Cinnamomum tamala leaf extract-mediated green synthesis of Ag nanoparticles and their use in pyranopyrazles synthesis

Article abstract of DOI:10.1016/S1872-2067(15)60853-1

A novel, biochemical, and eco-friendly method has been developed for the synthesis of Ag nanoparticles using an aqueous leaf extract of readily accessible Cinnamomum tamala as reducing and stabilizing agents. These Ag nanoparticles were used to catalyze t

Full text of DOI:10.1016/S1872-2067(15)60853-1

Chinese Journal of Catalysis 36 (2015) 1042–1046
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Cinnamomum tamala leaf extract-mediated green synthesis of Ag
nanoparticles and their use in pyranopyrazles synthesis
Sneha Yadav, Jitender M. Khurana *
Department of Chemistry, University of Delhi, Delhi110007, India
A R T I C L E I N F O
A B S T R A C T
Article history:
A novel, biochemical, and eco-friendly method has been developed for the synthesis of Ag nanopar-
ticles using an aqueous leaf extract of readily accessible Cinnamomum tamala as reducing and stabi-
lizing agents. These Ag nanoparticles were used to catalyze the synthesis of pyranopyrazoles. The
green nature and ease of recovery and reusability of the catalyst, together with high yields of prod-
ucts, make this protocol attractive and useful.
Received 20 January 2015
Accepted 17 March 2015
Published 20 July 2015
©
2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
Keywords:
Silver nanoparticle
Cinnamomum tamala leaf
Catalysis
Pyranopyrazole
1
.
Introduction
ploration of plant extracts as potential reducing and stabilizing
agents has heightened interest in the biological synthesis of
NPs. Extracts from plants such as Capsicum annum [14], Aloe
vera [15], Cinnamomum camphora [16], Acalypha indica [17],
Emblica officinalis [18], Jatropha curcas [19], Musa paradisiacal
[20], and Ocimum sanctum [21] have been used as reducing
agents for the reduction of Ag ions to Ag. There have been a few
reports of the use of Ag NPs as catalysts for oxidation and re-
duction of certain molecules [22–24], A coupling reactions
[25], synthesis of β-enaminones [26], Diels–Alder cycloaddition
[27], and hydrogenation of chloronitrobenzenes [28].
We have explored new and greener methods for Ag NP
preparation. We focused on Cinnamomum tamala leaves,
commonly known as Tejpat in India, and used extensively in
cooking for their distinctive flavor and fragrance. One of the
major components of the essential oil of C. tamala leaves is
Nanomaterials display interesting biological, optical, mag-
netic, and catalytic properties, which differ from those of the
bulk materials because of their small size. Noble-metal nano-
particles (NPs) have important applications in electronics,
magnetic materials, optoelectronics, and information storage
[1]. Ag NPs are excellent substrates for surface-enhanced Ra-
3
man scattering [2] for probing single molecules, and are attrac-
tive building blocks for nanomaterial architectures [3]. Ag NPs
have strong antibacterial [4,5] and anti-inflammatory proper-
ties [6]. Ag NPs can be synthesized using methods such as
chemical reduction [7], electrochemical reduction [8], ultra-
sound-assisted reduction [9], photoinduced or photocatalytic
reduction [10], microwave-assisted synthesis [11], microemul-
sion methods [12], and biochemical methods [13]. The focus in
recent years has been on developing greener approaches to NP
synthesis. The implementation of green chemistry principles in
the synthesis of metal NPs can be achieved using multipurpose
agents that perform both reduction and stabilization. The ex-
eugenol [29] (Scheme 1). Eugenol reduces AgNO because of
3
the inductive effects of the methoxy and allyl groups positioned
ortho and para to the proton-releasing –OH group, leading to
the formation of the resonating structure of the anionic form of
*
Corresponding author. Tel: +91-11-2766772; Fax: +91-1-27667624; E-mail: jmkhurana1@yahoo.co.in, jmkhurana@chemistry.du.ac.in
DOI: 10.1016/S1872-2067(15)60853-1 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 7, July 2015

Sneha Yadav et al. / Chinese Journal of Catalysis 36 (2015) 1042–1046
1043
O
extract residues, and then coated as a thin film on a glass slide.
The XRD pattern was obtained using a Brucker D8 instrument
operated at 40 kV and 40 mA, with Cu Kα radiation (λ =
HO
0.15406 nm).
4-Allyl-2-methoxy-phenol (Eugenol)
Scheme 1. Structure of eugenol.
2.3. General procedure for synthesis of pyranopyrazole IIa–l
eugenol [30].
We compared the properties of Ag NPs with those of NPs
prepared by other methods, and explored potential new appli-
cations of Ag NPs as catalysts for multicomponent reactions.
Ag NPs (0.01 mmol) were added to a mixture of an aldehyde
(1.0 mmol), ethyl acetoacetate (1.0 mmol), hydrazine hydrate
(1.0 mmol), and malononitrile (1.0 mmol) in water (5 mL). The
mixture was stirred at room temperature. The reaction pro-
gress was monitored by thin-layer chromatography (TLC), with
petroleum ether/ethyl acetate (7:3) as the eluent. After com-
pletion of the reaction, the solid product was filtered using a
pump, and washed and recrystallized with ethanol. The prod-
ucts were characterized based on spectroscopic data.
2.
Experimental
2.1. Nanocatalyst preparation
Dried C. tamala leaves (2 g) were washed thoroughly,
crushed, and stirred with deionized water (20 mL) at 60 °C for
5–20 min. The solution was filtered and the filtrate was used
1
2.4. General procedure for synthesis of pyranopyrazoles IIm-q
as a green reductant and stabilizing agent.
In a typical experiment, an aqueous solution of AgNO
3
(0.2
Ag NPs (0.01 mol) were added to a mixture of an aldehyde
(1.0 mmol), ethyl acetoacetate (1.0 mmol), phenylhydrazine
(1.0 mmol), and malononitrile (1.0 mmol) in water (5 mL). The
mixture was stirred at 60 °C. The reaction progress was moni-
tored by TLC, with petroleum ether/ethyl acetate (7:3) as the
eluent. After completion of the reaction, the solid product was
filtered using a pump, and washed and recrystallized with eth-
anol. The products were characterized based on spectroscopic
data.
mmol/L) was prepared. Leaf extract (10 mL) was added to the
aqueous solution of AgNO (80 mL) and the mixture was
3
stirred with a magnetic stirrer in the dark at room temperature.
After 1 h, the color of the solution changed to light yellow, and
then to orange–brown with continued stirring. The progress of
the reaction was monitored by measuring the ultravio-
let-visible (UV-Vis) absorbance (surface plasmon resonance) of
the reaction mixture at regular time intervals.
2.2. Characterization
3. Results and discussion
+
The reduction of Ag ions was monitored by periodic sam-
In the present study, we developed a new method for the
pling of aliquots (1 mL) of the aqueous reaction mixture. The
optical absorbance of the Ag NPs was recorded in the range
preparation of Ag NPs from aqueous AgNO
3
solution, using C.
tamala leaf extract as a reducing and stabilizing system. The Ag
NPs were characterized using TEM, XRD, EDX, and UV-Vis
spectroscopy. The Ag NPs obtained had sizes of 8 ± 2 nm, which
is comparable to or smaller than those of NPs synthesized using
other plant extracts.
The Ag NP synthesis was monitored by observing the color
change of the reaction mixture. The change in the solution color
to yellow–brown from colorless after 1 h indicated the for-
mation of Ag NPs (Fig. 1(a)). The characteristic absorption peak
300–500 nm using a Perkin Elmer Lambda 35 UV-Vis spectro-
photometer. High-resolution transmission electron microscopy
(
HRTEM) and energy-dispersive X-ray spectroscopy (EDX)
2
were performed (TECNAI G U-TWIN; 300 kV) by drop coating
Ag NPs on carbon-coated Cu grids. Ag NPs for X-ray diffraction
(XRD) were prepared as follows. An Ag NP solution was sub-
jected to repeated centrifugation at 6000 r/min, and the iso-
lated NPs were washed with absolute ethanol to remove the
0
0
.8
.7
(
b)
aq. AgNO
extract
3
(a)
0
0
0
0
0
0
0
.6
.5
.4
.3
.2
.1
.0
30 min
45 min
1 h
1
1
2
h 30 min
h 45 min
h
3
00
350
400
450
500
550
Wavelength (nm)
Fig. 1. (a) Color change after adding C. tamala leaf extract to aqueous solution of 0.2 mmol/L AgNO . (b) UV-Vis spectra of reaction mixture at differ-
3
ent time intervals.

1044
Sneha Yadav et al. / Chinese Journal of Catalysis 36 (2015) 1042–1046
60
50
40
30
20
10
0
(b)
(
a)
4
6
8
10
12
14
Particle size (nm)
Fig. 2. (a) HRTEM image of Ag NPs; (b) histogram showing average sizes of Ag NPs.
at 440 nm in the UV-Vis spectrum confirmed the formation of
Ag NPs. The intensity of the brown color increased in direct
proportion to the stirring time. This may be because of the
plasmon resonance displayed by Ag NPs. Fig. 1(b) shows the
UV-Vis spectra of the solution as a function of reaction time.
A HRTEM image of the Ag NPs is shown in Fig. 2(a). The NPs
were nearly spherical and measured 7–15 nm. The histogram
in Fig. 2(b) shows that the NPs were of average size 8 ± 2 nm. A
list of various plant extracts that have been used for the prepa-
ration of Ag NPs, along with their respective sizes, is given in
Table 1. EDAX showed a strong signal for Ag, confirming the
formation of Ag NPs. Signals corresponding to C and Cu arose
from the carbon-coated Cu grids used for the analysis (Fig. 3).
The XRD pattern showed three distinct diffraction peaks, at
in lower product yields, and higher molar concentrations did
not substantially improve the yield or reaction time. The reac-
tion scope was extended by performing the reaction with phe-
nylhydrazine instead of hydrazine hydrate, under similar reac-
tion conditions. However, the reaction was incomplete after
prolonged stirring at room temperature. When the catalyst
loading was increased, the reaction still did not go to comple-
tion. The reactions were then performed at higher tempera-
tures, and this improved the results. The reaction using phe-
nylhydrazine was complete in 30 min at 60 °C and yielded 90%
of IIm, without altering the catalyst loading. The optimized
conditions were then used to study the generality of the reac-
tion by screening a wide range of aldehydes (Scheme 2). The
reaction proceeded smoothly with various aldehydes, giving
3
8.06°, 44.02°, and 64.36°, which were indexed to the (111),
C
(200), and (220) planes of cubic face-centered Ag. The for-
mation of Ag(0) was therefore confirmed. The additional unas-
signed peaks in Fig. 4 can be attributed to crystallization of
bioorganic phases on the NP surfaces [31–34]. The average Ag
NP grain size was estimated to be 20 nm using the Scherrer
equation.
Ag
Cu
We then focused on using aqueous dispersions of these Ag
NPs as green catalytic systems for multicomponent reactions.
We investigated the synthesis of pyranopyrazoles [36–39] via a
four-component condensation. The reaction of 4-chloroben-
zaldehyde (1.0 mmol), malononitrile (1.0 mmol), ethyl aceto-
acetate (1.0 mmol), and hydrazine hydrate (1.0 mmol) in water
Cu
Ag
O
4
.00
8.00
12.00
16.00
20.00
24.00
28.00
(5 mL) was performed at room temperature, using various
Energy (keV)
amounts of catalyst (Ag NPs). The reaction with 0.01 mmol of
Ag NPs gave 6-amino-4-(4-chlorophenyl)-3-methyl-2,4-dihy-
dropyrano[2,3-c]pyrazole-5-carbonitrile (IIa) in 92% yield in
Fig. 3. EDX spectrum of Ag NPs synthesized using C. tamala leaf extract.
Ag(111)
15 min. Reactions with lower concentrations of Ag NPs resulted
Table 1
Plant extracts reported for use in synthesis of Ag NPs, and correspond-
ing Ag NP sizes.
Plant Extract
Ag NPs size (nm)
64.8
Ag(200)
C. camphora [16]
A. indica [17]
Ag(220)
20–30
E. officinalis [18]
J. curcas [19]
10–20
20–40
C. annum [14]
A. vera [15]
S. aromaticum [35]
10 ± 2
15.2 ± 4.2
20–149
30
35
40
45
50
o
55
60
65
70
2
/( )
Fig. 4. XRD pattern of synthesized Ag NPs.

Sneha Yadav et al. / Chinese Journal of Catalysis 36 (2015) 1042–1046
1045
O
O
Ar
2 4. 2
+ N H H O
PhNHNH
2
Ar
+
O
CN
O
CN
CN
CN
O
O
N
ArCHO
+
HN
N
O
NH2
Ag NPs, H
2
O
Ag NPs, H O
2
N
O
NH2
o
I
Ph
60 C
rt
IIm-q
IIa-l
Scheme 2. Ag-NP-catalyzed synthesis of pyranopyrazoles.
Table 2
NPs. The reaction of 4-chlorobenzaldehyde (1.0 mmol), malo-
nonitrile (1.0 mmol), ethyl acetoacetate (1.0 mmol), and hydra-
zine hydrate (1.0 mmol) in water (5 mL) was incomplete after
Ag-NP-catalyzed synthesis of pyranopyrazole derivatives by condensa-
tion of aldehydes, malononitrile, ethyl acetoacetate, and hydrazine
[
a]
[b]
hydrate /phenylhydrazine .
8
h and yielded only 25% of IIa. Moreover, the reaction with
Entry
Ar-CHO (I) Ar
4-ClC (Ia)
4-C (Ib)
4-O NC
4-FC
3,4,5-(CH
2-Furanyl (If)
2-Naphthyl (Ig)
Product (II) Time (min) Yield (%)
AgNO
3
in water was sluggish and only 22% of the desired
1
2
3
4
5
6
7
8
9
6
H
5
IIa
IIb
IIc
IId
IIe
IIf
15
15
20
25
10
25
20
30
25
15
25
30
30
35
25
25
30
92
90
93
92
93
93
90
88
95
91
94
90
89
90
91
93
90
product IIa was obtained. These results support the involve-
ment of Ag NPs in the formation of pyranopyrazoles.
Catalyst recovery and reusability are important aspects of
green synthesis. These properties of the Ag NPs were investi-
gated by solvent extraction of the product with ethyl acetate.
The aqueous layer containing Ag NPs was then reused to con-
duct the reaction under the original reaction conditions. The
reaction yields showed that the recycled NP catalyst could be
repeatedly used for four consecutive cycles without any signif-
icant loss in activity, after which a drop in yield was observed
(Fig. 5).
6
H
4
2
6
H
4
(Ic)
6
H
4
(Id)
3
O)
3
C
6
2
H (Ie)
IIg
IIh
IIi
2,4-Cl
3-HOC
4-CH
2
C
6
H
H
3
(Ih)
6
4
(Ii)
10
11
12
13
14
15
16
17
3
C
6
H
4
(Ij)
IIj
IIk
IIl
4-(HO)-3-(MeO)C
2,5-(CH O)
4-ClC
4-O NC
3,4-(CH O)
4-(HO)-3-(MeO)C
4-BrC (In)
6
H
3
(Ik)
3
2
C
6
H
4
(Il)
6
H
4
(Ia)
(Ic)
(Im)
(Ik)
IIm
IIn
IIo
IIp
IIq
2
6
H
4
4.
Conclusions
3
2
C
6
H
4
6
H
3
We have developed an eco-friendly, non-toxic, and cost-ef-
6
H
4
fective method for the synthesis of Ag NPs, using C. tamala leaf
extract in water. The Ag NPs dispersed in water were used as a
green catalytic system for the synthesis of pyranopyrazoles in
Reactions carried out at [a] room temperature and [b] 60 °C, respectively.
the products in excellent yields in 15–35 min. The results are
summarized in Table 2.
A reasonable mechanism for the synthesis of the pyranopy-
razoles via a tandem Knoevenagel–cyclocondensation is out-
lined in Scheme 3.
1
00
(
a)
8
6
4
2
0
0
0
0
0
The catalytic role of the Ag NPs was verified by a control
experiment, which was conducted in water in the absence of
Ag
2
H O
Ag
2
H O
O
H
N
CN
CN
+
Ar
CN
Ar
H
1
2
3
4
5
A
Cycles
O
Ag NPs
(b)
NH
2
NH
2
+
N
N
O
O
N
H
OH
N
O
H
B
Ar
Ag
2
H O
CN
CN
H
N
N
N
H
OH
N
Ar
CN
N
O
B
A
H
Ar
Ar
O
Ar
O
Ar
O
H
CN
H
CN
CN
CN
Ag NPs
C
N
N
N
HN
N
N
NH
N
NH2
N
NH2
N
H
O
20 nm
H
H
II
Scheme 3. Possible reaction pathway for synthesis of dihydropyra-
no[2,3-c]pyrazole derivatives in presence of Ag NPs.
Fig. 5. (a) Plot of number of cycles against isolated yield; (b) TEM image
of Ag NPs after four cycles.

1046
Sneha Yadav et al. / Chinese Journal of Catalysis 36 (2015) 1042–1046
Graphical Abstract
Chin. J. Catal., 2015, 36: 1042–1046 doi: 10.1016/S1872-2067(15)60853-1
O
Cinnamomum tamala leaf extract-mediated green synthesis of Ag
CN
CN
nanoparticles and their use in pyranopyrazles synthesis
Ar
O
+
2 4. 2
N H H O +
CN
NH
O
O
Sneha Yadav, Jitender M. Khurana*
University of Delhi, India
N
N
2
Ph
ArCHO
+
Ar
O
A novel, biochemical, and eco-friendly method was developed for the syn-
thesis of Ag nanoparticles, using an aqueous leaf extract of Cinnamomum
tamala as reducing and stabilizing agents. The Ag nanoparticles efficiently
catalyzed pyranopyrazole synthesis.
O
Ag NPs, H
2
O
CN
NH
HN
+
+
PhNHNH
2
N
O
2
O
CN
CN
quantitative yields under mild reaction conditions.
18: 105104
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Sneha is thankful to Council of Scientific and Industrial Re-
search (CSIR), New Delhi, India for the award of Senior Re-
search Fellowship and University Science Instrumentation
Center (USIC), University of Delhi for providing instrumenta-
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