Fabrication of Mn2O3 nanorods: An efficient catalyst for selective transformation of alcohols to aldehydes

Article abstract of DOI:10.1039/c5ra02504d

A facile wet chemical approach has been devised for the preparation of self-assembled, high surface area, nanostructured Mn₂O₃ through an effective polymer-surfactant interaction. Its outstanding catalytic property for the selective transformation of alcohols to aldehydes has been reported. The polyethylene glycol/sodium dodecyl sulphate conjugates act as soft templates for the formation of manganese oxide nanorods upon treatment of a weak base, namely, diethanolamine, with manganese acetate as a precursor under mild refluxing conditions. The Mn₂O₃ nanorods were found to be efficient and selective catalysts for the synthesis of valuable aldehydes and ketones over undesirable acid by-products using a low catalyst loading. The precursor alcohols bearing activated and unactivated aromatic rings, double and triple bonds, and chiral sugar moiety were tolerated in this direct oxidative transformation strategy developed under benign reaction conditions.

Full text of DOI:10.1039/c5ra02504d

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Fabrication of Mn2O3 nanorods: an efficient
catalyst for selective transformation of alcohols to
Cite this: RSC Adv., 2015, 5, 33923
aldehydes†
a
b
b
a
*
*
Hasimur Rahaman, Radha M. Laha, Dilip K. Maiti and Sujit Kumar Ghosh
A facile wet chemical approach has been devised for the preparation of self-assembled, high surface area,
nanostructured Mn2O3 through an effective polymer–surfactant interaction. Its outstanding catalytic
property for the selective transformation of alcohols to aldehydes has been reported. The polyethylene
glycol/sodium dodecyl sulphate conjugates act as soft templates for the formation of manganese oxide
nanorods upon treatment of a weak base, namely, diethanolamine, with manganese acetate as a
precursor under mild refluxing conditions. The Mn2O3 nanorods were found to be efficient and selective
catalysts for the synthesis of valuable aldehydes and ketones over undesirable acid by-products using a
low catalyst loading. The precursor alcohols bearing activated and unactivated aromatic rings, double
and triple bonds, and chiral sugar moiety were tolerated in this direct oxidative transformation strategy
developed under benign reaction conditions.
Received 9th February 2015
Accepted 24th March 2015
DOI: 10.1039/c5ra02504d
www.rsc.org/advances
properties21–24 in a diverse range of niche applications.25–27
Among the different oxidation states of manganese oxides,
1. Introduction
Catalysts are the work-horses in synthetic chemistry.1–3 The
robust reactivity and selectivity of catalysts lead to the efficient
transformation of raw materials into the desired pharmaceuti-
cals, fuels, agrochemicals, pigments, polymers, commercial and
natural compounds, which are essential for our highly
demanding modern society. In this context, nanomaterials have
tremendous potential to serve as catalysts with signicantly
improved performance because of their active surface and
interfacial atom effect, innovative new chemical property, high
reactivity, low catalyst loading, environmentally benign nature,
easy recovery and reusability.4–20 In recent years, the size and
shape-controlled synthesis of manganese oxides (MnOx) nano-
materials has attracted considerable interest from both
academia and industry due to their tuneable physicochemical
properties and applications in9–12 high-density magnetic storage
media,13 ion-exchange,14 molecular adsorption,15 electronics,16
biosensors,17 energy storage,18 batteries19 and catalysts.20
Manganese oxides are the most attractive inorganic materials
owing to their structural exibility and availability of different
oxidation states of manganese (II, III and IV), which are
responsible for their structural, transport and magnetic
Mn2O3 is well-known as a cheap and environmentally friendly
catalyst and could be employed as an ideal candidate for the
removal of CO and NOx from waste gas,28 decomposition of
H2O2 into hydroxyl radicals in the catalytic peroxidation of
organic effluents29 and as an oxygen storage component.30
Although catalytic activities over transition metal oxide catalysts
are lower than those over noble metal catalysts, the inherent
advantages of metal oxide catalysts, such as low cost, high
thermal stability, and high mechanical strength, make them a
promising alternative for outstanding catalytic applications.31
The catalytic activity of these materials at the nanoscale
dimension depends strongly on their surface properties, while
the reactivity and selectivity of nanoparticles can be tuned
through controlling the morphology because the exposed
surfaces of the particles have distinct crystallographic planes
depending on their shape.32 Therefore, the synthesis of Mn2O3
nanoparticles with well-controlled morphology and a narrow
size distribution is desirable for achieving practical applications
such as catalysis.
Diverse synthetic approaches have been implemented in the
literature for the fabrication of size and shape-selective Mn2O3
nanostructures, and their physical and chemical properties
have been exploited in a wide range of applications. Ganguli
and co-authors prepared nanorods of anhydrous manganese
oxalate as a precursor to synthesize single phase nanoparticles
of various manganese oxides, such as MnO, Mn2O3 and Mn3O4,
under specic reaction conditions and studied their eld-
dependent magnetization properties.33 Han and co-workers
reported the synthesis of Mn2O3 nanocrystals by the
aDepartment of Chemistry, Assam University, Silchar-788011, India. E-mail: sujit.
kumar.ghosh@aus.ac.in; Fax: +91-3842-270802; Tel: +91-3842-270848
bDepartment of Chemistry, University of Calcutta, Kolkata-700009, India. E-mail:
dkmchem@caluniv.ac.in
† Electronic supplementary information (ESI) available: Characterization details
of synthesized materials, reaction schemes, catalysis details with tables. See
DOI: 10.1039/c5ra02504d
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thermolysis of manganese(III) acetyl acetonate on a mesoporous
silica, SBA-15, and the nanocomposites showed signicant
catalytic activity toward CO oxidation below 523 K.34 Chen and
He described a facile synthesis of mono-dispersed Mn2O3
nanostructures by treating a mixture of KMnO4 solution and
oleic acid at low temperatures (below 200 ꢀC) and have
demonstrated the application of these particles as efficient
water puriers.35 Polshettiwar et al. devised a simple strategy
using an aqueous solution of K3[Mn(CN)6] under microwave
irradiation to afford a nanomaterial.12 Gnanam and Rajendran
described the preparation of a-Mn2O3 nanoparticles by drop-
wise addition of an aqueous ammonia solution to manganese(II)
chloride tetrahydrate (MnCl2$4H2O) in methanol with vigorous
stirring and reported the optical properties of the synthesized
materials.36 Yang et al. reported the size-controlled synthesis of
monodispersed Mn2O3 octahedra assembled from nano-
particles by a mediated N,N-dimethylformamide solvothermal
route, and the particles were found to exhibit catalytic activity
towards CO oxidation.37 Qiu et al. described the synthesis of
hierarchically structured Mn2O3 nanomaterials with different
Scheme
catalyst.
1
Direct synthesis of aldehydes using Mn2O3-nanorods
iodane46,47 as a stoichiometric oxidant under neutral and benign
reaction conditions (Scheme 1). In this article, we have reported
an innovative approach to fabricate rod-shaped Mn2O3 nano-
structures using a polymer–surfactant assembly as a so-
template, and their catalytic activity is discovered towards the
selective oxidation of alcohols to valuable aldehydes, chiral
analogues and ketones using phenyliododiacetate [PhI(OAc)2]
as an oxidizing agent.
2. Experimental
2.1 Reagents and instruments
morphologies and pore structures from precursors containing All the reagents used were of analytical reagent grade. Man-
the target materials interlaced with the polyol-based organic ganese(II) acetate tetrahydrate, diethanolamine (DEA), poly-
molecules and examined their potential as anode materials for ethylene glycol (PEG-400), sodium dodecyl sulphate (SDS) and
lithium ion batteries.38 Cao et al. reported large-scale synthesis phenyliodoacetate (PhI(OAc)2) were purchased from Sigma
of Mn2O3 homogeneous core/hollow-shell structures with cube- Aldrich and were used without further purication. Double
shaped and dumbbell-shaped morphologies, and the particles distilled water was used throughout the course of the investi-
were found to exhibit an excellent performance in waste water gation. The temperature was maintained at 298 ꢁ 1 K during
treatment.39 Najafpour et al. described the synthesis of nano- the experiments.
sized Mn2O3 particles by the decomposition of an aqueous
Absorption spectra were measured using a Shimadzu
ꢀ
solution of manganese nitrate at 100 C, and it was observed UV-1601 digital spectrophotometer (Shimadzu, Japan) by
that the particles possessed catalytic activities towards the water placing the sample in a 1 cm well-stoppered quartz cuvette. The
oxidation and epoxidation of olens in the presence of cer- surface and structural morphologies of Mn2O3 samples were
ium(IV) ammonium nitrate and hydrogen peroxide, respec- studied by scanning electron microscopic (SEM) images, which
tively.40 We envisioned the fabrication of Mn2O3 nanorods by a were recorded using a JSM-6360 (JEOL) instrument equipped
so-template strategy, which will provide a roughened high with a eld emission cathode having a lateral resolution of
surface area to offer an ideal platform for high and innovative approximately 3 nm by applying an acceleration voltage of 3 kV
chemical activity towards novel catalysis processes such as the aer sputtering the sample on a silicon wafer with carbon
most demanding direct synthesis of aldehydes and ketones (approx. 6 nm). Thin lms were prepared by drop-coating the
from alcohols under oxidative conditions.
aqueous-methanolic solutions of the respective samples onto
Aldehydes are valuable compounds and one of the most silicon wafers. Transmission electron microscopy was carried
frequently used ingredients of organic synthesis in industry and out on a JEOL JEM-2100 microscope operating at 200 kV.
academia. The tremendous importance of this class of Samples were prepared by placing a drop of solution on a
compounds is supported by the development of enormous carbon-coated copper grid and drying overnight under vacuum.
methodologies for their synthesis reported in the literature.41–45 High-resolution transmission electron micrographs and
The direct oxidative transformation of alcohols to aldehydes is a selected area electron diffraction (SAED) pattern were obtained
fundamental organic reaction. This approach suffers from a using the same JEOL JEM-2010 instrument, operating at 200 kV.
serious drawback of the generation of a large quantity of the Energy dispersive X-ray (EDX) analysis was performed on an
corresponding acid43 as a by-product because the trans- INCA Energy TEM 200 using an X-ray detector. Fourier trans-
formation of acid from the in situ generated desired aldehyde is form infrared (FTIR) spectra were recorded in the form of
more energetically favourable than the oxidation of alcohol to pressed KBr pellets in the range of 400–4000 cmꢂ1 with a
aldehyde. Thus, with the advent of synthesising metallic Shimadzu-FTIR Prestige-21 spectrophotometer. The powder
nanomaterials, silver, gold, palladium, ruthenium and plat- X-ray diffraction patterns were obtained using a D8 Advanced
inum nanoparticles are utilized under basic and/or stringent Bruker axs X-ray Diffractometer with CuKa radiation
ꢂ1
reaction conditions for the oxidation of alcohol to aldehyde.44,45 (l ¼ 1.540589 A); data were collected at a scan rate of 0.5 min
ꢀ
˚
To improve the substrate scope, selectivity and versatility in the in the range of 10–80ꢀ. Raman scattering measurements were
catalytic dehydrogenation process, we envisioned using carried out on a silicon substrate in the backscattering geometry
calcined manganese oxide nanorods and l3-hypervalent using a ber-coupled micro-Raman spectrometer equipped
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with a 488 nm (2.55 eV), 5 mW air-cooled Ar+ laser as the exci- (60–120 mesh) with ethyl acetate–petroleum ether (1 : 200, v/v)
tation light source, a spectrometer (model TRIAX550, JY) and a as an eluent in yields of 87% (92.5 mg, 0.87 mmol) and 4%
CCD detector. The powder specic surface area was measured (4.5 mg, 0.04), respectively. The structures of the desired
by BET analysis using a Micromeritics Tristar 3000 surface area product (2a) and by-product (3a) were conrmed with the help
analyzer. Thermogravimetric analysis was carried out on a of the boiling and melting points available in the literature;
Perkin-Elmer STA 6000 with a sample amount of 10 mg. The moreover, the recorded NMR (1H and 13C), FT-IR, and mass
measurements were performed under nitrogen with heating (HR-MS) spectra were compared with those available in the
from 40–800 ꢀC (rate: 10 ꢀC minꢂ1), and then maintaining at 800 literature. Similarly, other aldehydes (2b–e), ketones (4a and b),
ꢀC for half an hour. Before TGA measurements, the samples acids (3a–f) and sugar aldehyde (2f) were characterized by
measuring melting/boiling points and recording NMR (1H and
13C), FT-IR, and mass (HR-MS) spectra and optical rotation,
which were veried with the data and spectra reported in the
literature.
ꢀ
were dried overnight in a vacuum oven at 50 C.
2.2 Synthesis of manganese oxide nanorods in polymer–
surfactant conjugates
The nanostructures of manganese oxide were synthesised using
polymer–surfactant conjugates and manganese acetate tetra-
hydrate as the precursor salt. In a typical synthesis, an aliquot of
aqueous polyethylene glycol (PEG) (0.4 mmol dmꢂ3) was added
to an aqueous solution of sodium dodecyl sulphate (SDS)
(2 mmol dmꢂ3) in a two-necked round-bottom ask such that
the total volume of the solution was 25 mL, and the mixture was
stirred overnight at room temperature. Then, 0.245 g of
Mn(ac)2$4H2O was dissolved in the polymer–surfactant mixture
by reuxing on a water bath at 65 ꢀC. Aer the complete
dissolution of the precursor, 100 mL diethanolamine was added
and reuxing was continued for another 6 h. Aer about 30 min,
the reaction mixture turned yellowish brown from a colourless
solution indicating the formation of manganese oxide nano-
structures. As the reuxing was continued, the colour slowly
changed to deep brown, indicating the aggregation of the
ultrasmall manganese oxide particles to rod shaped nano-
structures. The water-bath was removed and the reaction
mixture was stirred for 12 h at room temperature. The particles
formed by this method were washed ve times with slightly hot
water and nally dispersed in water. The manganese oxide
nanostructures prepared by this method are stable for a month
and can be stored in a vacuum desiccator without any signi-
cant agglomeration or precipitation of the particles.
3. Results and discussion
In the present study, we have reported an innovative fabrication
approach for rod-shaped Mn2O3 nanostructures using a poly-
mer–surfactant assembly as a so-template, and their catalytic
activity towards the selective oxidation of alcohols to valuable
aldehydes, chiral analogue and ketones using phenyl-
iododiacetate [PhI(OAc)2] as an oxidizing agent has been
investigated.
The absorption spectral features of the as-synthesized
Mn2O3 sample in the solid state are shown in ESI 1.† The esti-
mated direct band gap of the Mn2O3 was found to be 1.29 eV;
this value is almost close to the reported value of Mn2O3
nanostructures.48 The morphology, composition and crystal-
linity of the particles synthesized using the polymer–surfactant
mixture are presented in Fig. 1. The representative scanning
electron micrograph (trace a) of the Mn2O3 particles shows a
bunch of elongated nanorods with length up to 1 ꢁ 0.3 mm and
width of 50 ꢁ 10 nm. To further examine the surface
morphology of the microstructures, high magnication SEM
images were recorded (trace b), and it was apparent that the
surface of the particles had roughened edges, which indicates
that the growth and slow transformation to rod-shaped nano-
structures occur through the oriented aggregation of primary
nanocrystals. At the very beginning of reux, the concentration
of reactants is comparatively high; therefore, some nuclei can
2.3 General procedure for the synthesis of aldehydes
The precursor alcohol (1 mmol), Mn2O3 (1.6 mg, 0.01 mmol), be formed rapidly, resulting in the occurrence of ultrasmall
PhI(OAc)2 (403 mg, 1.25 mmol) and MgSO4 (about 300 mg) were particles. Subsequently, the nuclei orient and grow fast along
placed together in ethylenedichloride (EDC, 25 mL) and stirred the (211) direction to form one-dimensional nanorods.49 The
magnetically at 45 ꢀC until the reaction was complete. The size and shape of the nanocrystals is further evident from the
progress of the reaction was monitored by TLC. Aer the transmission electron micrographs (panel c) of the Mn2O3
completion of the reaction, the post reaction mixture was particles formed using the polymer–surfactant assembly. The
ltered through a sintered funnel and the residue was washed high resolution TEM image (panel d) of the Mn2O3 nanorods
with EDC (2 ꢃ 5 mL). The combined EDC was transferred to a displays an interplanar distance of about 0.357 nm between the
separating funnel, washed with water (3 ꢃ 10 mL) and dried fringes, which corresponds to the distance between the (211)
using activated MgSO4. The solvent was removed using a rotary planes of the Mn2O3 crystal lattice.50 The selected area electron
evaporator at room temperature under reduced pressure. The diffraction pattern (panel e) of the Mn2O3 nanostructures is
crude product was puried by column chromatography over consistent with strong ring patterns due to (211), (222) and (400)
silica gel (60–120 mesh) using ethyl acetate–petroleum ether as planes, which conrms the crystallinity of the materials.51 The
eluent to afford the desired aldehyde and corresponding acid representative energy dispersive X-ray spectrum (panel f) of
byproduct. Thus, the reaction of benzyl alcohol (1a, 109 mg, Mn2O3 nanorods indicates that the particles are composed of
1.0 mmol) afforded benzaldehyde (2a) and benzoic acid (3a) Mn and O elements. The formation of manganese oxide parti-
aer purication by column chromatography on silica gel cles in the polymer–surfactant conjugates has been studied
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41-1442].34 Fig. 2 shows the Raman spectrum of the as-prepared
nanorods under ambient condition. The structure of Mn2O3
belongs to Ia3 symmetry group with a ¼ 9.41 and possesses
cubic bixbyite structures.53 The bands at 310, 366 and 655 cmꢂ1
could be ascribed to the out-of-plane bending modes of Mn2O3,
the asymmetric stretch of bridge oxygen species (Mn–O–Mn)
and the symmetric stretch of Mn2O3, respectively,54,55 in corre-
spondence to that obtained for bulk MnOx particles.56
Thermogravimetric analysis (ESI 4†) of the as-dried powder
sample shows two weight loss steps in the curve: 8.9 wt% loss
corresponding to the water desorption (up to 200 ꢀC) and a
weight loss of 32.1 wt% over 200–800 ꢀC as a result of the
decomposition of polymer–surfactant assemblies, verifying that
the polymer–surfactant conjugates are, indeed, incorporated
into the nanostructures.57 The textural properties of the Mn2O3
microrods were investigated by Brunauer–Emmett–Teller (BET)
gas-sorption measurements performed at 77 K for the as-dried
powder sample under vacuum, as shown in ESI 5.† The
specic surface area and Langmuir surface area of the micro-
rods were measured to be ca. 13.60 m2 gꢂ1 and 22.27 m2 gꢂ1
,
respectively, from which it is evident that Mn2O3 nanorods
synthesised in the present experiment manifest high BET
surface areas to provide a platform for the catalytic organic
transformation.30,58
In the initial experiments, we decided not to apply a high
temperature for the desired catalytic oxidation (Scheme 1) of
our model substrate, benzylalcohol (1a, R ¼ Ph, shown in ESI
6†) to benzaldehyde (2a) using l3-hypervalent iodane;46,47,59
thus, the possibility of forming byproduct benzoic acid (3a,
entry 1, Table 1) could be avoided. Aer several experiments
using as-synthesised Mn2O3 nanorods (1 mol%), we discovered
its catalytic property for the oxidative dehydrogenation reaction
using PhIO46 (1.25 mmol), which revealed about 60% conver-
sion at 50 ꢀC to afford benzaldehyde (2a; yield: 45%) with high
selectivity (2a : 3a ¼ 9 : 1). The yield (68%) was improved when
PhICl2 (entry 2) was used. Gratifyingly, utilizing commercially
available PhI(OAc)2,47 the conversion (100%), reaction rate (2 h),
yield (96%) and selectivity (2a : 3a ¼ 47 : 3) were signicantly
improved under the similar reaction conditions (entry 3). The
optimized oxidation process was found to utilize as low as
0.01 mol% of the nanorods as described in the entry 7, which
was obtained (entries 5–8) by changing the reaction tempera-
ture (50–40 ꢀC) and catalyst loading (1–0.005). The reaction rate
(70% in 12 h), yield (48%) and selectivity (2a : 3a ¼ 2 : 3) were
drastically reduced in the absence of the Mn2O3-NPs (entry 9).
Ethylene dichloride was found to be the suitable solvent
because the other polar aprotic solvents such as dichloro-
methane (CH2Cl2), tetrahydrofuran (THF) and acetonitrile
(entries 10–12), nonpolar toluene (entry 13) and protic meth-
anol or water (entries 14 and 15) were not effective for the
unprecedented catalytic process.
Fig. 1 (a) Scanning electron micrograph, (b) high resolution scanning
electron micrograph, (c) transmission electron micrograph, (d) high
resolution transmission electron micrograph, (e) selected area elec-
tron diffraction pattern, and (e) energy dispersive X-ray analysis of the
manganese oxide microrods in polymer–surfactant conjugates.
through FTIR spectroscopy (ESI 2†). It is seen that an Mn–O
bond stretching frequency appears in the range of 450–680
cmꢂ1 along with two strong peaks at 630 and 525 cmꢂ1, which
arise due to the stretching vibration of Mn–O and Mn–O–Mn
bonds,35 indicating the formation of Mn2O3 in the polymer–
surfactant conjugates.52 The X-ray diffraction pattern of the
representative hybrid rod-shaped assemblies is shown in ESI 3;†
all diffraction peaks, implying a crystalline structure, are
consistent with the standard values of bulk Mn2O3 [JCPDS no.
The diverse catalytic activity of the Mn2O3-nanorods was
evaluated utilizing various types of alcohols under the opti-
mized reaction conditions (entry 1, Table 2 as shown in ESI 6†).
The benzyl alcohols bearing activated (1b) and deactivated (1c)
aromatic moieties (entries 2 and 3, Table 2†) were tolerated in
this reaction to afford the corresponding aldehyde with
Fig. 2 Raman spectrum of the manganese oxide/polymer–surfactant
hybrid assemblies dried in air.
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Table 1 Synthesized aldehydes, sugar aldehyde and ketones
Reagent &
Conversion Desired aldehyde (2) or
Yield
Entry Alcohol (1)
Catalyst
conditions
(%)
ketone (4)
Acid (3)
(%, 2 : 3)
Mn2O3
(0.01 mol%)
PhI(OAc)2, EDC,
45 ꢀC 4.0 h
91
(24 : 1)
1
100
Mn2O3
(0.01 mol%)
PhI(OAc)2, EDC,
45 ꢀC 4.5 h
89
(19 : 1)
2
3
4
5
100
100
100
100
Mn2O3
(0.01 mol%)
PhI(OAc)2, EDC,
45 ꢀC 3.0 h
95
(23 : 2)
Mn2O3
PhI(OAc)2, EDC,
90
(19 : 1)
(0.01 mol %) 45 ꢀC 4.0 h
Mn2O3
PhI(OAc)2, EDC,
92
(19 : 1)
(0.01 mol %) 45 ꢀC 4.0 h
Mn2O3
(0.01 mol%)
PhI(OAc)2, EDC,
76
(91 : 9)
6
7
8
100
100
100
45 ꢀC 4.0 h
Mn2O3
(0.02 mol%)
PhI(OAc)2, EDC,
45 ꢀC 6.0 h
3a (not detected)
3a (not detected)
Mn2O3
(0.02 mol%)
PhI(OAc)2, EDC,
45 ꢀC 5.0 h
excellent yield and selectivity (entries 2 and 3). Interestingly, in aliphatic aldehyde (2f) with high yield (76%) and selectivity
the presence of the strongly electron withdrawing –NO2 group, (91 : 9). The diverse catalytic activity of the Mn2O3-nanorods was
the reaction rate was enhanced (from 4.5 to 3 h) with respect to also successfully exploited on functionalized secondary alco-
the activated aromatic nucleus (1b), which simultaneously hols (1g and 1h) to obtain corresponding ketones (4a and 4b,
reduced the selectivity from 19 : 1 to 23 : 2 (entries 2 and 3).
entries 8 and 9) without the formation of the by-product, ben-
The diverse catalytic activity of the Mn2O3-nanorods was zoic acid (3a). The catalytic reaction was tested with bulk
evaluated utilizing various types of alcohols under the opti- Mn2O3, and it was seen that the particles could not selectively
mized reaction conditions (entry 1, Table 2†). The benzyl alco- transform the alcohols to aldehydes. A comparative account
hols bearing activated (1b) and deactivated (1c) aromatic highlighting the utility of Mn2O3 nanorods and some other
moieties (entries 2 and 3, Table 2†) were tolerated in this catalysts60–63 towards the oxidation of alcohols is presented in
reaction to afford corresponding aldehyde with excellent yield ESI 7.† This unprecedented property of Mn2O3-nanorods under
and selectivity (entries 2 and 3). Interestingly, in the presence of very low catalyst loading (0.01 mol%) provides new prospects
strongly electron withdrawing –NO2 group, the reaction rate was and perspectives in catalysis towards the discovery of new
enhanced (from 4.5 to 3 h) with respect to the activated materials, innovative catalytic activity and novel organic trans-
aromatic nucleus (1b), which simultaneously reduced the formation to afford functional molecules for our highly
selectivity from 19 : 1 to 23 : 2 (entries 2 and 3). Another inter- demanding modern society.
esting feature observed in this reaction is the high chemo-
selectivity. Even the oxidation prone double and triple bond-
bearing allyl (1d) and propargyl (1e) alcohols (entries 4 and 5)
4. Conclusion
smoothly underwent oxidation to corresponding aldehydes with
90–92% yield and outstanding selectivity (19 : 1). We turned our
attention to applying this benign strategy for the oxidation of
sugar-based chiral alcohol (1f, entry 6), and under the similar
reaction conditions it afforded corresponding optically pure
In conclusion, the hydrolysis of manganese precursor in the
presence of polymer–surfactant so template has been found to
be an effective strategy for the fabrication of Mn2O3 nanorods.
The nanorods are crystalline and offer roughened surface and
large surface area that installs new and innovative catalytic
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Acknowledgements
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