Synthesis and characterization of a magnetically recoverable molybdenum(VI) nanocatalyst for eco-friendly oxidation of alcohols

Article abstract of DOI:10.1007/s11243-016-0077-9

A catalyst based on immobilization of a molybdenum(VI) Schiff base complex on γ-Fe₂O₃ magnetic nanoparticles has been synthesized and characterized. This catalyst was employed for the selective oxidation of alcohols to the corresponding carbonyl compounds in EtOH/H₂O₂. The catalyst can be easily separated from the reaction mixture by decantation using an external magnet and reused efficiently in five subsequent reaction cycles without any significant decrease in activity or selectivity.

Full text of DOI:10.1007/s11243-016-0077-9

Transit Met Chem
DOI 10.1007/s11243-016-0077-9
Synthesis and characterization of a magnetically recoverable
molybdenum(VI) nanocatalyst for eco-friendly oxidation
of alcohols
S. Saeednia1 M. Hatefi Ardakani1 Z. Pakdin Parizi2 M. Tavakoli Hafshejani1
•
•
•
Received: 7 April 2016 / Accepted: 23 June 2016
Ó Springer International Publishing Switzerland 2016
Abstract A catalyst based on immobilization of a
molybdenum(VI) Schiff base complex on c-Fe2O3 mag-
netic nanoparticles has been synthesized and characterized.
This catalyst was employed for the selective oxidation of
alcohols to the corresponding carbonyl compounds in
EtOH/H2O2. The catalyst can be easily separated from the
reaction mixture by decantation using an external magnet
and reused efficiently in five subsequent reaction cycles
without any significant decrease in activity or selectivity.
of current interest [6, 15–18]. In particular, molybdenum(VI)
complexes can act in a similar way to molybdoenzymes and
catalyze a variety of oxidation reactions [19–22]. Various
molybdenum complexes are very active homogeneous and
heterogeneous catalysts for oxidation–epoxidation reactions
[23, 24]. Although the oxidation of alcohols can be accom-
plished by these methods, most of the existing protocols
suffer from limitations such as low yields, long reaction
times, use of organic solvents or unrecyclable catalysts and
tedious work-up procedures leading to toxic waste. Recently,
magnetic nanoparticles (MNPs) have received increasing
interest as supporting materials for the synthesis of hetero-
geneous catalysts [25–28]. The advantages of MNPs include
easy preparation and functionalization, large surface area-to-
volume ratios, low toxicity and price [29–31]. A catalyst
supported on magnetic nanoparticles can be easily separated
from the reaction mixture by an external magnet and so
techniques such as filtration or centrifugation are not
required for catalyst recovery and recycling.
Introduction
One of the most fundamental organic transformations is the
oxidation of primary and secondary alcohols to the corre-
sponding carbonyl compounds [1, 2]. Oxidizing agents such
as hypervalent iodine reagents [3, 4], Cr(VI) salts [5–9] and
organic-based oxidants, such as the Dess-Martin [3] and
Swern [10] reagents, that are traditionally used for these
oxidations are often hazardous and can produce heavy metal
waste. Consequently, to overcome these shortcomings, a
substantial amount of research has been directed toward the
development of new and efficient catalytic systems based on
the use of aqueous 30 % H2O2 as a final green oxidant. The
advantages of H2O2 include low cost, environmental safety,
high atom economy and water as a byproduct [11–14].
Transition metal–catalyzed oxidation of organic substrates is
In this work, we report the synthesis, characterization
and performance of a new molybdenum(VI) Schiff base
complex anchored on c-Fe2O3 magnetic nanoparticles as
an efficient, highly recyclable and heterogeneous catalyst
for the oxidation of alcohols using H2O2 and EtOH as a
green oxidizing agent and solvent. The catalyst can be
easily and completely separated from the reaction mixture
by employing an external magnetic field.
& S. Saeednia
Experimental
sami_saeednia@yahoo.com; s.saeednia@vru.ac.ir
1
Chemicals were purchased from Merck. [MoO2(acac)2] was
prepared according to the method reported in the literature
[32]. The purities of the products and the progress of the
reactions were monitored by TLC on silica-gel polygram
Department of Chemistry, Faculty of Science, Vali-e-Asr
University of Rafsanjan, Rafsanjan 77188-97111, Iran
2
Department of Nuclear Medicine and Molecular Imaging,
Razavi Hospital, Mashhad 9198613676, Iran
123

Transit Met Chem
Synthesis of Schiff base immobilized on c-Fe2O3
(c-Fe2O3-L)
SILG/UV254 plates. TEM analysis was performed using a
TEM microscope (Philips CM30). FTIR spectra were
recorded in the 4000–400 cm-1 region using KBr disks on a
Thermo SCIENTIFIC model NICOLET iS10 spectropho-
tometer. Elemental analyses were obtained on a LECO
CHNS-932 analyzer. Thermogravimetric analysis (TGA)
was performed on a computer-controlled NETZSCH model
PC Luxx 409 apparatus. Power X-ray diffraction (XRD)
patterns were recorded on a Philips X’pert diffractometer
with Cu Ka (k = 0.154 nm) radiation. Room temperature
magnetization isotherms were obtained using a vibrating
sample magnetometer (VSM, LakeShore 7400). The content
of Mo in the catalyst was determined by ICP-OES VISTA-
PRO inductively coupled plasma analyzer.
c-Fe2O3-diamine (3.5 g) was sonicated in absolute
methanol (50 mL) for 30 min. Salicylaldehyde (1.5 mL)
was added slowly to the mixture, which was then stirred at
65 °C for 24 h. After cooling to room temperature, the
solid was separated by an external magnet, washed with
methanol and dried at 60 °C under vacuum.
Preparation of molybdenum Schiff base complex
immobilized on c-Fe2O3 (c-Fe2O3-MoO2L)
c-Fe2O3-L (3.5 g) was sonicated in dry methanol (30 mL)
for 30 min. MoO2(acac)2 (1.2 g) was added to the dis-
persed mixture under mechanical stirring, and the mixture
was refluxed for 24 h. The solid was separated by an
external magnet and washed three times with methanol. It
was then dried under vacuum at 60 °C overnight to furnish
the corresponding c-Fe2O3-supported complex.
Synthesis of c-Fe2O3 MNPs
c-Fe2O3 MNPs were synthesized by a reported procedure,
involving chemical co-precipitation of ferric and ferrous
ions in alkali solution with minor modifications [33, 34].
FeCl2Á4H2O (1.99 g) and FeCl3.6H2O (3.25 g) were dis-
solved in deionized water (30 mL) under an N2 atmosphere
at room temperature. A NH4OH solution (0.6 M, 200 mL)
was then added dropwise (drop rate 1 mL min-1) to the
stirring mixture at room temperature to give a pH of 11.
The resulting black dispersion was continuously stirred for
1 h at room temperature and then heated to reflux for 1 h to
yield a brown dispersion. The magnetic nanoparticles were
then separated by an external magnet and washed with
deionized water until neutralized. The synthesized sample
was heated at 2 °C min-1 up to 250 °C and then kept in a
furnace at 250 °C for 3 h to give a reddish-brown powder.
General procedure for oxidation of alcohols
Catalytic experiments were carried out in a 5-mL test tube.
In a typical procedure, to 1 mmol benzyl alcohol in 1 ml
solvent, 2 mol% (0.02 g) of c-Fe2O3-MoO2L and 2 mmol
of 30 % H2O2 was added. The reaction mixture was stirred
for 3 h at 80 °C. The reaction products were monitored by
TLC or GC. After completion of the reaction, the mixture
was diluted with EtOAc. The catalyst was separated by an
external magnet, washed with EtOAc, dried and reused for
a consecutive run under the same reaction conditions.
Evaporation of the solvent from the filtrate under reduced
pressure gave the crude products, which were then purified
by chromatography on silica gel eluted with n-hexane/
EtOAc (2:1).
Synthesis of chloro-functionalized c-Fe2O3
The prepared c-Fe2O3 (3.5 g) was sonicated in dry toluene
(50 mL) for 30 min. 3-Chloropropyltriethoxysilane (3.5 mL)
was added to the dispersed c-Fe2O3 in toluene under
mechanical stirring. The mixture was slowly heated to 105 °C
and kept at this temperature for 48 h. The solid was separated
by an external magnet, washed three times with ethanol and
dried under vacuum.
Results and discussion
Catalyst synthesis and characterization
Preparation of c-Fe2O3–diamine
The synthetic procedure to obtain the catalyst is outlined in
Scheme 1. First, c-Fe2O3 MNPs were synthesized by
chemical co-precipitation of ferric and ferrous ions from
alkaline solution [33, 34]. The resulting c-Fe2O3 was then
functionalized with 3-chloropropyltriethoxysilane. Next,
1,3-diamino-propan-2-ol was added to obtain c-Fe2O3-di-
amine. This reaction was followed by condensation with
salicylaldehyde to give a tridentate Schiff base immobi-
lized on c-Fe2O3 (c-Fe2O3-L). Finally, reaction with a
The chloro-functionalized c-Fe2O3 (3.5 g) was dispersed
by sonication in dry toluene (50 mL) for 30 min. 1,3-Di-
amino-propan-2-ol (0.4 g) was then added under mechan-
ical stirring. The mixture was slowly heated to 105 °C and
kept at this temperature for 24 h. The solid was separated
by an external magnet, washed three times with ethanol
and dried under vacuum.
123

Transit Met Chem
H2N
NH2
O
OH
ref., 24 h, Tuluene
ref., 48 h
Tuluene
γ-Fe2O3
γ-Fe2O3
Cl
Si
Si(OCH3)3
O
Si
Cl
O
O
H
O
O
H
OH
ref., 24 h,MeOH
γ-Fe2O3
O
γ-Fe2O3
N
NH2
O
Si
N
H
N C
H
O
O
OH
OH
HO
O
H
MoO2(acac)2
re
f., 2
4 h
, M
eOH
γ-Fe2O3
O
Si
N
H
N C
O
O
Mo
O
O
H3CO
O
H
Scheme 1 Synthesis of c-Fe2O3-MoO2L
methanol solution of MoO2(acac)2 gave c-Fe2O3-MoO2L
(Scheme 1).
same set of peaks was observed in the XRD pattern of
c-Fe2O3-MoO2L, indicating the stability of the crystalline
nanoparticles phase during surface modification. The
deduced average size of the c-Fe2O3-MoO2L nanoparticles
from Scherrer’s formula was about 15.8 nm.
The size and structure of the synthesized catalyst were
evaluated using transmission electron microscopy (TEM).
TEM images revealed an approximately spherical shape for
c-Fe2O3-MoO2L with an average diameter of 15 5 nm
(Fig. 1).
Thermogravimetric analysis (TGA) was used to study
the thermal stability of the catalyst. The thermal behavior
of c-Fe2O3-MoO2L is shown in Fig. 3. A weight loss of
about 8.55 wt% between 25–580 °C can be attributed to the
loss of organic components attached to the surface.
According to the TGA, the amount of organic components
functionalized on c-Fe2O3 was 0.18 mmol g-1. These
results were in good agreement with the elemental analysis
The crystalline structures of c-Fe2O3 and c-Fe2O3-
MoO2L were characterized by X-ray diffraction (XRD)
(Fig. 2). The XRD pattern of c-Fe2O3 showed character-
istic peaks that matched with those of standard c-Fe2O3
nanoparticles (JCPDS file no. 04-0755), with a unit cell
˚
dimension of 8.35 A and space group of P4132 (213). The
Fig. 1 TEM images of c-Fe2O3-MoO2L
123

Transit Met Chem
Fig. 2 XRD patterns of a c-Fe2O3 and b c-Fe2O3-MoO2L
Fig. 4 FTIR spectra of a c-Fe2O3, b chloro-functionalized c-Fe2O3,
c c-Fe2O3-L and d c-Fe2O3-MoO2L
metal. In the FTIR spectrum of c-Fe2O3-MoO2L, two
bands at 934 and 903 cm-1 can be assigned to the
stretching vibrations of the Mo=O groups loaded onto
MNPs [27]. A strong and broad band in the range of
2800–3700 cm-1 corresponds to the hydrogen-bonded
adsorbed water, overlapped with C–H stretching vibrations
of the phenyl and CH2 groups [27]. A band at 1660 cm-1
in Fig. 4a, b is assigned to adsorbed water [33].
Fig. 3 TGA diagram of c-Fe2O3-MoO2L
data (N = 0.54 %) and the ICP analysis, which showed
that 0.19 mmol of molybdenum was anchored on 1.0 g of
c-Fe2O3-MoO2L catalyst.
The immobilization of the molybdenum Schiff base
complex on c-Fe2O3 was monitored by FTIR spectroscopy
(Fig. 4). A band at around 550–650 cm-1 is assigned to the
Fe–O bond stretching vibrations in c-Fe2O3, while an
intense band in the range of 1000–1300 cm-1 is assigned
to the Si–O stretching bond in chlorosiloxane-functional-
ized c-Fe2O3 (Fig. 4b). In the FTIR spectrum of the Schiff
base immobilized on c-Fe2O3 (Fig. 4c), a band at
1650 cm-1 is assigned to the C=N stretch and some weak
bands at 1200–1300 cm-1 are assigned to the aromatic
rings of the Schiff base. These features were not present in
the parent c-Fe2O3. After reaction of c-Fe2O3-L with
The magnetization curves of c-Fe2O3 and c-Fe2O3-
MoO2L were measured at room temperature with a vibrat-
ing sample magnetometer (VSM). As shown in Fig. 5, no
reduced remanence and coercivity were detected, indicating
both unmodified and Mo-modified c-Fe2O3 are superpara-
magnetic. The saturation magnetic moments of c-Fe2O3 and
c-Fe2O3-MoO2L are 68.8 and 65.5 emu g-1, respectively.
Catalytic activities of c-Fe2O3-MoO2L
for the oxidation of alcohols
MoO2(acac)2, the imine stretch is shifted to 1620 cm-1
,
Following the successful synthesis and characterization of
c-Fe2O3-MoO2L, its catalytic activity was studied for the
Fig. 4d, indicating complexation of this group with the
123

Transit Met Chem
Table 1 Oxidation of benzyl alcohol to benzaldehyde under different
conditions
Entry
Oxidants
T (°C)
Solvent (0.5 mL)
Yielda (%)
1
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
O2b
80
80
80
60
55
60
80
60
80
80
50
80
80
80
80
80
80
80
80
80
80
–
60
2
EtOH
Toluene
CH3OH
THF
85
3
55
4
45
5
55
6
CHCl3
CH3CN
CH2Cl2
H2O
20
7
60
8
15
9
60
10
11
12
13
14
15
16c
17d
18e
19f
20g
21h
a
DMSO
EtOH
EtOH(1 mL)
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
Trace
50
50
Fig. 5 Magnetization curves of c-Fe2O3 and c-Fe2O3-MoO2L
TBHP
UHP
–
25
70
oxidation of alcohols to the corresponding aldehydes or
ketones with aqueous 30 % H2O2 as the terminal oxidant.
The oxidation of benzyl alcohol (1 mmol) to benzaldehyde
as a test reaction was first investigated in various solvents
and at different temperatures, to find the optimum reaction
conditions (Table 1). Initially, this reaction was investi-
gated under solvent-free condition, as well as in different
solvents (entries 1–10). The best yield of the desired pro-
duct was obtained in ethanol at 80 °C (entry 2). A similar
reaction at lower temperature required more time and
produced lower yields (entriy 11). Next, the influence of
different oxidants on the oxidation of benzyl alcohol in
ethanol at 80 °C was studied (entries 12–14). Hydrogen
peroxide proved to be the best choice among the examined
oxidants (entry 2). The reaction did not proceed well in the
absence of any oxidant, giving only a trace amount of the
desired product (entry 15). Similarly, when 1 mmol of the
oxidant was used, the yield of the desired product was
decreased (entry 16). Similar reactions performed in the
presence of different amounts of c-Fe2O3-MoO2L (entries
17 and 18) showed that 2 mol% of the catalyst gave the
best results (entry 2). The model reaction was also exam-
ined in the presence of c-Fe2O3 and MoO2(acac)2 rather
than the c-Fe2O3-MoO2L catalyst (entries 19–21) and low
amounts of the desired product were obtained.
Trace
60
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
50
85
Trace
10
30
Isolated yield, reaction conditions: benzyl alcohol (1 mmol), oxi-
dant (2 mmol, except for Entries 12–16), c-Fe2O3-Mo (2 mol%,
except for Entries 17–21), reaction time: 3 h
b
60 bubble/min
c
1 mmol H2O2
d
Catalyst: 1 mol%
e
Catalyst: 3 mol%
f
No catalyst
g
Catalyst: c-Fe2O3 (2 mol%)
h
Catalyst: MoO2(acac)2 (2 mol%)
same reaction conditions (entries 2, 3, 5). In particular, the
heteroaromatic furfuryl alcohol, which is considered to be a
challenging substrate in most transition metal catalyst
systems, was oxidized selectively to furfural in this system
(entry 7). Linear alcohols were also oxidized efficiently
with H2O2 by this catalyst (entries 8–10), while secondary
alcohols gave the corresponding ketones in good yields
(entries 11–16).
In order to establish the generality of this method, the
oxidation of a variety of primary and secondary alcohols
under the optimized reaction conditions was investigated
(Table 2). Substituted benzyl alcohols bearing either elec-
tron-releasing or withdrawing groups were also oxidized
selectively and afforded the corresponding aldehydes in
good to excellent yields (entries 1–6). Moreover, relatively
hindered benzyl alcohols were also converted to the cor-
responding aldehydes in good yields without any over-
oxidation to the corresponding carboxylic acid under the
In order to investigate the chemoselectivity of the sys-
tem, a competitive reaction was designed. A mixture of
equal amounts of benzyl alcohol and 2-phenyl ethanol was
subjected to oxidation under the condition given in Table 2
(Scheme 2). In this experiment, benzyl alcohol was oxi-
dized to benzaldehyde, but 2-phenyl ethanol was left
unreacted.
123

Transit Met Chem
Table 2 Oxidation of alcohols with H2O2 catalyzed by c-Fe2O3-MoO2L
Yielda
(%)
Entry
Alcohol
Product
Time( )
h
1
3
4
85
70
2
3
3
3
60
85
OH
O
4
3
3
4
80
85
60
5
6
7
4
4
60b
65b
8
9
O
70b
85
OH
3
3
10
11
OH
O
4
80
12
3
4
50b
65
13
O
C
O
C
O
C
OH
14c
O
O
O
C
O
H
123

Transit Met Chem
Table 2 continued
Yielda
(%)
Entry
15c
Alcohol
Product
Time( )
h
O
C
OH
O
C
O
C
3
3
65
C
H
16c
70
a
Isolated yield, conditions: alcohol (1 mmol), hydrogen peroxide (2 mmol), catalyst (2 mol%), temperature: 80° C
Yield determined by GC analysis
b
c
The alcohols were synthesized according to Ref [35]
Scheme 2 Chemoselectivity of
the catalyst
O
OH
OH
quantitative
trace
γ-Fe2O3-MoO2L
H
O
80 oC, EtOH, 30% H2O2
Fig. 7 Reusability of c-Fe2O3-MoO2L in selective oxidation of
benzyl alcohol to the benzaldehyde with 30 % H2O2
Fig. 6 a Reaction mixture, b Separation of c-Fe2O3-MoO2L from the
reaction mixture by an external magnet
washed with EtOAc and dried for 30 min at 80 °C. In this
way, the recycled catalyst was successfully used in at least
five reaction cycles with only slight decrease in catalytic
performance (Fig. 7). ICP analyses of c-Fe2O3-MoO2L after
five such cycles showed that only a very small amount of Mo
had been removed from the catalyst. The TEM image of used
c-Fe2O3-MoO2L (Fig. 8) compared with the fresh catalyst
showed that the morphology remained intact after five
cycles, while the FTIR spectrum (Fig. 9) of the reused
The recyclability of a heterogeneous catalyst is of great
importance and provides a critical advantage over homoge-
neous catalysts. The magnetic properties of c-Fe2O3-MoO2L
facilitate efficient recovery of the catalyst from the reaction
mixture. Thus, after performing the oxidation of benzyl
alcohol with hydrogen peroxide, the catalyst was separated
by an external magnet from the reaction mixture (Fig. 6),
123

Transit Met Chem
to excellent yields. The catalyst was successfully recovered
from the reaction mixture and reused for five subsequent
reaction cycles with only slight decrease in its activity.
Acknowledgments The support of this work by Vali-e-Asr Univer-
sity of Rafsanjan is acknowledged.
References
1. Hudlicky M (1990) Oxidation in organic chemistry, ACS
monograph series. American Chemical Scociety, Washington DC
2. Sheldon RA, Kochi JK (1984) Metal catalyzed oxidations of
organic compounds. Academic Press, New York
3. Dess DB, Martin JC (1983) J Org Chem 48:4155
4. Dess DB, Martin JC (1991) J Am Chem Soc 113:7277
5. Cainelli G, Cardillo G (1984) Chromium oxidation in organic
chemistry. Springer, Berlin
6. Matsumoto T, Ueno M, Wang N, Kobayashi S (2008) Chem
Asian J 3:196
7. Mallat T, Baiker A (2004) Chem Rev 104:3037
8. Jamwal N, Gupta M, Paul S (2008) Green Chem 10:999
9. Hackett SFJ, Brydson RM, Gass MH, Harvey I, Newman AD,
Wilson K, Lee AF (2007) Angew Chem Int Ed 46:8593
10. Mancuso AJ, Huang S-L, Swern D (1978) J Org Chem 43:2480
11. Biradar AV, Dongare MK, Umbarkar SB (2009) Tetrahedron Lett
50:2885
Fig. 8 TEM image after five times reuse of c-Fe2O3-MoO2L
12. Jones CW (1999) Applications of hydrogen peroxide and
derivatives, vol. 2. (Royal Society of Chemistry, 1999)
13. Centi G, Fabrizio C, Ferrucio T (2012) Selective oxidation by
heterogeneous catalysis. Springer Science & Business Media
14. Maggi R, Chitsaz S, Loebbecke S, Piscopo CG, Sartori G, Sch-
warzer M (2011) Green Chem 13:1121
15. Vinod CP, Wilson K, Lee AF (2011) J Chem Technol Biotechnol
86:161
16. Ciriminna R, Pagliaro M (2010) Org Process Res Dev 14:245
¨
17. Piera J, Backvall J-E (2008) Angew Chem 120:3558
¨
18. Piera J, Backvall J-E (2008) Angew Chem Int Ed 47:3506
19. Khanbabaee KK (1993) Ann Chem 905
20. Wang W, Daran JC, Poli R, Agustin D (2016) J Mol Catal A:
Chem 416:117
21. Ghorbanloo M, Mohamadi A, Amini M (2015) J Tao Transit
Metal Chem 40:321
22. Tadayonpour N, Rayati S, Sadr MH, Zare K, Wojtczak A (2015)
Transit Metal Chem 40:891
Fig. 9 FTIR spectrum of c-Fe2O3-MoO2L after five times reuse
23. Manyar HG, Chaure GS, Kumar A (2006) J Mol Catal A 243:244
24. Zhang J, Jiang P, Shen Y, Zhang W, Li X (2015) Microporous
Mesoporous Mater 206:161
catalyst also showed no detectable changes compared to the
fresh catalyst (Fig. 4).
25. Masteri-Farahani M, Kashef Z (2012) J Magn Magn Mater
324:1431
26. Rafiee E, Evani S (2011) Green Chem 13:2116
¨
27. Zare M, Moradi-Shoeili Z, Bagherzadeh M, Akbayrak S, Ozkar S
(2016) New J Chem 40:1580
Conclusions
In summary, a molybdenum Schiff base complex immo-
28. Rayati S, Abdolalian P (2013) C R Chim 16:814
29. Abu-Reziq R, Wang D, Post M, Alper H (2008) Chem Mater
20:2544
30. Keypour H, Balali M, Haghdoost MM, Bagherzadeh M (2015)
RSC Adv. 5:53349
31. Bezaatpour A, Khatami S, Amiri M (2016) RSC Adv. 6:27452
32. Chen GJJ, McDonald JW, Newton WE (1976) Inorg Chem
15:2612
33. Sobhani S, Pakdin-Parizi Z (2014) RSC Adv. 4:13071
34. Ho KM, Li P (2008) Langmuir 24:1801
35. Mavis ME, Yolacan C, Aydogan F (2010) Tetrahedron Lett
51:4509
bilized on c-Fe2O3 magnetic nanoparticles was synthe-
sized, characterized and applied as
a magnetically
recyclable heterogeneous catalyst in the activation of 30 %
H2O2 for the selective oxidation of alcohols to their cor-
responding carbonyl compounds. Primary aromatic and
aliphatic alcohols were selectively converted to the corre-
sponding aldehydes without over-oxidation to the corre-
sponding carboxylic acids. Moreover, secondary alcohols
were also oxidized to the corresponding ketones with good
123