Synthesis and characterization of chitosan pyridyl imine palladium (CPIP) complex as green catalyst for organic transformations

Article abstract of DOI:10.1007/s11696-021-01526-w

In this work, the modification of chitosan using 2-acetyl pyridine has been used to prepare an intermediate, chitosan pyridyl imine (CPI), in first step and then in second step it is further reacted with Pd(OAc)₂ to develop chitosan pyridyl imine palladium (CPIP) complex catalyst in a very simplistic way. The formed CPIP has been extensively characterized with respect to raw chitosan utilizing methods including FT-IR, pyrolysis GC–MS, XRD, XPS, FE-SEM, EDS, TGA-DTG and DSC. TG-DSC study suggested that the catalyst is thermally stable up to 300?°C. This catalyst shows an excellent activity in the reduction of toxic pollutant nitrobenzene to less toxic aniline. CPIP complex has also been found to give magnificent results in Suzuki–Miyaura and Heck cross-coupling reactions, and therefore, using this green catalyst, the toxic phosphine ligand can be excluded from cross-coupling reactions. This study furnishes an economic and eco-friendly catalyst for organic transformation in sustainable chemistry.

Full text of DOI:10.1007/s11696-021-01526-w

Chemical Papers (2021) 75:2835–2850
https://doi.org/10.1007/s11696-021-01526-w
ORIGINAL PAPER
Synthesis and characterization of chitosan pyridyl imine palladium
(CPIP) complex as green catalyst for organic transformations
Narendra Singh Chundawat1 · Sultan Pathan1 · Girdhar Pal Singh1 · Arup Saha Deuri2 · Payam Zarrintaj3 ·
Narendra Pal Singh Chauhan1
Received: 17 September 2020 / Accepted: 19 January 2021 / Published online: 3 February 2021
© Institute of Chemistry, Slovak Academy of Sciences 2021
Abstract
In this work, the modifcation of chitosan using 2-acetyl pyridine has been used to prepare an intermediate, chitosan pyridyl
imine (CPI), in frst step and then in second step it is further reacted with Pd(OAc)2 to develop chitosan pyridyl imine pal-
ladium (CPIP) complex catalyst in a very simplistic way. The formed CPIP has been extensively characterized with respect
to raw chitosan utilizing methods including FT-IR, pyrolysis GC–MS, XRD, XPS, FE-SEM, EDS, TGA-DTG and DSC.
TG-DSC study suggested that the catalyst is thermally stable up to 300 °C. This catalyst shows an excellent activity in the
reduction of toxic pollutant nitrobenzene to less toxic aniline. CPIP complex has also been found to give magnifcent results
in Suzuki–Miyaura and Heck cross-coupling reactions, and therefore, using this green catalyst, the toxic phosphine ligand
can be excluded from cross-coupling reactions. This study furnishes an economic and eco-friendly catalyst for organic
transformation in sustainable chemistry.
Keywords Chitosan · Pyridyl · Characterization · Palladium catalyst · Suzuki · Heck reaction · Reduction · Azo dye
Introduction
level (Anderson 2006). Thus, it is environmental need to
develop process which can facilitate to get rid of such pol-
lutants by greenway.
Nitrobenzene compounds are major pollutant due to their
explosive nature and high toxicity, carcinogenicity and other
adverse efects to living beings and environment. The study
by U.S. Environmental Protection Agency (EPA) found that
nitrobenzene content in water must be less than 17 ppm (Sun
et al. 2016,2019). Thus, it is important and equally necessary
to reduce nitrobenzene into relatively less toxic aniline by
using eco-friendly process. Suzuki–Miyaura and Heck cross-
coupling reactions requires ligand like phosphine which is
toxic and can cause disruption of neural tissues performance,
blocked energy metabolism and altered the cellular redox
Chitosan is a linear polysaccharide composed of ran-
domly distributed N-acetyl-D-glucosamine and D-glucosa-
mine (Jalali et al. , 2016). Chitin’s deacetylation results in
the formation of chitosan. Chitosan is used for adsorbent of
metals, wound dressings, drug dispensing and ophthalmic
lenses, and it can be easily developed into foils or fbrils
(Kumar 2000; Vincent and Guibal 2001). Chitosan plays
important role in catalysis support, and its activity has been
reported in various literature, e.g., in chromate reduction
(with use of Pd) (Huang et al. 2012; Molnár 2019), phenol
(Pd) (An et al. 1994; Tang et al. 1994), and nitro-aromatics
(Ni, Cu, Cr, Zn) (Han et al. 1996). Yin et al. narrated asym-
metric hydrogenation (Yin et al. 1999). The hydrophilic
characteristic of chitosan was used by Quignard et al. to
develop aqueous phase catalysts supported by chitosan, for
the allylic substitution reaction by palladium catalyst. (Buis-
son and Quignard 2002; Quignard et al. 2000) The chitosan
can be redesigned by inducing various functional groups
(Functionalization) to prepare divergent co-ordination
sites which can provide catalysts for olefns cyclopropa-
nation (Cu-Schif’s base) (Sun et al. 2002), alkylbenzenes
Narendra Singh Chundawat and Sultan Pathan have contributed
equally to this work.
* Narendra Pal Singh Chauhan
narendrapalsingh14@gmail.com
1
Department of Chemistry, Faculty of Science, Bhupal
Nobles’University, Udaipur 313001, India
2
Balakrishna Industries Lt (BKT), Bhuj, Gujrat, India
3
School of Chemical Engineering, Oklahoma State University,
420 Engineering North, Stillwater, OK 74078, USA
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oxidation (Mn or Ni-Schif’s base) (Chang et al. 2002), and
DOPA (3,4-dihydroxyphenylalanine) oxidation (Hu et al.
2001). The oxidation of DOPA involved the homogeneous
phase due to chitosan solubility in acetic acid, functionali-
zation and re-precipitation, while the others involved the
direct functionalization of the solid chitosan. N-allylation of
amines has been made utilizing a biodegradable and recy-
clable heterogeneous chitosan-supported palladium (Pd)
catalyst (Baig et al. 2015; Kawatsura et al. 2008; Plietker
2006; Polet et al. , 2006; Welter et al. 2004). Pd nanoparti-
cles encapsulated on thiourea-chitosan are utilized for green
Suzuki reaction (Afrose et al. 2015; Hajipour et al. 2015;
Sin et al. 2010), reduction of nitro to amine (Krogul-Sobczak
et al. 2019; Su et al. 2016; Wang et al. , 2017) and Heck
reaction (Hajipour et al. 2015; Sin et al. 2010; Kurandina
et al. 2018; Shao and Qi 2017). Cross-coupling reaction has
tremendous application in pharmaceuticals, agrochemical
and fne chemicals (Barder et al. 2005; Buchwald 2008; Cor-
bet and Mignani 2006; Magano and Dunetz 2011; Sedghi
et al. 2019; Torborg and Beller 2009; Chauhan et al. 2019;
Chauhan and Chundawat 2019; Marziale et al. 2011).
Chitosan forms Schif’s base with 2-acetyl pyridine to
give chitosan pyridyl imine (Kim et al. 2004; Li and Liu
2004). These N-heterocyclic imines behave as nitrogen-
based ligand which replaces phosphine ligands. N-heterocy-
clic imine is used as metal ligand; imine has more oxidizing
tendency than that of phosphine ligands that enhances the
stability of corresponding palladium toward the gases like
O2, etc., water and heat. Ligand N-heterocyclic imine has the
similar σ-donor and small π-acceptor properties, and thus,
N-heterocyclic imine forms frm bond with Co (Someya
et al. 2007), Pd (Peris and Crabtree 2004), Cu (Hu et al.
2004) and Ni (Dorta et al. 2005) metals. In cross-coupling
reactions, Pd metal complexes with N-heterocyclic imine are
better catalyst to achieve outstanding catalytic activities, and
this complex facilitates the reduction of nitro compounds
into amine. N-heterocyclic imine supports oxidative addition
of reagent and can aid in the reductive elimination of bi aryl
compounds due to its strong σ-donating properties (Fortman
and Nolan 2011; Li et al. 2012; Pathan et al. 2020).
characterized by FT-IR, XRD, Py-GC–MS, XPS FE-
SEM–EDS, BET surface area, TG-DTG and DSC. Sur-
prisingly, it has been found that the prepared CPIP com-
plex catalyst displayed excellent catalytic performance in
Suzuki–Miyaura and Heck coupling reactions at elevated
temperature without any phase transfer agents, toxic solvents
and inert atmosphere, achieving a green chemical synthesis.
Experimental
Reagents
All reagents and solvents were procured from mercantile
sources. Chitosan was purchased from Loba Chem. Com-
pound confrmed by TLC and analyzed against analytical
grade standard reference compound which is available in
market.
Synthetic method
Refux for around 6 h was carried out after addition of chi-
tosan (2.0 g, equivalent to 12 mmol NH2), 2-acetylpyridine
(2.05 g, 12 mmol to ethanol (75 ml) and acetic acid (20 ml).
The solid was fltered from the resultant mixture after cool-
ing. Approx. 3.75 g of chitosan pyridyl imine (CPI) was
obtained after ethanol wash and 6 h of vacuum drying.
Stirred 1 (2.0 g) with palladium acetate (0.25 g,
0.5 mmol) in acetone (100 ml) for 8 h at 25–30 °C. After Pd
adsorption, the solid was washed completely to draw out any
unadsorbed Pd. The catalyst was rinsed with ethanol 50 g,
dried to solid at 75 °C for 8 h under vacuum to give 2.05 g
chitosan pyridyl imine palladium (CPIP) complex catalyst
(Fig. 1). The intrinsic viscosity and viscosity average molec-
ular weight of CPI (η = 3.4 dL/g and Mv = 1.48 × 105 Da)
and CPIP (η=3.5 dL/g and Mv=1.63×105 Da) were deter-
mined by Ubbelohde viscometer using acetic acid as solvent.
It is clearly revealed from these results that both intrinsic
viscosity and viscosity average molecular weights directly
impact the functional groups present in chitosan.
‘Green’ cross-coupling reactions have concentrated on
scheming readily reclaimable catalysts, thus facilitating
the segregation of product and clinging to green chemistry
(Kashin et al. 2018; Lipshutz et al. 2010; Mai et al. 2019;
Sun et al. 2015; Sydnes 2017). Chitosan-supported silver
nanoparticles have been used for reduction of 4-nitrophenol
to 4-aminophenol in the presence of NaBH4 (Hasan et al.
2019). Chitosan Fe3O4–Pd nanoparticles as heterogeneous
catalyst were fabricated for Suzuki and Heck coupling reac-
tions in water. (Hasan 2020).
Instrumentations
FT-IR spectrometer (Perkin Elmer) in set up of KBr pellets
over the range of 400–4000 cm−1 wave numbers was used
for the Fourier transform infrared (FT-IR) studies. NMR test
was performed with 400 and 500 MHz spectrometers for 1H
NMR and 100 MHz for 13C NMR on Bruker Supercon Mag-
net Avance DRX-300 spectrometers in deuterated solvents
with TMS as a reference (chemical shifts δ in ppm, coupling
constant J in Hz.). Multiplicities are described as follows:
singlet (s), doublet (d), triplet (t), multiplet (m), and broad
singlet (br s). The ESI positive ion mode is used for mass
Herein, we demonstrate a facile synthesis of green
catalyst, chitosan pyridyl imine complex catalyst using
raw chitosan, 2-acetylpyridine and Pd(OAc)2. It has been
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Fig. 1 The chitosan pyridyl imine complex synthesis and conversion of it to corresponding Pd complex
spectra and HRMS. The progression of reaction was surveil-
led by thin-layer chromatography (TLC) on pre-coated silica
gel plates. All compounds were identifed and characterized
by TLC, 1H NMR, 13C NMR, MS and HRMS.
analysis zone. Chitosan and PDIP complex were launched
on a stainless steel sample holder and incubated for 12 h
under vacuum before transferring to the spectrometer analy-
sis chamber.
Py-GC/MS instrument was designed by Agilent tech-
nologies (Santa Clara, California, United States). Single-
shot pyrolyser unit from frontier laboratories with a plati-
num coil and a quartz sample tube was coupled to column.
Samples were heated up in furnace at 700 °C and an inter-
face at 280 °C@ 7 °C/min and held at this temperature for
1 min. The pyrolysis products were divided on an Ultra
alloy HP-5MS column (frontier laboratories, Tokyo, Japan)
with helium (99.998% pure) as carrier gas (100 kPa). The
pyrolysis chamber was maintained at 250 °C and purged
with helium (99.998% pure). The GC was programmed
from 75 °C (1 min) to 280 °C at 7 °C /min (elution time
40.28 min). The mass spectrometer was conducted with a
scan range of m/z = 15–450 in electron impact mode, and
the products were discovered by comparing to mass spectral
library of NIST and results in the previous researches. XRD
apparatus is equipped with x′ Celerator solid-state detec-
tor. The apparatus contains vertical theta-theta goniometer
(0° < 2θ < 160°). The radiation utilized is Cu K-alpha-1,
whereas nickel metal is utilized as beta flter.
Morphology of the synthesized PDIP complex was visu-
alized through feld emission scanning microscopy (FE-
SEM) on Hitachi-SU8010 microscope. Elemental analysis
of the yields was determined from EDS coupled with FE-
SEM apparatus. Dried pattern images were taken utilizing
Carl Zeiss Axio Imager 2Am microscope. Images were ana-
lyzed using axio-vision software. The surface of catalyst was
evaluated by the Brunauer–Emmett–Teller (BET) technique
on a Quanta chrome NOVA 2200E BET device; before each
assessment, the sample was heated to 50 °C and maintained
at such temperature for 12 h. The BET surface area was
computed based on the adsorption data in the relative pres-
sure range of 0.05 to 0.25.
The thermal stability of the chitosan and PDIP complex
was investigated using thermo-gravimetric analysis instru-
ment (PerkinElmer TGA 8000) from 30 to 600 °C at a heat-
ing rate of 10 °C/min under nitrogen atmosphere, and then,
after from 600 to 850 °C, oxygen was purged. The transition
temperature of both chitosan and PDIP complex was deter-
mined using diferential scanning calorimetry (PerkinElmer
DSC 4000) from 40 to 180 °C at a heating rate of 10 °C/min
under nitrogen atmosphere.
The XPS assay was conducted with a spectrome-
ter (model MULTILAB 2000 Base system with X-ray, Auger
and ISS attachments), using an Mg-Kα source (1253.6 eV)
(Twin Anode Mg/Al (300/400 W) X-ray Source.). The
X-ray source was operated at a power of 300 W (10 keV
and 30 mA). The pressure inside the vacuum chamber was
5 × 10−8 torr. A hemispherical analyser with 110 mm was
employed with 4 variable analyzer slits, viz 5, 2, 1 mm and
4 mm, which operates in constant analyser energy (CAE)
and constant retard ratio (CRR) modes. The CCD camera
and zoom microscope for optical viewing was utilized to
check the spectrum and to identify the analysis area size.
All spectra were achieved utilizing a 900-μm-diameter
Results and Discussions
FT‑IR analyses
The FT-IR spectra of the pristine chitosan and CPIP complex
in the 4000–400 cm−1 ranges are depicted in Fig. 2. The
absorption bands for chitosan at 3300–3350 related to the
N–H group and 2700–3000 cm−1 are ascribed to methylene
(-CH2) group. The wide band peak at 3450 attributed to the
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Chemical Papers (2021) 75:2835–2850
Fig. 2 FT-IR spectra of a chitosan, b CPIP complex catalyst
hydroxyl groups (Hada et al. 2019; Mozafari and Chauhan
2019; Sudheesh et al. 2010). The FT-IR spectrum of the
CPIP complex catalyst which was almost identical to the
corresponding chitosan except carbonyl stretching in acetyl
group, which was at 1640 cm−1, has completely vanished in
CPIP complex catalyst, which clearly revealed that de-acet-
ylation was completely done. The strength of the IR bond at
3300–3350 cm−1 reduced suggesting the stabilizing of the
palladium nanoparticles in the chitosan medium. The pres-
ence of new peaks at 1300–1500 cm−1 is attributed to C=N
groups of pyridyl moieties present in CPIP complex catalyst.
temperature. The whole ion chromatograms for chitosan
and CPIP pyrolysis were discovered by utilizing the Nist
library. For chitosan, there were fve peaks in pyrogram,
which may be due to acetic acid (RT 2.44 min; RA = 98%)
derived from chitin, pyrrol (RT 3.02 min; RA = 85%)
derived from chitin/chitosan, methylpyridine (RT
3.56 min; RA = 95%) derived from chitosan, acetylpyri-
dine (RT 6.25 min; RA = 95%) derived from chitosan
and an unknown compound (RT 9.15 min; RA = 75%))
derived from chitin, whereas for CPIP complex catalyst
there were three large peaks in pyrogram, which may
be due to acetic acid (RT 2.39 min; RA = 99%) derived
from chitin, pyrazine (RT 2.87 min; RA = 97%) derived
from chitosan, pyridine (RT 2.93 min; RA = 93%) derived
from chitin, acetamide (RT 3.22 min; RA = 93%) derived
from chitin, methyl pyrazine (RT 3.47 min; RA = 97%)
derived from chitosan and acetylpyrazine (RT 6. 13 min;
RA = 74%) derived from chitosan. These results suggest
that pyrolysis mechanism may be owing to unzipping, ran-
dom scission and side group removal. In such polymers,
pyrolysis provides fragmentation to tinier segments and
unzipping to monomer. The attached groups to the side
chain were weaker rather than backbone bonds. The side
groups are detached from the backbone before cracked
into tinier pieces; therefore, monomer and oligomers were
not observed.
Pyrolysis GC–MS
To analyze the intact insoluble organics, pyrolysis GC–MS
was used as it is uphill task to analyze them by traditional
chromatographic techniques. Pyrolysis decomposes insolu-
ble samples into volatile molecules and facilitates the seg-
regation and identifcation of decomposed fragments by gas
chromatography followed by mass spectrometry (Chauhan
et al. 2011). The mechanism of polymer degradation in
pyrolysis (GC/MS) is a technique founded on the volatile
fragments production by thermal energy and analyzed by
GC/MS (Chauhan et al. 2012; Chauhan 2013; Furuhashi
et al. 2009).
The degradation of polymers is basically a free radical
procedure commenced by bond separation at the pyrolysis
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Chemical Papers (2021) 75:2835–2850
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to the interaction with palladium acetate clearly suggested
XRD analyses
the proposed structure of CPIP complex catalyst.
The 2θ values are in between 10° and 20° in XRD pattern for
chitosan, which is probably attributed to hydrogen bonding
between –OH and –NH2 groups. XRD data for chitosan and
CPIP complex catalyst are given in Table 1. The character-
istic semicrystalline peaks of pure chitosan are observed at
9.4792° and 20.08° (Fig. 3). In the case of CPIP complex,
a change in the intensity of the chitosan peaks (8.9197° and
20.2420°) was observed on the addition of Pd(OAc)2 to chi-
tosan pyridyl imine. Shift in the peaks of chitosan is owing
XPS analysis
XPS (X-ray photo-electron spectroscopy) is a powerful
method to examine how metal ions bind onto these patterns.
To further investigate the mechanism of catalyst formation
and also the interaction present in between Pd and CPI, the
high-resolution C 1s XPS, N 1s XPS, Pd 3d v and O 1s XPS
spectra are depicted in Fig. 4a–h, and data for diferent runs
Table 1 XRD data of raw
Compound
Pos. (°2θ)
FWHM total (°2θ)
d-spacing (Å)
Rel. Int. (%)
chitosan and CPIP complex
catalyst
Raw chitosan
9.4792
20.0801
8.9197
3.6553
2.5878
2.8663
2.6531
9.32258
4.41845
9.90607
4.38348
69.32
100.00
28.71
CPIP complex catalyst
20.2420
100.00
Fig. 3 X-ray difractogram for a chitosan and b CPIP complex catalyst
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Fig. 4 XPS analyses (a, b) C 1s (c, d) N 1s, Pd 3d (e, f) and O 1s plus Pd 3p (g, h) for CPIP complex catalyst
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Table 2 Roles of major spectral bands based on binding energies (BE) and atomic concentration (AC) for CPIP complex catalyst
Element
Start BE
Peak BE
End BE
Height (counts FWHM eV
per second)
Atomic %
Assignments
C1s scan A
C1s Scan B
C1s Scan C
Pd3d5 Scan A
289.6
289.6
289.6
283.51
285.04
286.57
334.78
336.55
531.15
530.34
531.71
532.12
534.18
398.51
280.95
280.95
280.95
331.95
331.95
527.45
527.45
527.45
527.45
527.45
394.9
12,421.72
22,845.94
8156.23
4469.16
6766.66
11,092.64
12,040.92
29,038.1
11,453.78
1259.27
1.39
1.36
1.77
1.88
1.82
1.06
1.95
1.31
1.96
1.9
15.98
28.56
13.32
0.68
1
4.03
8.03
13.02
7.69
0.82
6.56
C–C or adventitious carbon
C–N, C=N, C–O or C–O–C
O–C–O, C=O
–
–
Pd–O
Pd–O
Pd–O
Pd–O
Pd–O
C–N
345.05
345.05
536.05
536.05
536.05
536.05
536.05
402.25
Pd3d5 Scan B
O1s Plus Pd 3p3 Scan A
O1s Plus Pd 3p3 Scan B
O1s Plus Pd 3p3 Scan C
O1s Plus Pd 3p3 Scan D
O1s Plus Pd 3p3 Scan E
N1s Scan A
6316.68
1.83
are given in Table 2. There are three N 1 s peaks located at
398.5 eV that are attributed to the existence of the nitro-
gen atom present in pyridine moiety, which is in very close
agreement with 398.7 eV for pyridine mentioned in pre-
viously published literature (Jansen and Bekkum 1995).
The XPS spectrum of Pd 3d in the CPIP complex catalyst
consists of single and intensive doublet (336.3 and 342 eV)
which may belong to the+2 oxidation state of Pd (Fig. 4e,
f) (Mauriello et al. 2015; Sun et al. 2014).
Table 3 Binding energy (eV) and atomic concentration of O 2 s, C
1 s, Pd 3d and N1s in CPIP complex catalyst
Element
Peak BE (eV)
Atomic %
O 2s
C 1s
Pd 3d
N 1s
25.18
285.06
336.29
398.86
24.4
66.14
1.8
7.3
Bands at 530.3 and 531.1 eV were discovered in the
spectrum (Fig. 4g) which might be ascribed to N…Pd–O
interaction present between CPI and Pd(OAc)2. Through
detailed peak ftting using the XPS peak software package,
the peak amounts were given to the presence of interaction
between Pd 3d and O 1s which indicated that Pd(OAc)2 were
more likely to bond with CPI. For the spectrum of O 1s,
the band of the initial chitosan was comprised of two sub-
bands, which are ascribed to the existence of OH (534.2 eV)
and the –O– in the ring and feasibly –O– between the rings
(532.1 eV) which are present in chitosan structure. The
bands appeared at 283.1 eV (C–C), 285 eV (C–N, C=N,
C–O or C–O) and 286.6 eV (C=O, O–C–O) also suggested
the formation of CPI and CPIP complex catalyst. On the
basis of above explanation, we speculated that Pd (OAc)2
was tetracoordinated to two nitrogen atoms present in CPI
and two oxygen present in acetate groups. The binding
energy and atomic percentage for CPIP complex catalyst
are given in Table 3 and XPS spectrum is shown in Fig. 5.
Fig. 5 XPS analysis (full) for CPIP complex catalyst
adsorption surveys. The BET surface area of the catalyst
was discovered to be ~1.84 m2 g−1 with a pore diameter of
227 Å.
FE‑SEM, and surface area analyses
The surface morphology of the CPIP complex examined by
FE-SEM images at diferent scale measurements is depicted
in Fig. 6, and its color image presented in Fig. 7 clearly
depicts the layered structure of catalyst). The catalyst sur-
face has a lower surface area, which is verifed by the N2
SEM–EDS analysis
SEM-EDS images of CPIP complex catalyst are displayed in
Figs. 8 and 9. SEM image suggested the binding of chitosan
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Fig. 6 FE-SEM images at
diferent measuring scale a
500 µm, b 5 µm, c 5 µm, d 1 µm
palladium and nitrogen with wt% (atomic%, series) as 41.2
(49.9, K), 44.5 (40.5, K), 3.8 (0.52, L) and 8.29 (8.61, K)
(Fig. 9).
TG‑DTG and DSC analyses
The thermal behavior of chitosan and CPIP complex catalyst
are depicted in Fig. 10. Chitosan and CPIP complex catalyst
have three main weight losses 30–250 °C; 250–600 °C; and
600–850 °C. The frst weight loss of ~10% was ascribed to
the elimination of physical adsorbed water molecules. The
second phase weight loss of 53.7% (chitosan) and 51.7%
(CPIP complex catalyst) is because of the decomposition
of the polysaccharide chain and decomposition of the poly-
saccharide framework and also loss of side chains such as
pyridyl groups, etc., and third stage weight loss for both
chitosan and CPIP complex catalyst is due to oxidation of
organic substance in form of carbon monooxide and carbon
dioxide because in experiment oxygen was purged from 600
to 850 °C. CPIP complex catalyst has higher decomposition
temperature (Td,1 =300.6 °C, Td,2 =614.1 °C) than chitosan
(Td,1 =297.9 °C, Td,2 =610.1 °C) which clearly suggest that
CPIP complex catalyst is slightly more thermally stable.
TG-DTG and DSC data for raw chitosan and CPIP complex
catalyst are given in Table 4.
Fig. 7 FE-SEM image (color) showing layered structure of CPIP
complex catalyst having well distribution of constituent elements car-
bon, oxygen, palladium and nitrogen using FE-SEM
pyridyl amine with Pd(OAc)2. It has been assumed that the
size and the uniformity of particles are related to the binding
of chitosan pyridyl amine with palladium acetate (Fig. 8).
EDS indicates that the CPIP comprised of carbon, oxygen,
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Chemical Papers (2021) 75:2835–2850
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Fig. 8 Layered structure seen from FE-SEM (a) and Al mapping of
the constituents elements present in CPIP complex catalyst by EDS
(b–e)
Fig. 10 TG-DTG thermogram a chitosan, b CPIP complex catalyst
The volatilization heat of polymers was calculated using
DSC where region beneath the endothermic peak was shown
to be linearly related to the volatilization heat. Melting tran-
sition temperature and heat of melting in endotherm for
Fig. 9 Energy-dispersive X-ray spectrum for CPIP complex catalyst
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Table 4 TG-DTG and DSC data for chitosan and CPIP complex catalyst
Compound
Stage
Δw(%)
Temperature
range (°C)
Maximum weight
Char yield (%)
Transition temperature(Tm; °C)
and enthalpy change (ΔH; J/g) by
DSC
change speed (mg/s)
Chitosan
I
10..1
53.7
35.2
10.4
51.7
36.7
30–250
–
297.9
610.1
-
300.6
614.1
1.1
1.2
127; 165
II
III
I
II
III
250–600
600–850
30–250
250–600
600–850
CPIP complex catalyst
120.8; 179.8
Fig. 11 DSC thermograms for a chitosan, b PDIP complex catalyst
chitosan were observed at 127.8 °C and 165 J/g, whereas
for CPIP complex catalyst it was 12.8 °C and 179.8 J/g
(Fig. 11).
(20 ml) for 6 h. Reaction monitor on TLC. Catalyst recov-
ered by fltration and amino aryl isolated by distillation of
ethanol, isolated yield 99% (Table 5).
Recovered catalyst was reused with 10% top-up fresh
catalyst, yield 97–98%; fve recycling of catalyst was per-
formed (Fig. 12).
Organic transformation
The weight % of Pd loading in catalyst is the real measure
of activity of the catalyst. It was found that 0.018 wt% of
Pd loading in catalyst and 0.138 mol% Pd were the active
concentration present in catalyst.
General procedure for Suzuki–Miyaura
cross‑coupling reaction
Aryl halide (5.0 mmol), phenylboronic acid (6.0 mmol),
potassium carbonate (15.0 mmol) and 50 mg of CPIP were
heated in sealed tube at 70–75 °C (under nitrogen atmos-
phere) in 30 ml ethanol/water (1:1) for 3hrs. After comple-
tion of the reaction, catalyst recovered by fltration. Filtrated
ethanol/water, distilled and compound, was purifed through
General procedure for hydrogenation of nitro aryl
to amino aryl (1a)
Nitro aryl compound (4.06 mmol) stirred in the presence of
CPIP (50 mg) and under hydrogen atmosphere in ethanol
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Chemical Papers (2021) 75:2835–2850
2845
Table 5 Hydrogenation of nitro
aryl to amino aryl
Reaction conditions: 4.06 mmol nitrobenzene, hydrogen gas, 25 mg CPIP, ethanol, stir at 25–30 °C, Iso-
lated yields were reported after distillation of ethanol from reaction
Recycling of catalyst Vs Yield (%)
a short column chromatography (silica gel 100–200 mesh)
using ethyl acetate and n-hexane (20% ethyl acetate in n-hex-
ane) to get the pure biaryl, isolated yield>97%, (Table 6).
Chlorobenzene was also tested, but the results were not sat-
isfactory and inactive in these reactions.
97.5
97
97
97
96.5
96
96
Recovered catalyst was reused with 20% top-up fresh
catalyst, yield 97–98%; fve recycling of catalyst was per-
formed (Fig. 13).
95.5
95
95
4
95
5
94.5
94
Reaction condition: 5 mmol aryl bromide, 6 mmol phe-
nylboronic acid, 50 mg CPIP, 15 mmol K2CO3, 30 ml etha-
nol/water (1:1), 70–75 °C; Isolated yields were reported
after column chromatography.
1
2
3
Recycling number
Fig. 12 Yield chart with fve recycling of catalyst (hydrogenation of
nitrobenzene to aniline)
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2846
Chemical Papers (2021) 75:2835–2850
Table 6 Suzuki–Miyaura cross-
coupling reaction
Recycling of catalyst Vs Yield (%)
97.5
97
General procedure for heck cross‑coupling reaction
97
97
96.5
96
Aryl halide (5.0 mmol), alkenes (6.0 mmol), cesium carbon-
ate (15.0 mmol) and 50 mg of CPIP were heated in sealed
tube at 100–105 °C (under nitrogen atmosphere) in 30 ml
toluene for 3 h. After completion of the reaction, catalyst
recovered by fltration. Filtrated toluene distilled and com-
pound purifed through a short column chromatography
(silica gel 100–200 mesh) using ethyl acetate and n-hexane
(20% ethyl acetate in n-hexane) to get the pure vinylbenzene,
isolated yield 75–92% ( Table 7).
96
95.5
95
95
4
95
5
94.5
94
1
2
3
Recycling number
Fig. 13 Yield chart with fve recycling of catalyst (Suzuki–Miyaura
cross-coupling reaction of bromo benzene with phenylboronic acid)
1 3

Chemical Papers (2021) 75:2835–2850
2847
Table 7 Heck cross-coupling
reaction
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2848
Chemical Papers (2021) 75:2835–2850
Recycling of catalyst Vs Yield (%)
hazardous waste. We have done fve recycling tasks with the
top catalytic converter. This catalyst at is at the frst stage of
generation, and there is a possibility of further improvement
in its activities and applications. There is a high demand for
further eforts to develop sustainable catalysts and appropri-
ate means of recovery, reactivation and regeneration (Molnár
and Papp 2017). Of course, catalytic deactivation in indus-
trial processes requires special attention, and regeneration
is a key issue in terms of economy and sustainability. Nowa-
days in commercial production, the catalyst is preferably
recycled with top-up. This is because there is a possibility of
a stuck reaction between the two if we use a catalyst without
a top-up. Top-up always increases the catalytic activity of
the reaction.
87.5
87
87
86.5
86.5
86
86
85.5
85
84.5
84
84
84
5
83.5
83
82.5
1
2
3
4
Recycling number
Figure14 Yield chart with fve recycling of catalyst (heck cross-cou-
pling reaction of bromobenzene with 3,3-dimethyl-1-butene)
Recovered catalyst was reused with 20% top-up fresh
catalyst, yield 75–92%; fve recycling of catalyst was per-
formed (Fig. 14).
Conclusion
In summary, we introduce a facile and green technique to
synthesize chitosan pyridyl imine palladium (CPIP) complex
catalyst from chitosan, 2-acetylpyridine and Pd(OAc)2. It
has been characterized using FT-IR, Py (GC–MS), XRD,
XPS, FE-SEM, BET adsorption, EDX, TG-DT and DSC.
From XPS study, it was revealed that Pd (OAc)2 has been
tetracoordinated to two nitrogen atoms present in CPI and
two oxygen present in acetate groups. TG-DTG results sug-
gested that this catalyst is thermally stable up to 300 °C.
This catalyst has proved to be active and recyclable catalysts
for both Suzuki and Heck reactions. It also exhibits excel-
lent catalytic performance for the nitrobenzene and azo dye
reduction. Benefted from increased catalytic performance,
high stability and ease of synthesis, CPIP complex catalyst
is very promising for applications in organic transformation.
Reaction conditions: 5.0 mmol aryl bromide, 6.0 mmol
alkene, 50 mg catalyst 2, 15 mmol Cs2CO3, 30 ml toluene,
100–105 °C. Isolated yields were reported after column
chromatography.
General procedure for degradation of aniline yellow
dye
Aniline yellow (5 mmol) stirred in presence of CPIP (50 mg)
and under hydrogen atmosphere in methanol (30 ml)
(Fig. 15) for 6 h. Initial yellow color of reaction disappears
during reaction hold period. Two spots corresponding to ani-
line and benzene-1,4-diamine was observed on TLC system
using 0.5% methanol and chloroform as solvent.
The primary objective of the present paper was to develop
a heterogeneous green catalyst that is recyclable and reduces
Fig. 15 Degradation of Aniline Yellow dye in presence of CPIP
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Chemical Papers (2021) 75:2835–2850
2849
Acknowledgements The authors are thankful to SAIF, Punjab Univer-
sity, Chandigarh for characterization like SEM, TEM, FT-IR and XRD.
We are also thankful to CECRI, Karaikudi, for XPS. Authors are also
thankful R &D, BKT tyre for py (GC-MS), TG-DTG, DSC, nitrogen
adsorption and FT-IR for analyses.
Hajipour A, Boostani E, Mohammadsaleh F (2015) Proline-function-
alized chitosan–palladium (ii) complex, a novel nanocatalyst for
C–C bond formation in water. RSC Adv 5:24742–24748
Han HS, Jiang SN, Huang MY, Jiang YY (1996) Catalytic hydrogena-
tion of aromatic nitro compounds by non-noble metal complexes
of chitosan. Polym Adv Technol 7:704–706
Hasan K (2020) Methyl salicylate functionalized magnetic chitosan
immobilized palladium nanoparticles: an efcient catalyst for the
Suzuki and heck coupling reactions in water. ChemistrySelect
5:7129–7140
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