Efficient catalytic systems based on cobalt for oxidation of ethylbenzene, cyclohexene and oximes in the presence of N-hydroxyphthalimide

Article abstract of DOI:10.1016/j.apcata.2013.06.045

The selective oxidation of ethylbenzene and cyclohexene to acetophenone and 2-cyclohexene-1-one using N-hydroxyphthalimide (NHPI) under oxygen atmosphere in the presence of an SiO₂/Al₂O₃-supported cobalt catalyst occurs with conversions of 83 and 75% and selectivities of 99%. The supported cobalt is also a suitable and efficient catalyst for the oxidative deprotection of oximes to the corresponding carbonyl compounds. The reaction conditions have been optimized considering the effect of various parameters such as reaction time, amount of catalyst, temperature and reusability of the catalyst after several runs. Moreover, some possible mechanisms for the oxidation of ethylbenzene, cyclohexene and oximes have been proposed.

Full text of DOI:10.1016/j.apcata.2013.06.045

Applied Catalysis A: General 466 (2013) 282–292
Contents lists available at SciVerse ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Efficient catalytic systems based on cobalt for oxidation of
ethylbenzene, cyclohexene and oximes in the presence of
N-hydroxyphthalimide
D. Habibia,∗, A.R. Farajia,∗, M. Arshadib, S. Heydaria, A. Gilc
a Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan 6517838683, Iran
b Department of Science, Fasa Branch, Islamic Azad University, PO Box 364, Fars 7461713591, Fasa, Iran
c Department of Applied Chemistry, Los Acebos Building, Public University of Navarre, Campus of Arrosadia, E-31006, Pamplona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The selective oxidation of ethylbenzene and cyclohexene to acetophenone and 2-cyclohexene-1-one
using N-hydroxyphthalimide (NHPI) under oxygen atmosphere in the presence of an SiO2/Al2O3-
supported cobalt catalyst occurs with conversions of 83 and 75% and selectivities of 99%. The supported
cobalt is also a suitable and efficient catalyst for the oxidative deprotection of oximes to the correspond-
ing carbonyl compounds. The reaction conditions have been optimized considering the effect of various
parameters such as reaction time, amount of catalyst, temperature and reusability of the catalyst after
several runs. Moreover, some possible mechanisms for the oxidation of ethylbenzene, cyclohexene and
oximes have been proposed.
Received 11 March 2013
Received in revised form 10 June 2013
Accepted 27 June 2013
Available online 5 July 2013
Keywords:
Cobalt supported catalyst
Oxidation, Ethylbenzene
Cyclohexene
© 2013 Elsevier B.V. All rights reserved.
Oxime
1. Introduction
perfumes and pharmaceuticals. Although, Friedel-Crafts acylation
of aromatics by acyl halide or acid anhydride can produce acetophe-
Oxidation reaction plays an important role in synthetic organic
chemistry and in this field variety of oxidants and substrates have
been developed. The oxidation of abundant and cheapness hydro-
carbons to produce more valuable compounds such as aldehydes
and ketones, needs the selective oxidation of C H bonds. There-
fore, selectivity control is a key issue in oxidation reactions. Recent
research has indicated that the heterogeneous catalysts have also
very efficient impact in enhancing selectivity. Aerobic oxidation of
organic substrates such as ethylbenzene, cyclohexene and oximes
to oxygenic compounds is an extremely consequential industrial
manufacture for the production of main chemicals and monomer
material [1,2]. The dominant position of oxygen for main part
of chemical oxy-functionalization is due to the fact that is eco-
nomically and eco-friendly, achievable oxidant and reasonable
chemical strategy for industrial processing. Furthermore, the cat-
alytic oxidation of ethylbenzene and cyclohexene are attracting
much attention because theirs oxidation products are very use-
ful synthetic intermediates. In fact, acetophenone, the valuable
product of the selective oxidation of ethylbenzene, has many appli-
cations in industries such as the production of synthetic musk for
none, but this manner leads to the formation of a large amounts of
hazardous and corrosive wastes. However, the allylic oxidation of
cyclohexene has been the subject of extensive investigations due
to the potential use of 2-cyclohexen-1-one as one of the impor-
tant products in organic synthesis, owing to the presence of a very
reactive carbonyl group, which is used in chemical industries (e.g.
cycloaddition reactions and pharmaceutical). Oximes are preferred
in readily preparation of derivatives of carbonyl compounds, which
also are used extensively for the protection, purification and char-
acterization of carbonyl compounds. The production of carbonyl
derivatives from them provides an alternative procedure for the
preparation of aldehydes and ketones [3,4]. Therefore considerable
attention has been given to developing methods for the regener-
ation of carbonyl compounds from ketoximes and aldoximes. The
large number of methods is consisting of oxidative and reductive
reactions, acid catalyzed and deoximation of exchange of oximes
with other carbonyl compounds. These methods suffer some dis-
advantages such as requirements for refluxing temperature, strong
mineral acids, generate equal amounts of toxic and hazardous
transition metal oxidants, not readily available, tedious work up,
the problems associated with waste disposal, long reaction times
and formation of polymeric by products [3]. Furthermore, these
reactions are usually carried out under acidic or basic conditions,
which are not suitable for acid sensitive functional groups. How-
ever, oximes can also be prepared from noncarbonyl compounds
∗
Corresponding authors. Tel.: +98 811 8282807; fax: +98 811 8380709.
E-mail addresses: davood.habibi@gmail.com (D. Habibi),
alireza ch57@yahoo.com (A.R. Faraji).
0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.06.045

D. Habibi et al. / Applied Catalysis A: General 466 (2013) 282–292
283
Scheme 1. Schematic representation of the preparation process for SiO2/Al2O3-APTMS-BPK-Co.
as the starting materials. Therefore, aldoximes and ketoximes
can be used in turn as synthetic precursors of the corresponding
carbonyl compounds. For example, this precursor applied in the
commercial synthesis of carvone, which is an essential oil used in
fragrance industry [5]. Therefore, oxidation of organic compounds
over heterogeneous catalysts using oxygen is an especially attrac-
tive goal but, O2 show a relatively little tendency to react with the
strong bond of C-H. To overcome this obstruction, several cata-
lyst and co-catalyst have been applied for the catalytic oxidation of
organic substrates [6–9]. Indeed, transition metals such as Co(OAc)2
[10], CuCl [11], Co(OAc)3 [12], and Mn(OAc)3 [13], are added in
the presence of nonmetallic compounds such as NHPI [10–13],
alkyl hydroperoxide [14,15], -azobisisobutyronitril [16], aldehydes
[17,18] and NO2 [19,20], because they are known to catalyze the ini-
tiation reaction [9,10,21–28]. However, finding a catalytic system
for aerobic oxidation of organic compound under mild conditions
is still a challenging issue. To extend previous study on the aero-
bic oxidation reaction by using NHPI/Co, we synthesized new type
of Co catalyst that immobilized onto the functionalized SiO2-Al2O3
through a Schiff base ligand, and have been investigated the oxida-
tion of ethylbenzene and cyclohexene in the presence of NHPI/Co
as the catalytic system. We have also studied oxidation of oximes to
show that cobalt-catalyst could serve as an efficient heterogeneous
catalyst for the cleavage of the C N bonds to the corresponding
carbonyl compounds without any over oxidation.
addition, energy dispersive X-ray analysis was conducted on each
sample. Size distribution was measured in order to number of
nanoparticles in reverse microemulsion by Zetasizer Nano-ZS-90
(ZEN 3600, MALVERN instruments).
2.2. Preparation of organometallic-SiO2/Al2O3
SiO2/Al2O3 was used as the support prepared by the sol-
gel method. First, some defined value of tetraethyl orthosilicate
(98%) and aluminum butyrate in n-butanol were dissolved. The
obtain solution was heated up to 70 ◦C and the components were
entirely mixed. Then it was coold down to the room tempera-
ture. 2,4-Pentandione (H-acac) as the complacing agent was added
to it. In this way, the apparent solution was obtained. After that
by adding deionized water (12.0 mol H2O/mol alkoxide) to the
obtained solution, the solution was hydrolyzed and the appar-
ent gel was produced. Then for removing the solvent and water
from the gel, it was dehydrated up to 100 ◦C. Also for eliminat-
ing of organic compounds, it was calcined at 550 ◦C for 5 h. So,
the synthesized solid SiO2/Al2O3 was being used as the support
in synthesis of the catalyst [29]. At first, 3.5 g of SiO2/Al2O3 was
activated at 500 ◦C for 5 h under air and then was refluxed with
4.3 cm3 of trimethoxysilylpropylamine (APTMS) in dry toluene
(50 cm3) for 24 h. The solid achieved during this process was fil-
tered and washed off with dry methanol at 100 ◦C under vacuum
for 5 h. Then, bipyridylketone (BPK) was added to a suspended
solution of SiO2/Al2O3-APTMS in dry methanol. To synthesize of
SiO2/Al2O3-APTMS-BPK-Co (Scheme 1), 2.0 g SiO2/Al2O3-APTMS-
BPK was suspended in 50 cm3 of ethanol in a round bottom flask
followed by adding of 3.0 mmol Co(OAc)2·4H2O. The mixture was
refluxed during 24 h under magnetically stirring.
2. Experimental
2.1. Materials and characterization techniques
All reagents were purchased from the Merck and Fluka chemi-
cal companies. Reagents were used without extra purification, but
solvents were purified with standard methods. Inductively coupled
plasma (ICP) measurements for cobalt content evaluation were
performed using a Perkin-Elmer ICP/6500. Infrared was collected
on KBr pellets using a JASCO FT/IR (680 plus) spectrometer. Dif-
fuse reflectance spectra were registered on a JASCO-550 UV–vis
spectrophotometer that was equipped with a Diffuse reflectance
attachment in which BaSO4 was as the reference. For elemental
analysis a CHN-Rapid Heraeus elemental analyzer (Wellesley MA)
was used. Before carrying out the nitrogen (99.999%) adsorption
experiments, the sample was outgassed at 393 K for 14 h, then the
experiment have been carried out at 77 K using a volumetric appa-
ratus (Quantachrome NOVA automated gas sorption analyzer). The
specific surface areas were calculated using the BET method. The
images of scanning electron micrograph (SEM) and transmission
electron microscopy (TEM) were taken using a Philips 501 micro-
scope and a Tecnai F30TEM operating at 300 kV, respectively. In
2.3. General procedure for oxidation of ethylbenzene and
cyclohexene
A suspension of the heterogeneous catalyst (0.1 g), solvent
(5 cm3 of acetic acid), 2 mmol substrate and N-hydroxyphthalimide
(2-hydroxy-1H-isoindole-1,3-dione, NHPI) (15 mol %) were mixed
in a three necked round bottom flask which was fitted with a
equipped water condenser through a balloon filled with O2. The
liquid phase oxidation reactions were carried out at desired tem-
perature with vigorous stirring. After filtration and washing with
solvent, the type and quantity of the resulting products from oxi-
dation were determined using a HP 6890/5973 GC/MS instrument.
Besides, a comparative experiments with various conditions was
carried out.

284
D. Habibi et al. / Applied Catalysis A: General 466 (2013) 282–292
Table 1
Chemical composition and physicochemical properties of the immobilized Co-catalyst on the SiO2/Al2O3 mixed oxide.
Sample
Elemental analysis (wt.%)b
Organic
functional
Immobilized
Co-Schiff
% Coordinated
Schiff base
Structural parameterse
group (mmol/g
base-complex
(mmol/g mixed
oxide)d
groups to Co ions
mixed oxide)c
C
N
Co
Surface Pore
Pore
area
volume
diameter
(Å)
(m2/g)
(cm3/g)
a
SiO2/Al2O3
–
–
–
–
–
1.14
–
–
–
–
–
–
–
58.7
498
378
320
281
0.045
0.031
0.026
0.021
36
25
20
18
SiO2/Al2O3 -APTMS
SiO2/Al2O3 -APTMS-BPK
SiO2/Al2O3 -APTMS-BPK-Co
8.13
10.9
7.459
3.75
4.92
1.38
2.67
3.51
0.98
0.193
a
Molar ratio of SiO2/Al2O3 was 60:40, determined from EDX analysis.
Nitrogen was estimated from the elemental analyses. Co content determined from EDX analysis.
Determined from the N-contents.
Determined from the Co-content, assume that cobalt ions coordinated with Schiff base ligands.
From N2 adsorption experiments.
b
c
d
e
2.4. General procedure for oxidation of oximes
The FT-IR spectra of SiO2/Al2O3-APTMS, SiO2/Al2O3-APTMS-
BPK, and SiO2/Al2O3-APTMS-BPK-Co are shown in Fig. 1. The
strong absorption bands related to Si-O-Si stretching vibra-
tions are observed in the spectrum of SiO2/Al2O3 at 798 and
1010–1290 cm−1. The FT-IR spectrum of SiO2/Al2O3-APTMS shows
several signals originating from amino propyl groups, which are
related to C H stretching modes of the propyl, appeared in the
area of 1450–1560 cm−1 and 2860–2935 cm−1. By observing the
FTIR results it could be concluded that the SiO2/Al2O3 was suc-
cessfully modified by amine spacer groups. The N H deformation
peak at 1540–1560 cm−1 confirms the successful functionalization
of the Si/Al mixed oxide with 3-APTMS. The C N imine vibration
signal was observed at 1630 cm−1, which shows the condensation
reaction between BPK with organo-functionalized SiO2/Al2O3 (see
Fig. 1B). The peaks in the 3020–3066 cm−1 ranges and the peaks
at 1434–1437 cm−1 are attributed to the C H stretching vibrations
of pyridine groups and C C stretching vibration of pyridine groups.
Furthermore, after complexing of cobalt with immobilized BPK over
modified SiO2/Al2O3, the weak absorption peak at 466 cm−1 was
appeared that is attributed to the Co N bands.
In this procedure, a suspension of the heterogeneous catalyst
(0.15 g), solvent (5 cm3 of toluene), oxime (2 mmol) and benzalde-
hyde (10 mol) were mixed in a three necked round bottom flask
which was fitted with a equipped water condenser with a balloon
filled of O2. The liquid phase oxidation reactions were carried out
at desired temperature with vigorous stirring. After completing the
reaction, the catalyst has been separated through filtering and the
products and the amounts of them have been quantified by GC–MS
and GC. Finally, a suitable reaction condition has been optimized
3. Results and discussion
3.1. Synthesis of cobalt-supported catalyst
Using BPK and Co(OAc)2·4H2O through the covalently immobi-
lization, the heterogeneous cobalt catalyst was synthesized onto
the SiO2/Al2O3 mixed oxides, as illustrated in Scheme 1. The load-
ing of cobalt in the heterogeneous cobalt catalyst was characterized
by elemental analyses. The final metal content was 0.193 mmol/g,
indicating that 58.7% of the immobilized ligands were complexed
with cobalt ions (see Table 1).
The UV–vis spectrum of the SiO2/Al2O3 had a side-band
adsorption near 249 nm. In the SiO2/Al2O3-APTMS-BPK transi-
tions ␲→␲* and n→␲* of the ligands caused strong adsorp-
tion in the 255–320 nm (see Fig. 2). After the reaction of
1466
1445
1491
1542
1384
1637
603
633
2852
2927
877
C
566
1467
3434
1384
1509
466
%T
B
1629\
1383
678
2925
1448
1563
1630
3432
A
2863
796
796
2935
3428
1058
457
457
1073
1074
4000
3000
2000
1000
400
Wavenumber [cm-1]
Fig. 1. FTIR spectra of: (A) SiO2/Al2O3-APTMS; (B) SiO2/Al2O3-APTMS-BPK; (C) SiO2/Al2O3-APTMS-BPK-Co.

D. Habibi et al. / Applied Catalysis A: General 466 (2013) 282–292
285
Fig. 4. Particle size distribution on the SiO2/Al2O3-APTMS-BPK-Co.
the EDS spectrum of the cobalt catalyst, signals related to Si, Al, O
and Co were observed. The existence of Co signal in the spectrum
resulted from the Co complexation with active sites of the organic
Fig. 2. UV–vis spectra of: (A) SiO2/Al2O3; (B) SiO2/Al2O3-APTMS; (C) SiO2/Al2O3-
APTMS-BPK; (D) SiO2/Al2O3 -APTMS-BPK-Co.
functional groups (
C N) that increased the catalytic activity of the
synthesized catalyst in comparison with the unmodified support.
Thermal stability of the synthesize materials were studied with
TGA (thermo gravimetric analysis) and DTG (derivative thermo-
gravimetric) in Ar atmospheres in the range of 25–1200 ◦C with
a rate of heating of 10 ◦C/min (see Fig. 6). Thermal analysis of
nanoscale SiO2/Al2O3 showed two stages of weight loss, stage I
(25–115 ◦C) corresponds to the desorption of physically held water
(2.6 wt.%), on the surface of SiO2/Al2O3, and Stage II (120–1200 ◦C)
is due to the condensation of Al-OH and Si-OH (13.4 wt.%), present
SiO2/Al2O3-APTMS-BPK with Co(OAc)2·4H2O, the color of the
reaction mixture was changed from yellow to deep brown. Con-
sequently, UV–visible spectra of the immobilized Co(II) species
indicated the appearance of several new metal d–d migration bands
around 570 nm upon complexation.
A selected image of scanning electron microscope (SEM) and
transmission electron microscope (TEM) of catalyst is shown in
Fig. 3, from which it can be seen that the nanoparticles appearance
and size of them were similar, demonstrating that the particles
of SiO2-Al2O3 have good mechanical stability and they have not
been destroyed during the whole modification. However, the aver-
age particle size in reverse micro emulsion solution of the catalyst
was around 28 nm (see Fig. 4). According to the small nanoparti-
cle size and ligand capping as an obstacle in agglomeration, the
Co-catalyst could be used as a suitable catalyst for oxidation of sev-
eral substrates such as ethylbenzene, and cyclohexene. The energy
dispersive spectrum (EDS) of Co-catalyst was shown in Fig. 5. In
in the structure of support (for example; 2Si OH → Si
O Si + H2O).
However, Co catalyst showed four distinct steps: at 25–94, 94–295,
295–549 and 549–1200 ◦C (see Fig. 6). Stages II and III (94–549 ◦C)
are due to desorption of water molecules from the pores of
SiO2/Al2O3 and also decomposition of the immobilized organic
functional groups (-pr-NH2). The additional weight losses in stage
IV could be observed due to the several phenomena; the calcination
of coke, the loss of the new generated Al OH and Si OH groups
and decomposition of the immobilized Co complex groups. From
Fig. 3. SEM and TEM images corresponding to SiO2/Al2O3-APTMS-BPK-Co sample.

286
D. Habibi et al. / Applied Catalysis A: General 466 (2013) 282–292
Fig. 5. EDS spectrum of SiO2/Al2O3-APTMS-BPK-Co.
thermogram analysis of samples, it could be concluded that thermal
stability of SiO2/Al2O3 in Co catalyst improved rather than unmod-
ified SiO2/Al2O3 and the weight losses of the modified SiO2/Al2O3
with Co complex groups in the temperature range of dehydration
are less than that for unmodified SiO2/Al2O3.
The XP spectroscopic analysis of the heterogeneous catalyst
was used to study for the characterization of oxidation state of
the active sites of immobilized cobalt complexes on the surface of
SiO2/Al2O3. This technique has previously been shown to provide
valuable information regarding the chemical state of the catalyti-
cally active sites in various catalysts [30–33]. The XPS spectrum of
Co catalyst produced a Co 2p3/2 peak at 781.61 eV, and is depicted in
Fig. 7. However, there is a satellite peak at 786.70 eV beside the main
peak of Co 2p3/2 in the catalyst. These results indicated that most
of the Co ions on the surface of the heterogeneous catalyst were in
+2 oxidation state (due to the binding energy (BE) 781.61 eV which
are attributed to Co(II) state of cobalt), and they are in accordance
with earlier literature data [34,35].
3.2. Oxidation of ethylbenzene
The oxidation of ethylbenzene with oxygen by the new cat-
alytic system using a heterogeneous transition metal in the
presence of NHPI was investigated. The effects of various operating
Fig. 6. TGA and DTG curves of the SiO2/Al2O3 and Co-catalyst.
Fig. 7. XPS image of the SiO2/Al2O3-APTMS-BPK-Co.

D. Habibi et al. / Applied Catalysis A: General 466 (2013) 282–292
287
O2
Co(II)
O
OH
OO
(Step 1)
+
Co(III)
NHPI
Scheme 2. Possible products of the oxidation of ethylbenzene.
OOH
OOH
(Step 8)
(Step 2)
Co(III)
parameters, such as the amount of the catalyst to NHPI, the
temperature, and the reaction time, on the performance of the
heterogeneous cobalt-catalyst was investigated in the oxidation of
ethylbenzene by O2 in the presence of the acetic acid as solvent. In
fact, due to its polar nature, NHPI has a low solubility in ethylben-
zene at the mild temperature employed in our protocol. Thus, the
use of acetic acid is mandatory in order to dissolve the quantities of
NHPI necessary for observing a good catalytic activity. Acetophe-
none and ␣-phenyl ethanol (Scheme 2) were the major reaction
products obtained. The GC analysis did not show any oxidation
products of the aromatic ring in effluents.
PINO
NHPI
(Step 5)
(Step 6)
(Step 3)
OO
(Step 4)
(Step 7)
O2
Among the several solvents, acetic acid was found to be the opti-
mum solvent [45–48]. In order to assess the effect of catalyst to
oxidant molar ratio on the catalytic activity and selectivity in acetic
acid under oxygen, the reactions were studied at various amount of
catalyst:NHPI (see Table 2). It was observed that catalytic activity
and selectivity is strongly affected by increasing amount of catalyst
to NHPI. The most promising observation is that acetophenone was
found to be the major product in most of the catalytic reactions. In
all EB oxidation reaction conditions, conversion and selectivity to
acetophenone increased with reaction time.
O2
O
O
O
O
H
(Step 9)
H
OH
O
+
Scheme 3. Proposed mechanism for the oxidation of ethylbenzene with the Co-
catalyst/NHPI system.
NHPI has been demonstrated to be a free radical oxidation
catalyst [36,37]. In contrast to transition metals, NHPI does not
accelerate the hydroperoxide decomposition reaction; therefore,
the catalytic activity of NHPI results from phthalimide-Noxyl rad-
ical (PINO) formation in the propagation step of the oxidation
process. In fact, transition metals, such as Co(II)/(III) and Mn(II)/(III),
are typically used as catalysts in these oxidation processes, that is,
their catalytic effect lowers the activation energy of the decompo-
sition reaction of the hydroperoxide. As it shown in the proposed
mechanism (see Scheme 3), at first step, by the complexation of
Co(II) with oxygen molecule a labile dioxygen complex such as
superoxocobalt(III) or peroxocobalt(III) complexes could be formed
[10,38]. However, it is observed that the oxidation of ethylbenzene
by the combined system of NHPI and Co(acac)3 did not take place,
since a cobalt-oxygen complex cannot be generated from Co(acac)3
and dioxygen under ambient conditions (data not published), while
in the presence of a small amount of benzaldehyde the oxidation
reaction was carried out, ethylbenzene was oxidized to acetophe-
none (27%), because Co(III) species is reduced by benzaldehyde to
Co(II) ion. Therefore, it is reasonable to assume that such cobalt
species assist in the generation of the PINO radical from NHPI under
these conditions [10,38,39]. Furthermore, for demonstrating the
role of the nano Co-catalyst pyridine molecule was added into the
system which resulted in decreasing the catalytic activity of cobalt
complex quickly, in fact, the nitrogen of pyridine molecule easily
occupies the active sites of the nano catalyst [45]. In the second step,
NHPI in situ could be converted to PINO by the reaction of NHPI
with the catalyst-oxygen complex that would be the most impor-
tant step in the present oxidation [10]. The BDE (Bond Dissociation
Energy) value of the O-H bond for NHPI is >86 kcal/mol by means
of ESR spectroscopy [40,41]. The BDE of the benzylic C H bond in
ethylbenzene is estimated to be about 87 kcal/mol. This suggests
that PINO could abstract the benzylic hydrogen atom of ethylben-
zene, therefore, at third step, PINO abstracts benzylic hydrogen of
ethylbenzene and eventually formed ethylbenzyl radical. However
capturing the obtaining ethylbenzyl radicals by dioxygen molecules
provides alkylperoxy radicals, which are eventually converted into
oxygenated products through ethylbenzylhydroperoxides (step 4).
This intermediate can produce acetophenone and 1-phenylethanol
in two paths (steps 5 and 7), at step 5, alkylproxy radical can
abstract hydrogen from NHPI and at step 7, two alkylproxy rad-
icals combine to form a tetroxide intermediate, which further
decomposes through a 6-membered ring transition state rear-
range to a molecule of oxygen, an alcohol, an acethophenone and
Table 2
Effect of temperature and amount of catalyst on the conversion and selectivity of the catalytic oxidation of ethylbenzene by Co-supported catalyst.
Entry
Catalyst (g)
Time (h)
T (◦C)
Conversiona (mol %)
TONb
Selectivity (mol%)
Acetophenone
␣-pheniletanol
1
2
3
4
5
6
7
8
9
–
10
25
25
25
25
100
25
25
25
100
8
12
–
31
40
46
62
82
58
64
69
98
69
60
54
38
18
42
36
31
2
0.02
0.03
0.05
0.05
0.1
0.1
0.15
0.1
10
10
10
8
63.15
47.01
36.84
134.7
10.94
24.21
20.35
85.26
13.4
17.5
64
10.4
23
2
10
10
8
29
81
a
Reaction condition: ethylbenzene; 2 mmol, solvent; 5 cm3 acetic acid, 15 mol% NHPI.
TON, turn over number, moles of substrate converted per mole of metal.
b

288
D. Habibi et al. / Applied Catalysis A: General 466 (2013) 282–292
phenylalcohol; well-known as Russell termination. It is expected
from this mechanism that the ratio of these products are 1.0. Dur-
ing the first 2 h of the reaction, ketone and alcohol formation takes
place only via Russell termination but at higher conversions it is
clear that other mechanisms play an important role [36,37,10].
In the next step, the ethylbenzylhydroperoxides was catalytically
decomposed by the Co(III) complex, so, the selectivity of ethylben-
zylhydroperoxides decreases after the increase of reaction time.
However, in the presence of acetic acid, the rate of this reac-
tion increased and the selectivity of ethylbenzylhydroperoxides
decreased, that is, the proton of solvent can prompt decomposition
of ethylbenzylhydroperoxides, and eventually this step becomes
more rapid [10,38]. The ethylbenzylhydroperoxides in the next
steps further converts to acetophenone and 1-phenylethanol (steps
8 and 9).
The high selectivity to acetophenone and the absence of
2-phenylacetaldehyde can be rationalized from the following dis-
cussion. The methyl group carries more number of hydrogen than
the methylene group that was not oxidized. However, the methyl
group might be rotating more rapidly than the methylene group
and hence its hydrogen was not abstracted by activated oxygen as
shown in Scheme 3. The existence of a barrier to rotation about
Csp2 Csp3 was already reported [42]. Therefore, the hydrogen of
methylene group was more readily available for oxidation than
that of methyl group. The distant chemisorbed oxygen abstracts
the hydrogen from the methylene group of ethylbenzene and fash-
ions phenyl ethyl radical and metal hydroperoxide. The free radical
rapidly reacts with metal hydroperoxide to form 1-phenylethanol.
The local magnetic field of active sites of heterogeneous cata-
lyst (cobalt ions) could be thought to retain the paramagnetic
phenyl ethyl radical until it is hydroxylated [43]. The obtaining
1-phenylethanol is rapidly acted upon by the chemisorbed oxy-
gen on the metal active site or PINO to form the product radical
as shown in the reaction (Scheme 3). Furthermore, the oxidation
of 1-phenylethanol might be more rapid than ethylbenzene, as the
rotation of -CHOH group is slower than the CH2 group. Con-
sequently, the hydrogen atom which reacted with active sites of
Co-supported catalyst was ejected by radical in order to form water
and acetophenone.
Scheme 4. Reaction products of catalytic oxidation of cyclohexene with SiO2/Al2O3-
APTMS-BPK-Co.
After the reaction, the products were identified and quantified by
GC–MS. The products of the reaction were cyclohexene (CH) oxide,
2-cyclohexene-1-one and 2-cyclohexene-1-ol (see Scheme 4).
Several results of the cyclohexene conversion and the selectiv-
ity of the products are summarized in Table 3. The oxidation of
CH using NHPI proceeded even at 25 ◦C to give 2-cyclohexene-1-
one in higher selectivity after 24 h (81.7%). As the reaction time
were raised from 2 to 24 h, the CH conversion and the selectiv-
ity to 2-cyclohexene-1-one increased from 44.0 to 84.2 and 88.4
to 99.9%, respectively, while the selectivity to cyclohexene oxide
and 2-cyclohexene-1-ol were decreased at 80 ◦C. In the oxidation
of cyclohexene, all the reaction conditions showed excellent selec-
tivity for the ketone with only trace amounts (in total <1.0%) of
by-products after 8 h at 100 ◦C.
The oxidation of CH in the absence of catalyst gives low con-
version and selectivity to 2-cyclohexene-1-one at 25 ◦C (entry 1).
Furthermore, no reaction was observed in the absence of NHPI
because no radical formations from Co centers occur under the con-
ditions selected in this work [37,38]. Reaction carried out to some
extent in the absence of the catalyst, but the activity is lower (4%)
than when this compound is present. NHPI oxidizes CH slowly, and
selectivity to 2-cyclohexene-1-one was not high after 24 h (58.9%).
This result is in accord to the previously reported reaction mech-
anisms [37,38], where NHPIs are responsible for radical formation
and the heterogeneous Co is the co-catalyst that enhance the activ-
ity of the NHPI. Therefore, these could be demonstrated again from
the results that under the mentioned reaction conditions, the allylic
hydrogen is more reactive than the C C double bond. However, the
abstraction of hydrogen from the allylic carbon leads to allylic rad-
ical, which requires lower activation energy than the reaction at
double bond [44].
Reusability of the immobilized Co catalyst onto the SiO2/Al2O3
was confirmed by performing a series of consecutive experiments
in which the used catalyst was filtered, washed with fresh sol-
vent, and employed without any further treatment in another run.
The results shown in Fig. 9 clearly prove that a slight decline of
activity and selectivity occurs after seventh run. Consequently,
the results clearly suggest that the cobalt catalyst efficiently cat-
alyze conversion of cyclohexene (75%) with ca. 99% selectivity to
2-cyclohexene-1-one under NHPI and oxygen in benzonitrile as
solvent.
Besides coordination to a Schiff base ligand, the cobalt ions may
also interact with the surface Si OH and Al OH groups of the
SiO2/Al2O3. Thus, the materials of blank SiO2/Al2O3 that adsorbed
cobalt acetate (0.1 g) were also used for oxidation experiment. It
turned out that the conversion of ethylbenzene was almost 9.2%
with TON of 39.14 (similar to the result of blank experiments,
Table 2, entry 1). Therefore, in the oxidation of ethylbenzene with
NHPI and oxygen under acetic acid, the cobalt ions absorbed on the
surface of the support did not contribute in the oxidation reaction.
The above observations suggest that the oxidation occurs due to
the catalytic nature of the chemically immobilized of Co catalysts
onto the Schiff base ligands.
3.4. Oxidation of oximes
To assess the reusability, the catalyst was separated by filtration
after the first run, washed with ether and dried at 100 ◦C under vac-
uum and then used for the next runs under the same conditions (see
Fig. 8). No significant loss of activity and selectivity was observed,
confirming that the Co-supported catalyst has high stability during
the oxidation process. To further proof that the reaction was cat-
alyzed by the cobalt sample, we added extra ethylbenzene to the
filtrate after the removal of the catalyst and found that no more
products were produced under the same conditions.
In this protocol, a novel useful procedure for the facile deox-
imation system by reusable Co supported catalyst and molecular
oxygen as oxidant were studied (see Scheme 5). The experiments
were designed with acetophenone oxime as a model substrate.
For optimizing the conditions in oxidation of oximes, several fac-
tors have been investigated such as the amount of catalyst, the
effect of temperature, the amount of benzaldehyde and the effect of
solvent. In this reaction, the main product for oximes with electron-
donating groups is carbonyl compounds. In order to examine the
effect of catalyst on deoximation reaction; the reaction was carried
out in the presence of various amounts of catalyst. The observations
indicated that in the case of absence of catalyst, the reaction is car-
ried out slowly while in the presence of the optimum amounts of
the catalyst, the reaction is performed considerably. The maximum
3.3. Oxidation of cyclohexene
To extend the present method, the oxidation catalytic activ-
ity of the cobalt catalyst has been examined using NHPI and
oxygen under benzonitrile as solvent at several temperatures.

D. Habibi et al. / Applied Catalysis A: General 466 (2013) 282–292
289
Table 3
Effect of the temperature and the reaction time on the conversion and selectivity of the catalytic oxidation of cyclohexene by Co-supported catalyst.
Entry
Time (h)
T (◦C)
Conversion (mol%)
TONa
Selectivity (mol%)
Alcohol
Ketone
Epoxide
1
2
3
4
5
6
7
8
24
2
6
25
25
25
25
25
25
25
25
25
60
60
60
60
60
60
60
60
80
80
80
80
80
80
80
80
100
100
100
100
100
100
100
100
4
15.4
21
26
30
32.4
37.9
41.8
47
32
49
54.6
59.4
61.5
64.8
67.9
71.4
44
62
66
70
75
78.7
79.5
84.2
53.5
66.9
71
74.7
78
79.5
82
–
23.6
54.9
40.6
33
24.5
17.4
13.1
10.5
8.6
25
17
14
8
5
4
2
0.7
10
3.5
1
0.8
0.4
–
–
–
6.8
1
0.6
–
–
–
–
–
58.9
44.6
53.9
57
62
68.4
73
77.5
81.7
70.7
80.4
83.6
88
91
95.6
97
17.5
0.5
5.5
10
13.5
14.2
13.9
12
9.7
4.3
2.6
2.4
4
4
0.4
1
0.8
1.6
1.5
3
1.2
0.6
0.1
8
10
12
16
18
24
2
9
49.47
75.15
88.63
97.89
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
6
8
10
12
16
18
24
2
98.5
88.4
95
96
98
6
8
10
12
16
18
24
2
99
99.9
99.9
99.9
92.6
98.8
99
99.9
99.9
99.9
99.9
99.9
trace
trace
trace
6
8
0.2
0.4
0.1
0.1
10
12
16
18
24
trace
trace
trace
93
a
TON, turn over number, moles of substrate converted per mole of metal.
selectivity of carbonyl compound was obtained with 0.15 g of cat-
alyst. The conversion of the acetophenone from 6% in the absence
of the catalyst, to higher than 99% in the presence of the catalyst
indicates that the catalyst has an efficient and effective role in this
reaction.
For examining the role and effect of the solvent in the reac-
tion, various solvents which are suitable for radical reactions
have been used [45]. Therefore, acetonitrile, benzene, toluene,
and cyclohexane solvents and water have been used (Table 4).
The results showed that in various solvents the selectivity was
100% and the conversion decreased in the following order:
toluene (99.9) > acetonitrile (87.0) > benzene (81.0) > cyclohexane
(19.0) > and water (0.0). The reaction at the presence of coordinat-
ing solvents such as water made no reaction. It seems that the donor
electrons of this solvent had more ability to occupy the vacant space
around the metal in the catalyst, so this prevents coordinating from
oxygen molecules [46]. In this work, toluene provided the highest
Conversion
Selectivity
Conversion
Selecꢀvity
100
90
80
70
60
50
40
30
20
10
0
1
2
3
4
5
6
7
Recycling number
Recycling number
Fig. 8. Reusability of the cobalt-supported catalyst on the oxidation of ethylben-
zene and selectivity to acetophenone. Conditions: ethylbenzene: 2 mmol; amount
of catalyst: 0.1 g; NHPI, 15%; acetic acid, 5 cm3; T = 100 ◦C.
Fig. 9. Reusability of the cobalt-supported catalyst on the oxidation of cyclohexene
and selectivity to 2-cyclohexene-1-one. Conditions: cyclohexene, 2 mmol; amount
of catalyst, 0.1 g; NHPI, 15%; benzonitrile, 5 cm3; T = 80 ◦C.

290
D. Habibi et al. / Applied Catalysis A: General 466 (2013) 282–292
immobilized of Co catalysts onto the Schiff base ligands. To fur-
OH
R
O
ther explore the utility of this catalytic system, oxidation of several
oximes (aldoximes and ketoximes) were also studied (see Table 5).
Aldehydes were obtained with excellent yields and the overoxi-
dation to carboxylic acid and Beckmann rearrangement were not
observed, which was another advantage of the proposed system.
Furthermore, steric structure almost has no effect on conversion
and selectivity of oxime (entry 14). The hydroxyl group in the ortho
position of oximes (entry 12 and 13) exerts only an partly induc-
tive effect, but hydrogen bonding between the OH and the nitrogen
atom in imine will decrease the electron density of the carbon atom
in the C N. This factor probably influences the reactivity of oxime.
Consequently, the yield of this oxime against with other oximes is
slightly decreased, and the reaction time is longer [48].
In order to verify the kind of mechanism, 2,6-di-tert-butyl-
4-methylphenol (BHT), as a scavenger of chemical radical was
used. The reaction appeared to be radical processes since it was
totally inhibited in the presences of radical trap (5 mol%). It seems
that oximes with different groups (electron-donating and electron-
drawing) go in various paths in the oxidation reaction with oxygen
over the catalyst (paths An and B). To further elucidate the reac-
tion mechanism, series of experiments were conducted, when the
oxidation of acetophenone oxime was conducted in the presence
of dioxygen and benzaldehyde, in the absence of Co catalyst, the
conversion of acetophenone could only reach 6%. However, the
conversion was remarkably increased by adding 0.15 g of cobalt
catalyst to the mixture (Table 1, 99%, entry 1). The results indi-
cate that cobalt catalyst is crucial for the deoximation reaction.
According to the proposed mechanism, at the first Co(II) ions and
benzaldehyde generate an acyl radical (ph-CO·) [49], so the radical
formed is quickly trapped by dioxygen to give an acylperoxy rad-
ical (ph-COO·). The acylperoxy radical acts as a carrier in a chain
mechanism by reaction with another benzaldehyde molecule to
give the peroxybenzoic acid, and generating another acyl radical
as well (Eq. (1)) [49–55]. The peroxybenzoic acid is assumed to
play important roles, where peroxybenzoic reacts with another
Co(II) catalyst molecule to generate high-valent cobalt intermedi-
ate (Eq. (2)). The color of the reaction mixture changed to green
which also indicated valence change of cobalt (Co(II) to Co(III))
[55,56]. Then, the intermediate attacks to the imine group of oxime
through a nucleophilic attack [55], thereby, the reaction of an
oxo-catalyst radical and oximes, which is proposed to generate a
nitroso oxy radical species eventually loses NO to generate an alde-
hyde and ketone. Via this process, oxime will be converted to its
N
Co(II), O2
Tolouene
R
R
R
Benzaldehyde
Scheme 5. Reaction products of the catalytic oxidation of oximes with SiO2/Al2O3-
APTMS-BPK-Co.
conversion and selectivity to acetophenone. Therefore, toluene as
a solvent plays an effective role in oxidation of oximes, because
toluene was reluctant to undergo free radical addition [45,47].
In oxidation of oximes, the presence of several amounts of
benzaldehyde can also have a determining role. Observations indi-
cated that in the absence of benzaldehyde, the reaction has a little
progress even in a long time period, but in the presence of benzalde-
hyde a great conversion was observed. This observation indicated
that benzaldehyde was used as the oxygen transfer agent in this
oxidation reaction. In addition, when isobutyraldehyde was used as
the only oxygen transfer agent, great conversion was not observed.
To estimate the reusability of the cobalt supported catalyst, after
the first performance the catalyst was filtrated and washed with
ether and dried at 120 ◦C under vacuum and then used for the
next performances under the same conditions. No apparent loss
of activity and selectivity was observed after 8th runs, confirm-
ing that the cobalt catalyst has high stability during the process.
To further proofs that the reaction was catalyzed by the hetero-
geneous Co-catalyst, we added extra acetophenone oxime to the
filtrate after the removal of the catalyst and found that no more
products were produced under the same conditions. In addition,
the Co ions absorbed on the surface of the support did not con-
tribute in the deoximation reaction. This observation indicated that
this reaction occurs due to the catalytic nature of the chemically
Table 4
Effect of solvent on the aerobic oxidation of acetophenoneoxime.a
Entry
Solvent
Conversion (%)
Selectivity (%)
1
2
3
4
5
Toluene
Acetonitrile
Benzene
Cyclohexane
Water
99.9
87.0
81.0
19.0
0.0
100
100
100
100
–
a
Reaction condition: Catalyst; 0.15 g, acetophenoneoxime; 2 mmol, benzalde-
hyde; 10 mmol, solvent; 5 cm3, O2 bubbling, Temperature; 50 ◦C.
Table 5
Several examples of aerobic oxidations of oximes by using Co-supported catalyst.
b
Entry
Substrate
Product (selectivity %)
t (min)
Con. (%)
>99
94
98
>99
97
95
93
92
95
95
97
93
>99
97
>99
97
94
42
53
TONa
TOF (min−1
)
1
2
3
4
5
6
7
8
Acetophenoneoxime
Acetophenone (100)
90
85
105
100
110
90
68.39
64.93
67.70
68.39
67.01
65.63
64.24
63.55
65.63
65.63
67.02
64.24
68.39
67.01
68.39
67.01
64.93
29.01
36.61
0.759
0.763
0.690
0.683
0.609
0.729
0.803
0.605
0.504
0.486
0.394
0.321
0.258
0.335
0.359
0.418
0.270
0.193
0.305
4-Bromobenzaldehyde oxime
3-Bromobenzaldehyde oxime
3-Methylbenzaldehyde oxime
4-Methylbenzaldehyde oxime
4-Methylacethophenon oxime
4-Cholorobenzaldehyde oxime
2, 4-Dicholorobenzaldehyde oxime
2,6-Dicholorobenzaldehyde oxime
3,4-Dimethoxybenzaldehyde oxime
3,4,5-Trimethoxybenzaldehyd oxime
2-Hydroxy benzaldehydeoxime
2-Hydroxynaphthaldehyde oxime
Benzophenoneoxime
4-Bromobenzaldehyde (100)
3-Bromo benzaldehyde (100)
3-Methyl benzaldehyde (100)
4-Methylbenzaldehyde (100)
4-Methyacetophenone (100)
4-Cholorobenzaldehyde (100)
2, 4-Dicholorobenzaldehyde (100)
2,6-Dicholorobenzaldehyde
3,4-Dimethoxy benzaldehyde (100)
3,4,5-Trimethoxybenzaldehyde (100)
2-Hydroxy benzaldehyde (100)
2-Hydroxynaphthaldehyde (100)
Benzophenone (100)
80
105
130
135
170
200
265
200
190
160
240
150
120
9
10
11
12
13
14
15
16
17
18
19
4-Cholorobenzophenone oxime
Cyclohexanoneoxime
Cinnamaldehydeoxime
2-Nitrobenzaldehyde oxime
4-Nitrobenzaldehyde oxime
4-Cholorobenzophenone (100)
Cyclohexanone (100)
Cinnamaldehyde (100)
2-Nitrobenzonitrile (62)
4-Nitrobenzonitrile (78)
a
TON, turn over number, moles of substrate converted per mole of metal.
TOF, turn over frequencies.
b

D. Habibi et al. / Applied Catalysis A: General 466 (2013) 282–292
291
O
O
O
O
H
O
.
O
OH
.
Co(II)
O2
H
O
O
1)
2)
+
O
O
O
OH
OH
O
Co(II)
Co(III)
+
+
OH2
R'
OH
O
N
O
N
O
N
O
Co(III)
H
RC
N
+
NOx
R'
R
(Path A)
(Path B)
R
R
R'
Co(III)
R
R'
Co(II)
H2O
Scheme 6. Proposed mechanism for the oxidation of oximes in the presence of molecular oxygen.
Table 6
Screening data (oxidations of ethylbenzene, cyclohexene and oximes).
Selectivity (%)
Conversion (%)
Product
Condition reactiona
Catalytic System
Substrate
85
75
99
98
69
26
64
47
24
45
83
73.6
Acethophenone
0.05 g Co-MCM-41(100), TBHP, solvent-free, 80 ◦C, 24 h
3 ␮mol Mn (␮- NO2 TDCPP)Cl, H2O2, 25 ◦C, 5.5 h
2.45 g NiAl-hydrotalcite, O2, solvent free, 135 ◦C, 9 h
0.09 g CoTPP-P(4VP-co-st)/SiO, O2, solvent -free, 95 ◦C, 0.2 h
0.1 g CNCr-2, TBHP, CH3CN, 70 ◦C, 8 h
Bhoware et al. [62]
Caveleiro et al. [63]
Jana et al. [64]
Baojiao et al. [65]
George et al. [66]
This work
Ethylbenzene
99
80.3
0.1 g Si/Al-ATMPS-BPK-Co/NHPI,O2,acetic acid, 100 ◦C, 8 h
5 mg (Ru/Co/Ce) (THNO), TBHP, CH2Cl2
2-Cyclohexen-
1-one
Ghiaci et al. [67]
Cyclohexene
100
10.2
55.6
60.8
99
50
(0.01 mol) t-BuCo/MCM- 41, H2O2,CH3CN, 60 ◦C, 5 h
100 mg Co (III) SBA-15, H2O2, CH3CN, 40 ◦C, 12 h
Mapolie et al. [68]
Park et al. [69]
Salavati [70]
Nykong et al. [71]
This work
34.8
43.6
92
75
99
1.02 × 10−5 mol [Co(H4C6N6 S2)], TBHP, CH2Cl2, 25 ◦C, 8 h
(1.7 mg/ml) CoPc, TBHP, DMF/dichloromethane, 25 ◦C, 8 h
0.1 g Si/Al-ATMPS-BPK-Co/NHPI, O2, benzonitrile, 80 ◦C, 8 h
(10−3 mmol)MnTPPCl,O2,toluene,benzaldehyde, 50 ◦C,2 h
100
Acetophenone
Cyclohexanone
Zhou et al. [72]
Acethophenon
oxime
100
100
100
100
82
92
99
93
(0.01 g) Metallophthalocyanine, (0.30 g) [bmim]Br, 50 ◦C, 1.3 h
(100 mg) CeO2–ZrO2,THBP, solvent-free, 80 ◦C, 5 h
Shaabani et al. [73]
Jayaram et al. [74]
This work
0.15 g Si/Al-ATMPS-BPK-Co, O2, toluene,benzaldehyde, 50 ◦C, 1.5 h
(10−3 mmol) MnTPPCl, O2,toluene, benzaldehyde, 50 ◦C, 5 h
Zhou et al. [72]
Cyclohexanone
oxime
100
100
30
93
(100 mg) CeO2-ZrO2,THBP, solvent-free, 80 ◦C, 12 h
2 mmol (HCHO)n, 0.25 mmol SiO2-OSO3H, SDS, H2O, 50 ◦C under
ultrasound irradiation, 1.5 h
Jayaram et al. [74]
Li et al. [75]
100
100
97
93
0.15 g Si/Al-ATMPS-BPK-Co, O2, toluene,benzaldehyde,50 ◦C, 2.6 h
PVCBSA, CCl4, reflux, 3 h
This work
Khazaei et al. [76]
4-Methyl
benzaldehyde
4-Methyl
Benzaldehyde
oxime
100
100
100
90
89
97
Al(NO3)3·9H2O, NaBr, CH2Cl2, 25 ◦C, 3.5 h
Ghorbani et al. [77]
Shaabani et al. [73]
This work
(0.01 g) Metallophthalocyanine, (0.30 g) [bmim]Br, 50 ◦C, 0.5 h
0.15 g Si/Al-ATMPS-BPK-Co, O2, toluene, benzaldehyde, 50 ◦C, 1.8 h
a
Co TPP- P (4VP- co- st)/SiO2: Co tetraphenylporphrins on P (4VP- co- st)/SiO2, CNCr-2: Cu1−xNixCr2O4(x = 0.5), THNO: Trimetallic hybrid nanomixed oxide (Ru/Co/Ce),
H6C6N6S2: 1,2,5,6,8,11-hexazacylodoca- 7, 12- dithione-2, 4,8,10- tetraene, MnTPPCl: Manganese meso-tetraphenylporphyrin chloride, PVCBSA: Poly[4-vinyl-N,N-
dichlorobenzenesulfonamide].
corresponding carbonyl compound. Although, the oxidation effi-
ciency was not affected by electron denoting group of substrate,
the presence of electron-drawing groups in oxime (like nitro group;
entry 15 and 16) will change the path of reaction so as the speed of
protonation of hydroxyl group in oxime will be more than the speed
of oxo-catalyst attack to imine bond, consequently, it produces
nitrile by the elimination of water, the same result was observed in
the literature [57–63] (see Scheme 6).
catalyst, short reaction time, high conversion and selectively, use of
dioxygen as a clean oxidant and widely used in catalytic oxidation
reactions (ethylbenzene, cyclohexene and various oximes as sub-
strates). Therefore, this protocol could be introduced for practical
organic synthesis.
4. Conclusions
To demonstrate the efficiency and effectiveness of the catalytic
system, the results were compared with other catalytic systems in
order to evaluate the benefits and disadvantages of this system. The
gathering results from the literature (see Table 6) demonstrated
that the catalytic system presented in this paper has advantages
in terms of solid nature of catalyst, inexpensive and stability of
A catalyst was developed based on the immobilization of
cobalt on SiO2/Al2O3 to efficiently promote the aerobic oxida-
tion of ethylbenzene, cyclohexene and oximes to acetophenone,
2-cyclohexene-1-one and carbonyl compounds, under oxygen
atmosphere Oxidation of alkyl aromatic and allylic site was resulted
with the oxidant of NHPI and O2 without the use of any reductant.

292
D. Habibi et al. / Applied Catalysis A: General 466 (2013) 282–292
The catalytic performance was remarkably high in the oxidation
reaction. The effect of the catalyst amount, reaction time, reac-
tion temperature and effect of various solvents on the oxidation
of ethylbenzene and cyclohexene were investigated. The results
indicated that catalyst/NHPI facilitated the generation of the active
species phtalimide-N-oxyl (PINO) radical which further catalyzed
the oxidation of ethylbenzene and cyclohexene. Furthermore, we
have reported a new and efficient methodology for the regenera-
tion of aldehydes and ketones from oximes. The extension of the
method to other catalysts is currently under investigation.
[30] Z. Ozaydin, S. Yasyerli, G. Dogu, Ind. Eng. Chem. Res. 47 (2008) 1035–1042.
[31] B.J. Aronson, C.F. Blanford, A. Stein, J. Phys. Chem. B 104 (2000) 449–459.
[32] S.H.Y. Lo, Y.Y. Wang, C.C. Wan, J. Colloid Interface Sci. 310 (2007) 190–195.
[33] X.J. Tang, J.H. Fei, Z.Y. Hou, X.M. Zheng, H. Lou, Energy Fuels 22 (2008)
2877–2884.
[34] L. Guezi, R. Sundararajan, Zs Koppany, Z. Zsoldos, Z. Schay, F. Mizukami, S. Niwa,
J. Catal. 167 (1997) 482–494.
[35] V.D. Chaube, S. Shylesh, A.P. Singh, J. Mol. Catal A: Chem. 241 (2005) 79–87.
[36] Y. Ishii, K. Nakayama, M. Takeno, S. Sakaguchi, T. Iwahama, Y. Nishiyama, J. Org.
Chem. 60 (1995) 3934–3935.
[37] Y. Ishii, S. Sakaguchi, T. Iwahama, Adv. Synth. Catal. 343 (2001) 393–427.
[38] Y. Ishii, S. Sakaguchi, Catal. Today 117 (2006) 105–113.
[39] H. Ma, J. Xu, Q. Zhang, H. Miao, W. Wu, Catal. Commun. 8 (2007) 27–30.
[40] S. Evans, J.L. Smith, J. Chem Soc, Perkin Trans. 2 (2000) 1541–1552.
[41] F. Minisci, C. Punta, F. Recupero, F. Fontana, G.F. Pedulli, Chem. Commun. 7
(2002) 688–689.
Acknowledgments
[42] T. Schaefer, W.K. Chan, R. Sebastian, R.W. Schurko, F.E. Hruska, Can. J. Chem. 72
(1994) 1972–1977.
[43] Patai series, The Chemistry of Functional Groups, the Chemistry of Phenols,
series editor: Zvi Rappoport, John Wiley & Sons, 2003.
[44] K.B. Wiberg, Oxidation in Organic Chemistry, Academic Press, New York, 1965.
[45] J.M. James, J.O. Philip, A.U. Gregg, L. Bruno, P.C. Dennis, Modern Solvents in
Organic Synthesis, Springer, New York, 1999.
[46] J.S. Uber, Y. Vogels, D. van den Helder, I. Mutikainen, U. Turpeinen, W.T. Fu, O.
Roubeau, P. Gamez, J. Reedijk, Eur. J. Inorg. Chem. (2007) 4197–4206.
[47] X.T. Zhoua, H.B. Ji, Q.L. Yuan, J. Porphyr. Phthalocyanine 12 (2008) 94–100.
[48] D. Habibi, M.A. Zolfigol, A.R. Faraji, P. Rahmani, Monatsh. Chem. 143 (2011)
809–814.
[49] Y. Kuang, Y. Nabae, T. Hayakawa, M. Kakimoto, Appl. Catal. A: Gen. 423–424
(2012) 52–58.
[50] T. Mukaiyama, T. Yamada, T. Nagata, K. Imagawa, Chem. Lett. (1993) 327–330.
[51] J.Y. Qi, Y.M. Li, Z.Y. Zhou, C.M. Che, C.H. Yeung, A.S.C. Chan, Adv. Synth. Catal.
347 (2005) 45–49.
[52] X.T. Zhou, H.B. Ji, Q.L.J. Yuan, Porphyr. Phthalocyanin 12 (2008) 94–100.
[53] R. Raja, G. Sankar, J.M. Thomas, Chem. Commun. 9 (2009) 829–830.
[54] S. Ellis, I.V. Kozhevnikov, J. Mol. Catal. A 187 (2002) 227–235.
[55] X.T. Zhou, Q.L.J. Yuan, H.B. Ji, Tetrahedron Lett. 51 (2010) 613–617.
[56] A. Nishinaga, S. Yamazaki, T. Miwa, T. Matsuura, React. Kinet. Catal. Lett. 43
(1991) 273–276.
Thanks are due to the Iranian Nanotechnology Initiative and
Chemistry Department of Bu-Ali Sina University for supporting of
this work.
References
[1] M. Hirano, S. Yakabe, H. Chikamori, J.H. Clark, T. Morimoto, J. Chem. Res, Synop.
6 (1998) 308–309.
[2] Y.C. Son, V.D. Makawana, A.R. Howell, S.L. Suib, Angew. Chem. Int. Ed. 40 (2001)
4280–4283.
[3] Z.W.C.S.Y. Wu, J. Chin, Org. Chem. 16 (1996) 121–132.
[4] G. Zhang, X. Wen, Y. Wang, W. Mo, C. Ding, J. Org. Chem. 76 (2011) 4665–4668.
[5] A. Grirrane, A. Corma, H. Garcia, J. Catal. 268 (2009) 350–355.
[6] V.D. Makawanna, L.J. Garces, J. Liu, J. Cai, Y.C. Son, S.L. Suib, Catal. Today 85
(2003) 225–233.
[7] Y.S. Ding, X.F. Chen, S. Sithambaram, S. Gomez, R. Kumar, V.M.B. Crisostomo,
S.L. Suib, M. Aindow, Chem. Mater. 17 (2005) 5382–5389.
[8] A.K. Vannucci, Z. Chen, J.J. Concepcion, T.J. Meyer, ACS. Catal. 2 (2012) 716–719.
[9] Y. Ishi, K. Nakayama, M. Sakaguachi, S. Iwahama, T. Nishiyama, J. Org. Chem. 60
(1995) 3934–3935.
[10] Y. Yoshino, Y. Hayashi, T. Iwahama, S. Sakaguchi, Y. Ishii, J. Org. Chem. 62 (1997)
6810–6813.
[57] R. De Paula, M.M.Q. Simoes, M.G.P.M. Neves, J.A.S. Cavaleiro, Catal. Commun.
10 (2008) 57–60.
[11] M. Nechab, C. Einhorn, J. Einhorn, Chem. Commun. (2004) 1500–1501.
[12] N. Sawatari, S. Sakaguchi, Y. Ishii., Tetrahedron. Lett. 44 (2003) 2053.
[13] R. Amorati, M. Lucarini, V. Mugnaini, G.F. Pedulli, J. Org. Chem. 68 (2003)
1747–1754.
[58] N.A. Stephenson, A.T. Bell, J. Am. Chem. Soc. 127 (2005) 8635–8643.
[59] G.S. Nunes, I. Mayer, H.E. Toma, K. Araki, J. Catal. 236 (2005) 55–61.
[60] H.Y. Chen, H.B. Ji, X.T. Zhou, J.C. Xu, L.F. Wang, Catal. Commun. 10 (2009)
828–832.
[14] I.W.C.E. Arends, M. Sasidharan, A. Kuhnle, M. Duda, C. Jost, R.A. Sheldon, Tetra-
hedron 58 (2002) 9055–9061.
[61] S.L.H. Rebelo, M.M. Pereira, M.M.Q. Simoes, M.G.P.M. Neves, J.A.S. Cavaleiro, J.
Catal. 234 (2005) 76–87.
[15] Y. Aoki, S. Sakaguchi, Y. Ishii, Adv. Synth. Catal. 346 (2004) 199–202.
[16] C. Einhorn, J. Einhorn, C. Marcadel, J.-L. Pierre, Chem. Commun. (1994)
447–448.
[62] S.S. Bhoware, A.P. Singh, J. Mol. Catal. A: Chem. 266 (2007) 118–130.
[63] S.L.H. Rebelo, S.L.H. Rebelo, M.M.Q. Simões, M.G.P.M.S. Neves, J.A.S. Cavaleiro,
J. Mol. Catal. A: Chem. 201 (2003) 9–22.
[17] S. Tsujimoto, S. Sakaguchi, Y. Ishii, Tetrahedron Lett. 44 (2003) 5601–
5604.
[18] M. Eikawa, S. Sakaguchi, Y. Ishii, J. Org. Chem. 64 (1999) 4674–4685.
[19] Y. Nisshawaki, S. Sakaguchi, Y. Ishii, J. Org. Chem. 67 (2002) 5663–5668.
[20] T. Iwahama, S. Sakaguchi, Y. Nishiyama, Y. Nishayama, J. Org. Chem. 61 (1996)
4520–4526.
[21] Y. Ishii, T. Iwahama, S. Sakaguchi, Tetrahedron Lett. 37 (1996) 4993–4996.
[22] Y. Ishii, J. Mol. Catal. A: Chem. 117 (1997) 123–137.
[23] S. Kato, T. Iwashama, S. Sakaguchi, Y. Ishii, J. Org. Chem. 63 (1998) 22.
[24] S. Sakaguchi, T. Takase, T. Iwahama, Y. Ishii, Chem. Commun. 18 (1998)
2037–2038.
[64] S.K.Jana, P. Wu, T. Tatsumi, J. Catal. 240 (2006) 268–274.
[65] R. Wang, B. Gao, W. Jiao, Appl. Surf. Sci. 255 (2009) 4109–4113.
[66] K.George, S. Sugunan, Catal. Commun. 9 (2008) 2149–2153.
[67] M. Ghiaci, B. Aghabarari, A.M.B.D. Rego, A.M. Ferraria, Appl. Catal. A: Gen. 393
(2011) 225–230.
[68] N. Malumbazo, S.F. Mapolie, J. Mol. Catal A: Chem. 312 (2009) 70–77.
[69] Sujandi, S.C. Han, D.S. Han, M.J. Jin, S.E. Park, J. Catal. 243 (2006) 410–416.
[70] M.Salavati-Niasari, J. Mol. Catal. A: Chem. 283 (2008) 120–128.
[71] N. Sehlotho, T. Nykong, J. Mol. Catal. A: Chem. 209 (2004) 51–57.
[72] X.T. Zhou, Q.L. Yuan, H.B. Ji, Tetrahedron Lett. 51 (2010) 613–617.
[73] A. Shaabani, E. Farhangi, Appl. Catal. A: Gen. 371 (2009) 148–152.
[25] T. Iwahama, S. Sakaguchi, Y. Ishii, Tetrahedron Lett. 39 (1998) 9059–9062.
[26] T. Iwahama, S. Sakaguchi, Y. Ishii, Chem. Commun. 7 (2000) 613–614.
[27] Y. Ishii, Catal. Today 117 (2000) 105–113.
[28] Y. Ishii, S. Sakaguchi, T. Iwahama, Adv. Synth. Catal. 343 (2001) 939–941.
[29] M. Arshadi, M. Ghiaci, A. Rahmanian, H. Ghaziaskar, A. Gil, Appl. Catal, B: Envi-
ron. 119–120 (2012) 81–90.
[74] S.S. Deshpande, S.U. Sonavane, R.V. Jayaram, J. Catal. Commun.
639–644.
[75] J.T. Li, X.T. Meng, B. Bai, M.X. Sun, Ultrason. Sonochem. 17 (2010) 14–16.
[76] A. Khazaei, R. Ghorbani Vaghei, Tetrahedron Lett. 43 (2002) 3073–3074.
[77] A. Ghorbani-Choghamarani, J. Zeinivand, Chin. Chem. Lett. 21 (2010)
1083–1086.
9 (2008)