Aerobic oxidation and oxidative bromination in aqueous medium using polymer anchored oxovanadium complex

Article abstract of DOI:10.1016/j.jorganchem.2014.03.009

Polymer anchored oxovanadium catalyst was synthesized and characterized. Its catalytic activity was evaluated for the oxidation of various primary and secondary alcohols with molecular oxygen under mild reaction conditions. This catalyst was also effective for the oxidative bromination reaction of organic substrates with 90-100% selectivity of mono substituted products with H ₂O₂/KBr at room temperature. The above reactions require low temperature, short time period and most importantly all the above reactions occur in aqueous medium. The developed catalyst can be facilely recovered and reused six times without significant decrease in activity and selectivity. 2014 Elsevier B.V. All rights reserved.

Full text of DOI:10.1016/j.jorganchem.2014.03.009

Journal of Organometallic Chemistry 761 (2014) 169e178
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Aerobic oxidation and oxidative bromination in aqueous medium
using polymer anchored oxovanadium complex
,
a
a
a
Sk. Manirul Islam a , Rostam Ali Molla , Anupam Singha Roy , Kajari Ghosh ,
*
Noor Salam a, Md. Asif Iqubal b, K. Tuhina c
,
**
a Department of Chemistry, University of Kalyani, Kalyani, Nadia 741235, W.B., India
b Department of Chemistry, IIT Roorkee, Roorkee 247667, Uttarakhand, India
c Department of Chemistry, B.S. College, Canning, S-24 PGS, 743329, W.B., India
a r t i c l e i n f o
a b s t r a c t
Article history:
Polymer anchored oxovanadium catalyst was synthesized and characterized. Its catalytic activity was
evaluated for the oxidation of various primary and secondary alcohols with molecular oxygen under mild
reaction conditions. This catalyst was also effective for the oxidative bromination reaction of organic
substrates with 90e100% selectivity of mono substituted products with H2O2/KBr at room temperature.
The above reactions require low temperature, short time period and most importantly all the above
reactions occur in aqueous medium. The developed catalyst can be facilely recovered and reused six
times without significant decrease in activity and selectivity.
Received 10 December 2013
Received in revised form
11 March 2014
Accepted 11 March 2014
Keywords:
Polymer anchored
Oxovanadium(IV) complex
Aerobic oxidation
Oxidative bromination
Aqueous medium
Molecular oxygen
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
use of bromide ion as a bromide source instead of bromine for
oxidative bromination [17e21].
The selective aerobic oxidation and oxidative bromination of
organic compounds are useful and fundamental transformations in
organic synthesis [1,2]. In recent years, there has been an increasing
interest in developing environmental friendly greener processes
which are also economically viable in industrial chemistry [3]. With
environmental and economic concerns, heterogeneous catalysis
reaction using molecular oxygen as an oxidant is developed as
desired green process for selective oxidation of alcohol and
oxidative bromination of various organic substrates [4e10].
Up to now, numerous expensive metal (e.g. palladium and
ruthenium) catalyst and toxic organic solvents have been tradi-
tionally used to accomplish most of the aerobic oxidation of alco-
hols [11e13]. On other hand, conventional bromination reaction
requires hazardous and toxic elemental bromine [14e16]. In order
to overcome these problems, several safe systems for the aerobic
oxidation and oxidative bromination have been developed. One is
the use of inexpensive metal catalyst for the aerobic oxidation and
We have chosen polymer anchored vanadium complex as the
heterogeneous catalyst and water as the green solvent for the
aerobic oxidation and oxidative bromination. Vanadium exists on
the surface of the earth more abundantly than copper, palladium or
ruthenium [22]. It plays an important role in aerobic oxidation and
oxidative bromination processes. In addition, heterogeneous cata-
lysts have some advantages compared to homogeneous catalyst.
Metals supported on materials such as alumina [23], amorphous
silicates [24], polymers [25], zeolites [26], and MCM-41 [27] are
commonly in use in heterogeneous catalysis. Nowadays function-
alized polystyrene anchored catalysts are used to carry out various
catalytic organic transformations [28e31]. Among them chlor-
omethylated polystyrene are widely used as polymer support.
These polystyrene anchored metal complexes are inert and reus-
able catalysts for various organic reactions.
In the chemical processes, traditional organic solvents are used
in large quantities, which have led to various environmental and
health concerns. As part of green chemistry efforts, a variety of
cleaner solvents have been used as replacements [32e35]. As an
alternative solvent, water has been paid extraordinary attention.
Apart from being a chemically interesting solvent, water provides a
cheap alternative for organic solvents, making it environmentally
* Corresponding author. Tel.: þ 91 33 2582 8750; fax: þ91 33 2582 8282.
** Corresponding author. Tel.: þ91 33 255263.
E-mail addresses: manir65@rediffmail.com (Sk.M. Islam), tuhina31@yahoo.com
(K. Tuhina).
http://dx.doi.org/10.1016/j.jorganchem.2014.03.009
0022-328X/Ó 2014 Elsevier B.V. All rights reserved.

170
Sk.M. Islam et al. / Journal of Organometallic Chemistry 761 (2014) 169e178
Table 1A
and economically interesting as well. So, based on the above two
concepts, we tried to synthesize a polymer anchored oxovanadium
complex which catalyse the aerobic oxidation of primary and sec-
ondary alcohols and oxidative bromination of various aromatic
amines, aldehydes in aqueous medium.
Chemical composition of polymer anchored ligand and oxovanadium complex.
Compound
Colour
C%
H%
Cl %
N%
Metal%
PS-teta
PS-tetaeVO
Yellowish
Greenish
77.76
70.60
6.52
5.96
3.37
3.30
7.20
6.56
e
4.72
Herein we report the synthesis and characterization of a poly-
mer anchored oxovanadium complex and illustrate its application
for the aerobic oxidation and oxidative bromination reactions in
aqueous medium using hydrogen peroxide as an oxidant.
filtered, washed thoroughly with ethanol, dioxane and methanol to
ensure the removal of any unreacted metal ions and dried in vac-
uum for 6 h at 90 ꢀC (Yield ¼ 80%).
Experimental
General procedure for aerobic oxidation reaction catalysed by PS-
tetaeVO
Materials and instruments
All the reagents used were chemically pure and were of
analytical reagent grade. The solvents were dried and distilled
before use following the standard procedures [36]. Chloromethy-
lated polystyrene was supplied by SigmaeAldrich chemicals
Company, USA. Other reagents were obtained from Merck or Fluka.
A PerkineElmer 2400C elemental analyzer was used to collect
micro analytical data (C, H and N). Vanadium content of the sample
was measured by Varian AA240 atomic absorption spectropho-
tometer (AAS). The FT-IR spectra of the samples were recorded on a
PerkineElmer FT-IR 783 spectrophotometer using KBr pellets.
Diffuse reflectance spectra (DRS) were registered on a Shimadzu
UV/3101 PC spectrophotometer. Mettler Toledo TGA/SDTA 851 in-
strument was used for the thermogravimetric analysis (TGA).
Morphology of functionalized polystyrene and complex was ana-
lysed using a scanning electron microscope (SEM) (ZEISS EVO40,
England) equipped with EDX facility.
The aerobic oxidation reactions were carried out in a 50 mL
stainless steel autoclave at different temperatures under vigorous
stirring for a certain period of time. We examined the catalytic
activity of vanadium complex using alcohol as the substrate and
molecular oxygen as the primary oxidant. The oxidation of alcohol
(5 mmol) was conducted under oxygen pressure (5.0 bar) at 60 ꢀC
for 5 h in the presence of vanadium complex (5 mg) in water (5 mL).
After the reaction, the organic products were separated from the
reaction mixture by extraction with dichloromethane (5 mL ꢁ 2).
The combined organic portions were dried and concentrated.
Product analysis was performed by Varian 3400 gas chromatograph
equipped with a 30 m CP-SIL8CB capillary column.
General procedure for oxidative bromination reaction of organic
substrates catalysed by PS-tetaeVO
In a typical reaction, aqueous 30% H2O2 (20 mmol) was added to
the mixture of substrates (10 mmol) and KBr (20 mmol) taken in
10 mL of water. Catalyst (50 mg) and HClO4 (5 mmol) were added to
it and the reaction mixture was stirred at room temperature. An
additional 15 mmol HClO4 was added to the reaction mixture in
three equal portions at 30 min intervals under continuous stirring.
After specified time of the reaction, the catalyst was filtered and the
solid was washed with ether. The combined filtrates were washed
with saturated sodium bicarbonate solution and then shaken with
ether in a separating funnel. The organic extract was dried over
anhydrous sodium sulphate. The products were analysed by Varian
3400 gas chromatograph equipped with a 30 m CP-SIL8CB capillary
column and a Flame Ionization Detector.
Synthesis of polymer anchored ligand PS-teta
Ligand was readily prepared in two steps. Firstly, chlor-
omethylated polystyrene (PSeCH2Cl) was converted into PSeCHO
according to literature [37]. Triethylenetetramine (teta) was reacted
with PSeCHO (in1:2 M ratio) in methanol solvent at refluxing
condition for 24 h to prepare the yellow Schiff base compound. The
mixture was cooled to room temperature and then filtered. The
residue was washed with ethanol and dried under vacuum
(Yield ¼ 60%).
Loading of metal ions on to the polymer anchored ligand PS-teta
The loading of metal ions on the polymeric support was carried
out as follows: the polymer anchored ligand (1.00 g) was stirred for
24 h with 0.100 g of VO(acac)2 in 20 mL of methanol under refluxing
condition. At the end of this reaction the metal loaded polymer was
Results and discussion
Characterization of polymer anchored oxovanadium complex
The reaction of aldehyde functionalised polystyrene and trie-
thylenetetramine (teta) in methanol leads to the formation of
polymer anchored Schiff base ligand. During this process CHO
group of the polymer reacts with amine group of the triethylene-
tetramine (teta) moiety as shown in Scheme 1. The polymer
anchored Schiff base ligand, on reaction with VO(acac)2, gave an
oxovanadium(IV) complex which we designate as PS-tetaeVO. The
physicochemical data of the polymer anchored ligand and polymer
Table 1B
Chemical composition of polymer supported oxovanadium complex.
Compound
Ligand loading
(mmol equiv. gꢂ1
of resin)
Metal ion loading
(mmol equiv. gꢂ1
of resin)
Ligand:metal
PS-tetaeVO
1.17
0.93.
1.26:1
Scheme 1. Preparation of polymer anchored VO(IV) complex.

Sk.M. Islam et al. / Journal of Organometallic Chemistry 761 (2014) 169e178
171
supported oxovanadium complex are presented in Table 1A. The
loading of ligand and vanadium metal per gm of polymer is
1.17 mmol and 0.93 mmol, respectively. These data show that metal
to ligand loading in polymer complex is close to 1:1 (Table 1B).
Scheme 1 presents the proposed structure of the anchored
complex. Due to insolubilities of the polymer anchored oxovana-
dium(IV) complex in all common organic solvents, its structure has
been established on the basis of elemental analyses, spectroscopic
FT-IR and electronic studies, scanning electron micrographs (SEM)
equipped with EDX facility and thermogravimetric analysis (TGA).
Fig. 1. FT-IR Spectra of polymer anchored ligand PS-teta (A) and PS-tetaeVO complex (B).

172
Sk.M. Islam et al. / Journal of Organometallic Chemistry 761 (2014) 169e178
Field emission-scanning electron micrographs of single bead of
polymer anchored ligand (PS-teta) and its complex PS-tetaeVO
were recorded and it was observed that the morphological changes
occurred on the polystyrene beads at various stages of the syn-
thesis. The SEM images of polymer anchored ligand (A) and the
immobilized vanadium complex (B) on functionalized polymer are
shown in Fig. 3. The polymer anchored ligand has a slight rough-
ening of the top layer of polymer beads. This roughening is rela-
tively more in complex. Also the presence of vanadium metal can be
further proved by energy dispersive spectroscopy analysis of X-rays
(EDAX) (Fig. 4) which suggests the formation of metal complex
with the polymer anchored ligand.
Thermal stability of the complex was investigated using TGA at a
heating rate of 10 ꢀC/min in air over a temperature range of 30e
600 ꢀC (Fig. 5). Polymer anchored ligand decomposed in the tem-
perature range 370e390 ꢀC. After complexation of vanadium on
polymer anchored ligand, thermal stability of the immobilized
complex improved. Polymer anchored oxovanadium complex
decomposed at 420e440 ꢀC. So from the thermal stability, it con-
cludes that polymer anchored metal complex degraded at consid-
erably higher temperature.
Fig. 2. DRS-UVevisible absorption spectra of the polymer supported oxovanadium
catalyst.
Catalytic activity
Since polymer anchored metal systems exhibit catalytic activity
in a wide range of the industrially important processes and have
been extensively studied, we have decided to investigate the cat-
alytic activity of polymer anchored oxovanadium complex in the
aerobic oxidation of primary and secondary alcohols. Also we have
studied the oxidative bromination reaction with H2O2 and molec-
ular O2 as oxygen sources.
The attachment of metal onto the support was confirmed by
comparison of the FT-IR spectra of the polymer before and after
loading of metal (Fig. 1). The IR spectrum of pure chloromethylated
polystyrene has an absorption band at 1261 cmꢂ1 due to the CeCl
group, which was weak in the ligand and in the catalyst. IR spectra
show a stretching vibration for eCH2 at 2920 cmꢂ1 in the polymer
bound ligand. The stretching vibration of C]N bond appeared at
1642 cmꢂ1 for the polymer-bound Schiff base ligand which is
lowered to 1611 cmꢂ1 in the metal complex, indicating the coor-
dination of azomethine nitrogen to the metal. A strong broad band
around 3429 cmꢂ1 in polymeric ligand is observed due to NH
(secondary amine) vibration which is lower to 3419 cmꢂ1 in metal
complex. Polymer anchored oxovanadium complex showed two
new bands at 546 and 463 cmꢂ1 assigned to v(VeO) and v(VeN),
respectively [25]. Again a band appeared around 968 cmꢂ1 due to
stretching vibration of V]O [38].
The electronic spectrum of the polymer anchored metal com-
plex has been recorded in diffuse reflectance spectrum mode as
MgCO3/BaSO4 disks (Fig. 2). In the UV spectrum of the catalyst, one
absorption band is observed around 350e450 which may be
assigned to the charge transfer transition. The band at around
580 nm is caused by ded electronic transition of vanadium present
in the complex [39].
Aerobic oxidation of primary and secondary alcohols catalysed by
PS-tetaeVO
To test the catalytic activity of the present catalyst, first aerobic
oxidation of primary alcohols was tested in at 60 ꢀC for 5 h. For
optimization of reaction conditions, we choose the aerobic oxida-
tion of benzyl alcohol as a probe reaction. In this case benzyl alcohol
is selectively converted to benzaldehyde (Scheme 2).
Effects of various solvents on the conversion of benzyl alcohol
and selectivity of benzaldehyde using polymer anchored VO(IV)
catalyst are summarized in Table 2. We investigated the ability of
various solvents like ACN, ethanol, toluene, DMSO and water
(Table 2, entries 1e5). Selectivity of benzaldehyde is low in ethanol
and DMSO as compared to the other solvents like ACN and toluene.
It was observed that vanadium complex exhibited highest catalytic
activity and selectivity towards the aerobic oxidation of benzyl
Fig. 3. FE-SEM images of polymer anchored ligand PS-teta (A) and PS-tetaeVO complex.

Sk.M. Islam et al. / Journal of Organometallic Chemistry 761 (2014) 169e178
173
Fig. 4. EDAX data of polymer supported ligand PS-teta (A) and PS-tetaeVO complex (B).
alcohol in water (Table 2, Entry 7). Polymer anchored catalyst
(3 mg) afforded a conversion of 64% within 5 h (Table 2, entry 5). No
by-products such as benzoic acid were detected under this reaction
condition. When the amount of the catalyst increased up to 4 mg,
the conversion had an apparent increase and a 76% conversion was
achieved but in this condition a little amount of benzoic acid was
detected (Table 2, entry 6). A further increase in catalyst amount up
to 5 mg led to an increase in the conversion of 92% (Table 2, entry 7).
However, when the catalyst amount continuously increased up to
6 mg, the conversion remains almost constant but the selectivity of
benzaldehyde reduces (Table 2, entry 8). These findings indicate
that the oxidation of benzyl alcohol is highly dependent on the
amount of the solid catalyst.
The conversion of benzyl alcohol is dependent on the amount of
oxygen pressure applied. The effect of the amount of O2 on the
Fig. 5. Thermogravimetric weight loss plots for the polymer supported ligand (a) (PS-
teta) (b) PS-tetaeVO complex.
Scheme 2. Aerobic oxidation of various benzyl alcohols.

174
Sk.M. Islam et al. / Journal of Organometallic Chemistry 761 (2014) 169e178
Table 2
Oxidative bromination reaction catalysed by PS-tetaeVO
Effect of solvent and catalyst amount on oxidation of benzyl alcohol using polymer
anchored oxovanadium catalyst.
Two different parameters such as volume of HClO4 and H2O2
were varied at room temperature. The role of hydrogen peroxide
was confirmed by conducting the oxidative bromination reaction
using 10 mmole20 mmol of H2O2 (Table 6, entries 1e4) whereas in
a blank experiment, in which H2O2 was absent, the formation of
bromo compound was significantly less (Table 6, entry 5). Con-
version of p-cresol significantly improves from 65% to 94% with the
increment of HClO4 from 10 mmol to 20 mmol (Table 6, entries 3
and 4). 20 mmol of HClO4 and 20 mmol of H2O2 were found to be
sufficient to give maximum conversion (Table 6, entry 4). The
bromination reaction proceeded to allow the formation of the
monobromide. This bromination was less effectively performed
under argon atmosphere (Table 6, entry 6). Under the air atmo-
sphere, the conversion of p-cresol was decreased slightly (Table 6,
entry 9). In absence of HClO4 under identical conditions showed a
48% yield (Table 6, entry 7). These results indicate that the presence
of the acid is essential for the efficient catalytic bromination. The
presence of excess acid may decompose the catalyst under the
above reaction conditions. HClO4 was added to the reaction mixture
in definite time interval to prevent decomposition of catalyst.
Approximately 94% conversion of p-cresol with PS-tetaeVO and
100% selectivity towards the formation of 2-bromo-p-cresol was
observed. In the initial stage of the reaction, 2-bromo-p-cresol was
selectively produce, if the reaction was carried out for longer time
(Table 6, entry 8) after consumption of the unreacted substrates,
the formation of 2,6-dibromo-p-cresol was started. With increase
of temperature the conversion of p-cresol was almost same. The
amount of KBr was also varied from 5 mmol to 20 mmol and the
maximum conversion of p-cresol was observed using 20 mmol of
KBr (Table 6, entries 1e4).
Entry
Solvent
Catalyst (mg)
Conversion (%)
Selectivity (%)
A
B
1
2
3
4
5
6
7
8
ACN
5
5
5
5
3
4
5
6
68
73
76
81
64
76
92
92.3
100
92
88
100
100
97
e
DMSO
EtOH
Toluene
H2O
H2O
H2O
08
12
e
e
03
04
14
96
86
H2O
Reaction conditions: benzyl alcohol (5 mmol), temperature (60 ꢀC), time (5 h) and
2 (5 bar).
The bold values signifies optimized conditions.
O
oxidation of benzyl alcohol into benzaldehyde was studied and the
results are shown in Table 3. The amount of pressure of molecular
oxygen was varied from 2 bar to 6 bar (Table 3, entries 3 and 6e9),
2 bar oxygen pressure resulted in 58% conversion when the amount
of catalyst was 5 mg and reaction time was 5 h at 60 ꢀC temperature
(Table 3, entry 6). When oxygen pressure was raised to 5 bar, the
conversion increased to 92% at 60 ꢀC (Table 3, entry 3). However,
the conversion was found almost constant when oxygen pressure
was further increased up to 6 bar (Table 3, entry 9). Therefore, 5 bar
oxygen pressure were found to be optimum. The reaction shows
very low conversion when molecular oxygen is absent (Table 3,
entry 5). The influence of temperature on the aerobic oxidation of
benzyl alcohol was investigated by performing the reaction at a
temperature range from 40 to 70 ꢀC (Table 3, entries 1e4) with all
other parameters fixed. The results are given in Table 3 which re-
veals that the conversion is dependent on temperature and
maximum conversion was recorded at 60 ꢀC. Therefore, 60 ꢀC was
selected as the optimum temperature. At lower temperature, the
conversion of benzyl alcohol into benzaldehyde was considerably
decreased.
In order to study the further catalytic activity of the catalyst for
the aerobic oxidation of aromatic alcohols, a series of benzyl alco-
hols bearing electron-withdrawing and electron donating groups
was studied in water (Table 4). Substrates having both electron
donating and electron withdrawing groups in the aromatic ring, 4-
methoxy and 4-nitro benzyl alcohols were oxidized to the corre-
sponding aldehydes in high yields. On the other hand, various
secondary alcohols could be oxidized by the use of PS-tetaeVO
catalyst. The general reaction is shown in Scheme 3 and the results
are summarised in Table 5.
Oxidative bromination reaction of other organic substrates has
been studied under optimized reaction conditions and the results
are shown in Table 7. In the present bromination system, simple
aromatic compound such as anisole was subjected to the mono-
bromination (Entry 2). Additionally, the phenol derivative bearing
the electron-withdrawing group was brominated smoothly to the
monobromide. 4-nitrophenol was also converted to the o-bromi-
nation product of 82% yield (Entry 4), whereas the bromination of
2-formylphenol resulted in the formation of 4-bromo-2-
formylphenol (Entry 1). Similarly, substrates like resorcinol, ani-
line and N,N-dimethylaniline showed high conversion and excel-
lent para-selectivity (Entries 3, 5 and 6).
Comparison with other reported system
Oxidation of primary, secondary alcohols and oxidative bromi-
nation of various aromatic substrates under heterogeneous condi-
tions over a variety of catalysts has been studied (Table 8). Table 8
provides a comparison of the results obtained for our present cat-
alytic system with those reported in the literature [1,3,6,40e42].
From Table 8, it can be concluded that the present catalyst follows a
green pathway and shows excellent catalytic activities as compared
to other reported systems [1,3,6,40e42]. Reactions conducted at
low or room temperature, shorter reaction time was required for
these reactions and most importantly most of the coupling re-
actions occurred in water using our vanadium catalyst.
Initially, the oxidative bromination reaction of p-cresol
(10 mmol) with PS-tetaeVO (0.050 g), KBr (20 mmol) in 10 mL of
water under molecular oxygen was investigated (Scheme 4) in
presence of HClO4 and H2O2.
Table 3
Effect of temperature and molecular oxygen on oxidation of benzyl alcohol using
polymer anchored oxovanadium catalyst.
Entry
Temperature (ꢀC)
O2 pressure (bar)
Conversion (%)
1
2
3
4
5
6
7
8
9
40
50
60
70
60
60
60
60
60
5
5
5
5
e
2
3
4
6
68
76
92
92
12
58
77
84
92
Test for heterogeneity
The leaching of vanadium from polymer anchored VO complex
was confirmed by analysis of the used catalyst (FTIR) as well as the
product mixtures (AAS and UVeVis). Analysis of the used catalyst
did not show appreciable loss in the vanadium content as
compared to the fresh catalyst. IR spectrum of the recycled catalyst
Reaction conditions: benzyl alcohol (5 mmol), water (5 mL), catalyst (5 mg) and time
(5 h).

Sk.M. Islam et al. / Journal of Organometallic Chemistry 761 (2014) 169e178
175
Table 4
Polymer supported oxovanadium complex catalysed aerobic oxidation of primary alcohols.
Entry
Substrate
Product
Conversion (%)a
92
TON
1
993.5
2
3
93
94
1004.3
1015.1
4
5
88
96
950.3
1036.7
6
7
81
79
874.7
853.1
8
9
77
78
831.5
842.3
10
84
907.1
11
12
75
74
809.9
799.1
Reaction condition: Substrate (5 mmol), water (5 mL), catalyst (5 mg), O2 (5 bar), time (5 h) at 60 ꢀC.
a
Determined by GC.
was quite similar to that of fresh sample indicating the heteroge-
neous nature of this complex. Analysis of the product mixtures
showed that if any vanadium was present it was below the detec-
tion limit. The UVevis spectroscopy was also used to determine the
stability of this catalyst. The UVevis spectra of the reaction solu-
tion, at the first run, did not show any absorption peaks
characteristic of vanadium metal, which indicates that the leaching
of metal did not take place during the course of the reaction. The
metal content of the recycled catalyst was determined with the
help of AAS and it was found that vanadium content of the recycled
catalyst remained almost unaltered. These observations strongly
suggest that the present catalyst is truly heterogeneous in nature.

176
Sk.M. Islam et al. / Journal of Organometallic Chemistry 761 (2014) 169e178
Table 7
Oxidative bromination of various organic substrates catalysed by polymer anchored
VO(IV) catalyst.
Entry
Substrate
KBr (mmol)
/time (h)
Product
Conversion
(%)
1
2
20/3
98
Scheme 3. Aerobic oxidation of secondary alcohols.
20/2.5
93
Table 5
Polymer supported oxovanadium complex catalysed aerobic oxidation of secondary
alcohols.
Entry
R
X
Time (h)
Conversion (%)a
TON
1
2
3
4
5
6
7
CH3
CH3
CH3
CH3
Ph
H
5
5
5
5
6
6
6
95
90
88
92
97
98
99
1025.9
971.9
950.3
CH3
OMe
Br
H
Cl
3
4
15/2.5
96
82
993.5
1047.5
1058.3
1069.1
Ph
iPr
H
Reaction condition: Substrate (5 mmol), water (5 mL), catalyst (5 mg), O2 (5 bar), at
60 ꢀC.
25/6
a
Determined by GC.
5
6
20/2.5
96
92
Scheme 4. Oxidative bromination of p-cresol in water.
20/3
Heterogeneity test was carried out for the oxidation of benzyl
alcohol as an example. For the rigorous proof of heterogeneity, a
test was carried out by filtering catalyst from the reaction mixture
at 60 ꢀC temperature at 2 h and the filtrate was allowed to react up
to the completion of the reaction (5 h). The reaction mixture of 2 h
7
20/3
87
Table 6
Effect of KBr, HClO4 and H2O2 on oxidative bromination of p-cresol.
Entry KBr
HClO4
H2O2
Conversiona Product selectivity (%)
Monobromo Dibromo
(mmol) (mmol) (mmol) (%)
1
2
3
4
05
10
20
20
20
20
20
20
20
10
10
10
20
20
20
e
10
15
20
20
e
37.0
54.0
65.0
94.0
25.0
79.0
48.0
94.3
91
100
100
100
100
100
100
100
95
e
e
e
e
e
e
e
05
8
20/3
92
5
6b
7c
8d
9e
20
20
20
20
20
20
100
9
20/3
93
Reaction conditions: substrate (10 mmol), water (10 mL), 5 mg catalyst at room
temperature under oxygen atmosphere.
The bold values signifies optimized conditions.
a
Determined by GC.
Under argon atmosphere.
Absence of acid.
Longer reaction time.
b
Reaction conditions: substrate (10 mmol); HClO4 (20 mmol); 30% aq. H2O2
(20 mmol), water (10 mL), 5 mg catalyst at room temperature, under oxygen
atmosphere.
c
d
e
Under air atmosphere.

Sk.M. Islam et al. / Journal of Organometallic Chemistry 761 (2014) 169e178
177
Table 8
Comparison of catalytic activities of the present catalyst in the oxidation and oxidative bromination reactions with other reported systems.
Reaction
Catalyst
Reaction conditions
Conversion (%)
TON
Ref.
Oxidation of alcohol
(VO)4(hpic)4
PSe[VO-An]
PanieVO(acac)2
O2 (1 MPa), 120 ꢀC, CH3CN
30% H2O2, 50 ꢀC, water
62a
96a
98a
95b
91b
92a
96b
96
186
74.4
42.61
41.30
[1]
[3]
[6]
O2 (1 atm), 100 ꢀC, toluene
[bmim]BF4eVO(acac)2
PS-tetaeVO
O2 (1 atm), 80 ꢀC, ionic liquid, Et3N
O2, 60 ꢀC, water
18.2
[40]
This work
993.5c
1036.7d
2254 (TOF)
75.97
Oxidative bromination of
salicylaldehyde
PS-im [VO2(pan)]
PSe[VO-An]
PSeK
H2O2, 40 ꢀC, water
H2O2, RT, water
H2O2, RT, water
[41]
[3]
[42]
98
85.2
775 (TOF)
[VO2(salinh)(im)]
PS-tetaeVO
H2O2, RT, water
98
2116.6
This work
a
Oxidation of benzyl alcohol.
Oxidation of p-methoxy benzyl alcohol.
b
and the filtrate were analysed by gas chromatography. No change in
the conversion as well as selectivity was found which indicates that
the present catalyst was heterogeneous in nature.
the catalyst for the selective aerobic oxidation of primary and
secondary alcohols to the corresponding carbonyl compounds via
ideal green process, i.e. water as the green solvent and with mo-
lecular oxygen as oxidant. This catalyst also shows excellent cata-
lytic activity in oxidative bromination reaction in water at room
temperature. Another important factor is the stability and recy-
clability of the catalyst under the reaction conditions used. This
heterogeneous catalyst shows no significant loss of activity in the
recycling experiments. The active sites do not leach out from the
support and thus can be reused without appreciable loss of activity,
indicating that the anchoring procedure was effective. The reus-
ability of this catalyst is high and can be reused six times without
significant decrease in its initial activity. We hope that the present
catalytic system has a bright future in industrial application.
Recycling of catalyst
The catalyst remains insoluble in the present reaction condi-
tions and hence can be easily separated by simple filtration fol-
lowed by washing. The catalyst was washed with dichloromethane
and dried at 100 ꢀC. Oxidation of benzyl alcohol was carried out
with the recycled catalyst under the optimized reaction conditions.
The catalyst was recycled in order to test its activity as well as
stability. The obtained results are presented in Fig. 6. As seen from
Fig. 6, the recycled catalyst did not show any appreciable change in
the activity which indicates that the catalyst is stable and can be
regenerated for repeated use. Similarly, recycling of the catalyst was
tested for the oxidative bromination reaction of p-cresol. No
appreciable change in conversion as well as selectivity indicates
that the catalyst can be reused.
Acknowledgements
SMI acknowledges Department of Science and Technology
(ref no: SB/S1/PC-107/2012), Council of Scientific and Industrial
Research (02(0041)/11/EMR-II) and UGC, New Delhi, Govt. of India
for financial support. RAM acknowledges UGC, New Delhi, India
(F no 39-847/2010(SR)) for his Maulana Azad National Fellowship
(F1-17.1/2012-13/MANF-2012-13-MUS-WES-9628/SA-III). ASR ac-
knowledges CSIR, New Delhi, India for his senior research fellow-
ship. NS acknowledges UGC, New Delhi, India for his senior
research fellowship. We acknowledge DST and UGC, New Delhi,
Govt. of India, for providing support to the Department of Chem-
istry, University of Kalyani under PURSE, FIST and SAP programme.
We acknowledge Professor B.C. Ranu, Department of Organic
Chemistry, IACS, Kolkata for his various support in our research.
Conclusion
In the present work, we have developed and characterized an
efficient polymer anchored oxovanadium Schiff base complex as
References
[1] S. Kodama, Y. Ueta, J. Yoshida, A. Nomoto, S. Yano, M. Ueshimaa, A. Ogawa,
Dalton Trans. (2009) 9708e9711.
[2] N. Kato, Y. Hayashi, Dalton Trans. 42 (2013) 11804e11811.
[3] S.M. Islam, A.S. Roy, P. Mondal, N. Salam, J. Mol. Catal. A: Chem. 358 (2012)
38e48.
[4] D. Obermayer, A.M. Balu, A.A. Romero, W. Goessler, R. Luque, C.O. Kappe,
Green Chem. 15 (2013) 1530e1537.
[5] S. Velusamy, M. Ahamed, T. Punniyamurthy, Org. Lett. 6 (2004) 4821e4824.
[6] S.R. Reddy, S. Das, T. Punniyamurthy, Tetrahedron Lett. 45 (2004) 3561e3564.
[7] P. Galloni, M. Mancini, B. Floris, V. Conte, Dalton Trans. 42 (2013) 11963e
11970.
[8] M.R. Maurya, U. Kumar, P. Manikandan, Dalton Trans. (2006) 3561e3575.
[9] Kotaro Kikushima, D.T. Moriuchi, P.T. Hirao, Chem. Asian J. 4 (2009) 1213e
1216.
[10] P. Das, N. Aggarwal, N.R. Guha, Tetrahedron Lett. 54 (2013) 2924e2928.
[11] Z. Huang, F. Li, B. Chen, T. Lu, Y. Yuan, G. Yuan, ChemSusChem 6 (2013) 1337e
1340.
[12] G. Wu, X. Wang, N. Guan, L. Li, Appl. Catal. B: Environ. 136e137 (2013)
177e185.
Fig. 6. Recycling efficiency for the aerobic oxidation of benzyl alcohol and oxidative
bromination of p-cresol with PS-tetaeVO complex.

178
Sk.M. Islam et al. / Journal of Organometallic Chemistry 761 (2014) 169e178
[13] G. Zhang, B.L. Scott, R. Wu, L.A. Silks, S.K. Hanson, Inorg. Chem. 51 (2012)
7354e7361.
[14] G. Rothenberg, J.H. Clark, Green Chem. 2 (2000) 248e251.
[15] G. Rothenberg, J.H. Clark, Org. Process Res. Dev. 4 (2000) 270e274.
[16] L. Yujin, J. Jie, J. Jianhong, S. Weijian, H. Liang, G. Jianrong, Chin. J. Chem. 28
(2010) 2428e2432.
[17] P. Gamez, I.W.C.E. Arends, J. Reedijka, R.A. Sheldon, Chem. Commun. (2003)
2414e2415.
[18] L. Lin, M. Juanjuan, J. Liuyan, W. Yunyang, J. Mol. Catal. A: Chem. 291
(2008) 1e4.
[19] A.V. Joshi, M. Baidossi, S. Mukhopadhyay, Y. Sasson, Org. Process Res. Dev. 8
(2004) 568e570.
[20] Q. Jiang, W. Shenga, C. Guo, Green Chem. 15 (2013) 2175e2179.
[21] K. Kikushima, T. Moriuchi, T. Hirao, Tetrahedron 66 (2010) 6906e6911.
[22] T. Hirao, Chem. Rev. 97 (1997) 2707e2724.
[29] S.M. Islam, A.S. Roy, S. Dalapati, R. Saha, P. Mondal, K. Ghosh,
S. Chatterjee, K. Sarkar, N. Guchhait, P. Mitra, J. Mol. Catal. A: Chem. 380
(2013) 94e103.
[30] S.M. Islam, A.S. Roy, P. Mondal, S. Mondal, M. Mubarak, D. Hossain, S. Sarkar,
J. Appl. Polym. Sci. 120 (2011) 2743e2753.
[31] S.M. Islam, P. Mondal, K. Tuhina, A.S. Roy, J. Chem, Technol. Biotechnol. 85
(2010) 999e1010.
[32] M.R. Maurya, C. Haldar, A.A. Khan, A. Azam, A. Salahuddin, A. Kumar,
J.C. Pessoa, Eur. J. Inorg. Chem. (2012) 2560e2577.
[33] M.R. Maurya, C. Haldar, A.A. Khan, A. Azam, A. Salahuddin, A. Kumar,
J.C. Pessoa, Eur. J. Inorg. Chem. (2009) 5377e5390.
[34] N. Li, X. Lang, W. Ma, H. Ji, C. Chen, J. Zhao, Chem. Commun. 49 (2013) 5034e
5036.
[35] T. Lu, Z. Du, J. Liu, H. Maa, J. Xu, Green Chem. 15 (2013) 2215e2221.
[36] A.I. Vogel, Test Book of Practical Organic Chemistry, fifth ed., Longman, Lon-
don, 1989.
[37] J.M. Frechet, C. Schuerch, J. Am. Chem. Soc. 93 (1971) 492e496.
[38] R.A. Shiel, K. Venkatasubbaiah, C.W. Jones, Adv. Synth. Catal. 350 (2008)
2823e2834.
[23] S. Mathew, H. Kathyayini, J.B. Nagy, N. Nagaraju, Catal. Commun. 10 (2009)
1043e1047.
[24] A. Modak, J. Mondal, A. Bhaumik, Green Chem. 14 (2012) 2840e2855.
[25] M.R. Maurya, M. Kumar, U. Kumar, J. Mol. Catal. A: Chem. 273 (2007) 133e143.
[26] E.M.E. Malki, P. Massiani, M. Che, Res. Chem. Intermed. 33 (2007) 749e774.
[27] A. Bhaumik, T. Tatsumi, J. Catal. 189 (2000) 31e39.
[28] S.M. Islam, A.S. Roy, P. Mondal, N. Salam, J. Inorg. Organomet. Polym. 22
(2012) 717e730.
[39] K.M. Parida, S. Singha, P.C. Sahoo, J. Mol. Catal. A: Chem. 325 (2010) 40e47.
[40] N. Jiang, A.J. Ragauskas, Tetrahedron Lett. 48 (2007) 273e276.
[41] M.R. Maurya, N. Chaudhary, F. Avecilla, Polyhedron 67 (2014) 436e448.
[42] M.R. Maurya, M. Kumar, Aarti Arya, Catal. Commun. 10 (2008) 187e191.