Green and selective oxidation of alcohols by immobilized Pd onto triazole functionalized Fe 3O 4 magnetic nanoparticles

Article abstract of DOI:10.1007/s12039-018-1567-4

Abstract: Carbonyl compounds were prepared by selective oxidation of alcohols in the presence of recoverable Fe ₃O ₄@ SiO ₂@ Pd magnetic nanocatalyst in aqueous media as a green solvent. Molecular oxygen served as an oxidant. The catalyst was removed from the reaction media by external magnetic field, washed with methanol, and reused for six more times without any considerable reduction in its reactivity. The chemoselectivity and regioselectivity of the catalyst can serve for selective oxidation of primary alcohols in the presence of secondary ones, and for oxidation of unhindered alcohols in the presence of hindered ones. Graphical Abstract: Selective and facile oxidation of alcohols to their corresponding carbonyl compounds in the presence of immobilized, recoverable, and magnetic nano Pd-particles in water by molecular oxygen. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-018-1567-4

J. Chem. Sci.
(2018) 130:162
© Indian Academy of Sciences
https://doi.org/10.1007/s12039-018-1567-4
REGULAR ARTICLE
Green and selective oxidation of alcohols by immobilized Pd onto
triazole functionalized Fe3O4 magnetic nanoparticles
AREFEH DADRASa, M REZA NAIMI-JAMALa,∗ , F MATLOUBI MOGHADDAMb and
SEYED EBRAHIM AYATIb
aDepartment of Chemistry, Iran University of Science and Technology, Tehran, Iran
bDepartment of Chemistry, Sharif University of Technology, Tehran, Iran
E-mail: naimi@iust.ac.ir
MS received 16 February 2018; revised 5 June 2018; accepted 4 October 2018
Abstract
Carbonyl compounds were prepared by selective oxidation of alcohols in the presence of recoverable
Fe3O4@SiO2@Pd magnetic nanocatalyst in aqueous media as a green solvent. Molecular oxygen served as an
oxidant. The catalyst was removed from the reaction media by external magnetic field, washed with methanol,
and reused for six more times without any considerable reduction in its reactivity. The chemoselectivity and
regioselectivity of the catalyst can serve for selective oxidation of primary alcohols in the presence of secondary
ones, and for oxidation of unhindered alcohols in the presence of hindered ones.
Keywords. Alcohol oxidation; magnetic nanocatalyst; recyclability; selectivity.
1. Introduction
limit their application, especially in industry. Moreover,
the final products can be polluted by the homogeneous
catalysts. On the contrary, heterogeneous catalysts are
non-soluble in reaction media and can be easily removed
from the reaction and reused for several times. The het-
erogeneous catalysts suffer from low yield, which can be
attributed to their poorly defined active sites. Therefore,
the quality of the surface area of a heterogeneous cata-
lyst determines the availability of catalytic active sites
for reactants. To increase the effectiveness of a hetero-
geneous catalyst, its surface area should be increased,
which is possible by using it in nanoscale.8 Although
the collision number increases by using nanoparti-
cles, they have generally high surface energy and are
thermodynamically unstable and susceptible to form
agglomeration. By using magnetic nanoparticles and
coating them with an organic linker, not only this defi-
ciency is obviated, but also the long, tedious filtration or
centrifugation removal of nanocatalyst becomes easier
by just applying an external magnetic field.9
Carbonyl compounds are excellent precursors for the
synthesis of molecules with versatile applications in
industry, pharmacology and other research work.1 So,
their synthesis from the corresponding alcohols is
of paramount importance.2 Many different ways and
reagents such as oxalyl chloride-dimethyl sulfoxide
(Swern oxidation),3 hypervalent iodine4 and stoichio-
metric amounts of Cr(VI) salts5 have been previously
reported, but they suffer from many drawbacks such as
toxic and hazardous reagents, nonselective alcohol oxi-
dation, noncompliance of atom economy, low yield and
high price, as well as serious environmental damages.
They also produce a lot of waste, which is not acceptable
from the green chemistry point of view. Consequently,
theselectiveoxidationofalcoholstotheircorresponding
carbonyl compounds with molecular oxygen, instead of
stoichiometric toxic oxidants in the green medium, has
attracted attention of researchers.6 Catalysts speed up
the reactions by reducing the activation energy with-
out being consumed. They are divided into two general
groups, heterogeneousandhomogenous.7 Amongthem,
homogenous ones are generally more effective, but the
time-consuming separation and expensive recyclability
Not all metals are magnetic, but it is possible to
couplethemwiththosewithmagneticpropertiesdirectly
or through a ligand. Metal leaching is the problem
of directly attached metals to magnetic nanoparticles,
which is solved by coating the core by organic link-
ers and anchoring active metals to them.10 Moreover,
it has been shown that the reactivity of a nanomagnetic
*
For correspondence
0123456789().: V,-vol

162 Page 2 of 10
J. Chem. Sci.
(2018) 130:162
catalyst can be even better than a corresponding 2.1d Preparation of Fe3 O4@Si O2@triazole: To
homogeneous catalyst.11
remove Cu from catalyst structure, 1.5 g potassium cyanide
For oxidation reactions, different metals like Fe,12
was dissolved in H2O/methanol (1/1, 10 mL) and the solu-
Cu,13 Co,14 Bi,15 and Au16 have been used as a cata-
tion was added to Fe3O4@SiO2@triazole@Cu which was
synthesized in the previous step and stirred for 5 h at room
lyst, but among them, palladium-based catalysts (both
temperature. The catalyst was then removed by an external
homogeneous and heterogeneous) have shown better
magnetic field, washed, and dried in air at room tempera-
activity.17 For green and selective alcohol oxidation,
different metals, oxidants, heterogeneous and homo-
ture.21
geneous catalysts have been reported in literature up
2.1e Preparation of Fe3 O4@Si O2@triazole@Pd:
Potassium chloride (0.3 g) was dissolved in methanol/water
(50/50, 10 mL), and 0.1 g palladium chloride was added to the
solution and stirred for 4 h at room temperature. The trans-
to now. Among them, the heterogeneous ones have
exceeded the homogeneous ones.18
In this work, we combined the advantages of eco-
friendly molecular oxygen as a green oxidation source,
Pd nanomagnetic particles as an efficient catalyst,
paredFe3O4@SiO2@triazolewasdispersedandsonicatedfor
parent and clear reddish solution was [K2PdCl4]. The pre-
and water as a green solvent for the selective oxida-
tion of alcohols in mild reaction conditions without
any environmentally unfriendly mediator, like 2,2,6,6-
tetramethylpiperidine-1-oxyl (TEMPO).19
15 min in 10 mL methanol. The [K2PdCl4] solution was added
to that and stirred for 24 h at room temperature. Then, the cat-
alyst was removed by an external magnetic field, washed 2
times with methanol and dried in air at room temperature.22
2.2 General procedure for alcohol oxidation
2. Experimental
A mixture of alcohol (1 mmol), K2CO3 (1 mmol), and catalyst
(1 mmol%) in H2O (5 mL) was prepared in a flask equipped
with a condenser. The flask was then filled with pure oxy-
gen and equi◦pped with an oxygen balloon. The mixture was
stirred at 80 C. The progress of the reaction was monitored
by thin layer chromatography (TLC) and gas chromatogra-
phy (GC). After completion of the reaction, the catalyst was
separated by an external magnetic field from the reaction
mediaandcorrespondingcarbonylcompoundswereextracted
with ethyl acetate. To have a complete extraction of products,
sodium chloride was added to the mixture and after separa-
tion of the aqueous layer, the organic solvent was evaporated
by rotary evaporator under reduced pressure. The products
were purified by column chromatography or re-crystallization
method. The separated catalyst was washed two times with
methanol, and dried overnight at room temperature and then
used directly for subsequent reaction runs.
2.1 General procedure for catalyst preparation
2.1a General procedure for preparation of Fe3 O4
@Si O2: FeCl3 (66.58 mmol) and FeCl2 (31.56 mmol)
were dissolved in 40 mL deionized water in an inert atmo-
sphere of argon. Ammonium hydroxide 28% (v/v) was
added to the solution to adjust pH=10. The solution was
mechanically stirred at room temperature for 20 min until a
black suspension was formed. The prepared Fe3O4 magnetic
nanoparticles were filtered, washed, and dried. The pow-
der was then dispersed ultrasonically in ethanol for 20 min.
3 mL of tetraethylorthosilicate (TEOS) was slowly added to
the solution. Ammonium hydroxide (3 mL) was added to the
solution within 15 min and stirred for 12 h at 40 ◦C. The silica
coated Fe3O4 magnetic nanoparticles (Fe3O4@SiO2) were
collected by external magnetic field, washed with methanol
and dried under vacuum in a rotary evaporator.20
3. Results and Discussion
2.1b Preparation of Fe3 O4@Si O2@3-glycidoxy-
propyltrimethoxysilane: 2 g of silica-coated Fe3O4
was sonicated in toluene for 30 min, and then 11.32 mmol
3-glycidoxypropyltrimethoxy-silane was added and refluxed
for 48 h. The prepared catalyst was washed with methanol
and dried under vacuum.20
3.1 Catalyst synthesis and characterization
The
catalyst
Fe3O4@SiO2@triazole@Pd
was
synthesized according to the previously described pro-
cedure by the authors (Scheme 1),19 and its structure
was re-characterized by field emission scanning elec-
tron microscope (FESEM) (Figure 1), thermal gravi-
metric analysis (TGA) (Figure 2), Fourier transform
infrared spectroscopy (FTIR) (Figure 3), CHN analy-
sis, vibrating sample magnetometery (VSM) (Figure 4)
and inductively coupled plasma optical electron spec-
2.1c Preparation of Fe3 O4@Si O2@triazole@Cu:
Fe3O4@SiO2@3-glycidoxypropyltrimethoxysilane(1g)and
18.2 mmol phenylacetylene were added to the solution of
sodium azide (22.7 mmol), copper(II) chloride (0.74 mmol)
and sodium ascorbate (0.76 mmol) in THF/water (80/20) for
10 h at 60 ◦C. The catalyst was removed, washed and dried.21 trometry (ICP-OES).

J. Chem. Sci.
(2018) 130:162
Page 3 of 10 162
Scheme 1. Catalyst preparation.
Figure 3. FT-IR spectra of the catalyst, (a) Fe3O4;
(b) Fe3O4@SiO2; (c) Fe3O4@SiO2@triazole; (d)
Fe3O4@SiO2@triazole@Pd.
Figure 1. FESEM image of the catalyst.
Figure 4. VSM of the catalyst.
According to the TGA analysis in Figure 2, adsorbed
waterincatalyststructureisremovedbefore200 ◦C. T◦he
catalyst decomposition occurs between about 190 C
and 540 ◦C, which is equal to ca. 21% of the weight of
the catalyst and certified the immobilization of organic
groups onto the magnetic core. As the catalyst is stable
up to ca. 200 ◦C, it can be also used for high-temperature
organic reactions.
The FT-IR spectra of the catalyst shows strong
absorption bands at 1150 cm−1 and 600 cm−1, which
refer to the Si-O and Fe-O vibrations, respectively
(Figure 3). The peaks at 2930 and 2910 cm−1 are
attributed to C-H stretching vibrations, which confirm
the presence of the alkylsilane groups on Fe3O4@SiO2.
The palladium loading on the catalyst surface was
Figure 2. TGA of the catalyst.
The catalyst shape and size was confirmed by
FESEM. The diameter of the nanoparticles is about determined by ICP-OES as 1.24 mmol.g−1, while the
50 nm, and they are approximately spherical (Figure 1). nitrogen content was determined by CHN analysis as

162 Page 4 of 10
J. Chem. Sci.
(2018) 130:162
of the catalyst was measured by a vibrating sample
magnetometer (VSM) at room temperature. According
to Figure 4, the saturation magnetization of the cata-
lyst is about 38 emu/g with a magnetic field within the
range of −9000 to 9000 Oe. This magnetization value is
enough for separating the magnetic catalyst from reac-
tion media by an external magnetic field.
Scheme 2. Various possibilities for coor-
dination of Pd atoms.
3.2 Catalytic experiments
3.00 wt%. This amount of nitrogen corresponds to ca.
0.71 mmol.g−1N3 moiety. This means that not all the To find the optimized reaction conditions, oxidation
Pd atoms are exclusively coordinated by the nitrogen of 1.0 mmol benzyl alcohol was chosen as the model
atoms in the N3 group, as shown in Scheme 1. There reaction. An oxygen balloon was chosen as an oxidant
are also some other possibilities as shown in Scheme source. The effect of the catalyst, base and solvent has
2. As shown, Pd atoms can also be chelated by oxygen been investigated (Table 1). As it is shown in Table 1
atoms present in the structure. It is also possible that a (Entries 1–3), in the absence of the catalyst, no prod-
Pd atom has been coordinated by a nitrogen atom of a uct was formed after 4 h in 3 different solvents. The
particle chain along with a nitrogen or an oxygen atom addition of the catalyst (0.5 mmol%) changed the yield
of another chain.
of the reaction in aqueous media considerably, whereas
Anyway, owing to the strong coordination of the reactions in toluene and H2O/tBuOH were not suc-
nitrogen and oxygen groups to palladium, metal loading cessful (Entries 4–6). By increasing the amount of the
was relatively high, and leaching during reactions was catalyst from 0.5 mmol% to 1 mmol%, the reaction yield
negligible. Furthermore, palladium black formation, was increased from 45 to 96% in water (Entries 6 and 9).
which is generally resulted from palladium nanoparti- The same reaction, as in Entry 9, was repeated but in the
cles agglomeration, was not formed here; so the activity absence of any base. As shown in Entry 11, it was real-
of palladium did not diminish. The magnetic property ized that the presence of a base is necessary. Obviously,
Table 1. Optimization of the conditions for the oxidation of benzyl alcohola.
Entry
Base
Solvent
Catal. (mmol%)
Temp. (◦C)
Time (h)
Yieldb(%)
1
2
3
4
5
6
7
8
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
–
Toluene
H2O/ tBuOH
H2O
Toluene
H2O/ tBuOH
H2O
Toluene
H2O/ tBuOH
H2O
–
–
–
0. 5
0. 5
0. 5
1
1
1
0. 5
1
1
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
4
4
4
4
4
4
4
4
4
10
15
4
4
24
Trace
Trace
Trace
Trace
Trace
45
Trace
18
96
65
Trace
15
15
60
Trace
9
10
11
12
13
c14
d15
H2O
H2O
H2O
H2O
H2O
H2O
Na2CO3
K3PO4
K2CO3
K2CO3
1
1
1
24
[a] reaction conditions: 1 mmol alcohol and 1 mmol base in 5 mL solvent equipped with a balloon of O2 at 80 ◦C.
[b] GC yields.
[c] in the presence of air as an oxidation source.
[d] in the absence of any oxygen source (N2 bubbling).

J. Chem. Sci.
(2018) 130:162
Page 5 of 10 162
Table 2. Oxidation of different alcohols using Fe3O4@SiO2@triazole@Pd catalysta.
OH
O
Cat. (1 mmol%), K2CO3 (1 mmol)
H2O (5 mL), 80 °C, O2 (1 atm)
R1
R2
R1
R2
1 mmol
No.
R1
R2
Time (h)
Yield (%)b
TON
TOF
1
2
3
4
5
6
7
8
CH3(CH2)6
CH3(CH2)4
C6H5
H
Me
H
H
H
H
H
H
H
18
18
4
10
12
4
10
4
10
24
24
16
16
10
10
12
12
85
83
96
93
Trace
97
41
97
39
77
Trace
90
85
89
85
93
90
850
830
960
930
–
970
410
970
390
770
–
900
850
890
850
930
900
47.2
46.1
240
93
4-ClC6H4
2-ClC6H4
4-MeC6H4
2-MeC6H4
4-MeOC6H4
2-MeOC6H4
4-NO2C6H4
2-NO2C6H4
C6H5
–
242.5
41
242.5
39
32
–
56.25
53.13
89
85
77.5
75
9
10
11
12
13
14
15
16
17
H
H
C6H5
C6H5CO
Me
C6H5
C6H5
C6H5
Et
Cyclohexanol
Cyclopentanol
[a] reaction conditions: 1 mmol alcohol and 1 mmol K2CO3 in 5 mL H2O, the balloon of O2.
[b] GC yields.
it seems that K2CO3 is the most suitable base among the
others (compare Entry 9 with 12 and 13).
In comparison to benzyl alcohol (as a primary
alcohol), 1-phenyl ethanol (as a secondary one) needed
The reaction with optimum amounts of the more time and gave less yield, obviously due to the steric
ingredients was tested in the air, instead of the oxygen effects and less activity (Table 2, Entries 3 and 14).
atmosphere. The yield was not desirable, and after 24 h,
The reaction is substantially dependent on the
only 60% benzaldehyde was gained (Table 1, Entry electron nature of the substituents and their positions.
14). The reaction was also investigated in the nitrogen Benzylic alcohols with electron donating groups at 4-
atmosphere (in the absence of any oxygen source). No position such as 4-methyl and 4-methoxy were oxidized
product was obtained, which shows that palladium can- with more yield in shorter reaction times (Table 2,
not act as the oxidant, solely (Table 1, Entry 15).
Entries 6 and 8), while benzylic alcohols with electron-
According to these data, the best result was obtained withdrawing groups such as 4-nitro need considerably
when 1 mmol% of Fe3O4@SiO2@triazole@Pd catalyst more times (24 h) and afford less yield (77%) (Table 2,
along with 1 mmol of K2CO3 in water media and oxygen Entry 10).
were used (Entry 9).
The benzyl alcohols with a substituent at 2-position
Encouraged by these results, the scope of the were substantially less active, because of steric hin-
reaction was expanded for oxidation of various alcohols. drance. 2-Methyl- and 2-methoxybenzyl alcohols were
The results have been summarized in Table 2. Differ- converted to their corresponding aldehydes with only 41
ent kinds of primary and secondary benzylic alcohols and 39% yield after 10 h (Table 2, Entries 7 and 9). The
with both electron-withdrawing and electron-donating less reactive 2-chloro and 2-nitrobenzyl alcohols were
groups were selectively oxidized to their corresponding not oxidized to their corresponding aldehydes.
carbonyl compounds with excellent yields. The cata-
To show the merit of this restriction, we have
lyst was also able to oxidize primary and secondary investigated the oxidation of 1 mmol of 4-methoxyben-
aliphatic alcohols 1-octanol and 2-heptanol to octanal zyl alcohol in the presence of 1 mmol of 2-methoxybe-
and heptanone, respectively, with good to excellent yield nzyl alcohol and monitored the progress of the reaction
(Table 2, Entries 1 and 2). It is noteworthy to mention after 2 and 4 h. The only product was 4-methoxybenzal-
that no over-oxidation of primary alcohols to carboxylic dehyde with 52% and 97% yield, respectively, which
acids was observed.
shows the selectivity of the catalyst for oxidation of

162 Page 6 of 10
J. Chem. Sci.
(2018) 130:162
Scheme3. Selectiveoxidationofunhinderedalcoholversus
hindered one.
Figure 5. Removal of the catalyst
with external magnetic field.
Scheme 4. Selective oxidation of primary alcohol versus
secondary one.
unhindered alcohols versus hindered ones (Scheme 3).
It is postulated that in the oxidation of alcohols by
Pd-species, the reaction proceeds via the formation
of a Pd(II)-alcoholate.17 f As in the Fe3O4@SiO2
@triazole@Pd catalyst, Pd (II) sites are chelated by
several nitrogen/or oxygen atoms, it is understandable
that less hindered alcohols react faster than the hindered
ones.
Figure 6. Reuse of catalyst in alcohol oxidation
reaction.
In order to examine the chemoselectivity of the
catalyst, a mixture of benzhydrol as a secondary alcohol
and benzyl alcohol as a primary alcohol was exam-
ined according to optimized reaction conditions. No
benzophenone was produced, while benzyl alcohol was
quantitatively reacted to benzaldehyde. This approves
the advantages of this catalyst for selective oxidation of
unhindered primary alcohols in the presence of hindered
secondary ones (Scheme 4).
3.3 Leaching test
In the middle of the model reaction, the catalyst was
removed from reaction media by a magnet, and the yield
of the product was determined by GC as 54%. The reac-
tion was continued for the rest of the time. No change
in the yield was observed, which is a confirmation to
declare that during the reaction, the palladium species
did not leach into the aqueous phase and hence, the cat-
alyst acts as a really heterogeneous catalyst.
Figure 7. FESEM image of the catalyst after
recovery.
was easily removed just by applying an external
magnetic field (Figure 5).
The catalyst was washed two times with methanol,
dried at room temperature and reused for at least six
3.4 Recovery test
The separation of the catalyst from the reaction media more times, without any negligible reduction in reactiv-
was very easy. At the end of each reaction, the catalyst ity (Figure 6).

J. Chem. Sci.
(2018) 130:162
Page 7 of 10 162
with Figure 1, it is clear that the size and the morphology
of the particles remained unchanged.
Figure 8 is the powder X-ray diffraction pattern of
the recovered catalyst, in the range of 2θ from 5 to
80 degrees. The diffraction pattern corresponds quite
well to the Fe3O4/SiO2 sample previously reported,
which means that the structure of the catalyst is
unchanged.30
3.5 Comparison of the effectiveness of the catalyst
Figure 8. X-ray diffraction pattern of the catalyst after
recovery.
A comparison between the present catalyst and other
catalysts for alcohols oxidation has been done and the
results are shown in Table 3. It is obvious that our cat-
alyst is comparatively good for selective oxidation of
The Pd content after the 7th run was measured by AAS alcohols to their corresponding carbonyl compounds, in
which showed no significant loss of Pd (1.16 mmol.g−1 the presence of molecular oxygen as an oxidant, water
vs. 1.24 mmol.g−1 at the beginning).
as a green media, and in shorter reaction time.
The morphology of the recovered catalyst was
The turnover frequency (TOF) and turnover number
analysed by FESEM (Figure 7). By comparing Figure 7 (TON) of the catalyst have been compared to some
Table 3. Comparison of different catalysts in the oxidation of benzyl alcohol.
No.
Catal.
Solvent
Time (h)
Temp. (◦C)
Yield (%)
Oxidant
Ref.
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
F
G
H
H2O
Toluene
Free
PhCF3
H2O
Toluene
Toluene
Toluene
H2O
4
1
1.5
8
0.33
3.5
5.5
12
4
80
rt
50
rt
50
80
80
80
50
96
99
85
100
91
99
99
80
100
O2
O2
O2
air
H2O2
O2
air
air
O2
This work
23
24
12
25
26
26
25
27
A: 1 mol% Fe3O4@ SiO2@triazole@ Pd.
B: 0.4 mol% Au@periodic mesoporous organosilica.
C: 0.06 g Fe3O4/Cys-Pd.
D: 0.5 mmol NaNO2, 0.5 mmol FeCl3·6H2O, 0.2 mmol TEMPO.
E: 10 mol% Fe3O4.
F: 0.4 mol% Pd@SBA-15.
G: 10 mol% Fe3O4.
H: 0.2 mol% nanopartice-TEMPO.
Table 4. The Comparison of TON and TOF of different catalysts in the oxidation of benzyl alcohol.
No.
Catal.
Time (h)
Temp. (◦C)
oxidant
TON
TOF
Ref.
1
2
3
4
A
C
I
5
1.5
6
80
50
80
39
O2
O2
H2O2
NMMN
960
480
720
445
240
320
120
178
This work
24
28
29
J
2.5
A: 1 mol% Fe3O4@ SiO2@triazole@ Pd.
C: 0.06 g Fe3O4/Cys-Pd.
I: 25 mmol% nano-Fe3O4−Pd.
J: 2 mmol% palladium triphenylphosphine complexes containing N-(2-pyridyl)–N-(salicylidene) hydrazine; NMMN: N-
methyl morpholine N-oxide.

162 Page 8 of 10
J. Chem. Sci.
(2018) 130:162
of the similar catalysts in literature. The data have
been summarized in Table 4, which show an accept-
able TON and TOF for benzyl alcohol oxidation by the
Fe3O4@SiO2@Triazole@Pd versus other mentioned
catalysts.
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4. Conclusions
In this work, we synthesized carbonyl compounds
by selective oxidation of alcohols in the presence
of recoverable Fe3O4@SiO2@Triazole@Pd magnetic
nanocatalyst in aqueous media as a green solvent.
Molecular oxygen served as an oxidant. The absence
of mediators like 2,2,6,6-tetramethylpiperidine-1-oxyl
(TEMPO) and eco-unfriendly oxidizing agents and
toxic and hazardous organic solvents make this method
more precious. The catalyst was removed from the reac-
tion media by a magnetic field, washed with methanol,
and reused for at least six more times without any con-
siderable reduction in its reactivity. The notable features
and major advantages are ease of catalyst preparation,
recyclability and reusability for several times, oper-
ational simplicity, and easy work-up procedure. The
chemoselectivity and regioselectivity of the catalyst
can serve for selective oxidation of primary alcohols
in the presence of secondary ones, and for the oxida-
tion of unhindered alcohols in the presence of hindered
ones.
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Acknowledgements
We are grateful to the Research Council of Iran University of
Science and Technology. We also thank the Faculty of Chem-
istry of Sharif University of Technology for partial supporting
of this work.
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