On-water synthesis of phenols using biogenic Cu2O nanoparticles without using H2O2

Article abstract of DOI:10.1039/c6ra22972g

In recent years the biogenic synthesis of metal oxide nanoparticles using natural resources has received significant attention due to their easy availability, low cost and environmentally benign protocol. In this study, Cu₂O nanoparticles have been synthesised using Syzygium jambos (L.) Alston plant extracts without using toxic chemicals. The average size of the nanoparticles is 7.6 nm which found to have excellent catalytic activity in the ipso-hydroxylation of arylboronic acids without using H₂O₂. Mild reaction condition, excellent yield, easy separation and reusability of the catalyst are the advantages of this method.

Full text of DOI:10.1039/c6ra22972g

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On-water synthesis of phenols using biogenic Cu2O nanoparticles
without using H2O2
Received 00th January 20xx,
Accepted 00th January 20xx
Rupom Borah, Eramoni Saikia, Sankar Jyoti Bora and Bolin Chetia*
DOI: 10.1039/x0xx00000x
In the recent years biogenic synthesis of metal oxide nanoparticles using natural resources have received significant
attraction due to their easy availability, low cost and environmental benign protocol. In this study, Cu2O nanoparticles
have been synthesised using Syzygium jambos (L.) Alston plant extracts without using toxic chemicals. The average size of
the nanoparticles is 7.6 nm which found to have excellent catalytic activity in the ipso-hydroxylation of arylboronic acids
without using H2O2. Mild reaction condition, excellent yield, easy separation and reusability of the catalyst are the
advantages of this method.
www.rsc.org/
(biosilica, acidic alumina etc.) and there are only a few reports
without using H2O2 (CuSO4/phenanthroline, CuCl2 Brij S-100,
[Ru(byp)3Cl2, NH2OH, NaClO2 etc.).19 Even all the existing processes
are effective for the conversion, but most of the methods have
some limitations such as use of strong oxidising agent, base, ligands
Introduction
Development of metal oxide nanoparticles in the current years has and also not recyclability of the catalyst (Table 2). We have
inspired the interest of scientists and researchers due to their designed an alternative protocol to synthesis phenolic derivatives
unique properties and potential applications. Cu2O nanoparticles from arylboronic acids without using H2O2, base, ligands, external
are found to be an important p-type semiconductor with a band oxygen source etc. The simple catalytic system, recyclability of the
gap approximately 2.1 eV1 and a promising inorganic catalyst in catalyst and mild reaction condition give advantages to the
various fields2-8. The conventional procedure for the synthesis of conversion.
Cu2O nanoparticles includes the hydrothermal9, electro-
deposition10 and chemical reduction methods11 having more or less
shortcomings e.g. high temperature, hazard chemicals, supporting
media etc12 (Table 1). To overcome these shortcomings, biogenic
Experimental section
synthesis of nanoparticles is considered as one of the most
General Information
convenient procedure as it is environmental benign, cost effective
and easy process. Although a lot of reports are found in literature
Chemicals and reagents were purchased from commercial suppliers
for the synthesis of Cu2O NPs using chemical reduction method,
and used without further purification. Reactions were monitored by
however only a few reports for biosynthesis13 are obtained. Herein
thin layer chromatography (TLC) on silica gel plates (60 F254),
visualizing with ultraviolet light. 1H-NMR and 13C-NMR spectras
attempts were made to synthesis Cu2O NPs using Syzygium jambos
(L.) Alston plant leaves extract.
were determined in CDCl3 solution by using 400 MHz spectrometer
Syzygium jambos (L.) Alston leaves extracts shows good
taking tetramethylsilane (TMS, δ=0.00) as internal standard and
antimicrobial14, anti-nociceptive15, and antioxidant16 activity, and
expressed in ppm. Spin multiplicities are given as s (singlet), d
the plant rich in vitamin C and many polyphenols17. Therefore this
(doublet), t (triplet) and m (multiplet) as well as b (broad). Infrared
plant was chosen to be the biogenic reducing agent for the
spectra were recorded on a FT-IR spectrometer.
synthesis of Cu2O NPs. The synthesised Cu2O NPs were also found
to have good catalytic activity in the ipso-hydroxylation of
Biosynthesis of Cu2O NPs
arylboronic acids. Most of the ipso-hydroxylation of arylboronic
18
acids involve the use of H2O2 in presence of various catalysts
Leaves of Syzygium jambos (L.) Alston were washed with distilled
water, air dried and 10 g of the leaves were placed into 100 ml of
distilled water in a round bottomed flask, heated at 50°C for 15 min
Department of Chemistry, Dibrugarh University, Dibrugarh-786004, Assam, India.
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
and filtered. 10 ml of 1 mM copper acetate solution was added to 2
ml of 1 mmol sodium hydroxide solution and to the resulting
DOI: 10.1039/x0xx00000x
solution 5 ml of aqueous extract was added and was stirred
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vigorously at 60°C for 2 hr. Sodium hydroxide solution was added to Cu2O octahedra. The strong and sharp peaks of the prepared Cu2O
the mixture to form copper(II) hydroxide from copper acetate. The octahedra indicate the high crystallinity of the NPs
Cu2O NPs were then separated by centrifugation at 1200 rpm for 10
min and then washed with ethanol several times and dried in an
oven at 50°C. Some existing technologies to produce Cu2O
nanoparticles were compared with our biosynthesis method (table
1) and it is clear that biosynthesis method is more efficient and
gives smaller size nanoparticles within a short period.
.
Table 1: Comparison of methodologies to synthesis Cu2O
nanoparticles
Type
Reducing
agent
o-
Temp
200 °C
200 °C
90 °C
Time
8 h
Size
Ref.
9 (a)
9 (b)
11 (a)
Hydrotherm
al
445 nm
anisidine
-
Hydrotherm
al
1-32
h
150-300
nm
Fig. 1 Powder XRD pattern of the synthesized octahedral Cu2O
Nanoparticles.
Chemical
Fehling
solution,
glucose
Plant
1-2 h
590-
1600 nm
The monodispersity and pure octahedral structures of the
nanocrystals (figure 2a and 2b) and extensive aggregation of the
small particles (figure 2c) were observed from the SEM images. The
Energy Dispersive X-ray (EDX) spectrum (figure 2d) shows the
presence of copper, oxygen and carbon element in which copper
and oxygen present in the ratio almost 2:1. Furthermore the
morphology and size of the Cu2O nanocrystals were also
determined through TEM and HR-TEM images (figure 3). The inset
figure (3b) shows the selected area electron diffraction (SAED)
pattern of the Cu2O NPs and contains the concentric diffraction
rings due to the (111), (200) and (220) reflection of the octahedral
Cu2O NPs. From the HR-TEM image (figure 3c) the separation of the
fringes was found to be 2.4 Å, which is good agreement with the
(111) plane and another magnified lattice fringe was found with a
spacing of 3.01 Å which corresponds to the lattice plane (110) of
Cu2O NPs. The average diameter of the NPs was found around 7.62
nm (figure 4).
Biosynthesis
60 °C
2 hr
4-10 nm
Our
present
work
extracts
Ipso-hydroxylation of arylboronic acids by Cu2O NPs
HO
R1
OH
OH
B
Cu2O NPs
/ 5 hours
R1
Scheme 1: Synthesis of phenols using Cu2O NPs
In a typical reaction 5 mg (0.041 mM) of phenyl boronic acid and 2
mg (0.014 mmol) of Cu2O NPs were added to 5 ml of water under
stirring at 60°C. The reaction was monitored by TLC. After
completion of the reaction the reaction mixture was diluted with 20
mL of water and extracted with 20 mL of diethylether and the
combined organic layer was washed with brine and dried over by
Na2SO4 and evaporated in a rotary evaporator under reduced
pressure. The products were confirmed by 1H-NMR, 13C-NMR and
FT-IR spectroscopy without any further purification by column
chromatography. The reaction was also performed using molecular
oxygen but the yield was same.
Result and Discussion
The biogenic Cu2O NPs were well characterized by powder XRD-
diffraction method as shown in the figure 1. The diffraction peaks
appeared 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) respectively and shows clearly the presence of pure crystalline
Fig. 2 SEM images of the pure Cu2O octahedral (a, b, c) and (d) EDX
images of the nanooctahedra.
2 | J. Name., 2012, 00, 1-3
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aReaction conditions: arylboronic acid (0.041 mmol), Cu2O NPs
(0.014 mmol) in 5 ml water at 60 °C.
bIsolated yields.
Some of the recently reported catalyst systems and their
comparison with the Cu2O nanoparticles catalyst are illustrated in
table 2. It is clear that Cu2O nanoparticles catalyst is more efficient
and greener catalyst than most of the reported catalysts.
Fig. 3 (a) TEM images and (b) corresponding SAED pattern of the
Table 2: Comparison of efficiency of Cu2O nanoparticles with some
reported catalysts for the ipso-hydroxylation of aryl boronic acids
nanoparticles and (c) HR-TEM image of selected region of one
nanoparticle
.
Catalyst
Time
2 h
Yield
(%)
95
Recyclability
No
Reference
19 (a)
CuSO4-
phenanthroline
CuCl2 Brij S-100
[Ru(byp)3Cl2].6
H2O
24 h
48 h
95
93
No
No
19 (b)
19 (c)
NH2OH
18 h
5 h
94
No
19 (d)
Present
work
Cu2O
100
Yes
nanoparticles
Recyclability Test
Fig. 4 Size distribution of the NPs
Recyclability of the catalyst is another attractive feature of this
protocol. As the catalyst is heterogeneous in nature, the catalyst is
recycled up to 5th cycle without significant loss of catalytic activity
(figure S1). Taking phenylboronic acid as model substrate we
carried out the catalyst recyclability test. After completion of the
reaction, products were extracted with diethylether and catalysts
separated from product was washed with more diethylether and
reused. The loss of the product yields after 5th cycle is due to the
loss of nanoparticles during the recycling process. There is no
change in the morphology and crystallinity of nanoparticles as
observed in the analysis of TEM images and XRD patterns of the
recycled nanoparticles after 5th cycle (figure 6).
Ipso-Hydroxylation of aryl boronic acids:
Using the above mentioned reaction conditions 12 different types
of arylboronic acids were converted to the corresponding phenols
with high yields.
OH
OH
OH
OH
CH3
OCH3
NO2
5h, 100% b
5h, 90%
5h, 92%
5h, 85%
OH
OH
OH
S
OH
OCH3
Cl
CH3
5h, 95%
OH
5h, 80%
5h, 90%
5h, 92%
OH
OH
O
OH
Fig. 6 Powder XRD and TEM image of Cu2O nanoparticles after 5th
CH3
5h, 93%
NO2
COCH3
5h, 85%
catalytic cycle of reaction
5h, 95%
5h, 92%
Fig. 5 Substrate scope: variation of the arylboronic acidsa
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Fig. 7 Proposed mechanism for ipso-hydroxylation of aryl boronic
acids with Cu2O nanoparticles
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Herein we have reported for the first time a facile, environment
friendly biogenic route to synthesis pure octahedral Cu2O NPs using
Syzygium jambos (L.) Alston leaves extracts. The synthesized NPs
were found in the average size range between 4 to 10 nm (TEM).
The biogenic Cu2O nanoparticles are directly utilised on water for
the ipso-hydroxylation of arylboronic acids with various
substituents with excellent yields. The catalyst works without using
H2O2, base, ligand, molecular oxygen and can be recycled several
times without significant loss of activity. The present catalytic
system shows better results and has some advantages in
comparison to other techniques to synthesis phenols from
arylboronic acids. We believe that this is the most greener and
efficient protocol for ipso-hydroxylation of arylboronic acids to
phenols from the environmental and economical point of view.
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Acknowledgement
BC gratefully acknowledges DST-SERB (project No.SB/FT/CS-
161/2012) for financial assistance, UGC-SAP and SAIF, NEHU-
Shillong for spectral data.
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