detected that enhancing of the loaded amounts of
the catalyst from 2.0 to 6.0 mol% awards higher yield per-
centages to 98% of the product (Table 1). Further increase
of involved amounts of the catalyst more than 6.0 mol%
resulted to reduce product yield percentages due to
absorption of the products on the catalyst surface. The
EtOH
MeOH
90
H
2
O
60
Solvent free
45

8
of 10
EL‐REMAILY ET AL.
SCHEME 2 Proposed Reactions
Mechanisms of the extracted TiO
Catalyzed for Synthesis of 1,2‐
dihydroquinolines 3
2
NPs
Particularly, the reaction is more proceeded in polar
protic solvents (EtOH, MeOH and water) giving good
yields, whereas, in the aprotic solvents, e.g., toluene,
the polarity of the reaction media, which could be the
main factor for the reactivity of the catalytic process to
improve the yield of the wanted product, i.e., the protic
solvents have larger dielectric constant values compared
with aprotic (non‐polar) solvents. The protic (polar)
solvents those have a high probability to donate proton
easily within hydrogen bonds formation with the
substrate.
CHCl and DCM, the catalytic process gives observable
3
low yield. The dielectric constant is a measurement of
Such mechanistic proposal for the formation of 1,2‐
dihydroquinoline 3 was reported previously and most
likely begins with the generation of an imine from the
aniline 2 and the ketoester 1 (Scheme 2), followed by
addition of the enolate to the imine. The extracted TiO2
NPs activated α‐ketoesters 5 reacted with imine 4 to give
[
42]
6
which is a good electrophile.
An electron‐rich ben-
zene ring could add to the keto ester group 7, and water
elimination followed by proton shift would eventually
form the 1,2‐dihydroquinoline 3.
2
FIGURE 7 Recyclability of TiO NPs in the model reaction
2 2
FIGURE 8 (a) TEM image for the recoverable TiO catalyst. (b): Particle size distribution of recoverable TiO catalyst

EL‐REMAILY ET AL.
9 of 10
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.3 | Reusability of the catalyst
The heterogeneous TiO2 NPs catalyst could be easily
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9
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| CONCLUSION
Green synthesis and characterization of TiO nanoparti-
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Chem. Pharm. Bull. 1998, 46, 1235.
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13] a) X.‐Y. Liu, C.‐M. Che, Angew. Chem. Int. Ed. 2008, 47, 3805;
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ORCID
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Mahmoud Abd El Aleem Ali Ali El‐Remaily https://orcid.
org/0000-0002-3591-0077
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