Banana pulp extract mediated synthesis of Cu2O nanoparticles: An efficient heterogeneous catalyst for the ipso-hydroxylation of arylboronic acids

Article abstract of DOI:10.1016/j.tetlet.2017.02.028

A green and facile novel procedure has been developed for the synthesis of Cu₂O nanoparticles within a very short reaction time using banana pulp extract as a reducing agent. The synthesized nanoparticles are well characterized by SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope) and powder XRD (X-ray Diffraction) methods. An environmental benign and highly efficient protocol for the ipso-hydroxylation of aryl and hetero arylboronic acids using bio-fabricated Cu₂O nanoparticles as a catalyst and aqueous H₂O₂as an oxidant has also been developed. The main advantages of this protocol are the base free reaction condition, reusable and heterogeneous catalytic system, and short reaction time with excellent yields.

Full text of DOI:10.1016/j.tetlet.2017.02.028

Accepted Manuscript
Banana Pulp Extract Mediated Synthesis of Cu O Nanoparticles: An Efficient
2
Heterogeneous Catalyst for The Ipso-Hydroxylation of Arylboronic Acids
Rupom Borah, Eramoni Saikia, Sankar Jyoti Bora, Bolin Chetia
PII:
S0040-4039(17)30204-6
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.02.028
TETL 48639
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
12 December 2016
8 February 2017
9 February 2017
Please cite this article as: Borah, R., Saikia, E., Bora, S.J., Chetia, B., Banana Pulp Extract Mediated Synthesis of
Cu O Nanoparticles: An Efficient Heterogeneous Catalyst for The Ipso-Hydroxylation of Arylboronic Acids,
2
Tetrahedron Letters (2017), doi: http://dx.doi.org/10.1016/j.tetlet.2017.02.028
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Cu O Nanoparticles: An Efficient
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Heterogeneous Catalyst for The Ipso-
Hydroxylation of Arylboronic Acids
Rupom Borah, Eramoni Saikia, Sankar Jyoti Bora and Bolin Chetia

1
Tetrahedron Letters
Banana Pulp Extract Mediated Synthesis of Cu O Nanoparticles: An Efficient
2
Heterogeneous Catalyst for The Ipso-Hydroxylation of Arylboronic Acids
Rupom Borah, Eramoni Saikia, Sankar Jyoti Bora and Bolin Chetia*
Department of Chemistry, Dibrugarh University, Dibrugarh-786004, Assam, India
Email: bolinchetia@dibru.ac.in Phone: +91-373-2370210
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
2
A green and facile novel procedure has been developed for the synthesis of Cu O nanoparticles
within a very short reaction time using banana pulp extract as a reducing agent. The synthesized
nanoparticles are well characterized by SEM (Scanning Electron Microscope), TEM
(Transmission Electron Microscope) and powder XRD (X-Ray Diffraction) methods. An
environmental benign and highly efficient protocol for the ipso-hydroxylation of aryl and hetero
Available online
2 2 2
arylboronic acids using bio-fabricated Cu O nanoparticles as a catalyst and aqueous H O as an
Keywords:
Ipso-hydroxylation
Banana extract
Cu O Nanoparticles
2
Arylboronic acids
Heterogeneous
oxidant has also been developed. The main advantages of this protocol are the base free reaction
condition, reusable and heterogeneous catalytic system, and short reaction time with excellent
yields.
2
009 Elsevier Ltd. All rights reserved.
Therefore, the development of more efficient, cost effective,
environmental benign and reusable catalyst is often required.
The synthesis of phenols and its derivatives has received much
attention in the present decade as it is the main constituents of
19
Recently Bora et al. introduced a new catalytic system using Ag-
nanoparticles supported with mont K-10. Inspired by their work, here
we wish to report another highly efficient protocol for ipso-
hydroxylation of arylboronic acids to phenols using bio-fabricated
1
2
3
various polymers , pharmaceuticals , agrochemicals , natural
4
antioxidants etc. The conventional procedures for the synthesis of
phenols and its derivatives involve conversion of aryl halides to
5
phenols by palladium catalyst , copper promoted conversion of
Cu
2
O nanoparticles as reusable heterogeneous catalyst and 30%
as an oxidant at room temperature under solvent free condition.
Initially we have synthesized Cu O nanoparticles by a green
6
7
arenes , aromatic nucleophilic substitution of activated aryl halides
2 2
H O
etc. But in these existing processes harsh reaction conditions are
2
8
required due to the inactive nature of the starting materials . On the
synthetic route using copper acetate as the metal precursor and
aqueous solution of ripe Musa balbisiana colla fruits as reducing
agent.
other hand palladium based catalytic systems are very expensive and
aren’t suitable for large scale synthesis. Therefore now a day the
synthesis of phenols and its derivatives from arylboronic acids
through ipso-hydroxylation receive enormous attention due to higher
stability, greater diversity of the functional groups and also easy
20
Cu
2
O nanoparticles are used as heterogeneous catalyst ,
21
22
23
photocatalyst , antibacterial agent , gas sensor and p-type
24
semiconductor with band gap of 1.7 eV. Although there are number
of chemical methods for the synthesis of Cu O nanoparticles but
availability of the precursors.
So the direct conversion of
2
arylboronic acids to phenols were achieved by different catalytic
most of the methods reported have some limitations such as use of
9
10
2
11
3
25
systems such as CuSO
4
-Phenanthroline , H
2 2
O -I
2
, H O
2
-Al
2
O
,
high temperature, toxic chemicals, supporting media etc. Although
1
2
13
14
15
NH
2
OH ,
H O
2 2
-WERSA , NaClO
2
,
PEG-H
18
O
2 2
,
organic
biosynthesis of nanoparticles has become one of the most convenient
method, but literature reveals only a few reports for the biosynthesis
1
6
17
hypervalent iodine (III) , TBHP , Bio-silica etc. Although most
of the reported methods are efficient for the conversion, these
methods have some limitations such as use of excess oxidizing agent,
basic and toxic solvents and more catalyst loading (table 4).
26
of Cu
straightforward green synthesis of Cu
using aqueous extract of Musa balbisiana colla at moderate
2
O
nanoparticles . Therefore herein
a
facile and
2
O nanoparticles is designed

2
temperature within a very short reaction of time. To the best of our
knowledge this is the most efficient method to synthesize Cu
nanoparticles. Fruits of Musa balbisiana colla contains reducing
monodispersity of the nanoparticles is clearly observed. The purity
2
O
of the nanoparticles are also observed from the Energy Dispersive X-
ray (EDX) spectrum which shows the presence of copper, oxygen
and carbon element.
-1
-1
sugars (146.0 g kg ), carbohydrate (262.4 g kg ), other minerals like
-1
-1
potassium (4679.0 mg kg ), magnesium (431.0 mg kg ), sodium
-1
-1 27
(
44.0 mg kg ), calcium (129.0 mg kg ) etc. and phenolic
-1 28
compounds (20.61 mg g ) . The high amount of reducing sugars
and poly-phenolic compounds present in the fruit extract are mainly
29
2
responsible for the rapid biosynthesis of Cu O nanoparticles .
The prepared Cu
aryl and hetero-arylboronic acids. In a typical reaction 50 mg (0.41
mmol) of phenyl-boronic acid, 2 mg (0.0139 mmol) of Cu O NPs
and 200 μL H were added to a round bottomed flask under
2
O NPs are used in the ipso-hydroxylation of
2
2 2
O
magnetic stirring at room temperature. After completion of the
reaction, product was extracted with diethyl ether. The obtained
1
13
products were characterized by H-NMR and C-NMR spectra.
HO OH
B
OH
Cu O NPs, H O
2 2
2
rt
Figure 2: SEM images of the Cu
2
O NPs (a, c) with spherical
structure and EDX image of the one spherical nanocrystal (b).
Scheme 1: Ipso-hydroxylation of phenyl boronic acid to phenol.
2
Furthermore the morphology and size of the Cu O nanocrystals
2
The powder XRD-diffraction pattern of the synthesized Cu O
were also determined through TEM images (figure 3). The average
diameters of the nanoparticles were also calculated from the TEM
images and found around 7.33nm. The grain size distribution of the
nanoparticles were also determined. The inset in figure 3 shows the
SAED (Selected Area Electron Diffraction) images of the
synthesised nanoparticles.
nanoparticles is shown below (figure 1). The various diffraction
peaks at 2θ = 29.58°, 36.5°, 42.36°, 61.64°, 73.62° and 77.62°
corresponding to the planes (110), (111), (200), (220), (311) and
(
222) are observed. The sharp diffraction peaks shows clearly the
presence of highly pure crystalline Cu O nano-balls. We have not
2
observed any specific plane for Cu(0) nanoparticles in our XRD
pattern.
Figure 3: TEM images of the synthesized nanoparticles (a) and the
SAED pattern (b) one nanoparticle (inset) and grain size distribution
of the nanoparticles (c).
2
Figure 1: Powder XRD pattern of Cu O NPs.
2
We applied the biogenic Cu O nanoparticles as a reusable
heterogeneous catalyst for the synthesis of various substituted
phenols from arylboronic acids. The experiments began with the
optimization of the reaction parameters, for which we took phenyl
boronic acid (1 mmol) as the model substrate (scheme 1) and the
The structure and morphology of the synthesized nanoparticles are
shown in the figure 2. From SEM images the structure of the
nanoparticles are found to be pure spherical and also the

3
reaction was carried out at room temperature. The results obtained
from the optimizations are summarized in the table 1. Use of H
under same reaction condition. After the first cycle, the product
2
O
2
was separated by diethyl ether and the catalyst was separated by
only as oxidant yields trace amount after 6 hours (table 1, entry 1).
The product yield was significantly increased to 96% by the addition
centrifugation and again used for the ipso-hydroxylation of phenyl
th
boronic acids. The effectiveness of the catalyst was found up to 5
of Cu
). To evaluate the optimal conditions we carried out the reaction
with different amount of Cu O NPs and 3 mol% catalyst was found
to be effective for the conversion. During the study we have found
00 μL H was optimal for effective conversion (table 1, entry 5).
We have also carried out the ipso-hydroxylation reaction of
phenylboronic acid in the presence of bulky Cu O powder in the
2
O NPs (Nanoparticles) to the reaction mixture (table 1, entry
cycle (table 3) with negligible decrease in the yield. The decrease in
the yields is mainly due to the loss of nanoparticles during the
recycling process. There is no change in morphology in the
nanoparticles as observed by the TEM image and powder XRD
5
2
th
2
O
2 2
pattern taken after 5 cycle in the recycling process (figure 4) which
2
confirms that Cu O NPs does not take part in the reaction.
2
optimized condition and found that it required more time to complete
the reaction (table 1, entry 8).
Table 2: Cu
2
O NPs catalyzed ipso-hydroxylation of arylboronic
acids
HO
OH
B
OH
Table 1: Optimization of the reaction parameters for Cu
2
O NPs
a
mediated ipso-hydroxylation
Cu2O NPs, H2O2
rt
b
Entry
Oxidant
Cu
2
O NPs
Time
(min)
6 h
Yield
(%)
R
R
(
mol %)
-
a
1
2
3
4
5
6
H
H
H
H
H
H
2
2
2
2
O
O
O
O
2
2
2
2
trace
Entry
R
H
Time(min)
Yield (%)
c
1
2
3
3
3
30
30
15
10
10
60
1
2
3
4
5
6
7
8
9
10
10
15
6
96
95
93
93
91
93
91
95
86
93
82
86
4-Me
4-Cl
90
90
4-COCH
3-OMe
4-NO2
4-OMe
3-NO2
2-Me
3-Me
3
d
2
O
2
96
13
7
e
O
2 2
96
f
15
15
15
10
20
30
7
8
-
3
3
24 h
10
trace
g
H
2
O
2
60
a
Reaction condition: phenyl boronic acid (1 mmol), 30%
10
H O
2 2
, (100 μL), room temperature.
b
11
2-Thiophen
2-Furan
isolated yield.
c
12
the reaction didn’t reach completion.
a
d
Isolated Yield.
200 μL H O
2 2
e
3
2
00 μL H O
2
f
Table 3: Reusability of Cu O NPs in the synthesis of phenols.
2
2
in presence of 500 μL H O
a
g
Entry
No of cycle
Yield
96
2
in presence of bulkyCu O powder
st
1
1
nd
2
2
92
With these optimized conditions the scope of the reaction was
explored to a variety of electronically diverse arylboronic acids
Table 2). It has been observed that both the electron withdrawing
rd
3
3
92
th
4
5
4
90
(
th
5
87
and electron donating substituents and also the position of the
substituents had little effect on the reaction process. Moreover the
hetero arylboronic acids also undergo transformations (entry 11, 12)
with high yields.
a
Isolated Yield
This catalytic system shows more efficient results and has the
advantages in comparison to other techniques such as use of less
amount of oxidant, less amount of catalyst loading, easy preparation
Reusability and heterogeneity is one of main advantages of
the catalyst. To investigate the reusability of the Cu
2
O NPs we
performed the ipso-hydroxylation of phenyl boronic acid (scheme 1)

4
and separation of the catalyst etc. Below table 4 shows the efficiency
of our catalyst in comparison to some other catalysts.
2 2 2
It is assumed that initially Cu O NPs trapped the H O molecules
on its surface and then reacts with the phenyl boronic acid to form an
adduct which on rearrangement and subsequent hydrolysis gives
phenol. As the ipso-hydroxylation reaction of phenylboronic acid in
the presence of bulky Cu
more time to complete the reaction which reveals that Cu
nanoparticles provide a solid support as well as high surface area in
comparison to bulky Cu O powder that facilitates the reactions to
2
O powder in the optimised condition took
2
O
2
complete within a short period of time.
In conclusion, we have reported for the first time a green, simple and
Figure 4: Powder XRD and TEM image of the recovered Cu
2
O
2
fast method (15 min) for the synthesis of Cu O nanoparticles using
th
nanoparticles (after 5 cycle).
biogenic route with Musa balbisiana colla fruit extracts and
developed a new reusable and heterogeneous catalytic system for the
effective conversion of aryl and heteroaryl boronic acids via ipso-
Table 4: Comparison of efficiency of Cu
2
O nanoparticles with some
reported catalysts for the ipso-hydroxylation of aryl boronic acids.
2 2
hydroxylation using H O as oxidant to phenols. This method is
found more effective due to short reaction time, high yield and reuse
Catalyst
H
2
O
2
(ml)
Catalyst
Loading
5 mol %
references
th
of the catalyst up to 5 cycle. In addition ligand, base and solvent-
Iodine
2
10
11
15
18
19
free make this method more effective for the conversion.
Acknowledgement:
Acidic Alumina
PEG-400
1.5
0.26
0.2
20 mg
2 ml
BC gratefully acknowledges DST-SERB (project No.SB/FT/CS-
1
61/2012) and SAP-DRS for financial assistance and SAIF, NEHU-
Bio-silica
5 mg
Shillong for spectral data.
Ag-NP Mont-K
0.5
5 mg
Supporting Information:
2
Cu O NP
0.2
2 mg (3 mol %)
Our present
work
Reaction condition: phenylboronic acid (1 mmol), room temperature,
air.
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5
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6
Highlights




Banana pulp extract mediated synthesis of Cu
2
O nanoparticles within 10 minutes
O nanoparticles
Ipso-hydroxylation of aryl and hetero arylboronic acids using Cu
2
Ligand, base and metal free reusable heterogeneous catalyst system
Reactions were carried out in very short reaction time at room temperature