Biogenic synthesis of Fe2O3@SiO2 nanoparticles for ipso-hydroxylation of boronic acid in water

Article abstract of DOI:10.1016/j.tetlet.2017.09.075

Here, biogenic synthesis of Fe₂O₃@SiO₂ nanoparticles using fruit extract of Zanthoxylum rhetsa is reported. The SiO₂ nanoparticles was synthesized using paddy straw which is a byproduct obtained in cultivation of rice. The composite was characterised by spectroscopic method like XRD, SEM, TEM and EDX analysis. The ipso-hydroxylation reactions were carried out with excellent yield within a moderate time period with mild reaction condition in all cases. Therefore, this approach may be considered as simple, easy, cheap and greener, environment friendly protocol for ipso-hydroxylation of arylboronic acids at 50 °C temperature.

Full text of DOI:10.1016/j.tetlet.2017.09.075

Accepted Manuscript
Biogenic synthesis of Fe2O3@SiO2 nanoparticles for ipso-hydroxylation of bor-
onic acid in water
Indarnirekha Saikia, Moushumi Hazarika, Najrul Hussian, Manash R Das,
Chandan Tamuly
PII:
S0040-4039(17)31227-3
https://doi.org/10.1016/j.tetlet.2017.09.075
TETL 49345
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
20 July 2017
19 September 2017
25 September 2017
Please cite this article as: Saikia, I., Hazarika, M., Hussian, N., Das, M.R., Tamuly, C., Biogenic synthesis of
Fe2O3@SiO2 nanoparticles for ipso-hydroxylation of boronic acid in water, Tetrahedron Letters (2017), doi: https://
doi.org/10.1016/j.tetlet.2017.09.075
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Biogenic synthesis of Fe2O3@SiO2 nanoparticles for ipso-hydroxylation
of boronic acid in water
Indarnirekha Saikiaa, Moushumi Hazarikaa, Najrul Hussianbc, Manash R Dasbc,
Chandan Tamulyac*
a CSIR-North East Institute of Science and Technology. Branch Itanagar Arunachal Pradesh-791110, India,
b CSIR-North East Institute of Science and Technology. Jorhat, Assam-785006, India
c Academy of Scientific and Innovative Research, CSIR-NEIST Jorhat, Assam India
e-mail: c.tamuly@gmail.com, Telefax: +913602244220
Abstract
Here, biogenic synthesis of Fe2O3@SiO2 nanoparticles using fruit extract of
Zanthoxylum rhetsa is reported. The SiO2 nanoparticles was synthesized using paddy
straw which is a by product obtained in cultivation of rice. The composite was
characterised by spectroscopic method like XRD, SEM, TEM and EDX analysis. The
ipso-hydroxylation reactions were carried out with excellent yield within a moderate time
period with mild reaction condition in all cases. Therefore, this approach may be
considered as simple, easy, cheap and greener, environment friendly protocol for ipso-
hydroxylation of arylboronic acids at 50ºC temperature.
Key words: Green synthesis; Nanoparticles; Biomaterials; ipso-hydroxylation
1. Introduction
In recent years, the development of greener, efficient, simple, eco-friendly and easy
reaction methodologies play a major role in organic chemistry, in industry as well as in
1
the academic world. The attempt to find simple, environmentally benign methods in
organic synthesis led to an enormous increase of research activities in the field of green
chemistry 2-3. In this regards, Fe2O3@SiO2 nanoparticles was synthesised using fruit
water extract of Zanthoxylum rhetsa. It is a very simple, easy, environment friendly and
1

cost effective method for synthesis of the Fe2O3@SiO2 nanoparticles. The SiO2
nanoparticles are synthesized using paddy rice straw. Further, the Fe2O3 nanoparticles
were loaded on SiO2 surface.
Zanthoxylum rhetsa is an important medicinal plant. It is used in the treatment of
different diseases like dyspepsia, bronchitis, toothache, asthma and rheumatism. The fruit
is use as fish poisoning fruit by indigenous people of Arunachal Pradesh 4. The presence
of phenolic acids and flavonoid compounds in the fruit extract may be responsible for the
synthesis of Fe2O3 nanoparticles. 5 Due to presence of such class bioactive compounds, it
is used for synthesis of Fe2O3@SiO2 nanocomposite.
Phenol and its derivatives are present in various natural products like aromatic
6
steroids, macrolides, quinines, terpenoids, alkaloids etc . Phenols and poly phenols are
7
used as anti-oxidant.
In general, phenols are prepared through the nucleophilic
8
substitution of an aryl halide using different catalysts like copper, palladium etc. which
suffer from several drawbacks like harsh reaction condition, poor functional group
compatibility, less substrate scope. Over the last few decades, phenylboronic acids and
their derivatives have considered an important moiety in a wide range of organic
9
reactions. It is also used for the preparation of phenol with catalysts like copper,
10
11
12
13
14
(NH4)2S2O8
,
I2,
iron(III)oxide,
hydrazine hydrate,
potassium
supported
peroxymonosulfate,15 Amberlite IR 120 resin H3BO3–H2O2, NaClO2
silver nano particle 19, WERSA 20 etc.
16
17
18
It was observed that SiO2 is a nonporous material having large surface area. It is
used as a supporting agent due to its large surface area. Beside this, the other advantages
are- easy surface modification and can be recovered using simple method from the
2

reaction medium. It is a non toxic material which can be economically used and no effect
on environment 21.
The basic objective in this study is to synthesis of biogenic Fe2O3@SiO2
nanoparticles using natural resources which can be utilised as very efficient catalyst for
ipso-hydroxylation of some phenylboronic acid without using H2O2 (Table 1) in presence
of water. The reaction was moderately fast and completed within 2-5 hr at 50ºC. To best
of our knowledge, it is the first report of ipso-hydroxylation of phenylboronic acid using
Fe2O3@SiO2 nanocomposite in water and oxygen from at 50ºC.
2. Experimental
2.1. Synthesis of Fe2O3 nanoparticles
For synthesis of Fe2O3@SiO2 nanocomposite, the fruit of Zanthoxylum rhetsa was
dried and grinded and powdered. About 5 gm of the powder of fruit was added into 30 ml
of distilled water for extraction. The extract is kept for 10 hr at room temperature and
filtered it. Further, 5 ml 1mM FeCl3.6H2O was added to the filtrate of extract and stirred
for 10 min. Finally, brown precipitate was formed. The precipitate was further filtered,
washed and heated for 3 hr at 140ºC for the formation of Fe2O3 nanoparticles.
2.2. Synthesis of silica from rice paddy straw:
300 gm of the rice paddy straw was burnt. 5 gm of burnt ash was added in 100 ml of
2.5 M NaOH and the mixture was boiled for 4 hr. After cooling the mixture was filtered
and treated with 5 M H2SO4 acid solution. The PH of the solution was maintained around
8.5-9.0. As the result, white precipitation was occurred and the material was dried at
100oC for 3 hr to produce the silica (SiO2).
2.3. Synthesis of Fe2O3@SiO2 nanoparticles:
3

Fe2O3 nanoparticles were synthesized using Zanthoxylum rhetsa further loaded in the
surface of SiO2. In this method, Fe2O3 and SiO2 were (1:12) refluxed in 15 ml methanol
for 5 hr. The nanocomposite was then filtered and washed with methanol and water:
methanol mixture (1:1) for 5-6 times. The composite material was dried at 100ºC
temperature for 2 hr. Finally, light brown nanocomposite Fe2O3@SiO2 was formed.
2.4. Characterization: Fourier-transform infrared (FT-IR) spectra were recorded in the
range of 400–5500 cm-1 (Shimadzu Corporation, Japan). X-ray diffraction (XRD)
analysis was carried out by Rigaku X-ray diffractometer (Model: ULTIMA IV, Rigaku,
Japan). Scanning electron microscopy- Energy Dispersive X-ray (SEM-EDX)
characterization was performed on JEOL JSM - 6360. The high resolution transmission
electron microscopy (HR-TEM) images were recorded by a JEOL Model 2100 EX, Japan
operated at voltage of 200 kV. Specific surface area, pore volume, average pore diameter
were measured with the Autosorb-1 (Quantachrome, USA). Nuclear Magnetic Resonance
(NMR) spectra were recorded by Advance DPX 500 MHz FT-NMR Spectrometer,
(Make Bruker).
2.3. General procedure for oxidation of boronic acid:
In a round bottomed flask 1 mmol phenyl boronic acid, and 4 mg of Fe2O3@SiO2 in 4
ml of the H2O were taken and stirred at room temperature for appropriate time. Progress
of the reaction was monitored by TLC. After completion of the reaction mixture was
extracted with Ethyl acetate. Further, the organic layer was separated and dried with
sodium sulfate. The mixture was concentrated in rotary evaporator and product was
1
purified by column chromatography. The product was analyzed by taking H and 13C
NMR spectroscopy.
4

The recyclability test was done for catalyst Fe2O3@SiO2 up to 5th times. In this case,
the catalyst was filtered and washed with water ethanol mixture 2/3 times. After washing
it was reused for evaluate its catalytic activity.
3. Results & Discussion
3.1. Characterization of Fe2O3@SiO2 nanoparticles
It is a very simple, eco-friendly method for biogenic synthesis of Fe2O3 nanoparticles
using the fruit extract of Zanthoxylum rhetsa. In this case, the fruit extract of
Zanthoxylum rhetsa was added in FeCl3·6H2O solution for formation of Fe2O3
nanoparticles. In this process, the reduction took place Fe3+ to formed Fe3O4. The
functional group (C=O) of phenolic acid or the flavonoid of extract may co-ordinated
with Fe3+ ion to form ferric protein chains. The HO----Fe3+ bond further transformed to
formed Fe(OH)3 . Accordingly, on slow evaporation, Fe(OH)3 is dehydrated (-H2O) when
heated at 160ºC in presence of oxygen to produced Fe2O3 nanoparticles. It is clearly
supported by reported information 21
.
The supporting agent i.e. SiO2 nanoparticles were also biosynthesized from rice
paddy straw which is a waste material or by product produced during cultivation of rice.
The SiO2 nanoparticles were characterized by SEM and TEM analysis. The SEM image
revealed the formation of the flake sheet of SiO2 [Figure 1S (A), supporting information
(SI)]. The TEM image revealed the formation of pentagonal, hexagonal sheet overlap
each other [Figure 1S (B), SI].
The Fe2O3@SiO2 nanoparticles was further characterised by basic spectroscopic
technique such as XRD, SEM, EDX and TEM analysis. In XRD analysis, the diffraction
peaks appeared at 2θ value 36.4º, 44.8º, 53.9º, and 63.6º were assigned to (311), (400),
5

(422), and (440) reflection in the unit cell respectively, which revealed the spinal
structure of Fe2O3 (JCPDS Card No.19–0629). The corresponding spacing i.e. ‘d’ value
of Fe2O3 nanoparticles are 2.48, 2.42, 2.02 and 1.48 respectively (Figure 1).
600
500
(311)
400
(400)
300
(422)
200
(440)
100
0
10
20
30
40
50
60
70
2Theta(degree)
Figure 1: XRD pattern of Fe2O3@SiO2 nanocomposite
The SEM analysis revealed the formation of sheet like morphology of Fe2O3@SiO2
nanocomposite which overlapped randomly (Figure 2A-B). This basic morphology
consists of small Fe2O3 nanoparticles decorated on SiO2 surface. It was difficult to
examine the surface image using SEM analysis. So, it was further examined by HR-TEM
analysis.
(A)
(B)
6

(C)
(D)
Figure 2: (A-B) SEM (C-D) TEM images of Fe2O3@SiO2 nanocomposite
The shape and size of the nanoparticles was further studied by HR-TEM analysis.
The HR-TEM results indicated the formation cluster like Fe2O3@SiO2 nanocomposite. It
also observed that most of Fe2O3 nanoparticles was dispersed on the surface of SiO2
(Figure 2C-D). But it was not in symmetric pattern. The size of the nanoparticles was
found in the range of 5.0 0.3 – 21.0 1.4 nm. The average size of the particles was
12.2 0.8 nm. It was supported by dynamic light scattering (DLS) study (Figure 2S, SI).
The EDX analysis was carried out for further evidence of Fe2O3@SiO2 nanoparticles.
This analysis showed that weight % of O, Si and Fe are 62.28, 33.81 and 3.91 and atomic
% is 75.34, 23.30 and 1.36 respectively. It strongly supported the presence of Fe, O and
Si elements respectively in nanocomposite (Figure 3S, SI).
From the literature, it was found that the H2O2 is used as oxidant in ipso-
hydroxylation reaction.15, 17 Different type strong bases, ligand were used for activated
the H2O2 in nucleophilic substitution. But there are some disadvantages in using strong
bases and drastic reaction condition. To avoid such condition a very simple, economic,
green easy method was used for oxidation of phenylboronic acid to phenols without using
7

H2O2. So, it has a significant scope in utilization of Fe2O3@SiO2 catalyst for ipso-
hydroxylation reaction in water.
3.2. Optimization of reaction condition
Further optimization was carried out in water at temperature 50ºC in presence of air for
conversion of phenylboronic acid is considered as model system. The optimization results
are depicted in Table 1. Initially the amount of the catalyst was optimized. In this study,
the mount of catalyst was varied from 1.0 to 5.0 mg in presence of water at 50ºC. It was
observed that the performance of the reaction was best when 4 mg of catalyst was used.
The yield was found 98% in 2 hr at 50ºC. The reaction was carried out with a mild
condition. As the results, lesser toxic, eco-friendly, simple, cost effective method was
observed with excellent yield. This makes this ipso-hydroxylation as one of the cleanest
and greenest alternative protocol.
Table 1: Optimization of amount of Fe2O3@SiO2 catalyst in presence of water at 50ºC.
Sl No
Amount of catalyst ( mg) Time (hr)
Yield (%)
1
2
3
4
5
1.0
2.0
3.0
4.0
5.0
8
5
5
2
2
70
92
94
98
98
Moreover, the reaction condition was optimized further by changing the other
condition like catalyst/solvent/base etc. (Table 2). We tried different type of solvent like
methanol, butanol, water, ethanol etc. Here, the water was found the best solvent in this
system. After optimization, the reaction was carried out in presence of different electron
8

donating and withdrawing group as well as hetero atom, aliphatic, benzene diboronic acid
and arylboronic acid.
Further the reaction was carried out without catalyst. It was observed that no
product was formed without the catalyst. So, phenol was not formed in presence water
only in this reaction. Further reaction was carried out in anhydrous condition. The
product was formed in this experiment. But yield was very low i.e. 41%. The ipso-
hydroxylation reaction also carried out in inert condition also. In such case, no product
was formed. It indicated that oxygen from air may participate in formation of phenol
along with water in this study 22.
Table 2: Optimization of solvent in presence of 4 mg of Fe2O3@SiO2 catalyst in water
and in formation of phenol from phenylboronic acid
Sl No
Solvent
Time (hr)
Yield (%)
1
2
3
4
5
CH3OH
C2H5OH
C4H9OH
H2O
2
2
2
2
2
55
60
75
98
95
H2O : CH3OH
As per our protocol, the reactions were carried out very smoothly and converting various
substrates of electron-donating and withdrawing groups bearing phenylboronic acids to
phenols with very good to excellent yield (Table 3) in mild reaction condition.
Table 3: Oxidation of different boronic acid a
OH
OH
B
OH
i) Fe2O3@SiO2
R
R
ii) H2O/O2 iii) 50 0C
9

Entry
1
R
Time (hr)
Yield bc
98
H
2
2
3
4
3
4
4
3
4
5
3
5
3
4
4
2
4-Cl
96
3
4-Br
95
4
4-OMe
3-Me-4-OMe
4-t-Butyl
3-OMe
3-NO2
91
5
93
6
95
7
90
8
94
9
2-NO2
93
10
11
12
13
14
15
4-NO2
92
4-CHO
1- Pyrene
4-Dibenzofuran
2-9H-Fluoren
90
88
90
90
6-2,3-
Dihydrobenzo[b][1,4]dioxin
91
16
17
18
2-OH
3-OH
3
3
4
86
89
88
4-OH-2-mercapto
pyrimidine
19
20
1-Octyl
3
3
92
Cyclohexyl
91
b
c
a Reaction conditions: phenylboronic acid (1 mmol), Fe2O3@SiO2 (4 mg), Water (4 ml) Isolated yield.
All compounds are characterized by 1H & 13C NMR spectroscopy
It was observed that substrate containing electron withdrawing groups were more
efficient than electrons donating groups in hydroxylation reaction (Table 3, Entry 1-11).
Moreover, single aryl ring system boronic acid is more effective then the double/triple
10

phenyl ring system of boronic acid in terms of conversion to phenols with respect to time
and yield (Table 3, Entry 12-15). Further, the hydroxylation was carried out for diboronic
acid, heterocyclic ring and aliphatic or aliphatic cyclic system (Table 3; Entry 16-20). In
case of phenyldiboronic acid the reaction was carried out with 1,2-phenyldiboronic acid
(Table 3; Entry 16) and 1, 3-phenyldiboronic acid (Table 3; Entry 17) with same reaction
condition. In both cases product was formed with 86% yield of 1, 2-dihydroxybenzene
and 89% of 1,3-dihydroxy benzene respectively. The lower yield of 1,2-dihydroxy
benzene may be due to presence of two bulky group[-B(OH)2] in 1,2 position. So, it is
clear that overall yield of the product is comparatively low if the reactant is a diboronic
acid. Another product i.e. 4, 6-dihydroxy-2-mercapto pyrimidine (Table 3, Entry 18) was
formed from respective diboronic acid with moderate yield (88%). The presence of
heteroatom ring system has no significant role in this study. In case of aliphatic chain or
cyclic system (Table 3, Entry 19-20) high yield was observed (91-92%). The aliphatic
boronic acids are easily converted to respective alcohol.
Till today, there is no earlier report on ipso-hydroxylation using such a mild,
simple, eco-friendly, green, efficient and economic reaction condition using Fe2O3@SiO2
in presence of water and air. Therefore, this seems to be a very efficient protocol with a
wide range of substrate scope for ipso-hydroxylation of phenylboronic acids to phenols.
All the 1H and 13C NMR analysis data are reported in scheme 1S
The recyclability of Fe2O3@SiO2 nanoparticles was tested by considering
phenylboronic acid as model substrate in ipso-hydroxylation reaction. The recirculation
of catalyst was done by simple filtration method. The recovered catalyst was wash with
water and water ethanol mixed solvent (1:1). Then the recovered catalyst reused for
11

further reaction. It was confirmed that efficiency remain almost same after five times
recycle of catalyst (1st recycle 98%, 2nd recycle 97% and 3rd recycle 96%, 4th recycle 94%
and 5th recycle 95% phenylboronic acid was obtained) (Figure 4S, SI). After completion
of the reactions, products were extracted with diethylether and Fe2O3@SiO2 separated by
filtration and washed with water/ethanol and reused. Thus we can consider Fe2O3@SiO2
as a reusable heterogeneous catalyst. The TEM and XRD image showed that the
morphology and size distribution of the Fe2O3@SiO2 nanocatalyst remain almost same
after use of 5th cycle of catalytic reaction [Figure 5S A-B, SI].
The reusability of the catalyst further investigated with precise evidence through N2
adsorption–desorption study. It was found that the BET surface area and total pore
volume of Fe2O3@SiO2 was 6.174 m2/g and 0.1143 m3/g respectively for the fresh
catalyst. Moreover, it was found that the total specific surface area of the catalysts after
5th cycle decrease significantly to 134 from 223 m2 g−1 of fresh catalyst [Figure 6S, SI].
The reduction of the surface area of the catalyst may be due to the partial degradation of
the support. The adsorption–desorption hysteresis loop of the catalyst shifted in the range
P/P0 = 0.30 and 0.90 to P/P0 = 0.45 and 0.84 used after the 5th run respectively. The
changed of the loop of the curve may be due to the change in the structure of pores. The
BJH pore size distribution curve of the catalyst after 5th cycle shows a slight widening of
the distribution pattern compared to fresh catalyst [Figure 7S, SI]. However, it is strongly
supported that there is no loss of efficiency of the catalyst after 5th recycle.
The extract mechanism of the ipso-hydroxylation of phenylboronic acid is not known.
Therefore we proposed a plausible mechanism for ipso-hydroxylation of phenylboronic
acid to phenol in presence of Fe2O3@SiO2 (Scheme 1). The reaction was take place via
12

oxidative addition followed by reductive elimination of the boronic acid 21 in presence of
H2O. For further evidence, the preliminary mechanistic study was carried using isotopic
labeled water (H2O18) was performed. When the reaction was carried out using H2O18 as
solvent under optimal condition incorporation of O18 in phenol was observed [Scheme
2S]. So, it is observed that the oxygen source of phenol due to presence of water in the
reaction mixture. It is also strongly supported by the reported data 22-24. But, there may be
a possibility to participate oxygen from the air in formation of phenol. The details of
mechanism of the reaction are yet to study. Moreover broaden the scope of the substrate
will be done. The reaction was occurs on the surface of the catalyst. After 5th cycle there
is no significant change on the surface of the catalyst.
Ar-B(OH)2
ArOH
(HO)2B
Ar
Water/O2
Ar
OH
H2O
HB(OH)2
(HO)2BO
Ar
= Fe2O3 @SiO2
Scheme 1: Plausible mechanism in ipso-hydroxylation of phenylboronic acid
From the literature it was found that, the phenol can be synthesized using various
methods with different reaction condition [Table 4]. It is compared with reported result 25-
30. But this is the simplest, easy, eco-friendly method for synthesis of phenol from
13

phenylboronic acid in water at 50ºC. Moreover there is no any hazardous chemical like
H2O2 was used in this study. This is the novelty of this study.
Table 4: A comparison between ‘green-ness’ among catalyst/reagents in the
hydroxylation of phenylboronic acid to phenol with reported data and present work
Sl No Catalyst
Oxidant
O2
H2O2
30% H2O2(0.2ml)
30% H2O2(0.2ml)
Time (min)
Yield (%)
Reference
25
1
2
3
4
5
6
8
N2H4/ Cs2CO3
60
5
94
97
93
98
95
96
98
26
27
28
29
30
Urea/MeOH
Biosilica
WERSA
5
5
NH4HCO3
Cu2O
Fe2O3@SiO2
30% H2O2(1.1ml) 120
30% H2O2 10
H2O/ O2 from air 120
Present
work
4. Conclusions
A simple efficient and inexpensive process of biosynthesis of Fe2O3@SiO2
nanocomposite was developed using Zanthoxylum rhetsa. The supporting agent i.e. SiO2
extracted from rice paddy straw which is a waste material. Here, we have developed a
very simple, green, mild and eco-friendly protocol for ipso-hydroxylation of arylboronic
acids to phenols without using H2O2 as oxidant in presence of biogenic Fe2O3@SiO2
nanocatalyst and air at 50ºC. It is very simple, cost effective and compatible with various
electron-donating and withdrawing groups. Further, there is lots of prospect and have
significant advantages made in presence of Fe2O3@SiO2 a very adaptable and
competitive catalyst system. So, it can be considered as clean and safer alternative for
various other reactions system as well as in chemical industry in near future
Acknowledgement
14

The authors thank Director, CSIR-North East Institute of Science & Technology, Jorhat,
Assam for valuable advice.
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Highlights
• Biosynthesis of Fe2O3@SiO2 nanoparticles using Zanthoxylum rhetsa
• A highly efficient protocol for ipso-hydroxylation of phenylboronic acid to
phenols
•
The reactions were carried out without using strong base and hazardous organic
solvent.
• A new avenue for ipso-hydroxylation of phenylboronic acid in water.
18

Graphical Abstract
Biogenic synthesis of Fe2O3@SiO2 nanoparticles and its application in ipso-hydroxylation of
phenylboronic acid to phenols in presence of water is reported here.
Zanthoxylum rhetsa
FeCl3.6H2O
Paddy straw
OH
OH
B
OH
i) Fe2O3@SiO2
R
R
ii) H2O/O2 iii) 50 0C