Palladium nanoparticles decorated on a novel polyazomethine as a highly productive and recyclable catalyst for Suzuki coupling reactions and 4-nitrophenol reduction

Article abstract of DOI:10.1016/j.jorganchem.2019.120886

This report displays the procedure in preparation of fast, highly productive, reusable, and easily retrievable Pd nanoparticles (NPs) as a heterogeneous catalyst (Pd NPs?P(3-MPAP)) immobilized on a novel polyazomethine with phenol group, Poly(3-methyl-4-((pyridin-2-ylmethylene)amino)phenol) (P(3-MPAP)), and the investigation of its catalytic efficiency in fabrication of several biaryl compounds by Suzuki coupling reactions and reduction of 4-nitrophenol to 4-aminophenol. The structures of the synthesized monomer, polymer support material and nanocatalyst were identified by UV–Vis, FT-IR, ¹H NMR, TGA, XRD, SEM and EDS methods. The catalytic activity of Pd NPs?P(3-MPAP) catalyst in the synthesis of various biaryls by Suzuki coupling reactions was explored using microwave irradiation, which is rapid, easy, solventless and environmentally friendly method. The nanocatalyst presented outstanding advantageous methodology containing easy work-up with high reaction yield (99%) at very short reaction time (5 min) in solventless media using very low catalyst loading (0.007 mol%) in the synthesis of biaryls. Additionally, the harmful 4-nitrophenol was completely reduced to industrially useful 4-aminophenol in the presence of Pd NPs?P(3-MPAP) with low catalyst amount (1 mg), at very short reaction time (60s) without any toxic solvent (in water) at room temperature. Additionally, reproducibility test results for both catalytic reactions show that the highly productive nanocatalyst was easily retrievable and reusable for six and five sequential cycles, respectively, for Suzuki coupling reactions and reduction of 4-NP without any notable loss in its catalytic activity.

Full text of DOI:10.1016/j.jorganchem.2019.120886

Journal Pre-proof
Palladium nanoparticles decorated on a novel polyazomethine as a highly productive
and recyclable catalyst for Suzuki coupling reactions and 4-nitrophenol reduction
Nuray Yılmaz Baran
PII:
S0022-328X(19)30329-8
DOI:
https://doi.org/10.1016/j.jorganchem.2019.120886
JOM 120886
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 30 June 2019
Revised Date: 2 August 2019
Accepted Date: 5 August 2019
Please cite this article as: Nuray.Yı. Baran, Palladium nanoparticles decorated on a novel
polyazomethine as a highly productive and recyclable catalyst for Suzuki coupling reactions and
4-nitrophenol reduction, Journal of Organometallic Chemistry (2019), doi: https://doi.org/10.1016/
j.jorganchem.2019.120886.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of
record. This version will undergo additional copyediting, typesetting and review before it is published
in its final form, but we are providing this version to give early visibility of the article. Please note that,
during the production process, errors may be discovered which could affect the content, and all legal
disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.

1
2
Palladium Nanoparticles Decorated on a Novel Polyazomethine as a Highly Productive
and Recyclable Catalyst for Suzuki Coupling Reactions and 4-nitrophenol Reduction
3
4
5
6
Nuray Yılmaz Baran *
*Aksaray University, Technical Vocational School, Department of Chemistry Technology,
Aksaray 68100, Turkey
7
8
9
Corresponding author:
10
11
Address: Aksaray University, Technical Vocational School, Department of Chemistry
Technology, Aksaray 68100, Turkey
12
13
14
Tel.: +90 3822882135; fax: +90 3822882028.
E-mail address: nybaran@aksaray.edu.tr (Nuray Yılmaz Baran)
15
16
17
18
19
20
21
1

1
Abstract
2
3
This report displays the procedure in preparation of fast, highly productive, reusable, and
easily retrievable Pd nanoparticles (NPs) as a heterogeneous catalyst (Pd NPs@P(3-MPAP))
immobilized on a novel polyazomethine with phenol group, Poly(3-methyl-4-((pyridin-2-
ylmethylene)amino)phenol) (P(3-MPAP)), and the investigation of its catalytic efficiency in
fabrication of several biaryl compounds by Suzuki coupling reactions and reduction of 4-
nitrophenol to 4-aminophenol. The structures of the synthesized monomer, polymer support
material and nanocatalyst were identified by UV-Vis, FT-IR, 1H-NMR, TGA, XRD, SEM and
EDS methods. The catalytic activity of Pd NPs@P(3-MPAP) catalyst in the synthesis of
various biaryls by Suzuki coupling reactions was explored using microwave irradiation,
which is rapid, easy, solventless and environmentally friendly method. The nanocatalyst
presented outstanding advantageous methodology containing easy work-up with high reaction
yield (99%) at very short reaction time (5 min.) in solventless media using very low catalyst
loading (0.007 mol%) in the synthesis of biaryls. Additionally, the harmful 4-nitrophenol was
completely reduced to industrially useful 4-aminophenol in the presence of Pd NPs@P(3-
MPAP) with low catalyst amount (1 mg), at very short reaction time (60s ) without any toxic
solvent (in water) at room temperature. Additionally, reproducibility test results for both
catalytic reactions show that the highly productive nanocatalyst was easily retrievable and
reusable for six and five sequential cycles, respectively, for Suzuki coupling reactions and
reduction of 4-NP without any notable loss in its catalytic activity.
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Keywords: Catalyst; Pd nanoparticles; Polyazomethines; reduction of 4-nitrophenol; Suzuki
coupling reactions.
23
24
2

1
1. Introduction
2
3
Palladium catalyzed cross coupling reactions emerged as extraordinarily method to form
carbon-carbon bonding in synthetic organic chemistry [1]. These coupling reactions have
been intensively utilized in the production of polymers and biaryls which play a key role in
various vital industrial applications thanks to their use in pharmaceutical intermediates,
agrochemicals, biologically active, and natural products [2-5]. Thus, palladium catalyzed
cross coupling reactions have attracted great attention of researchers in recent years. Among
these reactions, Suzuki coupling reactions, which have been performed by the reactions of
arylboronic acids with aryl halides, have been intensively preferred by many researchers
because of their outstanding properties such as mild reaction conditions, ease of separation of
byproducts from the reaction mixture, and high tolerance towards a wide range of functional
groups [6]. Homogeneous and heterogeneous palladium catalysts have been used for these
powerful synthetic organic reactions. Heterogeneous catalysts have gained enormous
relevance in terms of their superiorities such as ease of purification and separation of catalyst
and product, ease of retrievability, high reusability, high performance and selectivity of
catalyst, and minimization of palladium leaching, which make them stupendous candidates for
industrial applications, compared to homogeneous catalysts [7-9]. However, drawbacks such
as requirement of high temperature, long reaction time and toxic organic solvent in traditional
Suzuki coupling reactions led researchers to seek a new ways [10, 11]. Thus, several modern
methods such as ultrasound irradiation, microwave irradiation, photo-activated methods have
been recently developed to overcome these problems [12, 13]. Among these techniques,
microwave irradiation has been evaluated as a promising method for industrial applications
due to its priorities such as unnecessity of harmful organic solvent, requirement of very short
reaction time, low reaction temperature, less energy, low workforce and, attainable high
product yield [14].
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
3

1
2
Aromatic nitro compounds such as 4-nitrophenol (4-NP) are considered as the most common
organic pollutants in wastewaters. These harmful organic compounds are produced from
wastes of dye, explosive, and pharmaceutical factories, and their existence in water even at
minimum level threatens human, plant and aquatic life due to their high toxic, mutagenic and
carcinogenic effects [15, 16]. They have also been reported as high priority toxic pollutants by
the United States Environmental Protection Agency [17]. Thus, their removal or degradation
process is of great importance from the point of view life of all living creatures and
environmental. Therefore, various methods such as thermal decomposition [18], adsorption
[19], electrochemical degradation [20], biological degradation [21], photo catalysis [22],
electro-Fenton method [23] and catalytic reduction have been developed. Among them,
catalytic reduction which is an effective, economic, safe and green is the most preferred
method [24]. In catalytic reduction of 4-NP, this harmful compound is converted into 4-
aminophenol (4-AP) which is very useful and effective for many applications such as
photographic developer, anticorrosion lubricant, corrosion inhibitor, and analgesic and
antipyretic drugs [16, 25].
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
In this study, a novel polyazomethine containing phenol group supported Pd NPs catalyst
which was reusable, easily retrievable, fast and highly effective was designed for both the
synthesis of biaryls via Suzuki coupling reactions and the reduction of 4-NP to 4-AP. Firstly,
P(3-MPAP) was synthesized as support material via oxidative polycondensation reaction of 3-
methyl-4-((pyridin-2-ylmethylene)amino)phenol (3-MPAP) Schiff base in aqueous alkaline
medium with NaOCl oxidant. Then, Pd NPs was immobilized on P(3-MPAP) support
material. The structures of all the generated materials was illuminated by various
characterization methods. Then, the catalytic efficiency of Pd NPs@P(3-MPAP) was
investigated for I) the synthesis of various biaryl compounds by Suzuki coupling reactions
using microwave irradiation technique and II) the reduction of highly hazardous 4-NP to 4-
4

1
2
3
4
5
AP. Moreover, reusability and recoverability tests for Pd NPs@P(3-MPAP) were performed
in both catalytic conversion reactions. The obtained results revealed that the designed
nanocatalyst was highly active towards both Suzuki coupling reactions and reduction of 4-NP
and it could be easily regenerated and reused without any great loss in its catalytic efficiency
in both catalytic reactions.
6
2. Experimental
7
8
2.1. Materials
4-Amino-3-methylphenol, 2-pyridinecarboxaldehyde, phenyl boronic acid, aryl halides,
Palladium(II) chloride (PdCl2), 4-nitrophenol, cesium carbonate (Cs2CO3), potassium
carbonate (K2CO3), sodium carbonate (Na2CO3), magnesium sulfate (MgSO4), Sodium
borohydride (NaBH4), methanol, ethyl acetate, dimethylformamide (DMF), dimethyl
sulfoxide (DMSO), and toluene were purchased from Merck Chem. Co. (Germany). Sodium
hypochlorite (NaOCl, 15% aqu.) was obtained from Pl-dess Chemistry Co. (Turkey).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
2.2. Method
2.2.1. Synthesis of 3-MPAP
3-MPAP was synthesized as Schiff base monomer by condensation reaction of 4-amino-3-
methylphenol and 2-pyridinecarboxaldehyde (Scheme 1).
A
solution of 2-
pyridinecarboxaldehyde (10 mmol, 0.98 mL) in 5 mL methanol was added into the solution of
4-amino-3-methylphenol (10 mmol, 1.23g) in 15 mL methanol. The reaction was performed
by stirring at 60 ºC for 6 h. The finalization of the reaction was intervally monitored by TLC
and FTIR techniques. It was seen that yellow crystals formed in the red reaction mixture after
the reaction. The yellow crystals were filtered and washed with methanol. The obtained Schiff
base monomer was recrystallized twice from methanol and dried at room temperature. (Yield:
86%)
5

1
2
2.2.2. Synthesis of P(3-MPAP)
3
P(3-MPAP) was attained by oxidative polycondensation reaction of 3-MPAP Schiff base
monomer in aqueous alkaline medium using NaOCl oxidant. 1 mmol (0.212 g) of 3-MPAP
was dissolved in 0.01 M 10 mL KOH solution. When the determined polymerization
temperature was reached, 1 mmol NaOCl was dribbled to the dark yellow monomer solution
and it was seen that the color of the solution immediately turned to blackish brown. After the
decided reaction time ended up, the obtained solution was cooled and the synthesized polymer
was precipitated by adding 0.1 M HCl solution. Then, the acquired polymer was washed with
hot water (3x100 mL) and ethyl acetate (3x50 mL) to remove mineral salts and unreacted
monomer, respectively. It was dried in an oven at 80 ˚C.
4
5
6
7
8
9
10
11
12
13
14
15
Scheme 1. Synthesis of 3-MPAP and P(3-MPAP).
16
17
18
19
20
2.2.3. Preparation of Pd NPs@P(3-MPAP) catalyst
0.25 g of P(3-MPAP) which was dissolved in 10 mL ethanol was added to the solution of 0.05
°
g of PdCl2 in 20 mL ethanol. The reaction was performed at 70 C for 24 h by continuously
stirring under reflux. Then, the obtained reaction product was filtered, washed with ethanol,
and dried at 80 °C. (Yield: 90%)
21
22
23
2.2.4 General procedure for Suzuki coupling reactions
24
25
26
In the process of determination of the fabricated catalyst efficiency in Suzuki coupling
reactions, microwave irradiation technique, which is very fast, easy to use, highly productive
and nontoxic, was used. Firstly, the reaction of phenylboronic acid and 4-iodoanisol was
6

1
2
selected as the model coupling reaction for the synthesis of biaryl compounds by Suzuki
coupling reactions. Then, the effects of catalyst loading, reaction time, base type, and
microwave irradiation power on the biaryl product yield were investigated on the chosen
model coupling reaction. After the optimum reaction conditions were found, the general
method which was performed for the fabrication of different biaryls by Suzuki coupling
reactions was as follows: 1.87 mmol of phenyl boronic acid, 1.12 mmol of the selected aryl
halide, 3.75 mmol of potassium carbonate, and 0.007 mol% of Pd NPs@P(3-MPAP) were
added in a Schlenk tube. The coupling reactions were performed in solvent-free medium
using 400W microwave irradiation for 5 min. The obtained mixture was cooled to room
temperature (RT) at the end of the reaction. 5 mL toluene was added on the cooled mixture
and it was filtered. Then, the filtrate was extracted with 5 mL water twice. MgSO4 was added
on the separated organic phase which contains biaryl product to completely eliminate water.
Then, toluene in the obtained product was evaporated at room temperature. Finally, the
product yield was calculated and its chemical structure was identified by GC/MS analysis.
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
2.2. Catalytic reduction procedure of 4-nitrophenol
Aqueous solution of freshly prepared NaBH4 (0.05 M, 0.1 mL) was added on aqueous solution
of 4-NP (1.25 × 10−4 M, 2 mL) in a tube and the mixture was stirred at room temperature for 2
min. 1 mg of Pd NPs@P(3-MPAP) catalyst was added in the prepared mixture and stirred
until the yellow color of the mixture completely turned into colorless. The reduction process
was monitored by UV-Vis analysis. After the reduction reaction was completed, the
nanocatalyst was removed from the reaction mixture by filtering. The nanocatalyst was reused
after it was washed and dried in an oven.
7

1
2
2.3. Characterization
GPC analysis of the polymer was done using Shimadzu Prominence Gel Permeation
Chromatography with Nucleogel GPC 103-5 VA300/7.7 column (detector: refractive index
detector (RID), eluent: dimethylformamide (DMF), flow rate: 0.5 mL/min, temperature: 40
°C). UV-Vis spectra of 3-MPAP, P(3-MPAP) and Pd NPs@P(3-MPAP) were obtained by
Shimadzu UV-1700 PharmaSpec UV-Visible Spectrophotometer in DMSO in the wavelength
range of 260-800 nm. FTIR spectra of all the fabricated materials were recorded by Perkin
Elmer FTIR Spectrometer in the wavenumber range of 4000-650 cm-1. 1H-NMR spectra of 3-
3
4
5
6
7
8
°
9
MPAP and P(3-MPAP) were attained by Bruker Avance 500 MHz NMR in DMSO at 25 C.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Thermal analyses of 3-MPAP, P(3-MPAP) and Pd NPs@P(3-MPAP) catalyst were done
using EXSTAR S11 7300 Thermal Analyzer ( nitrogen atmosphere, heating range: 30-1200
°C, heating rate: 10◦C/min ). X-ray diffraction (XRD) pattern of Pd NPs@P(3-MPAP) catalyst
was attained from Rigaku Smart Lab X-Ray Diffractometer (at 40 kV, 30 mA, and 2θ with a
scan angle of 5−80°). SEM micrographs of 3-MPAP, P(3-MPAP) and Pd NPs@P(3-MPAP)
and EDS spectrum and EDS mapping analysis of Pd NPs@P(3-MPAP) were obtained by
FEI Quanta 450 FEG FE-ESEM-EDS. Palladium ion content of Pd NPs@P(3-MPAP) catalyst
was detected by Perkin Elmer Optima 2100 DV Inductively Coupled Plasma (ICP) Optical
Emission Spectrometer (OES). The chemical structures of the synthesized biaryl products
were illuminated by GC-MS Agilent GC-7890 A- MS 5975.
3. Results and Discussion
3.1. Determination of optimum polymerization conditions
The effects of NaOCl concentration, polymerization temperature, and time parameters on the
yield of P(3-MPAP) were investigated to determine optimum polymerization conditions and
the obtained results are given in Fig. 1. As seen in Fig.1.a., the polymer yield increased with
8

1
2
increasing NaOCl concentration up to 0.2 mol/L concentration (94.3%). It was observed that
the monomer precipitated at higher NaOCl concentration than 0.2 mol/L and thus the
polymerization process stopped. The polymer yield also increased with increasing
polymerization temperature up to 80 ˚C. After this temperature, the yield decreased with
increasing temperature (Fig.1.b.). Additionally, the polymer yield also increased with
increasing polymerization time up to 5 h when it was reached the highest yield (Fig.1.c.).
Then, the yield decreased after longer durations. The reason of decrease in the polymer yield
at higher temperatures and periods may be explained by the fact that polymer chains could be
broken at high temperatures and periods. These short broken chains may be removed by
dissolving during washing in the purification process [26-28]. Consequently, the highest
polymer yield was obtained at 80 ˚C for 5 h using 0.2 mol/L NaOCl concentration and P(3-
MPAP) which was synthesized under the determined optimum polymerization conditions was
used in all following process.
3
4
5
6
7
8
9
10
11
12
13
14
15
Figure 1. The effect of (a) NaOCl concentration, (b) polymerization temperature and (c) time
16
17
18
19
20
21
on the yield of P(3-MPAP).
3.2. Molecular Weight Distribution of P(3-MPAP)
Molecular weight distribution of P(3-MPAP) support material was determined by GPC
analysis. The analysis result showed that P(3-MPAP) had broad monomodal molecular weight
distribution. Number average molecular weight (Mn), weight average molecular weight (Mw)
9

1
2
and polydispersity index (PDI) values of P(3-MPAP) which were obtained at determined
optimum conditions were found as 85390, 23146 g/mol and 3.68, respectively.
3
4
3.3. Structures of 3-MPAP, P(3-MPAP) and Pd NPs@P(3-MPAP) catalyst
3.3.1. UV-Vis spectra
5
6
UV-Vis spectra of 3-MPAP, P(3-MPAP) and Pd NPs@P(3-MPAP) catalyst are given in Fig.
2. While two distinct bands were observed at 285 and 356 nm in the spectrum of the
monomer, the same bands were seen at 287 and 365 nm as imperceptible broad shoulder-
shaped in the broadened polymer spectrum. These bands can be ascribed to π-π∗ transitions of
benzene ring (-C=C) and imine functional groups and n-π∗ transitions of OH functional group
for the monomer and the polymer, respectively. When the polymer spectrum was compared to
that of the monomer, I) broadening, imperceptibility and shifting of bands and II) broadening
and extension of spectrum (to 700nm) were observed in the polymer spectrum. These
changes refer that the polymerization process was successfully achieved [29-32].
Additionally, only a broad band at 323 nm was observed in the UV spectrum of Pd NPs@P(3-
MPAP) catalyst compared to P(3-MPAP) spectrum. This band originates from surface
plasmon resonance corresponding to the reduction of PdII to Pd0 and the formation of Pd NPs
[33].
7
8
9
10
11
12
13
14
15
16
17
18
10

1
2
Figure 2. UV-Vis spectra of 3-MPAP, P(3-MPAP) and Pd NPs@P(3-MPAP) catalyst.
3
4
3.3.2. FTIR Spectra
5
FT-IR spectra of 3-MPAP, P(3-MPAP), and Pd NPs@P(3-MPAP) catalyst are displayed in
Fig. 3. The vibration peaks of HC=N- functional group, which are typical for Schiff bases,
their polymers and all derivatives, are detected at 1627, 1631, and 1617 cm-1 for 3-MPAP,
P(3-MPAP), and Pd NPs@P(3-MPAP) catalyst, respectively. The existence of this peak in the
polymer spectrum indicates that azomethine structure was also preserved in the polymer
backbone without degradation [26, 29, 30]. Other important peaks in the spectra of 3-MPAP,
P(3-MPAP), and Pd NPs@P(3-MPAP) catalyst are summarized as follows: OH vibrations at
3054, 3129, 3206 cm-1; C-H stretching vibrations at 2989, 2962, 2960 cm-1; C=C vibrations at
1584-1440; 1589-1434 and 1591-1441 cm-1; the plane aliphatic C-H bending vibrations at
1348, 1374, 1375 cm-1; C-O vibrations at 1221, 1211, and 1212 cm-1; C-N vibrations at 1047,
1094 and 1099 cm-1.
6
7
8
9
10
11
12
13
14
15
11

1
2
Figure 3. FTIR spectra of 3-MPAP, P(3-MPAP), and Pd NPs@P(3-MPAP) catalyst.
3
4
5
6
7
8
3.3.3.1H-NMR Spectra
1H-NMR analyses were carried out to determine the chemical structure of the synthesized
monomer and polymer support material. The signals of the proton of characteristic -OH
functional groups, –CH=N- and –CH3 groups are seen at 9.94 (s, 1H), 9.40 (s, 1H) and 2,48
(s, 3H) ppm and 10.19 (s, 1H), 9.60 (s, 1H) and 2,37 (s, 3H) ppm in the spectra of 3-MPAP
12

1
2
3
4
5
6
and P(3-MPAP), respectively. While the signals of protons belonging to aromatic structure
of 3-MPAP were recorded at δ= 8.65 (s, 1H,); 8.47 (d, 1H); 8.12 (d, 1H); 7.90 (t, 1H); 7.45 (t,
1H); 7.10 (d, 1H,); 6.65 (d, 1H); ppm, these signals were observed at δ= 8.20 (d, 1H); 8.09 (d,
1H); 7.95 (t, 1H); 7.60 (t, 1H); 7.21 (s, 1H) ppm for P(3-MPAP). When the obtained signals
are evaluated, it is seen that the synthesis of 3-MPAP and P(3-MPAP) were successfully
carried out.
7
8
3.3.4.Thermal Degradation Process
9
10
11
12
13
14
15
16
17
18
19
Thermal degradation behaviors of 3-MPAP, P(3-MPAP), and Pd NPs@P(3-MPAP) catalyst
were determined by TGA and the obtained curves are given in Fig. 4. Additionally, the
measured thermal degradation data for all the synthesized materials are presented in detail in
Table 1. When the thermal behaviors of 3-MPAP, P(3-MPAP), and Pd NPs@P(3-MPAP)
catalyst are compared to each other, the temperatures at which 50% weight losses occurred
are determined as 413, 788, and 831, respectively. These data indicate that while the
polymeric support material is more thermally stable than the monomer due to increasing
conjugation, the nanocatalyst is also more thermally stable than the polymeric support
material due to Pd0 content. Additionally, carbon residue of the monomer, polymer and
°
nanocatalyst at 1200 C were determined as 16.5%, 30.4%, and 31.6%, respectively. The
increment of undecomposed part of Pd NPs@P(3-MPAP) catalyst is due to Pd NPs content.
13

1
2
3
4
5
6
Figure 4. TG curves of 3-MPAP, P(3-MPAP), and Pd NPs@P(3-MPAP) catalyst.
Table 1. Thermal degradation data of 3-MPAP, P(3-MPAP), and Pd NPs@P(3-MPAP) catalyst.
Weight
Residue at
a
b
Ton
Temperature ranges of
weight loss stages (˚C)
losses at
each stage
(%)
Tmax
T50%
(˚C)
Compound
1200 °C
(%)
(˚C)
(˚C)
122-220
220-600
600-1200
4.4
62.9
16.2
185
361
-
122
413
16.5
3-MPAP
30-124
124-832
832-1200
1.3
49.8
18.4
75
362
-
124
134
788
831
30.4
31.6
P(3-MPAP)
30-134
134-1200
620-1200
4.8
35.2
28.4
62
289
Pd NPs@P(3-MPAP)
7
8
9
T
T
max represents the temperature at the maximum weight loss rate.
on represents the onset degradation temperature.
T50% represents the temperature at which 50% weight losses occurred.
10
11
12
3.3.5.XRD Analysis
13
14
15
XRD analysis was performed to identify both the crystalline structure of Pd NPs@P(3-
MPAP) catalyst and the presence of Pd NPs in the catalyst structure (Fig. 5). Broad peaks at
about 10° (2θ) and 25° (2θ) can be ascribed to the amorphous nature of the support material.
14

1
2
3
4
5
Three sharp diffraction peaks in the pattern of Pd NPs@P(3-MPAP) catalyst were determined
at 40.4° (2θ), 46.5° (2θ) and 66.7 (2θ). These peaks can be indexed to (111), (200) and (220)
planes of Pd and attributed to the face centered cubic palladium [16, 34-36] These diffractions
confirm the crystalline structure of the nanocatalyst and verify the presence of Pd NPs (Pd0)
and their purity [16].
6
7
8
Figure 5. XRD patterns of 3-MPAP, P(3-MPAP), and Pd NPs@P(3-MPAP) catalyst.
9
10
11
12
13
14
15
16
17
18
3.3.6.SEM, EDS and ICP-OES analysis
The surface morphologies of 3-MPAP, P(3-MPAP), and Pd NPs@P(3-MPAP) catalyst were
investigated by FE-SEM analysis. FE-SEM images of 3-MPAP and P(3-MPAP) in Fig. 6.a
and 6.b show that while 3-MPAP had irregular platelike surface with fissures, P(3-MPAP)
surface became more irregular surface with small particles after the oxidative
polycondensation reaction. It is seen in the SEM image of Pd NPs@P(3-MPAP) catalyst
(Figure 6.c) that Pd NPs had spherical shape and they were homogenously distributed on the
support material surface. The size of immobilized Pd NPs on the support material is estimated
about 50 nm.
15

1
2
3
Figure 6. SEM of micrographs of (a) 3-MPAP, (b) P(3-MPAP), and (c) Pd NPs@P(3-
MPAP) catalyst.
4
5
Additionally, EDS analysis was carried out for Pd NPs@P(3-MPAP) catalyst to determine the
elemental composition. The presence and distributions of carbon, oxygen, nitrogen and
palladium were determined by EDS spectrum and EDS mapping analysis, respectively (Fig.
7.). As seen in EDS mapping analysis, Pd NPs was homogenously distributed on the support
material. Additionally, the signals belonging to palladium are obviously observed in EDS
spectrum of Pd NPs@P(3-MPAP) catalyst. These results verify that the presence of palladium
in the composition of Pd NPs@P(3-MPAP) catalyst. Furthermore, the content of palladium in
Pd NPs@P(3-MPAP) catalyst was also found by ICP-OES technique. The quantity of
palladium in the nanocatalyst was measured as 23.12% and 23.68% by mass with ICP-OES
and EDS analyses, respectively.
6
7
8
9
10
11
12
13
14
16

1
2
3
Figure 7. EDS mapping analysis and spectrum of Pd NPs@P(3-MPAP) catalyst.
4
5
3.4 Catalytic performance of Pd NPs@P(3-MPAP) catalyst
3.4.1 Catalytic activity of Pd NPs@P(3-MPAP) catalyst in Suzuki-Miyaura reactions
Catalytic effectiveness of the designed Pd NPs@P(3-MPAP) was tested in the production of
biaryls by Suzuki coupling reactions using microwave irradiation which presents simple and
fast methodology with high reaction yield in solvent-free media. The coupling reaction
between 4-iodoanisole and phenylboronic acid was chosen as the representative reaction. To
find ideal reaction parameters, preliminary experiments were carried out in the presence of Pd
NPs@P(3-MPAP) catalyst and the obtained results are presented in Fig.8. As a result of the
experiments which were performed using different catalyst loadings, reaction time, bases, and
microwave powers, the highest reaction yield (99%) was reached with 0.007 mol% Pd
NPs@P(3-MPAP) catalyst (Fig.8.a.), for 5 min. reaction time, (Fig.8.b.) K2CO3 as base
(Fig.8.c.) and 400 W microwave power (Fig.8.d.), and these conditions were determined as
the ideal reaction conditions. The catalytic performance of Pd NPs@P(3-MPAP) was
evaluated in the synthesis of twenty different biaryls using microwave irradiation technique
6
7
8
9
10
11
12
13
14
15
16
17
17

1
2
under the determined ideal reaction conditions and the results are summarized in Table 1. As
seen in Table, Pd NPs@P(3-MPAP) was applied as the catalyst in Suzuki coupling reactions
of aryl iodides, which have different functional groups, and the desired biaryls were
synthesized with good yields up to 99%. Additionally, the activity of Pd NPs@P(3-MPAP)
was also assessed against cross-couplings of phenylboronic acid with various aryl bromides
and yields ranging between 97% and 65% were obtained. As the next step, coupling ability of
Pd NPs@P(3-MPAP) was also investigated using aryl chlorides which have poor activity. It
was found that Pd NPs@P(3-MPAP) catalyzed Suzuki coupling reactions of aryl chlorides
with good product yields. These results indicated that Pd NPs@P(3-MPAP) has good catalytic
performance against Suzuki cross coupling reactions by rapidly converting aryl halides into
desired biaryls. This result facilitates the use of the fabricated nanocatalyst in industrial
applications as an efficient material.
3
4
5
6
7
8
9
10
11
12
13
14
Figure 8. The effects of (a) catalyst loading, (b) reaction time, (c) base type and (d)
15
microwave power on catalytic activity of Pd NPs@P(3-MPAP).
18

1
2
Table 2. Suzuki coupling reactions of several aryl halides with phenylboronic acid in the
presence of Pd NPs@P(3-MPAP) catalyst.
Entry
1
X
R
Yield
99
93
86
67
71
81
91
92
97
98
90
97
78
81
65
69
69
73
79
77
I
I
I
I
I
I
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
4-OCH3
3-NO2
4-NH2
2-CH3
3-CH3
4-CH3
2-OCH3
3-OCH3
4-OCH3
4-CN
3-NO2
4-NO2
3-NH2
4-NH2
3-CH3
4-CH3
2-OCH3
3-OCH3
4-OCH3
3-NO2
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
3
4
5
Reaction conditions: 1.8 mmol aryl halides, 1.2 mmol phenyl boronic acid, 3.5 mmol K2CO3 and 0.007mol%
Pd NPs@P(3-MPAP) catalyst, 5 min, 400 W.
6
7
3.4.1 Catalytic activity of Pd NPs@P(3-MPAP) catalyst in the reduction of 4-NP
4-NP is one of the most common organic pollutants in wastewaters and known to have
carcinogenic, toxic and mutagenic effect for human beings and animals. Thus, degradation of
this harmful chemical to a harmless product is of great importance for all living creatures
from both industrial and environmental points of view. 4-AP which is reduction product of 4-
NP, is a byproduct used in fabrication of antipyretic and analgesic drugs and, hair dying
agents [37]. Thus, the reduction of harmful 4-NP to harmless 4-AP is a desirable eco-friendly
8
9
10
11
12
13
19

1
2
catalytic reaction. To be useful industrially and environmentally, the catalytic ability of the
fabricated nanocatalyst was also assessed toward the reduction of 4-NP to 4-AP with NaBH4
in water at room temperature (Scheme 2.) and the catalytic reduction studies were monitored
by UV-Vis analysis. As seen in Fig.9, 4-NP has a strong absorption band at 317ꢀnm. When
NaBH4 was added into 4-NP solution, the band of 4-NP shifted to 400 nm because of the
production of 4-nitrophenolate ion (4-NPT) [38]. The yellow color of 4-NP solution
simultaneously turned to bright yellow with the addition of NaBH4 which justifies the
fabrication of 4-NPT. After the addition of prepared nanocatalyst into the resulting mixture,
the intensity of absorbance peak at 400 nm decreased gradually as the catalytic reaction
progressed and finally disappeared within 60 s. Additionally a new band appeared at 296ꢀnm,
which is attributed to the formation of 4-AP, in parallel with the catalytic reaction [39].
Moreover, after the catalytic reaction was completed, bright yellow reaction solution turned to
colorless. These results indicated that the catalytic reduction of 4-NP to 4-AP was
successfully performed in 60 s in the presence of Pd NPs@P(3-MPAP) catalyst. On the other
hand, a control experiment was carried out without catalyst to reveal the catalytic activity of
the catalyst, and it was found that there is no reduction without its presence. This finding
reveals that the prepared nanocatalyst is necessary for the catalytic reduction of 4-NP. The
catalytic reduction of 4-NP followed pseudo-first-order kinetic and the rate constant was
determined as 0.04 s-1 by using the formula in below.
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
ln(A/A0)=ln(c/c0)ꢀ=ꢀ-kt
21
22
where c0 and c correspond to the initial concentration of 4-NP and concentration of 4-NP at
the measured reaction time, respectively, and k (s−1) is the rate constant.
20

1
2
Scheme 2. Reduction of 4-NP to 4-AP in the presence of Pd NPs@P(3-MPAP).
3
4
Figure 9. (a) UV–Vis absorption spectrum for the catalytic reduction of 4-NP in the presence
5
6
7
8
of Pd NPs@P(3-MPAP) catalyst and (b) linear dependence graph between ln (c/c0) and time.
(Reaction conditions: 4-NP: 1.25 × 10−4 M, NaBH4 : 0.05 M, Pd NPs@P(3-MPAP): 1 mg, in water, at
RT)
9
10
11
12
13
14
3.4.3 Reusability performance of Pd NPs@P(3-MPAP) catalyst in the catalytic systems
Reusability performance of any catalyst is an important parameter from the point of industrial
applicability and continuity by reducing cost [40]. Thus, reusability performance of Pd
NPs@P(3-MPAP) catalyst was investigated for both Suzuki coupling reactions and the
reduction of 4-NP. The reusability test of Pd NPs@P(3-MPAP) catalyst in Suzuki coupling
reactions was performed for the chosen model reaction under the found ideal reaction
21

1
2
conditions using microwave irradiation technique. After the completion of model reaction, the
filtered catalyst was washed with hot water and methanol for recovery process. The easily and
fast recovered catalyst was reused and these recovery and reuse processes were recurrently
repeated. At the end of the sixth subsequent cycle, the designed catalyst fabricated the desired
biaryl with a conversion of 84%.
3
4
5
6
The reusability performance of Pd NPs@P(3-MPAP) catalyst was also tested for the
reduction of 4-NP. In this process, the catalyst was filtered by simple filtration from the
mixture in which the reduction reaction was completed and washed ethanol and water. After
the obtained catalyst was dried in 80 ºC in an oven, it was used in other cycle. Even after four
recovery and recycle processes, the designed catalyst reduced 4-NP without no loss of its
catalytic efficiency.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Additionally, FTIR spectra which was recorded after the recycle processes indicated that the
spectra of the fresh and the recycled catalysts for both catalytic reactions were similar. These
results display that the chemical structures of the six and four times recovered and recycled
catalyst for Suzuki coupling reaction and reduction of 4-NP could be invariably preserved.
These results show that Pd NPs@P(3-MPAP) is an ideal nanocatalyst in production of biaryls
and the reduction of 4-NP for industrial applications in terms of its fast and easily
recoverability, high efficiency, good recyclability without any valuable loss of its catalytic
activity.
Hot filtration test
After model Suzuki coupling reaction was carried out for 3 min under optimum reaction
conditions, Pd NPs@P(3-MPAP)catalyst was filtered out from the reaction media and 55%
product yield was obtained in this process. Then, the reaction was allowed with the filtrate
(without catalyst) for another 2 min and no increase was observed in the reaction yield.
Additionally, after the reaction, palladium leaching in the filtrate was checked by ICP
22

1
2
analyses and no palladium content was detected. These findings showed that Pd NPs@P(3-
MPAP) catalyst had heterogeneous nature.
3
4
4. Conclusions
5
In summary, a novel highly effective, easily recoverable, repeatedly reusable, robust and
thermally stable Pd NPs@P(3-MPAP) catalyst was fabricated for the synthesis of several
biaryl compounds by Suzuki coupling reactions and the reduction of harmful 4-NP to 4-AP.
Thermal analysis results display that both the newly synthesized polyazomethine derivative
P(3-MPAP) support material and Pd NPs@P(3-MPAP) catalyst have high thermal stability.
This property could enable their utilization in industrial materials necessitating thermal
durability. The catalytic efficiency of the fabricated Pd NPs@P(3-MPAP) catalyst was
investigated against i) the synthesis of twenty different biaryl compounds by Suzuki coupling
reactions using simple, fast and nontoxic microwave irradiation technique and ii) the
reduction of 4-NP to 4-AP. Pd NPs@P(3-MPAP catalyst provided high product yield (up to
99%) with low catalyst loading (0.007 mol%) in solventless media at short reaction time (5
min) using microwave irradiation technique with simple work-up procedure for all Suzuki
coupling reactions. Additionally, the designed catalyst entirely reduced 4-NP, which is very
harmful for all creatures and environment, to 4-AP (100% yield), in mild reaction conditions
(at RT and in water) at very short reaction time (60 s). Moreover, reproducibility tests
showed that Pd NPs@P(3-MPAP)catalyst was an easily retrievable material with simple and
rapid procedure and could be reused at least six and four times with no valuable loss in Suzuki
coupling reaction and 4-NP reduction, respectively. The effective reusability and easy
recoverability of the fabricated nanocatalyst play a key role for commercial and industrial
applications to decrease cost. This paper reveals that polyazomethines can be good stabilizers
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
23

1
2
3
4
5
6
for different metallic nanoparticles and their catalysts can be used in various catalytic
systems.
Acknowledgments
I gratefully acknowledge the Aksaray University Research Funds for the financial support of
this work (Project No. 2018-065).
24

1
2
References
[1] A.F. Littke, G.C. Fu, Palladium-Catalyzed Coupling Reactions of Aryl Chlorides,
Angewandte Chemie International Edition 41(22) (2002) 4176-4211.
3
4
[2] M. Pérez-Lorenzo, Palladium Nanoparticles as Efficient Catalysts for Suzuki Cross-
Coupling Reactions, The Journal of Physical Chemistry Letters 3(2) (2012) 167-174.
[3] S.M. Islam, P. Mondal, A.S. Roy, S. Mondal, D. Hossain, Heterogeneous Suzuki and
copper-free Sonogashira cross-coupling reactions catalyzed by a reusable palladium(II)
complex in water medium, Tetrahedron Letters 51(15) (2010) 2067-2070.
[4] C. Torborg, M. Beller, Recent Applications of Palladium-Catalyzed Coupling Reactions in
the Pharmaceutical, Agrochemical, and Fine Chemical Industries, Advanced Synthesis &
Catalysis 351(18) (2009) 3027-3043.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
[5] J. Magano, J.R. Dunetz, Large-Scale Applications of Transition Metal-Catalyzed
Couplings for the Synthesis of Pharmaceuticals, Chemical Reviews 111(3) (2011) 2177-2250.
[6] R. Martin, S.L. Buchwald, Palladium-Catalyzed Suzuki−Miyaura Cross-Coupling
Reactions Employing Dialkylbiaryl Phosphine Ligands, Accounts of Chemical Research
41(11) (2008) 1461-1473.
[7] P. Veerakumar, P. Thanasekaran, K.-L. Lu, S.-B. Liu, S. Rajagopal, Functionalized Silica
Matrices and Palladium: A Versatile Heterogeneous Catalyst for Suzuki, Heck, and
Sonogashira Reactions, ACS Sustainable Chemistry & Engineering 5(8) (2017) 6357-6376.
[8] M. Nasrollahzadeh, B. Jaleh, A. Ehsani, Preparation of carbon supported CuPd
nanoparticles as novel heterogeneous catalysts for the reduction of nitroarenes and the
phosphine-free Suzuki-Miyaura coupling reaction, New Journal of Chemistry 39(2) (2015)
1148-1153.
[9] M. Nasrollahzadeh, S. Mohammad Sajadi, A. Rostami-Vartooni, M. Khalaj, Green
synthesis of Pd/Fe3O4 nanoparticles using Euphorbia condylocarpa M. bieb root extract and
25

1
2
their catalytic applications as magnetically recoverable and stable recyclable catalysts for the
phosphine-free Sonogashira and Suzuki coupling reactions, Journal of Molecular Catalysis A:
Chemical 396 (2015) 31-39.
3
4
[10] P. Das, C. Sarmah, A. Tairai, U. Bora, Highly efficient amine-based catalytic system for
room temperature Suzuki–Miyaura reactions of aryl halides with arylboronic acids, Applied
Organometallic Chemistry 25(4) (2011) 283-288.
5
6
7
[11] B. Talat, Y.B. Nuray, M. Ayfer, A new air and moisture stable robust bio polymer
based palladium catalyst for highly efficient synthesis of biaryl compounds, Applied
Organometallic Chemistry 32(2) (2018) e4076.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
[12] K. Martina, M. Manzoli, E.C. Gaudino, G. Cravotto, Eco-Friendly Physical Activation
Methods for Suzuki–Miyaura Reactions, Catalysts 7(4) (2017) 98.
[13] B. Talat, Y.B. Nuray, M. Ayfer, Sustainable chitosan/starch composite material for
stabilization of palladium nanoparticles: Synthesis, characterization and investigation of
catalytic behaviour of Pd@chitosan/starch nanocomposite in Suzuki–Miyaura reaction,
Applied Organometallic Chemistry 32(2) (2018) e4075.
[14] A.-R. Hajipour, F. Rafiee, Dimeric ortho-palladated complex of 2,3-
dimethoxybenzaldehyde oxime catalyzed Suzuki–Miyaura cross-coupling reaction under
microwave irradiation, Journal of the Iranian Chemical Society 12(7) (2015) 1177-1181.
[15] K. Naseem, R. Begum, Z.H. Farooqi, Catalytic reduction of 2-nitroaniline: a review,
Environmental Science and Pollution Research 24(7) (2017) 6446-6460.
[16] M. Atarod, M. Nasrollahzadeh, S. Mohammad Sajadi, Green synthesis of
Pd/RGO/Fe3O4 nanocomposite using Withania coagulans leaf extract and its application as
magnetically separable and reusable catalyst for the reduction of 4-nitrophenol, Journal of
Colloid and Interface Science 465 (2016) 249-258.
26

1
2
[17] M. Nasrollahzadeh, Z. Issaabadi, R. Safari, Synthesis, characterization and application of
Fe3O4@SiO2 nanoparticles supported palladium(II) complex as a magnetically catalyst for
the reduction of 2,4-dinitrophenylhydrazine, 4-nitrophenol and chromium(VI): A combined
theoretical (DFT) and experimental study, Separation and Purification Technology 209 (2019)
136-144.
3
4
5
6
[18] P.C. Chen, W. Lo, K.H. Hu, Molecular structures of mononitroanilines and their thermal
decomposition products, Theoretica Chimica Acta 95(3) (1997) 99-112.
7
8
[19] K. Li, Z. Zheng, X. Huang, G. Zhao, J. Feng, J. Zhang, Equilibrium, kinetic and
thermodynamic studies on the adsorption of 2-nitroaniline onto activated carbon prepared
from cotton stalk fibre, Journal of Hazardous Materials 166(1) (2009) 213-220.
[20] N.E. Jiménez Jado, C. Fernández Sánchez, J.R. Ochoa Gómez, Electrochemical
Degradation of Nitroaromatic Wastes in Sulfuric Acid Solutions: Part I, Journal of Applied
Electrochemistry 34(5) (2004) 551-556.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
[21] H. Börnick, P. Eppinger, T. Grischek, E. Worch, Simulation of Biological Degradation of
Aromatic Amines in River Bed Sediments, Water Research 35(3) (2001) 619-624.
[22] S. Liu, Y.-J. Xu, Efficient electrostatic self-assembly of one-dimensional CdS–Au
nanocomposites with enhanced photoactivity, not the surface plasmon resonance effect,
Nanoscale 5(19) (2013) 9330-9339.
[23] M.A. Oturan, J. Peiroten, P. Chartrin, A.J. Acher, Complete Destruction of p-Nitrophenol
in Aqueous Medium by Electro-Fenton Method, Environmental Science & Technology
34(16) (2000) 3474-3479.
[24] T. Baran, Biosynthesis of Highly Retrievable Magnetic Palladium Nanoparticles
Stabilized on Bio-composite for Production of Various Biaryl Compounds and Catalytic
Reduction of 4-Nitrophenol, Catalysis Letters 149(6) (2019) 1721-1729.
27

1
2
[25] E. Farzad, H. Veisi, Fe3O4/SiO2 nanoparticles coated with polydopamine as a novel
magnetite reductant and stabilizer sorbent for palladium ions: Synthetic application of
Fe3O4/SiO2@PDA/Pd for reduction of 4-nitrophenol and Suzuki reactions, Journal of
Industrial and Engineering Chemistry 60 (2018) 114-124.
3
4
5
[26] N. Yılmaz Baran, M. Saçak, Synthesis, characterization and molecular weight
monitoring of a novel Schiff base polymer containing phenol group: Thermal stability,
conductivity and antimicrobial properties, J. Mol. Struct. 1146 (2017) 104-112.
[27] N. Yılmaz Baran, M. Saçak, Preparation of highly thermally stable and conductive Schiff
base polymer: Molecular weight monitoring and investigation of antimicrobial properties, J.
Mol. Struct. 1163 (2018) 22-32.
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
[28] N. Yılmaz Baran, M. Saçak, Molecular weight monitoring of poly(2-[[4-
(dimethylamino)benzylidene]amino]phenol) depending on polymerization conditions:
investigation of thermal stability, antimicrobial properties, and conductivity enhancement,
Advances in Polymer Technology 37(8) (2018) 3007-3016.
[29] A. Özbülbül, H. Mart, M. Tunçel, S. Serin, A new soluble Schiff base polymer with a
double azomethine group synthesized by oxidative polycondensation, Designed Monomers
and Polymers 9(2) (2006) 169-179.
[30] C. Demetgül, A. Delikanlı, O.Y. Sarıbıyık, M. Karakaplan, S. Serin, Schiff Base
Polymers Obtained by Oxidative Polycondensation and Their Co(II), Mn(II) and Ru(III)
Complexes: Synthesis, Characterization and Catalytic Activity in Epoxidation of Styrene,
Designed Monomers and Polymers 15(1) (2012) 75-91.
[31] N. Yılmaz Baran, H.Ö. Demir, S. Kostekçi, M. Sacak, Poly-2-[(4-
methylbenzylidene)amino]phenol: Investigation of thermal degradation and antimicrobial
properties, Journal of Applied Polymer Science 132(14) (2015) n/a-n/a.
28

1
2
[32] N. Yılmaz Baran, M. Karakışla, H.Ö. Demir, M. Saçak, Synthesis, characterization,
conductivity and antimicrobial study of a novel thermally stable polyphenol containing
azomethine group, Journal of Molecular Structure 1123 (2016) 153-161.
3
4
[33] M. Nasrollahzadeh, S.M. Sajadi, E. Honarmand, M. Maham, Preparation of palladium
nanoparticles using Euphorbia thymifolia L. leaf extract and evaluation of catalytic activity in
the ligand-free Stille and Hiyama cross-coupling reactions in water, New Journal of
Chemistry 39(6) (2015) 4745-4752.
5
6
7
8
[34] N. Gogoi, U. Bora, G. Borah, P.K. Gogoi, Nanosilica-anchored Pd(II)-Schiff base
complex as efficient heterogeneous catalyst for activation of aryl halides in Suzuki–Miyaura
cross-coupling reaction in water, Applied Organometallic Chemistry 31(9) (2017) e3686.
[35] C. Sarmah, D. Sahu, P. Das, Anchoring palladium acetate onto imine-functionalized
silica gel through coordinative attachment: An effective recyclable catalyst for the Suzuki–
Miyaura reaction in aqueous-isopropanol, Catalysis Today 198(1) (2012) 197-203.
[36] T. Baran, Highly recoverable, reusable, cost-effective, and Schiff base functionalized
pectin supported Pd(II) catalyst for microwave-accelerated Suzuki cross-coupling reactions,
International Journal of Biological Macromolecules 127 (2019) 232-239.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
[37] Y.T. Woo, D.Y. Lai, Aromatic amino and nitro–amino compounds and their halogenated
derivatives, Patty's Toxicology (2001) 1-96.
[38] X. Gao, H. Zhao, Y. Liu, Z. Ren, C. Lin, J. Tao, Y. Zhai, Facile synthesis of
PdNiP/Reduced graphene oxide nanocomposites for catalytic reduction of 4-nitrophenol,
Materials Chemistry and Physics 222 (2019) 391-397.
[39] J. Nimita Jebaranjitham, C. Mageshwari, R. Saravanan, N. Mu, Fabrication of amine
functionalized graphene oxide – AgNPs nanocomposite with improved dispersibility for
reduction of 4-nitrophenol, Composites Part B: Engineering 171 (2019) 302-309.
29