Oxidation of organic compounds by hydrogen peroxide using polymer-anchored azo-metal catalysts

Article abstract of DOI:10.1007/s11243-012-9654-8

Polymer-anchored azo complexes of Cu(II) and Ni(II) were synthesized by the reaction of chloromethylated polystyrene, 3-aminophenol, and 1-nitroso-2-naphthol with the metal chlorides. The catalytic activities of these complexes were studied in the oxidation of various organic substrates including alkenes, alcohols, alkanes, and sulfides with 30 % aqueous hydrogen peroxide. The structures of both catalysts have been investigated by physiochemical methods. Both catalysts proved to be very stable and could be reused more than five times without significant loss of activity. Furthermore, these catalysts require very mild reaction conditions.

Full text of DOI:10.1007/s11243-012-9654-8

Transition Met Chem (2013) 38:7–14
DOI 10.1007/s11243-012-9654-8
Oxidation of organic compounds by hydrogen peroxide
using polymer-anchored azo-metal catalysts
•
Sk. Manirul Islam Sumantra Paul
•
•
•
Manir Mobarok Anupam Singha Roy
Paramita Mondal
Received: 19 July 2012 / Accepted: 27 September 2012 / Published online: 12 October 2012
Ó Springer Science+Business Media Dordrecht 2012
Abstract Polymer-anchored azo complexes of Cu(II) and
Ni(II) were synthesized by the reaction of chloromethy-
lated polystyrene, 3-aminophenol, and 1-nitroso-2-naph-
thol with the metal chlorides. The catalytic activities of
these complexes were studied in the oxidation of various
organic substrates including alkenes, alcohols, alkanes, and
sulfides with 30 % aqueous hydrogen peroxide. The
structures of both catalysts have been investigated by
physiochemical methods. Both catalysts proved to be very
stable and could be reused more than five times without
significant loss of activity. Furthermore, these catalysts
require very mild reaction conditions.
catalysts is drawing much current interest. Heterogeneous
catalysts are often sufficiently thermally stable to carry out
high temperature reactions and can also be easily separated
from the products and reused. Therefore, replacement of
homogeneous catalysts by heterogeneous catalysts is an
important goal in catalysis. The heterogeneous supports may
be a range of materials, including alumina [10], amorphous
silicates [11], polymers [12], zeolites [13], and functional-
ized Mobil crystalline materials or functionalized MCM-41
[14].
Functionalized polystyrene-anchored catalysts have
been used to carry out various catalytic organic transfor-
mations [15, 16]. Polystyrene-anchored transition metal
complexes can provide inert and reusable catalysts for the
conversion of various organic functional groups [17–19].
In this study, we report our initial efforts on the develop-
ment of a catalytic system which can oxidize organic
substrates under mild conditions. We chose hydrogen
peroxide as an oxidant because of its low toxicity [20]. We
have developed and characterized a polymer-supported
Cu(II)-azo catalyst (Cat-1) and Ni(II)-azo catalyst (Cat-2),
and their catalytic performances have been investigated in
the liquid-phase oxidation of a variety of organic substrates
using 30 % H2O2 as oxidant in acetonitrile medium. The
effects of different parameters have been investigated in
order to optimize the reaction conditions. We have also
investigated the effect of reuse of the catalysts on their
performance.
Introduction
Hydrocarbon oxidations are essential reactions in organic
chemistry, both for basic research and industrial purposes
[1, 2]. Oxidations of alkenes and saturated compounds to
give the corresponding oxo-products are vital and useful
reactions in various industries [3]. The oxidation of alco-
hols to carbonyl compounds is one of the most fundamental
transformations in organic chemistry and also one of the
key routes to synthesize benzaldehyde, which is a versatile
and widely used synthon in industrial chemistry [4, 5].
Metal complexes are extensively used for the catalytic
oxidation of various organic substrates [6, 7]. However, in
the work-up processes, homogeneous catalysts face many
drawbacks [8, 9]. Hence, the development of heterogeneous
Experimental
Sk. M. Islam (&) Á S. Paul Á M. Mobarok Á
A. S. Roy Á P. Mondal
Analytical-grade reagents and freshly distilled solvents
were used throughout the experiments. Liquid substrates
were pre-distilled and dried with the appropriate molecular
Department of Chemistry, University of Kalyani, Kalyani,
Nadia 741235, WB, India
e-mail: manir65@rediffmail.com
123

8
Transition Met Chem (2013) 38:7–14
sieve. Purification of the solvents and substrates was done
by standard procedures [21]. 3-aminophenol, 1-nitroso-2-
naphthol, and chloromethylated polystyrene were supplied
by Sigma-Aldrich. Other reagents were obtained from
Merck.
ethanolic solution of the appropriate metal chloride (CuCl2/
NiCl2) was added dropwise over a period of 30 min under
constant stirring. The resulting mixture was refluxed for
24 h. The resulting solid mixture was filtered off, washed
thoroughly with ethanol, and dried at room temperature
under vacuum and give the PS-Cu(II)-azo complex (Cat-1,
1.04 g) or PS-Ni(II)-azo complex (Cat-2, 1.03 g).
A Perkin-Elmer 2400 C elemental analyzer was used to
collect microanalytical data (C, H, and N). FTIR spectra
were recorded on a Perkin-Elmer FTIR 783 spectropho-
tometer using KBr pellets. A Mettler Toledo TGA/SDTA
851 instrument was used for the thermogravimetric (TGA)
analysis. Morphologies of the functionalized polystyrene
and complexes were analyzed using a scanning electron
microscope (SEM, ZEISS EVO40, England) equipped with
EDAX facility. Metal content in the catalyst was deter-
mined using a Varian AA240 atomic absorption spectro-
photometer (AAS).
Procedure for catalytic oxidation
A mixture of catalyst (0.1 mmol), MeCN (10 mL), and
substrate (5 mmol) was stirred vigorously at 60 °C in a
50-mL two-necked round-bottom flask equipped with a
condenser. H2O2 (10 mmol of 30 % aqueous solution) was
Preparation of the catalyst
P
NH2
P
CH2O
(A)
Synthesis of polymer-anchored ligand (A)
DMF/ NaH
at room temp./
10 h
NH2
OH
3-aminophenol (0.720 g) was reacted with chloromethy-
lated polystyrene (1.2 g, 5.5 mmol/g Cl) plus NaH
(0.200 g) in DMF (10 mL) at 0 °C with continuous stirring
for 2 h. The mixture was then left stirring and warming to
room temperature over 8 h. The resulting brown mixture
was filtered and the residue (pale brown) was washed with
ethanol until the filtrate became colorless, then dried under
vacuum to get PS-compound (A) (1.7 g).
HO
CH2Cl
NO
HO
MeOH/Reflux
24 h
P
CH2O
N
N
(B)
Synthesis of polymer-anchored azo ligand (B)
EtOH/Reflux
24 h
Polymer A (1.2 g) was added to a solution of 1-nitroso-2-
naphthol (1.2 g) in MeOH (10 mL) and the mixture was
heated to reflux with continuous stirring. The mixture was
then cooled to room temperature and filtered. The brown
beads were washed with ethanol until the filtrate became
colorless and dried under vacuum to give B (1.9 g).
MCl2
P
Cl OH2
CH2O
M
O
N
N
PP
= Polymer support
Synthesis of the polymer-anchored complexes
Cat-1 (M = Cu)
Cat-2 (M = Ni)
The polymer-anchored azo ligand B (1 g) was suspended in
ethanol (20 mL). To this mixture, 5 mL of a 1 % (w/v)
Scheme 1 Preparation of the polymer-anchored complexes
Table 1 Elemental analysis
Compound
C (%)
H (%)
N (%)
Cl (%)
Metals (%)
PS-compound (A)
79.08 (80.40)
78.02 (79.21)
69.30 (60.96)
69.81 (61.54)
6.44 (6.70)
5.49 (5.31)
5.37 (4.88)
5.39 (4.92)
5.05 (6.01)
6.20 (7.22)
5.48 (5.56)
5.52 (5.61)
3.08
2.23
5.57
5.61
–
PS-azo ligand (B)
–
PS-Cu(II)-azo complex
PS-Ni(II)-azo complex
5.79
4.98
Expected values are given in parenthesis
123

Transition Met Chem (2013) 38:7–14
9
Fig. 1 FE SEM image of polymer-anchored azo ligand (a) and polymer-anchored complexes Cat-1 and Cat-2 (b, c)
Fig. 2 EDAX data polymer-
anchored complexes Cat-1 and
Cat-2 (a, b)
added in three portions over 3 h. The resulting mixture was
then stirred at 60 °C for 8 h. After filtration, the filtrate was
concentrated and then analyzed using a Varian 3400 gas
chromatograph equipped with a 30 m CP-SIL8CB capil-
lary column and flame ionization detector. The products
were determined using cyclohexanone as internal standard.
All reaction products were identified using an Agilent GC–
MS.
Results and discussion
Characterization of the polymer-anchored complexes
Owing to the insolubilities of these polymer-supported
metal complexes in organic solvents, their structural
characterization was limited to their physicochemical
properties, chemical analysis, SEM, TGA, FTIR, and UV–
123

10
Transition Met Chem (2013) 38:7–14
Table 2 IR stretching frequencies of polymer-anchored azo ligand and complexes
Compound
Color
IR (cm-1, KBra)
NH2 (primary)
M–O
N=N
M–N
O–H
C–O
PS-compound (A)
PS-azo ligand (B)
PS-Cu(II)-azo complex
PS-Ni(II)-azo complex
a
Pale brown
Brown
3,463
–
–
–
–
1,370
1,370
1,357
1,357
–
–
–
–
1,452
1,440
1,440
–
3,401
Green
642
640
533
513
–
–
Greenish brown
Infrared spectra measured as KBr pellets
A
Scanning electron micrograph (SEM) images of the
polymer-supported azo ligand and its transition metal
complexes were recorded to understand the morphological
changes occurring on the surface of the polymer matrix.
Figure 1 shows the SEM images of the polymer-anchored
azo ligand (Fig. 1a) and the immobilized Cu(II) and Ni(II)
complexes (Fig. 1b, c, respectively). The original polymer
beads have a smooth and flat surface (not shown in Fig. 1).
The introduction of the ligand onto the polystyrene beads
causes a roughening on the surface layer. Images of the
metal complexes show further roughening on the surface.
Energy dispersive spectroscopy X-ray (EDX) analyses of
the complexes show the expected metal content along with
C, N, O, and Cl, consistent with the formation of the metal
complexes (Fig. 2). The ratios of metals and other elements
obtained from EDX analysis are quite similar to the data
obtained from elemental analysis (Table 1). The presence
of the metals is confirmed by energy dispersive spectros-
copy analysis of X-rays (EDAX).
PS-Cu(II)-azo complex
PS-Ni(II)-azo complex
100
200
300
400
500
600
°
Temperature ( C)
B
The mode of attachment of the transition metals onto the
support was confirmed by the comparison of the FTIR
spectral bands of the polymers before and after loading
with metals, both in the mid (4,000–400 cm-1) and far
(600–50 cm-1) IR regions (Table 2). The IR spectrum of
pure chloromethylated polystyrene has an absorption band
at 1,261 cm-1 due to the presence of the C–Cl group,
which was absent in the spectra of the anchored ligand and
the catalysts. The IR spectra show a stretching vibration for
CH2 at 2,918 cm-1 for the polymer bound ligand and its
complexes. The N=N stretches were observed at
1,452 cm-1 for the polymer bound azo ligand and
1,440 cm-1 in the two metal complexes, indicating the
coordination of nitrogen to the metal. Bands at 3401 (only
in B) and 1,370 cm-1 (in both A and B) have been
assigned to the stretching vibrations of the frequency of
phenolic –OH and free C–O stretches, respectively. In the
PS-M(II)-azo complexes, a new peak at 1,357 cm-1 can be
attributed to a shift in the C–O stretch as a result of
coordination through the phenolic oxygen [22]. The M–O
peaks for the metal complexes are observed around
630–680 cm-1 [23]. In the far IR, bands due to the M–N
stretching vibration are observed at 520–580 cm-1 [23],
PS-azo ligand
100
200
300
400
°
Temperature ( C)
Fig. 3 Thermal studies of polymer-anchored complexes Cat-1 and
Cat-2 (a) and polymer-anchored azo ligand (b)
Vis spectroscopic data. Table 1 provides the elemental
analysis data. The metal contents of the supported catalysts
(5.79 % for the Cu complex and 4.98 % for the Ni com-
plex) were estimated by atomic absorption spectrometry.
The outline for the preparation of polymer-anchored azo
complexes is given in Scheme 1.
123

Transition Met Chem (2013) 38:7–14
11
Fig. 4 DRS-UV–visible
absorption spectra of polymer-
anchored complexes Cat-1
(a) and Cat-2 (b)
O
complex, decomposition started at around 290–300 °C,
whereas the Ni(II) complex decomposed at 330–380 °C.
Hence, these polymer-supported metal complexes degrade
at fairly high temperatures and the Ni(II) complex is the
most thermally stable.
CHO
COOH
PS-M(II) complex
+
+
H2O2, ACN, 600C, 8hr
trace
minor
major
The electronic spectra (Fig. 4) of the supported metal
complexes were recorded in diffuse reflectance spectrum
mode as MgCO3/BaSO4 discs, due to their solubility lim-
itations in common organic solvents. Cat-1 and Cat-2
exhibit bands around 310–440 and 300–400 nm, respec-
tively, which may be assigned to p ? p* transitions of
intra-ligand charge transfer of the benzenoid moiety and
n ? p* transition of the azo group.
Scheme 2 Oxidation of styrene
Table 3 Styrene oxidation using different solvents with Cat-1 and
Cat-2
Sl.
No.
Solvent Conversion (%)a
Selectivity of styrene
oxide (%)a
(PS-Cu(II)-azo/PS-
Ni(II)-azo)
PS-Cu(II)- PS-Ni(II)-
azo
azo
1
2
3
4
5
Toluene Nil
Nil
40
52
90
72
Nil
31
44
79
63
Catalytic oxidation of styrene
MeOH
H2O
20/12
52/41
95/82
Oxidation of styrene, catalyzed by both supported com-
plexes using H2O2 as an oxidant, gives styrene oxide as
major product, as shown in Scheme 2. We have optimized
the reaction conditions by varying different parameters,
namely the amount of oxidant, amount of catalyst, and
temperature. The epoxidation of styrene was also examined
using different solvents. Table 3 shows the influence of
solvents on the conversion of styrene and yields of styrene
oxide for the two catalysts. Acetonitrile proved to be the
best solvent for these reactions. An interesting result is that
the PS-Cu(II)-azo catalyst is more efficient than the PS-
Ni(II)-azo catalyst.
ACN
DMSO 76/63
Reaction conditions: catalyst (0.1 mmol), styrene (5 mmol), solvent
(10 mL), H2O2 (10 mmol), 60 °C, time: 8 h
a
Determined by GC
which supports the formation of the metal complexes
through M–N bonds. The metal complexes also show a
characteristic (Cu–Cl) frequency at 314 cm-1 [24] and (Ni-
Cl) frequency at 247 cm-1
.
The thermal stabilities of the complexes were investi-
gated using TGA at a heating rate of 10 °C/min in air over
a temperature range of 50–600 °C. The TGA curves are
shown in Fig. 3. For the polymer-supported Cu(II)
The effects of different oxidants like TBHP, H2O2,
PhIO, and KHSO5 with these catalysts have also been
examined. The results are given in Table 4. Hydrogen
123

12
Transition Met Chem (2013) 38:7–14
Table 4 Oxidation of styrene using different oxidants with Cat-1
Sl. No. Oxidant Conversion (%)a Yield (%)a
(PS-Cu(II)-azo/
PS-Ni(II)-azo)
(Styrene oxide/
Benzaldehyde)
PS-Cu(II)-azo PS-Ni(II)-azo
1
2
3
4
5
None
PhIO
Nil
Nil/Nil
35/30
40/27
63/12
86/7
Nil/Nil
23/35
30/32
53/14
65/11
71/62
K2SO5 76/69
TBHP
H2O2
79/70
95/82
Reaction conditions: catalyst (0.1 mmol), styrene (5 mmol), ACN
(10 mL), oxidant (10 mmol), 60 °C, time: 8 h
a
Determined by GC
Fig. 6 Effect of substrates-to-oxidant molar ratio on oxidation of
styrene as a function of time using Cat-1. Reaction condition: Styrene
(5 mmol), ACN (10 mL), catalyst (0.1 mmol), temperature = 60 °C
and time = 8 h
peroxide proved to be the most suitable oxidant for both
catalytic systems. Again, that copper catalyst is more active
than the nickel catalyst.
To determine the optimum reaction temperature, we
studied the epoxidation of styrene at temperatures between
40 and 70 °C, using H2O2 as oxidant and acetonitrile as
solvent (Fig. 5). We found 60 °C to be the optimum
reaction temperature; at higher temperatures, the selectivity
for styrene oxide decreases due to decomposition.
Next, three different amounts, specifically 0.05, 0.1, and
0.2 mmol of catalyst, have been used under the above
reaction conditions. Using 0.05 mmol of catalyst, conver-
sion was only 65 % while using 0.1 and 0.2 mmol of cat-
alyst conversions reached 95 and 96 %, respectively.
Hence, 0.1 mmol of PS-Cu(II) catalyst is sufficient to carry
out the reactions.
(10 mmol) and catalyst (0.1 mmol) in acetonitrile (10 mL),
at 60 °C. As illustrated in Fig. 6, the conversion of styrene
improved from 52 to 95 % upon increasing the styrene to
aqueous 30 % H2O2 molar ratio from 1:1 to 1:2, though
selectivity at 1:1 ratio was high. The conversion remained
nearly constant upon further increasing the ratio to 1:3, but
the selectivity toward styrene oxide decreased; hence, a
large amount of oxidant is not an essential condition to
improve the selectivity for this reaction.
In summary, we find the optimized reaction conditions
for the oxidation of styrene are; substrate 5 mmol, catalyst
0.1 mmol, substrate/oxidant ratio 1:2, solvent (acetonitrile)
10 mL, and temperature 60 °C. The PS-Ni(II) complex was
less reactive than the PS-Cu(II) catalyst under the opti-
mized reaction conditions. Next, we studied the activities
of the catalysts with other olefins. Cyclic olefins such as
limonene and a-pinene are oxidized with high selectivity
(81 and 83 %), and generally similar results were obtained
(Table 5).
To find the optimum ratio of substrate to oxidant, 1:1,
1:2, and 1:3 ratios were investigated with styrene
100
100
95
90
85
80
75
70
90
80
70
60
50
40
30
20
Oxidation of other substrates
In order to explore further the catalytic activity and
selectivity of these catalysts, oxidations of alkanes, alco-
hols, and sulfides were investigated under the optimum
reaction conditions, with some excellent results (Table 6).
Ethylbenzene was transformed into acetophenone in up to
75 % yield. The catalysts also gave good results with the
substituted benzyl alcohols and sulfides.
Conversion of styrene
Selectivity of styrene oxide
35
40
45
50
55
60
65
70
75
°
Temperature ( C)
It is clear from Tables 5 and 6 that olefins are selectively
oxidized to their corresponding epoxides, while alkanes and
alcohols are selectively oxidized to aldehydes or ketones,
and sulfides are selectively oxidized to their corresponding
Fig. 5 Effect of temperature on the oxidation of styrene using Cat-1.
Reaction condition: styrene (5 mmol), ACN (10 mL), H2O2
(10 mmol), catalyst (0.1 mmol)
123

Transition Met Chem (2013) 38:7–14
13
Table 5 Oxidation of Olefins using Cat-1 and Cat-2
Table 7 Comparison of polymer-anchored complex catalysts Cat-1
and Cat-2
SL.
No.
Olefins
Conversion (%)a Selectivity of the
epoxide (%)a
Substrates Catalysts
Conversion
(%)
Reference
(PS-Cu(II)-azo/
PS-Ni(II)-azo)
(PS-Cu(II)-azo/
PS-Ni(II)-azo)
O
1
2
3
5
6
7
8
Styrene
95/72
90/79
84/66
66/53
62/49
87/76
80/68
90/76
80/68
87/78
81/69
83/72
91/79
88/74
p-Methylstyrene
p-Metoxystyrene
a-Pinene
Cat.1
95
90
This work
Limonene
Cyclohexene
Cyclooctene
Reaction conditions: catalyst (0.1 mmol), substrate (5 mmol), ACN
(10 mL), oxidant (10 mmol), 8 h, 60 °C
Cat-2
PS-
72
57
76
This work
25
a
Determined by GC and GC–MS
3.6
[Cu(ligand)n]
CHO
sulfoxides. Comparison of our results with other reported
catalysts (Table 7) reveals that the present system gives
better conversions than other catalysts.
Cat.1
96
90
This work
OH
Heterogeneity and recycling tests
To check that the catalyst is actually functioning in a
heterogeneous manner, a hot-filtration test was performed
on the oxidation reaction. During the catalytic oxidation of
styrene, the solid catalyst was separated from the reaction
mixture by filtration after 4 h of reaction and the obtained
filtrate was continually stirred under the same reaction
conditions for a further 3 h. Gas chromatographic analysis
showed no increment in the conversion, and atomic
absorption spectrometric analysis of the filtrate confirmed
that no metals were present in the reaction mixture. The
metal content of the recycled catalysts was also unaltered,
Cat.2
PyC4
81
83
This work
26
93.6
90.5
indicating no leaching of the metal from the polymer
support during the catalytic oxidation reactions.
The recyclability of the catalysts was studied in repeated
styrene oxidation reactions (Table 8). The catalysts were
separated from the reaction mixture after each experiment
Table 6 Oxidation of different
substrates using Cat-1 and Cat-2
Sl. No.
Substrate
Conversion (%)a
Selectivity of the product (%)a
(PS-Cu(II)-azo/PS-Ni(II)-azo)
(PS-Cu(II)-azo/PS-Ni(II)-azo)
Aldehyde
Ketone
Sulfoxide
Alkanes
1
2
Ethylbenzene
75/62
35/21
–
79/59
–
–
–
Toluene
100/79
Alcohols
3
4
5
6
Benzyl alcohol
4-Methylbenzyl alcohol
4-Nitrobenzyl alcohol
4-Bromobenzyl alcohol
Sulfides
96/81
94/76
87/69
92/78
90/83
89/74
91/80
86/72
–
–
–
–
–
–
–
–
Reaction conditions: catalyst
(0.1 mmol), substrate (5 mmol),
ACN (10 mL), oxidant
7
8
9
1-Propenphenyl sulfide
Di-phenyl sulfide
Di-methyl sulfide
91/83
90/76
87/74
–
–
–
–
–
–
98/79
100/82
91/78
(10 mmol), 8 h, 60 °C
a
Determined by GC and
GCMS
123

14
Transition Met Chem (2013) 38:7–14
References
Table 8 Recycling efficiency of the catalysts for the oxidation of
styrene
1. Fredrich B, Gerhartz C (eds) (1985) W. Ullmann’s encyclopedia
of Industrial chemistry. Weinheim, New York
2. McGarrigle EM, Gilheany DG (2005) Chem Rev 105:1563–1602
3. Shulpin GB (2002) J Mol Catal A Chem 189:39–66
4. Backvall JE (2004) Modern oxidation methods. Wiley-VCH,
Weinheim, pp 21–39
5. Haines AH (1985) Methods for the oxidation of organic com-
pounds. Academic Press, New York
6. Blakemore PR, Burge MS (2007) J Am Chem Soc 129:
3068–3069
Reuse time
Conversion (%)a
Cat-1
Cat-2
First time
95
93
92
91
90
80
79
77
76
75
Second time
Third time
Fourth time
Fifth time
7. Egami H, Katsuki T (2007) J Am Chem Soc 129:8940–8941
8. Valodkar VB, Tembe GL, Ravindranathan M, Rama HS (2004)
J Mol Catal A Chem 223:31–38
9. Singla M, Mathur P, Gupta M, Hundal MS (2008) Transit Metal
Chem 33:175–182
Reaction conditions: catalyst (0.1 mmol), substrate (5 mmol), ACN
(10 mL), oxidant (10 mmol), 8 h, 60 °C
a
Determined by GC
10. Handzlik J, Ogonowski J, Stoch J, Mikołajczyk M (2005) Catal
Lett 101:65–69
11. Mureseanu M, Parvulescu V, Ene AR, Cioatera AN, Pasatoiu TD,
Andruh M (2009) J Mater Sci 44:6795–6804
12. Lei Z (2000) React Func Polym 43:139–143
13. Salvati-Niasari M (2005) Inorg Chem Comnmun 8:174–177
14. Thitsartarna W, Gularib E, Wongkasemjita S (2008) Appl Or-
ganometal Chem 22:97–103
by filtration, washed with methanol, and dried carefully
before reuse in subsequent runs. After five consecutive uses
of the catalyst, the styrene conversion was 85 %. The
recovered catalysts showed no change in their IR and UV–
vis spectra. Hence, the nature and activity of the catalyst
was not significantly altered after five repeat runs.
15. Sakthivel A, Dapurkar SE, Selvan P (2003) Appl Catal A Gen
246:283–293
16. Dapurkar SE, Sakthivel A, Selvan P (2003) New J Chem
27:1184–1190
17. Islam SM, Tuhina K, Mubarak M, Mondal P (2009) J Mol Catal
A Chem 297:18–25
Conclusion
18. Islam SM, Mondal P, Singha Roy A, Mondal S, Hossain D (2010)
Tetrahedron Lett 51:2067–2070
19. Gruenwald KR, Kirillov AM, Haukka M, Sanchiz J, Pombeiro
AJL (2009) Dalton Trans 12:2109–2120
Polymer-anchored azo-metal complexes of Cu(II) and
Ni(II) have been synthesized and characterized by spec-
trophotometric methods. The catalytic activities of these
complexes were tested for the liquid-phase oxidation of
olefins using hydrogen peroxide as the oxidant. Excellent
conversion and selectivity toward the oxidation of olefins,
aromatic alcohols, alkanes, and sulfides were observed.
These polymer-anchored catalysts are easy to prepare, air-
stable, and inexpensive solids. Easy product recovery and
recycling efficiency along with high selectivity of these
catalysts may be useful for the synthesis of different fine
chemicals under mild conditions.
20. Hagen J
Weinheim
(2006) Industrial catalysis. Wiley-Interscience,
21. Vogel AI (1989) Text book of practical organic chemistry
(Quantitative Analysis), 5th edn. Longman, London
22. Marvel CS, Aspey SA, Dudley EA (1956) J Am Chem Soc
78:4905–4909
23. Sallam SA, Orabi AS (2002) Transit Met Chem 27:447–453
24. Gnanasoundari VG, Natarajan K (2004) Transition Met Chem
29:511–515
25. Maurya MR, Arya A, Adao P, Pesso C (2008) Appl Catal A Gen
351:239–252
26. Ming-Lin G, Hui-Zhen L (2007) Green Chem 9:421–423
Acknowledgments We thank the Indian Association for the Culti-
vation of Science, Kolkata, for providing the instrumental support. MI
acknowledges Department of Science and Technology (DST),
Council of Scientific and Industrial Research (CSIR) and University
Grant Commission (UGC), New Delhi, India, for funding.
123