Wool supported manganese dioxide nano-scale dispersion: A biopolymer based catalyst for the aerobic oxidation of organic compounds

Article abstract of DOI:10.1039/c5ra10522f

A wool supported manganese dioxide nano-scale dispersion (MnO₂@wool) was synthesized by soaking wool in a potassium permanganate solution and characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The synthesized catalyst, MnO₂@wool complex, has been found to be able to catalyze the selective aerobic oxidation of alkyl arenes, alcohols, oximes, and sulfides to their corresponding carbonyl and sulfoxide compounds in the absence of additional oxidizing reagent. The selective conversion of thiols to disulfides was carried on by this biopolymer based supported catalyst, too.

Full text of DOI:10.1039/c5ra10522f

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Wool supported manganese dioxide nano-scale
dispersion: As a biopolymer based catalyst for the
aerobic oxidation of the organic compounds
*
Ahmad Shaabani , Zeinab Hezarkhani, and Elham Badali
Faculty of Chemistry, Shahid Beheshti University, G. C., P. O. Box 19396-4716, Tehran,
Iran
Email: a-shaabani@sbu.ac.ir
Abstract
2
Wool supported manganese dioxide nanoꢀscale dispersion (MnO @wool) were synthesized by
soaking wool in a potassium permanganate solution and characterized by xꢀray diffraction (XRD),
thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The synthesized
2
catalyst, MnO @wool complex, has been found to be able to catalyze the selectively aerobic
oxidation of alkyl arenes, alcohols, oximes, and sulfides to their corresponding carbonyl and
sulfoxide compounds in the absence of additional oxidizing reagent. The selectively conversion of
thiols to disulfides was carried on by this biopolymer based supported catalyst, too.
Introduction
Manganese dioxide occurs naturally as the mineral pyrolusite. This blackish
or brown solid is a cheap, renewable, mild, easily handled, and low toxic reagent,
which has been extensively used as catalyst for the oxidations of a variety of
1
ꢀ3
functional groups. MnO
2
usually provides a relatively low surface area (10–80
2
ꢀ1
4
m g ) because of its aggregation which impresses its catalytic activities.
Producing of manganese dioxide nanostructures provides the large surface area of
5
catalyst. By using of supports for the distribution of MnO
2
nanostructures,
4, 6
aggregation of MnO is prevented and high catalytic activity is accessible.
2
Industrial applications of MnO
2
have become more attractive environmentally
7
by the introduction of a process for recycling MnO
2
. For this reason, it is
important that at the end of the catalytic oxidation process, the MnO is
2
2
separable from supports. Although the procedure for separating MnO from
8
9
10
11
supports such as kieselguhr , aluminum silicate, alumina, or silica, has not
1

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6
been described before, but in our previous work it was suggested that it
possible to separate the MnO
decomposing of bioꢀsupport.
2
from a bioꢀsupport by burning or chemical
The oxidation of organic compounds to their corresponding oxygenated
compounds by air as green oxidant using a bioꢀsupport catalyst is of main
12
importance for both economic and environmental reasons. Natural biopolymers
5,
6
13
14
15
such as cellulose,
chitosan, starch, and protein with emphasis on
environmentally friendly, sustainable resources and reusable catalytic processes
have been used as supports in various oxidation processes. However, to the best of
our knowledge, the use of natural wool as attractive candidate to be solid support
for oxidation reactions has not been explored until now.
Wool is a very cheap natural biopolymer of amino acids crossꢀlinked by S–S
bonds and its main component is keratin. The mentioned biopolymer contains
2
numerous amino acids units with –NH–CO–, –NH , and –S–S– functional
1
6
groups. The metal uptake by wool fibers can be enhanced by chemically
+
modifying the fibers with oxidation of –S–S– and –NH–CO– to –SO
3
H, –NH
3
ꢀ
17
and–CO
2
groups that able to coordinate metals in the surface of the wool.
Furthermore, the loaded metal particles could be distributed evenly on the surface
1
8
of the wool. As mentioned the aggregation and agglomeration of MnO
2
particles
into less active large particles and bulk MnO during the reaction decreased its
2
catalytic activities. To settle the matter, wool can be used as support for
manganese dioxide nanostructures. Due to the structurally ordered amino acid
chains, the aggregation of MnO2 could be prevented. The structure of
2
MnO @wool complex is shown in Scheme 1.
2

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2
Scheme 1 The possible structure of MnO @wool
As part of our ongoing program related to developing new methods using
1
9, 20
heterogeneous catalysts for organic transformations,
and based on our
and due to the importance of the using
heterogeneous catalyst based on immobilization of
nanoparticles on wool was synthesized and applied for selective aerobic
6, 21, 22
2
previous investigations on MnO ,
16ꢀ18
wool as a bioꢀsupport,
MnO
2
oxidative transformations of alkyl arenes, alcohols, oximes, and sulfides into the
corresponding carbonyl compounds and sulfoxides, in the absence of any other
oxidizing reagent or initiator. Disulfides can also be prepared by aerobic
2
oxidation of thiols using MnO @wool catalyst. It is important to note that these
aerobic transformations did not proceed without air blowing.
Materials and methods
1
General
Natural white wool (sheep of Kangavar/Iran) was washed with NaOH
solution, distilled water and methanol, and then cut into very short pieces. All
reagents were obtained from Aldrich or Merck and used without further
purification. Mn(IV) determination was carried out on an FAAS (Shimadzu
model AAꢀ680 flame atomic absorption spectrometer) with a Mn hollow
cathode lamps at 279.5 nm, using an airꢀacetylene flame. Thermogravimetric
analysis (TGA) was carried out using STA 1500 instrument at a heating rate of
−
1
1
0 ºC min in air. Products were analyzed using a Varian 3900 GC. Xꢀray
diffraction (XRD) pattern of catalyst was recorded on a STOE STADI P with
3

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scintillation detector, secondary monochromator using Cu Kα radiation (λ =
.1540 nm). Scanning electron microscopy (SEM) observations were carried out
0
on an electron microscopy Philips XLꢀ30 ESEM. All samples were sputtered with
gold before observation.
2
Experimental: preparation of supported manganese dioxide
nanostructures on wool
Natural white wool was washed with NaOH solution (0.01 M), distilled
water and methanol and dried at 60 °C, then cut with scissors to very short
pieces (about 20ꢀ500 µm, based on SEM images). To a magnetically stirred
mixture of the wool pieces (1.00 g) in 200 mL of H
KMnO (130 mL) was added dropwise during 12 h at room temperature and
stirring was continued at room temperature for 12 h. Then, the mixture was
filtered and washed with CHCl (3 × 7 mL) and EtOH (3 × 10 mL),
2
O, a 0.01 M solution of
4
3
successively and dried under vacuum at 60 °C for 12 h to give MnO
brown color, 1.1 g).
2
@wool (as
3
Analysis and results
The Mn(IV) content of the MnO @wool catalyst was determined using
2
FAAS method and the amount of MnO
2
was determined 7.9% in this catalyst. The
@wool were employed to investigate the
XRD patterns of wool fibers and MnO
2
structure of the synthetic catalyst. As shown in Fig. 1ꢀI, two broad peaks of wool
fibers are observed around 2θ of 9° and 21° that clearly these peaks exist in the
diagram II of Fig.1. It can be seen from Fig. 1ꢀII that all the diffraction peaks of
2
MnO nanostructures rather than the peak of wool fibers are extremely weak in
intensity and four weak peaks at 2θ = 13.90°, 24.28°, 34.60°, and 65.26° can be
ascribed to the MnO nanostructures dispersed onto the surface of wool fibers.
2
4

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2
Fig. 1 XRD patterns of wool fibers (I) and MnO nanoparticle coated wool fibers (II).
TGA demonstrated that wool was decomposed in three stages (Fig. 2ꢀI): the
removal of adsorbed water (stage 1) and decomposition of wool (stages 2 and 3).
In fact, decomposition of wool was happened in two stages above 241 °C and 487
°C, which showed relatively high thermal stability of the wool fibers in air (Fig. 2ꢀ
I). High thermal stability was observed for MnO @wool (Fig. 2ꢀII), too. In the
2
2
TGA curve of MnO @wool catalyst, three stages could be observed. In the low
temperature range (up to 242 °C), the mass slowly decreased by 1.9% that should
be related to the removal of adsorbed water on the surface in MnO @wool. In the
2
range of 242ꢀ516 °C and 516ꢀ735 °C in two stages large weight loss for this
catalyst was observed, which is attributed to the decomposition of wool.
2
Fig. 2 TG curves of wool (I) and MnO nanoparticle coated wool fibers (II) in air.
2
Fig. 3 reveals the surface morphology of the wool fibers and MnO @wool.
Clearly, the wool fibers have a length of about 20ꢀ500 µm (Fig. 3a) and its
surface has a wrinkled structure (Fig. 3b). The structure and morphology of the
2 2
obtained MnO @wool composites were illustrated by SEM (Fig. 3c, d) and MnO
nanostructures could be observed on the wool fiber surface which nanoparticles
are well dispersed on the wool fiber surface (Fig. 3d).
5

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2
Fig. 3 SEM images of wool (a, b) and MnO @wool (c, d).
Additionally, for determination of the chemical composition of MnO
2
@wool
composite, the energy dispersive spectroscopy (EDS) analysis was employed that
2
proves the presence of manganese in the MnO @wool composite (Fig. 4).
Fig. 4 SEMꢀEDS results for MnO @wool catalyst.
2
4
Oxidation of alkyl arenes; General procedure
2
In a typical reaction, an alkyl arene (1.00 mmol), MnO @wool (0.11 g, 10
mol% of MnO ), and oꢀxylene (5.00 mL) were added to a twoꢀnecked flask. The
2
mixture was stirred under reflux conditions and air blowing for the indicated
time in Table 2. The thin layer chromatography (TLC) method was used to
investigate the progress of the reaction. Upon completion, analysis of the crude
product has been done by GC method.
6

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5
Oxidation of alcohols; General procedure
In a typical reaction, an alcohol (1.00 mmol) was added to a twoꢀnecked flask
containing MnO @wool (0.11 g, 10 mol% of MnO ), K CO (0.50 mmol), and
ꢀxylene (5.00 mL) and stirred under room temperature and air blowing for the
2
2
2
3
o
indicated time in Table 4. The progress of the reaction was followed by TLC.
After completion of reaction and then filtration, the filtrate was analyzed by GC
method.
6
Oxidation of oximes; General procedure
MnO @wool (0.11 g, 10 mol% of MnO ) and an oxime (1.00 mmol) were
2
2
well ground at room temperature using a pestle. The progress of the reaction was
monitored by TLC. After the indicated time in Table 6 which the reaction was
complete, the solid was washed with dichloromethane (3 × 5 mL). After the
filtration of the reaction mixture, the filtrate were evaporated to give crude
product. Analysis of the crude product has been done by GC method.
7
Oxidation of sulfides and thiols; General procedure
In a round bottom flask, to a solution of sulfide or thiol (1.00 mmol) in oꢀ
xylene (5.00 mL), MnO
2
@wool catalyst (0.11 g, 10 mol% of MnO
2
for
oxidation of sulfides and 0.22 g, 20 mol% of MnO
2
for oxidation of thiols) was
added and the mixture was stirred magnetically at room temperature for the
indicated time in Table 5. the progress of the reaction was monitored by TLC.
After completion, the reaction mixture was filtered and the filtrate was
evaporated under reduced pressure to give the corresponding pure sulfoxide or
disulfide. All of the products were characterized by melting points which were
2
3ꢀ25
compared with those obtained from authentic samples.
Results and discussion
The natural wool was treated by potassium permanganate. The KMnO
able to oxidize and modify the surface of wool, and in situ was reduce to MnO
nanostructures as a catalyst. KMnO molecules were adsorbed by the wool fibers
4
is
2
4
4 4
and the maximum absorption of KMnO is at the edge of scale layer. The KMnO
can attack the disulfides linkage and the peptide bonds of the wool fiber and
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2
6
reduced to MnO
act not only as a reduction agent to produce MnO
impregnate MnO nanostructures on its surface (Scheme 2).
2
covering on the surface of this fiber. In fact, the wool fibers
2
, but also has support role to
2
2
Scheme 2 The preparation of MnO @wool catalyst.
After the successful production of catalytic systems in which wool plays
dual role: as a in situ reducing agent of KMnO to generate MnO
nanostructures and as the support to achieve a suitable catalytic system for
aerobic oxidation, we examined MnO @wool catalyst in the reaction media.
Aerobic oxidation of indane was selected as a model reaction. Indane (0.12 g,
.00 mmol), MnO @wool, solvent (5.00 mL) were added to a twoꢀnecked
flask equipped with a gas bubbling tube. Air that used as an environment
4
2
2
1
2
ꢀ
1
friendly oxidant, was bubbled at a rate of 5 mL min . After completion of
reaction, as indicated by TLC or GC method, catalyst was filtered and washed
with acetone (2
× 5 mL), and EtOH (2 × 5 mL). The analysis of the crude
product using GC method showed that corresponding aldehydes and ketones
was produced.
In order to find the best reaction conditions, optimization studies were
performed in various solvents (Table 1, Entries 2ꢀ10). The efficiency of
MnO
2
@wool catalyst in
o
ꢀxylene was higher than other solvents (Table 1,
Entries 10). Therefore
o
ꢀxylene was selected as the preferred solvent for the
aerobic oxidation of indane.
From the data presented in the Table 1, it is clear that the prepared catalyst,
2 2
MnO @wool, has better catalytic role than aggregated MnO (Entries 1 and 10).
8

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The comparison of the results related to the effect of various amounts of
MnO @wool revealed that the 10 mol% of MnO is providing the best result
Table 1, Entries 10ꢀ12).
2
2
(
Table 1 Optimization of the reaction conditions for aerobic oxidation of alkyl arenes by
a
MnO @wool catalyst
2
Amount of catalyst
MnO content/mol%)
Yield
(%)
24
61
49
22
19
Trace
Trace
25
Entry
Catalyst
MnO
Solvent
b
(
2
1
2
3
4
5
6
7
8
9
2
0.01 g (10)
0.11 g (10)
0.11 g (10)
0.11 g (10)
0.11 g (10)
0.11 g (10)
0.11 g (10)
0.11 g (10)
0.11 g (10)
0.11 g (10)
0.09 g (8)
o-xylene
nꢀhexane
MnO
MnO
MnO
MnO
MnO
MnO
MnO
MnO
2
2
2
2
2
2
2
2
@wool
@wool
@wool
@wool
@wool
@wool
@wool
@wool
CH
CH
2
Cl
CN
2
3
THF
MeOH
EtOH
DMF
toluene
o-xylene
oꢀxylene
oꢀxylene
83
99
63
46
1
1
1
0
1
2
MnO
2
@wool
@wool
@wool
MnO
MnO
2
2
0.07 g (6)
a
b
2
Reaction conditions for MnO @wool catalyst: indane (1.00 mmol), solvent (5.00 mL), air as oxidant, reflux, 10 h.
Yield determined by GC analysis.
Finally, the oxidation of the various alkyl arenes to related carbonyl
2
compounds using MnO @wool catalyst in oꢀxylene as the preferred solvent
under reflux conditions was studied. The oxidation of the alkyl arenes was
proceeded effectively and selectively without any overoxidation to carboxylic
acid during the reaction (Table 2).
a
Table 2 Aerobic oxidation of variuos alkyl arenes to corresponding ketones
Time
h)
Yeild
(%)
Time
(h)
Yeild
(%)
Entry
1
Alkyl arene
Product
b
Entry
6
Alkyl arene
Product
b
(
10
12
93
95
10
12
91
84
2
2
7
3
4
5
12
9
86
100
99
8
9
9
9
99
94
89
O
10
10
10
a
b
Reaction conditions: alkyl arene (1.00 mmol), MnO
Yield determined by GC analysis.
2
@wool (0.11 g), oꢀxylene (5.00 mL), air as oxidant, reflux.
The oxidation of the alkyl arenes has been carried out successfully using
the MnO @wool catalyst, therefore the usability of this catalytic system has
2
been examined for the oxidation of the alcohols, as well. Optimization studies
were performed with aerobic oxidation of 1ꢀindanol, as a model substrate. As
9

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indicated in Table 3, the best result is related to the 10 mol% of of MnO
xylene as a preferred solvent, and K CO as base (Entry 10).
2
, oꢀ
2
3
Table 3 Optimization of the reaction conditions for aerobic oxidation of alcohols by MnO @wool
2
a
catalyst
Amount of catalyst
MnO content/mol%)
Yield
(%)
32
91
48
19
28
trace
trace
33
89
98
69
44
54
36
27
Entry
Catalyst
MnO
Solvent
Base (mmol)
b
(
2
1
2
3
4
5
6
7
8
9
2
0.01 g (10)
0.11 g (10)
0.11 g (10)
0.11 g (10)
0.11 g (10)
0.11 g (10)
0.10 g (10)
0.09 g (10)
0.11 g (10)
0.11 g (10)
0.09 g (8)
o-xylene
nꢀhexane
K
2
K
2
K
2
K
2
K
2
K
2
K
2
K
2
K
2
K
2
K
2
K
2
CO
CO
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
3
3
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
(0.5)
MnO
MnO
MnO
MnO
MnO
MnO
MnO
MnO
2
2
2
2
2
2
2
2
@wool
@wool
@wool
@wool
@wool
@wool
@wool
@wool
CH
2
Cl
2
CH
3
CN
THF
MeOH
EtOH
DMF
toluene
o-xylene
oꢀxylene
oꢀxylene
o-xylene
oꢀxylene
oꢀxylene
1
1
1
1
1
1
0
1
2
3
4
5
MnO
2
@wool
@wool
@wool
@wool
@wool
@wool
CO
CO
CO
3
MnO
MnO
MnO
MnO
MnO
2
3
2
2
2
2
0.07 g (6)
3
0.11 g (10)
0.08 g (10)
0.11 g (10)
KOH (0.5)
Na
2
CO
ꢀ
3
(0.5)
a
b
Reaction conditions: 1ꢀindanol (1.00 mmol), solvent (5.00 mL), air as oxidant, r.t., 8 h.
Yield determined by GC analysis.
To extend the scope of the prepared catalyst, the oxidation of the alcohols
to the related carbonyl compounds have been investigated The results of the
.
mentioned reactions have been presented in the Table 4. The reactions were
done under air blowing at room temperature with good to high yields. Selectivity
for the oxidation of the alcohols to the corresponding carbonyl compounds had
been observed, too (Table 4).
a
Table 4 Selective aerobic oxidation of variuos alcohols to corresponding aldehydes and ketones
Time
Yield
(%)
Time
(h)
Yield
(%)
Entry
1
Alcohol
Product
b
Entry
11
Alcohol
Product
b
(
h)
8
98
93
12
96
89
2
3
4
8
8
8
12
13
14
14
92
93
13
14
90
85
5
6
8
7
95
98
15
16
13
13
93
88
7
8
98
17
13
86
1
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c
8
9
6
99
18
19
6
94
c
c
6
9
97
87
13
13
87
89
1
0
20
a
Reaction conditions: alcohol (1.00 mmol), MnO
2
@wool (0.11 g), K
2
CO
3
(0.50 mmol), oꢀxylene (5.00 mL), air as
oxidant, r.t.
b
Yield determined by GC analysis.
The yield of only ketone product determined by GC analysis and the integrals of the H NMR.
c
1
2
According to Table 4, MnO @wool catalyst showed high selectivity for
the oxidation of the benzylic alcohols to the related carbonyl compound, and
no carboxylic acid was produced (Entries 1ꢀ10). The prepared catalyst has
same selectivity for the oxidation of allylic and aliphatic alcohols to
corresponding aldehydes and ketones (Entries 11ꢀ17).
Variety of reagents are available to selectively oxidize a secondary alcohol
in the presence of primary alcohol. The rate of these used reagents to oxidize
secondary alcohols is slightly faster than primary alcohols but some of reagents
have not been highly selective for oxidation of secondary alcohols because of
the small magnitudes of rate differences. In fact, when the substrate structure
is compatible with the reaction mechanism of the reagent, high selectivity is
2
7
possible. Between these reagents, MnO
2
acts highly selective for the
oxidation of secondary aliphatic and benzylic alcohols in the presence of
6
primary ones. In our previous work, examples of interꢀ and intramolecular
competition experiments and regioselective oxidations was shown basis on the
evidence for secondaryꢀprimary selectivity of MnO
2
stable nanoꢀscale
6
dispersion.
In this report, mixed primary and secondary benzyl alcohols (Entry 18) and
alkylalcohols (Entry 19) as the reactants was used to investigate the selectivity of
the MnO @wool catalytic system. The results showed that the oxidation of the
2
secondary functional group is favored and only one of the reactants undergoes
oxidation reaction. The oxidation of 2ꢀethylheptaneꢀ1,3ꢀdiol, a diol with both
primary and secondary hydroxyl functional groups revealed that only product 3ꢀ
(hydroxymethyl)octanꢀ4ꢀone was obtained (Entry 20). In both cases (interꢀ and
intramolecular competition experiments), at first step the oxidation of the
1
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secondary functional group was done and in continue after the completion of
this reaction, the transformation of the primary alcohol was started.
The production of sulfoxide containing compounds as important
intermediates in organic chemistry, medicinal chemistry and drug metabolism are
28
very important. Since oxidation of sulfides with manganese dioxide is known to
22
give only sulfoxides, the oxidation of the sulfides to the related sulfoxides
compounds using MnO @wool has been investigated as well. The obtained
2
results (Table 5, Entries 1ꢀ7) showed that the oxidation of sulfides to sulfoxides
has been carried out without any overoxidation to sulfones. Aerobic oxidation
2
of thiols to the related disulfides using MnO @wool catalyst was done and the
obtained data have been shown in the Table 5 (Entries 8ꢀ10).
a
Table 5 Selectively aerobic oxidation of variuos sulfides to corresponding sulfoxides
Time
Yield
(%)
Time
(h)
Yield
(%)
Entry
1
Sulfide or thiol
b
Entry
6
Sulfide or thiol
b
(
h)
3
97
94
5
6
96
88
2
3
4
7
7
8
90
1
93
4
5
7
5
87
91
9
1.5
1.5
96
87
10
a
Reaction conditions: sulfide or thiol (1.00 mmol), MnO
and 0.22 g, 20 mol% of MnO for oxidation of thiols), o-xylene (5.00 mL), air as oxidant, r.t.
Yield determined by GC analysis.
2 2
@wool (0.11 g, 10 mol% of MnO for oxidation of sulfides
2
b
Imine derivatives of carbonyl compounds (such as oximes, semicarbazones
and phenylhydrazones) are used extensively for the characterization, isolation, and
purification of carbonyl compounds. Oximes are also used as carbonyl protectors
2
9, 30
of parent carbonyl compounds
because of their hydrolytic stability and could
be regenerated at the completion of a synthetic procedure. On the other side
oximes can also be prepared from noncarbonyl compounds. The carbonyl
generation from these compounds provides an alternative method for the
31
preparation of aldehydes and ketones . Many methods such as hydrolytic,
reductive, and oxidative reactions and reagents have been reported for
1
2

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DOI: 10.1039/C5RA10522F
regeneration of carbonyl compounds from oxime derivatives. Using mild reagents
and reaction conditions will cause the regeneration of the carbonyl compound to
be done without modification to the rest of the molecule.
Thus, oxidation of oximes to the related carbonyl compounds has been
studied under solventꢀfree conditions at room temperature with the yields
between 87 and 99. The obtained results have been presented in the Table 6. It
is important to note that with adding several drops of any solvent which can solve
the oximes, and oxidation reactions were accelerated.
a
Table 6 Selectively oxidation of variuos oximes to corresponding aldehydes and ketones
Time
Yield
Time
(min)
Yield
Entry
1
Alcohol
Entry
5
Alcohol
b
b
(
min)
(%)
(%)
7
94
91
7
7
96
94
2
3
7
9
6
7
87
90
6
5
97
99
4
9
8
a
b
Reaction conditions: oxime (1.00 mmol), MnO
Yield determined by GC analysis.
2
@wool (0.11 g), room temperature.
2
Recyclability of the MnO @wool catalyst was examined in the oxidation
reaction of indane, 1ꢀindanol, 2,3ꢀdihydroꢀ1Hꢀindenꢀ1ꢀone oxime, and methyl
phenyl sulfide. Catalyst was recovered from reaction media by filtration and
reused for three repetitive cycles in the reaction. The results revealed that the
2
activity of the MnO @wool was saved during successive uses (Fig. 5).
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Fig. 5 Successive use of the prepared catalyst for the oxidation of indane, 1ꢀindanol, 2,3ꢀdihydroꢀ
1
Hꢀindenꢀ1ꢀone oxime, and methyl phenyl sulfide.
The results of our investigations have been compared to previous reports of
6
, 8, 9, 11, 32ꢀ35
MnO
2
.
2
The results show that MnO impregnated on wool is one of the
best oxidant systems in reaction times and yield viewpoints (Table 7).
Table 7 Comparison of the results obtained from active MnO
2
, MnO
2
on different supports and
nano MnO
2
impregnated on wool for the oxidation of benzylalcohol
Molar ratio
substrate to
Time
h)
Yield
(%)
Entry
Catalyst
Conditions
Ref.
(
MnO
2
1
2
3
4
5
active MnO
active MnO
2
2
solvent free/ r.t.
toluene/O /110 °C
2
1:0.08
1:0.80
1:2.00
1:2.00
1:2.00
48
4
10
10
3
77
85
92
90
95
[32]
[33]
[34]
[35]
[8]
2
MnO /Graphite
CH
CH
2
Cl
Cl
2
/ref.
/ref.
2
MnO /Kieselguhr
2
2
MnO
MnO
2
/Kieselguhr
solvent free/50ꢀ55 °C/grind
2
/Aluminum
Silicate
6
7
CH Cl /ref.
2
2
1:3.00
12
96
[9]
solvent free/ref./Microwave
irradiations
MnO /Silica
Nano MnO /Cellulose
Nano MnO @wool
2
1:5.00
1:0.10
1:0.10
0.3
7
88
99
98
[11]
8
9
2
oꢀxylene/air/r.t.
[6]
This
work
2
oꢀxylene/air/r.t.
8
Conclusion
Manganese dioxide nanostructures supported on wool which composed of
protein with repeated unit of amino acid, as bioꢀsupported heterogeneous catalyst,
were synthesized and used for the selective oxidation of a variety of functional
2
groups. The distribution of MnO on the surface of wool fibers gave an active
catalytic system. The prepared catalyst showed high selectivity for the aerobic
oxidation of the alkyl arenes, alcohols, and sulfides to the related carbonyl and
sulfoxide compounds without any overoxidation. Use of air as oxidant
(inexpensive oxidant), the absence of any coꢀpromoter and additional oxidizing
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reagent, the recyclability of catalyst with no loss in its activity, excellent yield,
and easy workup are several advantages of MnO @wool catalyst. This catalyst
2
has high selectivity for the oxidation of oximes to related aldehydes and
ketones.
Acknowledgements
We gratefully acknowledge financial support from the Iran National Science
Foundation (INSF), the Research Council of Shahid Beheshti University and
Catalyst Center of Excellence (CCE) at Shahid Beheshti University.
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