Heterogeneous Palladium–Chitosan–CNT Core–Shell Nanohybrid Composite for Ipso-hydroxylation of Arylboronic Acids

Article abstract of DOI:10.1007/s10562-019-02682-1

Abstract: A novel palladium-nanohybrid (Pd–Chitosan–CNT) catalytic composite has been developed using CNT–chitosan nanocomposite and palladium nitrate. The prepared catalytic platform displays excellent catalytic reactivity for the ipso-hydroxylation of various arylboronic acids with a mild oxidant aqueous H₂O₂ at room temperature, affording the corresponding phenols in excellent yields. Significantly, the easy recovery and reusability by simple manipulation demonstrate the green credentials of this catalytic platform. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-019-02682-1

Catalysis Letters
https://doi.org/10.1007/s10562-019-02682-1
Heterogeneous Palladium–Chitosan–CNT Core–Shell Nanohybrid
Composite for Ipso-hydroxylation of Arylboronic Acids
Eun‑Jae Shin1 · Han‑Sem Kim2 · Seong‑Ryu Joo1 · Ueon Sang Shin2,3 · Seung‑Hoi Kim1
Received: 7 September 2018 / Accepted: 19 January 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
A novel palladium-nanohybrid (Pd–Chitosan–CNT) catalytic composite has been developed using CNT–chitosan nanocom-
posite and palladium nitrate. The prepared catalytic platform displays excellent catalytic reactivity for the ipso-hydroxylation
of various arylboronic acids with a mild oxidant aqueous H2O2 at room temperature, affording the corresponding phenols in
excellent yields. Significantly, the easy recovery and reusability by simple manipulation demonstrate the green credentials
of this catalytic platform.
Graphical Abstract
recycle
Pd-Chit-CNT
reuse
R
X
OH
R
X = B(OH)2 BF3K
H2O2 (30% aq)
17 samples
up tp 97%
rt/15 min
O
O
O
B
B
O
Keywords Palladium–chitosan–CNT nanohybrid · Arylboronic acid · Phenol · Ipso-hydroxylation · Hydrogen peroxide
Boronic acids containing one C–B bond and two OH groups
are trivalent organoboron derivatives. Owing to their unique
nature such as low toxicity, high stability in air, mild organic
Lewis acid and ease of handling, boronic acids have found
remarkable applications in a wide range of chemistry areas
[1]. Among the outstanding performances of boronic acids,
the palladium-catalyzed cross-coupling reaction, i.e. the
Suzuki–Miyaura reaction, has been recognized as one of the
most precious reactions in organic synthesis [2, 3]. Along
with this transformation, the oxidation of boronic acids to
the corresponding alcohols in the presence of a suitable oxi-
dant is also a highly valuable synthetic process.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-019-02682-1) contains
supplementary material, which is available to authorized users.
* Ueon Sang Shin
usshin12@dankook.ac.kr
In consideration of the important role of phenols as ver-
satile intermediates and building blocks in the chemical and
pharmaceutical industries [4–6], the oxidative conversion of
arylboronic acids could be a straightforward approach for the
production of phenolic compounds.
* Seung-Hoi Kim
kimsemail@dankook.ac.kr
1
2
Department of Chemistry, Dankook University,
Cheonan 31116, Republic of Korea
The first study on the oxidation of arylboronic acids with
alkaline hydrogen peroxide to produce phenols was reported
by Challenger [7]. Since then, numerous efforts have been
devoted to search for more efficient reaction conditions.
Milder oxidants such as anhydrous trimethylamine N-oxide
Department of Nanobiomedical Science & BK21
PLUS NBM Global Research Center for Regenerative
Medicine, Dankook University, Cheonan 31116,
Republic of Korea
3
Institute of Tissue Regeneration Engineering (ITREN),
Dankook University, Cheonan 31116, Republic of Korea
Vol.:(0123456789)
1 3

E.-J. Shin et al.
[8, 9], oxone [10–13], hypervalent iodine [14], hydroxy-
lamine [15] and peroxides [16, 17] have been explored. In
addition, metal-free bio-catalysts [18, 19] and light-active
photo-catalysts have been successfully used for the ipso-
hydroxylation of arylboronic acids [20–24]. Finally, vari-
ous copper complexes have also been reported to effectively
catalyze this transformation [25–29].
With this novel catalytic platform in hand, we immedi-
ately exploited its application in organic functional group
transformations. Herein, we wish to report its promising
performance in the ipso-hydroxylation of arylboronic acids,
furnishing the corresponding phenols.
A Pd(NO3)2–chitosan–CNT solution was first prepared
by the homogenization of a solution of palladium nitrate
(10 wt%), chitosan, and pristine CNTs at room temperature.
Next, the solution was treated with hydrazine monohydrate
to reduce the palladium nitrate. After suitable treatments,
such as neutralization, dialysis, washing, and drying, the
Pd–Chit–CNT nanohybrid membrane was successfully
obtained as a thin black film.
In order to accomplish the oxidation of arylboronic acids,
aqueous hydrogen peroxide is generally considered a ver-
satile oxidant due to environmentally benign oxidant that
displays high efficiency per weight of oxidant and, is easy
to handle [30]. For these reasons, numerous studies using
H2O2 for the ipso-hydroxylation of arylboronic acids have
been recently conducted. In most cases, the system involves
a combination of H2O2 with urea [31], biosilica [32], PEG-
400 [33], H3BO3 [34], Al2O3 [35], I2 [36], amberlite IR-120
resin [37] and poly(N-vinylpyrrolidone) or poly(4-vinylpyr-
idine) [38]. Lately, the use of nanoparticles in the hydroxy-
lation of boronic acids is an emerging approach toward the
preparation of phenol derivatives. In this context, a very
recent report described a ligand-free hydroxylation of phe-
nylboronic acid using reusable Pd-nanoparticles [39]. The
biosynthesis of Fe2O3@SiO2 nanoparticles and their applica-
tion in ipso-hydroxylation reaction was also reported [40]. A
method for the synthesis of phenols using mont K-10-sup-
ported silver nanoparticles was also appeared [41].
For qualitative analysis, the FT-IR spectrum of the pre-
pared Pd–Chit–CNT membrane was compared to those of
pristine CNT and chitosan, showing the characteristic bands
at 3200–3630 cm−1 (–OH and –NH for Chit part stretch-
ing), 2915 and 2865 cm−1 (–CH stretching of –CH2 for
Chit part), 1648 cm−1 (C=O for Chit part stretching), and
1634 cm−1 (C=C for pCNT part stretching). Significantly,
the C=O stretching band of pure chitosan was shifted from
1648 to 1515 cm−1 in the composite because of either the
increased participation of C=O functional groups in a net-
work of intermolecular hydrogen bonds or reorganizing the
network of intermolecular hydrogen bonds. The core–shell
structure and presence of Pd nanoparticles were investigated
by FE-SEM analysis of the Pd–Chit–CNT, Chit–CNT, and
pristine CNT samples. The images of Pd–Chit–CNT and
Chit–CNT clearly showed the rough surface of individual
CNT, indicating the presence of a chitosan layer on the CNT
surfaces. Also, Pd nanoparticles (approximately 10–20 nm)
are clearly observed deposited on or inserted in the chitosan
layer over the CNTs.
Notwithstanding the previous protocols with excellent
activity, continuous efforts are being devoted to the improve-
ment the efficiency of boronic acid hydroxylation process
with a special focus on greener conditions and more efficient
catalysts.
On account of the aspects of sustainable chemistry, recy-
cling environmentally hazardous catalysts could be suitable
way to reduce the economic and environmental burden. To
address this issue, heterogeneous metal-catalytic systems
that are recyclable and reusable are considered a suitable
approach [42]. In order to achieve this goal, palladium–metal
and/or –complexes have been most frequently employed
[43–56].
When the pyrolysis behaviors of pure chitosan and CNTs
in the temperature range of 25–900 °C was compared to that
of the nanohybrid membrane (Pd–Chit–CNT), a different
thermal degradation pattern and/or incomplete degradation
behavior were observed. For instance, intensive weight loss
occurred in three steps between 200 and 600 °C for pure chi-
tosan, while this occurred between 600 and 700 °C for pure
CNT. Pyrolysis of the Pd–Chit–CNT nanohybrid membrane
before use as a catalyst afforded a degradation pattern simi-
lar to that of pure chitosan, demonstrating the nonflammable
nature of Pd metal (10 wt%). Interestingly, the degradation
pattern after the catalysis showed a pattern very similar to
that of fresh Pd–Chit–CNT, indicating that the Pd concen-
tration on the membrane was not reduced after use (Fig. 1).
Our initial investigation focused on the activity of the
Pd–Chit–CNT catalyst system for the ipso-hydroxylation
of arylboronic acids. A mixture of phenylboronic acid (1a)
and aqueous hydrogen peroxide (30%) as the oxidant in the
absence of Pd–Chit–CNT was stirred at room temperature
for 15 min, giving rise to only a small amount of phenol
In the context of our ongoing concerns on metal-cata-
lyzed transformation, we were interested in developing an
environmentally friendly catalytic system with good recy-
clability and sustainability of the catalyst. Interestingly, we
have recently developed chitosan–carbon nanotube (CNT)
nanocomposites using a high-pressure homogenizer, result-
ing in close-packing CNT–core and chitosan–shell nanofib-
ers [57]. Since the surface of the nanocomposite material
was wrapped with chitosan which exhibits excellent adsorp-
tivity toward metal ions, we decided to explore the possibil-
ity of embedding transition metal on the surface. To our
delight, palladium-metal was successfully deposited onto the
CNT–chitosan film, furnishing a Pd–chitosan–CNT nanohy-
brid (hereafter denoted as Pd–Chit–CNT).
1 3

Heterogeneous Palladium–Chitosan–CNT Core–Shell Nanohybrid Composite for Ipso-hydroxylation…
and 7, Table 1). Next, we attempted to identify any solvent
effects on the conversion, which resulted in no improvement
of the isolated yield (entries 8–10, Table 1).
With the most suitable reaction conditions in hand (entry 4,
Table 1), we next turned our attention to the substrate scope. A
series of electronically diversified arylboronic acids were tested
and smoothly oxidized to the corresponding phenols in good to
excellent yields. The results are summarized in Table 2.
Interestingly, our catalytic platform tolerates a wide range
of functionalities including electron-donating and electron-
withdrawing groups such as OCH3, Me, t-butyl, F, Cl, CN,
CHO, NO2, and COCH3.
No significant effects were observed for sterically
demanding ortho-substituents and good yield of isolated
product (2b) was obtained. Naphthaleneboronic acids also
underwent this ipso-hydroxylation transformation in excel-
lent yield under the same reaction conditions.
Fig. 1 Thermo gravimetric analysis curves
Since Pd–Chit–CNT is a solid heterogeneous cata-
lyst, it should be easily recovered by a simple operation.
Accordingly, the recyclability of the catalyst was tested
for the model reaction with phenylboronic acid (1a). The
Pd–Chit–CNT catalyst was simply filtered after the reac-
tion, and then washed with distilled water followed by ether.
After drying at room temperature, it was reused for the sub-
sequent hydroxylation reactions without any further activa-
tion. These experiments proved the excellent recyclability
of the catalyst with no significant loss of activity in terms
of isolated yield even after six consecutive runs (Table 3).
(entry 1, Table 1). The incorporation of the Pd–Chit–CNT-
catalyst dramatically increased the isolated yield up to 95%
under similar conditions (entry 3, Table 1). The conversion
was completed at room temperature within 15 min regardless
of the amount of H2O2, producing the product in a similar
fashion (entries 3–5, Table 1). However, a critical effect of
the amount of catalyst was observed, whereby lower cata-
lyst loadings afforded lower yields of the product (entries 6
Table 1 Optimization of the ipso-hydroxylation of phenylboronic
acid (1a)
Table 2 Scope of boronic acids
OH
Pd-Chit-CNTa
OH
Pd-Chit-CNTa
B
OH
B
OH
2b - 2q
H2O2 (30% aq)
rt/15 min
R
R
H2O2 (30% aq)
rt/15 min
OH
OH
(3.0 mmol)
1b - 1q
(3.0 mmol)
2a
1a
CH3
OH H3C
OH
OH
OH
H3C
MeO
O2N
Ph
Entry
Pd-cat (mg)a
H2O2 (mL)
Solventb
Yield (%)c
b
2b
(81%)
2e
2i
(80%)
2c
2d
2h
(94%)
(90%)
1
2
3
4
5
6
7
8
9
–
5.0
–
–
28
NRd
95
95
93
64
50
89
61
32
3.0
3.0
3.0
3.0
2.0
1.0
3.0
3.0
3.0
H2O2
–
–
–
–
–
H2O2
CH3CN
EtOH
MeO
MeO
OH
(H3C)2N
OH
OH
OH
5.0
3.0
1.0
3.0
3.0
3.0
3.0
3.0
NC
Cl
2f
2j
2g
(84%)
(81%)
(71%)
(91%)
(63%)
OH
(48%)
OH
OH
OH
HOC
H3COC
2k
(65%)
OH
2l
2m
(88%)
(90%)
10
OH
a10 wt% Pd-content
b5.0 mL of solvent used
cIsolated yield
OH
OH
O
S
2q
(52%)
2n
2p
(72%)
2o
(92%)
a 10 wt% Pd-content b number in parenthesis is isolated yield
dNo reaction occurred at room temperature in 24 h
1 3

E.-J. Shin et al.
Pd-Chit-CNTa
H2O2 (30% aq)b
rt/15 min
Table 3 Reusability test
1a
(3.0 mmol)
2a
Run
1st
96
2nd
95
3rd
95
4th
93
5th
94
6th
93
Yield (%)
a10 wt% Pd-content, 3.0 mg used
b3.0 mL used
their fundamental limitations is leaching of the metal
catalyst into the solution, especially when the reaction is
carried out in aqueous media [28]. Therefore, we addi-
tionally performed leaching tests by collecting aliquots of
the aqueous phase during the reaction, which were sub-
sequently analyzed by ICP-AES, revealing the leaching
of only 0.07% of palladium. This strongly indicates that
our catalytic platform is robust enough for use as an eco-
friendly heterogeneous catalyst. To examine the feasible
utility of our system, conditional tests were executed. The
ipso-hydroxylation of 1a was carried out using commer-
cially available Pd(PPh3)2Cl2 and Pd(OAc)2 instead of
Pd–Chit–CNT nanohybrid film under the same condition
used before, giving rise to 2a in 37% and 70% isolated
yield, respectively. The results clearly verified the effi-
ciency of our nanohybrid system.
O
O
O
O
BF3K
B
B
3a 2a
to
4a 2a
to
5a 2a
to (84%)
(86%)
(82%)
Scheme 1 Application to arylboronic acid derivatives
Surprisingly, not only arylboronic acids, but other boronic
acid surrogates such as potassium phenyltrifluoroborate (3a)
and phenyl boronic esters (4a, and 5a) were also found to be
suitable substrates for hydroxylation under the same condi-
tions. The corresponding product phenol (2a) was furnished
in satisfactory yields from the corresponding derivatives
(Scheme 1).
To further characterize the active surface of the catalyst,
we analyzed and compared the surface of Pd–Chit–CNT
films before and after use by SEM. As shown in Fig. 2,
no significant differences were detected. (more detailed
information on the preparation and characterization of
Pd–Chit–CNT is provided in the Supporting Information).
Although the use of heterogeneous catalytic systems
presents several advantages in organic synthesis, one of
Fig. 2 SEM images of Pd–Chit–CNT; before (left) and after use (right)
1 3

Heterogeneous Palladium–Chitosan–CNT Core–Shell Nanohybrid Composite for Ipso-hydroxylation…
24. Zou YQ, Chen JR, Liu XP, Lu LQ, Davis RL, Jorgensen KA, Xiao
1 Conclusion
WJ (2012) Angew Chem Int Ed 51:784
25. Xu J, Wang X, Shao C, Su D, Cheng G, Hu Y (2010) Org Lett
12:1964
A newly designed palladium catalyst platform, nanohybrid
Pd–Chit–CNT, was successfully prepared using a modi-
fied high-pressure homogenizer. The as-prepared platform
in combination with hydrogen peroxide was effectively
employed in the ipso-hydroxylation of arylboronic acids,
leading to the corresponding phenols in excellent yields.
Moreover, the platform could be efficiently recovered by
simple manipulation and reused in subsequent reactions. A
preliminary study on the catalyst-leaching into the solution
also confirmed that Pd–Chit–CNT is a robust heterogeneous
catalyst. Our strategy thus represents an alternative protocol
for the facile synthesis of phenol derivatives. The applica-
tion of this new catalytic system is currently being extended
to other functional group transformations in our laboratory.
26. Inamoto K, Nozawa K, Yenomoto M, Konda Y (2011) Chem
Commun 47:11775
27. Dar BA, Hatti PB, Singh AP, Lazar A, Sharma PR, Sharma M,
Singh B (2013) Appl Catal A 466:60
28. Affrose A, Azath IA, Dhakshinamoorthy A, Pitchumani K (2014)
J Mol Cata A 395:500
29. Bora SJ, Chetia B (2017) J Organomet Chem 851:52
30. Piera J, Backvall JE (2008) Angew Chem Int Ed 47:3506
31. Gupta S, Chaudhary P, Srivastava V, Kandasamy J (2016) Tetra-
hedron Lett 57:2506
32. Mahanta A, Adhikari P, Bora U, Thakur AJ (2015) Tetrahedron
Lett 56:1780
33. Gohain M, du Plessis M, van Tonder JH, Bezuidenhoudt BCB
(2014) Tetrahedron Lett 55:2082
34. Gogoi K, Dewan A, Gogoi A, Borah G, Bora U (2014) Heteroat
Chem 25:127
35. Gogoi A, Bora U (2013) Tetrahedron Lett 54:1821
36. Gogoi A, Bora U (2012) Synlett 23:1079
37. Mulakayala N, Kumar KM, Rapolu RK, Kandagatla B, Rao P,
Oruganti S, Pal M (2012) Tetrahedron Lett 53:6004
38. Prakash GKS, Chacko S, Panja C, Thomas TE, Gurung L, Rasul
G, Mathew T, Olah GA (2009) Adv Synth Catal 351:1567
39. Khazaei M, Khazaei A, Nasrollahzadeh M, Tahsili MR (2017)
Tetrahedron Lett 73:5613
Compliance with Ethical Standards
Conflict of interest The authors declare no conflict of interest.
40. Saikia I, Hazarika M, Hussian N, Das MR, Tamuly C (2017) Tet-
rahedron Lett 58:4255
References
41. Begum T, Gogoi A, Gogoi PK, Bora U (2015) Tetrahedron Lett
56:95
1. Hall DG (2011) Boronic acids: preparation and applications
in organic synthesis, medicine and materials, 2nd edn. Wiley,
Weinheim
42. Bradley JS, Schmid G (1994) Clusters and colloids: from theory
to applications. VCH, Weinheim, p 523
43. Okumura K, Tomiyama T, Okuda S, Yoshida H, Niwa M (2010)
J Catal 156:273
2. Miyaura N, Suzuki A (1979) J Chem Soc Chem Commun 0:866
3. Miyaura N, Yanagi T, Suzuki A (1981) Synth Commun 11:513
4. Tyman JHP (1996) Synthetic and natural phenols. Elsevier, New
York
44. Park JC, Heo E, Kim A, Kim M, Park KH, Song H (2011) J Phy
Chem C 115:15772
45. Zhi J, Song D, Li Z, Lei X, Hu A (2011) Chem Commun 47:10707
46. Lamblin M, Nassar-Hardy L, Hierso JC, Fouquet E, Felpin FX
(2010) Adv Synth Catal 33:352
5. Rappoport Z (2003) The chemistry of phenols. Wiley, Weinheim
6. Fyfe CA (1971) The chemistry of the hydroxyl group. Part 1,
vol 1. Wiley, New York
47. Dhakshinamoorthy A, Asiri AM, Garcia H (2015) Chem Soc Rev
44:1922
7. Ainley AD, Challenger F (1930) J Chem Soc 2171
8. Zhu C, Wang R, Falck JR (2012) Org Lett 14:3497
9. Kabalka GW, Hedgecock HC Jr (1975) J Org Chem 40:1776
10. Molander GA, Cavalcanti LN (2011) J Org Chem 76:623
11. Maleczka RE Jr, Shi F, Holmes D, Smith MR III (2003) J Am
Chem Soc 125:7792
48. Paul S, Islam MM, Islam SM (2015) RSC Adv 5:42193
49. Garcia-Bernab A, Tzschucke CC, Bannwarth W, Haag R (2005)
Adv Synth Catal 347:1389
50. Schweizer S, Becht JM, Drian CL (2007) Adv Synth Catal
349:1150
12. Travis BR, Ciaramitaro BP, Borhan B (2002) Eur J Org Chem
3429
51. Webb JD, MacQuarrie S, McEleney K, Crudden CM (2007) J
Catal 97:252
13. Webb KS, Levy D (1995) Tetrahedron Lett 36:5117
14. Chatterjee N, Goswami A (2013) Tetrahedron Lett 56:1524
15. Kianmehr E, Yahyaee M, Tabatabai K (2007) Tetrahedron Lett
48:2713
52. Khler K, Heidenreich RG, Soomro SS, Prockl SS (2008) Adv
Synth Catal 350:2930
53. Qiu H, Sarkar SM, Lee DH, Jin MJ (2008) Green Chem 10:37
54. Sawai K, Tatumi R, Nakahodo T, Fujihara H (2008) Angew Chem
Int Ed 47:6917
16. Guo S, Lu L, Cai H (2014) Synlett 24:1712
17. Chen DS, Huang JM (2013) Synlett 24:499
18. Silveira-Dorta G, Mozon DM, Crisostomo FP, Martin T, Martin
VS, Carrillo R (2015) Chem Commun 51:7027
55. Scheuermann GM, Rumi L, Steurer P, Bannwarth W, Mulhaupt R
(2009) J Am Chem Soc 131:8262
56. Jin MJ, Taher A, Kang HJ, Choi M, Ryoo R (2009) Green Chem
11:309
19. Kotoucova H, Strnadova I, Kovandova M, Chudoba J, Dvorakova
H, Cibulka R (2014) Org Biomol Chem 12:2137
20. Wang ZJ, Li R, Landfester K, Zhang KAI (2017) Polymer 126:291
21. Xie HY, Han LS, Hung S, Lei X, Cheng Y, Zhao W, Sun H, Wen
X, Xu QL (2017) J Org Chem 82:5236
57. Hwang JY, Kim HS, Kim JH, Shin WS, Lee SH (2015) Langmuir
31:7844
22. Sawant SD, Hudwekar AD, Kumar KAA, Venkateswarlu V, Singh
PP, Vishwakarma RA (2014) Tetrahedron Lett 55:811
23. Matsui K, Ishigami T, Yamaguchi T, Yamaguchi E, Tada N, Miura
T, Itoh A (2014) Synlett 25:2613
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.
1 3