Waste corn-cob cellulose supported bio-heterogeneous copper nanoparticles for aza-Michael reactions

Article abstract of DOI:10.1039/c5nj02437d

Bio-heterogeneous poly(amidoxime) copper nanoparticles were prepared on the modified surface of waste corn-cob cellulose through a graft copolymerization process. The Cu-nanoparticles (0.05 mol% to 50 mol ppm) selectively promoted the aza-Michael reaction of aliphatic amines to give the corresponding alkylated products at room temperature in methanol. The supported nanoparticles were easy to recover and reused eight times without a significant loss of their activity.

Full text of DOI:10.1039/c5nj02437d

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ARTICLE
Waste Corn-cob Cellulose Supported Bio-Heterogeneous
Copper Nanoparticles for Aza-Michael Reactions
Cite this: DOI: 10.1039/x0xx00000x
Shaheen M. Sarkar*, Tahnim Sultana, Tapan Kumar Biswas, Md. Lutfor Rahman*,
Mashitah Mohd Yusoff
Received 00th January 2012,
Accepted 00th January 2012
Bioꢀheterogeneous poly(amidoxime) copper nanoparticle was prepared onto the modified surface of
waste cornꢀcob cellulose through graft copolymerization process. The Cuꢀnanoparticle (0.05 mol% to 50
mol ppm) was selectively promoted AzaꢀMichael reaction of aliphatic amines to give the corresponding
alkylated products at room temperature in methanol. The supported nanoparticle was easy to recover and
reused eight times without significance loss of its activity.
DOI: 10.1039/x0xx00000x
www.rsc.org/
Keywords: Amine, AzaꢀMichael reaction, Cornꢀcob, Cellulose, Copper nanoparticles.
cellulose would be the most acceptable material, which is widely
abundant in nature. Develop of bioꢀbased materials and composites
1. Introduction
Conjugate reaction of various amines with α, βꢀunsaturated carbonyl
compounds provides βꢀamino carbonyl ingredients, which have
attracted great attention to the synthesis of biological active
molecules and some essential intermediate of antibiotics and
pharmaceutical products [1ꢀ6]. The conjugate addition of amines to
α, βꢀunsaturated compounds, which is known as atom economic
AzaꢀMichael reaction and very simple to carry out. Generally, Azaꢀ
Michael addition is proceeded in presence of strong acid or bases
and some side products are formed. Thus, chemists have paid more
attentions to the development of more mild catalytic systems. A
number of homogeneous catalyzed AzaꢀMichael reaction such as
AlCl3 [7], PtCl4·5H2O [8], InCl3/TMSCl [9], Bi(NO)3 [10] samarium
iodobinaphtholate [11] boric acid [12], [Ni(PPP)(THF)](ClO4)2 [13],
Pd(N,N´ꢀppo)Cl2 [14], and ionic liquids [15ꢀ18], TMSClꢀpromoted
transition metal [19] have been reported. Since the loss of material
and difficulty of purification in each step reaction will also
dramatically reduce the overall efficiency of a synthetic process.
Thus, not only the catalytic activity and selectivity but also the
stability and reusability for safe, nonꢀtoxic, sustainable chemistry,
and green organic synthesis, development of heterogeneous metal
catalysts become a particular interest. Therefore, to devise a perfect
heterogeneous metal catalyst that matches the reactivity, selectivity,
broad applicability and reusability of the catalyst would be highly
acceptable. In this context, a lot of heterogeneous metal catalysts are
employed. For instant MOFꢀ99 [20] polystyrene supported CuIꢀ
imidazole complex [21] biomaterial supported organoꢀcatalyst [22]
silica sulfuric acid [23] phosphate impregnated titania [24]
nanocrystalline copper(II) oxide [25], PANIꢀCu [26] PANIꢀIn [27],
could be a promising solution both in terms of environmental and
performances aspects. The structure of biopolymers provides several
advantages such as low density and cost, bioꢀrenewable character,
ubiquitous availability and their interesting mechanical properties
compared with glass fibres [38]. Thus, natural celluloses would be
highly desirable attractive candidates to explore the solid support of
catalysts [39]. Cellulose has interesting features for example, high
sorption capacity, stability and physical and chemical versatility
makes them attractive to use as supports. Cellulose can be
chemically modified and effective chelating ligands can be
introduced onto the cellulose backbone [40, 41]. Recently, several
biopolymers, for example alginate [42], gelatin [43], starch [44] and
chitosan [45] derivatives have been utilized as supports for catalytic
applications. Thus, development of a general, simple and convenient
method, which can be applied to a number of substrates of different
natures in a catalytic process under milder and environmentally
friendly conditions, is highly desirable. Recently, we developed
waste cornꢀcob cellulose supported poly(amidoxime) ligand which
successfully absorbed a lot of metal complexes from the industrial
waste water [46].
Herein we report cornꢀcob cellulose supported poly(amidoxime)
copper nanoparticles (CuN@PA) catalyzed regioselective Azaꢀ
Michael reaction of aliphatic amines with α, βꢀunsaturated
compounds in methanol at room temperature. The CuN@PA
showed high efficiency (0.05 mol% to 50 mol ppm) and it was
reused several times without significance loss of catalytic activity.
2. Experimental
PSSA
[28],
Amberlystꢀ15
[29],
celluloseꢀCu(0)
[30],
CeCl3·7H2O/NaI/Al2O3 [31], polystyreneꢀAlCl3 [32], enzymes [33,
34] showed good catalytic activity for the Michael additions.
Although many economic and sustainable protocols have been
employed by the researchers dedicated to the development of green
processes for AzaꢀMichael additions, some of catalysts have poor or
even weak catalytic effect [35ꢀ37].
2.1 General Information
All manipulations were performed under atmospheric conditions
otherwise noted. Reagents and solvents were obtained from
commercial suppliers and used without further purification. Water
was deionized with a Millipore system as a MilliꢀQ grade.
CuSO4·5H2O was purchased from Aldrich Chemical Industries, Ltd.
1H NMR (500 MHz), 13C NMR (125 MHz) spectra were measured
Recently, scientists are searching cheap and more environmentally
friendly sustainable resources and processes. In this connection,
This journal is © The Royal Society of Chemistry 2013
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DOI: 10.1039/C5NJ02437D
with a BRUKERꢀ500 spectrometer, central laboratory, University separated from the hydroxylamine solution by filtration followed by
Malaysia Pahang. The 1H NMR chemical shifts were reported washed with aqueous methanol. The obtained cellulose based
relative to tetramethylsilane (TMS, 0.00 ppm). The 13C NMR amidoxime ligand was neutralized with 100 mL of methanolic 0.1 M
chemical shifts were reported relative to CDCl3 (77.0 ppm). HCl solution. The ligand was filtered and washed several time with
Inductively coupled plasma atomic emission spectrometry (ICPꢀ aqueous methanol and dried at 50 °C for 6 h [48, 49].
AES) was performed on a Shimadzu ICPSꢀ8100 equipment by the
central laboratory, University Malaysia Pahang. FTIR spectra were
measured with a Perkin Elmer (670) spectrometer equipped with an
2.5 Preparation of the poly(amidoxime)copper complex 2
ATR device (ZnSe crystal), FIST, University Malaysia Pahang. XPS An aqueous solution of CuSO4·5H2O (126 mg, in 5 mL H2O) was
spectra were measured with an ESCALA 250 (Thermo Fisher added into a stirred mixture of 1 g of poly(amidoxime) ligand 1 in 25
Scientific K.K.) by HiꢀTech Instruments SDN BHD, Puchong, mL water at room temperature. The blue CuSO4 was immediately
Malaysia. FEꢀSEM was measure with JSMꢀ7800F, central turned into green colour and the mixture was stirred for 1 h at room
laboratory, University Malaysia Pahang. TEM was measure with temperature. The reaction mixture was filtrate and washed several
HTꢀ7700, HiꢀTech Instruments SDN BHD, Puchong, Malaysia. TLC times with excess amount of water, MeOH and dried at 60 °C for 1
analysis was performed on Merck silica gel 60 F254. Column h. The ICPꢀAES analysis showed that 0.5 mmol/g of copper [49]
chromatography was carried out on silica gel (Wakogel Cꢀ200).
was coordinate with the poly(amidoxime) ligand.
2.2 Materials
2.6 Preparation of the poly(amidoxime) Cu-nanoparticles
(CuN@PA)
The waste cornꢀcob was obtained from Gambang, Pahang, Malaysia.
Cornꢀcobs were cut into small size (3 cm long average). The raw
cornꢀcob (100 g) was boiled with 10% NaOH (800 mL), glacial
acetic acid (800 mL) for 4 h and 2 h respectively, and washed with
distilled water. The raw cornꢀcob cellulose was bleached with
hydrogen peroxide (500 mL) and 5% NaOH (300 mL), washed with
distilled water (500 mL) several times and oven dried at 50 °C
before use. Acrylonitrile monomer purchased from Aldrich and
monomer was passed through the columns filled with
chromatographic grade activated alumina to remove the inhibitor.
Other chemicals such as ceric ammonium nitrate (CAN) (Sigmaꢀ
Aldrich), methanol (Merck), and other analytical grade reagents
were used without purification.
Poly(amidoxime)copper complex 2 (500 mg) was dispersed in 50
mL deionized water and then hydrazine hydrate 0.7 mL was added.
The resulting dark brown color CuN@PA materials were collected
by centrifugation, washed with methanol, acetone, and dried under
vacuum at 100 °C and stored under nitrogen atmosphere.
2.7 General procedure for Aza-Michael reaction
In a typical experiment, a mixture of amine (1 mmol), α, βꢀ
unsaturated Michael acceptor (1.1ꢀ4 mmol), cornꢀcob cellulose
supported CuN@PA (0.05 mol%) in 2 mL MeOH was stirred at
room temperature for 1 h. The reaction progress was monitored by
TLC analysis. After completion of the reaction, CuN@PA was
filtered, washed with MeOH (3 x 5 mL), dried, and reused in the
next run under the same reaction conditions. The filtrate was
concentrated to give the crude product, which was purified by
2.3 Graft copolymerization
The graft copolymerization reaction was carried out in 1 L threeꢀ
neck round bottom flask equipped with stirrer and condenser in column chromatography (hexane/ethyl acetate) to give the
corresponding Michael addition products.
3. Results and discussion
thermostat water bath. The cellulose slurry was prepared by stirring
6 g of cornꢀcob cellulose in 150 mL distilled water for overnight.
The N2 gas was purged into the flask to remove oxygen during the
grafting process. The slurry was heated to 55 °C and 2.17 mL of
diluted sulphuric acid (H2SO4/H2O, 1:1) was added to the mixture.
After 5 min, 2 g of CAN (in 10 mL solution) was added and the
reaction mixture was stirred continuously. After 20 minutes, 14 mL
of acrylonitrile monomer was added into the cellulose suspension
and stirred for 4 h under nitrogen atmosphere. The reaction mixture
was cold and the obtained cellulose was washed several times with
aqueous methanol (methanol/water, 4:1). The product was finally
oven dried at 50 °C to obtain a constant weight [47].
The waste cornꢀcob was obtained from Gambang, Pahang, Malaysia.
2.4 Synthesis of poly(amidoxime) ligand 1
Hydroxylamine hydrochloride (NH2OH·HCl) 20 g was dissolved in
500 mL of aqueous methanol (methanol/water, 4:1) and neutralized
by NaOH solution and the resulting NaCl precipitate was removed
by filtration. The pH of the reaction was adjusted to pH 11 by adding
of NaOH solution. The ratio of methanol and water was maintained
as 4:1 (v/v). Poly(acrylonitrile) grafted cornꢀcob cellulose 10 g was
placed into a twoꢀneck round bottom flask equipped with a stirrer,
condenser and thermostat water bath. The hydroxylamine solution
was then added to the flask and the reaction was starred at 70 °C for
4 h. After completion of reaction, the chelating ligands were
Scheme 1. Synthesis of waste cornꢀcob celluloseꢀsupported
CuN@PA.
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The waste cornꢀcobs were cut into small pieces and successively to the CH2 symmetric stretching [50]. A small peak at 1371 and a
boiled with 10% NaOH and glacial acetic acid for 4 h and 2 h broad band at 1162 cmꢀ1 showed for CꢀO stretching. The CꢀOꢀC
respectively. The resulting cellulose was washed with water and pyranose ring skeletal vibration gives a strong band at 1062 cmꢀ1. A
bleached with hydrogen peroxide and 5% NaOH respectively. The small sharp peak at 892cmꢀ1 corresponds to the glycosidic C1ꢀH
obtained white colour cellulose was graft polymerized with deformation with ring vibration contribution and OH bending, which
acrylonitrile using ceric ammonium nitrate as a redox initiator to is characteristic of αꢀglycosidic linkages between glucose in
give cellulose supported poly(acrylonitrile) which was further cellulose [46, 48]. The IR spectrum of acrylonitrileꢀgrafted cellulose
reacted with hydroxylamine provided poly(amidoxime) chelating exhibited a new absorption band at 2244 cmꢀ1 attributed to the CN
ligand 1 (Scheme 1).
stretching of nitrile.
The poly(amidoxime) chelating ligand showed new absorption
bands at 1676 and 1649 cmꢀ1 correspond to the C=N stretching and
NꢀH bending modes, respectively. In addition, a shoulder created at
3303 cmꢀ1 for NꢀH and OH stretching bands and 1406 cmꢀ1 for
bending. A clear evidence for the CN band for 2244 cmꢀ1 was
disappeared and a new absorption bands for amidoxime group was
appeared, which confirmed the successful production of
poly(amidoxime) function onto the cronꢀcob cellulose grafted
copolymers. The poly(amidoxime) function was then treated with
aqueous copper sulphate at room temperature to give blue colour
poly(amidoxime) copper complex 2 (Fig. 1c). The IR of 2 showed at
3303 cmꢀ1 and 1125 cmꢀ1 [51], which indicated the copper salt was
coordinate with the poly(amidoxime) ligand 2. The copper complex
2 was then treated with hydrazine hydrate [52] to give dark brown
(c)
(d)
(b)
(a)
(e)
(f)
colour copper nanoparticles CuN@PA (Ø = 8.0 ± 7 nm) which were
stabilized by the poly(amidoxime) ligands (Fig. 1d and 1l).
Table 1. AzaꢀMichael addition reaction of aminesa
(h)
(g)
(i)
(j)
(k)
(l)
Fig 1. (a) Photo image of waste cornꢀcob, (b) Photo image of 1,
(c) Photo image of 2, (d) Photo image of CuN@PA, (e) XPS of
CuN@PA, (f) XPS of used CuN@PA, (g) IR spectrum of
cellulose and modified cellulose, (hꢀk) SEM images of
cellulose, cellulose supported poly(acrylonitrile), 1, and copper
complex 2 respectively, (l) TEM image of CuN@PA.
Figures 1aꢀd are showing the photographic images of waste cornꢀ
cob, cornꢀcob cellulose, poly(amidoxime) copper complex 2, and
CuN@PA respectively. The IR spectrum of cellulose showed the
absorption bands at 3432 cmꢀ1 and 2924 cmꢀ1 for OꢀH and CꢀH
stretching, respectively (Fig. 1g). A small peak at 1424 cmꢀ1 belongs
aReactions were carried out using 1 mmol of amine, 1.1 mol equiv of
Michael acceptor, 0.05 mol% of CuN@PA in 2 mL MeOH at room
temperature for 1 h.
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The XPS spectrum showed (Fig. 1e) a single Cu 2p3/2 peak at 932.2 observed under the same reaction conditions as for initial run. The
eV, which is assigned for the binding energy of Cu(0) [52]. The FEꢀ slight loss of catalyst activity was observed after five cycles due to
SEM micrograph of the cornꢀcob cellulose showed unsmooth the loss of CuN@PA during the filtration process. A trace amount
morphologies including fine crystalline surface (Fig. 1h). The FEꢀ of copper species (<0.11 mol ppm of Cu, ICPꢀAES) was leached out
SEM micrograph of the poly(acrylonitrile) grafted cornꢀcob from the reaction mixture. Thus, it is reasonable to believe that the
cellulose showed spherical shape beads structure which is cellulose supported copper catalyst can be repeatedly used for largeꢀ
distinguishable surface (Fig. 1h) of cornꢀcob cellulosic fine scale production without significant loss of its catalytic activity.
crystalline structure and it is clear evidence for grafting occurred on
The chemoselectivity of CuN@PA was then investigated. Thus, a
the cellulosic materials (Fig. 1i). The poly(amidoxime) chelating mixture of aniline and piperidine were exposed to acrylonitrile (4
ligand 1 showed distinct morphologies with finest beads structure mol equiv) under the present reaction conditions (Scheme 2).
looks small gain like structure (Fig. 1j). The SEM micrograph of Interestingly, aniline was not underwent the reaction only the mono
poly(amidoxime) ligand after adsorption of CuSO4 is compact Michael adduct of piperidine was obtained exclusively. It is clearly
surface (Fig. 1k), which is different with finest beads structure of 1 reflects the chemoselectivity of aliphatic amines versus aromatic
(Fig. 1j). The TEM image showed the well dispersion of copper
nanoparticles on to the cellulose surface (Fig. 1k).
amines. This selectivity is due the less reactivity of aromatic amines
in comparison to aliphatic amines. This selectivity could be useful to
discriminate the two types of amines for synthetic applications.
To check the reactivity of CuN@PA we applied this cornꢀcob
cellulose supported copperꢀnanoparticles CuN@PA to the conjugate
addition of aliphatic amines with different Michael acceptors at
room temperature and the results are summarized in Table 1. The
cellulose supported copper nanoparticles CuN@PA was efficiently
(0.05 mol%) promoted AzaꢀMichael reaction in methanol at room
temperature. The α, βꢀunsaturated carbonyl Michael acceptor,
methyl acrylate was smoothly promoted the AzaꢀMichael reaction
with secondary aliphatic amine such as dibutylamine, piperidine,
morpohline and sterically hindered secondary dibenzylamine to give
the corresponding products in up to 95% yields (5a-d). Similarly,
butyl acrylate was efficiently provided the corresponding Michael
addition adducts in up to 96% yields (5e-i). The α, βꢀunsaturated
acrylonitrile was also promoted the addition reaction to give the
mono alkylated products (5j-n). It should be noted that,
cyclohexylamine and ethylenediamines ware also efficiently
underwent the AzaꢀMichael reaction to give poly alkylated products
5o-q with methyl, butyl acrylate and acrylonitrile Michael acceptor
respectively.
The recycling of the catalyst is an important issue in
heterogeneous catalysis system. Again, we turn our attention to reuse
our cellulose supported copper nanoparticles CuN@PA and the
results are summarized in Table 2. After competition of the first run,
the reaction mixture was filtrated and washed with methanol. The
XPS image (Fig. 1f) of reused CuN@PA showed similarity with the
fresh CuN@PA (Fig. 1e). The solid brown colour CuN@PA was
dried at 80 °C under vacuum, and then used it in the next run without
changing of the reaction conditions.
Scheme 2. Chemoselective AzaꢀMichael reaction.
To investigate the highest catalytic activity obtainable for the
AzaꢀMichael reaction was also performed (Scheme 3). The Michael
addition reaction was carried out using 10 mmol of dibutyl amine
and acrylonitrile in presence of 50 mol ppm (0.1 mg) of CuN@PA
which was still efficiently promoted the AzaꢀMichael reaction to
provide 5j in 94% yield. The TON and the turnover frequency (TOF)
of the catalyst reached 18412 and 7364 h−1, respectively; these are,
as far as we know, the highest TON and TOF obtained for a
cellulose supported CuN@PA catalysed AzaꢀMichael reaction.
Table 2. AzaꢀMichael reaction by recycled catalyst CuN@PAa
Scheme 3. Lower catalytic loading (50 ppm) in the AzaꢀMichael
reaction.
Conclusion
In summary, the waste cornꢀcob cellulose supported
poly(amidoxime) copperꢀnanoparticle was efficiently promoted
chemoselective AzaꢀMichael addition of aliphatic amines with
conjugate α, βꢀunsaturated Micheal acceptors. The addition
reactions were efficiently (0.05 mol% to 50 mol ppm) promoted
to provide the corresponding products with excellent yields.
After completion of the reaction, supported nanoparticle was
separated from the reaction mixture by simple filtration, and it
was reused several times without significance loss of activity.
Cycle
Yield (%)a
Cycle
Yield (%)a
1
2
3
4
96
94
94
93
6
7
8
93
92
91
94 (<0.11 mol ppm
Cu was leached out)
5
aReaction was carried out using 1 mmol of piperidine, 1.1 mmol of butyl
acrylate, 0.05% of CuN@PA in 2 mL of MeOH at room temperature.
Acknowledgement
This work is supported by Ministry of Education Malaysia, fund no.
RDU 140124. Authors are grateful to Nor Hafizah Bt Zainal Abidin,
scientific officer, and central lab, University Malaysia Pahang.
The CuN@PA could be used eight times without significance loss
of catalytic activity. Only slight loss of catalytic activity was
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DOI: 10.1039/C5NJ02437D
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Fax: +609 5492766; Tel: +609 5492399; Eꢀmail:
sha_inha@yahoo.com; shaheen@ump.edu.my
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J. Name., 2014, 00, 1-3 | 5

New Journal of Chemistry
Page 6 of 6
View Article Online
DOI: 10.1039/C5NJ02437D
Graphical abstract
Waste corn-cob cellulose supported Cu-nanoparticle was found as a highly effective catalyst
for Aza-Michael reaction at room temperature.