An efficient base and H2O2 free protocol for the synthesis of phenols in water and oxygen using spinel CuFe2O4 magnetic nanoparticles

Article abstract of DOI:10.1080/00958972.2020.1802437

An efficient base and H₂O₂ free protocol was used for the synthesis of phenols from boronic acids using biogenic CuFe₂O₄ magnetic nanoparticles as catalyst at room temperature in water and oxygen. The catalyst was prepared using the flowers of Lantana camara. The size of the nanoparticles was 4.27 nm. Base free and ligand free protocol, less time, excellent yields, room temperature, biogenic synthesis of the catalyst, use of O₂ as an environmentally friendly oxidant are the advantages of the present protocol. The recyclability of the catalyst was for 5 cycles without loss of magnetic property or catalytic activity.

Full text of DOI:10.1080/00958972.2020.1802437

Journal of Coordination Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
An efficient base and H2O2 free protocol for the
synthesis of phenols in water and oxygen using
spinel CuFe2O4 magnetic nanoparticles
Rituparna Chutia & Bolin Chetia
To cite this article: Rituparna Chutia & Bolin Chetia (2020): An efficient base and H2O2 free
protocol for the synthesis of phenols in water and oxygen using spinel CuFe2O4 magnetic
nanoparticles, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2020.1802437
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JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2020.1802437
An efficient base and H2O2 free protocol for the synthesis
of phenols in water and oxygen using spinel CuFe2O4
magnetic nanoparticles
Rituparna Chutia and Bolin Chetia
Department of Chemistry, Dibrugarh University, Dibrugarh, Assam, India
ABSTRACT
ARTICLE HISTORY
Received 24 March 2020
Accepted 13 July 2020
An efficient base and H2O2 free protocol was used for the synthe-
sis of phenols from boronic acids using biogenic CuFe2O4 mag-
netic nanoparticles as catalyst at room temperature in water and
oxygen. The catalyst was prepared using the flowers of Lantana
camara. The size of the nanoparticles was 4.27 nm. Base free and
ligand free protocol, less time, excellent yields, room temperature,
biogenic synthesis of the catalyst, use of O2 as an environmentally
friendly oxidant are the advantages of the present protocol. The
recyclability of the catalyst was for 5 cycles without loss of mag-
netic property or catalytic activity.
KEYWORDS
Arylboronic acids; magnetic
nanocatalayst; heteroge-
neous catalysis; easy
recyclability; green synthesis
1. Introduction
Phenol and its derivatives have received attention as it is the major constituent of vari-
ous pharmaceuticals [1, 2], polymers [3], natural antioxidants [4], etc. They also play an
important role in the prevention and treatment of various diseases. Phenolic com-
pounds obtained from natural products exhibit wide biological activities including
anticancer, anti-allergic, antioxidant [5–8], etc. Given the importance of phenols, a
wide range of reactions have been used to prepare them. Phenols are generally
CONTACT Bolin Chetia
bolinchetia@dibru.ac.in
Department of Chemistry, Dibrugarh University, Dibrugarh
786004, Assam, India
Supplemental data for this article is available online at https://doi.org/10.1080/00958972.2020.1802437.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
R. CHUTIA AND B. CHETIA
synthesized [9] by nucleophilic substitution of an aryl halide with catalyst like palla-
dium, copper, etc. But these reactions suffer from several disadvantages like poor func-
tional group compatibility, harsh reaction conditions, and less substrate scope.
Recently various transformations of boronic acids, oxidative C-B bond cleavage and
oxidative hydroxylation (ipso-hydroxylation) of aryl boronic acids are used for prepar-
ation of phenols. Literature cited ipso-hydroxylation of boronic acids to phenols using
various methods with different catalysts and reaction conditions. Various oxidants
were cited in literature for the synthesis of phenols and its derivatives, which includes
ozone [10], m-chloroperoxybenzoic acid [11], sodium perborate [12], hydroxylamine
[13], tert-butyl hydroperoxide [14], N-oxide [15], H2O2 [16–19], etc.
The desire for eco-friendly, greener, simple and easy reaction methodologies [20]
has led to enormous advancement [21]. Compared to the other oxidants and reaction
conditions, the use of molecular oxygen and air have been well established as envir-
onmentally friendly and inexpensive oxidants for oxidations reactions [22, 23]. Wang
et al. [24] used CuSO4-catalyzed aerobic oxidative hydroxylation of arylboronic acid to
phenols. Yang et al. [25] synthesized CuFe2O4 magnetic nanocatalyst for the ipso-
hydroxylation of aryl boronic acid using air and oxygen. The easy recyclability of the
catalyst from the reaction media with the use of an external magnet added as an
advantage compared to previously reported methods but the reaction proceeded with
the addition of base and took about 24 h for completion. A temperature of 40–50 ꢀC
was also favorable for the reaction. Thus a mild protocol for the synthesis of phenols
was necessary.
Looking at the immense applications of phenols we have also performed oxidative-
hydroxylation (ipso-hydroxylation) previously using CuFe2O4 magnetic nanoparticles
(MNPs) which were prepared by co-precipitation method [26]. The use of NaBH4 as a
reducing reagent in the preparation of the catalyst and the use of H2O2 as an oxidizing
agent in the process of ipso-hydroxylation prevent it from being as a green protocol.
Thus, we have modified our method and report herein a green pathway for the synthesis
of the catalyst as well as for ipso-hydroxylation. We obtained nanoparticles with smaller
size and better catalytic activity in comparison to earlier reported catalysts.
We have synthesized here biogenic CuFe2O4 MNPs using flowers of Lanatana
camara under mild reaction conditions. The nanoparticles are then used for ipso-
hydroxylation of aryl boronic acids to phenols at room temperature within a very short
reaction time without the use of a base. The presence of different phenolic com-
pounds in the flowers might be mainly responsible for efficient ipso-hydroxylation
with excellent yields.
Lantana camara is an aromatic perennial shrub with a wide range of flower color
viz. red, white, yellow, pink, violet found in many countries of the world. It is mainly
used as an ornamental plant in hedges of public and private gardens. In the present
study the flower extract of Lantana camara is used as a reducing agent for the synthe-
sis of CuFe2O4 MNPs. This plant also has medicinal value [27, 28], a rich source of
many bioactive molecules, containing many triterpenes, steroids and flavonoids [29,
30]. The flower extracts mainly contained higher levels of carbohydrates compared to
the leaves. Moreover, ontogenic variation in secondary metabolites such as phenolics,
anthocyanins, and proanthocyanidins in Lantana camara have also been reported [31].

JOURNAL OF COORDINATION CHEMISTRY
3
Table 1. Comparison with other reported CuFe2O4 nanocatalysts prepared using plants.
Reaction
temperature
Annealing
Plant
Method
(ꢀC)/time (h)
temp (ꢀC)/time (h)
Size (nm)
50-200
Reference
[32]
Hibiscus rosa sinensis
Conventional
combustion method
Biogenic
Green combustion route
Sol-gel method
Biogenic
rt, several hours
1100, 4
Neem
rt, 1
rt, several hours
75, 12
800, 4
500, 5 min
600, 4
19.7
12
14
[33]
[34]
[35]
Jatropha oil
Tragacanth gum
Lantana camara
flowers
rt, 1
300, 2
4.27
This work
The presence of high phenolic content in this plant might be mainly responsible for
its reducing character. Thus, owing to importance of this plant we tried to use it for
the preparation of CuFe2O4 MNPs.
2. Experimental
2.1. General information
All reagents of analytical grade were used without purification. Ferric chloride (FeCl3),
cupric acetate monohydrate [(CH3ꢁCOO)2CuꢁH2O], sodium hydroxide (NaOH), ethanol,
diethylether, anhydrous Na2SO4 and different arylboronic acids were purchased from
commercial suppliers. By using thin layer chromatography on silica gel plates (60 F254
the progress of the reaction was monitored. The products were confirmed by H NMR
and 13C NMR spectroscopy.
)
1
2.2. Preparation of the catalyst
According to a literature survey, CuFe2O4 MNPs have been synthesized using different
plants by many researchers [32–35]. The prepared catalyst was compared with other
reported CuFe2O4 catalyst synthesized by using different plant extracts and it was
found that our catalyst required less annealing temperature and was cost efficient
(Table 1).
For the preparation of the catalyst we used the flowers of Lantana camara which
were collected from the Sivasagar District of Assam, India. The nanocatalyst was pre-
pared in a similar manner to our previously reported work [36, 37].
3. Results and discussion
3.1. Characterization of the catalyst
The biogenic CuFe2O4 MNPs were characterized by XRD diffraction (Figure 1). The
sharp diffraction peaks from the XRD analysis reveal the crystalline nature of the
MNPs. The diffraction peaks at 2h ¼ 24.20ꢀ, 30.25ꢀ, 31.66ꢀ, 33.19ꢀ, 35.66ꢀ, 38.74ꢀ,
40.90ꢀ, 45.39ꢀ, 49.51ꢀ, 54.1ꢀ, 56.51ꢀ, 57.62ꢀ, 62.47ꢀ and 64.04ꢀ correspond to planes
(111), (202), (220), (113), (311), (222), (004), (400), (331), (422), (333), (511), (404) and
(440), respectively (JCPDS 34-0425). The diffraction peaks with the Miller indices sug-
gest inverse tetragonal spinel structure of the MNPs. Some additional peaks showing

4
R. CHUTIA AND B. CHETIA
Figure 1. Powder XRD pattern of the synthesized CuFe2O4 MNPs.
traces of CuO were also noticed which corresponds to JCPDS card No. 48-1548. From
the XRD analysis, distance between the planes (d) can also be found which is given by
using the Bragg’s equation (1):
k ¼ 2dsinh
(1)
where k is the wavelength of X-ray and h represents the Bragg’s reflection angle. The
value of “d” calculated from the above equation was 0.249 nm.
From the SEM images (Figure S1) monodispersity of the nanocrystals was observed.
There was slight aggregation of the nanoparticles as seen from the SEM images. The
Energy Dispersive X-ray (EDX) spectrum (Figure 2) shows the presence of copper, iron
and oxygen in the nanoparticle. As detected from the EDX analysis the maximum
intensity was found with Cu ion with the second and third intensity peaks of Fe and
O, respectively. The spectrum provided the final confirmation of CuFe2O4 nanopar-
ticles. The inset clearly shows the atomic and weight percentage of CuFe2O4 with cor-
responding stoichiometry values of existing Fe, Cu and O elements.
From the TEM image (Figure 3(a)) the size and morphology of the nanoparticles
were determined. The selected area electron diffraction (SAED) pattern of the CuFe2O4
MNPs showed bright circles which indicated the polycrystalline nature of the nanopar-
ticles (Figure 3(b)). Moreover, the crystallographic planes viz., (111), (202), (220), (113),
(311), (222), (004), (400), (331), (422), (333), (511), (404) and (440) were clearly indexed
in this SAED pattern. The HR-TEM image (Figure 3(c)) shows the fringe separations of
4.09 Aꢀ and 2.79 Aꢀ, in agreement with (111) and (311) planes; this also confirmed the
polycrystalline nature of the synthesized MNPs as the orientations of planes are in

JOURNAL OF COORDINATION CHEMISTRY
5
Figure 2. EDX image of the CuFe2O4 MNPs.
Figure 3. (a) TEM images, (b) corresponding SAED pattern of the nanoparticles, (c) HR-TEM image
of selected region of CuFe2O4 MNPs and (d) size distribution of the CuFe2O4 MNPs.

6
R. CHUTIA AND B. CHETIA
Figure 4. VSM of CuFe2O4 MNPs (inset shows the enlarged VSM plot).
different directions. From the size distribution histogram as determined by a large
number of particles of TEM image the size of the nanoparticle was 4.27 nm
(Figure 3(d)).
By using a vibrating sample magnetometer (VSM), magnetic study was carried out
at room temperature for the biogenic CuFe2O4 MNPs (Figure 4). An S-type plot was
shown by the M-H curve. The coercivity (Hci) of 159.05 G, magnetization (Ms)
12.932 emu/g and retentivity (Mr) 2.1927 emu/g were found from the VSM analysis.
These data confirmed that the nanoparticles were ferromagnetic. This ferromagnetic
property of the nanoparticles helped in the easy recyclability and reuse of the catalyst
several times. The inset in Figure 4 shows the enlarged hysteresis loop of the
CuFe2O4 MNPs.
3.2. Synthesis of phenols by using CuFe2O4 MNPs
The synthesized nanoparticles were used for ipso-hydroxylation of aryl boronic acid to
phenols. Arylboronic acids react in the presence of water and molecular oxygen to
give phenols in good to excellent yield, without a toxic oxidizing agent or base
(Scheme 1).
Our first aim was to optimize the amount of catalyst and the source of -OH under
different conditions so that it can be applied to a variety of substrates. The optimiza-
tion was done using 4-methoxy phenyl boronic acid as the model substrate (Table 2).

JOURNAL OF COORDINATION CHEMISTRY
7
Scheme 1. General scheme of ipso-hydroxylation of aryl boronic acids to phenols.
Table 2. Optimization of the catalyst and reaction conditions.a
Entry
Catalyst (mol%)
Reaction condition (rt)
Time (h)
Yield (%)b
1
2
3
4
5
1
3
6
6
6
O2
O2
O2
N2
Air
5
4
60
70
95
85
88
40 min
20
10
aReaction conditions: 4-methoxy phenyl boronic acid (0.20 mmol), 3 mL water, rt (27 ꢀC).
bIsolated yields.
Only 6 mol% of the catalyst was necessary for complete conversion to 4-methoxy phe-
nol. Moreover, the reaction proceeded smoothly with the use of O2 and H2O within a
short reaction time. The reaction required longer time when N2 gas was used (Table 2,
entry 4). By using only H2O, isolated product was obtained but the reaction took
about 10 h for completion (Table 2, entry 5). Thus, it was confirmed that both molecu-
lar O2 and H2O was necessary for the progress of the reaction.
After identification of the proper optimized conditions 16 different phenols were
synthesized from aryl boronic acids and aryl boronic esters (Table 3). Both electron-
withdrawing and electron-donating groups and the position of the substituent had lit-
tle effect on the reaction conditions. The heteroarylboronic acids also gave excel-
lent yields.
We extended our study to ipso-hydroxylation of boronic esters (Table 4).
Heteroarylboronic acid esters were conveniently converted to their corresponding phe-
nols and alcohol in a short reaction time.
The ipso-hydroxylation of arylboronic acid to phenol was compared with other
reported catalysts (Table 5). Our catalyst was superior and greener than other
reported catalysts.
3.3. Mechanism
The exact mechanism for the formation of phenols by ipso-hydroxylation is unknown.
Based on the previously reported mechanisms using a solid support in organic synthe-
sis we provide a brief mechanistic pathway [45, 46] (Figure 5). When the reaction was
carried out in the presence of H2O, it required longer reaction time (Table 2, entry 5),
confirming that O2 was necessary for the smooth and fast progress of the reaction.
Therefore we tried to provide a brief mechanistic pathway using H2O and molecular
O2 as the green oxidizing agent in the reaction.
Initially, the boron atom adopts sp2 hybridization in organoboronic acids [47] and
gets activated by coordinating on the surface of the CuFe2O4 as Lewis acidic sites. The
boron group thus changes from being a low reactive electrophile into a moderately

8
R. CHUTIA AND B. CHETIA
Table 3. CuFe2O4 MNPs catalyzed ipso-hydroxylation of aryl boronic acids.a
aReaction conditions: arylboronic acid (0.20 mmol), CuFe2O4 MNPs (6 mol%) in 3 mL water
and molecular O2, rt (27 ꢀC).
bIsolated yields.
Table 4. Ipso-hydroxylation of boronic esters.a
S. No.
Substrate
Product
Time (min)
40
Yield (%)b
95
1.
2.
3.
45
50
90
90
aReaction conditions: arylboronic ester (0.20 mmol), CuFe2O4MNPs (6 mol%) in 3 mL water and molecular O2,
rt (27 ꢀC).
bIsolated yields.

JOURNAL OF COORDINATION CHEMISTRY
9
Table 5. Comparison of ipso-hydroxylation with reported catalysts.
Catalyst
Time (h)
Catalyst (mol%)
Yield (%)
Recycle
Reference
CuSO4
Photocatalyst a-Fe2O3
NH2OH
Cu2O nanoparticles
UNLPF-12
3
5
26
5
10
25
150
34
90
90
68
95
93
No
No
No
Yes
No
[24]
[38]
[13]
[39]
[40]
8
0.5
N
O
42
1
97
No
[41]
Cu NPs-EA
Light
Photo organocatalytic
8
8
72
16.7
—
20
6
91
92
76
97
Yes
No
No
[42]
[43]
[44]
CuFe2O4 MNPs
45 min
Yes
This work
Figure 5. Proposed mechanism for the formation of phenols by ipso-hydroxylation.
reactive electrophile due to its coordination to the acidic sites on the surface of the
catalyst. The addition of O2þH2O generates a tetravalent boron “ate” complex and
induces rehybridization to form sp3 boron in the –O2H oxidative pathway. Due to the
high electron density on boron and increased steric crowding in the “ate” complex
the C-B bond dissociates and subsequent aryl migration to the adjacent acceptor oxy-
gen with retention of configuration takes place with elimination of H2O. This H2O

10
R. CHUTIA AND B. CHETIA
Figure 6. (a) Recyclability of CuFe2O4 MNPs. (b) XRD of the recycled catalyst taken after the fifth
cycle. (c) TEM image of recyclable CuFe2O4 MNP’s. (d) SAED pattern (fifth cycle).
molecule than approaches the intermediate (a) and hydrolysis step occurs to form the
final phenol product.
3.4. Recyclability
Recyclability is a major advantage of a heterogeneous catalyst. The prepared catalyst
was easily recyclable with the help of an external magnet without filtration or tedious
workup (Figure 6). The catalyst was easily recyclable up to the fifth cycle without sig-
nificant loss in catalytic activity. The sharp XRD diffraction peaks taken after the fifth
cycle depict that the crystalline nature of the MNPs was retained in the recycled cata-
lyst. The TEM image (Figure 6(c)) taken after the fifth cycle showed no change in the
morphology, and the bright rings in the SAED pattern (Figure 6(d)) of the recycled
catalyst also represent the crystallinity of the nanocatalyst. The slight loss in catalytic
activity after the fifth cycle might be due to loss of the nanoparticles due to the recy-
cling process.
4. Conclusion
An environmentally friendly, biogenic route has been designed for the synthesis of
CuFe2O4 MNPs with 4.27 nm size using the flowers of Lantana camara. The catalyst
worked without the use of a toxic oxidizing agent such as H2O2 or harsh reaction con-
ditions. Only water and molecular O2 were necessary for the synthesis of phenols from

JOURNAL OF COORDINATION CHEMISTRY
11
arylboronic acid at room temperature within a short reaction time. The catalyst proved
to be superior compared to reported catalysts. This is a green route for the synthesis
of phenols with high yield products both from environmental and economic point
of view.
Acknowledgement
The authors gratefully acknowledge DST-SERB (Project No. SB/FT/CS-161/2012) for financial
assistance, UGC-SAP, CSIC Dibrugarh University for SEM-EDX, XRD analysis, IIT Guwahati for VSM
analysis and SAIF, NEHU Shillong for spectral data.
Disclosure statement
No potential conflict of interest was reported by the authors.
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