Organic inorganic hybrid catalyst synthesized by doping of cobalt phthalocyanine (CoPc) on polyaniline support (CoPc/PANI) exhibited higher activity for the oxidation of various alcohols to the corresponding carbonyl compounds in high to excellent yield using molecular oxygen as oxidant and isobutyraldehyde as a sacrificial agent. Notably, the synthesized catalyst was found to be truly heterogeneous in nature and could be easily recovered, recycled for several recycling runs without loss of catalytic activity

1. Accepted Manuscript
Organic inorganic hybrid cobalt phthalocyanine/polyaniline as efficient catalyst
for aerobic oxidation of alcohols in liquid phase
Vineeta Panwar, Pawan Kumar, Siddharth S. Ray, Suman L. Jain
PII: S0040-4039(15)00792-3
DOI: http://dx.doi.org/10.1016/j.tetlet.2015.05.003
Reference: TETL 46275
To appear in: Tetrahedron Letters
Received Date: 11 February 2015
Revised Date: 30 April 2015
Accepted Date: 2 May 2015
Please cite this article as: Panwar, V., Kumar, P., Ray, S.S., Jain, S.L., Organic inorganic hybrid cobalt
phthalocyanine/polyaniline as efficient catalyst for aerobic oxidation of alcohols in liquid phase, Tetrahedron
Letters (2015), doi: http://dx.doi.org/10.1016/j.tetlet.2015.05.003
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2. Graphical Abstract
Organic inorganic hybrid cobalt phthalocyanine/polyaniline
as efficient catalyst for aerobic oxidation of alcohols
in liquid phase
Vineeta Panwar,a
Pawan Kumara
Siddharth S. Raya
and Suman L. Jaina
Leave this area blank for abstract info.

3. 1
Tetrahedron Letters
jo urn al homepage: www.els evier.com
Organic inorganic hybrid cobalt phthalocyanine/polyaniline as
efficient catalyst for aerobic oxidation of alcohols in liquid phase
Vineeta Panwar,a
Pawan Kumara
Siddharth S. Raya
and Suman L. Jaina
a
Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun-248005 (India)
Catalytic liquid phase oxidation of compounds
particularly oxidation of alcohols is an important synthetic
transformations in organic chemistry.1-5
This transformation
is traditionally carried out using stoichiometric quantities of
inorganic oxidants, which are relatively expensive, highly
toxic and environmentally undesirable.6-13
Therefore,
development of non-precious polymer supported catalysts
with high reactivity and efficient recycling ability for this
transformation is an area of tremendous importance in recent
decades.14-18
The use of polymer-supported catalysts offers
several advantages such as they increases the stability19-21
of
the catalyst, combine the advantages of both homogeneous
catalysts like higher reactivity and selectivity as well as
heterogeneous catalyst such as facile recovery and recycling
ability.22-24
Numerous materials such as mesoporous silica,
activated carbon, organic and bio-polymers have been
employed as support for aerobic oxidation of alcohols.25-29
Polyaniline (PANI) is one of the polymers which have
been used as a matrix for grafting of homogeneous metal
complexes. It is cheap, easy to synthesize and insoluble in a
large majority of commonly used solvents, which is the main
advantage of supported catalysts.30
Moreover, PANI is
thermally stable to 300°C and chemical resistant to
oxidation.31
Polyaniline involves both electron and proton
exchange and exist in three most stable forms as shown in
Scheme 1.
Scheme 1 Redox forms of polyaniline
Pielichowski and Iqbal have reported first time the use of
polyaniline supported catalytic systems based on cobalt (II)
salts and its complexes for the oxidation of alkenes.32-35
Inspired with their reports, herein we report an efficient,
easily recyclable organic inorganic hybrid material fabricated
by doping of tetrasulfonated cobalt(II) phthalocyanine
(CoPcS) on to polyaniline (CoPc/PANI) as catalyst for the
oxidation of alcohols using molecular oxygen as oxidant and
isobutyraldehyde as sacrificial agent under milder reaction
conditions.
ARTICLE INFO ABSTRACT
Article history:
Received
Received in revised form
Accepted
Available online
Organic inorganic hybrid catalyst synthesized by doping of cobalt phthalocyanine (CoPc) on
polyaniline support (CoPc/PANI) exhibited higher activity for the oxidation of various alcohols
to the corresponding carbonyl compounds in high to excellent yield using molecular oxygen as
oxidant and isobutyraldehyde as a sacrificial agent. Notably, the synthesized catalyst was found
to be truly heterogeneous in nature and could be easily recovered, recycled for several recycling
runs without loss of catalytic activity.
2009 Elsevier Ltd. All rights reserved.
Keywords:
Hybrid material
Heterogeneous catalyst
Oxidation
Alcohol
Polyaniline

4. Tetrahedron2
Scheme 2: CoPc/PANI-catalyzed oxidation of alcohols
Synthesis and characterization of the catalyst
Synthesis and characterization of CoPc/PANI catalyst
The desired CoPc/PANI catalyst was synthesized from
emeraldine salt form of polyaniline and using tetrasulfonated
cobalt phthalocyanine as dopant ion as shown in Scheme 3.
Scheme 3: Synthesis of cobalt phthalocyanine doped polyaniline (CoPc/PANI)
The surface morphology of polyaniline and the CoPc/PANI
catalyst was determined with the help of SEM as shown in
Fig 1. In the SEM image of polyaniline (PANI) many
nanofibrillar structures can be seen which confirms the
fibrous polymeric structure of polyaniline Fig 1a. After the
doping with CoPcS, the fibre like morphology changed to
granular structures which are most likely due to the ionic
interaction between CoPc and polyaniline Fig 1b. Energy
dispersive X-ray spectroscopy analysis (EDX) pattern of
polyaniline(PANI) shows absence of any metal ions but in
CoPc/PANI, the presence of cobalt confirmed the successful
doping of support matrix with metal complex units (Fig 1c,d).
The low intensity of peak clearly indicated the lower loading
of cobalt in CoPc/PANI.
Fig. 1: SEM images of a) PANI and b) CoPc/PANI and EDX pattern of
c) PANI and d) CoPc/PANI
The successful doping of cobalt phthalocyanine on
polyaniline matrix was further confirmed by FTIR studies. Fig 2
shows the FTIR absorption spectrum for CoPc, PANI, CoPc/PANI
samples.In case of FTIR spectrum of PANI, the characteristic
bands due to quinoid ring at 1562 cm-1
and benzoid ring at 1471
cm-1
clearly indicated the existence of these two states in the PANI
polymer chains. In the presence of phthalocyanine the intensity of
quinoid ring and benzoid ring shifts to 1594 cm-1
and 1498 cm-
1
respectively. Further the C-N stretching vibrations are appeared at
1301 cm-1
in pure PANI which was shifted to 1307 cm-1
in
CoPc/PANI. The absorption at 1110 cm-1
in PANI is due to
N=Q=N (where N is for quinoid) which was shifted to1166 cm -1
in CoPc/PANI and N-H stretching shifted from 802 to 827 cm-1
.
The data represented for these polymers is well matched with
the reported literature IR data for polyaniline and
phthalocyanine.36-41
Fig. 2: FTIR Spectra of a) CoPc and b) PANI and c) PANI-CoPc
Fig 3 shows UV-Vis spectra of CoPc, PANI and CoPc/PANI.
The UV-Vis spectrum of CoPc shows its characteristics
intense peaks at 670 nm (Q band) and 320 nm (Soret band)
due to specific macrocyclic π-π* ring transitions (Fig 3a).42
In
pure PANI the band observed at 330-370 nm corresponds to
n-π* transition of aniline and broad band at around 630 nm
represent the transition of the quinoid rings in long PANI
chains (Fig 3b).43-44
Interestingly, in CoPc/PANI, the main
absorption band of PANI at 320 nm and 670 nm were
affected due to the presence of CoPc in the polymer matrix

5. 3
(Fig 3c). The observed enhancement in the absorption profile
of CoPc/PANI was most likely due to the presence of CoPc
complex units.
Fig. 3: UV-Vis Absorption Spectra of a) CoPc and b) PANI and c)
CoPc/PANI
Fig 4 depicted the XRD pattern of PANI and
CoPc/PANI.45,46
The XRD diffractogram of PANI shows a
broad peak at 2θ value ≈ 25o
due to the 200 plane of carbon of
aromatic sheets (Fig 4a). This pattern was specific for
aromatic graphitic type sheet structure. Further absence of
any sharp peak confirms that material was amorphous in
nature. In CoPc/PANI the incorporation of CoPc in polymeric
matrix altered the graphitic structure and therefore the peak at
2θ value ≈ 25o
was found to be diminished (Fig 4b).
Fig. 4: XRD Diffractogram of a) PANI and b) CoPc/PANI
Thermal stability of the synthesized materials was determined
by thermo gravimetric analysis (Fig 5). In case of CoPc (Fig.
5a), the first weight loss at around 100 ᵒC was due to the
evaporation of water. The second very minor weight loss
around 220 ᵒC was assumed due to the breaking of –SO2Cl
moieties presented in phthalocyanine ring. The third major
weight loss at 400 ᵒC was observed due to the degradation of
phthalocyanine ring structure after that a linear weight loss
was observed for continuous degradation of material (Fig 5a).
For PANI the small weight loss at 100 ᵒC was due to the
evaporation of water and later on two major weight losses at
around 175 ᵒC and 520 ᵒC were specific to the PANI polymer
chains as suggested in literature (Fig 5b).47-50
However, in
CoPc/PANI, the additional weight loss at 400 ᵒC was
observed due to the degradation of doped CoPc units in
polymer chains (Fig 5c).
Fig. 5: TGA thermogram of a) CoPc and b) PANI and c) CoPc/PANI
Catalytic activity
After the successful synthesis of CoPc/PANI catalyst, we
aimed to explore the catalytic activity of the catalyst for
oxidation of alcohols using molecular oxygen as oxidant and
isobutyraldehyde as a sacrificial agent. Benzhydrol was
chosen as a model substrate to perform the optimization
experiments by varying the reaction parameters. The results
of these experiments are summarized in Table 1. Initially the
reaction was carried out in different solvents such as
acetonitrile, DMF, toluene and p-xylene. Aromatic solvents
such as toluene and p-xylene were found to be almost
ineffective and no reaction did occur in these solvents (Table
1, entries 1 and 2). Further, the reaction was found to be slow
in water under reflux conditions and gave moderate yield of
the product (Table 1, entry 3). Aprotic polar solvents such as
acetonitrile and DMF were found to be most effective and
afforded higher yield of the product (Table 1, entry 4-5).
Further, the effect of reaction temperature was investigated.
The reaction was found to be very slow at room temperature;
however at 65 °C using acetonitrile as solvent was found to
be optimum which gave highest value of turnover frequency
(TOF) and 76 % isolated yield of the benzophenone in 3.5 h
(Table 1, entry 4). The presence of isobutyraldehyde was
found to be vital and in its absence very poor yield of
benzophenone as well as TOF was obtained (Table 1, entry
6). Further, we checked the effect of catalyst loading by
varying the catalyst amount from 0.5 to 5 mol % under
otherwise identical experimental conditions. The reaction was
found to be increased with the catalyst amount from 0.5 to 2
mol % and gave desired product in lesser reaction time.
However, the turnover frequency was found to be decreased
with increasing the catalyst amount as shown in Table 1
(entry 7-9). Further increase in catalyst amount from 2 to 5
mol % gave lowest TOF with the marginal increase in the
product yield (Table 1, entry 7-9). As the difference in the
product yields between 1 and 2 mol % was marginal, we have
considered the 1 mol % catalyst loading as the optimum
amount for the reaction. Furthermore, we also performed the
oxidation of benzhydrol in the absence of oxygen (inert
condition) under otherwise identical reaction conditions

6. Tetrahedron4
(Table 1, entry 10). The reaction did not proceed and the
original substrate could be recovered at the end.
Table 1: Results of the optimization experimentsa
Entry Solvent Temp.
(o
C)
Cat.
(mol%)
Time
(h)
Yield
(%)b
TOF
(h-1
)
1 Toulene reflux 1.0 6.0 20 3.3
2 p-xylene 60 1.0 5.0 10 2.0
3 H2O reflux 1.0 6.5 40 6.1
4 CH3CN rt
50
65
1.0 3.5
3.5
3.5
15
24
76
4.2
6.8
21.7
5 DMF 65 1.0 3.5 72 20.6
6 CH3CN 65 1.0 3.5 15c
-
7 CH3CN 65 0.5 5.0 70 28.0
8 CH3CN 65 2.0 3.0 77 12.8
9 CH3CN 65 5.0 2.5 77 6.16
10 CH3CN 65 1.0 6.0 - -
a
Reaction conditions: benzhydrol(1 mmol), isobutarldehyde (1.5
mmol), catalyst (1 mol%, 0.01 mmol) in solvent (5 mL) under
oxygen atmosphere; b
Isolated yield; c
In the absence of
isobutyraldehyde; d
Turnover frequency=number of moles of the product/ number of
moles of cobalt in catalyst x reaction time
Next, the scope of the developed catalytic system was studied
by performing the oxidation of a variety of primary and
secondary alcohols under the described reaction conditions.
The results are presented in Table 2. A variety of secondary
alcohols including benzoins could be oxidized to the
corresponding ketones in good to excellent yields under the
described reaction conditions (Table 2, entries 1–9). The
presence of catalyst was crucial for the oxidation of alcohols
and in its absence the reaction did not take place even in a
prolonged reaction time of 12 h (Table 2, entry 1). We also
investigated the catalytic activity of homogeneous CoPcS
catalyst for oxidation of benzhydrol under otherwise similar
reaction conditions. The reaction was found to be slow and
gave comparatively poor product yield (Table 2, entry 1).
These findings showed the merits of supported catalyst
exhibiting higher catalytic activity with the additional benefits
of facile recovery and recycling of the catalyst. The
developed catalytic system demonstrated higher reactivity
and selectivity for the oxidation of benzyl alcohols to
corresponding benzaldehydes without any evidence for the
formation of over-oxidation products, i.e. carboxylic acids
(Table 2, entry 10-15). Among the various benzylic alcohols,
those substituted with electron-donating groups were found to
be more reactive as compared to those having electron
withdrawing substituents (Table 2, entry 14-15). Furfuryl
alcohol was selectively converted to furfuraldehyde in good
yield under the developed reaction conditions (Table 2, entry
16). Under the described reaction conditions, primary
aliphatic alcohols (1-octanol, 1-decanol) gave an intricate
mixture of the unidentified products, which were difficult to
analyze by GC (Table 2, entry 17-18). Furthermore, we
performed the oxidation of benzyl alcohol under drastic
conditions i.e. 10 mol % catalyst, 80 o
C temperature and 10 h
as the reaction time. Under these conditions, benzyl alcohol
was quantitatively converted to the corresponding benzoic
acid. These results suggested that the reaction parameters
such as catalyst loading, temperature and reaction time played
a crucial role in the selectivity of the reaction.
Table 2: CoPc/PANI-catalyzed oxidation of alcohols using molecular
oxygen as an oxidanta
Entr
y
Substrate Product T/
h
Yield
(%)b
TOF
(h-1
)
1 3.5
12
3.5
76
-c
72d
21.7
-
20.6
2 OH O
3.5 84 24
3 OH O
4 83 20.7
4 OH O
4 87 21.7
5
OH O
6.5 77 11.8
6
OH
OH
O
O
3.5
88 25.1
7
OH
OH
CH3
H3C
O
O
CH3
H3C
3.5 87 24.8
8
3.5 86 24.5
9 O
OH
OMe
MeO
O
O
OMe
MeO
3.5 85 24.2
10 CH2OH CHO
4
82 20.5
11
CH2OH
CH3
CHO
CH3
3 80 26.6
12
CH2OH
CH3
H3C CH3
CHO
CH3
H3C CH3
4 72 18.0
13 CH2OH
OCH3
CHO
OCH3
4 78 19.5
14 CH2OH
Cl
CHO
Cl
4 75 18.75

7. 5
15 CH2OH
NO2
CHO
NO2
4.5 70 15.5
16
O
OH
O CHO
4 85 21.25
17e OH
- 6 -
18e OH
- 6 -
a
Reaction conditions: substrate (1 mmol), isobutarldehyde (1.5 mmol),
catalyst (1 mol % 0.01 mmol) in acetonitrile (5 mL) at 65 o
C under oxygen
atmosphere, b
Isolated yield; c
in the absence of catalyst; d
using homogeneous
CoPcS as catalyst; e
mixture of unidentified products was obtained.
Furthermore, we have tested the recycling of the developed
heterogeneous catalyst by choosing the benzhydrol as the
model substrate. After the completion of the reaction, the
catalyst could be easily recovered by centrifugation followed
by washing with methanol and reused for subsequent runs.
The recovered catalyst showed an efficient recycling ability
without giving any change in the reaction time and the yield
of the product (Fig. 6). After six recycling the cobalt content
of catalyst was determined with ICP-AES was found to be
1.46 wt% that was comparable to 1.5 wt% for freshly
synthesized catalyst.
Fig. 6: Results of catalytic recycling experiments
Although the mechanism of this reaction is not clear at this
stage, however in analogy to the mechanism suggested by
Mukaiyama et al,51
the initial step might involve the free
radical autoxidation of the aldehydes to generate an acyl
radical. The acyl radical RC(O)· then reacted with O2 to
give an acylperoxyl radical RC(O)OO· (dioxygen
activation step), which subsequently abstract hydrogen
from alcohol to convert it into corresponding carbonyl
compound.
In conclusion, we have demonstrated an efficient organic-
inorganic hybrid fabricated by doping of easily accessible
cobalt phthalocyanine on to polyaniline support as catalyst
for the oxidation of alcohols using molecular oxygen as
oxidant. The developed catalyst exhibited superior activity
as comparable to the homogeneous cobalt phthalocyanine
catalyst with the added benefits of facile recovery and
recycling of the catalyst. Notably, benzylic alcohols were
oxidized to their corresponding carbonyl compounds
selectively in high to excellent yields without giving any
over-oxidation product. The catalyst was found to be highly
stable and could be recycled several times without any
significant loss in catalytic activity
Acknowledgments
We are thankful to the Director, IIP for his permission to
publish these results. PK and VP are thankful to CSIR, New
Delhi for providing research fellowships.
References and notes
Synthesis of polyaniline (PANI)52
The polymerization of aniline has been carried out by free radical
chemical oxidative polymerization method by using ammonium
persulphate (APS) as an oxidant in non-oxidizing protonic acid
like HCL. In a chemical reaction 1ml of aniline is dissolved in 50
ml HPLC water and 2.8 g of ammonium persulphate in 50 mL
HPLC water. Then both the solutions were mixed with constant
stirring at room temp. Then 0.2 M HCL in 50 mL HPLC water is
added drop wise to the above reacting mixture for 3-4 h and
allowed to stir overnight. Then the dark green precipitate so
obtained was filtered and washed repeatedly with distilled water
till the pH of the filtrate became neutral. This precipitate was then
dried in an oven overnight.
Synthesis of tetrasulfonated cobalt phthalocyanine (CoPcS)53
Tetrasulfonated cobalt phthalocyanine (CoPcS) was prepared by
following the literature procedure. In briefly cobalt phthalocyanine
was added slowly to 10 times by weight chlorosulfonic acid with
stirring. Then temperature of reaction mixture was increased in
steps up to 130- 135 °C and maintained for 4 h. The obtained
reaction mixture was cooled to 60 °C and little more than two-fold
excess by weight of thionyl chloride were slowly added. This
mixture was heated to 79 °C and maintained at this temperature for
1 h.Reaction mixture, after cooling at room temperature, was
slowly added to crushed ice by keeping the temperature preferably
below 5 °C. The precipitated cobalt phthalocyanine tetrasulfonyl
chloride was filtered and washed thoroughly with cold water and
dried in vacuum and stored in air tight vial.
Synthesis of CoPc/PANI catalyst54
Tetrasulfonated cobalt phthalocyanine (CoPcS) (0.125 g) was
dissolved in a 10 mL of DMF, then polyaniline (0.5 g) is added to
it and reaction was stirred at room temperature for five min. Then
2 mL of triethyl amine was added to the above reacting mixture.
Now this solution is allowed to stir for 24 h at 80 ºC. After
thorough mixing of the solution, the solution was filtered, washed
with distilled water and ethanol. The obtained precipitate was
dried at 120 ºC overnight then grinded for further use. Finally the
black green colored polyaniline doped cobalt phthalocyanine
(CoPc/PANI) was obtained. The percentage of cobalt in the
synthesized catalyst was found to be 1.5 % as determined by ICP-
AES analysis.
General procedure for the oxidation
A mixture of benzhydrol (1 mmol, 0.184 g), isobutyraldehyde (1.5
mmol, 0.108 g) and catalyst (1 mol % 0.01 mmol) in acetonitrile
(15 mL) was heated at 60 °C under stirring by using an oxygen
balloon. The progress of the reaction was monitored by thin layer
chromatography on silica gel. On completion, the reaction mixture

8. Tetrahedron6
was cooled to room temperature and centrifuged to separate the
catalyst. The product was identified with GCMS. The solvent was
removed under reduced pressure and the product was obtained by
passing it through a short column of silica gel using EtOAc–
hexane (1: 9) as eluent. The identity of the product was confirmed
by comparing the physical and spectral data (1
H & 13
C NMR) with
the reported compound. The recovered catalyst was dried at 50 °C
for 2 h and can be reused for recycling experiments.
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