Highly efficient, recyclable and alternative method of synthesizing phenols from phenylboronic acids using non-endangered metal: Samarium oxide

Article abstract of DOI:10.1016/j.inoche.2021.108749

Oxidation of phenylboronic acid to phenol is one of the important industrial processes and it is generally employed in the plastic, explosive and drug manufacturing industries. Over the past decades, numerous efficient methods have been described for the generation of phenols from phenylboronic acids in the presence of oxidant. However, these methods suffered from various limitations, including the use of expensive, toxic reagents and sophisticated protocol to synthesise the phenols. Additionally, some of these reported literatures employed endangered metals, in which mankind is facing the risk of limited supply of these elements in 20 years’ time from now. As such, a viable alternative and green method for achieving organic synthesis is highly sought after by the chemists of today. Herein, we report for the first time a facile, efficient and alternative method in the preparation of phenols from phenylboronic acids using non-endangered metal as catalyst. In all cases, all phenols were afforded in satisfactory yields (81–96%) by employing column-free method. In the recyclability study, the Sm₂O₃ catalyst was found to possess good catalytic performance, even after being reused for five consecutive times (96–91%). In addition, SEM result revealed that the morphology of the recycled Sm₂O₃ catalyst was well preserved after five successive uses, which indicate no observable changes occurred in the recovered catalysts. As a final note, the current method is anticipated to be useful for industries manufacturing chemical intermediates as it provides an alternative method of catalysis by using a non-endangered metal in organic transformations.

Full text of DOI:10.1016/j.inoche.2021.108749

Inorganic Chemistry Communications 130 (2021) 108749
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Short communication
Highly efficient, recyclable and alternative method of synthesizing phenols
from phenylboronic acids using non-endangered metal: Samarium oxide
Hanis Mohd Yusoffa, Prasana Devi Bala Chandrana, Fatin Amira Binti Sayutib, Su-Yin Kanc,
,b,d,*
Siti Aisha Mohd Radzib, Fu-Siong Julius Yongb, Oon Jew Leea, Poh Wai Chiaa
a Faculty of Science and Marine Environment, Universiti Malaysia Terengganu, 21030 Terengganu, Malaysia
b Institute of Marine Biotechnology, Universiti Malaysia Terengganu, 21030 Terengganu, Malaysia
c Faculty of Health Sciences, Universiti Sultan Zainal Abidin, 21300 Terengganu, Malaysia
d Eco-Innovation Research Interest Group, Faculty Science and Marine Environment, Universiti Malaysia Terengganu, 21030 Terengganu, Malaysia
A R T I C L E I N F O
A B S T R A C T
Keywords:
Oxidation of phenylboronic acid to phenol is one of the important industrial processes and it is generally
employed in the plastic, explosive and drug manufacturing industries. Over the past decades, numerous efficient
methods have been described for the generation of phenols from phenylboronic acids in the presence of oxidant.
However, these methods suffered from various limitations, including the use of expensive, toxic reagents and
sophisticated protocol to synthesise the phenols. Additionally, some of these reported literatures employed en-
dangered metals, in which mankind is facing the risk of limited supply of these elements in 20 years’ time from
now. As such, a viable alternative and green method for achieving organic synthesis is highly sought after by the
chemists of today. Herein, we report for the first time a facile, efficient and alternative method in the preparation
of phenols from phenylboronic acids using non-endangered metal as catalyst. In all cases, all phenols were
afforded in satisfactory yields (81–96%) by employing column-free method. In the recyclability study, the Sm2O3
catalyst was found to possess good catalytic performance, even after being reused for five consecutive times
(96–91%). In addition, SEM result revealed that the morphology of the recycled Sm2O3 catalyst was well pre-
served after five successive uses, which indicate no observable changes occurred in the recovered catalysts. As a
final note, the current method is anticipated to be useful for industries manufacturing chemical intermediates as
it provides an alternative method of catalysis by using a non-endangered metal in organic transformations.
Non-endangered metal
Organic transformations
Samarium oxide
Recyclable catalyst
Phenols
1. Introduction
involves a green oxidation process that is efficient and eco-friendly is
highly sought after among the scientists and industrial players alike.
Oxidation reaction is considered as one of the most fundamental
reactions in chemistry [1–3]. In particular, the oxidation of cumene and
decomposition of cumene peroxide to yield phenol, is one of the com-
mon strategies in the industrial preparation of phenol and acetone [4].
In the chemical industry, phenols are widely used as the starting mate-
rials in the manufacturing of pharmaceuticals, polymers, natural prod-
ucts and agrochemicals [5,6]. Unfortunately, the cumene process is a
multistep process and encompasses the use of high temperature to
obtain the phenol. This process has also several other drawbacks such as
low yield and high operational cost [2,4]. Furthermore, it is known that
oxidation process is commonly unstable and this may lead to the pro-
duction of environmentally harmful by-products. As such, a viable
alternative route to phenols synthesis is urgently needed, especially if it
Over the years, enormous literatures were generated based on the
use of the phenylboronic acids to produce phenols. These methods were
capable to facilitate efficient oxidation of phenylboronic acids to syn-
thesize phenols, while producing fewer toxic by-products into the
environment [5–7]. Additionally, the use of hydrogen peroxide (H2O2)
as oxidant offers various benefits, which includes low cost, high oxygen
content, eco-benign and safer method of oxidation [8–11]. However,
most of these methods require the utilization of suitable catalysts. In
some cases, the utilization of transition metals and unsustainable
methods for facilitating the oxidation of phenylboronic acids to phenols
were also reported [6,12–15].
According to a survey, the technological development in industries
are not neutral in the use of all elements. Certain metals such as
* Corresponding author.
E-mail address: pohwai@um.edu.my (P.W. Chia).
https://doi.org/10.1016/j.inoche.2021.108749
Received 4 April 2021; Received in revised form 2 June 2021; Accepted 13 June 2021
Available online 15 June 2021
1387-7003/© 2021 Elsevier B.V. All rights reserved.

H.M. Yusoff et al.
Inorganic Chemistry Communications 130 (2021) 108749
palladium, copper, nickel and gold are favoured, contributing to their
fast depletion known as resource deficits. Considering the ill-effect
contributed by the unsustainable use of elements on our environment,
society and the economy, scientists have put forth a vital move to protect
these “endangered elements”. Elemental Sustainability is a philosophy
that is coined to protect these endangered elements, and at the same
time, encourage the balance use of elements in periodic table to achieve
industrial development and sustainable synthesis [16].
with hydrogen peroxide 30% wt/v (3 mL) as oxidant, and samarium
oxide (10 mmol) as catalyst. The mixture was then heated at about 80 ◦C
for 4 h. Product formation was monitored by using thin layer chroma-
tography (TLC). The reaction mixture was left to cool at room temper-
ature and the catalyst was separated from the reaction mixture by
filtration. Subsequently, the organic layer was separated, washed with
sodium bicarbonate solution and the resulting aqueous layer was
washed three times with ethyl acetate (3 × 10 mL). The combined
organic layers were concentrated under reduced pressure to obtain the
dried crude product. Lastly, the single pure product was afforded by
using the precipitation method. The recycled samarium oxide was
employed to synthesize different phenols under the same condition.
As part of our continuous effort in the search for efficient and sus-
tainable catalyst for organic transformations, herein, we would like to
demonstrate the use of samarium oxide (Sm2O3) as an alternative
method in achieving sustainable production of phenols via phenyl-
boronic acids in the presence of H2O2 (Fig. 1). Lately, the use of
lanthanide metals has gained much attention among scientists due to its
unique electron configuration, robustness and high catalytic activity of
surface structure in catalysing chemical processes [17]. One such
example is the recently developed samarium nanoparticles as sustain-
able catalysts in Pechmann and coupling reactions [18,19]. To date, our
group is the first to report on the utilisation samarium oxide to produce
phenols. The current method is of significant and useful in the chemical
industry for manufacturing chemical intermediates as it encompasses
the use of non-endangered metal for organic transformation.
3. Results and discussion
The Sm2O3 catalyst were characterized by XRD and SEM analyses as
shown in Fig. 2. The synthesized precipitates transformed from amor-
phous intermediate phase to crystalline Sm2O3 phase when calcined at
750 ◦C. The Sm2O3 phase was found to be cubic single phase without any
presence of secondary phase (Fig. S1). This highly crystalline Sm2O3
phase matched with Inorganic Crystal Structure Database (ICSD) 98-
001-2948. Based on the SEM image (Fig. S2), it can be observed that
most of the particles are spherical with a size distribution between 120
and 300 nm. In order to investigate the uniformity of element distri-
bution in Sm2O3, EDX mapping was carried out. The inset of Figure S2
show the elemental mapping of O and Sm, demonstrating homogeneous
distribution of Sm2O3 with high purity. FTIR spectrum as shown in
Fig. S3 indicated that the stretching vibrations of Sm3+-O are located at
877 cmꢀ 1, 522 cmꢀ 1 and 439 cmꢀ 1, respectively. The strong band at
1427 cmꢀ 1 was ascribed to the Sm-O-Sm deformation vibration whereas
the weak band at 3788 cmꢀ 1, 2323 cmꢀ 1 and 2968 cmꢀ 1 corresponded
to the stretching and bending vibrations of –OH. These weak –OH bands
were observed due to the marginal presence of water within the Sm2O3
nanoparticles.
2. Experimental
2.1. Chemicals and instrument
All chemicals and solvents utilized in this study were purchased from
Sigma-Aldrich Malaysia. They were used without purification unless
stated. The phase formation and nanostructure of Sm2O3 were per-
formed using an X-ray diffractometer (X’Pert Pro PW3040 MDP/Pan-
alytical) with Cu-K
α radiation source and a scanning electron
microscope (JEOL JSM-6360LA). The X-ray diffraction (XRD) pattern
was collected within 20–80◦ in with increment step size of 0.033◦. In
addition, a Bruker Nuclear Magnetic Resonance (NMR) spectrometer
was employed to analyze samples and all the spectra were recorded on
proton (1H) (400 MHz) and carbon-13 (13C) (100 MHz). All chemical
shifts (δ) were quoted in the NMR as parts per million (ppm). The mo-
lecular mass of the samples was analyzed over the Shimadzu QP2010SE
Gas Chromatography Mass Spectrometry (GC–MS). The values of all
molecular mass were recorded in spectra as unit of mass over charge
ratio (m/z).
In the optimisation study of reaction condition, a round bottom flask
(50 mL) were equipped with phenylboronic acid (1 mmol) as the model
substrate, hydrogen peroxide 30% (3 mL) as oxidant and Sm2O3 (10
mmol) as catalyst. The reaction mixture was subject to heating at 60 ◦C
for about 1 h. The formation of 3a was monitored using TLC analysis. At
this stage, about 54% reaction’s yield was observed for 3a after 1 h
(Table 1, entry 1). Increasing the reaction temperature has also
increased the yield of 3a (Table 1, entry 3). Furthermore, it was observed
that amount of Sm2O3 used could also affect the catalytic performance
on 3a synthesis. The increased amount of Sm2O3 has resulted a better
yield of 3a with 10 mmol Sm2O3 as the optimum amount of catalyst in
3a synthesis (Table 1, entry 7. In addition, different amounts of
hydrogen peroxide used also have an effect on the yield of 3a formation.
Laboratory result showed that 3 mL of H2O2 gave the best result in the
formation of 3a (96%), when employed for the oxidation of
2.2. Synthesis of Sm2O3 catalyst
The Sm2O3 nanoparticles were synthesized via hydrothermal method
starting from 99.9% Sm(NO3)3⋅6H2O. A Sm(NO3)3 solution was pre-
pared and mixed with oleic acid (OA) and tert-butylamine (TA) in a fixed
ratio of 1:1:1 for Sm:OA:TA. The clear homogeneous solution was
adjusted to pH 12 with NaOH. The mixture was transferred into a Teflon
lined stainless steel autoclave and heated at 200 ◦C for 72 h in an oven.
The obtained precipitate was washed with ethanol for several times
before calcination at 750 ◦C in a furnace to obtain the Sm2O3
nanoparticles.
2.3. General method for phenols synthesis
Phenylboronic acid was added to a round bottom flask suspended
Sm2O3, H2O2
80
B(OH)2
OH
°
C
R1
R1
Fig. 1. Conversion of phenylboronic acids to phenols using samarium oxide as
catalyst and hydrogen peroxide as oxidant.
Fig. 2. Recyclability experiment using 3a as a model product.
2

H.M. Yusoff et al.
Inorganic Chemistry Communications 130 (2021) 108749
substrates (3a-j). In all cases, all phenols were afforded in satisfying
yields (Table 2, entries 2–10) by using Sm2O3 as catalyst. Interestingly,
napthol was also able to be synthesized from the same procedure by
using a fused ring system, and the yield of the corresponding product
was found to be in 90% (Table 2, entry 10). In this work, the hydrogen
peroxide was chosen as the oxidant in the conversion of phenylboronic
acids to phenol due to the simplicity and clean profile of hydrogen
peroxide [29]. Furthermore, it is also noteworthy to report that the
phenols produced from this work was afforded via the precipitation
method. All synthesised phenols were characterized via the NMR and
GC–MS experiments. Overall, the current protocol was considered as
more superior than previous reported methods [20–28], as it uses a non-
endangered metal, solvent-free method and non-sophisticated protocol
in the synthesis of phenols (3a-j).
Table 1
The optimization experiment conducted by using phenylboronic acid to syn-
thesize 3a.
Entry
H2O2
(mL)
Sm2O3
Time
(h)
Temperature
(◦C)
Yielda
(%)
(mmol)
1
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
–
10
10
10
10
–
1
1
1
2
1
1
1
1
1
1
1
1
60
70
80
90
80
80
80
80
80
80
80
80
54
67
79
78
–
83
90
89
–
2
3
4
5
6
5
7
10
15
10
10
10
10
8
9
10
11
12
1.0
2.0
3.0
91
93
96
Next the reusability of the Sm2O3 catalyst was investigated after
separation from the crude reaction. In the recyclability test, our labo-
ratory result showed that the Sm2O3 catalyst is not only recoverable, but
also catalytically active even after reused for five consecutive times. As
illustrated in Fig. 2, the catalytic activity of the Sm2O3 was mostly
retained, with the desired products afforded in excellent yields
(91–96%) after five consecutive runs. In addition, the SEM result
(Fig. S4) revealed that the morphology of the recycled Sm2O3 catalyst
was well preserved which is comparable to Fig. S2 This indicates that
there were no observable changes occurred in the recovered catalyst
after five successive uses. Based on these results, the current protocol fits
the green requirement, since the current protocol promotes the use of
sustainable catalyst and the catalyst is catalytically active and reusable
as shown in the recyclability experiment [30–34].
a
Isolated yield of product 3a.
phenylboronic acid (Table 1, Entry 12). On the contrary, when Sm2O3
was used alone in the absence of H2O2, 3a was not formed and it was
quite clear that the H2O2 acted as oxidant in this reaction (Table 1, entry
9). Based on all the results on hand, it was determined that 3 mL of H2O2
and 10 mmol of Sm2O3 (Table 1, entry 12) were suffice to promote
oxidation of phenylboronic acid into phenol with excellent yield.
To widen the scope of our study, the optimized condition was applied
to synthesize different phenols, using different phenylboronic acids
bearing with the electron-withdrawing and donating groups as
Last but not least, the merit of this work was analyzed by comparing
the catalytic performance of current work to previous literatures in the
synthesis of phenol (3a). Based on Table 3, it was found that the catalytic
performance of current method is comparable to previous methods,
judging from 3a synthetic yield. Moreover, most of these reported
methods adopted the use of endangered metals as catalysts, toxic re-
agents and tedious protocol in the preparation of phenols from phe-
nylboronic acids. The use of non-endangered metal as catalyst is
significant for promoting a more sustainable and greener organic
transformations. This environmental-friendly catalyst holds promising
potential in both the chemical industry and academia in accomplishing
organic processes.
Table 2
Formation of phenols from phenylboronic acids with the aid of Sm2O3 as
catalyst.
Entry
1
Compound
3a
Substrate
Product
Yielda
(%)
96
2
3
3b
3c
94
4. Conclusion
95
In this work, a facile, efficient and the use of non-endangered metal
for synthesizing phenols from phenylboronic acids is reported. Various
benefits resulting from the use of Sm2O3 as catalyst have been identified,
4
5
3d
3e
92
93
Table 3
Analysis of the merits of current protocol in the synthesis of 3a by comparing its
6
7
3f
86
85
yield to previous literature.
Entry
1
Catalyst
Time
Yield
(%)
Reference
(hour)
3g
Sm2O3/ H2O2
1
96
Current
work
[20]
2
3
Copper nanoparticle biohybrid
C70 fullerene/Photocatalyst/O2/
CHCl3
6
90
99
12
[21]
8
9
3h
3i
81
83
4
5
6
Graphitic carbon nitride/Blue LED
Pd/Bentonite nanocomposite/H2O2
2,2-Methoxy-2-
6
95
94
76
[22]
[23]
[24]
0.25
72
phenylacetophenone/DIPEA/light
bulb irradiation
7
8
Pd/KB Polymeric nanocomposite
tert-Butyl hydrgen peroxide/
Potassium tert-Butoxide.
0.08
5
95
92
[25]
[26]
10
3j
90
9
Sodium sulphite/oxygen in air
Silica chloride/ H2O2/Acetonitrile
1
100
100
[27]
[28]
10
0.08
3

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CRediT authorship contribution statement
Hanis Mohd Yusoff: Conceptualization, Methodology, Investiga-
tion, Data curation, Writing - original draft. Prasana Devi Bala Chan-
dran: Conceptualization, Methodology, Investigation. Fatin Amira
Binti Sayuti: Conceptualization, Methodology, Investigation. Su-Yin
Kan: Conceptualization, Methodology, Investigation. Siti Aisha Mohd
Radzi: Data curation, Writing - original draft. Fu-Siong Julius Yong:
Data curation, Writing - original draft. Oon Jew Lee: Conceptualization,
Methodology, Investigation, Data curation, Writing - original draft. Poh
Wai Chia: Conceptualization, Methodology, Investigation, Data cura-
tion, Writing - original draft, Supervision.
[18] G.K. Hodgson, S. Impellizzeri, J.C. Scaiano, Single molecule study of samarium
oxide nanoparticles as a purely heterogeneous catalyst for one-pot aldehyde
chemistry, Catal. Sci. Technol. 6 (2016) 7113–7121, https://doi.org/10.1039/
C6CY00894A.
[19] G.K. Hodgson, S. Impellizzeri, J.C. Scaiano, Dye synthesis in the Pechmann
reaction: catalytic behaviour of samarium oxide nanoparticles studied using single
molecule fluorescence microscopy, Chem. Sci. 7(2016) 1314-1321. https:// doi.
org/10.1039/C5SC03214H.
[20] C. McCarthy, N. Losada-Garcia, J.M. Polomo, Direct synthesis of phenols from
phenylboronic acids in aqueous media catalyzed by a Cu 0)-nanoparticles
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Declaration of Competing Interest
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photocatalytic ipso-hydroxylation of aryl boronic acids: synthesis of phenols, Adv
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C3N4-catalyzed hydroxylation of aryl boronic acids in water under visible light:
synthesis of phenols under ambient conditions and room temperature, ACS Sustain.
Chem. Eng. 8 (2020) 2682–2687, https://doi.org/10.1002/adsc.201701573.
[23] M. Nasrollahzadeh, S.M. Sajadi, M. Maham, I. Kohsari, Biosynthesis,
characterization and catalytic activity of the Pd/bentonite nanocomposite for base-
and ligand-free oxidative hydroxylation of phenylboronic acid and reduction of
chromium (VI) and nitro compounds, Micropor. Mesopor. Mat. 271 (2018)
128–137, https://doi.org/10.1016/j.micromeso.2018.05.045.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgements
The current work was supported by the Fundamental Research Grant
Scheme (FRGS) (Vot. No. 59499), UMT/RMIC/FRGS/1/2018/59499(1)
provided by the Ministry of Higher Education Malaysia. The author
would like to thank the Universiti Malaysia Terengganu for providing
research facility to accomplish the study.
[24] I.K. Sideri, E. Voutyritsa, C.G. Kokotos, Green photoorganocatalytic synthesis of
phenols from arylboronic acids, Synlett 29 (2018) 1324–1328, https://doi.org/
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