Cobalt(II) phthalocyanine covalently anchored to cellulose as a recoverable and efficient catalyst for the aerobic oxidation of alkyl arenes and alcohols

Article abstract of DOI:10.1016/j.molcata.2014.09.003

Cobalt(II) phthalocyanine covalently immobilized on cellulose as a heterogeneous catalyst was synthesized and characterized. The catalyst showed good catalytic activity for the aerobic oxidation of alkyl arenes and alcohols under relatively mild reaction conditions. The catalyst can readily be recovered from the reaction mixture and reused for several runs without significant decrease in catalytic activity.

Full text of DOI:10.1016/j.molcata.2014.09.003

Journal of Molecular Catalysis A: Chemical 395 (2014) 494–499
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Cobalt(II) phthalocyanine covalently anchored to cellulose as a
recoverable and efficient catalyst for the aerobic oxidation of alkyl
arenes and alcohols
Ahmad Shaabani∗, Sajjad Keshipour, Mona Hamidzad, Shabnam Shaabani
Faculty of Chemistry, Shahid Beheshti University, G.C., P.O. Box 19396-4716, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 April 2014
Received in revised form 6 August 2014
Accepted 4 September 2014
Available online 16 September 2014
Cobalt(II) phthalocyanine covalently immobilized on cellulose as a heterogeneous catalyst was synthe-
sized and characterized. The catalyst showed good catalytic activity for the aerobic oxidation of alkyl
arenes and alcohols under relatively mild reaction conditions. The catalyst can readily be recovered from
the reaction mixture and reused for several runs without significant decrease in catalytic activity.
© 2014 Elsevier B.V. All rights reserved.
Keywords:
Cobalt(II) phthalocyanine
Cellulose
Heterogeneous catalysis
Aerobic oxidation
Alkylarenes
1. Introduction
[11]. The main purpose to use a support for MPc is to increase the
effective surface area of the catalyst.
The selective aerobic oxidation of hydrocarbons and alcohols
are very important commercial processes for the production of
aldehydes and ketones. Conventionally, for effective oxidation of
alcohols and alkylarenes, stoichiometric amounts of hazardous and
toxic oxidants such as nitric acid, potassium permanganate, potas-
sium dichromate, sodium hypochlorite or organic peroxides are
necessary. However, these oxidants generate copious amounts of
wastes. In this regard, environmentally benign procedures such
as using green oxidants and heterogeneous recoverable catalysts
are especially attractive for the synthesis of pharmaceuticals, fla-
vors and fragrances, and agrochemicals. Thus, there is an increasing
demand for catalytically oxidation processes with green, economic,
and efficient strategies [1–3].
Metal phthalocyanines (MPcs) as macrocyclic complexes are
easily accessible, stable and cost effective biomimetic oxidation
catalysts which widely used in organic reactions [4–10]. Recently,
MPcs were used widely for the oxidation of organic compounds
[11]. Immobilization of these catalysts via covalent attachment to
the functionalized polymers is an interesting approach to facilitate
catalyst recovery, recycling, and to reduce effluent contamination
As the most important structural material in plants, cellulose is a
highly functionalized and linear stiff-chain homopolymer, formed
by the repeated connection of d-glucose building blocks. This
polysaccharide has fascinating properties such as hydrophilicity,
chirality, biodegradability and broad chemical modifying capac-
ity. Recently, modifying of cellulose with various functionalities
for catalytic purposes has attracted more attentions [12–15] and
in this regard, Co(II) Pc as a useful catalyst was immobilized on
cellulose by the reaction of amine groups on Co(II) tetraamino
Pc with the aldehyde groups which were created on cellulose
[16,17]. However, the attachment of Pc to cellulose established
using imine bonds which such connection is corruptible due to
hydrolyzing particularly in aqueous media and acidic conditions
[18].
In continuation of our efforts to synthesis of chemically
supported heterogeneous cellulose-based catalysts [19,20] and
oxidation of organic compounds with phthalocyanines [21,22],
herein we wish to introduce a new and efficient strategy for
immobilization of Co(II) Pc on cellulose which are useful for envi-
ronmentally benign aerobic oxidation of alkyl arenes and alcohols.
Co(II) 4,9,16,23-tetraamine-phthalocyanine supported on cellu-
lose (CoPc@Cell) was prepared through covalent immobilization of
Co(II) 4,9,16,23-tetraamine-phthalocyanine onto chemically mod-
ified cellulose (Scheme 1).
∗
Corresponding author. Tel.: +98 2129902800.
E-mail address: a-shaabani@sbu.ac.ir (A. Shaabani).
http://dx.doi.org/10.1016/j.molcata.2014.09.003
1381-1169/© 2014 Elsevier B.V. All rights reserved.

A. Shaabani et al. / Journal of Molecular Catalysis A: Chemical 395 (2014) 494–499
495
OH
OTs
H
OH
OH
OH
H
O
O
O
O
O
TsCl
O
O
O
OH
HO
HO
HO
HO
OH
OH
n
n
NH2
NH2
N
H2N
N
N
N
N
N
H2N
N
N
N
N
N
NH2
N
N
N
OH
OH
NH
H
H2N
O
O
H2N
O
O
HO
HO
OH
n
Scheme 1. Preparation of CoPc@Cell.
2. Experimental procedures
2.2. Materials and methods for determination of Co(II) on
CoPc@Cell using flame atomic absorption spectroscopy (FAAS)
2.1. Preparation of CoPc@Cell
CoPc@Cell (0.05 g) was added to a mixture of HCl:HNO3 (3:1)
(10 mL) and sonicated for 3 h. Then, the mixture was filtered and the
total volume of the filtrate made up to about 30 mL with distilled
water. The final solution was aspirated into the flame of the AAS
against the blank prepared with cellulose. The Co(II) concentration
was obtained using calibration curve prepared with cobalt solution
standards.
In a typical procedure, a mixture of cellulose (2.00 g) and
LiCl (0.05 g) in 20 mL of DMF was prepared. After 8 h stirring
at room temperature, 8 mmol tosylchloride and 0.10 mL triethyl-
amine were added to the mixture, and stirring continued for
24 h at 8 ◦C to afford cellulose tosylate (CT) as a white solid
powder. Then, the mixture containing CT was treated with 9 mL
water and 7.00 mmol Co(II) 4,9,16,23-tetraamine-phthalocyanine.
Instantly, temperature was raised to 100 ◦C and stirring contin-
ued. After 24 h, the mixture cooling down to room temperature
and it was poured into 60 mL acetone. The polymer was fil-
trated and washed with acetone (2× 5 mL) and H2O (3× 10 mL).
It was dried under vacuum at 60 ◦C to afford CoPc@Cell as a gray
powder.
2.3. Typical procedure for the oxidation of 1-phenyl-ethanol
1-Phenyl-ethanol (0.14 g, 1.00 mmol) was added to a two-
necked flask equipped with a gas bubbling tube containing colloidal
of CoPc@Cell (0.05 g) and KOH (0.25 mmol) in o-xylene (5 mL) at
room temperature. The mixture was stirred at room temperature
under O2 atmosphere provided with a balloon. The progress of the
reaction was followed by thin layer chromatography (TLC). Upon
completion, CoPc@Cell was separated by filtration and washed with
acetone (5 mL). Acetophenone was isolated from the mixture using
column chromatography with n-hexane in 90% yield.
2.4. Typical procedure for the oxidation of tetraline
N-Hydroxyphthalimide (0.01 g, 0.06 mmol) was added to a
two-necked flask equipped with a gas bubbling tube contain-
ing colloidal of CoPc@Cell (0.05 g), tetraline (0.13 g, 1.00 mmol)
and KOH (0.25 mmol) in o-xylene (5 mL). The mixture was stirred
under reflux conditions in O2 atmosphere provided with a balloon.
The reaction temperature was raised to refluxing o-xylene. The
progress of the reaction was followed by TLC. Upon completion,
CoPc@Cell was separated by filtration and washed with acetone
(5 mL). Tetralone was isolated from the mixture using column chro-
matography with n-hexane:ethyl acetate (10:1) in 88% yield.
3. Results and discussion
Cellulose tosylate was prepared as previously reported method
[7] and converted to CoPc@Cell via a nucleophilic substitution reac-
tion of amine groups of 4,9,16,23-tetraamino phthalocyanine with
tosylate functionality of cellulose.
The synthesized catalyst was characterized by FT-IR, XRD, FAAS
and elemental analysis. Phthalocyanine content on the cellulose
was calculated to be 0.06 mmol g−1, according to the nitrogen
Fig. 1. FT-IR spectra of cellulose and CoPc@Cell.

496
A. Shaabani et al. / Journal of Molecular Catalysis A: Chemical 395 (2014) 494–499
Fig. 2. XRD pattern of CoPc@Cell.
Table 1
Optimization of the reaction conditions for aerobic oxidation of tetraline.a
Entry
Co (mol%)
Base (mol%)
Solvent
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
0.01
0.02
0.03
0.04
0.02
0.02
0.02
0.02
0.02
0.02
0.02
KOH (25)
KOH (25)
KOH (25)
KOH (25)
NaOH(25)
K2CO3(25)
Et3N (25)
KOH (25)
KOH (25)
KOH (25)
KOH (25)
o-Xylene
o-Xylene
o-Xylene
o-Xylene
o-Xylene
o-Xylene
o-Xylene
MeCN
10
10
10
10
10
24
24
18
24
24
24
79
87
88
88
56
0
0
81
0
9
10
11
H2O
EtOH
n-Hexane
0
0
a
Reaction conditions: tetraline (1.00 mmol), NHPI (0.06 mmol), solvent (5 mL), under O2 balloon, reflux.
Isolated yield.
b
content on the EDACs measured by CHN analysis. The Co loading
the best result (Table 1, entries 5–7). Moreover, the effect of various
solvents was investigated on the reaction yields and the reaction
gave high yield in o-xylene (Table 1, entries 8–11).
in CoPc@Cell was determined to be 0.36 wt% based on the FAAS
analysis. Immobilization of the Co(II) Pc on cellulose was confirmed
by FT-IR spectroscopy. For the catalyst a characteristic strong band
for C N bonds is seen at 1600 cm−1 next to cellulose band at
1646 cm−1. In addition, the FT-IR spectrum of CoPc@Cell has some
weak bands at 2846, 838 and 778 cm−1 which did not observed for
cellulose (Fig. 1).
Finally, the structure of CoPc@Cell was determined by powder
XRD. Characteristic diffraction peaks at 2Â = 21.90◦, 30.40◦, 31.50◦
and 44.38◦ can be clearly observed for the CoPc@Cell (Fig. 2).
At the onset of the research, we made a conscious effort to
develop a heterogeneous catalytic system for the aerobic oxida-
tion of various alkyl arenes to the corresponding aldehydes and
ketones. During the preliminary studies with the CoPc@Cell the aer-
obic oxidation of tetraline to tetralone was investigated as a model
substrate in the presence of various amounts of CoPc@Cell using a
base and N-hydroxyphthalimide under O2 balloon. At low amounts
of CoPc@Cell, the reaction gave low yields even in long duration
time. As the Co amount was increased to 0.02 mol%, the reaction
carried out more efficiently (Table 1, entries 1–4). The addition of
a base increased the reaction yield, with KOH in 25 mol% providing
The efficiency of the catalyst was studied for the selective oxi-
dation of a large variety of alkyl arenes to the corresponding
aldehydes and ketones using O2 as an oxidant (Table 2). The results
showed that CoPc@Cell was highly active and extremely selective
for the oxidation of all substrates, indicating a high versatility of the
CoPc@Cell. It is interesting to note, o-xylene as an alkyl arene did not
oxidize under our reaction conditions and we used it as the solvent.
To extend catalytic applications of CoPc@Cell, selective aero-
bic oxidation of various benzylic, allylic and aliphatic alcohols to
the corresponding aldehydes and ketones was studied. The reac-
tion conditions were optimized for 1-phenyl-ethanol as the model
substrate with 0.02 mol% of Co and 25 mol% of KOH in o-xylene at
room temperature without using N-hydroxyphthalimide under O2
balloon as the best reaction conditions (Table 3, entry 2).
The efficiency of the catalyst was studied for the selective oxi-
dation of a large variety of alcohols to the corresponding aldehydes
and ketones in the presence of KOH in o-xylene using the opti-
mum 0.02 mol% of Co (Table 4). The results showed that CoPc@Cell
was highly active and extremely selective for the oxidation of

A. Shaabani et al. / Journal of Molecular Catalysis A: Chemical 395 (2014) 494–499
497
Table 2
Aerobic oxidation of various alkyl arenes to the corresponding aldehydes and ketones.a
Entry
Alcohol
Product
Time (h)
10
Yield (%)b
89
O
1
O
2
3
4
12
14
9
85
85
91
O
Ph
(CH2)
6
O
O
O
O
5
6
13
11
88
91
O
O
O
O
7
8
12
11
87
87
O
Ph
Ph
Ph
Ph
O
9
10
82
a
Reaction conditions: alkyl arene (1.00 mmol), CoPc@Cell (0.05 g), KOH (0.25 mmol), NHPI (0.06 mmol), o-xylene (5 mL), under O2 balloon, reflux.
Isolated yield.
b
all substrates. A high versatility of the secondary benzylic alco-
through a syringe filter during the heterogeneous oxidation reac-
tion of tetraline, the solvent was evaporated, and the residue was
dissolved in HNO3. The analysis of these samples with FAAS showed
that the Co concentration in the reaction solution was less than
the detection limit. The same result was obtained when the com-
plete reaction mixture of the heterogeneous oxidation reaction of
1-phenyl-ethanol was filtered, the solvent was evaporated, and the
residue was dissolved in HNO3. Both findings indicate that virtu-
ally no Co leaches from the surface into the solution. Also, did not
observe any change in IR spectrum and XRD analysis for the catalyst
recovered from the reaction.
hols, especially alcohols with two phenyl groups as the substitutes,
was converted to the corresponding ketones in quantitative yields
(Table 4, entries 5–8). 2-Hydroxy-1,2-diphenylethanone was also
rapidly oxidized into the corresponding ketone in excellent yield
(Table 4, entry 9). A high conversion was achieved for allylic alcohol
to the desired aldehyde (Table 4, entry 10).
Despite the low reactivity of aliphatic alcohols, CoPc@Cell was
also applicable to the oxidation of various cyclic and acyclic
aliphatic alcohols to afford the corresponding aldehydes and
ketones in high yields but in relatively long durations at room
temperature (Table 4, entries 11–15).
The recyclability of CoPc@Cell was surveyed for aerobic oxida-
tion of tetraline and 1-phenyl-ethanol, separately. After carrying
out the oxidation reaction of tetraline and 1-phenyl-ethanol, the
Potential Co leaching into the reaction mixture was also ana-
lyzed with FAAS analysis. For this purpose, samples were taken
Table 3
Optimization of the reaction conditions for aerobic oxidation of 1-phenyl-ethanol.a
Entry
Co (mol%)
Base (mol%)
Solvent
Time (h)
Yield (%)b
1
2
3
0.01
0.02
0.03
0.04
0.02
0.02
0.02
0.02
0.02
0.02
0.02
0.02
KOH (25)
KOH (25)
KOH (25)
KOH (25)
KOH (25)
NaOH(25)
K2CO3(25)
Et3N (25)
KOH (25)
KOH (25)
KOH (25)
KOH (25)
o-Xylene
o-Xylene
o-Xylene
o-Xylene
o-Xylene
o-Xylene
o-Xylene
o-Xylene
MeCN
5.5
5.5
5.5
5.5
4
10
24
24
18
24
24
24
81
90
91
91
92
65
0
0
83
0
4
5c
6
7
8
9
10
11
12
H2O
EtOH
n-Hexane
0
0
a
Reaction conditions: 1-phenyl-ethanol (1.00 mmol), solvent (5 mL), under O2 balloon, room temperature.
Isolated yield.
Reflux conditions.
b
c

498
A. Shaabani et al. / Journal of Molecular Catalysis A: Chemical 395 (2014) 494–499
Table 4
Aerobic oxidation of various alcohols to the corresponding aldehydes and ketones.a
Entry
1
Alcohol
Product
Time (h)
8.5
Yield (%)b
83
Ph
O
Ph
OH
OH
O
2
3
8
9
83
78
Cl
Cl
OH
O
Cl
Cl
O
4
8
79
O2
Ph
N
5
6
5.5
3.5
91
87
O
Ph
OH
OH
Ph
O
Ph
Ph
Ph
OH
O
7
8
2.5
4
90
93
OH
O
OH
O
Ph
Ph
Ph
Ph
Ph
Ph
9
1.5
3.5
90
86
O
O
OH
O
10
OH
O
11
12
10.5
10
85
90
O
OH
Ph
Ph
OH
O
13
14
9.5
12
81
88
90
OH
O
OH
O
15
12
a
Reaction conditions: alcohol (1.00 mmol), CoPc@Cell (0.05 g), KOH (0.25 mmol), o-xylene (5 mL), under O2 balloon, room temperature.
Isolated yield.
b
reaction mixtures were filtered off, and CoPc@Cell and KOH sepa-
rated as a gray solid. CoPc@Cell was washed with acetone (2× 5 mL)
and H2O (3× 5 mL) to remove KOH and organic impurities, and
reused. Only minor decreases in the reaction yield was observed
after five repetitive cycles (Fig. 3).
We proposed a mechanism for this reaction in the absence of
NHPI, previously [22]. In this reaction, NHPI with a radical proton
abstraction from alkyl arene 1 produced intermediate 2. Benzylic
radical 2 reacted with a O2 molecule which activated by PcCo(II)
to give intermediate 3. An intermolecular radical proton trans-
fer of 3 was afforded intermediate 4 which under leaving of a
hydroxyl radical gave ketone 5. For the alcohols, the mechanism
proceeded through the removal of a hydrogen atom from the car-
bon attached to the hydroxyl group of alcohols by phthalocyanine
superoxocobalt(III) (8). The results of this radical proton abstraction
are intermediates 7 and 9. Finally, compound 9 was reacted with
7 to yield product 5 and H2O2 as a by-product (Scheme 2). Also,
application of base for improving the reaction yield is necessary
[23].
Fig. 3. Successive trials by using recoverable CoPc@Cell for aerobic oxidation of 1-
phenyl-ethanola and tetralineb. a Reaction conditions for alcohol: 1-phenyl-ethanol
(1.00 mmol), CoPc@Cell (0.05 g), KOH (0.25 mmol), o-xylene (5 mL), under O2 bal-
loon, room temperature. Reaction conditions for arene: tetraline (1.00 mmol),
CoPc@Cell (0.05 g), KOH (0.25 mmol), NHPI (0.06 mmol), o-xylene (5 mL), under O2
b
The results of our catalyst are compared with some recent
reports for oxidation reaction of alcohols using Co-phthalocyanines
balloon, reflux.

A. Shaabani et al. / Journal of Molecular Catalysis A: Chemical 395 (2014) 494–499
499
Scheme 2. Proposed mechanisms for the aerobic oxidation of alkyl arenes and alcohols.
Table 5
Comparasion of the results for oxidation of alcohols using CoPc@Cell and some other Pcs.
Entry
1
Catalyst
Substrate
Oxidant
H2O2
Temp. (◦C)
60
Time (h)
3
Selectivity (%)
88
Yield (%)
100
Co(II)-tetrachlorophthalocyanine supported
on SiO2 [24]
1-Phenyl-ethanol
2
Co(II)-tetrachlorophthalocyanine supported
on nano-SiO2 [25]
Benzyl alcohol
H2O2
70
5
38.9
92.7
3
5
Co(II) phthalocyaninenano-shell carbon [26]
This work
1-Phenyl-ethanol
1-Phenyl-ethanol
O2/benzaldehyde
Air
110
Room temp.
16
5.5
100
100
98
90
with respect to their yields, selectivity, the time and temperature
required for the reaction and used oxidant. As shown in Table 5,
CoPc@Cell has some advantages such as a cheap and green oxidant,
high selectivity, relatively short reaction time and progress of the
reaction without using co-oxidant such as H2O2, initiator such as
NHPI and activation (room temperature reaction conditions).
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Cobalt(II) 4,9,16,23-tetraamino phthalocyanine chemically sup-
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and allylic primary and secondary alcohols to the corresponding
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Acknowledgements
We gratefully acknowledge financial support from the Research
Council of Shahid Beheshti University and Catalyst Center of Excel-
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Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
2014.09.003.