Heterogeneous green catalyst for oxidation of cyclohexene and cyclooctene with hydrogen peroxide in the presence of host (nanocavity of Y-zeolite)/guest (N4-Cu(II) Schiff base complex) nanocomposite material

Article abstract of DOI:10.1002/cjoc.201180414

Copper(II) complex of a Schiff base ligand derived from pyrrolcarbaldehyde and o-phenylenediamine (H₂L) has been synthesized and encapsulated in Y-zeolite matrix. The hybrid material has been characterized by elemental analysis, IR and UV-Vis s

Full text of DOI:10.1002/cjoc.201180414

FULL PAPER
Heterogeneous Green Catalyst for Oxidation of Cyclohexene
and Cyclooctene with Hydrogen Peroxide in the Presence of
Host (Nanocavity of Y-zeolite)/Guest (N4-Cu(II) Schiff Base
Complex) Nanocomposite Material
Lashanizadegan, Maryama
Rayati, Saeed*,b
Dejparvar Derakhshan, Zeinaba
a Department of Chemistry, Faculty of Science, Alzahra University Vanak, Tehran, P. O. 1993891176, Iran
b Department of Chemistry, K. N. Toosi University of Technology, Tehran P. O. Box 16315-1618, Iran
Copper(II) complex of a Schiff base ligand derived from pyrrolcarbaldehyde and o-phenylenediamine (H2L) has
been synthesized and encapsulated in Y-zeolite matrix. The hybrid material has been characterized by elemental
analysis, IR and UV-Vis spectroscopic studies as well as X-ray diffraction (XRD) pattern. The encapsulated cop-
per(II) catalyst is an active catalyst for the oxidation of cyclooctene and cyclohexene using H2O2 as oxidant. Under
the optimized reaction conditions 81% conversion of cyclohexene with 65% selectivity for 2-cyclohexenone forma-
tion and 87% conversion of cyclooctene with 46% selectivity for epoxide formation were obtained.
Keywords Schiff base, copper, zeolite, hydrogen peroxide, catalyst
Introduction
toward oxidative degradation.
In this paper, we report the synthesis and characteri-
zation of copper complex of N4 Schiff base ligand en-
capsulated within the nano pores of Y-zeolite and its
catalytic efficiency in oxidation of cyclohexene and
cyclooctene has been investigated.
Schiff base transition metal complexes immobilized
in zeolitic cavity are one of the subjects of current ca-
talysis research.1-5 Immobilization of suitable molecular
species inside zeolite cavities induced a new type of
functional materials.6-9 These nanocomposite materials
have been suggested as heterogeneous redox industrial
catalysts,10 photoredox,11 photo catalysis12 and photo-
chemical storage of light energy.13 Since zeolite replaces
the protein mantle of the enzyme in the model com-
pound, zeolite encapsulated metal complexes (ZEMC)
have been suggested as a model compound for enzyme
mimicking and often referred to as “zeozymes”.14
Therefore, attempts have been made to encapsulate
copper complexes in zeolite matrix to mimic this type of
enzyme. Recently, organic dye molecules have been
immobilized in a zeolite or a molecular sieve to prepare
sensors.15,16 On the other hand, copper(II) ions act as the
active center in many metalloenzymes,17-19 such as ga-
lactose oxidase, and the coordination sphere around
copper center in the titled N4-Cu(II) Schiff base com-
plex, mimics the coordination environment of the cop-
per(II) ion of galactose oxidase.
Experimental
General
Infrared spectra were recorded as KBr pellets using
Bruker Tensor 27 spectrometer. The visible spectra were
determined using a Perkin Elmer, Lambda 35 UV-Vis
Spectrometer. 1H NMR spectra were obtained on a
Bruker Avance 300 MHz spectrometer using TMS as
internal standard. The reaction products of oxidation
were determined and analyzed by Agilent Series 6890.
X-ray diffractograms of the catalyst were recorded using
XRD, Seifect, 3003 PTS diffractometer with a Cu-Kα
target. The metal contents were measured by using
PU900 Philips atomic absorption spectrophotometer.
Elemental analysis was performed using a CHN Perkin
Elmer 2400 Sereis II.
Analytical reagents grade cyclohexene, cyclooctene,
o-phenylenediamine, pyrrolcarbaldehyde, tert-butyl-
hydroperoxide (solution 80% in di-tert-butylperoxide)
and hydrogen peroxide were procured from Merck.
Other reagents and solvents used were AR grade.
NaY-zeolite was procured from Spag, Iran.
Development of non-heme transition metal catalysts
for the oxidation of organic substrates with H2O2 is of
interest especially during the past two decades.20-24
Therefore, immobilization of the catalysts on the solid
supports improves their recyclability of these expense
catalysts and also enhances the stability of the catalysts
*
E-mail: rayati@kntu.ac.ir
Received April 22, 2011; revised May 26, 2011; accepted July 26, 2011.
Chin. J. Chem. 2011, 29, 2439— 2444
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2439

Lashanizadegan, Rayati & Dejparvar Derakhshan
FULL PAPER
Synthesis of ligand (H2L)
migration of copper(II) ions from the vicinity of the su-
percage.27
To
a stirred ethanolic solution (10 mL) of
o-phenylenediamine (0.6 g, 5.5 mmol), pyrrolcarbalde-
hyde (1 g, 11 mmol) in 5 mL ethanol was added. The
reaction mixture was stirred and heated to reflux for 4 h.
The product was kept at ambient temperature, and the
red shiny crystals were filtered, washed with cold etha-
nol and dried. The ligand (Scheme 1, II) was recrystal-
lized from ethanol to give pure product with 67% yield
and m.p. 168 ˚C. 1H NMR (DMSO-d6, 300 MHz) δ:
6.01—7.27 (m, 10H, ArH), 7.77 (s, 2H, HC＝N).
Immobilization of CuL in Cu-NaY
An amount of 1.0 g Cu-NaY and acetonitrile solution
of 2.5 g H2L were mixed in a round bottom flask. The
reaction mixture was heated at 100 ℃ for 5 h in an oil
bath with constant stirring. The resulting material was
taken out and extracted with acetonitrile using Soxhlet
extractor till the complex was free from unreacted
ligand. The non-complexed metal ions present in the
zeolite were removed by exchanging with aqueous 0.01
mol/L NaCl solution (Scheme 1). The resulting solid
was finally washed with hot distilled water till no pre-
cipitation of AgCl was observed on reacting filtrate with
AgNO3 solution. This was then dried at 150 ℃ for sev-
eral hours till constant weight was achieved.
Preparation of copper(II) complex (CuL)
The ligand, (H2L) (0.09 g, 0.3 mmol) was dissolved
in 5 mL of ethanol. An ethanolic solution of
Cu(CH3COO)2•H2O (0.06 g, 0.3 mmol) was added to
above solution and the reaction mixture was refluxed for
3 h. After cooling down to room temperature for over-
night, a reddish precipitate of copper complex was fil-
tered off, washed with ethanol and dried in vacuum over
calcium chloride to give 90% yield and decomposition
point 298 ℃.25
Homogeneous oxidation of cyclohexene
To a solution of cyclohexene (10 mmol) and neat
copper(II) complex (0.3 mmol) in CH3CN (10 mL),
aqueous 30% H2O2 (25 mmol) was added. The resulting
mixture was refluxed and the products were collected at
different time intervals and the crude analyzed by GC
and GC-MS. The concentration of products was deter-
mined using benzyl chroride as internal standard.
Incorporation of copper(II) in NaY (metal ex-
changed Y-zeolite)
4 g Na-Y zeolite was suspended in 100 mL distilled
water which contained copper(II) nitrate (4 mmol). The
mixture was then stirrer for 24 h. The solid was filtered
and washed with deionized water and dried at room
temperature to give a light blue powder of Cu-NaY
(Scheme 1, I).26 Calcination of the prepared cop-
per(II)-incorporated zeolite was avoided to arrest the
Heterogeneous oxidation of cyclohexene
A mixture of 0.05 g catalyst, 10 mL of CH3CN and
10 mmol cyclohexene was stirred in a 50 mL
round-bottom flask equipped with a condenser and 25
mmol of H2O2 (30% in water) was added. The resulting
Scheme 1
2440
www.cjc.wiley-vch.de
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2011, 29, 2439— 2444

Heterogeneous Green Catalyst for Oxidation of Cyclohexene and Cyclooctene
mixture was then refluxed with continuous stirring in an
oil bath. After filtration and washing with solvent, the
filtrate was concentrated and then subjected to GC
analysis.
sulated complex may be due to stronger ligand field
after immobilization of the copper complex in the zeo-
lite cavity.33
Table 2 IR and electronic spectral data of the ligand, pure and
encapsulated complexes
Results and discussion
IR ν/cm－
λ/nm, (lg ε)
1
Compound
H2L
Characterization of catalyst
3150, 1617, 1414, 738 360 (4.6), 407 (4.2)
Encapsulation of CuL complex in nano-cavities of
zeolite was carried out by a “ship-in-bottle” synthesis
technique.28 The ligand slowly enters into the zeolite
pores due to their flexible nature and forms complex
with Cu. The resulting complex is being physically
trapped in the supercage as well as on the surface of the
Y zeolite. Since the complex is neutral, weak forces
such as van der Waals interactions or electrostatic at-
tractions are operative here to hold the complex in the
cavity of the zeolite. It seems that unreacted ligand was
effectively removed from the zeolite cavities via Soxhlet
extraction. A sharp color change (red-gray) of complex
was observed on being immobilized in Cu-NaY, such
phenomena were rarely observed when metal complexes
are encapsulated in zeolites.14,29-31 The percentages of
metal contents were determined before and after encap-
sulation (Table 1). The chemical analyses of the sample
reveal the presence of organic matter with a C/N ratio
roughly similar to that for neat complex.
CuL
1597, 1399, 739
1583, 1403, 1016,
725, 457
340 (4.4), 437 (3.4), 501 (sh)
CuL-NaY
312, 355 (sh), 464 (sh)
X-ray powder diffraction studies
The X-ray powder diffraction patterns of Na-Y,
Cu-NaY and encapsulated copper complex was recorded
at 2θ values between 11° and 80°. The XRD patterns of
representative copper exchanged zeolite and zeolite en-
capsulated copper complex along with Na-Y are pre-
sented in Figure 1. The diffraction patterns of encapsu-
lated copper complex, Cu-Y and Na-Y are essentially
similar except a slight change in the intensity of the
band in encapsulated complex. These observations in-
dicate that the framework of the zeolite has not structur-
ally changed during encapsulation.
Table 1 Elemental analysis for the neat complex, CuL-NaY and
Cu-NaY
Found (calc.)
Compound
C%
H%
N%
C/N Cu%
Cu-NaY
CuL
—
—
—
—
6.7
19.4
3.8
59.13
(59.22)
2.37
3.65
(3.71)
2.31
17.45
(17.29)
0.78
3.38
(3.42)
3.04
CuL-NaY
Figure 1 XRD patterns of Na-Y (a), Cu-NaY (b) and CuL-NaY
(c).
Spectral studies
The IR spectrum of the ligand (H2L) exhibits the
Catalytic activity study
sharp band at 1617 cm－ due to the ν(C＝N) (azome-
1
Oxidation of cyclohexene The oxidation of cyclo-
hexene was carried out by H2O2 and tert-butylhydroper-
oxide (TBHP) using CuL-NaY as catalyst and two
oxidation products, 2-cyclohexene-1-ol and 2-cyclo-
hexenone along with minor amounts of other products
were obtained.
In order to obtain suitable reaction conditions to
achieve the maximum oxidation of cyclohexene, the
effect of different reaction parameters, such as the kind
of oxidant, amount of oxidant and catalyst, temperature
of the reaction mixture and solvent have been studied in
details using CuL-NaY as a representative catalyst.
The effect of the kind of oxidant on the oxidation of
cyclohexene has been studied and the results are illus-
trated in Figure 2. Two different oxidants (H2O2 and
tert-butylhydroperoxide) were considered while keeping
the other parameters fixed as cyclohexene (10 mmol),
thine), free [CuL] showed a sharp band at lower fre-
quency in 1597 cm－ 1 attributed to the azomethine group
which indicated its coordination to copper. The IR spec-
tra of hybrid material [CuL]-NaY showed a weak band
at 1583 cm－ due to their low concentration in zeolite
1
matrix. Comparison of the spectra of Cu-NaY,
[CuL]-NaY with the ligand provides evidence for the
coordinating mode of ligand in catalyst. IR spectra of
the hybrid material showed an intense band at ca. 1016
cm －
attributable to the asymmetric stretching of
1
Al-O-Si chain of zeolite. The symmetric stretching and
bending frequency bands of Al-O-Si framework of zeo-
－
1
lite appear at ca. 725 and 457 cm , respectively.32
Electronic spectral studies of H2L, CuL and
CuL-NaY have been studied. Their spectral data are also
presented in Table 2. The blue shift observed for encap-
Chin. J. Chem. 2011, 29, 2439— 2444
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
2441

Lashanizadegan, Rayati & Dejparvar Derakhshan
FULL PAPER
catalyst (0.05 g) in 20 mL acetonitrile and the reaction
was carried out at 80 ℃. The higher conversion (87%)
and selectivity (65%) for 2-cyclohexenone formation
was obtained using H2O2.
Figure 4 Effect of solvent on the oxidation of cyclohexene.
Figure 2 Effect of the kind of oxidant on the oxidation of
cyclohexene.
The effect of amount of catalyst on the rate of reac-
tion is shown in Figure 3. Four different amounts of
catalyst (0.03, 0.04, 0.05 and 0.06 g) were considered
and an amount of 0.05 g is sufficient to obtain almost
comparable results for the fixed amount of oxidant and
substrate in acetonitrile.
Figure 5 Effect of H2O2 concentration (H2O2∶ cyclohexene) on
cyclohexene oxidation.
capsulated in Y-zeolite and CuL catalyst shows that the
neat complex gave lower conversion of cyclohexene
than their corresponding CuL-NaY (Figure 6). Homo-
geneous catalyst is more prone to deactivation because
of two factors, the formation of Cu-O-Cu species, and
the oxidative degradation of metal complex. Encapsula-
tion of the catalyst in the walls of the nanopores of the
zeolite can improve the stability of the catalyst via steric
effects and also can tune the selectivity of the reaction.
Selectivity of the reaction for 2-cyclohexenone forma-
tion was enhanced for CuL-NaY (Figure 7).
Figure 3 Effect of amount of catalyst per unit weight of cyclo-
hexene.
In order to obtain the best reaction solvent, three
different solvents viz. acetonitrile, ethanol and
chloroform were used to see their effect on the reaction
rate.
Figure
4
shows the percentage cyclohexene
conversion for different solvents. Solvents have great
influence on the reaction rates through competitive
sorption/adsorption phenomenon in the super cages of
zeolite. Polarity, hydrophilicity and size of the solvent
molecule may also play some roles on the reaction
rate.34 Catalytic activity decreases in the order
acetonitrile＞ chloroform＞ ethanol.
The influence of concentration of the oxidant, on
cyclohexene conversion is given in Figure 5. The results
indicate that maximum conversion was obtained at 1∶
2.5 molar ratio of cyclohexene to hydrogen peroxide.
Comparing between copper Schiff base complex en-
Figure 6 Effect of encapsulation of CuL in Y-zeolite on the
oxidation of cyclohexene.
Oxidation of cyclooctene The oxidation of
cyclooctene was carried out by H2O2 and tert-butyl-
hydroperoxide (TBHP) (Figure 8) using CuL-NaY as
catalyst and the major oxidation product was cyclooc-
tene oxide with minor amount of alcohol product (Fig-
ure 9). Two different oxidants (H2O2 and TBHP) were
used for oxidation of cyclooctene and the higher con-
version and selectivity for epoxide formation was
2442
www.cjc.wiley-vch.de
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2011, 29, 2439— 2444

Heterogeneous Green Catalyst for Oxidation of Cyclohexene and Cyclooctene
Table 3 Comparison of the activity of Cu(II) complexes in the
oxidation of cyclohexene
Olefin
Cu(II) complex
Conversion/% Ref. Oxidant
Cyclohexene
Cyclohexene
[Cu(sal-dach)]-Y
PS-[Cu(ligand)n]
18.1
51.0
40.1
41.4
60.1
56.9
35 H2O2
38 H2O2
33 H2O2
Cyclohexene [Cu(H4C6N6S2)]–NaY
Cyclohexene [Cu(sal-1,3-phen)]-NaY
Cyclohexene[Cu(Me2salpnMe2)]-Al2O3
Cyclohexene [Cu(salpnMe2)]-Al2O3
2
TBHP
37 TBHP
38 TBHP
Figure7 Oxidation products distribution in acetonitrile with
CuL-NaY.
This
H2O2
study
Cyclohexene
CuL-NaY
81.0
hexenyl radical that reacts with LCuIII-OH to yield
2-cyclohexene-1-ol. Then 2-cyclohexene-1-ol reacts
with another LCuIII-OH to yield 2-cyclohexenone
(Scheme 2).
Scheme 2
Figure 8 Effect of the kind of oxidant on the oxidation of
cyclooctene.
Conclusions
CuL complex has been encapsulated in the super
cages of Y-zeolite by flexible ligand method and its en-
capsulation has been ensured by different studies. This
complex has potential catalytic activity for the oxidation
of cyclohexene and cyclooctene with hydrogen peroxide
as oxygen source. Reaction conditions have been opti-
mized considering different parameters to get maximum
conversion. Under the optimized reaction conditions,
CuL-NaY gave 81% conversion of cyclohexene with
two major oxidation products, 2-cyclohexene-1-ol and
2-cyclohexenone. Also, 87% conversion was obtained
using CuL-NaY as catalyst with cyclooctene oxide as
major product. The catalytic activity of neat complex
using similar molar concentration as that used for en-
capsulated complex under above reaction conditions has
also been tested for comparison. It has been observed
that the corresponding neat complex has shown lower
catalytic activity than encapsulated one.
Figure 9 Oxidation products distribution in oxidation of
cyclooctene in the presence of CuL-NaY.
achieved with hydrogen peroxide (Figure 8).
The results of the oxidation of cyclohexene, in the
presence of various Cu(II) complexes (encapsulated in
Zeolite-Y or supported on alumina or polymer-anchored
catalyst) with H2O2 or TBHP are summarized in Table 3.
The conversion of cyclohexene oxidation by the
CuL-NaY-H2O2 system is better and mostly comparable
with the results of the oxidation by other catalytic sys-
tems.
Proposed mechanism
In the proposed reaction mechanism, hydrogen per-
oxide will be activated by coordination to CuL-NaY and
generate hydroxyl radical and LCuIII-OH. The formed
hydroxyl radical reacts with cyclohexene to yield cyclo-
Acknowledgments
The authors would appreciate the University of Al-
zahra and K. N. Toosi University of Technology for fi-
Chin. J. Chem. 2011, 29, 2439— 2444
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
2443

Lashanizadegan, Rayati & Dejparvar Derakhshan
FULL PAPER
nancial support
20 England, J.; Britovsek, G. J. P.; Rabadia, N.; White, A. J. P.
Inorg. Chem. 2007, 46, 3752.
21 Kryatov, S. V.; Rybak-Akimova, E. V.; Schindler, S. Chem.
Rev. 2005, 105, 2175.
22 Payeras, A. M. I.; Ho, R. Y. N.; Fujita, M.; Que, L. Chem.
Eur. J. 2004, 10, 4944.
23 Roelfes, G.; Lubben, M.; Hage, R.; Que, L.; Feringa, B. L.
Chem. Eur. J. 2000, 6, 2152.
24 Salavati-Niasari, M.; Zamani, E.; Bazarganipour, M. Appl.
Clay Sci. 2007, 38, 9.
25 Weber, J. H. Inorg. Chem. 1967, 6, 258.
26 Koner, S. Chem. Commun. 1998, 593.
27 Delabie, A.; Pierlook, K.; Groothaert, M. H.; Schoonheydt,
R. A.; Vanquickenborne, L. G. Eur. J. Inorg. Chem. 2002,
515.
28 Bedioui, F. Coord. Chem. Rev. 1995, 144, 39.
29 Bakus, Jr. K.; Eisa, M.; Levedo, R. J. Am. Chem. Soc. 1995,
117, 10753.
30 Vankelecom, I. F. J.; Tas, D.; Parton, R. F.; Van de Vyver, V.;
Jacobs, P. A. Angew. Chem., Int. Edi. Engl. 1996, 35, 1346.
31 Deshpande, S.; Srinivas, D.; Ratnasamy, P. J. Catal. 1999,
188, 261.
32 Barrer, R. M.; Hydrothermal Chemistry of Zeolite, Aca-
demic Press, New York, 1982.
33 Salavati-Niasari, M. J. Mol. Catal. A: Chem. 2008, 283,
120.
34 Raja, R.; Ratnasamy, P. Catal. Lett. 1997, 48, 1.
35 Maurya, M. R.; Chandrakar, A. K.; Chand, S. J. Mol. Catal.
A: Chem. 1997, 270, 225.
36 Maurya, M. R.; Arya, A.; Adão, P.; Pessoa, J. C. Appl. Catal.
A: Gen. 2008, 351, 239.
37 Salavati-Niasari, M.; Salemi, P.; Davar, F. J. Mol. Catal. A:
Chem. 2005, 238, 215.
References
1
2
3
4
5
Maurya, R. M.; Chanadrakar, A. K.; Chand, S. J. Mol. Catal.
A: Chem. 2007, 274, 192.
Salavati-Niasari, M.; Zamani, E.; Ganjali, M. R.; Norouzi, P.
J. Mol. Catal. A: Chem. 2007, 261, 196.
Dutta, B.; Jana, S.; Bera, R.; Saha, P. K.; Koner, S. Appl.
Catal. A: Gen. 2007 318, 89.
Saha, P. K.; Dutta, B.; Jana, S.; Bera, R.; Saha, S.; Okamoto,
K.; Koner, S. Polyhedron 2007, 26, 563.
Salavati-Niasari, M.; Shaterian, M.; Ganjali, M. R.; Norouzi,
P. J. Mol. Catal. A: Gen. 2007, 261, 147.
Salavati-Niasari, M. Polyhedron 2008, 27, 3207.
Meng, X.; Namaz, F.; Xiaom, F. S. Nano Today 2009, 4,
292.
6
7
8
9
Wei, R.; Guo, M.; Wang, J. Chin. J. Chem. Eng. 2009, 17,
58.
Zhang, Y. J.; Zhang, L.; Li, S. Int. J. Hydrogen Energy 2010,
5, 438.
10 McKittrick, M. W.; Jones, C. W. J. Am. Chem. Soc. 2004,
126, 3052.
11 Maruszewski, K.; Kincaid, R. Inorg. Chem. 1995, 34, 2002.
12 Subba Rao, K. V.; Srinivas, B.; Subrahmangan, M. Catal.
Lett. 1993, 90, 95.
13 Sykora, M.; Kincaid, J. R. Nature 1997, 387,162.
14 Herron, N. Inorg. Chem. 1986, 25, 4714.
15 Bein, T. Studies Surface Sci. Catal. 2007, 170, 41.
16 Kecht, J.; Mintovam, S.; Bein, T. Microporous Mesoporous
Mater. 2008, 116, 258.
17 Kyritsis, P.; Khozhuma, T.; Sykes, A. G. Biochim. Biophys.
Acta 1996, 1295, 245.
18 Wright, C.; Skyes, A. G. J. Org. Biochem. 2001, 85, 237.
19 Messerschmidt, A. Comprehensive Natural Products II, El-
sevier, Amsterdam, 2010, pp. 489— 545.
38 Salavati-Niasari, M.; Hassani-Kabutarkhani, M.; Davar, F.
Catal. Commun. 2006, 7, 955.
(E1104223 Sun, H.)
2444
www.cjc.wiley-vch.de
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2011, 29, 2439— 2444