Synthesis and characterization of copper nanoparticles on walnut shell for catalytic reduction and C-C coupling reaction

Article abstract of DOI:10.1080/24701556.2018.1503676

Walnut shell-stabilized copper nanoparticles (CuNP/WS) were successfully prepared by a simple reaction of copper sulfate and Sodium borohydride. Formation of copper nanoparticles in this bio-nanocomposite was observed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscope (EDX). CuNP/WS was found to be an efficient, inexpensive, easy to prepare, green and reusable catalyst in the reduction of aromatic nitro and nitrile compounds to their corresponding amines with NaBH₄ at 35 °C in aqueous medium. We continued our studies on the application of this nanocomposite in the classic Ullman reaction to synthesize biaryl. This method has the advantages of high yields, elimination of expensive stabilizer and homogeneous catalysts, simple methodology and easy work up. The catalyst can be recovered from the reaction mixture and reused several times without any significant loss of catalytic activity.

Full text of DOI:10.1080/24701556.2018.1503676

Inorganic and Nano-Metal Chemistry
ISSN: 2470-1556 (Print) 2470-1564 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt21
Synthesis and characterization of copper
nanoparticles on walnut shell for catalytic
reduction and C-C coupling reaction
Asghar Zamani, Ahmad Poursattar Marjani, Abbas Nikoo, Mojtaba
Heidarpour & Ahmad Dehghan
To cite this article: Asghar Zamani, Ahmad Poursattar Marjani, Abbas Nikoo, Mojtaba Heidarpour
&
Ahmad Dehghan (2018): Synthesis and characterization of copper nanoparticles on walnut
shell for catalytic reduction and C-C coupling reaction, Inorganic and Nano-Metal Chemistry, DOI:
0.1080/24701556.2018.1503676
1
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INORGANIC AND NANO-METAL CHEMISTRY
https://doi.org/10.1080/24701556.2018.1503676
SHORT COMMUNICATION
Synthesis and characterization of copper nanoparticles on walnut shell for
catalytic reduction and C-C coupling reaction
a
b
b
a
a
Asghar Zamani , Ahmad Poursattar Marjani , Abbas Nikoo , Mojtaba Heidarpour , and Ahmad Dehghan
a
b
Department of Nanotechnology, Urmia University, Urmia, Iran; Department of Organic Chemistry, Faculty of Chemistry, Urmia University,
Urmia, Iran
ABSTRACT
ARTICLE HISTORY
Walnut shell-stabilized copper nanoparticles (CuNP/WS) were successfully prepared by a simple
reaction of copper sulfate and Sodium borohydride. Formation of copper nanoparticles in this
bio-nanocomposite was observed by transmission electron microscopy (TEM) and energy
dispersive X-ray spectroscope (EDX). CuNP/WS was found to be an efficient, inexpensive, easy to
Received 15 December 2016
Accepted 16 July 2018
KEYWORDS
Nanocatalysis; nitros and
nitriles; Ullman reaction;
biomass; green synthesis
prepare, green and reusable catalyst in the reduction of aromatic nitro and nitrile compounds to
ꢀ
their corresponding amines with NaBH
4
at 35 C in aqueous medium. We continued our studies
on the application of this nanocomposite in the classic Ullman reaction to synthesize biaryl. This
method has the advantages of high yields, elimination of expensive stabilizer and homogeneous
catalysts, simple methodology and easy work up. The catalyst can be recovered from the reaction
mixture and reused several times without any significant loss of catalytic activity.
Introduction
exceedingly efficient catalysts for the selective reduction of
[
14–16]
aromatic nitro compounds.
copper nanoparticle (CuNP)-catalyzed ones were described
only a few examples of
The catalytic hydrogenation of nitroarenes and nitriles to
the corresponding amines is one of the most fundamental
transformations because of the wide-spread application of
amine containing structures as important building blocks of
agrochemicals, dyes, polymers, rubbers, pharmaceuticals,
[
17–19]
in the literature.
In the recent years, bio-based economy and use of renew-
able biomass as the raw material have been considered as
sustainable options to tackle the problems associated with
local and global pollutions. Along this line, Lignocellulose-
rich biomass as one of the most abundantly available agri-
cultural wastes has been advocated as a choice for the pro-
[
1]
photographic developers and corrosion inhibitors.
The
conventional routes for the reduction of nitroarenes and nir-
tiles proceed through chemical reductions that many of
these processes use gaseous hydrogen at a high pressure and
[20]
[2,3]
[4,5]
duction of fine chemicals.
One of opportunities in order
temperature,
or harmful mineral acids.
Noteworthy is
to apply greener method for the synthesis of MNPs by the
6] reduction of transition metal salts is the use of green stabil-
izer. Since in this regard, these renewable and low cost bio-
masses appear to be promising candidate for stabilizing
of MNPs.
that the chemoselectivity of these methods in the presence
of other functional groups is the critical challenge.
[
Thus, from the standpoint of environmental and economic
concerns, catalytic reduction with safer reducing agents
is the preferred approach, especially heterogeneous cata-
[7–9]
In the present work, we wish to report here utilizing wal-
lyst system.
[
21]
nut shell (WS) which contains cellulose and lignin,
in the
On the other hand, Due to the advantages of metal nano-
particles (MNPs) such as great ratio of surface atoms and
high activity compared to traditional heterogeneous cata-
lysts, increasing interest has recently been directed toward
stabilizing of copper nanoparticles and application of this
green nanocomposite (CuNP/WS) as a reusable and efficient
catalyst in the reduction of nitroarenes benzonitriles to cor-
responding amines with NaBH4 at room temperature in
[
10]
these materials as nanocatalysis.
Because of high surface-
energy of naked MNPs (meta stable state), they tend to rap- aqueous phase. Also due to importance of Cu catalyzed for-
idly aggregate together to form larger, more thermodynam- mation of biaryl “Ullmann reaction” for preparing numerous
ically stable particles which results in the decrease of natural compounds, pharmaceutical products and polymers
[11]
[22]
catalytic efficiency of NPs.
supports have been used to stabilize the nanoparticles.
Although supported MNPs have recently emerged as in the classic Ullman reaction to synthesize biaryl in
Various organic and inorganic in the material science industries,
we study catalytic
[12,13]
properties of this nanocomposite by applying it as a catalyst
CONTACT Asghar Zamani
a.poursattar@urmia.ac.ir
a.zamani@urmia.ac.ir
Department of Nanotechnology, Urmia University, Urmia, Iran; Ahmad Poursattar Marjani
Department of Organic Chemistry, Faculty of Chemistry, Urmia University, Urmia, Iran.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsrt
Supplemental data for this article can be accessed on the publisher’s website
ß 2018 Taylor & Francis Group, LLC

2
A. ZAMANI ET AL.
Figure 1. The TEM image of (A) CuNP/WS-1 (B) CuNP/WS-2 (C and D) CuNP/WS-3.
ꢀ
optimized reaction conditions which gave maximum yield mixed in the flasks and in 50 C for 2 h, followed by evapor-
with high purity.
2
þ
ation of water in a rotary evaporator. The reduction of Cu
was carried out by the drop-wise addition of 0.25 M ethanol
solution of NaBH (30 ml, 70 ml, 140 ml) to the ethanol mix-
4
Experimental
ture of obtained solid and intensive stirring was continued
for 3 h. After filtering and washing the mixture, we obtained
Cu loading on WS was 1.35% (CuNP/WS-1), 3.03% (CuNP/
WS-2) and 8.14% (CuNP/WS-3), respectively, based on
Atomic Absorption Spectroscopy (AAS) analysis.
General Remarks
Chemicals were purchased from Merck and Fluka chemical
companies. The products were characterized by comparison
of their physical data with those of known samples or by
1
13
their spectral data. H NMR and C NMR spectra were
recorded on a Bruker Advance DPX 400 MHz spectrometer General procedure for the reduction of nitroarenes and
in CDCl or DMSO- as the solvent and TMS as internal
3
d6
benzonitriles
standard. Most of the products are known, and all of the
isolated products gave satisfactory UV-vis, IR and NMR
spectra. FT-IR spectra of the powders were recorded using
Thermo Nicolet Nexus 670 FT-IR spectrometer. UV-vis
spectra were recorded using a Biochrom WPA 80-3003-75
Biowave II UV/vis spectrophotometer TEM analysis was per-
formed with an instrument CM30, Philips, using an acceler-
ating voltage of 150 kV.
In a 25 mL round bottom flask, CuNP/WS was added into a
mixed solution containing 5 mL doubly distilled water
and1 mmol nitroarene or benzonitrile. Next, 4 mmol NaBH4
was added in 4 portions to the reaction mixture and stirred
at room temperature for the appropriate amount of time.
The progress of the reaction was monitored by TLC [using
ethyl acetate/n-hexane as eluent: 1/5]. After completion of
the reaction, the reaction mixture was filtered off and the
catalyst rinsed twice with dichloromethane. The organic
extracts were washed with H O, dried over MgSO and
Catalyst preparation
2
4
evaporated in vacuo to give corresponding amines.
The walnut shells used in this work was obtained from a local
walnut tree in Urmia, Iran. The walnut shells were washed
and dried at room temperature and crushed using a high-
speed rotary cutting mill and screened to collect the particles
General procedure for the classic Ullman reaction
with a size smaller than 0.45 mm. 10g of WS and 100mL of Iodoarene (1 mmol), CuNP/WS and DMF (10 mL) were
CuSO aqueous solution (0.03 M, 0.07 M and 0.14 M) were added to a round bottomed flask fitted with a reflux
4

INORGANIC AND NANO-METAL CHEMISTRY
3
Table 1. Reduction of nitroarenes and benzonitriles in water.
NO2
NH2
R1
(
R1
1 mmol)
CuNP/WS-1
NaBH (4-6 mmol)
4
o
H O/ 35 C
2
NH2
CN
R2
(
R2
1 mmol)
a
Entry
R1
H
2-OH
3-OH
4-OH
4-Me
4-CHO
4-CN
4-NH
3-NH
2,3- di Me
R2
Time (h)
Cat. (gr)
Yield (%)
1
2
3
4
5
6
7
8
9
–
–
–
–
–
–
–
–
–
–
–
H
3
5
4
2
3
6
3
5
6
6
2
1
1
1.5
5
5
4
0.1
0.1
0.1
0.1
0.1
0.2
0.1
0.1
0.1
0.2
0.1
0.1
0.1
0.2
0.4
93
99
90
91
100
b
89
c
95
2
88
90
98
2
Figure 2. EDX spectroscopy of CuNP/WS-1.
10
11
12
4-CO
2
H
93
–
–
–
–
–
–
100
d
condenser and a small stirring bar was added to the flask. 13
The resulting mixture was refluxed in an oil bath and pro-
Ph HC
75
2
1
1
4
5
2-Cl
3-Cl
4-Cl
85
98
97
96
2
gress of the reaction was monitored by TLC (25% CH Cl2
16
in hexane). After complete conversion of aryl iodide, mix- 17
2,4-di Cl
0.2
a
ture cooled to room temperature and the nanocomposite Cu
catalyst was separated using filtration and were washed sev-
eral times with DMF. Finally the residue was diluted with
water and extracted with diethyl ether. The organic phase
GC yield.
b
c
4
-Amino benzaldehyde as product.
4
-Cyano aniline as product.
d
2
,2-Diphenylethenamine as product
were washed with brine and dried over MgSO and evapo-
rated in vacuo and the crude product was purified by flash
column chromatography to yield pure crystal of biaryl.
4
Table 2. Size-dependence of CuNP/WS catalysts in reduction reactions
OH
OH
NO2
NH2
CuNP/WS
2 mol%)
(
(
1 mmol)
Results and discussion
NaBH (4-6 mmol)
2
4
o
H O/ 35 C
The copper catalyst was easily synthesized by stirring of the
NH
2
CN
copper precursor, CuSO , with WS in water followed by the
4
evaporation of solvent and reduction of metal with ethanolic
(1 mmol)
solution of NaBH . The copper content was determined by
4
a
Time (h)/ yield (%)
atomic absorption spectroscopy.
Entry
Catalyst (2 mol%)
benzonitrile
2-nitrophenol
1
2
3
CuNP/WS-1
CuNP/WS -2
CuNP/WS -3
1/100
2.5/91
10/93
5/99
5/85
6/88
Charactrization of the catalyst
High resolution transmission electron microscopy (HRTEM)
studies of the copper supported catalyst, was carried out
before and after the reduction experiments in order to
understand the decrease in the catalytic activity encountered
during the recycling experiments. TEM images of the as-pre-
pared CuNP/WS-1, CuNP/WS-2, CuNP/WS-3 showed
a
GC yield.
ꢁ1
[23]
copper(I) oxide NPs and the peak at 622 cm correspond
to Cu-O vibration of Cu O nanoparticles.
based on the XPS analysis (electronic supplementary mater-
ial) Cu2p3/2 and Cu2p1/2 signals centered at 932.7 and 952.
In addition
2
1
5–22 (Figure 1a) and 60–80 nm (Figure 1b) particles
0
þ
respectively and extensive aggregation of metallic nanopar-
ticles and non-supported ones were observed in the case of
CuNP/WS-3 (Figure 1c and d). EDX can offer clear evidence
about the elements present in the samples. Figure 2 showed
6
eV respectively were consistent with Cu or Cu (Cu O).
The structure stability of CuNP/WS-1samples was inves-
2
[
24]
tigated by the thermogravimetric (TGA) under air (elec-
tronic supplementary material).The TGA of this
the EDX patterns of CuNP/WS-1 which confirms that the nanocomposite showed the first mass decrease below 100 C
nanoparticles are Cu. The carbon and oxygen peaks arise due to desorption of physisorbed water. This was followed
ꢀ
from the walnut shell.
FT-IR spectrum of CuNP/WS-3 is presented in electronic between 200 C to 500 C that was attributed to the decom-
by a weight-reduction of ca. 90wt% in the temperature range
ꢀ
ꢀ
ꢁ
1
supplementary material. The peak at 1622 cm are due to position of nanocomposite. Thus, this TGA result showed
carboxylate ions (-COO ) responsible for stabilization of that CuNP/WS sample is stable up to 200 C.
ꢁ
ꢀ

4
A. ZAMANI ET AL.
Scheme 1. Competitive reduction of nitrobenzene and benzonitrile using CuNP/WS-1.
Scheme 2. Selective reduction of p-nitrobenzonitrile to p-aminobenzonitrile using CuNP/WS-1.
Table 3. Comparison of our protocol with different CuNP-based catalytic systems.
a
ꢀ
b
Entry
Conditions
(10 mol%), EtOH
Cu NP@ magnetic carbon (16 mol%), H
Sodium dodecyl benzene sulfonate stabilized
CuNPs (10 mol%), THF/H
Our protocole: CuNP/WS-1 (2 oml%), H
Substrate
Temp. ( C)
Time (h)
5
0.5
yield (%)
Ref.
1
2
3
CuBr
2
nitrobenzene
4-nitrophenol
nitrobenzene
r.t.
r.t.
50
90
–
98
[17]
[18]
[19]
c
2
O
2
3
2
2
O
4
2
O
nitrobenzene
35
35
93
91
4
-nitrophenol
a
4
All cases, in the presence of NaBH .
GC yield.
b
c
Conversion: 100%.
Catalytic reduction of nitroarenes and benzonitriles with Table 4. C-C Ullmann coupling reaction.
CuNP/WS-1 (30 mol%)
copper supported catalysts
R
I
R
R
base (3 equiv.)
solvent
To test the catalytic activity of CuNP/WS-1 as a heteroge-
neous we selected the reduction of different nitroarenes and
benzonitriles in aqueous medium. In a typical experiment,
reflux
a
Entry
R
Solvent
Base
Time (h)
Yield (%)
nitrobenzene (1 mmol) and NaBH (4–5 mmol) were stirred
at 35 C in water (Table 1). The reduction of nitroarenes
and benzonitriles carrying activated and deactivated groups
1
2
3
4
5
6
7
8
9
H
H
H
H
H
H
H
H
Me
Ac
Cl
MeO
H
DMF
DMF
DMF
DMF
DMF
DMSO
K3PO4
NaOAC
5
5
5
5
5
24
24
24
8
3
5
88
27
30
35
69
4
ꢀ
Na
2
CO
3
NaHCO
K2CO3
3
such as OH, NH , Me, Cl, CHO and CN took place effi-
2
K
K
K
K
K
K
K
K
K
3
PO
3
PO
3
PO
3
PO
3
PO
3
PO
3
PO
3
PO
3
PO
4
4
4
4
4
4
4
4
4
11
ciently and easily to give the corresponding aniline and ben-
zylamines as exclusive products according to TLC and GC.
The scope and generality of this process is demonstrated
with wide variety of nitroarenes and benzonitriles and the
2
H O
N.R.
N.R.
91
99
95
PhMe
DMF
DMF
DMF
DMF
DMF
DMF
1
1
12
0
1
results are summarized in Table 1. Reaction of NaBH and
4
24
5
5
33
b
1
1
a
3
4
45
9
2
,2-diphenylacetonitrile
yields
2,2-diphenylethenamine
c
H
through imine-enamine tautomerism (Table 1, Entry 13). By
using the reduction reaction of benzonitrile, it was found
that this supported catalyst has been recovered and reused
up to 4 times (yield of 1st run: 100% 1 h, 2nd run: 99% 1 h,
GC yield.
b
c
cat.: CuNP/WS-2.
cat.: CuNP/WS-3.
3
rd run: 95% 1 h, 4th run: 89% 1 h, 5th run: 41%, 2 h). We
selective reduction of p-nitrobenzonitrile to p-aminobenzo-
nitrile (Scheme 2). Because of diverse applications and uses
of p-aminobenzonitrile in pharmaceuticals, agrochemicals,
and fine chemicals, high selectivity to this target amine
have investigated the effect of Cu particle size on catalytic
performances of the CuNP/WS catalysts in the reduction of
benzonitrile and 2-nitrophenol (Table 2). It is of interest
that different size of CuNPs exhibit different catalytic activ-
ity but in comparison with 2-nitrophenol, reduction of ben-
zonitrile is more dependent to the size of CuNPs. However,
[
25]
product is challenging
.
In order to show the importance of this protocol for the
reduction of nitroarenes and benzonitriles, Table 3 describes
other CuNP-based catalytic systems previously reported in
the literature. In addition to green dimensions of catalyst, to
CuNP/WS-1
contains
smaller
metal
nanoparticles
(15–22 nm) exhibited the highest activity in reduction of
both substrates. The efficiency of CuNP/WS-1 was also dem- the best of our knowledge, it is the first report on CuN
onstrated in the reduction of nitrobenzene in the presence Pacting as a catalyst for the reduction of benzonitriles. On
of benzonitrile (Scheme 1). Notably, nitrobenzene was effi- the other hand, the advantages of CuNP/WS-1 catalyst is
ciently converted to aniline while benzonitrile was not more apparent in terms of higher yield at low catalyst loading
reduced at all. Also CuNP/WS-1 was employed in the (2 mol%) compared to other CuNP-based catalysts.

INORGANIC AND NANO-METAL CHEMISTRY
5
Classic Ullman reaction catalyzed by with copper
supported catalysts
NMR data for some of the products
1
4
6
-Bromoaniline: H NMR (400 MHz, CDCl
3
): d ¼ 3.68 (br, 2H, NH
2
),
1
3
.56 (d, 2H), 7.23 ppm (d, 2H);
C
NMR (100 MHz, CDCl
3
)
In the next step, we tested the catalytic activity of CuNP/
WS-1 for the C-C Ullmann coupling reaction. To find out
the optimum reaction conditions, we initially selected phenyl
d ¼ 110.15, 116.65, 131.90, 145.33 ppm.
1
Benzene-1,2-diamine: H NMR (400 MHz, CDCl
3
): d ¼ 3.35 (br, s,
13
4
H, 2ꢂNH
2
), 6.58 ppm (m, 4H);
C
NMR (100 MHz, CDCl ):
3
iodide as a model reaction and studied the effects of the sol- d ¼ 116.75, 138.50 ppm.
1
2
,2-Diphenylethenamine: H NMR (400 MHz, CDCl
3
): d ¼ 3.56 (br,
13
vents and base on that. Among the different bases such as
K PO , NaOAc, Na CO , NaHCO and K CO , K PO
2
2H, NH ), 6.67 (br, 1H), 7.16 (m, 5H), 7.35 ppm (m, 5H); C NMR
3
4
2
3
3
2
3
3
4
(
1
100 MHz, CDCl3) d ¼ 123.11, 124.8, 128.3, 127.9, 131.4, 132.1, 130.5,
showed the maximum yield for homocoupling of phenylio-
dide to give biphenyl in 88% yield in DMF as solvent under
reflux conditions (Table 4, entry 1). On the other hand, (d, 4H), 7.50 ppm (d, 4H); C NMR (100 MHz, CDCl
among various solvents that were used, such as DMF,
DMSO, toluene and water, it turned out that DMF led to
much better results in terms of product yields (Table 4,
entries 1, 6–8).
39.1, 139.8 ppm.
0
0
1
4
,4 -Dichloro-1,1 -biphenyl: H NMR (400 MHz, CDCl
3
): d ¼ 7.43
1
3
3
) d ¼ 128.25,
1
29.07, 133.77, 138.45 ppm.
0
0
1
4,4 -Dimethoxy-1,1 -biphenyl: H NMR (400 MHz, CDCl
3
): d ¼ 3.89
1
3
(
s, 6H, 2ꢂOMe), 7.00 (d, 4H), 7.52 ppm (d, 4H); C NMR (100 MHz,
CDCl
3
) d ¼ 55.36, 114.20, 127.76, 133.51, 158.73 ppm.
To demonstrate the general applicability of the CuNP/
WS-1 nanocomposite for Ullmann coupling different substi-
tuted aryliodides were examined. As shown in Table 4, the
Funding
The authors gratefully acknowledge the financial support of this work
homocoupling reaction of different iodobenzenes including by the research council of Urmia University.
electron-rich and electron-poor substrates proceeded
smoothly using as low as 30 mol% of catalyst to give the
corresponding products in excellent yields (Table 4, entries
References
1
, 9–12). For electron-neutral and electron-rich aryl iodides,
good yields of the homocoupling products were obtained at
–24 h (Table 4, entries 1, 9 and 12). Electron-poor iodoben-
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10.1002/14356007.a02_303.pub2.
zenes reacted under the present reaction conditions to pro-
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2
.
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3.
.
of iodobenzene, it was found that this nanocomposite cata-
lyst has been recovered and reused up to 3 times (yield of
4
1
4
st run: 100% 5 h, 2nd run: 99% 8 h, 3rd run: 95% 15 h,
th run: 89% 24 h). Also a size-dependence study showed
2
005; pp. 76.
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7.
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8.
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In conclusion, we have presented a new green, simple and
inexpensive method of making copper nanoparticle catalyst
supported on walnut shell. This material was characterized
by TEM, EDX, TGA and AAS. It showed the isolated copper
9. Bethold, H.; Schotten, T.; H o€ nig, H., Transfer Hydrogenation in
Ionic Liquids under Microwave Irradiation. Synthesis 2002, 11,
1607–1610.
1
5–22 nm nanoparticles were formed and immobilized onto
the walnut shell. This catalyst was found to be efficient for
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1
0. Astruc, D.; Lu, F.; Aranzaes, J. R., Nanoparticles as recyclable
catalysts: the frontier between homogeneous and heterogeneous
catalysis. Angew. Chem. Int. Ed. 2005, 44, 7852–7872.
4
and recovering and reusing of the catalyst happens to be 11. Jia, C. J.; Sch u€ th, F., Colloidal metal nanoparticles as a compo-
nent of designed catalyst. Phys. Chem. Chem. Phys. 2011, 13,
easy. Also we have developed a green and economic catalyst
2457–2487.
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walnut shell-stabilized copper nanoparticles (CuNP/WS-1)
as the catalyst in DMF. The homocoupling reactions of
iodoarenes, produce the corresponding coupling products in
good to excellent yields at the present reaction conditions.
1
2. Karimi, B.; Behzadnia, H.; Farhangi, E.; Jafari, E.; Zamani, A.,
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