Bio-heterogeneous Cu(0)NC@PHA for n-aryl/alkylation at room temperature

Article abstract of DOI:10.1016/j.poly.2021.115310

A pure cellulose was derived from waste fibre and it was chemically modified to a hydroxamic acid ligand. The poly(hydroxamic acid) was treated with an aqueous copper solution to afford the greenish stable five-membered copper complex; namely Cu(II)@PHA. Further, the Cu(II)@PHA was treated with a reducing agent hydrazine hydride to give brown colour cellulose supported copper nanocomplex (Cu(0)NC@PHA). The Cu(0)NC@PHA was characterised by ATR-FTIR, FE-SEM & EDS, TEM, ICP-OES, TGA, XRD and XPS analyses. The cellulose-based Cu(0)NC@PHA was used for the n-aryl/alkylation (Michael addition) reaction with a variety of α,β-unsaturated Michael acceptors to produce the corresponding n-aryl/alkyl products with an excellent yield at room temperature. The Cu(0)NC@PHA showed extraordinary stability and it was easily filtered out from the reaction mixture and may potentially recycled up to five times without loss of its original catalytic ability.

Full text of DOI:10.1016/j.poly.2021.115310

Journal Pre-proofs
Bio-heterogeneous Cu(0)NC@PHA for n-aryl/alkylation at room temperature
Choong Jian Fui, Tang Xin Ting, Mohd Sani Sarjadi, Shaheen M. Sarkar,
Baba Musta, Md Lutfor Rahman
PII:
S0277-5387(21)00292-8
DOI:
Reference:
https://doi.org/10.1016/j.poly.2021.115310
POLY 115310
To appear in:
Polyhedron
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Revised Date:
Accepted Date:
24 April 2021
22 May 2021
29 May 2021
Please cite this article as: C. Jian Fui, T. Xin Ting, M. Sani Sarjadi, S.M. Sarkar, B. Musta, M. Lutfor Rahman,
Bio-heterogeneous Cu(0)NC@PHA for n-aryl/alkylation at room temperature, Polyhedron (2021), doi: https://
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Bio-heterogeneous Cu(0)NC@PHA for n-aryl/alkylation at
room temperature
Choong Jian Fui1, Tang Xin Ting1,Mohd Sani Sarjadi1, Shaheen M. Sarkar2, Baba Musta1, and Md Lutfor Rahman1,3
*
1
Industrial Chemistry, Faculty of Science and Natural Resources, Universiti Malaysia Sabah, 88400 Kota Kinabalu,
Sabah, Malaysia;
2
3
Department of Chemical Sciences, Bernal Institute, University of Limerick, Ireland;
Seaweed Research Unit , Faculty of Science and Natural Resources,Universiti Malaysia Sabah, Kota Kinabalu, Sabah,
Malaysia.
* Correspondence: lutfor73@gmail.com (M.L.R); Tel.: +06016-9399011
Abstract: A pure cellulose was derived from waste fibre and it was chemically modified to a hydroxamic
acid ligand. The poly(hydroxamic acid) was treated with an aqueous copper solution to afford the greenish
stable five-membered copper complex; namely Cu(II)@PHA. Further, the Cu(II)@PHA was treated with a
reducing agent hydrazine hydride to give brown colour cellulose supported copper nanocomplex
(Cu(0)NC@PHA). The Cu(0)NC@PHA was characterised by ATR-FTIR, FE-SEM & EDS, TEM, ICP-
OES, TGA, XRD and XPS analyses. The cellulose-based Cu(0)NC@PHAwasusedfor the n-aryl/alkylation
(Michael addition) reaction with a variety of ,-unsaturatedMichaelacceptorsto produce the corresponding
n-aryl/alkyl products with an excellent yield at room temperature. The Cu(0)NC@PHA showed
extraordinary stability and it was easily filtered out from the reaction mixture and may potentially recycled
up to five times without loss of its original catalytic ability.
Keywords: aza-Michael addition, Cu(0)NC@PHA, heterogeneous catalyst, poly(hydroxamic acid).
1. Introduction
Due to the awareness of environmental protection, the effect of developing simple, environmentally
friendly and cost-effective synthetic process is highly desirable to the chemical community. In this regard, a
heterogeneous catalyst derived from recyclable biomass that paves the way for the economic transition of
organic reactions that has attracted considerable attention in recent decades [1]. In terms of environment-
friendly and renewable resources and sustainable processes, biomass based solid supported catalysts may be
a good choice due to their cost effective, high activity, ease of recovery, and reusability and tolerability under
harsh reaction conditions [2]. Synthetic solid support namely, metal-organic framework (MOF) [3],
polystyrene [4], non-magnetic and magnetic [5], carbon nanotube [6], and Mobil Composition of Matter
No. 41 (MCM-41) [7] showed good catalytic activity towards the various organic reactions. However, these
heterogeneous catalysts suffer from economical and sustainable protocol approaches which are involved in
the developing of green processes. Taking into consideration, natural polymers are currently used as solid
support for metal catalyzed reactions such as alginate [8], gelatin [9], starch [10], chitosan [11], and cellulose
[12]. Among these natural polymers, cellulose is the most satisfying material in nature due to its high
abundance, low density, universal availability, low cost, and excellent mechanical and chemical properties
[13]. Therefore, cellulose is a good candidate to serve as a solid support for the synthesis of catalysts.
1

Recently cellulose was isolated from the waste corn-cob [14] and functionalized to poly(amidoxime)
chelating group. Later copper nanoparticles were incorporated onto the poly(amidoxime) chelating ligand
and it was utilized for the aza-Michael addition reaction [15]. The aza-Michael reaction was first discovered
in 1887 which one of the most effective technique for the preparation of β-aminoketone reaction between
electron-poor olefins and amines [16]. This reaction has significant application to the synthesis of a huge
number of medicinal compounds, antibiotics, auxiliaries, natural products and n-containing heterocycles [17].
Severalcatalytic methods have been introduced for the aza-Michael addition such as organocatalysts [18], β-
cyclodextrin [19], PEG [20], ionic liquids [20] and iodine [17]. However, these catalysts suffer from green-
sustainable protocols, therefore it is necessary to develop a reactive, cost-effective, biodegradable
heterogeneous catalyst to overcome the current limitations.
In this study, we have isolated biodegradable cellulose from the pandanus fruit. The cellulose’s surface
was reformed through the copolymerization with methyl acrylate and further it was transformed into a
poly(hydroxamic) acid bidentate ligand [21,22]. The strong bidentate ligand was easily absorbed copper
species from an aqueous solution of CuSO4 to afford a green color five-membered Cu(II) complex
(Cu(II)@PHA). The coppercomplex wasfurther treatedwith hydrazine hydrate to furnish deep-brown color
Cu(0) nanocomplex (Cu(0)NC@PHA) with an averaged diameter of 28 nm. The nanocomplex
Cu(0)NC@PHA was utilized to attain the n-aryl/alkyl products through the aza-Michael addition reaction of
aliphatic, aromatic and heterocyclic amines with a variety of 훼, 훽-unsaturated compounds in ethanol at room
temperature. The Cu(0)NC@PHA showed high catalytic performance with easy recovery from the reaction
vial and can be reused up to five times without noticeable dropped of its catalytic proficiency.
2. Materials and Methods
2.1. General methods
All controls were performed under atmospheric conditions if else noticed. All commercial chemicals were
obtained from the Merk or Sigma-Aldrich and used as it is original. 1H NMR (600 MHz) spectra were
obtained via BRUKER-600 spectrometer, Transmission Electron Microscope (TEM) was executed on a
Tecnai G2 and nanoplus zeta/nano particular analyser was performed on a Particulate system. The chemical
shift of 1H NMR was based on tetramethylsilane (TMS) at 0.00 ppm. ICP-OES (Optima 5300-DV, Perkin
Elmer) and thermal gravimetric analysis (TGA/DSC +3, Mettler Toledo) was fully equipped. The mass
spectra of all resultant compounds were analysed by GC-MS (Shimadzu GC-MS-TQ8050 NX). The FE-SEM
and EDX were performed with JSM-7900F. The XRD is measured with Rigaku multipurpose and XPS was
performed on a PHI Versa Probe II.
2.2. Cellulose extraction
The pandanus fruit was obtained from the seaside near the Papar area, Kota Kinabalu, Sabah, Malaysia
(image shown at ESI, Fig. S1a). The pandanus fiber was cut into small size and dry in the oven for three days
at 55℃. The pandanus fruit fiber (300 g) was boiled with 20% of sodium hydroxide for three hours and it
was washed with water. The dark brown colour pandanus fiber was further boiled with 800 mL of glacial
acetic acid and 600 mL of H2O2 for 1 h and the cellulose waswashedwith water repeatedly until free of acetic
acid and H2O2 respectively. The resulted white colour cellulose was dried in an oven at 50℃ (ESI, Fig. S1b)
[15,23].
2.3. Hydrolysis of extracted cellulose
To a 500 mL beaker 10.0 g of pandanus cellulose was treated with 300 mL 45% of concentrated sulfuric
acid at 50℃. After being stirring for two hours, the resultant product was decanted into ice water and washed
2

until it is neutralized. The product was dried in over at 55℃ for one day to get a persistent mass (ESI, Fig.
S1c) [24].
2.4. Synthesis of poly(methyl acrylate) 1
To a 1L three-neck round bottom flask 6.0 g of cellulose was suspended in water (50 mL) and it was
heated at 75℃ for 1 h. After being stirring for 1h, 3 mL of conc. sulfuric acid and 2 g of ceric ammonium
nitrate were added and stirred for 15 minutes under nitrogen atmosphere. Then, 15 mL of methyl acrylate
was added slowly into the flask and it was further stirred at 75℃ for five hours under nitrogen atmosphere.
The reaction mixture was cool at room temperature and the resulted product 1 (ESI, Fig. S1d) was washed
with water and methanol (MeOH:H2O, 3:1) [15,23,25].
2.5. Synthesis of poly(hydroxamic acid) ligand 2
Hydroxylamine hydrochloride (NH2OH•HCl, 20 g) was dissolved in aqueous ethanol (100 mL water and
400 mL EtOH) and controlled the pH 13 by adding of NaOH solution (ethanol: water 5:1). Then 10 g of
poly(methyl acrylate) 1 was measured into a bottom flask equipped with the following apparatus e.g. stirrer,
condenser and a temperature-controlled water-bath. The prepared hydroxylamine solution was then
transferred into the reaction flask and heated at 80℃ for five hours. The resulted product 2 (Fig. S2a) was
separated on a vacuum filtration and washed with water, ethanol and dried in an oven at 50℃ to get a
persistent mass [15,23].
2.6. Preparation of poly(hydroxamic acid) Cu(II) complex (Cu(II)@PHA)
An aqueous Cu(II) sulphate solution (18.66 g in 100 mL of water) was added into a stirred suspension of
poly(hydroxamic acid) ligand 2 (10 g in 50 mL of water) at room temperature in presence of a buffer solution
(pH 6.5). The colourless ligand 2 was instantly turned into a green colour copper complex Cu(II)@PHA.
The Cu(II)@PHA (Fig. S2b) was filtered out and washed with water, ammonium chloride solution and
methanol. The ICP-OES analysis showed that 0.02 mmol/g of copper was contained onto the Cu(II)@PHA
[15,23].
2.7. Preparation of poly(hydroxamic acid) Cu(0) nanocomplex (Cu(0)NC@PHA)
The green color Cu(II)@PHA (5 g) was suspended into 10 mL of methanol. To the suspension, 3 ml of
hydrazine hydride was added and the resulting mixture was stirred for two hours at room temperature. The
green Cu(II)@PHA was reduced in presence of hydrazine and turned into dark brown color Cu(0)
nanocomplex (Cu(0)NC@PHA). The Cu(0)NC@PHA (Fig. S2c) was separated by filtration and washed
with acetone, , dried at 50℃ for four hours and stored under nitrogen atmosphere.
2.8. General procedure of Aza-Michael addition reaction
A mixture of Cu(0)NC@PHA (5mg), amine (1.0 mmol) and Michael acceptor(1.5 mmol) in ethanol was
stirred at room temperature and the reaction progress wasmonitored by TLCand GC analyses. Aftercomplete
consumption of amine, Cu(0)NC@PHA was separated by filtration and the organic layer was concentrated
under reduced pressure. The crude product was purified by silica gel column chromatography (ethyl
acetate/hexane) to give the corresponding n-aryl/alkylated product [15,26]. The chemical structures of all n-
aryl/alkylated products were determined by using of GC-MS and NMR analysis (ESI, Fig. S3-S51).
3

3. Result and discussion
3.1. Synthesis of Cu(0)NC@PHA
The free-radical reactions have been extensively used to create a radical on the cellulose molecule
throughout and subsequent reaction with vinyl or acrylic monomers [27,28]. One alternative process among
the existing methods is utilization of transition metal which can generate a free radical on the oxygen atom
of primary -OH groups within the anhydroglucose units (AGU) [29]. The free radicals bearing on AGU react
with olefin additional on the cellulosic backbone through the propagation reaction and ultimately resulted the
cellulose-graft-polymer materials. The present study highlights the graft co-polymerisation of pandanus
cellulose with methyl acrylate initiated by the ceric ions as a radical initiator (Scheme 1). Methyl acrylate
(MA) was used as a co-polymerization reactant, which react with active pandanus cellulose to forward the
grafting process according to the reported work [30-32]. The poly(methyl acrylate) 1 was then converted into
poly(hydroxamic acid) 2 through the Loosen rearrangement [33]. In this rearrangement, methyl acrylate
reacted with the hydroxylamine to afford the corresponding -NHOH group. This functional group
transformation reaction was carried out in pH 13 according to the reported procedure [27].
The copper metal complex Cu(II)@PHA was prepared through the ligand-metal ion adsorption process.
The poly(hydroxamic acid) ligand 2 was easily adsorbed Cu2+ ion from an aqueous solution of CuSO4 to give
a five-membered green color strong complex Cu(II)@PHA (Scheme 1). According to the reported work by
Eigen and Tamm, the coordination was begun to form an electrostatic ion pair between the metal ions and
the ligand [34-36]. Finally, the Cu(II)@PHA was treated with hydrazine hydride which reduced the
oxidation state of copper specie in the Cu(II)@PHA to afford brown color cellulose supported Cu(0)
nanocomplex Cu(0)NC@PHA (Scheme 1) [37].
HO
HO
NH
NH
OMe
OMe
O
OH
O
n
O
nCell
O
n
OH
O
H2NOH
pH 13
CAN
Cell
O
Cell
HO
Cell
n
O
O
HO
CO2Me
O
O
O
O
OH
n
OH
HN
HN
OMe
OMe
OH
OH
Cellulose
Poly(methyl acrylate) 1
Poly(hydroxamic acid) ligand 2
O
O
O
O
O
nCell
NH
NH
HN
HN
Cu
Cu
Cu
Cu
O
n
O
n
O
nCell
CuSO4•5H2O
hydrazine hydrate
Cell
Cell
MeOH, r.t.
O
O
O
O
Cu
Cu
Cu(0)
Cu
Cu
NH
HN
NH
HN
Cu(II)
O
O
O
O
Cu(II)@PHA
Cu(0)NC@PHA
Scheme 1. The synthetic route of Cu(0)NC@PHA
3.2. Infrared spectroscopy analysis
A comparison study of the IR analyseswasmade betweenall the resultant products starting from extracted
cellulose, grafting of methyl acrylate onto the cellulose, conversion of the grafting product into chelating
ligand and copper complex. All respective spectrums are represented in Fig. 1. The extracted cellulose
spectrum displayed an absorption peaks at 3333 cm-1 stretching and 1427 cm-1 for the bending of hydroxyl
group on the cellulose. The aliphatic C-H stretching was detected at 2897 cm-1 (Fig. 1a) and the results are
agreed with the reported literature [30,31]. A small peak shows at 1158 cm-1 due to the stretching of C-O
bond in the cellulose glycosidic unit [30]. The hemiacetal C-O-C pyranose ring skeletal was detected at 1052
4

cm-1. A small peak at 897 cm-1 was observed due to the glycosidic C1-H distortion with the bending mode of
O-H indicates the connection of 훼-glycosidic units [30].
Fig. 1. IR spectra of (a) cellulose (b) poly(methyl acrylate) 1, (c) poly(hydroxamic acid) ligand 2, (d) Cu(II)@PHA, (e)
Cu(0)NC@PHA.
A new and strong peak at 1727 cm-1 was detected in the poly(methyl acrylate) 1 spectrum (Fig. 1b). This
result confirmed the successfully polymerization of cellulose with methyl acrylate. After conversion of ester
group into the poly(hydroxamic acid) ligand 2 (Fig. 1c), the C=O stretching (Fig. 1b) was shifted from 1727
cm-1 to 1677 cm-1. A new peak at 1648 cm-1 was attributed for the N-H bending mode and a board peak at
3119 cm-1 was observed due to the O-H and N-H stretching. The shifting of C=O and new peaks for N-H
confirmed the successfulconversion of poly(methyl acrylate) 1 to poly(hydroxamic acid) ligand 2. In the IR
spectrum of Cu(II)@PHA it was observed that the C=O peak was shifted to 1652 cm-1 after incorporation of
copper species with the poly(hydroxamic acid) ligand 2 (Fig. 1d). The N-H starching peak at 3119 cm-1 was
affected due to the complex formation with the copper species. After reduction of Cu(II) into Cu(0), the color
of the sample was dramatically changed from green to brown and the resulted IR spectrum of
Cu(0)NC@PHA showed similar spectrum with the Cu(II)@PHA (Fig. 1e) however the C=O peak was
further little shifted from 1652 cm-1 to 1645 cm-1.
3.3. Field Emission Scanning Electron Microscope (FE-SEM) analysis
Fig. 2a shows the surface morphology of the original pandanus fiber however after chemical treatment of
the pandanus fiber, the resulted cellulose showed an obviously smooth wooden stick-like structure (Fig. 2b).
After copolymerization of the cellulose, poly(methyl acrylate) 1 was represented with a rough surface with
deformed spherical-like morphology (Fig. 2c). The poly(hydroxamic acid) ligand 2 showed a rough surface
with a discernable tiny sphere shape morphology (Fig. 2d). When poly(hydroxamic acid) ligand 2 was
coordinated with the Cu(II) species (Fig. 2e) and followed by the reduction of copper species the
Cu(0)NC@PHA showed a smaller and aggregated spherical shape morphology due to the accumulation of
poly(hydroxamic acid) ligand 2 (Fig. 2f) [32,38].
5

Fig. 2. FE-SEM of (a) pandanus fruit fibre, (b) cellulose, (c) poly(methyl acrylate) 1, (d) poly(hydroxamic acid) ligand
2, (e) Cu(II)@PHA, (f) Cu(0)NC@PHA.
3.4. Transmission Electron Microscope (TEM) and Energy Dispersive X-ray (EDX) analysis
TEM analysis was measured with Tencai G2 Spirit BioTwin TEM, using carbon supported copper TEM
grids with size 200 mesh at 120 kV. TEM analysis showed the presence of copper species onto the
Cu(0)NC@PHA (Fig. 3a), and the average size of Cu(0) nanocomplex was found ∅= 28.7 ± 2 nm (Fig. 3b).
The dimension of Cu(0) in the Cu(0)NC@PHA determined by TEM accompanying with the mean value of
crystalsize calculated by the Scherrerequation as28.7 nm and 28.1 nm, respectively. The Cu(0) nanocomplex
exhibited spherical morphology with an uneven distribution onto the surface of modified pandanus cellulose.
ESI, Fig. S1e represents the EDX spectra of Cu(0)NC@PHA. From the EDX analysis copper species were
observed that the copper was anchored onto the Cu(0)NC@PHA (ESI, Fig. S2e).
6

Fig. 3. (a) TEM image of Cu(0)NC@PHA, (b) Size distribution of Cu(0)NC@PHA. The sizes were determined for
100 nanoparticles selected randomly.
3.5. Thermal Gravimetric analysis
TG analysis is a common technique regularly in verified the stability of the materials [39]. Thermal
behaviour of the synthesized martial were performed with a heating rate of 10 min-1 under inert condition.
The TGA curve of poly(methyl acrylate) 1 showed lower thermal stability in the temperature ranging of 500
to 800 ℃ (Fig. 4e). Both Cu(II)@PHA and Cu(0)NC@PHA showed a satisfactory result, which is
acceptable behaviour in term of degradation at the end of the experiment (Fig. 4a and 4b).
A minor mass decrease was detected for all compounds before 150 ℃. These may due to the evaporation
of the remaining water which is present at the inner and outer cavities of the cellulose (6%), poly(methyl
acrylate) 1 (2%), poly(hydroxamic acid) ligand 2 (11%), Cu(II)@PHA (9%) and Cu(0)NC@PHA (8%).
The high-water content in the poly(hydroxamic acid) 2 indicates its hydrophilic nature. A noteworthy weight
decreases in the cellulose from 315 ℃ to 390 ℃ due to the degradation of -OH and -CH2OH groups presented
in the cellulose surface (Fig. 4d) [40].
Two significant degradation wasobserved in the poly(methyl acrylate) 1 curve within a temperature range
of 210-500 ℃ (Fig. 4e). The first degradation (~12%) was occurred around 215 ℃ and second significant
degradation (~81%) was detected around 390 ℃ due to the dehydrogenation of ester group in first
degradation and degradation of methyl propenoate chain in the polymer [40]. The second dramatically
degradation curve proved that a huge amount of methyl propionate was grafted onto the cellulose backbone.
The Fernandez’s research team found that thermal stability of graft copolymer is decreased with an increases
of grafting yield [41,42]. Herein, small degradation was observed at 200-350 ℃ however a significant
degradation was observed at 310-460 ℃ which comply with Fernandez's finding.
Fig. 4. TGA graphs of (a) Cu(0)NC@PHA, (b) Cu(II)@PHA, (c) poly(hydroxamic acid) ligand 2, (d) cellulose and
(e) poly(methyl acrylate) 1.
7

In between 140-470 ℃ of temperature range, the poly(hydroxamic acid) ligand 2 exhibit four continuous
degradation (Fig. 4c). This degradation was observed due to the decomposition of the hydroxamic acid and
cellulosic materials. A crossing point between poly(methyl acrylate) 1 (Fig. 4c) and poly(hydroxamic acid)
ligand 2 (Fig. 4e) was noted at 450 ℃. After this intersection, poly(hydroxamic acid) 2 started stable while
poly(methyl acrylate) 1 keep on degradation until 500 ℃. The overall weight loss of poly(hydroxamic acid)
ligand 2 and poly(methyl acrylate) 1 was 65% and 80%, respectively.
Fig. 5. TGA graphs of (a) Cu(0)NC@PHA and (b) Cu(II)@PHA under inert condition, (c) Cu(0)NC@PHA and (d)
Cu(II)@PHA under oxygen condition.
The complex Cu(II)@PHA and Cu(0)NC@PHA were stable than ligand 2 at around 425 °C as the sign
point and the weight loss around 50% was reached at 550°C respectively (Fig. 4a, 4b). Whereas 70% and
90% losses were reached for poly(hydroxamic acid) ligand 2 and poly(methyl acrylate) 1, respectively at 550
°C (Fig. 4c, 4e). Generally, poly(hydroxamic acid) ligand 2, Cu(II)@PHA and Cu(0)NC@PHA were good
stability than its precursors, which is acceptable behaviour in terms of the thermal degradation. The thermal
behaviour of the Cu(II)@PHA and Cu(0)NC@PHA were also performed in an oxygen atmosphere with a
heating rate 10 min-1 and the TGA results were presented in Fig. 5. As a result, Cu(II)@PHA and
Cu(0)NC@PHA both showed almost the same behaviour as in an inert condition. Therefore, Cu(II)@PHA
and Cu(0)NC@PHA have stratified thermal stability in both inert and oxygen conditions.
3.6. X-ray Diffraction analysis (XRD)
The X-ray diffraction was carried out on a Rigaku automated multipurpose XRD, using CuKα at 40Kv
and 50mA. All the compounds were scanned through the range of 2θ = 3-80° with the scan rate at 4°/min.
The XRD spectrum of pure fibre and extracted cellulose were presented in Fig. 6 and the crystalline index
(CrI) was computed based on the Segal crystallinity index method with following equation [43].
퐴
푐푟푦푠푡푎푙푙ꢀ푛푒
CI % =
× 100
(1)
퐴
+ 퐴
푐푟푦푠푡푎푙푙ꢀ푛푒
푎푚표푟푝ℎ표푢푠
Where: Aamorphous and Acrystalline are the area under amorphous and sample curve respectively.
The XRD diffraction pattern peaks for cellulose at 2θ = 15.43°, 22.65° and 34.40° are corresponding to
the lattice planes 110, 200 and 004 respectively (Fig. 6a, 6b) [44,45]. The prominent crystalline peak was
detected at 22.65° with 100% intensity, which confirmed the cellulose having higher crystallinity [46]. The
8

untreated pandanus fruit fiber showed a broad and dim spectrum with crystalline index 35.3%. These
indicating that the untreated pandanus fruit fiber presence other amorphous substances (Fig. 6a). After
chemical treatment of pandanus fruit fiber, the number of non-cellulose substances decreases and the degree
of crystallization increases to 78.2% [44-47].
Fig. 6. XRD spectrumof (a) cellulose, (b) Untreated pandanus fiber.
The XRD of poly(methyl acrylate) 1 showed (Fig. 7b) diffraction peaks at 7°, 11°, 12.8°, 17° and 19.6°
with a minor different in diffraction intensity which were similar to the cellulose. This result proved that the
ordered structure of cellulose does not changed after the grafting process onto the cellulose surface. The X-
ray diffraction of poly(hydroxamic acid) ligand 2 is shown in Fig. 7c where diffraction peaks at7°, 11°, 12.8°,
17° and 19.6° were disappeared and new peaks at 20.9°, 31.5°, 32°, 33.4° and 35.2° were observed which
indicate the successful conversion of hydroxamic functional group (-NHOH) [48].
Fig. 7. XRD spectrums of (a) Pandanus cellulose, (b) poly(methyl acrylate) 1, (c) poly(hydroxamic acid) ligand 2, (d)
Cu(0)NC@PHA.
The X-ray diffraction pattern of Cu(0)NC@PHA is presented in Fig. 7d. The Bragg's reflections of
metallic copper were observed at 43.3°, 50.4° and 74.1° corresponding to the miller indices (111), (200) and
(220), respectively. These diffraction peaks indicate the angular positions to FCC copper crystalline structure
[49-52]. However, the size of the Cu(0)NC@PHA was small and Scherer's equation (2) was used to
calculated the average size of the nanocomplex [53]. The average size of copper nanocomplex calculated by
XRD data was 28.1 nm.
9

0.9 휆
d =
(2)
훽cos휃
Where d is the width of nanocomplex, λ is the wavelength of the X-ray source, β is the full angular width at
half maximum (FWHM) of the X-ray diffraction peak at the diffraction angle.
3.7. X-ray photoelectron spectroscopy analysis (XPS)
X-ray photoelectron spectroscopy was carried out to analysis the oxidation state of copper and the
presence of elements in the synthesized materials (Fig. 8). The bidentate ligand hydroxamic acid strongly
binds with copper species therefore the XPS analyses have been extensively studied to determine the binding
technique of copper with hydroxamic acid. The full scan XPS of poly(hydroxamic acid) ligand 2 showed
binding energies (BEs) peaks at 284.0, 398.5 and 531.0 eV corresponding to 1s of carbon, nitrogen and
oxygen respectively (Fig. 8a). After successfully Cu(II) complex with ligand 2, Cu(II)@PHA shows new
BEs peaks at 935.5, 955.5, 125.5 and 80.5 eV corresponding to Cu2p3/2, Cu2p1/2, Cu3s and Cu3p3,
including the peaksbelongs to the C 1s, N 1s and O1s and rational increased BEsfor each1s atom wasfound
due to electron density decreased (Fig. 8b). The BEs values to the corresponding 1s atoms are presented at
Table 1. Cu(0)NC@PHA shows slight lower BEs than Cu(II)@PHA, but decent higher BEs than ligand 2.
Cu(0)NC@PHA shows peaks at 935.0, 954.0, 125.0 and 80.0 eV correspond to Cu2p3/2, Cu2p1/2, Cu3s
and Cu3p3 due to the changed of oxidation state of copper species (Fig. 9c) including other elements (Table
1).
Table 1. Survey scans of XPS of poly(hydroxamic acid) ligand 2, Cu(II)@PHA and Cu(0)NC@PHA.
Binding energies (eV)
Samples
C 1s
N 1s
O 1s
Cu2p3/2
-
935.5
935.0
Cu2p1/2
-
955.5
954.0
Poly(hydroxamic acid) ligand 2 284.0
398.5
402.5
401.0
531.0
534.5
533.0
286.5
285.5
Cu(II)@PHA
Cu(0)NC@PHA
Cu 2p3/2
30000
20000
10000
0
Cu 2p1/2
O 1s
(b)
(c)
C 1s
N 1s
Cu3p3
Cu3s
O KLL
(a)
O2s
1000
800
600
Binding Energy (eV)
Fig. 8. XPS spectra of (a) poly(hydroxamic acid) ligand 2, (b) Cu(II)@PHA, (c) Cu(0)NC@PHA.
400
200
0
The narrow scan spectra of Cu(II)@PHA and Cu(0)NC@PHA are presented in Fig. 9 to evaluate the
change of oxidation state of copper. The Cu(II)@PHA showed BEs peaks at 935.5 eV and 955.5 eV
correspond to Cu2p3/2, Cu2p1/2 which represent the oxidation state of Cu(II) (Fig. 9a). However, upon
10

reduction of Cu(II) to Cu(0), the BEs of Cu(0)NC@PHA was observed slight lower at 935.0 eV and 954.0
eV (Fig. 9b). Two satellite peaks were detected at BEs of 945 eV and 966 eV, which represent the
Cu(II)@PHA exhibits a d9 configuration in the ground state of Cu(II) (Fig. 9a) [54]. Besides, as compared
to the narrow scan of the Cu(0)NC@PHA for Cu(0), these two satellite peaks disappeared, which confirmed
the reduction of the Cu(II)@PHA was successful (Fig. 9b).
12000
Cu2p3/2
10000
Cu2p1/2
8000
(b)
(a)
6000
4000
925 930 935 940 945 950 955 960 965 970
Binding Energy (eV)
Fig. 9. Narrow scan of copper in (a) Cu(II)@PHA and (b) Cu(0)NC@PHA.
In addition, Fig. 10(I) shows the narrow scan of O atom of Cu(II)@PHA, which possess the increased
binding energy as compared to the poly(hydroxamic acid) ligand 2. Binding energy of N atom for the
Cu(II)@PHA also increased with the same trend as shown in Fig. 10(II). However, the binding energy of O
and N atoms in Cu(0)NC@PHA was slightly reduced compared to Cu(II)@PHA, because the electron
density of copper increased in the reduction process Fig. 10(I) and (II).
3000
Poly(hydroxamic acid) 2
Cu(II)@PHA
Poly(hydroxamic acid) 2
Cu(II)@PHA
Cu(0)NC@PHA
8000
7000
6000
5000
4000
3000
2000
1000
(II)
(I)
Cu(0)NC@PHA
2500
2000
1500
1000
(c)
(b)
(b)
(c)
(a)
(a)
396
398
400
402
404
406
408
526
528
530
532
534
536
538
540
Binding Energy (eV)
Binding Energy (eV)
Fig. 10. Plot I shows the narrow scan of the O atom, (a) poly(hydroxamic acid) ligand 2, (b) Cu(II)@PHA and (c)
Cu(0)NC@PHA; plot II shows the narrow scan of N atom, (a) poly(hydroxamic acid) ligand 2, (b) Cu(II)@PHA and
(c) Cu(0)NC@PHA.
For the confirmation of copper complex with hydroxamic ligand, we also investigated the narrow scans
of oxygen and nitrogen atoms. Before complexation, the XPS spectra of poly(hydroxamic acid) ligand 2
showed two peaks at the BEs of 530.8 eV and 532.3 eV, which corresponds to the O 1s in the O-NH and
C=O groups respectively (Fig. 11a). However, after complexation with copper to form the Cu(II)PHA, the
BEs of O 1s in O-NH was increased from 530.8 eV to 531.4 eV. For Cu(II)PHA, the O 1s in C=O was split
11

into two peaks with increased BEs of 533.0 eV and 534.5 eV (Table 2). The peak appeared at BEs of 533.0
eV corresponds to O 1s in C=O and BEs of 534.5 eV corresponding to the oxygen atom bind with copper
(C=O-Cu) (Fig. 11b). After reduction of copper from Cu(II) to Cu(0), the BEs of O 1s in O-NH shifted from
531.4 to 531.1 eV and O 1s in C=O shifted from 534.5 eV to 533.5 eV (Table 2). While the BEs of O 1s in
C-O-Cu also shifted from 533.0 to 532.0 eV. These indicated the reduction of Cu(II) to Cu(0) (Fig. 11c).
25000
Experimental
Sum
C=O
(a) O 1s
Poly(hydroxamic acid)
ligand 2
20000
15000
10000
5000
HN-OH
526
528
530
532
534
536
Binding Energy (eV)
(b) O 1s
Cu(II)@PHA
Experimental
Sum
NH-O
C=O-Cu(II)
C=O
7000
6000
5000
4000
3000
2000
528
530
532
534
536
538
540
Binding Energy (eV)
(c) O 1s
Cu(0)NC@PHA
Experimental
Sum
NH-O
C=O-Cu(II)
C=O
7000
6000
5000
4000
3000
2000
528
530
532
534
536
538
Binding Energy (eV)
Fig. 11. O 1s core-level XPS spectra of (a) poly(hydroxamic acid) ligand 2, (b) Cu(II)@PHA, (c) Cu(0)NC@PHA.
Similarly, the core-level 1s N in poly(hydroxamic acid) ligand 2 showed BEs at 398.8 eV and 400.5 eV
corresponding to the nitrogen atoms for N-OH and N-H functional groups (Fig. 12a). After complexation
with copper, the BEs of N 1s in N-OH and N-H were increased to 399.5 eV and 402.5 eV, respectively (Fig.
12b). After complexation, the BEs of N-OH and N-H were also shifted to higher BEs (Table 2), which
confirmed that the nitrogen atom wasparticipated to the complex formation with copper species. These higher
12

BEswere observed due to electron donation properties of oxygen and nitrogen atoms in the poly(hydroxamic
acid) [55]. After reduction to Cu(0), the BEs of N 1s in N-OH and N-H was slightly lower than Cu(II) (Table
2) which confirmed the reduction of Cu(II) to Cu(0) (Fig. 12c).
Table 2. Core-level scans of XPS of poly(hydroxamic acid) ligand 2, Cu(II)@PHA and Cu(0)NC@PHA.
Binding energies (eV)
Samples
O 1s
N 1s
O-NH
C=O
532.3
533.0
532.0
C-O-Cu
-
534.5
533.5
N-OH
398.8
399.5
398.8
N-H
Poly(hydroxamic acid) ligand 2 530.8
400.5
402.5
401.2
531.4
531.1
Cu(II)@PHA
Cu(0)NC@PHA
1200
(a) N 1s
Experimental
Poly(hydroxamic acid)
ligand 2
Sum
N-OH
N-H
1100
1000
900
800
700
396
398
400
402
Binding Energy (eV)
(b) N 1s
Cu(II)@PHA
1900
1800
1700
1600
1500
1400
1300
1200
Experimental
Sum
N-OH
N-H
396
398
400
402
404
406
Binding Energy (eV)
(c) N 1s
Cu(0)NC@PHA
Experimental
2600
2400
2200
2000
1800
1600
1400
1200
Sum
N-OH
N-H
396
398
400
402
404
406
Binding Energy (eV)
Fig. 12. N 1s core-level spectra of (a) poly(hydroxamic acid) ligand 2, (b) Cu(II)@PHA, (c) Cu(0)NC@PHA.
13

3.8. Cu(0)NC@PHA catalysed aza-Michael addition.
After fully characterized of Cu(0)NC@PHA we focused on the catalytic activity toward the Michael
addition reaction. The catalytic applicability of Cu(0)NC@PHA was investigated by choosing of aniline and
methyl acrylate as starting materials. The aza-Michaelreaction was performed between aniline (1 mmol) and
methyl acrylate (1.5 mmol) in the presence of 0.03 mol% (15 mg) of Cu(0)NC@PHA in DMF at room
temperature for 8 hours. It was observed that Cu(0)NC@PHA forwarded the reaction smoothly to afford the
corresponding product 3a with 75% yield (Table 3, entry 1). By changing of solvent DMF to DMA slight
improved yield 77% was obtained (entry 2). Interestingly, quantitative yield was achieved (96%) when the
reaction was conducted in the presence of ethanol (entry 3). Nevertheless, the formation of corresponding
product 3a was not enhanced when dichloromethane (CH2Cl2), acetonitrile (MeCN), acetone (Me2CO) and
tetrahydrofuran (THF) were used as solvents (entries 4-7). We then accomplished the reaction by switching
of the catalyst doses. Interestingly, the addition reaction was still efficiency forwarded even using 0.02-0.001
mol% (10-2.5 mg) of Cu(0)NC@PHA in ethanol (entries 8-10). However, only 17% yield of 3a was
observed when the reaction wascarried out without using of Cu(0)NC@PHA(entry11). It should be notated
that, only 23% yield wasobservedwhen the reaction wasperformedusing 0.01 mol% of Cu(II)@PHA(entry
12). Therefore, we eventually found that 0.01 mol% of Cu(0)NC@PHA could be sufficient to promote the
aza-Michael reaction efficiently within 4 h at room temperature (entry 9).
Table 3. Screening of aza-Michael addition reaction
O
Cu(0)NC@PHA
NH
OMe
+
NH2
OMe
solvent
r.t., time
O
3a
Entry
Solvent
Cu(0)NC@PHA (mg)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
DMF
15
8
8
2
6
6
6
8
3
4
7
8
6
75
77
96
71
72
76
68
90
94
78
17
23
DMA
EtOH
CH2Cl2
MeCN
Me2CO
THF
EtOH
EtOH
EtOH
EtOH
EtOH
15 (0.03 mol%)
15
15
15
15
15
10
5 (0.01 mol%)
2.5
0
9
10
11
12b
5 (0.01 mol%)
Conditions: Aniline (1 mmol), methyl acrylate (1.5 mmol), a catalytic amount of Cu(0)NC@PHA in 5
mL of solvent. bReaction was carried out in presence of Cu(II)@PHA. The GC was used to determine
the quantitative yield of the product. Structure of product was determined by MS and proton NMR.
Having the optimized situations in hand, we explored the extensive applicability of Cu(0)NC@PHA in
the aza-Michael addition reaction of substituted aromatic amines with a variety of ,-unsaturated Michael
acceptors and the results are summarized in Table 4. As illustrated in Table 4, Cu(0)NC@PHA was
efficiently promoted the aza-Michael addition reaction of aniline with butyl acrylate and acrylonitrile to
afford the respective n-alkylated products 3b and 3c with 73% and 80% yield respectively. Similarly, 4-
aminophenol and 4-aminobenzenethiol were smoothly underwent the addition reaction with methyl acrylate,
butyl acrylate and acrylonitrile to afford the corresponding alkylated products 3d-3i with 70-95% yield. It
should be noted that, no tress amount of O-alkylated and S-alkylated products were observed in the 1H NMR
14

and MS spectra. Therefore, our catalytic system could be utilized for selective N-alkylation when it is
necessary. Aniline having electron-withdrawing group e.g. 4-aminobenzoic acid, 1-(4-
aminophenyl)ethenone, methyl 4-aminobenzoate were smoothly forwardedthe aza-Michaeladdition reaction
with ,-unsaturated Michael acceptors methyl acrylate, butyl acrylate and acrylonitrile to afford the
respective Michael addition products 3j-3p in up to 90% yield. The n-methylaniline was also smoothly
underwent the addition reaction to give the corresponding products 3q-3s up to 90% yield. The amine
substituted aniline e.g. benzene-1,2-diamine was efficiently promoted the addition reaction in presence of
four mole equivalent of Michael acceptors to afford the dialkylated products 3t-3v in up to 80% yield.
Table 4. Aza-Michael addition of arylamine
Cu(0)NC@PHA
5 mg (0.01 mol%)
Ar
NH2
R
ArHN
R
EtOH, r.t, 4 h
3
Amine
Michael acceptor
Product
Yield (%)
3b (73)
3c (80)
3d (75)
HO
NH
BuO
O
3e (70)
3f (73)
3g (95)
3h (85)
3i (80)
3j (85)
3k (90)
3l (78)
3m (60)
3n (88)
3o (70)
3p (90)
3q (88)
3r (70)
3s (90)
HS
NH
CN
3t (80)
3u (65)
3v (75)
Conditions: Arylamine (1 mmol), Michael acceptor(1.5 mmol), 0.01 mol% of Cu(0)NC@PHA in
5 mL of ethanol. The GC was used to determine the quantitative yield of the respective products.
1
Structure of all products were determined by MS and H NMR (ESI).
15

The aza-Michael reaction of aromatic amine is generally slower than alkyl amine [56]. The
Cu(0)NC@PHA was then further utilized in the Michael addition reaction of aliphatic amies with ,-
unsaturated Michael acceptors at ambient temperature (Table 5). The addition reaction of diethyl amine and
methyl acrylate was smoothly forwarded to afford the corresponding n-alkylated product 4a in 78% yield
within one hour. The addition reaction of diethyl and dibutyl amines were efficiently forwarded the addition
reaction with different Michael acceptors to give the respective products 4b-4f in up to 97% yield.
Interestingly, when the addition reaction of aliphatic amine having acetylene functionality e.g.
propargylamine was carried out with Michael acceptors to afford the respective desire N-alkylated products
4g-4i in up to 95% yield without affecting the acetylene group. A substituted aliphatic cyclic amine e.g. N-
methylcyclohexanamine and sterically hindrance benzyl amines were also promoted the addition reaction to
give the corresponding products 4j-4o with 85% to 95% yield. Recently, Puthiaraj [57] and Kantam[58] were
reported BDC-MOF and Al-CO3 supported copper nanoparticles catalyzed aza-Michael reaction of 10 and 20
amines respectively. In their study, they used 16 mol% and 34 mol% of copper nanoparticles respectively,
where generally required longer reaction time and high temperature. However, in our study we used green
and biodegradable biopolymer instead of synthetic inorganic material as a solid-supported, which is
efficiently (0.01 mol% of copper) promoted the addition reaction at room temperature.
Table 5. aza-Michael addition of aliphatic amines
Amine
Michael acceptor
Product
Yield (%)
4a (78)
4b (85)
4c (96)
4d (88)
4e (95)
4f (97)
4g (92)
4h (88)
4i (95)
4j (88)
4k (90)
4l (97)
4m (90)
4n (85)
4o (95)
16

Conditions: Aliphatic amine 1 mmol, Michael acceptor1.5 mmol, 0.01 mol% of Cu(0)NC@PHA
in 5 mL of ethanol.The GC was used to determine the quantitative yield of the respecive products.
1
Structure of all products were determined by MS and proton H NMR (ESI).
Begin inspired by the successfulapplication of Cu(0)NC@PHA in aza-Michaeladdition of aromatic and
aliphatic amines we then investigated the catalytic applicability of Cu(0)NC@PHA toward aliphatic cyclic
and heterocyclic amines. The Michael addition reaction of pyrrolidine and methyl acrylate was carried out
using 0.01 mol % of Cu(0)NC@PHA at room temperature to afford the respective n-alkylated product 5a in
93% yield (Table 6). In the same fashion pyrrolidine wassmoothly underwent the addition reaction with butyl
acrylate and acrylonitrile to afford the corresponding n-alkylated product 5b and 5c with 85% and 95% yield
respectively. The cyclic and heterocyclic aliphatic amine e.g. piperidine and morpholine were also efficiently
forwarded the Michael addition reaction with methyl acrylate, butyl acrylate and acrylonitrile to give the
respective products 5d-5i in up to 96% yield. Interestingly a quaternary hydroxy substituted cyclic amine e.g.
4-phenylpiperidin-4-ol was smoothly afforded the respective n-alkylated products 5j-5l with 45-60% yield.
Table 6. aza-Michael addition of cyclic amines
Cu(0)NC@PHA
R1
0.01 mol%
R1
NH
N
EtOH, r.t., 1h
5
Amine
Michael acceptor
Product
Yield (%)
5a (93)
5b (85)
5c (96)
5d (75)
5e (66)
5f (90)
5g (95)
5h (96)
5i (95)
5j (45)
5k (50)
5l (60)
Conditions: Heterocyclic amine 1 mmol, Michael acceptor1.5 mmol, 0.01 mol% of Cu(0)NC@PHA
in 5 mL of ethanol. The GC was used to determine the quantitative yield of the corresponding
1
products. Structure of all products were determined by MS and proton H NMR (ESI).
17

Chemoselectivity is a vital issue in organic synthesis. Hence, we turned our attention to investigate the
chemoselectivity of Cu(0)NC@PHA in the aza-Michael addition reaction. The chemoselectivity study was
carried out using a mixture of aniline (1 mmol), propargylamine (1 mmol) and methyl acrylate (1 mmol) in
the present of 0.02 mol% of Cu(0)NC@PHA in ethanol at room temperature (Scheme 2). It was fascinating
that aniline and propargylamine were reacted with methyl acrylate to give the N-alkylated aniline derivative
3a in 35% and propargylamine derivative 4g in 42% due to the competition of the reaction. Interestingly, no
trace amount of 6 was observed in this addition reaction. Therefore, it should be noted that only aromatic
amine selectively react with olefin rather than acetylene to give the respective alkylated product which could
be utilised in the selective organic synthesis.
NH CO2Me
Cu(0)NC@PHA
(0.02 mol%)
CO2Me
NH2
3a: 35%
CO2Me
+
NH2
EtOH, r.t., 1h
HN
4g: 42%
NH
6: 0%
NH2
Scheme 2. Chemoselectivity of aza-Michael addition reaction
The possible mechanism for pandanus nanocellulose-supported Cu(0)NC@PHA catalyzed aza-Michael
addition reaction is present in Scheme 3 [59,60]. The reaction was started by the adsorption of Michael
acceptor on to the surface of Cu(0)NC@PHA through oxygen atom. The Cu(0) was easily coordinated with
the oxygen atom rather than the unsaturated carbon. Through this scenario, copper make a coordination bond
with the oxygen atom and demonstrates σ-Lewis acid character [61]. This circumstance increase the
electrophilic character of the unsaturated carbon. Then the intermediated species (i) will react with the amine
to generate a new C-N bond (ii) and intermolecular proton (iii) transfer was occurred. Finally, β-amino
carbonyl compound was generated with regeneration of Cu(0)NC@PHA [62].
Scheme 3. A plausible mechanism for aza-Michael addition.
18

3.9. Recycling of Cu(0)NC@PHA in aza-Michael addition.
Stability and recycling of catalyst are the critical parameter of a real heterogeneous catalyst, thus we
investigated the recyclability of Cu(0)NC@PHA (Fig. 13). After the first run of addition reaction (3k), the
reaction mixture was filtered out, and Cu(0)NC@PHA was washed with acetone and dried at 50℃. The
Cu(0)NC@PHA wasthenusedin the next run of addition reaction without changing the reaction parameters.
The Cu(0)NC@PHA wasnotedto function effectively up to five times exclusive of its catalytic activity. The
only minor defeat of catalytic activity was detected compared to the preliminary run. While the reduction of
addition product was noticed after the fifth cycles owing to the loss of Cu(0)NC@PHA during the filtration
and washing process and some Cu(0) was oxidized and back to green color Cu(II). The presence of any
significant leaching of copper metal in the reaction mixture was also further checked by ICP analysis.
Regarding to the ICP result, it was discovered only a trace amount of copper (<0.05 mol ppm of copper) was
leached into the reaction mixture after four consecutive runs. Thus, it reasonably accepted that the
Cu(0)NC@PHA could be recycled and reused several times with no significant loss of its catalytic
performance.
Fig. 13. Reusability of Cu(0)NC@PHA.
3.10. Comparison with other work.
In order to investigate the efficiency of Cu(0)NC@PHA we compared the results with the reported
procedures and the data are represented in Table 7. From the literature surveyed we eventually found that our
catalytic system showed better catalytic activity, mild and greener process. Therefore, cellulose-supported
Cu(0)NC@PHA enjoys the advantages of easy separation and reusability and takes advantage of a cost-
effective, low loading of copper catalytic aza-Michael addition reaction.
Table 7. A comparison study in the copper catalyzed aza-Michael reaction
Entry
Type of support
Cat. mol%
Conditions
Yield (%)
Ref.
DMF, 60℃, 10 h
DMF, 75℃, 4 h
MeOH, 60℃, 0.5-8h 88-95
1
2
3
4
5
6
7
8
9
BDC-MOF
polystyrene
polyaniline
MOF-199
Cellulose-PA
MOF
SiO2
Fe3O4@L-DOPA
Graphene
16
8.5
2.5
5
0.5
5
1.08
5
0.7
75-92
77-90
[57]
[63]
[64]
[65]
[15]
[66]
[67]
[68]
[69]
MeOH, r.t, 2 h
60-80
80-90
62-98
70-90
55-80
80-98
MeOH, r.t, 5.5 h
MeOH, r.t, 2-24 h
H2O, r.t, 5-30min
Et3N, CH2Cl2, r.t
MeCN, 82℃, 3-4 h
19

10
11
12
13
AlPO-5
CNFs
Al-CO3
Cellulose-PHA
4.6
2
34.55
0.01
MeOH, r.t, 10 h
MeOH, r.t, 20 min
MeOH, r.t, 3-5 h
This study
75-99
56-99
70-90
45-97
[70]
[71]
[58]
-
4. Conclusion
We have synthesized pandanus fruit fiber cellulose-supported Cu(0)NC@PHA and it was fully
characterized. Cu(0)NC@PHA was efficiently promoted the aza-Michael addition reaction of aromatic,
aliphatic cyclic/heterocyclic and alicyclic amines with a number of Michael acceptors to afford the
corresponding n-alkylated products selectively. A small quantity (±5.0 mg/ 0.01 mol%) of Cu(0)NC@PHA
was required to forward the addition reaction at room temperature which produced up to 97% yield of the n-
alkylated product. We observed that Cu(0)NC@PHA was selectively promoted only n-alkylated reaction
while the aromatic amine bearing a phenol and thiophenol groups. The Cu(0)NC@PHA was simple to
recoverfrom the reaction mixture and might be reusedup to five cycles exclusive of its catalytic performance.
From the comparison data based on catalytic reactivity and catalytic doses we realized that Cu(0)NC@PHA
is a promising, reusable, environment-friendly catalyst that can be used for potential applications in the
organic synthesis.
Author Contributions
This manuscript was presented through the contributions of all authors. All authors have given comment and
approval for the final version of this manuscript.
Acknowledgements
Generous support of the Skim UMSGreat, funding no. GUG0382-1/2019 and UMS Innovation grant
(SGI0061-2018) by Universiti Malaysia Sabah is gratefully acknowledged.
Conflicts of Interest
All authors declare no conflict of interest.
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