Preparation of Au nanoparticles by Anthemis xylopoda flowers aqueous extract and their application for alkyne/aldehyde/amine A3-type coupling reactions

Article abstract of DOI:10.1039/c5ra08927a

This paper reports on the green synthesis of gold nanoparticles (Au NPs) by Anthemis xylopoda flowers aqueous extract without the addition of surfactant agents and their application as stable catalysts for propargylamines through one-pot three-component condensation reaction of aldehydes, amines, and alkynes. FT-IR, UV-vis spectroscopy and transmission electron microscopy (TEM) are used for the characterization of Au NPs. Polyphenolics are believed to play an important role in Au NPs biosynthesis through the reduction of gold ions. This method provides high yields and easy work up. In comparison with homogeneous and traditional heterogeneous catalysts, metallic NPs display greater catalytic activity due to the increased metal surface area and require less metal to be used in catalysis. Also, in every case, the Au NPs could be easily recovered and reused several times, and at the end of the process, the product was metal-free. This journal is

Full text of DOI:10.1039/c5ra08927a

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Preparation of Au nanoparticles by Anthemis
xylopoda flowers aqueous extract and their
Cite this: RSC Adv., 2015, 5, 46240
application for alkyne/aldehyde/amine A3-type
coupling reactions
a
Mahmoud Nasrollahzadeh and S. Mohammad Sajadib
*
This paper reports on the green synthesis of gold nanoparticles (Au NPs) by Anthemis xylopoda flowers
aqueous extract without the addition of surfactant agents and their application as stable catalysts for
propargylamines through one-pot three-component condensation reaction of aldehydes, amines, and
alkynes. FT-IR, UV-vis spectroscopy and transmission electron microscopy (TEM) are used for the
characterization of Au NPs. Polyphenolics are believed to play an important role in Au NPs biosynthesis
through the reduction of gold ions. This method provides high yields and easy work up. In comparison
with homogeneous and traditional heterogeneous catalysts, metallic NPs display greater catalytic activity
due to the increased metal surface area and require less metal to be used in catalysis. Also, in every case,
the Au NPs could be easily recovered and reused several times, and at the end of the process, the
product was metal-free.
Received 13th May 2015
Accepted 18th May 2015
DOI: 10.1039/c5ra08927a
www.rsc.org/advances
Due to high surface-to-volume ratio and nanoparticles highly
active surface, heterogeneous catalysts are more and more used
in the form of nanoparticles.5 Additionally, nanocatalysis can
1. Introduction
Propargylamines are major skeletons and synthetically key
intermediates in the synthesis of various natural products and
therapeutic drug molecules.1
make the products easily removable from the reaction mixtures
and make the catalysts recyclable.5 Among various metallic
nanoparticles, gold nanoparticles (Au NPs) have been used
widely in recent years due to their broad applicability in
biomedicine, catalysis, and biosensing.6 The use of Au NPs
allows “ligand-free” synthesis, which reduces costs, simplies
work-up procedures, and facilitates the separation of the nal
product. It is found that Au NPs are effective catalysts for some
chemical transformations in organic solvent the catalysis
occurs on the Au surface.7 However, Au NPs require more
complex production methods which oen imply the use of toxic
and hazardous reagents.8 Therefore, the development of newer,
economic and eco-friendly techniques for the synthesis of Au
NPs is very desirable.
Green synthesis of NPs by plants extract and trees gum has
been studied in the recent two decays.9 Formation of metal NPs
by plants extract is one of convenient, simple and clean
methods to produce these particles. Green synthesis of nano-
particles makes use of environmental friendly, non-toxic and
safe reagents. Indeed green synthesis of metal NPs, in contrast
to chemical and physical methods, can be performed in a clean,
well-controlled environment, such as water, giving to rise
production of pure nanomaterials. Recently, our group has
successfully demonstrated the rapid synthesis of metal NPs
using plants extract or trees gum.9 The major advantage of using
extracts is that they are the mild, renewable and non-toxic
Traditionally these compounds are prepared by nucleophilic
attack of lithium acetylides or Grignard reagents on imines or
their derivatives in the presence of homogeneous palladium
complexes with coordinating phosphine or other ligands in toxic
organic solvents.2 These reagents are highly moisture sensitive
and used in stoichiometric amounts. There are alternative
processes for synthesis of propargylamines by three component
one-pot coupling reaction (A3 coupling) of aldehydes, alkynes and
amines in the presence of homogeneous and heterogeneous
catalysts such as Ag(I) salts,3a Au(III) salen complexes,3b Cu(I)
salts,3c Cu–Ru bimetallic system,3d heteropolyacid-supported
silver (Ag-HPA),3e hydroxyapatite-supported copper (Cu-HAP),3f
AgY zeolite in water or organic solvents.3g The available method
for preparation of propargylamines in water is limited for cyclic
amines.4 The problem with homogeneous catalysis is the diffi-
culty to separate the catalyst and the impossibility to reuse it in
consecutive reactions. In order to solve the problem, alternative
environmentally benign processes for the recovery of catalyst
should be developed.
aDepartment of Chemistry, Faculty of Science, University of Qom, Qom 37185-369,
Iran. E-mail: mahmoudnasr81@gmail.com; Fax: +98 25 32103595; Tel: +98 25
32850953
bDepartment of Petroleum Geoscience, Faculty of Science, Soran University, PO Box
624, Soran, Kurdistan Regional Government, Iraq
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Gas Chromatograph (GC-10A) instrument with a ame ioniza-
tion detector using
a column of 15% carbowax 20 M
chromosorb-w acid washed 60–80 mesh. Column chromatog-
raphy was carried out on short columns of silica gel 60 (70–230
mesh) in glass columns (2–3 cm diameter), using 15–30 grams
of silica gel per gram of crude mixture. Transmission Electron
Microscopy (TEM) by Philips EM208S transmission electron
microscope operating at an acceleration voltage of 100 kV. The
UV-visible measurements were performed at room temperature
by a Perkin Elmer 550ES.
2.2. Preparation of Anthemis xylopoda owers extract
50 g of dried aerial parts of Anthemis xylopoda owers was
powdered and reuxed at 80 ꢀC with 300 mL of sterile distilled
water for 2 h. Then the mixture was allowed to cool to room
temperature and aqueous extract was easily obtained by
ltration.
Fig. 1 Image of the Anthemis xylopoda flowers.
2.3. Preparation of Au NPs
reducing and stabilizing agents, eliminating the need for
chemical reducing agents such as sodium borohydride and
expensive polymeric capping agents and stabilizers.
In a typical synthesis of Au NPs, 50 mL of the aqueous extract of
plant owers was added dropwise to 50 mL of well-mixed
0.003 M aqueous solution of HAuCl4 with constant stirring at
60 ꢀC for 2 h. Aer 7 min the color of the solution was changed
to black due to excitation of surface plasmon resonance which
indicates the formation of Au nanoparticles, as monitored by
UV-vis spectroscopy. The obtained solution of nanoparticles
centrifuged at 6500 rpm for 30 min and obtained precipitation
washed three times using absolute ethanol to remove possible
impurities then air dried for 24 h at room temperature,
Scheme 1.
The genus Anthemis xylopoda (Fig. 1) belongs to the family
Asteraceae (Compositae), is a multi-branched aromatic annual
herbs that spread quickly native to northern Europe and West
Asia The species of the Anthemis genus are widely used in the
pharmaceutics, cosmetics and food industry.10 The owers of
the genus have well-documented use as antiseptic and healing
herbs because of its natural phenolics and essential oils
content.10
As part of our ongoing interest in heterogeneous nano-
catalysts,11 we now wish to report a facile and effective route for
preparation of Au NPs by Anthemis xylopoda owers aqueous
extract without using any other capping agent. Furthermore, the
catalytic efficiencies of Au NPs were evaluated by A3-coupling
reaction of aldehydes, amines and alkynes via C–H activation.
To date, there is no report on the green synthesis of Au NPs by
utilizing the Anthemis xylopoda owers aqueous extract.
2.4. Typical procedure for the synthesis of propargylamines
To a mixture of aldehydes (1.0 mmol), amine (1.0 mmol), and
alkyne (1.2 mmol) in CH3CN (5.0 mL), catalyst (10 mol%) was
added and the mixture was vigorously stirred at 75 C under a
ꢀ
nitrogen atmosphere for the time specied in Table 2. Aer
completion (as monitored by GC and TLC), the reaction mixture
was cooled to room temperature, centrifuged and organic phase
was separated, dried over anhydrous MgSO4, and evaporated
under reduced pressure. The residue was puried by column
chromatography on silica-gel by using n-hexane/EtOAc (15%
ethyl acetate in n-hexane) as an eluent to afford propargylamine.
All the products are known and the spectroscopic data (FT-IR
and NMR) and melting points were consistent with those
reported in the literature.12
2. Experimental
2.1. Instruments and reagents
All reagents were purchased from the Merck and Aldrich
chemical companies and used without further purication.
Products were characterized by comparison of their physical
and spectral data with authentic samples. The NMR spectra
1
were recorded in DMSO. H NMR spectra were recorded on a
2.5. Spectral data for selected products
Bruker Avance DRX 400 MHz instruments. The chemical shis
(d) are reported in ppm relative to the TMS as an internal
1-[1-(4-Methylphenyl)-3-phenylprop-2-yn-1-yl]morpholine
1
standard and J values are given in Hz. 13C NMR spectra were (Table 2, entry 5). H NMR (CDCl3, 400 MHz, ppm): dH ¼ 7.46–
recorded at 100 MHz. FT-IR (KBr) spectra were recorded on a 7.33 (m, 9H), 4.76 (s, 1H), 3.22–3.16 (m, 4H), 2.67–2.55 (m, 4H),
Perkin-Elmer 781 spectrophotometer. Melting points were 2.35 (s, 3H).
taken in open capillary tubes with a BUCHI 510 melting point
1-[1-(4-Methoxyphenyl)-3-phenylprop-2-yn-1-yl]piperidine
1
apparatus and were uncorrected. The purity determination of (Table 2, entry 7). H NMR (CDCl3, 400 MHz, ppm): dH ¼ 7.82–
the substrates and reaction monitoring were accomplished by 7.70 (m, 9H), 4.81 (s, 1H), 3.74 (s, 3H), 2.66–2.54 (m, 4H),
TLC on silica gel PolyGram SILG/UV254 plates or by a Shimadzu 1.80–1.73 (m, 4H), 1.60–1.44 (m, 2H).
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Scheme 1 Green synthesis mechanism of Au NPs using aqueous extract of Anthemis xylopoda flowers.
1-[1-(4-Methoxyphenyl)-3-phenylprop-2-yn-1-yl]pyrrolidine
1-[1-(2-Furfuryl)-3-phenylprop-2-yn-1-yl]piperidine (Table 2,
1
(Table 2, entry 8). 1H NMR (CDCl3, 400 MHz, ppm): entry 14). H NMR (CDCl3, 400 MHz): dH ¼ 7.53–7.47 (m, 5H),
dH ¼ 7.61–7.58 (m, 9H), 4.87 (s, 1H), 3.82 (s, 3H), 2.64– 6.35–6.14 (m, 3H) 4.85 (s, 1H), 3.11–2.86 (m, 4H), 1.67–1.60
1.79 (m, 8H).
(m, 4H), 1.51–1.38 (m, 2H).
1-[1-(4-Bromophenyl)-3-phenylprop-2-yn-1-yl]piperidine (Table 2,
5-Phenyl-5-(piperidin-1-yl)pent-3-yn-1-ol (Table 2, entry 22).
1
entry 12). H NMR (CDCl3, 400 MHz): dH ¼ 7.93–7.90 (m, 9H), 1H NMR (CDCl3, 300 MHz): dH ¼ 7.63–7.27 (m, 5H), 4.54 (s, 1H),
4.82 (s, 1H), 2.66–2.53 (m, 4H), 1.80–1.66 (m, 4H), 1.51–1.47 (m, 3.80–3.73 (m, 2H), 2.62–2.45 (m, 5H), 2.17–2.09 (m, 4H),
2H).
1.42–1.38 (m, 4H).
Table 1 The effects of various variables in the three-component coupling reaction between benzaldehyde, piperidine and phenylacetylenea
Entry
Au NPs (mol%)
Solvent
Temperature (ꢀC)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
—
10
10
10
10
10
15
5
CH3CN
THF
75
75
25
25
75
75
75
75
10
5
10
10
5
5
5
5
0
89
0
CH2Cl2
Cyclohexane
Methanol
CH3CN
CH3CN
CH3CN
0
94
97
97
87
a
Reaction conditions: benzaldehyde (1.0 mmol), piperidine (1.0 mmol), phenylacetylene (1.2 mmol), solvent (5.0 mL), N2. b Yields are aer work-up.
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Table 2 Three-component reaction of various aldehydes, secondary amines and alkynes catalyzed by Au NPsa
Entry
R1
Amine
R4
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
Ph
Ph
Ph
Piperidine
Morpholine
Pyrrolidine
Piperidine
Morpholine
Pyrrolidine
Piperidine
Pyrrolidine
Piperidine
Morpholine
Piperidine
Piperidine
Morpholine
Piperidine
Morpholine
Piperidine
Piperidine
Pyrrolidine
Piperidine
Morpholine
Piperidine
Piperidine
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
5
8
7
12
9
12
9
10
5
7
5
7
7
4
5
5
7
7
6
6
97 (97, 96, 94, 92)c
86
72
83
90
74
90
80
98
94
97
96
97
86
86
94
90
87
92
91
91
82
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-OCH3C6H4
4-OCH3C6H4
4-ClC6H4
4-ClC6H4
3-ClC6H4
4-BrC6H4
4-BrC6H4
2-Furfuryl
2-Furfuryl
2-Thiophenyl
Ph
9
10
11
12
13
14
15
16
17
18
19
20
21
22
4-CH3C6H4
4-CH3C6H4
n-Bu
n-Bu
n-Bu
Ph
Ph
Ph
4-ClC6H4
Ph
6
6
CH2CH2OH
a
Reaction conditions: catalyst (10 mol%), aldehyde (1.0 mmol), amine (1.0 mmol), alkyne (1.2 mmol), CH3CN (5.0 mL), N2, 75 ꢀC. b Yields are aer
work-up. c The yields from four subsequent runs using the same recovered catalyst.
transition localized within the ring of cinnamoyl system;
whereas the band around 240 nm (band II) is for absorbance of
ring related to the p / p* transitions of benzoyl system.13
3. Results and discussion
3.1. Green synthesis of Au NPs in water
Therefore, these absorbance bands conrm the presence of
phenolics and ability of plant extract for green synthesis of
nanoparticles.
The reaction of Au nanoparticles was completed aer 7 min
following the formation of nanoparticles monitored by UV-vis
spectroscopy, Fig. 3. The Au NPs showed a characteristic peak
centered at 535 nm indicating the surface plasmon absorption
Compared to most investigations on the synthesis of metal NPs,
which are conducted under vacuum conditions or in an inert
atmosphere, the experimental setup for preparation of NPs
under biosynthesis conditions is relatively simple. In our
method, the Au NPs were prepared by Anthemis xylopoda owers
aqueous extract in water without using any capping agent. The
main aim of the study was to develop a cost-effective and eco-
friendly technique for the synthesis of Au NPs with non-
extreme operational conditions from a gold salt solution. The
source of palladium was HAuCl4 in distilled water. The Au NPs
were characterized by a variety of standard analytical tech-
niques such as UV-vis, FT-IR and TEM.
The previous studies on Anthemis xylopoda owers extract
revealed the presence of potent antioxidant avonoid glycosides
such as luteolin glucoside, apigenin glucoside and quercetin
glucoside.10 These phytochemicals can serve both as effective
metal-reducing agents and as capping agents to provide a
robust coating on the Au NPs in a single step.
Au NPs formation was monitored visually and by UV-visible
spectroscopy. Moreover, the UV spectrum of owers extract of
the plant (Fig. 2) shows specied signals of phenolics inside
Fig. 2 UV-vis spectrum of the aqueous extract of the Anthemis
the plants as the bands at lmax 325 nm (band I) due to the xylopoda flowers.
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synthesized gold nanoparticles by this method are quite stable
with no signicant variance in the shape, position and
symmetry of the absorption peak even aer one month.
Beside the reports on Anthemis xylopoda owers for detection
the phytoconstituents inside the plant extract, for more conve-
nience the FT-IR analysis was carried out to demonstrate the
responsible phytochemicals during the green synthesized of Au
NPs. The FT-IR spectrum of the crude extract, (Fig. 4A) depicted
some peaks at 3420 cmꢁ1, 2925 cmꢁ1, 1687 cmꢁ1 and 1432 cmꢁ1
which represent free OH in molecule and OH group forming
hydrogen bonds, saturated hydrocarbons (Csp3–H), carbonyl
group (C]O) and stretching C]C aromatic ring, respectively.
Because of presence these functional groups inside the structure
of antioxidant polyphenolics, the spectrum can demonstrate the
presence of phenolics in the plant extract and support the results
of related literatures. Furthermore, FT-IR spectrum of Au NPs is
shown in Fig. 4B. The appeared bands are lattice vibrational
Fig. 3 UV-vis spectrum of green synthesized Au NPs using aqueous
extract of Anthemis xylopoda flowers ranging 5 min to 30 days.
of nanosized Au particles and formation of nanoparticles. modes indicating the functional groups of biomolecules adsorbed
Furthermore, the stability of Au NPs was monitored by UV-vis on nanoparticles. The broad band in 3492 cmꢁ1 is –OH stretching
spectroscopy at the times ranging 5 min to 30 days, the bond of hydroxyl functional group. The band around 1515 cmꢁ1 is
Fig. 4 FT-IR spectra of aqueous extract of Anthemis xylopoda flowers (A) and green synthesized Au NPs (B).
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generally attributed to the bending vibration of sp2-carbon groups longer times and gave slightly lower yields compared to alde-
for aromatic and 1715 cmꢁ1 for carbonyl functional group.
Morphology was investigated by transmission electron
microscopy. TEM image of Au nanoparticles is presented in
Fig. 5. It is observed that the particles are nanosized and
approximately spherical. We observed that the prepared Au NPs
was steady for several months without any agglomeration.
hydes containing electron withdrawing groups.
3.3. Catalyst recyclability
For a heterogeneous catalyst, it is important to examine its ease
of separation, good of recoverability and reusability. This
heterogeneous Au NPs catalyst can be easily recovered by a
simple centrifugation and washed with ethanol and dried. The
reusability of Au NPs was examined by the model reaction of
benzaldehyde, piperidine, and phenylacetylene and the results
are given in Table 2, entry 1. The recovered catalyst was reused
under similar conditions for the next run under identical
conditions. It can be showed that aer four recycles; the
product yield was still up to 92%, which indicates that Au NPs
have high catalytic activity and stability in our experimental
conditions.
3.2. Catalytic activity of Au NPs in an A3-type coupling
reaction for the synthesis of propargylamines
The catalytic behaviour of Au NPs was studied for the A3-coupling
reaction of aldehydes, amines and alkynes to produce prop-
argylamines. Initially, we employed benzaldehyde (1.0 mmol),
piperidine (1.0 mmol), and phenylacetylene (1.2 mmol) as model
substrates for the development of optimized conditions
(Table 1). No reaction occurred in the absence of the catalyst
(Table 1, entry 1). The results indicate that solvent signicantly
inuence the product yield in the A3-coupling reaction. It was
observed that much better yield was obtained when the reaction
was carried out in acetonitrile at 70 ꢀC compared to other
solvents. To investigate the effect of the catalyst concentration,
systematic studies are carried out in the presence of different
amounts of the Au NPs. As shown in Table 1, the best yield is
found in the presence of just 10 mol% Au NPs, and the use of
higher amounts of catalyst does not improve the result to an
appreciable extent. The use of lower catalyst loadings resulted in
incomplete reactions.
With this catalytic system in hand, we then examined this
coupling reaction with alkynes, a variety of structurally diverse
aldehydes and amines possessing a wide range of functional
groups (Table 2) and all the substrates produce the desired
propargylamines in good to excellent yields. The aldehydes used
in this study included aromatic and heterocyclic examples and
the reaction was found to be highly effected by the nature of the
aldehyde. In the case of aldehydes containing an electron
donating group, it was observed that they required relatively
4. Conclusions
In summary, we have successfully developed a hitherto unre-
ported, inexpensive, nontoxic, eco-friendly and facile method to
synthesize Au NPs by Anthemis xylopoda owers aqueous extract
without employing any capping reagent. Catalytic efficiencies of
Au NPs were evaluated for the synthesis of propargylamines via
C–H activation. This method offers several advantages
including high yields, a simple work-up procedure, ease of
separation and recyclability of the catalyst, as well as the ability
to tolerate a wide variety of substitutions in the reagents. Easy
synthesis, high catalytic activity, and recyclability make this
catalyst interesting for further studies.
Acknowledgements
We gratefully acknowledge the Iranian Nano Council and the
University of Qom for the support of this work.
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