Bio-waste corn-cob cellulose supported poly(hydroxamic acid) copper complex for Huisgen reaction: Waste to wealth approach

Article abstract of DOI:10.1016/j.carbpol.2016.09.021

Corn-cob cellulose supported poly(hydroxamic acid) Cu(II) complex was prepared by the surface modification of waste corn-cob cellulose through graft copolymerization and subsequent hydroximation. The complex was characterized by IR, UV, FESEM, TEM, XPS, E

Full text of DOI:10.1016/j.carbpol.2016.09.021

Carbohydrate Polymers 156 (2017) 175–181
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Bio-waste corn-cob cellulose supported poly(hydroxamic acid)
copper complex for Huisgen reaction: Waste to wealth approach
Bablu Hira Mandala,b, Md. Lutfor Rahmanc, Mashitah Mohd Yusoffa, Kwok Feng Chonga,
Shaheen M. Sarkara,∗
a Faculty of Industrial Sciences and Technology, University Malaysia Pahang, Gambang 26300, Pahang, Malaysia
b Department of Chemistry, Jessore University of Science and Technology, Jessore 7408, Bangladesh
c Faculty of Science and Natural Resources, University Malaysia Sabah, Kota Kinabalu 88400, Sabah, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 July 2016
Received in revised form 30 August 2016
Accepted 6 September 2016
Corn-cob cellulose supported poly(hydroxamic acid) Cu(II) complex was prepared by the surface modi-
fication of waste corn-cob cellulose through graft copolymerization and subsequent hydroximation. The
complex was characterized by IR, UV, FESEM, TEM, XPS, EDX and ICP-AES analyses. The complex has been
found to be an efficient catalyst for 1,3-dipolar Huisgen cycloaddition (CuAAC) of aryl/alkyl azides with
a variety of alkynes as well as one-pot three-components reaction in the presence of sodium ascorbate
to give the corresponding cycloaddition products in up to 96% yield and high turn over number (TON
18,600) and turn over frequency (TOF 930 h−1) were achieved. The complex was easy to recover from the
reaction mixture and reused six times without significant loss of its catalytic activity.
Keywords:
Corn-cob
Cellulose
Copper
Poly(hydroxamic acid)
Huisgen reaction
© 2016 Elsevier Ltd. All rights reserved.
1. Introduction
Hiemstra, & Maarseveen van, 2006; Kim, Park, Kang, Song, & Park,
2010), CuI/PEG-400, (Daugaard, Hvilsted, Hansen, & Larsen, 2008)
The Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition of azide-
alkyne, the most common “Click” reaction discovered by Sharpless
and co-workers (Huisgen, 1963; Rostovtsev, Green, Fokin, &
Sharpless, 2002; Tornoe, Christensen, & Meldal, 2002) have stimu-
lated an increasing interest for a wide range of pharmaceuticals and
medicinal chemistry such as anti-bacterial, anti-viral, antibiotic,
magnetic resonance imaging, anti-allergic and trypanocidal activ-
ities (Goh, Chai, & Chen, 2014; Hassan & Müller, 2015; Jiang et al.,
2015; Koganei, Tachikawa, E-Zaria, & Nakamura, 2015; Lee et al.,
2007; Papadopoulou et al., 2012; Silva et al., 2008; Tang & Becker,
2014; Thomas, Adhikari, & Shetty, 2010; Wacharasindhu, Bardhan,
Wan, Tabei, & Mansour, 2009; Xia et al., 2006). The early Huis-
gen cycloaddition process required a strong electron-withdrawing
substituent on either azide or alkyne, high temperature, long
reaction time and it often afforded a mixture of 1,4-and 1,5-
disubstituted isomers (Tornoe et al., 2002). So far, Cu(I) salts,
Cu(II) salts together with a reducing agent (Tavassoli et al., 2015),
Cu(II)/Cu(0) comproportionation (Appukkuttan, Dehaen, Fokin, &
der Eycken, 2004), mixed Cu/Cu-oxide nanoparticles (Pachón,
Maarseveen, & Rothenberg, 2005), CuSO4/sodium ascorbate (Bock,
and Cu(OAc)2·3H2O/H2O (Rajender, Uma, Rajgopal, & Lakshmi,
2008) have been used as catalysts for the Huisgen cycloaddition
reaction. Recently, Cu(II) catalyzed Huisgen reaction have been
reported and their mechanism also described (Brotherton et al.,
2009; Jiang et al., 2014; Kantam, Reddy, & Rajgopal, 2006; Kuang,
Michaels, Simmons, Clark, & Zhu, 2010;). However, these homo-
geneous catalyzed Huisgen reactions have major disadvantages
associated with the difficulties in recovery of metal catalysts and
reuse for successive reaction cycles as well as the possibility of
metal contamination in the end-products. In order to overcome
these drawbacks, recent works have concentrated on heteroge-
neous catalytic systems which have several advantages like good
dispersion of active sites, easier and safer handling, easy separation
of the products from the reaction mixture and reusability of the
catalyst. Thus, a good number of heterogeneous catalytic systems
have been developed. For instance, copper on charcoal (Lipshutz &
Taft, 2006), zeolites (Chassaing, Kumarraja, Sido, Pale, & Sommer,
2007), polymers (Gala et al., 2014; Girard et al., 2006; Tano, Mieda,
Sugimoto, Ogura, & Itoh, 2014; Tavassoli et al., 2015; Yamada,
Sarkar, & Uozumi, 2012), non-magnetic and magnetic supported
variants (Fernandez, Munoz, Jaramillo, Mateo, & Gonzalez, 2010),
hydroxyapatite (Masuyama, Yoshikawa, Suzuki, Hara, & Fukuoka,
2011), silica (Mnasri et al., 2015; Roy et al., 2014) and dendrimer
nanoreactor (Deraedt, Pinaud, & Astruc, 2010) have been reported.
∗
Corresponding author.
E-mail address: sha inha@yahoo.com (S.M. Sarkar).
http://dx.doi.org/10.1016/j.carbpol.2016.09.021
0144-8617/© 2016 Elsevier Ltd. All rights reserved.

176
B.H. Mandal et al. / Carbohydrate Polymers 156 (2017) 175–181
However, long reaction times, high temperature, formation of
homocoupling products of alkynes (Glaser coupling) and the use of
large amounts of copper catalysts are the drawbacks of these meth-
ods (Eglinton & Galbraith, 1956; Siemsen, Livingston, & Diederich,
2000). Therefore, the development of a reusable, eco-friendly and
more convenient catalyst for the regioselective synthesis of 1, 4-
disubstituted 1,2,3-triazoles still remains a major challenge.
In the recent years, scientists are searching for more nature-
friendly as well as sustainable resources and processes. Thus,
biopolymers like alginate, gelatin, starch, and chitosan derivatives
have been utilized as supports for catalytic applications (Huang,
Xue, Hu, Huang, & Jiang, 2002; Wei, Zhu, Zhao, Huang, & Jiang,
2004; Zhang et al., 2001). Cellulose, a biopolymer can also be a
very suitable candidate for this purpose because of its low-cost,
wide natural abundance, ubiquitous availability and bio-renewable
character. In view of these advantages, natural cellulose have been
considered as a highly desirable alternative substance as a solid
support of metal catalysts (Guibal, 2005; Reddy, Kumar, Sreedhar, &
Kantam, 2006). Furthermore, chemical modifications of primary or
secondary hydroxyl groups in cellulose allow introducing an effec-
tive chelating ligands on to the cellulose backbone (Islam et al.,
2016; O’Connell, Birkinshaw, & O’Dwyer, 2008).
Corn-cob is left as waste but it is a potential source of cellu-
lose. If it could be used intelligently, this waste may come out as
wealth instead of waste. In this context, we have recently devel-
oped waste corn-cob cellulose supported poly(amidoxime) ligand
which had been successfully applied for the removal of metal ions
from wastewater and the anchored metal (Cu) in this ligand has
been used as an efficient catalyst for Aza-Michael reactions (Islam
et al., 2016; Rahman, Rohani, Mustapa, & Yusoff, 2014; Rahman
et al., 2016a, 2016b, 2016c; Sarkar, Sultana, Biswas, Rahman, &
Yusoff, 2016). As a continuation of our studies, herein we report
waste corn-cob cellulose supported poly(hydroxamic acid) Cu(II)
complex catalyzed Huisgen 1,3-dipolar cycloaddition reaction in
the presence of sodium ascorbate under mild reaction conditions.
tated out and it was removed by filtration. The pH of the reaction
mixture was adjusted to 11 by controlled addition of NaOH solu-
tion and the ratio of methanol and water was maintained at 4:
1 (v/v). The poly(methyl acrylate) grafted corn-cob cellulose 1
(4.5 g) was placed into a two-neck round bottom flask equipped
with a stirrer, condenser and thermostat water bath. The pre-
pared hydroxylamine solution was then added to the flask and the
reaction was carried out at 70 ◦C for 6 h. The resulting chelating
polymeric ligand 2 was separated from hydroxylamine solution by
filtration followed by washing with aqueous methanol. Further, the
ligand 2 was treated with 200 mL of 0.1 M HCl (in methanol) solu-
tion for 5 min to neutralize the reaction mixture. The ligand was
filtered and washed several times with methanol and dried at 50 ◦C
to obtain a constant weight (Rahman et al., 2016a, 2016b, 2016c).
2.3. Preparation of the poly(hydroxamic acid) Cu(II) complex 3
An aqueous solution of CuSO4·5H2O (246 mg, in 10 mL H2O) was
added into a stirred mixture of poly(hydroxamic acid) ligand 2 (1 g)
in 25 mL water at room temperature. The blue CuSO4 was immedi-
ately turned into green colour and the mixture was stirred for 2 h at
room temperature. The reaction mixture was filtrated and washed
several times with NH4Cl, water, MeOH and dried at 60 ◦C for 1 h
(1.033 g). The ICP-AES analysis showed that 0.5 mmol/g of copper
(Sarkar et al., 2016) was coordinated with the poly(hydroxamic
acid) ligand.
2.4. General procedure for the one-pot three-component Huisgen
reaction
A 5-mL glass vessel was charged with 3 (1 mg, 0.05 mol%), alkyne
(1 mmol), sodium azide (1.1 mmol), and the corresponding aryl
halide (1 mmol) in 3 mL 5 mol% aqueous solution of sodium ascor-
bate. The reaction mixture was stirred at 70 ◦C for 3 h during which
time colourless triazoles were precipitated. The reaction mixture
was diluted with EtOAc and the insoluble 3 was recovered by cen-
trifugation. The organic layer was separated and the aqueous layer
was extracted with EtOAc (3 × 2 mL). The combined organic layers
were dried over MgSO4, and concentrated under reduced pressure
to give the corresponding 1,2,3-triazole. The crude product was
purified by silica gel column chromatography (EtOAc/hexane, 1:4).
2. Experimental
2.1. Graft copolymerization
Pure cellulose was extracted from waste corn-cob according
to the method described elsewhere (Rahman et al., 2014, 2016a).
Graft copolymerization reaction was carried out in 1 L three-neck
round bottom flask equipped with stirrer and condenser in thermo-
stat water bath. The cellulose slurry was prepared by stirring 4.0 g
of corn-cob in 400 mL distilled water for overnight. The mixture
was then heated to 55 ◦C with stirring and 1.1 mL of diluted sul-
phuric acid (50%) was added. After being stirred for 5 min, 1.10 g of
ceric ammonium nitrate (CAN, 10 mL aqueous solution) was added
and the reaction mixture was stirred under nitrogen atmosphere.
After 20 min, 10 mL methyl acrylate purified monomer was added
into the reaction flask and stirred for another 4 h under nitrogen
atmosphere. The mixture was cooled, filtrated on a glass filter and
washed several times with aqueous methanol (methanol: water:
4:1) to give corn-cob cellulose supported poly(methyl acrylate) 1.
The product was finally oven dried at 50 ◦C to get a constant weight
and yield of grafted copolymer was 8.48 g Rahman et al., 2016a,
2016b, 2016c.
2.5. General procedure for Huisgen reaction of azides and
terminal alkynes
The aromatic/aliphatic azide (1 mmol), alkyne (1 mmol), cop-
per complex 3 (0.05 mol%) and sodium ascorbate 5 mol% (3 mL)
were measured in a 5 mL glass vessel and the reaction mixture was
heated at 70 ◦C for 2.5 h. After completion of the reaction, it was
cooled to room temperature and diluted with ethyl acetate. The
copper complex 3 was removed by centrifugation and the organic
layer was extracted with ethyl acetate, dried over MgSO4 and con-
centrated under reduced pressure. The crude product was purified
by silica gel column chromatography (EtOAc/hexane, 1:4) to give
the corresponding triazole.
2.6. Recycling of the Cu(II) complex 3
The recycle experiment was done for the reaction of pheny-
lacetylene (4a), benzyl azide (5a) in the presence of sodium
ascorbate (Table 1) using 0.25 mol% (5 mg) of 3 at 70 ◦C. The Cu(II)
complex 3 was recovered and reused by the following steps: after
competition of the first cycle, the reaction mixture was cooled to
room temperature, diluted with EtOAc and centrifuged. The organic
and aqueous layers were decanted and the remained solid catalyst
(in the glass vessel) was washed by water, methanol and dried at
2.2. Synthesis of poly(hydroxamic acid) ligand 2
Hydroxylamine solution was prepared by dissolving 10 g of
hydroxylamine hydrochloride (NH2OH·HCl) in 300 mL of aqueous
methanol (methanol: water; 4:1). A cold NaOH solution (50%) was
added into the hydroxylamine solution when NaCl was precipi-

B.H. Mandal et al. / Carbohydrate Polymers 156 (2017) 175–181
177
Table 1
Optimization of the Huisgen reaction.a
(a)
80
908
845
695
1655
(b)
1450
1385
2915
1162
3430
1085
1650
1742
2870
2980
585
(c)
1402
1180
1475
60
1478
1410
1127
Entry
3 (mol%)
Temp. (◦C)
Time (h)
Yield (%)
1651
2815
2930
(d)
1690
3185
1
2
3
4
5
6
0.1
0.5
50
70
50
70
70
80
90
70
70
4
3.5
5
2.5
6
5
2.5
2.5
2.5
91
96
94
96
91
94
94
0
615
1209
1450
0.05
0.05
0.005
0.005
0.005
–
559
2875
2929
40
1736
1032
1058
1618
1162
1111
Corn-cellulose
Corn-g-PMA
Poly(hydroxamic acid)
PHA-Cu
1564
7
8b
9c
20
4000
3500
3000
2500
cm
2000
-1
1500
1000
500
2 (0.05)
10
a
Conditions: 4 (1 mmol), 5 (1 mmol), 3 (0.1–0.005 mol%), sodium ascorbate
(5 mol%, 3 mL).
b
Reaction was carried out without 3.
Reaction was carried out using 2.
Fig. 1. IR spectrum of (a) corn-cob cellulose, (b) poly(methyl acrylate) 1, (c)
poly(hydroxamic acid) 2, (d) Cu(II) complex 3.
c
80 ◦C under vacuum. The reaction glass vessel was then charged
with phenylacetylene (4a), benzyl azide (5a), sodium ascrobate
and the reaction was carried out without changing the reaction
conditions (Fig. 3a).
112% grafted copolymer. The poly(methyl acrylate) 1 was treated
with hydroxylamine to produce poly(hydroxamic acid) chelating
ligand 2 with 98% conversion (Rahman et al., 2014), which was
further treated with aqueous CuSO4 to give green colour cellulose
supported Cu(II) complex 3 (Cu, 0.5 mmol/g, ICP-AES) (Scheme 1).
The IR spectrum of fresh corn-cob cellulose showed adsorption
3. Results and discussion
bands at 3430 and 2915 cm−1 which referred to O H and C
H
The waste corn-cobs were successively boiled with NaOH and
glacial acetic acid. The resulting cellulose was washed with water
and bleached with hydrogen peroxide to obtain pure cellulose
(Rahman et al., 2014, 2016a). The cellulose supported poly(methyl
acrylate) 1 was obtained by the graft copolymerization of cellu-
lose with methyl acrylate in the presence of CAN as an initiator
under the nitrogen atmosphere and product 1 was obtained about
stretching, respectively (Fig. 1). The band at 1655 cm−1 was due
to the bending mode of OH (Bonacorso et al., 2013) and a smaller
peak at 1450 cm−1 was observed for CH2 symmetric stretching.
The absorbance at 1385 and 1162 cm−1 originated from the O
H
bending and C O stretching, respectively. The C
O C pyranose
ring skeletal vibration was observed at 1085 cm−1. A small sharp
peak at 908 cm−1 corresponded to the glycosidic C1 H deforma-
Scheme 1. Synthesis of cellulose supported Cu(II) complex 3.

178
B.H. Mandal et al. / Carbohydrate Polymers 156 (2017) 175–181
tion with ring vibration contribution and OH bending indicating
␤-glycosidic linkages between glucose units in cellulose (Chuan
et al., 2006). The IR spectrum of poly(methyl acrylate) grafted cellu-
lose 1 showed new absorption band at 1475 and 1402 cm−1 due to
scissoring and wagging stretching of the methyl group respectively
(Haron, Tiansih, Ibrahim, Kassim, & Wan Yunus, 2009). In addition,
new absorption bands at 1742 and 845 cm−1 due to C O and CH3
stretching (Rahman et al., 2016b) were found. Whereas, the peaks at
2980 and 2870 cm−1 represent C H (sp3) stretching of the methyl
group. The poly(hydroxamic acid) 2 showed new absorption bands
at 1690 and 1651 cm−1 corresponding to the C O stretching and
the suitable condition (entry 4) to carry out the Huisgen reaction
with this Cu(II) complex 3.
Having the optimum reaction conditions in hand, we applied
the Cu(II) complex 3 to a variety of azides and alkynes. The p-
methyl/methoxy substituted benzyl azides (5b) and (5c) efficiently
reacted with 4a under optimized reaction conditions to afford the
corresponding triazoles 6b and 6c in up to 95% yield (Table 2,
entries 1 & 2). The substituted alkyne i.e. p-tolylacetylene (4b)
reacted with benzyl azide (5a), 1-azido-2-phenylethane (5d) and
1-azidodecane (5e) to generate the corresponding products 6d-f
in 91–96% yields (entries 3–5). An aliphatic alkynol, hex-5-yn-1-ol
(4c) readily reacted with a variety of benzylic and aliphatic azides
to give the corresponding triazoles 6g-k in 89–96% yields (entries
6–10). The Cu(II) complex 3 also promoted the reaction of alkynes
bearing tertiary alcohol, acetal, and amine moieties with 5a to give
the corresponding products 6l-n in 90–92% yields (entries 11–13).
It is interesting to note that alcohol, acetal and amine groups
remained intact and they did not affect the reactivity of 3 dur-
ing the cyclization. Therefore, 3 is tolerant to different functional
groups/functionalities in both alkynes and azides.
The recycling of the catalyst plays an important role in hetero-
geneous catalytic system. So, our attention turned to the reusability
of 3. After completion of the reaction of 4a with 5a, the complex
3, recovered by centrifugation was washed with water, methanol
and dried at 80 ◦C. It was then used in the next run under identi-
cal reaction conditions. Following this process, the complex 3 was
submitted to the reactivity process for six successive turns under
the same conditions (Fig. 3a). Only slight loss of catalytic activity
was observed for initial run was due to the loss of 3 during the
centrifugation process. No copper species was leached out into the
reaction mixture (ICP-AES) from the support during the reaction
progress. Thus, it is reasonable to believe that the cellulose sup-
ported poly(hydroxamic acid) Cu(II) complex 3 has high stability
and can be repeatedly used without significant loss of its catalytic
activity.
N
H bending modes. Additionally, a new broad band at 3185 cm−1
for N H stretching and 1410 cm−1 for OH bending were observed.
It was found that the C O band at 1742 cm−1 in 1 shifted to lower
wavelength 1690 cm−1 which confirmed the successful production
of hydroxamic acid ligand onto the corn-cob cellulose. After incor-
poration of copper salt with the poly(hydroxamic acid) ligand, the
colour of 2 changed to green colour and a new absorption band at
1736 cm−1 was observed which corresponding to C O stretching
for hydroxamic acid (Prenesti & Berto, 2002; Rafiee-Moghaddam
et al., 2014). The peaks are at 1618, 1209 and 1162 cm−1 were
assigned for C N and C O stretching respectively. A peak at
615 cm−1 confirmed the successful incorporation of Cu(II) with the
poly(hydroxamic acid) ligand 2 (Rafiee-Moghaddam et al., 2014).
The FESEM of corn-cob cellulose showed wooden stick like mor-
phology (Fig. 2a) whereas, poly(methyl acrylate) 1 grafted cellulose
showed distinguishable grafting occurred on the surface of wooden
stick like cellulosic structure having rough surface surrounding
the stick (Fig. 2b). The poly(hydroxamic acid) chelating ligand
2 showed small spherical shaped morphology (Fig. 2c) whereas,
poly(hydroxamic acid) ligand after adsorption of Cu(II) showed
compact bigger spherical shape morphology (Fig. 2d) which has
significantly different characteristics than other surface structures.
The TEM analysis of 3 also displayed the presence of copper
(Ø = 17.2 4 nm) onto the cellulose backbone (Fig. 2e). The UV–vis
spectrum of 3 exhibited a single absorption at 687 nm (Fig. 2f)
which was assigned as Cu-O coordination (Gala et al., 2014; Tano
et al., 2014). The EDX spectra (Fig. 2g) also revealed the incorpo-
ration of Cu(II) onto the cellulose surface. Furthermore, XPS of Cu
2p3/2 showed a peak at 934.5 eV (Fig. 2h) which was assigned for the
binding energy of Cu(II) (Yamada et al., 2012). These results sug-
gested that the poly(hydroxamic acid) ligand 2 coordinated with
copper to yield corn-cob cellulose supported polymeric Cu(II) com-
plex 3.
A hot filtration test was also conducted to justify the heterogene-
ity of the cellulose supported Cu(II) complex 3 during cycloaddition
reactions. The experiment was performed in a similar manner as
the Huisgen cycloaddition reaction (Table 1, 6a). After 52% conver-
sion (1 h), the reaction mixture was filtered off at hot conditions,
and the aqueous solution was heated under identical reaction con-
ditions for an additional 3 h as well as was analyzed for further
conversions (Fig. 3b). No more starting material was converted to
The corn-cob cellulose supported poly(hydroxamic acid) Cu(II)
complex 3 was used as the catalyst for the catalytic investigation of
Huisgen reaction of organic azides and terminal alkynes. The sum-
mary of optimization tests for the cycloaddition of phenylacetylene
(4a) and benzyl azide (5a) to produce 1-benzyl-4-phenyl-1H-1,2,3-
triazole (6a) is depicted in Table 1. Initially, the reaction was carried
out using 0.1 mol% of 3 at 50 ◦C for 4 h in presence of 5 mol% aque-
ous solution of sodium ascorbate and the reaction was smoothly
afforded to the desired product 6a in 91% yield (entry 1). Whereas,
96% yield was obtained when the same reaction was performed at
70 ◦C for 3.5 h (entry 2). We observed that, reaction time is period-
ically increased upon decreasing the catalyst loading, (entries 3–5)
and reaction time is decreased when the temperature is increased
(entries 6 & 7). It is noted that sodium ascorbate reduced Cu(II)
to Cu(I), by changing the colour of Cu(II) complex 3 from green
to yellow during the reaction. The cycloaddtion reaction was not
proceeded at all when the reaction was carried out without cop-
per complex 3 (entry 8). However, only 10% yield was obtained
when poly(hydroxamic) acid was used (entry 9). Hence, from the
screening of the reaction progress it can be concluded that cat-
alytic loading 0.05 mol% and reaction temperature 70 ◦C would be
Table 2
Huisgen cycloaddition reaction of azides and alkynes.a
Entry
R1
R2
Yield (%)
1
2
3
4
5
6
7
8
4a
4a
5b (p-MeC6H4)
5c (p-MeOC6H4)
5a
6b 94
6c 95
6d 96
6e 93
6f 91
6g 92
6h 90
6i 89
6j 96
6k 94
6l 92
6m 91
6n 90
4b (p-MeC6H4)
4b
5d (PhCH2)
4b
5e (n-C9H19)
4c (HO-(CH2)4)
4c
4c
5b
5d
5e
9
4c
5f (p-NO2C6H4)
10
11
12
13
4c
5g (o-napth)
4d [c-(CH2)5C]OH
4e ((EtO)2CH)
4f (NMe2CH2)
5a
5a
5a
a
Conditions: 4 (1 mmol), 5 (1 mmol), 3 (0.05 mol%), sodium ascorbate (5 mol%,
3 mL), 70 ◦C, 2.5 h.

B.H. Mandal et al. / Carbohydrate Polymers 156 (2017) 175–181
179
Fig. 2. (a) SEM image of corn-cob cellulose, (b) poly(methyl acrylate) 1, (c) poly(hydroxamic acid) 2, (d) Cu(II) complex 3, (e) TEM of 3, (f) UV–vis spectrum of 2 & 3, (g) EDX
of 3, (h) XPS of 3.
the corresponding product after removal of the Cu(II) complex 3
from the reaction mixture (Phan, Sluys, & Jones, 2006). This exper-
iment indicated that the Huisgen reactions proceeded through the
heterogeneous catalytic pathway.
Since 3 efficiently drove the click reaction of alkynes and organic
azides, the one-pot three-component cyclization of aryl/alkyl
halides, sodium azide and alkynes were also investigated (Table 3).
The reaction of phenylacetylene (4a), benzyl bromide (7a) and
sodium azide was carried out in presence of 5 mol% sodium ascor-
bate at 70 ◦C to produce triazole 6a in 95% yield within 3 h (entry 1).
Benzyl chloride (7b) was also took part the cycloaddition reaction
to give 6a in 93% yield (entry 2). Benzyl bromide with methyl sub-
stituent (7c), 2-naphthylmethyl bromide (7d), ethyl bromoacetate
(7e) and cinnamyl chloride (7f) efficiently reacted with pheny-
lacetylene (4a) to afford the corresponding triazoles 6b, 6o-q in
91–95% yields (entries 3–6). The reactions of 4-tolylacetylene (4b)
100
(a)
(b)
80
96
94
93
96
92
91
60
53
52
51
50
40
20
0
1
2
3
4
1
2
3
4
5
6
Time (h)
Run
Fig. 3. (a) Huisgen reaction by recycled Cu(II) complex 3, (b) hot filtration test of Huisgen reaction.

180
B.H. Mandal et al. / Carbohydrate Polymers 156 (2017) 175–181
Table 3
with 4a and sodium azide led to the formation of a tris(triazole) 6 w
in 94% yield.
Three components Huisgen cycloaddition reaction.a
4. Conclusion
In summary, we prepared highly active bio-waste corn-cob
cellulose supported poly(hydroxamic) copper complex which effi-
ciently promoted Huisgen reactions of terminal alkynes and organic
azides as well as one-pot three-component cycloadditions. Since
we have used waste materials as source of catalytic support and
the synthesized catalyst is recyclable, it would be a promising
environment-friendly as well as cost-effective bio-heterogeneous
catalyst in chemical synthesis. Therefore, waste materials like corn-
cob can be utilized as a heterogeneous solid support for metal
catalyzed chemical transformation reactions to ensure maximum
use of our limited wealth.
Entry
R1
R2
Yield (%)
1
2
3
4
5
6
8
9
4a
4a
4a
4a
4a
4a
4b
4b
4b
4c
7a (Ph, X = Br)
7b (Ph, X = Cl)
7c (p-MeC6H4, X = Br)
7d (o-naph, X = Br)
7e (CO2Et, X = Br)
7f (cinnamyl chloride)
7e
7c
7d
7a
6a 95
6a 93
6b 93
6o 93
6p 95
6q 91
6r 93
6s 95
6t 94
6u 94
10
11
a
Conditions: 4 (1 mmol), 7 (1 mmol), NaN3 (1.1 mmol), 3 (0.05 mol%), sodium
Acknowledgments
ascorbate (5 mol%, 3 mL), 70 ◦C, 3 h.
This work is supported by the Ministry of Education of Malaysia,
funding no. RDU 140124. Authors are grateful to Nor Hafizah Bt
Zainal Abidin scientific officer, and the central lab of University
Malaysia Pahang, Malaysia.
Notes and references
Appendix A. Supplementary data
Scheme 2. Lower catalytic loadings in the Huisgen reaction.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.carbpol.2016.09.
021.
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