An easily accessible and recyclable copper nanoparticle catalyst for the solvent-free synthesis of dipyrromethanes and aromatic amines

Article abstract of DOI:10.1039/c6ra21315d

A facile method to prepare a reusable copper nanocatalyst is reported. Transmission electron microscopy shows that the CuNPs are spherical in nature and reside in the nanoscopic template of the capping agent, guar gum. Powder X-ray diffraction studies confirm the crystalline nature of the CuNPs. The catalytic efficiency and recyclability of the synthesized CuNPs were demonstrated through the synthesis of dipyrromethanes (DPMs) and aromatic amines. Various DPMs are obtained in very good yields under solvent-free conditions and nitroarenes are converted to the corresponding amino compounds within 10 min, as evidenced by the kinetic study.

Full text of DOI:10.1039/c6ra21315d

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: M. Sengan, K. B.
Ayaz Ahmed, R. Rajamani, P. Vairaprakash and A. Veerappan, RSC Adv., 2016, DOI: 10.1039/C6RA21315D.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
RSC Advances
Page 1 of 7
View Article Online
DOI: 10.1039/C6RA21315D
Journal Name
COMMUNICATION
Easily accessible and recyclable copper nanoparticle catalyst for
solvent-free synthesis of dipyrromethanes and aromatic amines
Received 00th January 20xx,
Accepted 00th January 20xx
Sengan Megarajan, Khan Behlol Ayaz Ahmed, Rajamani Rajmohan, Pothiappan Vairaprakash*,
Veerappan Anbazhagan*
DOI: 10.1039/x0xx00000x
www.rsc.org/
A facile method to prepare reusable copper nanocatalyst was demonstrated through the synthesis of dipyrromethanes and
reported. Transmission electron micrograph showed that the aromatic amines. Dipyrromethanes (DPMs) are versatile key
CuNPs are spherical in nature and reside in the nanoscopic intermediates in constructing various functional organic
template of the capping agent, guar gum. Powder x-ray diffraction molecules such as BODIPY dyes,4 porphyrins,5 chlorins,6
studies support the crystalline nature of the CuNPs. The catalytic corroles7 etc for photonics/electronics applications including (i)
efficiency and recyclability of synthesized CuNPs were photo-induced electron transfer,8 (ii) molecular switches,9 (iii)
demonstrated through the synthesis of dipyrromethanes (DPMs) spin switching,10 (iv) triplet sensitized conjugated polymers,11
and aromatic amines. Various DPMs are obtained in very good (v) dyes,12 (vi) bio-imaging,13 (vii) photodynamic therapy,14 (viii)
yield under solvent-free condition and nitroarenes are converted electrocatalytic oxygen reduction,15 (ix) sensors,16 (x)
to corresponding amino compounds within 10 min, as evidenced fluorescent probe17 etc. Traditionally, DPMs are synthesized in
by the kinetic study.
a reaction of pyrrole with aldehydes, catalyzed by Lewis or
Brønsted acids including HCl, CF3COOH, InCl3, I2/AcOH, CAN,
BF3–etherate, TsOH and cation exchange resins.18 These
reactions hardly stop at dipyrromethane stage and proceeds to
oligomeric/polymeric compounds, necessitating tedious
purification processes and also resulting in low yield. To avoid
the formation of polymeric byproducts and selectively stop the
reaction at dipyrromethane stage, several modifications has
been introduced in the synthesis as (i) employing 2,4-
substituted pyrrole,19 (ii) solventless synthesis employing
pyrrole as reagent and solvent.20,21 The former case is only
applicable to the synthesis of BODIPY dyes, as substituted
DPMs were obtained and these substituted DPMs cannot be
converted into tetra-pyrrolic macrocycles. In the later case, use
of the excess pyrrole limits the versatility of this methodology.
In these reactions, the acidity of the catalyst has a significant
impact on reaction outcome and selectivity.21 Among the
catalysts reported for DPM synthesis, promising results were
obtained in reaction employing more expensive InCl3 catalyst
and 100 equivalent of pyrrole.21 The milder acidity of InCl3
resulted in the selective formation of DPM.21 Recently, we
have disclosed the synthesis of dipyrromethane analogs from
fructose derived HMF using celite supported InCl3 as a
recyclable catalyst.22 Herein we are reporting simple, easily
accessible and recyclable copper nanoparticles for DPM
synthesis. These CuNPs are providing more selectivity towards
DPM synthesis. In addition to DPM synthesis, our catalyst
system is found to be more efficient in reducing aromatic nitro
compound to the corresponding amines.
Introduction
The physiochemical nature of a material gets modified
when translated into nanodimension and offer improved
physical, chemical and biological activity. For example, gold is
considered as an inert metal in its bulk form, at the same time
nanogold exhibits excellent catalytic activity in several organic
transformations.1 Nanocatalysts are highly advantages than
regular catalyst because it provides increased catalytic surface
to volume ratio thereby minimize the catalytic loading. Of late,
the catalytic activities of copper nanoparticles (CuNPs) are
explored in Ullman reactions, Heck reactions, Sonogashira
reactions,1 dipolar cycloaddition, Huisgen [3+2]-cycloaddition
and so forth.2 Economical and eco-friendly access and
reusablilty facilitates the materials to be easily adaptable in
industry. Herein, we report an easy method to synthesis CuNPs
using biopolymer, guar gum as capping agent. The choice of
guar gum was based on their benign nature and easy to obtain
from the renewable resources.3 The synthesized CuNPs were
characterized by transmission electron microscopy, powder X-
ray diffraction and energy dispersive X-ray spectroscopy. The
effectiveness and reusability of the catalyst were
Department of Chemistry, School of Chemical and Biotechnology, SASTRA
University, Thanjavur, Tamil Nadu, India. E-mail: vairaprakash@scbt.sastra.edu;
anbazhagan@scbt.sastra.edu; anbugv@gmail.com
Electronic Supplementary Information (ESI) available: Supporting data, NMR
spectra (1H) and UV-vis spectra are provided. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 7
View Article Online
DOI: 10.1039/C6RA21315D
COMMUNICATION
Journal Name
The reduction of aromatic nitro compounds to the
Energy dispersive X-ray spectroscopy (EDS) confirms the
corresponding amine is an active area of research; as the presence of copper in our preparation (Fig. 2A). The noticeable
amines and their derivatives are important starting material amount of oxygen in EDS can be attributed to the oxygen rich
for the synthesis of chemicals including dyes, pharmaceuticals, capping agent. X-ray diffraction showed diffraction pattern
and anticorrosive lubricants.22 In light of the commercial peaks at 43.32o, 50.39o and 74.08o, which corresponds to the
importance, many methods are developed for the production crystal planes (111), (200) and (220), respectively (Fig. 2B). The
aromatic amines which include catalytic hydrogenation of absence of diffraction peaks corresponds to copper oxides
aromatic nitro compound with hydrogen gas in the presence of (CuO, Cu2O), suggested that the prepared NPs is composed of
Pd, Pt, Ni and Rh metal.23 In recent years, instead of H2 gas, metallic copper. Transmission electron microscopy (TEM)
sodium borohydride has been used as a hydrogen source with revealed that the particles are spherical nature with the size
metal nanoparticles as the catalyst.24 Among the available range from 100 to 300 nm. TEM images clearly showed that
methods for the synthesis of aromatic amines, nitroarene CuNPs are residing in the nanoscopic template of the capping
reduction using NaBH4/metal nanoparticles is considered agent (Fig. 3). The observed ring pattern in the selected area
trusted model reaction to explore the catalytic activity of diffraction confirms the crystalline nature of the prepared
nanoparticles.25 In this work, we exploited the chromophoric CuNPs.
nature of the aromatic NO2 group and determined the rate of
Synthesis of dipyrromethanes
the reduction using absorbance spectroscopy and the results
are discussed.
The catalytic behavior of the CuNPs was explored in the
synthesis of dipyrromethanes and aromatic amines. In the
synthesis of DPM, a mixture containing anisaldehyde and
pyrrole (10 equiv) was treated with a suspension of CuNPs in
water at 30 °C. Under this condition, aldehyde was consumed
completely in 8 h. Analysis of reaction mixture showed the
formation of more byproducts and DPM was obtained in very
low yield (~5%, Table 1, entry 1). When the reaction was
repeated under solventless condition using 10 equiv of pyrrole,
complete consumption of aldehyde was observed after 15 h
with very good selectivity towards product and the
corresponding DPM was obtained in 63% isolated yield (Table
1, entry 2). Formation of DPM in trace quantities in an
experiment carried out without CuNPs evidently indicated the
role of CuNPs as a catalyst in DPM synthesis (Table 1, entry 3).
The catalytic behavior of CuNPs is attributed to the increase in
nucleophilicity of pyrrole on adsorption over CuNPs.
Results and Discussion
Synthesis of copper nanoparticles
The reusable copper nanocatalyst (CuNPs) was synthesized
by bottom-up approach using the precursor copper sulfate and
the biopolymer guar gum and hydrazine as capping and
reducing agent, respectively. The aqueous CuNPs was
o
dehydrated by heating at 100 C. The colloidal reddish brown
solution turns to brownish black precipitate confirms the
removal of water (Fig. 1). The obtained precipitate is insoluble
in water indicating that the average strength of biopolymer-
biopolymer interaction is significantly increased than the
water-polymer interaction.
Aqueous CuNPs
(A)
ꢀ100oC
3h
600
(B)
(1 1 1)
400
Grounded
EtOH washed
Dried at 60oC
(2 0 0)
200
(2 2 0)
*
*
*
*
0
40
50
60
70
80
90
2Θ
Fig. 2 (A) EDS spectra and (B) Powder x-ray diffraction pattern of CuNPs. The
sharp peaks (blue star) can be attributed to the capping agent guar gum, which is
known for crystalline nature.
Reusable CuNPs
Fig. 1 Photograph representing the preparation of reusable CuNPs catalyst.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 7
View Article Online
DOI: 10.1039/C6RA21315D
Journal Name
COMMUNICATION
obtained even after 24 hrs stirring at room temperature (Table
, entries 14 and 15).
1
Table 1 Solvent free synthesis of dipyrromethanesa
Entry
1b
Reactant
Product
Time (h)
Yield (%)
5
8
2
15
24
63
3c
Trace
4
5
6
15
15
15
65
71
63
7
12
75
Fig. 3 Transmission electron micrograph of CuNPs at scale bar (A) 500 nm and (B)
200 nm. Inset corresponds to the SAED pattern.
8
12
12
12
12
77
73
71
74
9d
On adsorption over CuNPs, the nucleophilicity of pyrrole is
increased and reacted with electrophilic carbon of aldehyde.
The resulting intermediate reacts with another pyrrole
adsorbed on CuNPs to yield dipyrromethane after removal of
the water molecule. The reactivities of other aryl aldehydes
10e
11f
were tested at this temperature (Table
1, entries 4 - 8).
12g
13h
0.5
0.5
75
72
Electron withdrawing substituent present in aldehyde
facilitated the better conversion to DPM. Among various
aldehydes, the better conversion was obtained with 3-
nitrobenzaldehyde and the product was obtained in 77% yield
(Table
1, entry 8). In all experiments, the catalyst was
recovered by diluting reaction mixture with dichloromethane
(5 mL), followed by centrifugation for 15 min and catalyst was
recovered as a residual fraction. The recovered catalyst
showed similar catalytic activity without any deterioration in
14
15
Acetophenone
Cyclohexanone
--
--
24
24
--
--
aA mixture of aldehyde (0.5 mmol), pyrrole (5 mmol, 10 equiv.) and copper
nanoparticle (5 mg) was stirred at 30 oC. After the completion of reaction,
reaction mixture was diluted with dichloromethane (5 mL), centrifuged and
the catalyst was recovered as residual fraction. The supernatant was
purified by column chromatography. bReaction was carried out in water.
cReaction without CuNPs. dRecycled catalyst (II cycle). eRecycled catalyst (III
cycle). fRecycled catalyst (IV cycle). gA mixture of 3-nitrobenzaldehyde (0.5
mmol), 2,4-dimethylpyrrole (5 mmol, 10 equiv.) and copper nanoparticle (5 mg)
yields up to 4 cycles (Table 1, entries 8-11). In an experiment
using 2,4-dimethylpyrrole, 3-nitrobenzaldehyde was consumed
with in 30 mins and the corresponding DPMs were obtained in
75% yields (Table
stoichiometric amount (3 equiv) did not deteriorate the
product yield (Table , entry 13). In the copper nanoparticle
1, entry 12). Use of 2,4-dimethylpyrrole in
1
was stirred at 30 oC. hExperiment was carried out with
3 equiv of 2,4-
catalyzed reaction of pyrrole with aromatic and aliphatic
ketones, the corresponding dipyrromethanes were not
dimethylpyrrole.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 7
View Article Online
DOI: 10.1039/C6RA21315D
COMMUNICATION
Journal Name
2.0
constant, t is the reaction time. At and A0 are the absorbance
of the substrate at time t and 0, respectively. Fig. 5B shows the
plot of ln(At/A0) versus reaction time for the reduction of
nitrophenol. The rate constant, k was obtained directly from
the slope of the linear part of the kinetic trace and presented
in Table 2. Nitroarene reduction was preceded through IV
steps as described in Fig. 5.26 In the first step, hydrogen
released from NaBH4 gets adsorbed on nanoparticle surfaces
followed by adsorption of nitroarenes on nanoparticle surfaces
through the nitro group (Step II). Then, nitroarenes on the
nanoparticle surfaces were reduced by adsorbed hydrogen to
aromatic amines. The scope of the catalytic system was tested
with several other nitroaromatic compounds (Table 2).
Formation of amine is confirmed by 1H NMR spectroscopic
analysis of resulting crude mixture (Table 2, entries 2 & 8; Fig
S20 & S21).
(A)
nitrophenol
nitrophenolate ion
aminophenol
1.6
1.2
0.8
0.4
0.0
300
400
500
600
Wavelength (nm)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(B)
Table 2 Catalytic activity of CuNPs for nitroaromatic reductiona
0
100
200
300
400
500
600
Time (s)
Induction
Entry
1.
Reactant
Product
k (s-1)
Fig. 4 (A) UV-Vis spectra for the reduction of nitrophenol to aminophenol in the
presence of CuNPs catalyst and NaBH4 in water. 100 µM nitrophenol, 1 mg
CuNPs, 20 mg NaBH4 (B) time-dependent absorption of nitrophenolate ion at 400
nm, with an induction period of t0. The line corresponds to the linear section,
from which k was determined.
time (s)
40.2
0.00267b
0.00198c
0.00288d
0.00258e
0.00199f
Nitroarenes reduction kinetics
In the synthesis of aromatic amines, nitroarenes are
allowed to react with NaBH4 in the presence of CuNPs at room
temperature. Under this condition, nitroarenes were
converted to corresponding amines within 10 min. Taking
advantage of the chromophoric nature of the nitroaromatics,
the reaction was followed by UV-Vis spectroscopy. During the
subsequent addition of CuNPs, the absorbance peak at 400 nm
disappears with an appearance of a new peak at 300 nm,
indicating the conversion of nitrophenol to aminophenol. In a
typical reaction of 4-nitrophenol, the addition of NaBH4
induces a bathochromic shift from 317 nm to 400 nm due to
the formation of nitrophenolate ion (Fig. 4).
2.
70.2
0.00343
3.
4.
79.8
0.00077
0.00211
110.4
5.
110.4
0.00237
Interestingly, neither NaBH4 nor CuNPs alone reduces the
nitroaromatics, suggesting that the CuNPs and NaBH4 serve as
a catalyst and reducing agent, respectively and both are
required for this chemical transformation. The change in the
absorption peak during the progress of the reduction reaction
allowed us to determine the kinetics of the reduction process
the reduction process using the absorption spectroscopy. The
kinetic experiment was initiated by adding NaBH4 and CuNPs
to the nitrophenol aqueous solution and followed the time-
dependent change in the absorbance at 400 nm. Initially, an
induction time (t0) was observed, which is typical for a
heterogeneous catalytic process and commonly attributed to
activation or restructuring of the metal surfaces by the
substrate before initiating the reaction.26
6.
7.
170.4
110.4
0.00659
0.00236
8g
--
--
After t0, the reduction reaction starts as evidenced by the
decrease in the absorbance at 400 nm and stops changing
aNaBH4 (20 mg) and copper nanoparticle (1 mg) was added to 3 mL of
aqueous solution/suspension of nitrocompound (0.1 mmol) and followed
after all the substrate converted to the product (Fig. 4A). In the absorption spectra changes with respect to time. Kinetic trace was
fitted with pseudo first order equation and k value is reported. bUsing fresh
this catalytic reaction, the concentration of NaBH4 was much
catalyst. cUsing recycled catalyst (II Cycle). dUsing recycled catalyst (III
higher than that of the substrate. Therefore, the reduction
f
Cycle). eUsing recycled catalyst (IV cycle). Using recycled catalyst (V cycle).
kinetics can be described by pseudo first-order rate law:
ln(At/A0) = – kt, where k is the apparent first-order rate
gNo appreciable change in absorbance spectrum on nitro-reduction, hence
monitored by TLC analysis and confirmed by 1H NMR spectroscopy.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Page 5 of 7
RSC Advances
View Article Online
DOI: 10.1039/C6RA21315D
Journal Name
COMMUNICATION
Conclusions
In summary, we have developed an easy access to dry
copper nanoparticles with retained morphology of solution
state. The isolated nanoparticle has been tested in the
synthesis of dipyrromethanes and aromatic amines. In the
synthesis of DPMs, nucleophilicity of pyrrole is enhanced on
adsorption over the CuNps and reacted at the electrophilic site
of aldehyde. The corresponding DPMs were obtained in very
good yields. In addition, the catalytic efficiency of the CuNPs
was investigated with well-known 4-nitrophenol reduction
kinetics experiment and extended to nitroarenes. Irrespective
of the substituent, all the tested nitroarenes get reduced to
amino compounds in less than 10 min. The recyclability of
CuNps was exhibited evidently in both the synthesis. These
findings on easy access to CuNPs and their use in synthesis of
dipyrromethane and aromatic amines will provide a boost for
the exploration of applications of simply accessed CuNPs in
various organic syntheses.
Experimental
Fig. 5 Nitro-reduction over CuNPs using NaBH4
General information
1H NMR (300 MHz) spectra were recorded on Bruker-300-
AVANCE II spectrometer, with chloroform-d as solvent and
In all experiments, the catalyst was recovered by
centrifugation and the residue was subjected to acetone wash
prior to use in the next cycle. The reusability of the catalyst
was studied with nitrophenol system. The recovered catalyst
efficiently converted nitrophenol to aminophenol upto five
cycles as evidenced by the similar rate constant (10-3 s-1). The
XRD and TEM analysis of the recovered catalyst after 5th cycle
affirmed that there is not a considerable change in the
morphology of the catalyst (Figure S18). As noted from Table
2, irrespective of the substituent, all the tested nitro-aromatic
compounds showed a rate constant in the order of 10-3 s-1,
which is consistent with that of substrate-supported metallic
nanoparticles catalyzed reactions reported in the literature.27
The difference in the induction time observed for the different
substrate can be attributed to the steric hindrance, which may
delay the activation or restructuring of the substrate on the
metal surface. Nevertheless, the procedure described here is
simple to prepare amino compounds from nitroarenes in the
shorter time. With our recyclable and easily accesible copper
catalyst system, we have obtained rate consant values for
nitro reduction reactions as comparable with that of previously
tetramethylsilane (TMS) as reference (δ = 0 ppm). The
chemical shifts are expressed in downfield from the signal of
δ
internal TMS. All yields reported are of isolated materials
judged homogeneous by TLC, and NMR spectroscopy. The size,
morphology and crystallinity were characterized by high-
resolution transmission electron microscopy (HR-TEM) (JEOL-
JEM 1011, Japan) with an accelerated voltage of 200 kV.
Samples of TEM measurements were prepared by placing a
drop of NP solution on the graphite grid and drying it in a
vacuum
Preparation of recyclable CuNPs catalyst: About 500 mg of
guar gum was suspended into 50 mL of double distilled water.
To the aqueous suspension, 85 mg of copper(II) chloride was
added slowly under vigorous stirring at room temperature.
After the complete solubilization of CuCl2,
1 mL of
concentrated ammonia solution was added. The color changes
from greenish blue to blue due to the formation of copper-
ammonia complex. After 5 min of gentle mixing, 2 mL of
hydrazine hydrate was added as a reducing agent. After
stirring the solution for 5 min, the reaction was allowed to
proceed at room temperature for 3 h without stirring. The
formation of copper nanoparticles was easily noticeable due to
the change in the color of the solution to wine red – the
characteristic color of the copper nanoparticles (CuNPs). As
prepared CuNPs was coated on a thin glass plate and dried in
reported nano catalystic systems (Table 3
).28
Table 3. Comparison of Rate Kinetics
Rate constant
(s-1)
Entry Nanocatalyst
Ref (year)
1
2
3
4
5
6
7
Au NPs
0.00919
14.57
27a (2011)
27b (2013)
27c (2013)
27d (2014)
27e (2016)
27f (2016)
this study
Ag NPs
o
the pre-heated hot air oven set at 100 C. After 3 h, the plate
G6-OH(Pd28Cu28
)DENs
0.12
was removed and cooled to room temperature and the dried
material was collected by simple scratching. The obtained
material was grounded well with the help of mortar and pestle
and washed three times with absolute ethanol and then dried
Ag NPs
0.033
Au NPs
4.35
Ag NPs
0.00212
0.00267
Cu NPs
o
at 60 C for 2 h to obtain 310 mg of copper nanocomposite.
The amount of metallic copper present in nanocomposite was
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 6 of 7
View Article Online
DOI: 10.1039/C6RA21315D
COMMUNICATION
Journal Name
3
4
D. Das, T. Ara, S. Dutta and A. Mukherjee, Bioresource
Technology 2011, 102, 5878-5883.
(a) A. Kamkaew, S. H. Lim, H. B. Lee, L. V. Kiew, L. Y. Chung
and K. Burgess Chem. Soc. Rev. 2013, 42, 77-88; (b) J. Zhao,
K. Xu, W. Yang, Z. Wang and F. Zhong Chem. Soc. Rev. 2015,
44, 8904-8939.
Z. Yao, J. Bhaumik, S. Dhanalekshmi, M. Ptaszek, P. A.
Rodriguez and J. S. Lindsey, Tetrahedron 2007, 63, 10657-
10670; (b) T. Sahin, P. Vairaprakash, K. E. Borbas, T.
Balasubramanian and J. S. Lindsey, J. Porphyrins
Phthalocyanines 2015, 19, 664-678.
(a) M. Krayer, M. Ptaszek, H.-J. Kim, K. R. Meneely, D. Fan, K.
Secor and J. S. Lindsey J. Org. Chem. 2010, 75, 1016–1039;
(b) K. Aravindu, O. Mass, P. Vairaprakash, J.W. Springer, E.
Yang, D. M. Niedzwiedzki, C. Kirmaier, D. F. Bocian, D. Holten
determined by atomic absorption spectroscopy. About 0.28
mg of copper was present in the 5 mg of the nanocomposite.
The morphology, size and crystallinity of CuNPs were
measured by transmission electron microscope (TEM).
Samples for TEM were prepared by placing a drop of NP
solution on the graphite grid and drying it in the vacuum. The
EDS spectrum of the solution containing CuNPs confirmed the
presence of an elemental copper signal without any peaks of
impurities. Powder X-ray diffraction (XRD) measurements of
CuNPs were done on an XRD-Bruker D8 Advance X-ray
diffractometer using monochromatic Cu Kα radiation.
5
6
General procedure for synthesis of dipyrromethane:
A
mixture of aldehyde (0.5 mmol), pyrrole (5 mmol, 10 equiv.)
and copper nanoparticle (5 mg) was stirred at 30 oC for a
stipulated period of time. After the complete consumption of
aldehyde, the reaction mixture was diluted with
dichloromethane (5 mL), centrifuged and the catalyst was
recovered as a residual fraction for reuse. The supernatant was
concentrated by rotary evaporation under reduced pressure
and the resulting mixture was purified by column
chromatography. The product was characterized by 1H NMR
spectral analysis. The NMR data are well in accordance with
literature data.
and J. S. Lindsey Chem. Sci. 2013,
Lindsey Chem. Rev. 2015, 115, 6534-6620.
(a) D. T. Gryko and K. J. Jadach, Org. Chem. 2001, 66, 4267-
4275; (b) D. T. Gryko and K. E. Piechot, J. Porphyrins
Phthalocyanines 2002, 6, 81-97; (c) G. Aydin, B. Temelli and
4, 3459-3477; (c) J. S.
7
C. Unaleroglu Eur. J. Org. Chem. 2015, 7583-7593.
8
9
T. Higashino, T. Yamada, M. Yamamoto, A. Furube, N. V.
Tkachenko, T. Miura, Y. Kobori, R. Jono, K. Yamashita and H.
Imahori Angew. Chem. Int. Ed. 2016, 55, 629-633.
R. Arumugaperumal, V. Srinivasadesikan, R. Ramakrishnam,
V. Mandapati, M.-C. Lin, T. Shukla, R. Singh and H.-C. Lin ACS
Appl. Mat. Inter. 2015, 7, 26491-26503.
10 M. Dommaschk, C. Naether and R. Herges J. Org. Chem.
2015, 80, 8496-8500.
11 R. Andernach, H. Utzat, S. D. Dimitrov, I. McCulloch, M.
Heeney, J. R. Durrant and H. Bronstein J. Am. Chem. Soc.
2015, 137, 10383-10390.
12 (a) H. Zhao, J. Long, X. Luo, B. Zhao, S. Tan and S. Dyes
Pigments 2015 122, 168-176; (b) J. Liao, Y. Wang, Y. Xu, H.
Zhao, X. Xiao and X. Yang Tetrahedron 2015, 71, 5078-5084.
13 (a) M. Jurasek, S. Rimpelova, E. Kmonickova, P. Drasar and T.
Ruml J. Med. Chem. 2014, 57, 7947-7954; (b) R. Xiong, J.
Hydrogenation of nitroarenes: Typically, 20 mg of NaBH4 and
1 mg of CuNPs were added to 3 mL aqueous solutions of
nitrocompounds (100 µM) aqueous solution and measured the
absorbance changes. The change in absorbance was used for
kinetic analysis. All experiments were performed in triplicate
and the average value is reported. To rule out the possibility of
formation of the metal oxide layer and catalytic surface
poisoning, the samples were carefully degassed before adding
NaBH4.
Andres, K. Scheffler and K. E. Borbas Dalton Trans. 2015, 44
2541-2553; (c) D. Kand, T. Saha, M. Lahiri and P. Talukdar,
Org. Biomol. Chem. 2015, 13, 8163-8168.
,
To calculate rate constant, the obtained kinetic trace was
analyzed by pseudo first-order rate law: ln(At/A0) = −kt(1)
where k is the apparent first-order rate constant, t is the
reaction time. At and A0 are the absorbance of substrate at
time t and 0, respectively (Fig. 5B). The rate constant, k was
obtained directly calculated from the slope of the linear part of
the kinetic trace
14 (a) R. Bonnett Chem. Soc. Rev. 1995, 24, 19-33; (b) J. M.
Dabrowski, L. G. Arnaut, M. M. Pereira, C. J. P. Monteiro, K.
Urbanśka, S. Simões and G. Stochel Chem. Med. Chem. 2010,
5
Milanesio and E. N. Durantini Eur. J. Med. Chem. 2014, 83
, 1770-1780; (c) M. B. Ballatore, M. B. Spesia, M. E.
,
685-694.
15 S. Amanullah, P. K. Das, S. Samanta and A. Dey, Chem.
Commun. 2015, 51, 10010-10013.
16 (a) A. Hafuka, R. Kando, K. Ohya, K. Yamada, S. Okabe and H.
Satoh Bull. Chem. Soc. Japan 2015, 88, 447-454; (b) Z. Li, L.-J.
Li, T. Sun, L, Liu and Z. Xie Dyes and Pigments 2016, 128, 169-
169.
A
cknowledgments
PV (SB/FT/CS-003/2014) and VA (SB/FT/LS-217/2012)
thank the Department of Science and Technology, 17 J. C. Er, C. Leong, C. L. Teoh, Q. Yuan, P. Merchant, M. Dunn,
D. Sulzer, D. Sames, A. Bhinge, D. Kim, S.-M. Kim, M.-H. Yoon,
L. W. Stanton, S. H. Je, S.-W. Yun and Y.-T. Chang Angew.
Chem. Int. Ed. 2015, 54, 2442-2446.
Government of India for the financial support. P.V. thanks
SASTRA University, Thanjavur for Prof. T. R. Rajagopalan
research grant. The central research facility (R&M/0021/SCBT-
007/2012-13), SASTRA University is acknowledged for the
infrastructure.
18 (a) N. A. M. Pereira and T. M. V. D. PinhoeMelo Org. Prep.
Proc. Int. 2014, 46, 183-213; (b) D. T. Gryko, D. Gryko and C.-
H. Lee Chem. Soc. Rev. 2012, 41, 3780-3789. (c) Y. Pareek, M.
Ravikanth and T. K. Chandrashekar Acc. Chem. Res. 2012, 45
1801. (d) J. S. Lindsey Acc. Chem. Res. 2010, 43, 300. (e) L.
Zoli and P. G. Cozzi ChemSusChem 2009, , 218.
19 (a) D. A. Smithen, A. E. G. Baker, M. Offman, S. M. Crawford,
T. S. Cameron and A. Thompson J. Org. Chem. 2012, 77
,
2
Notes and references
1
2
M. Stratakis and H. Garcia, Chem. Rev. 2012, 122, 4469-4509.
M. B. Gawande, A. Goswami, F. X. Felpin, T. Asefa, X. Huang,
R. Silva, X. Zou, R. Zboril and R. S. Varma Chem. Rev. 2016,
116, 3722-3811.
,
3439-3453. (b) F. E. Alemdaroglu, S. C. Alexander, D. Ji, D. K.
Prusty, M. Börsch, A. Herrmann, Macromolecules 42 (2009)
6529-6536.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 7 of 7
View Article Online
DOI: 10.1039/C6RA21315D
Journal Name
COMMUNICATION
20 C.-H. Lee and J. S. Lindsey Tetrahedron 1994, 50, 11427-
11440.
21 J. K. Laha, S. Dhanalekshmi, M. Taniguchi, A. Ambroise and J.
S. Lindsey Org. Process Res. Dev. 2003,
22 R. Rajmohan, S. Gayathri and P. Vairaprakash RSC Adv. 2015,
, 100401–100407.
7, 799-812.
5
23 (a) S. Panigrahi, S. Basu, S. Praharaj, S. Pande, S. Jana, A. Pal,
S. K. Ghosh and T. Pal J. Phys. Chem. C 2007, 111, 4596; (b)
M. J. Vaidya, S. M. Kulkarni, R. V. Chaudhari, C. V. Rode, M. J.
Vaidya and R. V. Chaudhari, Org. Process Res. Dev. 1999, 3,
465; (c) N. Comisso, S. Cattarin, S. Fiameni, R. Gerbasi, L.
Mattarozzi, M. Musiani, L. Vazquez-Gomez and E. Verlato
Electrochem. Commun. 2012, 25, 91; (d) K. B. Narayanan and
N. Sakthivel J. Hazard. Mater. 2011, 189, 519; (e) T. L. Lai, K.
F. Yong, J. W. Yu, J. H. Chen, Y. Y. Shu and C. B. Wang J.
Hazard. Mater. 2011, 185, 366; (f) D. Makovec, M. Sajko, A.
Selisnik and M. Drofenik Mater. Chem. Phys. 2011, 129, 83.
24 (a) P. Lara and K. Philippot K Catal. Sci. Technol. 2014, 4,
2445-2465; (b) J. Liu, J. Cui, F. Vilela, J. He, M. Zeller, A. D.
Hunter and Z. Xu Chem. Commun. 2015, 51, 12197−12200;
(c) W.-G. Jia, Y.-C. Dai, H.-N. Zhang, X. Lu, E.-H. Sheng, RSC
Adv. 2015, 5, 29491−29496; (d) Z. Zhao, H. Yang, Y. Li and X.
Guo, Green Chem. 2014, 16, 1274−1281; (e) X.-J. Yang, B.
Chen, L.-Q. Zheng, L.-Z. Wu and C.-H. Tung Green Chem.
2014, 16, 1082−1086; (f) X. Liu, S. Ye, H.-Q. Li, Y.-M. Liu, Y.
Cao and K.-N. Fan Catal. Sci. Technol. 2013, 3, 3200−3206
25 (a) S. Janani, S. Priscilla and V. Anbazhagan Colloids Surf. B
2014, 117, 528-533; (b) A. A. Khan Behlol, S. Sweetha, S.
Aravind, V. Ganapathy and V. Anbazhagan Spectrochim Acta
Part A 2014, 130, 54-58; (c) V. Showmya, V. Ganapathy, E.
Elangovan and V. Anbazhagan RSC Adv 2014,
4, 15003-
15006; (d) Q. Cui, A. Yashchenok, L. Li, H. Mohwald and M.
Bargeheer Colloids and Surfaces A: Physicochem. Eng.
Aspects 2015, 470, 108–113.
26 T. Aditya, A. Pal and T. Pal Chem. Commun. 2015, 51, 9410-
9431.
27 P. Hervés, M. Pérez-Lorenzo, L. M. Liz-Marzán, J. Dzubiella, Y.
Lu and M. Ballauff Chem. Soc. Rev. 2012, 41, 5577.
28 (a) A. Gangula, R. Podila, M. Ramakrishna, L. Karanam and C.
Janardhana, A. M. Rao. Langmuir, 2011, 27, 15268–15274;
(b) L. Ai and J. Jiang Bioresource Technology, 2013, 132, 374–
377; (c) A. Zachary, D. Pozun, S. E. Rodenbusch, E. Keller, K.
Tran, W. Tang, K. J. Stevenson and G. Henkelman J. Phys.
Chem. C 2013, 117, 7598−7604; (d) V. Anbazhagan, K. B. Ayaz
Ahmed and S. Janani Sensors and Actuators B, 2014, 200, 92–
100; (e) A. Kumar, K. Smita, E. Sánchez, S. Guerra and L.
Cumbal, Adv. Nat. Sci.: Nanosci. Nanotechnol. 2016, 7,
25013; (f) J. Safari, A. E. Najafabadi, Z. Zarnegar and S. F.
Masoule Green chem. Lett. Rev. 2016, 9, 20–26.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins