Synthesis, catalytic oxidation and antimicrobial activity of copper(II) Schiff base complex

Article abstract of DOI:10.1016/j.molcata.2011.01.006

A new polymer supported Cu(II) Schiff base complex was synthesized. The solid complex was characterized by Fourier transform infrared spectroscopy (FT-IR), UV-vis diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Its homogeneous analogue was also prepared. The catalytic performances of the copper complex in oxidation reactions were evaluated for both homogeneous and heterogeneous systems. The copper(II) complex was found to be efficient catalyst for the oxidation of alkenes, alkanes and aromatic alcohols in the presence of hydrogen peroxide as oxidant at room temperature. The catalytic investigation revealed that the solid complex performs better than the homogeneous one as an oxidation catalyst. The solids containing the immobilized complex can be recovered from the reaction medium and reused almost five times, maintaining good catalytic activity. Furthermore, the in vitro toxicity of the ligand and complex was tested against the growth of bacterial species, viz., Staphylococcus aureus and Escherichia coli.

Full text of DOI:10.1016/j.molcata.2011.01.006

Journal of Molecular Catalysis A: Chemical 336 (2011) 106–114
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Synthesis, catalytic oxidation and antimicrobial activity of copper(II) Schiff base
complex
a,∗
a
a
a
a
S.M. Islam , Anupam Singha Roy , Paramita Mondal , Manir Mubarak , Sanchita Mondal ,
a
b
b
Dildar Hossain , Satabdi Banerjee , S.C. Santra
Dept. of Chemistry, University of Kalyani, Kalyani, Nadia 741235, W.B., India
a
b
Dept. of Env. Science, University of Kalyani, Kalyani, Nadia 741235, W.B., India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new polymer supported Cu(II) Schiff base complex was synthesized. The solid complex was character-
ized by Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS),
thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Its homogeneous analogue
was also prepared. The catalytic performances of the copper complex in oxidation reactions were evalu-
ated for both homogeneous and heterogeneous systems. The copper(II) complex was found to be efficient
catalyst for the oxidation of alkenes, alkanes and aromatic alcohols in the presence of hydrogen peroxide
as oxidant at room temperature. The catalytic investigation revealed that the solid complex performs bet-
ter than the homogeneous one as an oxidation catalyst. The solids containing the immobilized complex
can be recovered from the reaction medium and reused almost five times, maintaining good catalytic
activity. Furthermore, the in vitro toxicity of the ligand and complex was tested against the growth of
bacterial species, viz., Staphylococcus aureus and Escherichia coli.
Received 11 October 2010
Received in revised form 3 January 2011
Accepted 7 January 2011
Available online 15 January 2011
Keywords:
Polymer supported
Copper(II) Schiff base complex
Oxidation
H2O2
Antibacterial activity
©
2011 Elsevier B.V. All rights reserved.
1
. Introduction
applications in the industry of perfumery, pharmaceutical, dyestuff
and agrochemicals [12,13].
The oxidation of organic compounds with an eco friendly oxi-
In the recent past, there has been an increasing interest in devel-
oping environmental friendly greener processes which are also
economically viable. However, some problems such as excessive
use of oxidants, corrosion, difficulty in recovery and separa-
tion of the catalyst from reaction mixtures are associated with
homogeneous catalysts and make such systems environmentally
unsuitable [14]. In recent years, the design and synthesis of catalyti-
cally active supported metal complexes have received considerable
interest. Many effective and recyclable heterogeneous catalysts
have been studied for the liquid phase oxidation [15,16]. Various
approaches have been focused on the incorporation of metal-based
catalysts onto or into inert supports by different methods, such
as alumina [17], amorphous silicates [18], polymers [19], zeolites
[20] and MCM-41 [21]. Application of polymer supported cata-
lysts in oxidation reactions has been received attention in recent
years due to their potential advantages over the homogeneous one
[22–24]. The activity of polymer supported Schiff base complexes
of transition metal ions varies with the type of Schiff base ligands,
coordination sites and metal ions used in their formation.
dant, aqueous hydrogen peroxide, is a challenging goal of catalytic
chemistry [1–3]. In recent years, a considerable amount of research
was dedicated to the preparation of various solid heterogeneous
copper catalysts and their application for oxidations of various
organic compounds [4–8].
Olefin oxidation is especially interesting because of the indus-
trial importance of this type of reaction. Oxidation of alkenes to give
oxygen containing value added products like alcohols, aldehydes,
ketones, acids, epoxides, etc. is an extremely important and useful
reaction in both chemical and pharmaceutical industries [9]. Acti-
vation of the carbon–hydrogen bonds of an alkane is considerably
more difficult due to its stability. The energy required to overcome
this stability leads to deep oxidation rather than selective oxidation
[
10,11]. On the other hand, the oxidation of primary and secondary
alcohols to carbonyl compounds (corresponding aldehydes and
ketones) is one of the simplest and most useful transformations
in organic chemistry. In particular, the oxidation of benzyl alcohol
to benzaldehyde is an important organic transformation which has
In this work, we have prepared homogeneous and its immobi-
lized polymer anchored Cu(II) Schiff base complex. The catalytic
efficiency of the neat and polymer supported metal Schiff base
complexes was tested in the oxidation of alkenes, alkanes and aro-
∗ Corresponding author. Tel.: +91 33 2582 8750, fax: +91 33 2582 8282.
E-mail address: manir65@rediffmail.com (S.M. Islam).
1
381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.01.006

S.M. Islam et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 106–114
107
matic alcohols using H O2 as oxygen source. Polymer supported
(1 g) was kept in contact with methanol (10 ml) in a round bot-
tom flask. To this, methanolic solution (10 ml) of CuCl2 (1%, w/v)
was added over a period of 45 min and refluxed for 6 h. Then green
coloured copper loaded beads were filtered carefully, washed with
methanol and dried in vacuum.
2
copper catalyst showed excellent catalytic activity and selectivity.
Comparison of homogeneous and supported catalyst for oxidation
reaction was also done. The catalytic activities were also tested with
the recycled catalyst. Further, the antibacterial activity of the Schiff
base and its copper complex was examined.
2.4. General procedure for oxidation of alkenes, alkanes and
2
. Experimental
aromatic alcohols catalyzed by PS-[Cu(L)(Cl)2]
2.1. Materials
All of the reactions were carried out at room temperature under
air in a 25 ml flask equipped with a magnetic stirrer. 30% H O2
2
All the reagents used were chemically pure and were of ana-
solution (10 mmol) was added to a mixture of alkene or alkane
or aromatic alcohol (5 mmol), catalyst (0.05 g) in CH3CN (10 ml).
After filtration and washing with solvent, the filtrate was concen-
trated and then analyzed with Varian 3400 gas chromatograph
equipped with a 30 m CP-SIL8CB capillary column and a Flame Ion-
ization Detector. The concentration of products was determined
using cyclohexanone as internal standard. All reaction products are
identified by using an Agilent GC–MS.
lytical reagent grade. The solvents were dried and distilled before
use following the standard procedures [25]. Chloromethylated
polystyrene was supplied by Sigma–Aldrich Chemicals Company,
USA. Alkenes, alkanes and aromatic alcohols were obtained from
Merck or Fluka.
2
.2. Physical measurements
A Perkin-Elmer 2400C elemental analyzer was used to col-
2.5. General procedure for oxidation of alkenes, alkanes and
aromatic alcohols catalyzed by [Cu(L)(Cl)2]
lect micro analytical data (C, H and N). The copper content of
the samples was measured by Varian AA240 atomic absorption
spectrophotometer (AAS). The FT-IR spectra of the samples were
recorded on a Perkin-Elmer FT-IR 783 spectrophotometer using
KBr pellets. Diffuse reflectance spectra (DRS) were registered on a
Shimadzu UV/3101 PC spectrophotometer. Magnetic measurement
was carried out on a Sherwood Scientific magnetic balance using
Gouy method. Mettler Toledo TGA/SDTA 851 instrument was used
for the thermogravimetric analysis (TGA). Morphology of function-
alized polystyrene and complex were analyzed using a scanning
electron microscope (SEM) (ZEISS EVO40, England) equipped with
EDX facility.
To a 25 ml round-bottom flask containing alkene or alkane or
−
5
aromatic alcohol (5 mmol), neat metal complex (1.20 × 10 mol)
in CH3CN (10 ml) were added a solution of 30% H2O2 (10 mmol). The
resulting mixture was then stirred at room temperature under air,
the solvent was evaporated under reduced pressure and the crude
was analyzed by GC and GC–MS. The concentrations of products
were determined using cyclohexanone as internal standard.
2.6. Procedure for antibacterial studies
The nutrient agar medium was prepared by taking 1 l of dis-
tilled water in a conical flask followed by the addition of following
ingredients one by one (i) beef extract = 10.0 g, (ii) glucose = 1.0 g,
(iii) peptone = 10.0 g and (iv) sodium chloride = 5.0 g. The resulting
solution was stirred well to get a clear solution. The pH of the
solution was adjusted to 7.5. After that, 20.0 g of agar was added
2
.3. Synthesis of catalyst
The outline for the preparation of homogeneous and polymer
supported Cu(II) Schiff base complexes is given in Scheme 1.
◦
2
.3.1. Synthesis of 4-acetylpyridine thiosemicarbazone (L)
to the solution. The above said set up was sterilized at 120 C
The Schiff base ligand 4-acetylpyridine thiosemicarbazone was
for 15 min. A total of 20 ml of the sterilized medium was poured
into the sterilized Petri plates and allowed to solidify. The plates
were then inoculated with bacterial suspension of Escherichia coli
(E. coli) and Staphylococcus aureus (S. aureus) through spread plate
techniques. Various concentrations (50, 75, 100, 150 ppm) of each
compound were made. For each concentration separate Petri plate
with preinoculated bacteria was used. On each plate three cups
were made and 1 ml of each test compound and Streptomycin were
poured on each cup carefully. All the Petri plates were then incu-
prepared by mixing 4-acetylpyridine and thiosemicarbazide in a
stoichiometric ratio [26]. A mixture of 4-acetylpyridine (0.10 mol),
thiosemicarbazide (0.10 mol) and methanol (100 ml) was heated
under reflux for 2 h after cooling the precipitate was filtered off,
washed with methanol, crystallized from methanol to give white
crystals.
2
.3.2. Synthesis of the [Cu(L)(Cl) ] complex
2
◦
The copper complex [Cu(L)(Cl) ] was prepared by mixing
bated at 37 ± 2 C for 48 h. The diameter (mm) of inhibition zone
2
equal volumes (50 ml) of methanol solution of CuCl2 (0.170 g,
.0 mmol) with 4-acetylpyridine thiosemicarbazone solution
around each cups were measured separately against each concen-
tration and also against each test bacterium. Streptomycin solution
was also treated as reference plate.
1
(
2
◦
0.195 g, 1.0 mmol). The mixtures were refluxed at about 75 C for
–3 h on a water bath. On cooling immediately precipitates were
settle down and filtered off, washed several times by minimum
amount of hot methanol and dried under vacuum over anhydrous
CaCl2.
3. Results and discussion
3.1. Characterization of metal Schiff base complex
2
.3.3. Synthesis of polymer supported Cu(II) Schiff base catalyst
Due to insolubilities of the polymer supported Cu(II) Schiff base
complex in all common organic solvents, its structural investiga-
tions were limited to their physicochemical properties, chemical
analysis, SEM, TGA, IR and UV–vis spectral data. Table 1 provides the
data of elemental analysis, from which it is clear that the obtained
values of soluble metal complex are quite comparable with the
calculated values. Elemental analysis indicates that the complex is
monomeric formed by coordination of 1 mol of metal ion and 1 mol
PS-[Cu(L)(Cl)2]
It was readily prepared in two steps. The chloromethy-
lated polystyrene (2 g) was added to methanolic solution of
4
refluxed for 24 h. After cooling to room temperature, the light yel-
low coloured polymer beads were filtered, washed thoroughly with
methanol and dried in vacuum. The polymer supported Schiff base
-acetylpyridine thiosemicarbazone (1.07 g in 20 ml) and then

1
08
S.M. Islam et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 106–114
N
S
O
MeOH
H N
N
2
+
Reflux
H C
C
N
3
CH3
N
H
NH2
HN
C
P
CH Cl
2
H N
MeOH
2
S
(
L)
P
CH2
NH
CH3
C
NH
MeOH CuCl2
N
S
N
C
N
MeOH CuCl2
H C
C
N
3
P
CH2
NH
CH3
C
C
NH
Cl
Cl
HN
C
N
Cu
S
N
H N
S
Cu
2
Cl
Cl
a
b
Scheme 1. Synthesis of homogeneous (a) and polymer supported (b) Cu(II) Schiff base complex.
of Schiff base ligand. The metal content of the polymer supported
catalyst was estimated by atomic absorption spectrometer and was
found to be 2.34%. The chemical composition confirmed the purity
and stoichiometry of the neat and polymer supported complexes.
the SEM image of polymer supported Schiff base ligand (A) and
the immobilized copper complex (B) on functionalized polymer are
shown. The pure chloromethylated polystyrene bead has a smooth
surface (not shown). Introduction of ligands into polystyrene beads
through covalent bonding causes the light roughening of the top
layer of polymer beads. After metal loading on polymer anchored
ligand, changes in morphology of the ligand surface was observed
by SEM picture. As expected smooth and flat surface of polymer
bead shows slight roughening on complexation. Also presence of
copper metal along with sulfur and chlorine can be further proved
by energy dispersive spectroscopy analysis of X-rays (EDAX) (Fig. 2)
3.1.1. Scanning electron micrographs (SEMs) and energy
dispersive X-ray analyses (EDAX)
Field emission-scanning electron micrographs for single beads
of polymer supported Schiff base ligand and complex were
recorded to understand the morphological changes occurred on
the polystyrene beads at various stages of the synthesis. In Fig. 1
Table 1
Chemical composition and IR stretching frequencies of homogeneous and polymer supported metal Schiff base complexes.
Compound
C (%)
H (%)
N (%)
Cu (%)
ꢀC Na
␯M–Na
␯M–Sa
␯M–Cla
L: 4-acetylpyridine thiosemicarbazone
49.15 (49.48)
29.08 (29.22)
65.54
4.97 (5.15)
2.89 (3.04)
5.44
28.32 (28.86)
16.95 (17.04)
17.93
1635
19.12 (19.33) 1592
[CuL(Cl)2]
530
528
323
322
354
353
PS-L
PS-[CuL(Cl)2]
-
1639
1615
45.68
3.86
12.32
2.34
Calculated values are given in parentheses.
a
Infrared spectra measured as KBr pellets.

S.M. Islam et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 106–114
109
Fig. 1. FE SEM images of polymer supported Schiff base (A) and polymer supported Cu(II) Schiff base complex (B).
which suggests the formation of metal complex with the polymer
anchored ligand.
4-acetylpyridine thiosemicarbazone.
.1.3. TGA–DTA studies
3
Thermal stability of complex was investigated using TGA–DTA
3
.1.2. IR spectral study
A partial list of the IR spectral data of Schiff base and sup-
◦
at a heating rate of 10 C/min in air over a temperature range of
◦
3
0–600 C. TGA curves of polymer supported Schiff base ligand
ported complex along with their respective neat complex are
presented in Table 1. In 4-acetylpyridine thiosemicarbazone (L)
the infrared bands for the –NH and NH groups appeared at 3456
and Cu(II) complex are shown in Fig. 3. Polymer supported Schiff
◦
base ligand decomposed in the temperature range 370–380 C.
2
After complexation of copper metal on polymer supported lig-
−1
and 3170 cm , respectively. The bands due to ꢀ(C S) and ꢀ(C N)
and, thermal stability of the immobilized complex improved by
−1
groups appeared at 1110 and 1635 cm . On complexation the
bands respect to ꢀ(C S) and ꢀ(C N) are shifted towards lower fre-
quency. This suggests that the ligand acts as bidentate chelating
agent coordinated through ‘N’ (azomethine) and ‘S’ atom [27,28].
The pyridine ring vibrations are quite similar to those of the phenyl
ring which was assigned at 1598, 1572, 1479 and 766 cm [29,30];
these bands are existed in 4-acetylpyridine thiosemicarbazone cop-
per complex; this mean that the pyridine ring not participated in
◦
2
0–30 C. Polymer supported Cu(II) Schiff base complex decom-
◦
posed at 390–400 C. So from the thermal stability, it concludes
that polymer supported metal complex degraded at considerably
high temperature.
−
1
3
.1.4. Electronic spectral studies and magnetic moment
The electronic spectra of both 4-acetylpyridine thiosemicar-
bazone ligand (L) and its copper complex were measured in DMSO
and shown in Fig. 4. Within the UV spectrum of the ligand, two
absorption bands are observed at the range 202–260 nm which
assigned to ␲ → ␲* transition [35] and the second appeared at
the range 285–360 nm due to intraligand n → ␲* transition [36,37].
These absorptions also present in the spectra of the copper com-
plex but they are shifted. This shift in the spectra of the complex
attributed the complexation behavior of the ligand and supports
the coordination of the ligand to metallic ion. The electronic spec-
the complexation. In [Cu(L)(Cl) ] complex, new absorption bands
at 530 cm , 323 cm and 354 cm are assigned to ꢀ(Cu–N) [31],
2
−
1
−1
−1
ꢀ
(Cu–S) [32] and ꢀ(Cu–Cl) [33], respectively.
In the case of immobilized complex, the FT-IR spectra of poly-
mer supported Schiff base ligand and polymer supported complex
was studied. The intensity of the IR spectrum of polymer supported
metal complex was weak due to the low concentration of the com-
plex. The IR spectrum of supported complex is similar to that of
the free metal complex. In polymer supported Schiff base ligand,
−
1
trum of the [Cu(L)(Cl) ] complex exhibits band at 420 nm (sh.) that
the sharp C–Cl peak (due to –CH Cl groups) at 1264 cm in the
2
2
is assigned to d ↔ d transition [38]. The magnetic moment for cop-
per complex is found to be 1.73 BM. This value suggests square
planar geometry around copper(II) ion.
starting polymer was seen as a weak band or absent [34]. The band
for the –NH2 group in free Schiff base ligand was shifted to lower
frequency after attachment of chloromethylated polymer to the

1
10
S.M. Islam et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 106–114
Fig. 2. EDX images of polymer supported Schiff base (A) and polymer supported Cu(II) Schiff base complex (B).
0
0
0
0
0
0
0
0
0
0
.9
.8
.7
.6
.5
.4
.3
.2
.1
.0
Polymer supported Schiff base
[
PS-Cu(L)(Cl) 2 ]
b
a
200
300
400
500
600
100
200
300
400
0
500
600
Wavelength (nm)
Temperature ( C)
Fig. 4. Electronic spectra of 4-acetylpyridine thiosemicarbazone Schiff base (a) and
Cu(L)(Cl)2] complex (b).
Fig. 3. Thermogravimetric weight loss plots for polymer supported Schiff base and
polymer supported Cu(II) Schiff base complex.
[

S.M. Islam et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 106–114
111
Table 2
3.1.5. DRS-UV spectroscopy
Oxidation of styrene using different oxidants and solvents catalyzed by polymer
supported Cu(II) Schiff base complex.
The electronic spectrum of the polymer supported metal Schiff
base complex was recorded in diffuse reflectance spectrum mode
as MgCO /BaSO disc due to their solubility limitations in common
Entry
Solvent
Oxidant
Conversion (%)a
3
4
organic solvents. The diffuse reflectance spectra of Cu(II), complex
was almost identical before and after supporting on polymer, indi-
cating the complex maintains its geometry after supported. The
UV–vis spectrum (DRS) is shown in Fig. 5. For example, in the spec-
trum of polymer supported copper complex, a absorption band at
ranges 320–380 nm is observed when highly concentrated sam-
ple was used to record the spectrum and this is due to intraligand
n → ␲* transition. A band around 415–425 nm (weak) is due to
d–d transition in the complex and indicates a square-planar struc-
ture present on the polymer support. Based on the above results of
elemental analysis, IR, electronic spectra, magnetic moment mea-
surements and thermal analysis, the structure of the copper(II)
complex is suggested and is given in Scheme 1.
1
2
3
4
5
6
7
8
CH CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3OH
CH3CH2OH
CH3COCH3
NaOCl
NaIO4
H2O2
45
81
98
25
68
71
62
78
3
Tert-butylhydroperoxide
KHSO5
H2O2
H2O2
H2O2
Reaction condition: styrene (5 mmol), oxidant (10 mmol), solvent (10 ml), room
temperature and time (6 h).
a
Determined by GC.
3.2.2. The effect of solvent on the oxidation of styrene catalyzed
by PS-[Cu(L)(Cl)2]
The oxidation of styrene was studied in various solvents at room
temperature (Table 2). Methanol, ethanol, acetone and acetoni-
trile were used as solvent. Among them, acetonitrile was chosen
as the reaction medium, because highest conversion was obtained
in acetonitrile solvent. The higher catalytic activity in acetonitrile
3
.2. Catalytic activity
Since polymer supported metal systems exhibit catalytic activ-
ity in a wide range of the industrially important processes and
have been extensively studied, we decided to investigate the cat-
alytic activity of polymer supported Cu(II) Schiff base complex in
the oxidation of alkenes, alkanes and aromatic alcohols at room
is attributed to the polarity of the solvent and solubility of H O2 in
2
the solvent.
3
.2.3. Oxidation of alkenes with H O catalyzed by
2 2
temperature with H O2 as oxygen source.
2
PS-[Cu(L)(Cl)2]
The above optimized reaction conditions could be applied to
the oxidation reaction of other olefins by polymer supported Cu(II)
catalyst and the results are shown in Table 3. Reactions were per-
3
.2.1. The effect of oxidants on the oxidation of styrene catalyzed
by PS-[Cu(L)(Cl)2]
In the catalytic oxidation of alkenes the choice of oxygen donor
and solvent is importance. In this study, we investigated the abil-
formed at room temperature under air in CH CN containing alkene,
3
oxidant and catalyst. This catalyst efficiently converts olefins to
their corresponding allylic products. Styrene was converted to ben-
zaldehyde in high yield. In the oxidation of cyclohexene, allylic
products 2-cyclohexene-1-one and 2-cyclohexene-1-ol were pro-
duced. Substituted styrene produced selectively corresponding
aldehydes. Acetophenone was detected in the oxidation of ␣-
methyl styrene as major product. trans-Stilbene was also oxidized
by this heterogeneous catalyst in high yields. trans-Stilbene gives
benzaldehyde as major product with benzil. This catalytic system
shows a good activity in the case of limonene and ␣-pinene. In
the oxidation of ␣-pinene, the major products were verbenone and
ity of different oxidants, such as NaOCl, NaIO , H O , KHSO5 and
4
2
2
tert-butylhydroperoxide, in the oxidation of styrene catalyzed by
the heterogeneous Cu(II) complex. The results are summarized in
Table 2. When NaOCl, NaIO4 and tert-butylhydroperoxide were
used as the oxygen source in acetonitrile, only low conversion of
styrene was detected in the reaction mixture. The use of KHSO5
was not favored because of disadvantages such as using a buffered
media during the oxidation reactions. The results show that in the
presence of the catalyst, H O2 is the best oxygen source, because
of good oxidation conversions and high solubility in the CH CN.
2
3
Fig. 5. DRS-UV–vis absorption spectra of polymer supported Cu(II) Schiff base complex.

1
12
S.M. Islam et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 106–114
Table 3
Oxidation of alkenes with 30% H2O2 catalyzed by [Cu(L)(Cl)2] and PS-[Cu(L)(Cl)2] complex.
a
Product selectivity (%)a
Entry
Olefins
Conversion (%) /time (h)
[
PS-Cu(L)(Cl)2]
[Cu(L)(Cl)2]
88/6
([PS-Cu(L)(Cl)2]/[Cu(L)(Cl)2])
1
2
Styrene
98/6
82/6
Benzaldehyde (92/83)
Styrene oxide (8/17)
2-Cyclohexene-1-one (72/65)
Cyclohexene
74/6
2-Cyclohexene-1-ol (21/21)
Cyclohexene epoxide (7/14)
3
4
5
6
␣-Methyl styrene
␣-Pinene
Limonene
88/6
55/6
56/6
76/6
79/6
48/6
47/6
68/6
Acetophenone (100/91)
Verbenol (32/28), verbenone (55/47), ␣-pinene oxide (13/25)
Carvenol (25/21), Carvenone (67/61), limonene oxide (1,2) (8/18)
Benzaldehyde (78/69)
trans-Stilbene
Benzil (16/20), trans-stilbene oxide (6/11)
4-Chloro benzaldehyde (88/78), 4-Chlorostyrene epoxide (12/22)
4-Methyl benzaldehyde (86/72), 4-methylstyrene epoxide (14/28)
4-Nitro benzaldehyde (84/66)
7
8
9
4-Chlorostyrene
4-Methylstyrene
4-Nitrostyrene
83/6
79/6
71/6
77/6
68/6
67/6
4-Nitro styrene oxide (16/34)
1
0
1-Hexene
47/6
39/6
2-Hexanone (98/84)
Reaction condition: alkene (5 mmol), 30% H2O2 (10 mmol), CH3CN (10 ml), room temperature.
a
Determined by GC.
verbenol. Limonene selectively oxidized to Carvone and Carveol
with other coproducts. Blank experiment in the presence of oxidant
under the same experimental conditions in the absence of cata-
lyst was also investigated in the oxidation of styrene. The obtained
diameter of the zone is measured to the nearest millimeter (mm).
The standard error for each assay is presented in the parenthesis.
From the results (Table 6), it has been observed that copper com-
plex showed slight better activity than the free ligand. This can be
explained by Tweedy’s chelation theory [39]. This copper complex
possesses activity and its effectiveness is greater than the stan-
dard drug Streptomycin. The inhibition activity of the compounds
increases with increase in the concentration of the solution.
results showed that H O2 has poor ability to oxidize the styrene.
2
3
.2.4. Oxidation of alkanes with H O2 catalyzed by
2
PS-[Cu(L)(Cl)2]
The catalytic oxidation of alkanes with 30% H O2 under mild
2
reaction conditions is especially an interesting topic, because direct
functionalization of inactivated C–H bonds in saturated hydro-
carbons usually requires drastic reaction conditions such as high
pressure and high temperature. As shown in Table 4, we have found
that the supported copper catalyst is an efficient catalyst for the oxi-
4. Influence of support
In order to demonstrate the effect of supporting on the catalytic
activity of homogeneous copper complex in the oxidation of alkene,
alkane and aromatic alcohol with hydrogen peroxide, we repeated
all reactions with the same reaction conditions and [Cu(L)(Cl)2]
catalyst, substrate, H O2 in CH CN. The obtained results are sum-
dation of saturated hydrocarbons with H O2 at room temperature.
2
Ethylbenzene and propylbenzene only produced the correspond-
ing ketones. Toluene selectively converted to benzaldehyde. In the
case of adamantane, the 1-adamantanol and 2-adamantanone were
produced in the reaction mixture.
2
3
marized in Tables 3–5. The obtained results showed that the
production of by-products in the heterogenized system decreased
in comparison with the homogeneous system in the alkene, alkane
and alcohol oxidation. Selectivity and stability of the heterogeneous
catalyst are better than the homogeneous catalyst. On the other
hand, the heterogeneous catalyst can be recovered several times
without loss of its activity. The most disadvantageous of homo-
geneous complex is the catalysts degradation in the presence of
oxidant, while, the heterogenized complex can be reused several
times without significant loss of its activity.
3
.2.5. Oxidation of aromatic alcohols with H O2 catalyzed by
2
PS-[Cu(L)(Cl)2]
The selective oxidation of alcohols into their correspond-
ing carbonyl compounds is one of the fundamental reactions in
organic chemistry. Selective oxidation of aromatic alcohols to
aldehydes was investigated with H O2 under mild reaction condi-
2
tions by polymer supported copper catalyst. Experimental results
are shown in Table 5. Benzyl alcohol selectively converted to
benzaldehyde. Substituted benzyl alcohols are also oxidized to cor-
responding aldehydes. In all above cases trace amount of acids
were observed. On the other hand, 1-phenyl ethanol selectively
converted to acetophenone on oxidation with this catalyst.
Many efficient heterogeneous catalysts have been reported
for the oxidation of alkenes, alkanes and aromatic alcohols with
30% H2O2 [23,40–42]. Comparison of this catalyst with previously
reported systems reveals that the present system gives better con-
version than other catalyst.
5. Stability and recycling of catalyst
3.3. Antimicrobial studies
To check the leaching of metal into the solution during the reac-
The Schiff base ligand and copper(II) complex were screened
tion, styrene oxidation was carried out under the optimum reaction
conditions. The reaction was stopped after the reaction proceeds
3 h. The separated filtrate was allowed to react for another 3 h under
the same reaction condition, but no further increment in conver-
sion was observed in gas chromatographic analyses. The UV–vis
spectroscopy was also used to determine the stability of this het-
erogeneous catalyst. The UV–vis spectra of the reaction solution,
at the first run, did not show any absorption peaks characteristic
of copper metal, indicating that the leaching of metal did not take
place during the course of the oxidation reaction. These results sug-
in vitro for their microbial activity against two bacterial species
using the well diffusion method. These compounds were found
to exhibit considerable activity against Gram +ve (S. aureus) and
Gram −ve (E. coli). The test solutions were prepared in N,N-
dimethylformamide and the results are summarized in Table 6.
Blank experiment with CuCl was carried out under identical exper-
2
imental conditions and showed the inability of the complex to
inhibit the bacterial growth. The effectiveness of an antimicro-
bial agent in sensitivity is based on the zones of inhibition. The

S.M. Islam et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 106–114
113
Table 4
Oxidation of alkanes with 30% H2O2 catalyzed by [Cu(L)(Cl)2] and PS-[Cu(L)(Cl)2] complex.
a
Product selectivity (%)a
Entry
Alkane
Conversion (%) /time (h)
[PS-Cu(L)(Cl)2]
[Cu(L)(Cl)2]
([PS-Cu(L)(Cl)2]/[Cu(L)(Cl)2])
1
2
3
4
Ethyl benzene
Propylbenzene
Toluene
76/8
61/8
41/8
52/8
70/8
56/8
35/8
44/8
Acetophenone (100/92)
Ethylphenyl ketone (100/89)
Benzaldehyde (96/81)
Adamantane
1-Adamantanol (76/61)
2-Adamantanone (24/39)
Reaction condition: alkane (5 mmol), 30% H2O2 (10 mmol), CH3CN (10 ml), room temperature.
a
Determined by GC.
Table 5
Oxidation of aromatic alcohols with 30% H2O2 catalyzed by [Cu(L)(Cl)2] and PS-[Cu(L)(Cl)2] complex.
a
Product Selectivity (%)b
Entry
Aromatic alcohol
Conversion (%) /time (h)
[
PS-Cu(L)(Cl)2]
[Cu(L)(Cl)2]
89/6
([PS-Cu(L)(Cl)2]/[Cu(L)(Cl)2])
1
2
3
4
Benzyl alcohol
96/6
81/6
84/6
77/6
Benzaldehyde (97/86)
Benzoic acid (3/14)
4-Methyl benzaldehyde (90/74)
4-methylbenzyl alcohol
4-nitrobenzyl alcohol
1-phenyl ethanol
77/6
76/6
69/6
4
-Methyl benzoic acid (10/26)
4-Nitro benzaldehyde (88/69)
-Nitro benzoic acid (12/31)
Acetophenone (100/89)
4
Reaction condition: aromatic alcohol (5 mmol), 30% H2O2 (10 mmol), CH3CN (10 ml), room temperature.
a
Determined by GC.
Table 6
Antibacterial activities of copper(II) Schiff base complex.
Compound
Diameter of inhibition zone (mm)
E. coli (Gram −ve)
S. aureus (Gram +ve)
50 ppm
75 ppm
100 ppm
150 ppm
50 ppm
75 ppm
100 ppm
150 ppm
L
Cu(L)(Cl)2]
Streptomycin
22.0(± 0.35 2) 2.0 (± 0.58)
24.0(± 0.58 2) 4.0 (± 0.80)
11.3 (± 1.4)12.0 (± 0.8)
24.0 (± 0.65)
26.0 (± 0.77)
13.0 (± 0.12)
24.0 (± 0.24)
26.0 (± 0.54)
13.5 (± 0.8)
20.0 (± 1.65)
22.0 (± 0.40)
11.9 (± 0.5)
22.0 (± 0.58)
24.0 (± 0.54)
12.0 (± 0.12)
22.0 (± 0.38)
24.0 (± 0.51)
12.5 (± 0.12)
26.0 (± 0.80)
26.0 (± 0.65)
13.0 (± 0.50)
[
no reduction in the amount of transition metal ions. The results
indicate that this complex is stable to be recycled for the oxidation
reaction without much loss in activity.
The recyclability of the catalyst is important for the catalysis
reaction. The rerecycling experiment also confirms the heteroge-
nization of complex into polymer. To investigate the reusability of
polymer supported copper Schiff base complex, this catalyst was
separated by filtration after the first catalytic reaction finished. For
the next reaction cycle, we recover the catalyst by washing with
solvent and dried under vacuum then subjected to the second run
under the same reaction conditions. The catalytic run was repeated
with further addition of substrates in appropriate amount under
optimum reaction conditions and the nature and yield of the final
products were comparable to that of the original one. Fig. 6 illus-
trates the reusability of the catalyst for the oxidation of styrene,
ethylbenzene and benzyl alcohol during five recycles. It was found
that the catalytic activity did not change significantly after five
repeat runs.
6. Conclusions
In summary, we have successfully synthesized polymer
Fig. 6. Recycling efficiency for the oxidation of styrene, ethyl benzene and benzyl
alcohol with [PS-Cu(L)(Cl)2] complex. Reaction condition: [substrate] = 5 mmol, [30%
H2O2] = 10 mmol, catalyst (0.05 g), CH3CN (10 ml), room temperature, time (6 h).
anchored Cu(II) Schiff base complex. The developed heterogeneous
catalyst shows high catalytic activity in oxidation of alkene, alkane
and aromatic alcohol. The results show that the immobilized cat-
alyst is slightly more active than its homogeneous analogue. The
heterogeneous and homogeneous complexes produce selectively
allylic oxidation products for alkenes, alcohols and ketones from
alkanes and aldehydes from aromatic alcohols. Another important
gest that this catalyst was heterogeneous in nature. IR spectrum of
the recycled catalyst was quite similar to that of fresh sample indi-
cating the heterogeneous nature of this complex. The analysis of
the recovered catalyst by atomic absorption spectroscopy showed

1
14
S.M. Islam et al. / Journal of Molecular Catalysis A: Chemical 336 (2011) 106–114
factor is the stability and recyclability of the catalyst under the
reaction conditions used. This heterogeneous catalyst shows no sig-
nificant 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 proce-
dure was effective as observed from UV–vis spectroscopy. Leaching
test indicates that the catalytic reaction is mainly heterogeneous in
nature. The reusability of this catalyst is high and can be reused five
times without significant decrease in its initial activity. We hope
that the present catalytic systems would be useful to synthesize
industrially important organic compounds.
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