Solar energy assisted starch-stabilized palladium nanoparticles and their application in C-C coupling reactions

Article abstract of DOI:10.1166/jnn.2013.7583

Present work reports a novel one step, greener protocol for the synthesis of starch-stabilized palladium nanoparticles (PdNPs) with an average particle diameter of 30-40 nm. These particles were stable and uniform in size. In present protocol, the concentrated solar energy mediated reduction of palladium chloride was achieved by using citric acid as a reducing agent and starch as a capping agent. UV-Visible spectroscopy, Transmission Electron Microscopy, Field Emission Gun-Scanning Electron Microscopy, Selected Area Electron Diffraction and Electron dispersive X-ray Spectral analysis techniques were used to characterize this starch capped PdNPs. Herein; we are reporting such combination of starch and citric acid in the synthesis of PdNPs for the first time. The catalytic activity of synthesized nanoparticles has been checked for Suzuki and Heck cross coupling reactions. The product yield was confirmed by GC. The products were confirmed using GC-MS analysis and also using GC with the help of authentic standards. Solar energy assisted starch stabilized PdNPs showed excellent activity in the C C bond formation between aryl halides (I, Br) with phenyl boronic acid and its derivatives. In addition, the catalyst showed good activity in the Heck coupling reaction of C C bond formation of aryl halides with aromatic alkene. The use of starch, citric acid, water and solar energy makes present protocol greener. Copyright

Full text of DOI:10.1166/jnn.2013.7583

Copyright © 2013 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 13, 5061–5068, 2013
Solar Energy Assisted Starch-Stabilized Palladium
Nanoparticles and Their Application in
C—C Coupling Reactions
Aniruddha B. Patil and Bhalchandra M. Bhanage∗
Department of Chemistry, Institute of Chemical Technology, Autonomous,
N. M. Parekh Marg, Matunga, Mumbai 400019, India
Present work reports a novel one step, greener protocol for the synthesis of starch-stabilized palla-
dium nanoparticles (PdNPs) with an average particle diameter of 30–40 nm. These particles were
stable and uniform in size. In present protocol, the concentrated solar energy mediated reduction of
palladium chloride was achieved by using citric acid as a reducing agent and starch as a capping
agent. UV-Visible spectroscopy, Transmission Electron Microscopy, Field Emission Gun-Scanning
Electron Microscopy, Selected Area Electron Diffraction and Electron dispersive X-ray Spectral anal-
ysis techniques were used to characterize this starch capped PdNPs. Herein; we are reporting
such combination of starch and citric acid in the synthesis of PdNPs for the first time. The catalytic
activity of synthesized nanoparticles has been checked for Suzuki and Heck cross coupling reac-
tions. The product yield was confirmed by GC. The products were confirmed using GC-MS analysis
and also using GC with the help of authentic standards. Solar energy assisted starch stabilized
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PdNPs showed excellent activity in the C C bond formation between aryl halides (I, Br) with phenyl
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boronic acid and its derivatives. In addition, the catalyst showed good activity in the Heck coupling
Copyright: American Scientific Publishers
reaction of C C bond formation of aryl halides with aromatic alkene. The use of starch, citric acid,
water and solar energy makes present protocol greener.
Keywords: Solar Energy, Citric Acid, Starch, Suzuki, Heck.
1. INTRODUCTION
effect of PVP and PVA, starch as a dispersing agent is
more effective in restricting the size of nanostructures.10
In this regards, Wallen et al. prepared starched silver
nanoparticle from soluble starch as a stabilizer.11 Recently
in carbohydrate research Valodka et al. reported car-
bohydrate stabilized silver nanoparticles,12 whereas Liu
et al. reported water soluble starch stabilized palladium
nanoparticle.13 Similar to starch, citric acid is also consid-
ered as a renewable material which acts as a shape selec-
tive reducing agent in the nanoparticle synthesis.14 Water is
an inexpensive, environmentally benign and green solvent.
In literature there are many reports for the Pd nanoparticle
synthesis in aqueous media.15–17
Solar energy is widely considered as a largest source
of carbon neutral renewable energy. It is non-polluting,
non-toxic, and traceless in chemical processes. In spite
of such attractive features its applications in the synthesis
are limited. In view of this we have paid special atten-
tion to the development of greener protocols with avail-
able solar energy source for replacement of conventional
energy sources. Earlier, we have reported the synthesis of
metal and metal oxide nanoparticles by the application of
Palladium nanoparticles (PdNPs) synthesis has attracted
a great attention due to their applications in catalysis,1
hydrogen storage materials2 and Photonics.3 Till date sev-
eral methods are reported for the preparation of PdNPs,
like aqueous phase reflux condensation,4 polyol process,5
template assisted,6 sonochemical,7 UV-photo-irradiation,3
laser ablation8 and chemical vapour deposition.9 Although,
these methods have proven their utility in the nanoparticle
synthesis, they suffer from one or more drawbacks, like
use of sophisticated instrument set-up, conventional energy
sources, use of toxic chemicals which are non-greener and
economically unviable.
Starch is a carbohydrate consisting of a large number
of glucose units joined together by glycosidic bonds. It is
one of the most abundant inexpensive materials with wide
applicability. Starch is edible and nontoxic, widely used in
food, drug carrier, medicine and industry. Recent investi-
gations have shown that in comparison to the stabilizing
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2013, Vol. 13, No. 7
1533-4880/2013/13/5061/008
doi:10.1166/jnn.2013.7583
5061

Solar Energy Assisted Starch-Stabilized PdNPs and Their Application in C C Coupling Reactions
Patil and Bhanage
concentrated solar energy.18ꢀ19 Herein we are developing
a greener protocol for the palladium nanoparticle synthe-
B(OH)2
R
Starch-PdNPs
base, 100 °C, water
+
X
R
sis wherein all the parameters used for the nanoparticle
synthesis like starch, citric acid, water and solar energy
are greener and renewable. The concept of using ‘Fresnel
lens’ to concentrate the solar radiation helps to reduce the
Pd (II) to Pd (0) and thus it can be used for the starch-
PdNPs synthesis. Using this concept we were successful in
synthesizing PdNPs of 30–40 nm size. To the best of our
knowledge this is first report wherein starch and citric acid
combination used for the synthesis of palladium nanopar-
ticle. The catalytic activity of prepared starch-PdNPs was
studied for the Suzuki and Heck coupling reaction of aryl
halides using water as a benign reaction medium. The
Starch stabilized PdNPs showing excellent yield for the
Suzuki coupling reaction of aryl Iodides with derivatives
of phenyl boronic acids. It also shows good activity in
the C C bond formation of aryl halides with aromatic
alkenes in aqueous media.
X = I, Br
Scheme 1. Starch-PdNPs catalyzed Suzuki cross coupling reaction of
aryl halides and phenyl boronic acid.
Electron Diffraction (SAED) was recorded with a Philips
model CM 200, Field Emission Gun-Scanning Electron
Microscopy (FEG-SEM) and Electron dispersive X-ray
Spectral analysis EDAX images were recorded with a
JEOL JSM-7600 F.
2.4. Typical Procedure for Suzuki
Cross Coupling Reaction
The reaction was carried out in a sealed tube with spin
bar consisting iodobenzene (1 mmol), phenylboronic acid
(1.2 mmol), potassium hydroxide (2 mmol) and PdNPs
solution (50 ꢁL, 0.0005 mmol) in aqueous medium for
1 hr at 100 ꢀC with constant stirring (Scheme 1). The reac-
tion progress was monitored using GC analysis (Perkin
Elmer, Clarus 400). After completion of the reaction,
the solution was allowed to reach at room temperature
and biphenyl was extracted with ethyl acetate with three
subsequent extractions, the combined extracts were then
2. EXPERIMENTAL DETAILS
2.1. Materials
Palladium (II) chloride purchased from M/s Parekh Plat-
inum Ltd. Citric acid from M/s Polypharm and Starch from
M/s SRL Pvt. Ltd. All the experiments were carried out
dried over Na SO , filtered up and volatiles removed
under reduced pressure. The obtained crude product was
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using deionized water prepared by distillation and water
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purification system (Milli-Q). Glassware was cleaned with
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then purified by column chromatography using silica gel,
(100–200 mesh size) with petroleum ether/ethyl acetate
(PE–EtOAc, 95:05) as eluent to give pure product. All the
products are well known and were confirmed by GC-MS
(Shimadzu GC-MS QP 2010) and also with GC using
authentic standards.
ꢀ
acetone, followed by drying at 125 C in an oven.
2.2. Preparation
In a typical experiment for the synthesis of starch-PdNPs,
starch (30 mg) and citric acid (60 mg) were added to pal-
ladium (II) chloride (11 mg) dissolved in 15 ml deionized
water. The obtained mixture was irradiated under solar
radiations concentrated by a Fresnel lens at noon time in
summer for 5 h (10 am to 3 pm wherein, temperature
2.5. Typical Procedure for Heck Coupling Reaction
The reaction was carried out in a sealed tube with
spin bar consisting styrene (1.2 mmol), iodobenzene
(1 mmol), potassium hydroxide (2 mmol) and PdNPs solu-
tion (100 ꢁL, 0.001 mmol) in aqueous medium for 10 h
at 100 ꢀC with constant stirring (Scheme 2). The GC anal-
ysis was done to check the reaction progress. Then as
per above mentioned procedure reaction mixture was pro-
cessed to yield the product, which was further purified by
column chromatography over silica gel. All the synthe-
sized products are well known and confirmed by GC-MS
ꢀ
range was 90 5 C). The synthesized nanoparticles solu-
tion was diluted up to 100 ml with deionized water and
used as a stock solution for the Suzuki and Heck cross
coupling reaction.
The author’s laboratory is located at Matunga, Mum-
bai (Geographical location: Greater Bombay, Maharashtra,
India, Asia. Geographical Coordinates: 19ꢀ 2’0” North, 72ꢀ
51’0ꢁꢁ East). The energy input for the reaction is measured
by the pyranometer DWR 8101 which was recorded as
570 W ft−2
.
R
R
CH2
+
Starch-PdNPs
2.3. Characterization of Prepared PdNPs
KOH, 100 °C,
10 h, water
X
Prepared nanoparticles were characterized by analytical
methods. The reduction of Pd (II) to Pd (0) were confirmed
with a UV spectrophotometer (Shimadzu 1650), Trans-
mission electron microscopy (TEM) and Selected Area
X = I, Br
Scheme 2. Starch-PdNPs catalysed Heck coupling reaction of aryl
halides and Aryl alkene.
5062
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Patil and Bhanage
Solar Energy Assisted Starch-Stabilized PdNPs and Their Application in C C Coupling Reactions
(Shimadzu GC-MS QP 2010) and with GC using authentic
standards.
(5) 4-styrylaniline ꢂTable III, entry 5ꢃ
GC-MS (EI) m/z (%) = 195(17.5) [M]+, 194(100),
193(20.2), 180(15.0), 179(96.8), 178(69.1), 165(11.2),
152(9.1), 115(13.3), 96(16.0), 89(8.9), 76(9.9), 65(8.5),
51(7.1).
2.6. GC Analysis
(6) 1-styrylnaphthalene ꢂTable III, entry 6ꢃ
GC-MS (EI) m/z (%) = 230(100) [M]+, 229(98.5),
228(33.4), 227(14.9), 226(18.0), 215(20.1), 202(11.1),
152(22.4), 115(10.3), 114(18.6), 113(11.4), 101(13.9),
77(4.2).
The reaction mixture was analysed by gas chromatogra-
phy equipped with a flame ionization detector (FID) and
a capillary column (Perkin-Elmer, Clarus 400, 30 m ×
0.32 mm×0.25 ꢁm). The GC parameters were as follows:
Initꢀial time 1 min; solvent delay 3 min; initial temperature
ꢀ
80 C; temperature ramp 1 for 10 C/min; final tempera-
ꢀ
ture ꢀ250 C; final time 40 min; injector port temperature
3. RESULTS AND DISCUSSION
ꢀ
250 C; detector temperature 250 C and injection volume
0.5 ꢁL.
3.1. Preparation and Characterization PdNPs
Present work is focused on a developing greener syn-
thesis of starch-PdNPs by PdCl2, wherein all reactants
are greener like starch as a capping agent, citric acid as
reducing agent; concentrated solar radiations as an energy
source and water as a greener reaction medium. In case
of PdNPs formation using PdCl2, the synthesis is associ-
ated with the reduction of Pd (II) to Pd (0) and it requires
higher driving force, which is not possible to obtain under
the intensity of normal solar energy, so we have introduced
a novel concept of concentrated solar energy, which was
reported in our previous study.16 The use of citric acid as
2.7. Spectral Data of Selected Products
2.7.1. Characterization of Biphenyls
(1) 1,1ꢁ-biphenyl ꢂTable II, entry 1, 6ꢃ
GC-MS (EI) m/z (%) = 154(100) [M]+, 153(37.8),
152(26.2), 151(8.3), 77(8.2), 76(16.7), 63(7.6), 51(8.7).
(2) 3-methoxy1,1ꢁ-biphenyl ꢂTable II, entry 2ꢃ
GC-MS (EI) m/z (%) = 184(100) [M]+, 155(13.9),
154(25.1), 153(17.5), 141(24.6), 115(25.4).
(3) 2-chloro-1,1ꢁ-biphenyl ꢂTable II, entry 3ꢃ
GC-MS (EI) m/z (%) = 188(100) [M]+, 153(27.5),
reductant helps to synthesis both decahedra and icosahedra
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shapes considered as MTPs (Multiple tuned particles).20
152(45.8), 151(13.8), 76(22.5), 63(8.2).
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(4) N,N-dimethyl-[1,1ꢁ-biphenyl]-3-amCionpeyrigꢂhTta:bAlemeriIcIa, n Scientific Publishers
We experienced that the synthesized PdNPs solution was
entry 4ꢃ
stable for several months without any aggregate forma-
tion indicating that starch serve as an efficient capping
agent.
To check the necessity of concentrated solar energy in
the synthesis of PdNPs we carry out the nanoparticle syn-
thesis at room temperature as well as under normal sun
light, but even after longer time interval we didn’t observe
GC-MS (EI) m/z (%) = 197(100) [M]+, 196(99.1),
153(13.4), 152(22.5), 98(17.2), 76(8.1), 42(7.3).
(5) 3,5-dimethyl-1,1ꢁ-biphenyl ꢂTable II, entry 5ꢃ
GC-MS (EI) m/z (%) = 182(100) [M]+, 181(17.1),
167(54.2), 166(16.9), 165(31.4), 152(13.3), 89(8.3),
77(6.6), 76(6.4).
2.7.2. Characterization of Diphenylethenes
(1) 1,2-diphenylethene ꢂTable II, entry 1ꢃ
GC-MS (EI) m/z (%) = 180(100) [M]+, 178(85.0),
177(53.1), 176(9.5), 165(42.9), 152(13.3), 115(4.5),
89(27.3), 77(7.4), 76(14.6), 63(8.4), 51(9.5).
(2) 1-methyl-4-styrylbenzene ꢂTable III, entry 2ꢃ
GC-MS (EI) m/z (%) = 194(82.4) [M]+, 193(19.0),
180(11.4), 179(80.0), 178(56.5), 165(9.2), 152(9.1),
115(10.5), 96(14.3), 89(6.2), 76(8.9), 65(8.3).
(3) 1-methoxy-2-styrylbenzene ꢂTable III, entry 3ꢃ
GC-MS (EI) m/z (%) = 210(100) [M]+, 179(13.7),
178(9.2), 167(22.3), 166(11.6), 165(37.1), 152(23.4),
119(25.8), 104(23.0), 91(27.1), 82(8.2), 77(7.6), 63(6.1).
(4) 1-nitro-4-styrylbenzene ꢂTable III, entry 4ꢃ
GC-MS (EI) m/z (%) = 225(97.0) [M]+, 195(10.7),
179(40.0), 178(100), 177(16.7), 176(18.0), 165(11.8),
152(25.8), 151(10.0), 89(13.7), 76(17.2), 63(8.4), 51(7.8).
Fig. 1. Schematic representation of reaction setup for the synthesis of
starch stabilized PdNPs.
J. Nanosci. Nanotechnol. 13, 5061–5068, 2013
5063

Solar Energy Assisted Starch-Stabilized PdNPs and Their Application in C C Coupling Reactions
Patil and Bhanage
Fig. 5. SAED pattern of starch-PdNPs after 5 h irradiation.
Fig. 2. UV-vis spectrum of starch-PdNPs with reaction progress by
change in colour.
dark brown colour solution (characteristic colour of metal-
lic palladium). This observation proves that concentrated
solar energy is essential for the synthesis of PdNPs. The
solar radiations are concentrated using the ‘Fresnel lens’
(Fig. 1). The incident solar energy will have a spatial and
temporal variation. Thus to avoid this variability, we have
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conducted all the experiments in the summer days and also
during 10 am to 3 pm at a special location within the insti-
tute. After 5 h reaction time the reaction mixture showing
colour change from pale yellow to dark brown (Fig. 2
(inset)), giving the first point of evidence to support the
Table I. Effect of reaction parameters on Suzuki coupling reaction of
iodobenzene with phenyl boronic acid.a
Entry Catalyst conc. (mmol)
Base
Time (min) Yield (%)b
Fig. 3. TEM image of starch-PdNPs after 5 h irradiation.
Effect of catalyst loading
1
2
3
4
0ꢄ001
0ꢄ0005
0ꢄ00025
0ꢄ0000
KOH
KOH
KOH
KOH
60
60
60
60
98
95
63
NR
Effect of base
5
6
7
8
0ꢄ0005
0ꢄ0005
0ꢄ0005
0ꢄ0005
NaOH
KOH
K2CO3
Na2CO3
60
60
60
60
93
95
80
82
Effect of time
9
0ꢄ0005
0ꢄ0005
0ꢄ0005
0ꢄ0005
0ꢄ0005
KOH
KOH
KOH
KOH
KOH
10
30
45
60
120
17
64
90
95
97
10
11
12
13
Notes: aReaction conditions: phenyl boronic acid (1.2 mmol), iodobenzene
(1 mmol), base (2 mmol), water (4 ml), Reaction temperature (100 ꢀC); bGC yield.
Fig. 4. FEG-SEM image of starch-PdNPs after 5 h irradiation.
5064
J. Nanosci. Nanotechnol. 13, 5061–5068, 2013

Patil and Bhanage
Solar Energy Assisted Starch-Stabilized PdNPs and Their Application in C C Coupling Reactions
synthesis of starch stabilized PdNPs under concentrated
solar energy. This observation is then supported by the
UV-Visible analysis (Fig. 2).
In UV-Vis spectrum the standard absorption peak of
PdCl2 at 384 nm is absent in the reaction mixture after 5 h
concentrated solar energy irradiation indicates the reduc-
tion of the Pd (II) ions to Pd (0).21 The morphology of
the synthesized PdNPs was investigated by Transmission
Electron Microscopy (TEM) demonstrate that the product
formed is in the nano region with the size ranging from
30–40 nm (Fig. 3). We also observed that, along with vari-
ous shapes MTPs are in good percentage; this is due to cit-
ric acid which helps to block oxidative itching. FEG-SEM
image gives an idea about three dimensional structure of
synthesised starch stabilised PdNPs (Fig. 4). The synthe-
sized starch-PdNPs are in crystalline form and which was
Table II. Starch-PdNPs catalysed Suzuki cross coupling reaction of aryl halides and phenyl boronic acid.a
B(OH)2
R
Starch-PdNPs
+
base, 100 °C, water
X
R
X = I, Br
Entry
1
Aryl iodide
Aryl boronic acid
B(OH)2
Product
Yield (%)b
95
I
I
B(OH)2
92
2
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OCH
Copyright: American Scientific Publishers
3
OCH3
C l
I
Cl
91
94
95
3
4
B(OH)2
I
CH3
CH3
N
N
B(OH)2
H3C
H3C
I
H3C
5
B(OH)2
H3C
CH3
CH3
B(OH)2
Br
6c
70
Notes: aReaction conditions: aryl halide (1 mmol), arylboronic acid (1.2 mmol), Pd(0) nanoparticles (0.0005 mmol), KOH (2 mmol), water 4 ml, 100 ꢀC, 60 min; bGC
yield; cReaction time (5 h).
J. Nanosci. Nanotechnol. 13, 5061–5068, 2013
5065

Solar Energy Assisted Starch-Stabilized PdNPs and Their Application in C C Coupling Reactions
Patil and Bhanage
confirmed by the SAED pattern (Fig. 5). The presence of
metallic palladium was showing by EDAX pattern (Fig. 6).
aqueous medium. The obtained results demonstrated that
synthesized starch-PdNPs are highly active catalyst at mild
reaction conditions. The probable reason for high cat-
alytic activity is might be due to the crystalline homoge-
neous nanoparticles having well dispersed in the aqueous
medium. Because of good dispersion all available faces of
nanoparticles are available for the reaction, which might
be responsible to speed up the reaction.
The amount of catalyst employed for the reaction is
an important aspect in transition metal catalysed reac-
tions, considering which optimum concentration of cata-
lyst was, determined (Table I, entries 1–4). 0.001 mmol
catalyst loading was used initially, where we obtained
98% yield, then the catalyst loading was decreased to
3.2. Catalytic Activities of Starch-PDNPS for
Cross-Coupling Reactions
To optimize the reaction parameters, series of experi-
ments were carried out for the model reactionof iodoben-
zene with phenylboronic acid. Under varying conditions
of catalyst loading, base and time effect on the reaction
progress was checked for a model coupling reaction as
shown in Table I.
Initially, the stock solution of starch-PdNPs was directly
employed for model Suzuki cross coupling reactions under
Table III. Starch-PdNPs catalysed Heck coupling reaction of aryl halides and Aryl alkene in N2 atmosphere.a
R
R
CH2
+
Starch-PdNPs
KOH, 100 °C,
10 h, water
X
X = I, Br
Yield (%)b
70
Entry
1
Aryl iodide
Aryl alkene
Product
I
CH
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I
CH2
CH2
H3C
74
75
2
H3C
OCH3
OCH3
I
3
4
I
I
CH2
CH2
O2N
H2N
54
66
O2N
H2N
5
6
I
CH2
61
Notes: aReaction conditions: aryl halide (1 mmol), aryl alkene (1.2 mmol), Starch-PdNPs (0.001 mmol), KOH (2 mmol), water 4 ml, 100 ꢀC, 10 h; bGC yield.
5066
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Patil and Bhanage
Solar Energy Assisted Starch-Stabilized PdNPs and Their Application in C C Coupling Reactions
Table IV. Activities of various Pd [0] nanoparticles catalyst in terms of
(0.0005 mmol) and it was observed that reaction gave
yield (95%). A further decrease in the catalyst loading
(0.00025), we observed the product yield of 63%. To check
the requirement of PdNPs in the reaction, the model exper-
iment was carried out in the absence of catalyst keeping
other reaction parameters constant however no yield of the
desired product was obtained, signifying that starch-PdNPs
was responsible for the respective transformation.
Various inorganic bases (Table I, entries 5–8) were also
screened, among those screened inorganic bases such as
KOH, NaOH, Na2CO3 and K2CO3 we found that KOH
gave an excellent yield of the desired product (95%).
Accordingly further studies were carried out with KOH as
a base.
TOF values have been tested for Suzuki cross-coupling of aryl halides
and phenylboronic acid for same amount of reactants in water (1.0 mmol
aryl bromide and 1.2 mmol phenylboronic acid).
R
B(OH)2
Catalyst
R
+
base, water
X
Catalyst
loading Time Yield TOF
Entry
X
Catalyst
(mmol) (min.) (%) (h−1
)
Ref.
1
2
3
4
5
I
Br
Starch-PdNPs
Starch-PdNPs
0.0005
0.0005 240
0.01
0.5
0.001
60
95 1900 This study
70
96
95
92
350 This study
Br PSSA-co-MA-Pd0
300
5
720
20
23
77
[22]
[23]
[24]
Br
Br
Pd-SDS
Pd-1/FSG
To optimize the reaction time we have carried out the
model reaction for different time intervals in the range
of 10 min to 120 min (Table I, entries 9–13), and it
was observed that desired products were obtained with
an excellent yield in 60 min. Hence, the optimized reac-
tion parameters for the Suzuki C C coupling reaction are
iodobenzene (1 mmol), phenyl boronic acid (1.2 mmol),
PVP stabilized decahedral PdNPs (0.0005 mmol), KOH
of aryl halides with phenylboronic acid under the opti-
mized reaction conditions. TOF values 1900 and 280 h−1
(Table IV, entries 1 and 2) for Suzuki coupling reactions of
iodobenzene and bromobenzene with phenylboronic acid
catalysed by starch-PdNPs in water respectively, are one
of the highest values.
ꢀ
(2 mmol), at 100 C for 1 h in aqueous medium (Table I,
entry 2).
4. CONCLUSION
These optimized reaction parameters with few changes
were also used in Heck coupling reaction, wherein catalyst
loading was increased to 0.001 mmol from 0.0005 mmol
and reaction time 10 h from 1 h in aqueous medium.
These optimized parameters were applied to the C
In summary, we have demonstrated a simple, one stroke,
rapid, greener and high yielding synthetic route for
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starch-stabilized palladium nanoparticles synthesis. Con-
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C
Copyright: American ScceienntrtaiftiecdPsuoblalirsheenresrgy mediated reduction of palladium
coupling of various aryl halides (I, Br) with phenyl boronic
chloride by citric acid as a reducing agent and starch
as a capping agent has been investigated, wherein stable
and uniform starch-stabilized palladium nanoparticles with
average diameter 30–40 nm were successfully synthesized.
Herein, first time reporting the combination of starch and
citric acid for the synthesis of PdNPs. The catalytic activity
of synthesized nanoparticles has been checked for Suzuki
and Heck cross coupling reactions. Synthesized PdNPs
shows excellent activity for the Suzuki reaction between
aryl halides (I, Br) with phenyl boronic acid and its deriva-
tives, whereas shows and a good activity for Heck reaction.
The use of starch, citric acid, water and solar energy make
the protocol greener.
acids and its derivatives and the results were summa-
rized in Table II. Various electron donating groups like
–CH3, –OCH3, –COCH3, –NH2and withdrawing like –Cl
on phenyl boronic acid smoothly undergoes Suzuki cou-
pling reaction afforded the corresponding biaryls in excel-
lent yields in the presence of starch stabilized palladium
(0) nanoclusters in water (Table II, entry 1–5). The reac-
tion was also studied for aryl bromides in which the reac-
tion of bromobenzene with phenyl boronic acid gave a
good yield of the desired product under the optimized reac-
tion conditions (Table II, entry 6).
The above optimised parameters of Suzuki coupling
reaction were used for the Heck (C C) coupling reaction
with few changes like the catalyst loading was 0.001 mmol
from 0.0005 mmol and reaction time was increases from
1 h to 10 h and all experiments were carried out in the
nitrogen atmosphere. Table III (entry 1–6) includes various
Acknowledgment: The authors express their grati-
tude towards DAE-ICT (Department of Atomic Energy
and Institute of Chemical Technology, Mumbai, India)
and Department of Science and Technology, Govern-
ment of India for DST-Nanomission Project SR/NM/NS-
1097/2011 for financial assistance.
C
C coupling reactions of aryl iodides and its deriva-
tive’s with styrene. Various electron donating groups like
–CH3, –OCH3, –NH2 and withdrawing group like –NO2 on
aryl halides undergoes Heck reaction with styrene afforded
the corresponding diphenylethene with good yields in the
presence of starch-PdNPs in water (Table III, entry 1–6).
Table IV showing the comparative data between various
catalytic systems wherein, starch-PdNPs synthesized by
this protocol shows excellent catalytic activity in coupling
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Received: 5 September 2012. Accepted: 12 October 2012.
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