Mild, selective oxidation of aromatic alcohols using β-cyclodextrin- functionalized glass microparticles: Characterization, stability, and application

Article abstract of DOI:10.1080/00397911.2013.797469

The surface of glass microparticle (GMP) was functionalized with β-cyclodextrin (→ GMP-β-CD) and was characterized by x-ray photoelectron spectroscopy (XPS). GMP-β-CD was used to catalyze oxidation of alcohols into aldehydes and katones with excellent yield (86-92%). The modified surface of GMP-β-CD showed no change or degradation after repeated use as confirmed from XPS analysis after 10 cycles. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications for the following free supplemental resource(s): Full experimental and spectral details.] Copyright

Full text of DOI:10.1080/00397911.2013.797469

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Mild, Selective Oxidation of Aromatic
Alcohols Using β-Cyclodextrin-
Functionalized Glass Microparticles:
Characterization, Stability, and
Application
Muhammad Nazir Tahir a , Riaz-ul Qamar b , Ahmad Adnan c , Abdul
Ghaffar d , Bong-Hyun Jun a , Jae-Hyuk Yu e & Seunho Jung a
a Department of Bioscience and Biotechnology, Bio/molecular
Informatics Center and Institute for Ubiquitous Technology and
Application (CBRU) , Konkuk University , Seoul , Republic of Korea
b Department of Organic Chemistry , University of Würzburg ,
Würzburg , Germany
c Department of Chemistry , GC University , Lahore , Pakistan
d Department of Chemistry , Baghdad-ul-Jadeed Campus, The
Islamia University of Bahawalpur , Pakistan
e Departments of Bacteriology and Genetics, and Molecular and
Environmental Toxicology Center , University of Wisconsin ,
Madison , Wisconsin , USA
Accepted author version posted online: 28 Oct 2013.Published
online: 27 Dec 2013.
To cite this article: Muhammad Nazir Tahir , Riaz-ul Qamar , Ahmad Adnan , Abdul Ghaffar , Bong-
Hyun Jun , Jae-Hyuk Yu & Seunho Jung (2014) Mild, Selective Oxidation of Aromatic Alcohols Using
β-Cyclodextrin-Functionalized Glass Microparticles: Characterization, Stability, and Application,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 44:5, 589-599, DOI: 10.1080/00397911.2013.797469
To link to this article: http://dx.doi.org/10.1080/00397911.2013.797469
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Synthetic Communications1, 44: 589–599, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2013.797469
MILD, SELECTIVE OXIDATION OF AROMATIC
ALCOHOLS USING b-CYCLODEXTRIN-
FUNCTIONALIZED GLASS MICROPARTICLES:
CHARACTERIZATION, STABILITY, AND APPLICATION
Muhammad Nazir Tahir,1 Riaz-ul Qamar,2 Ahmad Adnan,3
Abdul Ghaffar,4 Bong-Hyun Jun,1 Jae-Hyuk Yu,5 and
Seunho Jung1
1Department of Bioscience and Biotechnology, Bio=molecular Informatics
Center and Institute for Ubiquitous Technology and Application (CBRU),
Konkuk University, Seoul, Republic of Korea
2Department of Organic Chemistry, University of Wu¨rzburg, Wu¨rzburg,
Germany
3Department of Chemistry, GC University, Lahore, Pakistan
4Department of Chemistry, Baghdad-ul-Jadeed Campus, The Islamia
University of Bahawalpur, Pakistan
5Departments of Bacteriology and Genetics, and Molecular and
Environmental Toxicology Center, University of Wisconsin, Madison,
Wisconsin, USA
GRAPHICAL ABSTRACT
Abstract The surface of glass microparticle (GMP) was functionalized with b-cyclodextrin
(! GMP-b-CD) and was characterized by x-ray photoelectron spectroscopy (XPS).
GMP-b-CD was used to catalyze oxidation of alcohols into aldehydes and katones with
excellent yield (86–92%). The modified surface of GMP-b-CD showed no change or
degradation after repeated use as confirmed from XPS analysis after 10 cycles.
Received March 11, 2013.
Address correspondence to Seunho Jung, Department of Bioscience and Biotechnology, Bio=
molecular Informatics Center and Institute for Ubiquitous Technology and Application (CBRU),
Konkuk University, Seoul 143-701, Republic of Korea. E-mail: shjung@konkuk.ac.kr
589

590
M. N. TAHIR ET AL.
[Supplementary materials are available for this article. Go to the publisher’s online edi-
tion of Synthetic Communications1 for the following free supplemental resource(s): Full
experimental and spectral details.]
Keywords Aromatic alcohols; N-bromosuccinimide; catalysis; b-cyclodextrin; glass
functionalization; oxidation
INTRODUCTION
Selective oxidation is a fundamental and pivotal class of chemical transforma-
tions and is extensively used for organic synthesis and industrial manufacturing.[1–4]
Catalysts, mostly based on transition metals (e.g., Cu, Pd, Ru, Mn, Ti, and Pt), are
used for this purpose, which apparently cause serious heavy-metal pollution.[5–9]
Therefore, such metal catalysts are often considered unsuitable for the synthesis of
intermediates used in pharmaceutical products.[10] Moreover, oxidation by such
metal-based catalysts is considered a costly method.[11] Although new oxidation
methods have been developed over recent decades,[12] more clean and environmen-
tally friendly methods for such chemical reactions are still needed.
In the past few years, there have been many reports where native or modified
b-cyclodextrin (b-CD) has been applied as a catalyst in different chemical reac-
tions.[9,13–16] b-CD has certain advantages over heavy-metal-based traditional
catalysts (e.g., low cost, nontoxic, biocompatible, biodegradable, and water sol-
uble). Although there are some examples where free b-CD was used as a catalyst
in the oxidation reactions,[17–20] to our knowledge there is no example in literature
where immobilized b-CD (or any other CD) was used for such a purpose. A com-
mon problem observed when using free b-CD in chemical reactions is its ability to
complex with water-insoluble substrates to make them water soluble (product
moves in aqueous phase during extraction), leading to decrease in yield.[21] b-CD
immobilized on a solid surface has many advantages over free b-CD, such as easy
separation after completion of reaction and the possibility of applying such modi-
fied surfaces in a continuous process. Repeated use of b-CD can make the process
economical but its recovery from the reaction mixture after completion of a
reaction is time-consuming and laborious work. However, all these problems can
be solved by using b-CD immobilized on solid support, such as glass microparti-
cles (GMP). Other materials including silicon, quartz, and organic polymers have
also been used to manufacture functional surfaces, but glass is more attractive
because it is readily available at low cost and has high mechanical stability, and
easy surface-modification techniques are known for this material.[22–24] Because
of these advantages, GMP (30–50 mm) was functionalized with b-CD ((GMP-b-
CD) through a click reaction and applied as a green catalyst for oxidation of
the aromatic alcohols.
RESULTS AND DISCUSSION
Modification of Glass Microparticles
The surface modification of GMP was started with the formation of an
epoxide-terminated monolayer on the glass surface (Scheme 1). The layer was

OXIDATION OF ALCOHOLS BY GMP-b-CD
591
Scheme 1. Immobilization of b-CD on glass microparticles.
characterized by X-ray photoelectron spectroscopy (XPS) and elemental analysis.
The narrow-scan C1s XPS spectrum (Fig. 1a), formed from the electrons emitted
from C atoms in the alkyl chain of the epoxide terminated monolayer, displayed a
signal at 285.0 eV corresponding to C-C bonds and a signal at 287.02 eV correspond-
ing to C-O bonds in the monolayer.[25] The experimental ratio of C-O=C-C bonds
calculated from XPS spectrum (Fig. 1a) is 0.41, which is in good agreement with
the theoretical value of 0.42. These results indicate that high-quality epoxide mono-
layers on glass surface were obtained. The change in elemental composition (Table 1)
confirms the XPS data. The thickness of the formed epoxide layer, calculated using
Eq. (1), was 1.12 nm and is slightly greater than the length of the 1,2-epoxy-9-decene
molecule (1.11 nm, as calculated with Chem3D), confirming the monolayer
character.

592
M. N. TAHIR ET AL.
Figure 1. Narrow-scan C1s XPS spectra of epoxide terminated monolayer (a, 1), propargyl terminated
monolayer (b, 2), narrow-scan N1s XPS spectrum of propargyl terminated layer (c, 2), and C1s XPS spec-
trum after immobilization of b-CD on glass micro-particles (d, 3). (Figure is provided in color online.)
ꢀ
ꢁ
ꢀd
Isi ¼ Is1i exp
ð1Þ
k
si;c cos h
The variables Isi (absolute silicon peak intensity), Is1i (absolute silicon peak intensity
of the unmodified glass), d (thickness of the adsorbed layer), ksi, c (attenuation length
Table 1. Elemental composition of glass microparticles: without and after functionalization with epoxide,
and alkynyl-terminated monolayers, and after click reaction of b-CD-N3 and relative proportion of differ-
ent types of linkages
Elemental comp. atomic (%)
Si
C-C bond
C-Xa bond
Substrate
O
C
N
Ther. Expt. Ther. Expt.
Blank glass (before modification)
With epoxide-terminated monolayer (1)
32.96 67.04 0.00 0.00
22.43 36.84 40.74 0.00
7
9
7
7.1
9.1
3
4
2.9
3.9
With propargyl-terminated monolayer (2) 23.11 32.32 41.78 2.79
13.87 29.73 50.52 5.88
With b-CD immobilized on glass
surface (3), – fresh
11.14
48
41.86
After 5 cycles of repeated use (3)
After 10 cycles of repeated use (3)
14.23 29.97 49.99 5.81
14.26 30.05 49.92 5.77
7
7
11.65
11.71
48
48
41.35
41.29
Note. All XPS spectra are available in the Supplementary Material.
a
=
C-X C-O þ C-N bond linkages.

OXIDATION OF ALCOHOLS BY GMP-b-CD
593
of Si2p electrons in the hydrocarbon layer), and h (electron takeoff angle) were
calculated from the XPS data as described in Ref. 26.
The epoxide-functionalized glass surface (1) was subsequently converted into an
alkynyl terminated surface (2) via a reaction with propargylamine as described in the
experimental section. In the XPS spectrum (Fig. 1b), three signals corresponding to
C-C (285.0 eV), C-O (287.05 eV), and C-N (288.49 eV) bonds appeared. Excellent
agreement between measured (0.43) and theoretical (0.44) values for the ratio of
=
C-X=C-C (where C-X C-O þ C-N bond linkages) corresponds to 98% conversion
of epoxide to propargyl-terminated surface. In addition, appearance of a signal of
organic nitrogen at 400.0 eV (Fig. 1c) from the resultant monolayer also indicates
the successful reaction between propargylamine and the epoxide-terminated layer (1).
In the last step of this reaction, b-CD was converted into its monofunctionlal-
zidazide (b-CD-N3) following the procedure from literature[27,28] and immobilized on
a glass surface as described in the experimental section. In the XPS spectrum (Fig. 1d)
only two signals corresponding to C-C (285 eV) and C-X (C-O þ C-N, 286.56 eV)
appeared due to overlapping of C-O and C-N signals. Ratio of C-X=C-C (theoretical
6.85, experimental 3.75) indicates that 55% of the alkynyl groups (2) were clicked
with b-CD-N3. Degree of conversion was probably restricted by steric hindrance
for the bulky cyclodextrin derivative. Increase of the C content from 41.78 to
50.52% and of N from 2.79 to 5.88% along with decrease in Si content from 23.11
to 13.87% after the click reaction of the alkynyl-terminated layer (2) to b-CD-N3
(Table 1) also indicate the successful immobilization of b-CD on the glass surface.
Oxidation of Alcohols Aatalyzed by GMP-b-CD (3)
In the general procedure, aromatic alcohols were oxidized selectively to alde-
hydes and ketones with N-bromosuccinimide (NBS) in water at room temperature
Scheme 2. Oxidation of aromatic alcohols using b-cyclodextrin immobilized on glass microparticles
(GMP-b-CD, 3) and proposed mechanism for host–guest complex formation of b-CD with alcohol with
the help of N-bromosuccinimide.

594
M. N. TAHIR ET AL.
Table 2. Oxidation of alcohols into ketones using N-bromosuccinimide in water and catalyzed by
b-cyclodextrin immobilized on glass microparticles (GMP-b-CD, 3)
Entry
Substrate
Product
Time (h)
Yield (%)
1
4
92
2
3
4
4
5
5
91
92
88
5
6
4.5
4
90
92
7
8
4
94
91
4.5
9
4
4
87
10
86
88
11
12
5
5.5
91
(Continued )

OXIDATION OF ALCOHOLS BY GMP-b-CD
Table 2. Continued
595
Entry
13
Substrate
Product
Time (h)
5
Yield (%)
91
14
6
87
15
16
17
6
80
88
89
5.5
5.5
18
5.5
88
using GMP-b-CD (3) as a catalyst (Scheme 2). The course of the reaction was followed
by thin-layer chromatography and the product was characterized by NMR spec-
troscopy. Results from both techniques indicate that the reaction went smoothly,
and no side product was detected. As a control, the same reaction under the same
conditions but without GMP-b-CD was carried out in parallel, but no product was
detected. The same observation was reported by other researchers.[19] Oxidation
remained selective and no over oxidation to acids was detected by thin-layer chroma-
tography (TLC) or by NMR spectroscopy. Also it was observed that reaction was
selective in the case of vicinal diols, and only secondary alcohol was oxidized selectively
(entries 16–18, Table 2). Moreover, no side reaction was observed in the compounds
where other functional groups such as methoxy, nitro, halo, amino, hydroxy, and
alkene double bonds (see entries 6, 7, 8, 11, 13, and 18 in Table 2) were present.
The mechanism for host–guest complex of b-CD with NBS and aromatic
alcohols in such reactions is already reported in the literature.[19] It is suggested that

596
M. N. TAHIR ET AL.
Figure 2. Narrow-scan C1s XPS spectra of b-CD immobilized on glass microparticles after 5 (a) and
10 cycles of repeated use (b) for oxidation of benzyl alcohol (see Scheme 2). (Figure is provided in color
online.)
b-CD forms an inclusion complex with alcohol from the secondary side with the
attack of NBS from the primary side of the b-CD, enabling the reaction to proceed
(Scheme 2).
Repeated Use and Stability of the Functional Glass Surface
(GMP-b-CD, 3)
For implementation of such process at an industrial scale, where many cycles of
good yield are required, the stability of b-CD immobilized on a glass surface should be
high enough to permit its repeated use. To test stability, GMP-b-CD (3) was applied
as a catalyst for the oxidation of benzyl alcohol for 10 cycles. For this purpose, GMP-
b-CD was taken out of the reaction mixture after completion of the reaction, washed
with water and acetone, dried under a nitrogen stream, and used again for the next
cycle. Stability of b-CD on the glass surface was determined from the change in
elemental composition (Table 1) and by recording XPS spectra after 5 and 10 cycles
of repeated use (Fig. 2). During repeated use, no change in the yield of the product
or reaction rate for the oxidation of benzyl alcohol was observed. Comparison of
the XPS spectra recorded for freshly prepared GMP-b-CD (Fig. 1d) and that of after
5 and 10 cycles (Fig. 2) indicate that there was almost no change in the relative pro-
portion of different bond linkages or in elemental composition (Table 1). These results
indicate that the modified glass surface remained stable and can be used for several
cycles without losing efficiency. Moreover, it also confirms that no side reaction
(e.g., oxidation of immobilized b-CD) occurred on modified surface.
EXPERIMENTAL
Materials and methods
b-cyclodextrin(ꢁ97%),N-bromosuccinimide(99%),acetone(99.9%),hydrochlo-
hydrochloric acid (37%), dimethyl sulfoxide (99.9%), propagylamine (98%),

OXIDATION OF ALCOHOLS BY GMP-b-CD
597
N,N-diisopropylethylamine (99.5%), and copper(I) iodide (99.5%) were purchased
from Sigma-Aldrich. 1,2-Epoxy-9-decene (96%) was from Tokyo Chemical Industry,
Japan. Methanol (99.9%), n-hexane (99.9%), isopropanol (99.9%), ethyl alcohol
(99.9%), acetonitrile (99.9%), diethyl ether (99.9%), ethyl acetate (99.9%) and sodium
hydroxide were from Duksan. Sodium azide was from Junsei Chemical Co., Ltd.,
Korea; glass microparticles (GMP, 30–50 mm) were purchased from Polysciences
Inc., USA; and dimethyl sulfoxide (DMSO-d6) was from Cambridge Isotope
Laboratories, Inc., USA.
Water was purified using Direct-Q Millipore water purification system from
SAM WOO S&T Co., Ltd., Korea. b-CD was dried under vacuum until constant
weight, 1,2-epoxy-9-decene was further purified by column chromatography
(EtOAc=Et2O 3:1), solvents used for column chromatography were distilled while
other chemicals were used without further purification.
NMR spectra were recorded on a Bruker AMX spectrometer at 500 MHz.
Thin-layer chromatography (TLC) was carried out on Merck Kieselgel 60 F254
plates. X-ray photoelectron spectroscopic (XPS) spectra were recorded by using
a Sigma Probe (ThermoVG, UK) photoelectron spectrometer. High-resolution
spectra were obtained using monochromatic Al-Ka X-ray radiation at 15 kV and
100 W and an analyzer pass energy of 50 eV (1.0 eV step size) for wide scan and
20 eV (0.1 eV step size) for narrow scan. All high-resolution spectra were corrected
with a linear background before fitting. Mono-6-(p-toluenesulfonyl)-6-deoxy-
cyclodextrin (b-CD-OTs) was synthesized from b-CD as described in Ref. 27, which
in the next step was converted into mono-6-azido-b-cyclodextrin (b-CD-N3) accord-
1
ing to the procedure described in Ref. 28. H NMR data of the products was in
accordance with Refs. 27 and 28 (detailed procedure is described in the electronic
supplementary material). b-CD-N3 was immobilized on the glass surface through
a click reaction.
Modification of Glass Surface with Epoxide-Terminated
Monolayer (1)
Modification was carried out as described in Ref. 25 with some changes. GMP
(5 g) was washed with acetone, n-hexane, methanol, and ethanol, followed by sonica-
tion for 5 min per solvent and etched for 30 min in a freshly prepared solution of HCl
(37%) and ethanol (1:1 v=v). After etching, the samples were rinsed with ultrapure
water and methanol for 5 min per solvent and dried under nitrogen stream. Immedi-
ately after cleaning and drying, GMP were transferred into a dried glass flask followed
by addition of 1,2-epoxy-9-decene (5 g, 32.4 mmol) while keeping under nitrogen
atmosphere before closing tightly. To remove the traces of oxygen and moisturethat
might enter into the reaction flask, it was dipped into the liquid nitrogen to freeze the
coated 1,2-epoxy-9-decene on GMP (while under a nitrogen atmosphere) and allowed
to liquefy again at room temperature under vacuum. This freeze–thaw cycle was
repeated three times. Finally, the reaction flask was backfilled with nitrogen, dipped
into silicon oil bath, and heated at 130ꢂC for 24 h while under slight nitrogen pressure
(Scheme 1). GMP coated with epoxide-terminated layer (1) was removed from the
reaction flask, washed thoroughly with deionized water, n-hexane, and acetone, soni-
cated for 5 min per solvent, and dried under a nitrogen stream.

598
M. N. TAHIR ET AL.
Alkynyl Functionalization of Glass Surface (2)
Subsequently, the GMP was transferred to degassed propargylamine. The
reaction was carried out at 40ꢂC for 20 h, followed by washing and cleaning steps
as described previously.
Immobilization of b-CD on Glass Surface (3)
b-CD-N3 (675 mg, 0.57 mmol) was dissolved in DMSO=H2O (8:1, 36 mL) fol-
lowed by addition of N,N-diisopropylethylamine (222 mg, 1.71 mmol, 3 eq.=azide
group) and CuI (28.5 mg, 0.15 mmol, 0.25 eq.=azide group). The GMP functiona-
lized with propargylamine (2) was incubated in the reaction mixture and heated at
40ꢂC for 24 h followed by cleaning and drying steps.
General Procedure for Oxidation of Alcohols
Aromatic alcohol (1–2 mmol) was dissolved in methanol (or acetone in some
cases, 2–4 mL) at room temperature, followed by addition of the aqueous solution
of N-bromosuccinimide (1.5 eq.=alcohol) with continuous stirring. GMP-b-CD (3,
100 mg=mmol of alcohol) were added in the reaction mixture and stirring was con-
tinued. Progress of the reaction was monitored by TLC until the reaction was com-
pleted (4–6 h). GMP was separated by filtration after completion of the reaction. The
reaction mixture was extracted with ethyl acetate (4 ꢃ 5 mL), combined organic
layers were dried over Na2SO4, and solvent was removed under reduced pressure.
The product was further purified by flash column chromatography and analyzed
by NMR spectroscopy.
CONCLUSION
The glass microparticle surface was successfully functionalized with b-CD.
Modified glass microparticles can be used as a green catalyst (instead of heavy-metal-
based catalysts) for the oxidation of a variety of alcohols in water using NBS. The
modified surface remained stable and can be used for several cycles without losing
efficiency. Thus, this simple and clean methodology can be applied for continuous
process at larger scale. This environmentally benign technique may can be applied
in surface coating of microreactors for continuous process for the same or other
synthetic reactions.
SUPPLEMENTARY MATERIAL
Synthetic procedure for b-CD-N3 and XPS spectra are available in the
Supplementary Material.
ACKNOWLEDGMENTS
Financial support from Konkuk University (KU Brain Pool) for M. N. T is
gratefully acknowledged. This work was supported by Priority Research Centers
Program through the National Research Foundation of Korea Grant funded by

OXIDATION OF ALCOHOLS BY GMP-b-CD
599
the Korean Government (Ministry of Education, Science, and Technology NRF
2012-0006686) and was partly supported by the National Research Foundation of
Korea Grant funded by the Korean Government (NRF-20110024008 and KRF
2011-619-E0002).
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