Catalytic activity and electrochemical properties of Cu(II)-Schiff base complex encapsulated in the nanocavities of zeolite-Y for oxidation of olefins and sulfides

Article abstract of DOI:10.1080/00958972.2017.1369052

Copper(II) complex of a Schiff base ligand (H₂L) was synthesized, characterized, and encapsulated in the cavities of zeolite-Y by a fixed ligand method. The zeolite encapsulated metal complex (CuL-Y) was characterized using FT-IR, UV–Vis and atomic absorption spectroscopy, thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), scanning electron microscopy images (SEM), energy-dispersive X-ray spectroscopy (EDX), and Brunauer-Emmett-Teller (BET). The catalytic activity and electrochemical behavior of the encapsulated complex has been studied in the oxidation of a wide range of sulfides and olefins using H₂O₂ in ethanol. This heterogeneous catalytic system shows a dramatic increase in total turnover number (46,500) for oxidation of styrene. It could be readily reused for at least eight successive times without discernible activity and selectivity deterioration, which displays potential for practical applications.

Full text of DOI:10.1080/00958972.2017.1369052

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Catalytic activity and electrochemical properties
of Cu(II)-Schiff base complex encapsulated in
the nanocavities of zeolite-Y for oxidation of
olefins and sulfides
Saeed Rayati, Elham Khodaei & Majid Jafarian
To cite this article: Saeed Rayati, Elham Khodaei & Majid Jafarian (2017): Catalytic activity
and electrochemical properties of Cu(II)-Schiff base complex encapsulated in the nanocavities
of zeolite-Y for oxidation of olefins and sulfides, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2017.1369052
To link to this article: http://dx.doi.org/10.1080/00958972.2017.1369052
Accepted author version posted online: 17
Aug 2017.
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Date: 20 August 2017, At: 00:12

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://doi.org/10.1080/00958972.2017.1369052
Catalytic activity and electrochemical properties of Cu(II)-Schiff base
complex encapsulated in the nanocavities of zeolite-Y for oxidation of
olefins and sulfides
SAEED RAYATI*, ELHAM KHODAEI and MAJID JAFARIAN
Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran15418, Iran
Copper(II) complex of a Schiff base ligand (H2L) was synthesized, characterizedand
encapsulated in the cavities of zeolite-Y by a fixed ligand method. The zeolite encapsulated
metal complex(CuL-Y)was characterized using FT-IR, UV-Vis and atomic absorption
spectroscopy,thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), scanning
electron microscopy images(SEM),energy-dispersive X-ray spectroscopy (EDX) and Brunauer-
Emmett-Teller (BET). The catalytic activity and electrochemical behavior of the encapsulated
complex has been studied in the oxidation of a wide range of sulfides and olefins using H2O2in
ethanol. This heterogeneous catalytic system shows a dramatic increase in total turnover number
(46,500) for oxidation of styrene. It could be readily reused for at least eightsuccessive times
without discernible activity and selectivity deterioration, which displays potential for practical
applications.
Keywords: Green oxidation; Heterogeneous catalyst; Zeolite-Y; Schiff base; Olefin; Sulfide
1. Introduction
Schiff base ligands and their metal complexes are attractive because of physicochemical
properties of metal complexes and broad range of utilities in various areas of science such as
electrochemical investigations, biological studies and catalytic fields [1-4]. Catalytic oxidation of
organic compounds is an important domain of chemical research for producing valuable
compounds. Although transition metal complexes are efficient homogeneous catalysts, one of the
*Corresponding author. Emails: rayati@kntu.ac.ir;srayati@yahoo.com
1

major drawbacks of homogeneous catalysts is the problem of separation and recovery from the
reaction mixture at the end of the process [5-7]. Nowadays, many researchers use different
methods for catalyst recovery [8]. Indeed, using heterogeneous catalysts are capable of
catalyzing organic reactions without obvious decrease in catalytic activity. Besides these
methodologies, heterogenization of homogeneous catalyst via encapsulation or immobilization
into solid support has been found to be advantageous over various other techniques which can
provide high activity, selectivity and reusability of catalysts [9-12]. Several examples of
heterogenization of homogeneous catalysts onto some inorganic supports, such as MCM-41
[13, 14], SBA-15 [15,16], nanomaterials and zeolites [17-19], have been explored. Among some
of these supports, zeolites are excellent materials for encapsulation of transition metal complexes
because of their low cost and intracrystalline cavities. In addition, the development of
heterogeneous copper-based systems is another attractive area of research because of its unique
characteristics, such as low toxicity, low price and powerful catalytic ability [20].In this study, in
order to perform selective oxidation of sulfides to sulfoxides and olefins to the corresponding
epoxy products, acopper(II) Schiff-base complex was encapsulated in thecavities of zeolite-
Y.Furthermore, from green chemistry point of view, hydrogen peroxide is considered as the
oxidant for oxidation reactions.
2. Experimental
2.1. Instruments and reagents
Infrared spectra were recorded as KBr pellets using UnicamMatson 1000 FT-IR. A Varian
(AA 240) atomic absorption spectrometer was used for copper determination. X-ray powder
diffraction (XRD) was carried out on a Philips PW 3710 diffractometer with CuKα radiation.
Scanning electron microscopy (SEM) images were obtained on aVEGA3TESCANfield emission
scanning electron microscope using HV voltage of 20 kV. The oxidation products were analyzed
by HP Agilent 7890 gas chromatograph equipped with a HP-5 capillary column (phenyl methyl
siloxane 30 m × 320 µm× 0.25 µm) and a flame ionization detector. Thermogravimetric analysis
(TGA-DSC) was obtained using a Mettler-Toledo.Brunauer-Emmett-Teller
(BET)micromeriticsTriStarII3020V1.03 is used as a high-quality surface area and porosity
measurements by using the technique of gas adsorption.TheUV-Visabsorptionspectrawere
measuredon Unico 4802 double-beam spectrophotometer. Electrochemical studies of catalysts
2

were carried out by solartron model SI 1287 electrochemical interface. A glassy carbon (GC)
disc electrode and graphite electrode were used as working and counter electrode,
respectively.1,2-Propanediamine, 2,4-
dihydroxyacetophenone,copper(II)nitratetrihydrate,hydrogen peroxide (solution 30% in
water),tetrabutylammoniumhexafluorophosphate (TBAH)and zeolite-Y
(Na52[(AlO2)52(SiO2)140])were obtained from Merck. Other materials were purchased from
Sigma-Aldrich or Flukachemical companies.
2.2. Preparation of bis(2,4-dihydroxyacetophenone)-1,2-propandiimine (H2L)
To a stirred ethanolic solution (20 mL) of 1,2-propanediamine(0.074 g, 1
mmol),2,4-dihydroxyacetophenone(0.304 g, 2 mmol) was added. The mixture was stirred and
heated to reflux for 1 h. A yellow precipitate was filtered and washed with cold ethanol
[21].C19H22N2O4: Yield (94%), m.p.= 180 °C. 1H NMR (δ, in ppm): 1.26, 1.28 (d, 3H,
NCH2CH(CH3)N), 2.2-2.49 (s, 6H, (CH3)C=N), 3.3–3.7 (m, 1H, NCH2CH(CH3)N)2CH2N),
4.18-4.19 (m, 2H, NCH2CH(CH3)N), 6.01-7.41 (m, 6H, ArH), 16.52–16.67 (s, 4H, OH). 13C
NMR (δ, in ppm): 14.34 (NCH2CH(CH3)N), 19.61 (CH3)C=N), 52.85 (NCH2CH(CH3)N), 54.06
(NCH2CH(CH3)N), 130–170 (ArC), 172.36 (CH3)C=N).
2.3. Preparation of copper(II) complex (CuL)
The copper(II) complex was prepared as follows: the Schiff base ligand H2L (0.34 g, 1 mmol)
was dissolved in 20 mL ethanol. An ethanolic solution of copper(II) nitrate (0.31 g, 1.2 mmol)
was added and the reaction mixture was refluxed for 2 h. The solution was concentrated to dark
brown powders. The products were washed with cold ethanol and dried at 80°C. (CuC19H20N2O4:
Yield (83%), m.p. = 265 °C.Anal. Calc. for CuC19H20N2O4 (403.92): C, 56.49; H,4.99; N,6.93.
Found: C, 56.63; H, 4.91; N, 6.86%.
2.4. Preparation of the Cu-Y
Cu-Y was prepared by ion-exchange method. Copper(II) nitrate (3.1 g, 12 mmol) dissolved in
100 mL deionizedwaterwas addedto a suspension of 1.25 g Na-Y in deionized water (100 mL).
The mixture was stirredunder refluxfor 24 hand the obtained solid was filtered off and washed
with distilled water, and finally dried in 150 °C.
3

2.5. Preparation of the CuL-Y
Encapsulation of metal complex was performed with the flexible ligand method. Cu-Y (0.7 g)
and 1.25 g of H2L were mixed in 50 mL of methanol, and the reaction mixture was refluxed for
17 h in an oil bath under stirring. The resulting material was separated by filtration and then
extracted with methanol using a Soxhlet extractor for 72 h to remove unreacted ligands from the
cavities of the zeolite as well as those located on the surface of the zeolite along with neat
complex. The unreacted metal ions present in the zeolite were removed by stirring with aqueous
0.01M NaCl solution. The resulting solid was filtered and washed with distilled water until free
from chloride ions. Finally, it was dried at 120 °C. Scheme 1 shows the structure of copper
complex encapsulated in the cavities of zeolite-Y.
2.6. General procedure for catalytic oxidation of sulfides with hydrogen peroxide
In a typical procedure, to a mixture of methylphenylsulfide (0.104 mmol, 12.31 µL) and catalyst
(0.0013 mmol, 0.009 g) in ethanol (1 mL), H2O2 (1.04mmol, 81 µL) was added. The reaction
mixture was stirred for 20 min at room temperature. The progress of the reaction was monitored
by GC.
2.7. General procedure for catalytic oxidation of olefins with hydrogen peroxide
In a typical procedure, to a mixture of cyclooctene (0.072 mmol, 9.4 µL) and catalyst
(0.0013 mmol, 0.009 g) in ethanol (1 mL), H2O2 (0.786 mmol, 50.80 µL) was added. The
reaction mixture was heated to 50 °C for 1 h. The progress of the reaction was monitored by GC.
3. Results and discussion
3.1. Characterization of the catalyst
The FT-IR spectra of the Schiff base ligand, free complex, zeolite Na-Y and encapsulated
complex are presented in table 1. The IR spectrum of the ligandexhibits a sharp band at 1630 cm-
1which is characteristic of azomethine group. Copper Schiff base complex showsa sharp band
at1605cm-1 for C=N group. This indicates that the ligand is coordinated to the copper ion through
the nitrogen atom of theazomethine group [22].The IR bands of the encapsulated complex are
weak in comparison with the neat complex due to the low concentrations of metal complex in
4

zeolite cages. The characteristic IR bands of the zeolite framework occur in the range 200-1300
cm-1. The strong and broad band at 1000 cm-1 can be attributed to the asymmetric stretching
vibrations of (Si/Al)O4 units [23]. A broad band in the range 3200-3600 cm-1 is attributed to the
surface hydroxyl groups [24].
Electronic spectral data of the ligand and complex in ethanol solution are summarized in
table 2. The Schiff base ligand shows two intense bands which are assigned toπ→π* or
n→π*transitions. Both bands are shifted to higher wavelengths in the complex, indicating
coordination of the imine nitrogen atoms to the copper center. Ligand-to-metal charge transfer
(LMCT) band was also observed at 344 nm for CuL. The free Cu-complex also showsa weak
and broad band at 580 nm (CuL) which is assigned to d→dtransition. The electronic spectra of
the encapsulated complex suggest the existence of Cu(II) Schiff base complex in the cage of
zeolite, even though the peaks exhibit some shift and broadening compared to Cu-Y. This might
be due to some distortions of the Cu(II) Schiff base complex occurring inside the zeolite cage.
The scanning electron micrographs for Na-Y andCuL-Y are shown in figure1. Analysis
of the micrographs of Na-Y and the heterogeneous catalyst shows that there are no changes in
the zeolite morphology or structure upon encapsulation.
The results of BET for Cu-Y andCuL-Y are shown in figure2. The surface area and pore
volume of copper exchanged zeolite and the encapsulated copper complex are presented in
table 3.The surface area of Cu-Y was 427.96 m2g−1.However, in the case of CuL-Y, the surface
area was drastically reduced to 418.3 m2g−1. The average pore size of Cu-Y was 102.17 Å, and it
reduced to 88.26 Å on CuL-Y [25]. The decrease in the pore volume clearly suggests that the
metal complexwas encapsulated in the zeolite cavities.
The energy-dispersive X-rayspectroscopy (EDX) spectrumof Na-Y andCuL-Y (figure 3)
showed the presence of N, O and Si as well as Cu in the encapsulated complex.The powder X-
ray diffractograms of Na-Y and encapsulated Cu-complex are shown in figure 4.Comparison of
the XRD pattern of zeolite Na-Y and the encapsulated Cu complex indicated no new crystalline
pattern for the lattice. Therefore, the crystallinity of Cu-Y is almost intact after encapsulation of
the complex [26]. These results further suggest that the reduction in surface area of the
encapsulated complex is not due to any collapse of the crystalline structure [27].
The thermal properties of the copper(II) Schiff-base complex encapsulated in zeolite-
Ywereinvestigated by TGA analysis method. The encapsulated copper complex was heated from
5

100 °C to 700 °C at a rate of 10 °min-1 in nitrogen atmosphere. The thermogramisgiven in
figure5. The endothermic peak observed at below 200 °C in the TGA curve is due to desorption
of physically adsorbed and occluded water. The exothermic peak between 268-500 °C is
attributed to the combustion of copper complex encaged in the host [28].
The Cu-content of the encapsulated catalyst determined by atomic absorption
spectroscopy revealed that the metal content of the catalyst is 0.45 mmol per gram of the
catalyst.
3.2. Catalytic activity of the prepared catalyst
The catalytic activity of the heterogeneous catalyst was investigated in the oxidation of various
sulfides and olefins with hydrogen peroxide as green oxidant in ethanol. We first examined the
oxidation of methyl phenyl sulfide and cycloocteneas the representative substrates for the
optimization of reaction conditions withCuL-Y. In this study, several parameters, such as
reaction time, temperature, molar ratios of the oxidant and the concentration of the catalyst were
investigated during the optimization of the reaction.
3.2.1. Oxidation of sulfides. The oxidation of methyl phenyl sulfide with hydrogen peroxide in
ethanol which led to the formation of only 13% product in the absence of catalyst was used as a
model reaction. Different amounts of oxidant (H2O2) have been studied in the oxidation of
methyl phenyl sulfide (table 4, entries 1-6). It was observed that oxidation of methyl phenyl
sulfide required 10mmol of H2O2 for completion at 25 °C.
The catalytic activity has been remarkableinfluenced by the nature of the solvent
and,therefore, catalytic potential of the heterogeneous catalyst in differentsolvents (acetonitrile,
ethanol, dichloromethane and chloroform) was studied (figure 6) andthe
highestconversion(100%)was obtained in ethanol and,consequently, ethanol as green solvent was
selected for the oxidation of sulfides. The oxidation of different substrates with hydrogen
peroxide necessitates the departure of an “OH” group in the form of hydroxyl anion (OH-) or
water (H2O). The higher dielectric constant of ethanol and acetonitrile as well as their hydrogen-
bond forming ability assist departure of the leaving group and accelerate the oxidation reaction
[29,30].
The effect of the catalyst concentration (0.003 g, 0.006 g and 0.009 g)was studied. The
6

results are presented in figure 7. In the absence of catalyst, only13% of methyl phenyl sulfoxide
was obtained and by increasing the amount of the catalyst, the catalytic potential of CuL-Y was
improved.
Comparison of the catalytic activity of homogeneous catalyst (CuL) with the
encapsulated one in the optimum conditions indicates littlelower catalyticactivity of the
unsupported catalyst (CuL, 97%) in the oxidation of methyl phenyl sulfide. The heterogeneous
catalyst can be recovered quantitatively by simple filtration and reused several times without
significant loss of activity. The catalyst could be reused at least eight times without appreciable
loss of its catalytic performance (table 5).
The heterogeneous catalystwas used for oxidation of a wide range of sulfides (table 6).
The performance of thecatalystwasexcellent for the oxidation of various sulfides to their
corresponding sulfoxides.
3.2.2. Oxidation of olefins. Catalytic activity of the encapsulated catalyst for oxidation of
olefins with H2O2has been studied. Oxidation of cyclooctenewith H2O2 in the presence of
catalytic amounts of CuL-Y led to the formation of cyclooctene oxide as the sole product
(table 7). Thedifferentconcentrations of hydrogen peroxide have been examined and the results
indicatedthat the maximum conversion was obtained at 10:1H2O2:cyclooctene molar ratio
(table 7, entries 1-6).To optimize the solvent, oxidation of cyclooctene was conducted in
different solvents (chloroform, acetonitrile, dichloromethane and ethanol)and resultsshow that
the highest conversion (100%) was achieved in ethanol (table7, entries 6-9). The effect of
temperature (25, 35, 50 and 55C) on the heterogeneous oxidation of cycloocteneshows that an
increase in the reaction temperature to 55C results ina decrease of reaction time to 1 h (table 7,
entries 10-13). The effect of catalyst concentration (0.003 g, 0.006 g and 0.009 g) on the
oxidation of cyclooctene shows that in the absence of catalyst,only 9% cyclooctene oxide was
obtained while in the presence of 0.009 g CuL-Y,complete conversion of cyclooctene was
achieved (table 7, entries 13-16).
Thelower catalytic activity of the homogeneous catalyst(CuL, 93%) with respect to the
encapsulated ones in the oxidation of cyclooctene may be due to the degradation of the
homogeneous catalyst. Also the oxidation of cyclooctene in the presence of Cu-Y proceeds very
slowly and leads to the formation of only around 9% product.The solid catalyst could be easily
7

recoveredfrom the reaction mixture by direct filtration and reused multiple times (table 8).
In orderto investigate the efficiency of the heterogeneous catalyst, further investigations
were carried out ona wide range of olefins (table 9). Excellent conversion and selectivity
forepoxide products were obtained within 1 h for a wide range of the olefins.
Many Schiff base complexes have been reported for olefin epoxidation. The results of the
oxidation of cyclooctene in the presence of various heterogeneous complexes are summarized in
table 10. Comparison of this catalytic system with previously reported systems shows that higher
conversion and selectivity in the shorter reaction time was achieved in the oxidation of
cyclooctene.
In order to estimate the longevity of the heterogeneous catalytic system, total turnover
number (TON) has been studied. The catalyst exhibited excellent activities for oxidation of
styrene in ethanol solution under mild conditions (Cat:Styrene:H2O2 is 1:50,000:600,000) with a
TON of 46,500 for CuLafter 24 h which is one of the highest values reported for Schiff base
complex encapsulated in zeolite-Y.
3.3. Electrochemical studies
The electrochemical behavior of the copper(II) complex as heterogeneous catalyst for the
oxidation of methyl phenyl sulfide or cyclooctene in the potential range of -3 to +3 V in CH3CN
containing 0.1 M TBAH as the supporting electrolyte at scan rate of 100 mVs-1 has been studied
(figure8).In this study, calomel (Hg/Hg2Cl2), graphite and glassy carbon were used as the
reference electrode, counter electrodeand working electrode, respectively.Voltammetric study
showed a higher current intensity for copper encapsulated complex compared to the blank
experiments which illustratethe important role of the catalyst in oxidation of sulfides (figure8).
Cyclic voltammograms of glassy carbon/CuL-Y in the presence of 80 mmolof methyl phenyl
sulfide using 800 mmol H2O2 at various scan rates are displayed in figure9. The oxidation or
reduction peaksbecame broader with increasing scan rate. In addition, at higher scan rates, the
oxidation peaksshiftedto more positive potentials for sulfide oxidation which indicates that the
electro-oxidation of copper species to higher valance state is much faster than the catalytic
oxidation of substrates. This reveals thatan increasein scan rate decreasesthe rate of
sulfideoxidation. Furthermore, the anodic peak currents that are linearly proportional to the
square root of scan rate suggest that the overall oxidation of sulfide at this electrode is controlled
8

by the diffusion of sulfide to the surface redox sites [33].Chronoamperograms of the acetonitrile
solution of the CuL-Yand blank in the presence of methyl phenyl sulfide (figure10) or
cyclooctene(figure 9) exhibited the higher catalytic activity of the catalyst compared to the blank
one. This result was revealed from the current intensity in oxidation and reduction potentials.
Similar results were achieved in the oxidation of cyclooctene in the presence ofheterogeneous
catalyst. The growth of reduction and oxidation peaks for heterogeneous catalystcompared to the
blank one illustrated the importance of the catalyst in the oxidation of olefins (figure9).
4. Conclusion
Atetradentate (N2O2) Schiff base ligand (H2L) and its corresponding copper(II) complex (CuL)
was synthesized and encapsulated in the cavities of the zeolite-Y. The heterogeneous catalyst
was characterized by different techniques. Selective oxidation ofvarious sulfides to sulfoxides
and olefins to epoxides is foundto enhance in the presence of the encapsulated complex using
H2O2 as green oxidant in ethanol by approaching to the green chemistry. During reusability
experiments, the heterogeneous catalyst was able to recovered and reusedinmultiple
consecutiverunswithout loss in activity or selectivity. The synthesized heterogeneouscatalyst
exhibited excellent activity foroxidation of styrene in ethanol with a turnover number of 46,500
(CuL-Y) after 72 h, which is one of the highestvalues reported for a heterogeneous catalytic
system.In addition, the electrochemical behavior of CuL-Y was investigated in different
conditions by cyclic voltammetry and chronoamperometrytechniques.
Acknowledgements
The financial support of this work by K.N. Toosi University of Technology research council is
acknowledged.
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11

OH
HO
O
N
O
Cu
N
Me
Me
Me
Scheme 1. Proposed framework structure of zeolite encapsulated metal Schiff base complexes.
12

(a)
(b)
Figure 1. SEM photographs of (a) Na-Y (b) CuL-Y.
13

(b)
(a)
Figure2.N2 isotherms of (a)Cu-Y and (b) CuL-Y with their pour volume.
14

(a)
(b)
Figure3. The energy-dispersive X-ray spectroscopy (EDX) spectrum of (a)Na-Y and (b) CuL-Y.
15

Figure4. XRD patterns of (a) Cu-Y and (b) Cu1-Y.
16

Figure5. (a) TGA curves of the CuL-Y.
17

100
80
60
40
20
0
Chloroform
Dichloromethane
Acetonitrile
Ethanol
0
2
4
6
8
10 12 14 16 18 20
Time(min)
Figure 6. The effect of various solvents on the oxidation of methyl phenyl sulfide with H2O2in
the presence ofCuL-Y.Reaction conditions: catalyst(mmol):sulfide:H2O2 is 1:80:800 at 25°C.
18

100%
100
80
60
40
20
0
73%
29%
13%
0 g
0.003 g
0.006 g
0.009 g
amount of catalyst
Figure 7. The influence of catalyst concentration on the oxidation of methyl phenyl sulfidewith
H2O2 catalyzed by CuL-Y.
19

2.50E-03
2.00E-03
1.50E-03
1.00E-03
5.00E-04
0.00E+00
-5.00E-04
-1.00E-03
-1.50E-03
-2.00E-03
1.00E-03
5.00E-04
0.00E+00
-5.00E-04
-1.00E-03
-1.50E-03
-2.00E-03
-2.50E-03
-3.00E-03
CuL-Y
blank
(b)
(a)
1
-3
-2
-1
0
1
2
3
800
600
400
200
100
-3 -2 -1
0
2
3
V
V
1.00E-05
9.00E-06
8.00E-06
7.00E-06
6.00E-06
5.00E-06
4.00E-06
3.00E-06
2.00E-06
1.00E-06
0.00E+00
2.00E-03
(c)
0.00E+00
-2.00E-03
-4.00E-03
-6.00E-03
-8.00E-03
-1.00E-02
CuL-Y
0
20
40
60
80
100
BLANK
(d)
Blank
CuL-Y
0
20
40
60
80 100
t/s
t/s
Figure8. The voltammetric behavior of (a) CuL-Yand blankat 100 mV/s.The voltammetric
behavior of (b) CuL-Y at different scan rates (100, 200, 400, 600, 800
(mV/s)).Chronoamperograms of (c) CuL-Yand blankin oxidation potential (0.89 V) and (d) in
reduction potential (-1.64 V) in EtOH for oxidation of methyl phenyl sulfide. Reaction
conditions: catalyst(mmol):methyl phenyl sulfide:H2O2 is 1:80:800 at room temperature between
-3 and +3 V in acetonitrile solution containing 0.1 M TBAH as supporting electrolyteand
calomel (Hg/Hg2Cl2), graphite and glassy carbon were used as the reference electrode, counter
electrodeand working electrode, respectively.
20

0.001
0.0008
0.0006
0.0004
0.0002
0
3.00E-03
2.00E-03
1.00E-03
0.00E+00
-1.00E-03
-2.00E-03
-3.00E-03
-4.00E-03
-5.00E-03
-6.00E-03
800
600
400
200
(b)
(a)
-3
-2
-1
0
1
2
3
-3
-2
-1
0
1
2
3
v
-0.0002
-0.0004
-0.0006
Blank
V
CuL-Y
1.00E-05
9.00E-06
8.00E-06
7.00E-06
6.00E-06
5.00E-06
4.00E-06
3.00E-06
2.00E-06
1.00E-06
0.00E+00
0.00E+00
-1.00E-03
-2.00E-03
-3.00E-03
-4.00E-03
-5.00E-03
-6.00E-03
-7.00E-03
-8.00E-03
-9.00E-03
(c)
0
20
40
60
80
100
CuL-Y
BLANK
(d)
Blank
CuL-Y
0
20
40
60
80 100
t/s
t/s
Figure9. The voltammetric behavior of (a) CuL-Yand blankat 100 mV/s.The voltammetric
behavior of (b) CuL-Y at different scan rates (100, 200, 400, 600, 800
(mV/s)).Chronoamperograms of (c) CuL-Yand blankin oxidation potential and (d) in reduction
potential in EtOH for oxidation of cyclooctene. Reaction conditions:
catalyst(mmol):sulfide:H2O2 is 1:50:500at room temperature between -3 and +3 V in acetonitrile
solution containing 0.1 M TBAH as supporting electrolyte and calomel (Hg/Hg2Cl2), graphite
and glassy carbon were used as the reference electrode, counter electrodeand working electrode,
respectively.
21

Table 1. IR spectral data (wavenumbers in cm-1) of ligands and zeolite encapsulated
metal complexes.
Samples
H2L
( Al-O-Si)
(Al-O-Si)
(C=C)
1537
1534
-
(C=N)
1630
1605
-
(O-H)
3410
3474
3506
3512
-
-
CuL
-
-
Cu-Y
CuL-Y
795
794
1021
1168
1536
1630
22

Table 2. Electronic spectral data of the ligand and copper(II) complex
encapsulated in zeolite in ethanol.
Compound
H2L1
λmax (nm)(ε, M−1cm−1)
Assignment
227 (3373)
312 (2881)
239 (21686)
298 (15420)
344 (9363)
580 (800)
230
π→π*
n→π*
π→π*
n→π*
MLCT
d-d
CuL
CuL1-Y
π→π*
n→π*
MLCT
d-d
296
373
583
23

Table 3. Textural properties of Cu-Y and its complex-encapsulated analogue.
Sample
SBET (m2g−1)
Average pore size(Å)
Pore volume(cm3g−1)
Cu-Y
427.9644
418.3000
102.1748
88.2604
1.093179
0.922983
CuL-Y
24

Table 4.The effect of amount oxidant and temperature on the oxidation of methyl phenyl
sulfide in the presence of CuL-Y in ethanol.a
Entry
mmol sulfide/oxidant Time (min)
Temperature (°C)
Conversion %
1
2
3
4
5
6
1:1
1:2
1:3
1:4
1:5
1:10
20
20
20
20
20
20
25
25
25
25
25
25
6
15
26
38
53
100
aReaction conditions: catalyst(mmol):methyl phenyl sulfide is 1:80.
25

Table 5.Reuse of the heterogeneous catalysts in the oxidation of methyl phenyl sulfide.
Run
Conversion (%)a
Selectivity (sulfoxide) %
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
Cycle 6
Cycle 7
Cycle 8
100
100
100
98
100
100
100
100
100
100
100
100
98
95
94
94
aReaction conditions: catalyst:sulfide:H2O2= 1:80:800 at 25 °C for a 20-min reaction
time.
26

Table 6. Oxidation of various sulfides with H2O2 in the presence of CuL-Y.a
Selectivity %
Substrates
Conversion % CuL-Y
(Sulfoxide) (CuL-Y)
S
100
100
H3C
Cl
97
90
S
H3C
S
100
93
100
95
H3C
Cl
S
H3C
F
S
CH2
55
100
100
100
S
100
95
100
100
S
OCH3
H3C
S
CN
100
100
100
100
H3C
S
S
aReaction conditions: catalyst:sulfide:H2O2= 1:80:800 at 25 °C for a 20-min
reaction time.
27

Table 7. The effect of various conditions on the oxidation of cyclooctene catalyzed by CuL-Y.
Time
(h)
Temperature
(ºC)
Conversion
(%)
Selectivity
Epoxide%
Catalyst
(g)
Entry
Oxidant
Alkene/oxidant
Solvent
1
4
4
4
4
4
4
4
4
4
1
1
1
1
1
1
1
25
25
25
25
25
25
25
25
25
25
35
50
55
55
55
55
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
1:1
15
24
29
36
41
91
21
84
27
41
70
94
100
69
38
9
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
CHCl3
CH3CN
CH2Cl2
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
0.009
0.009
0.009
0.009
0.009
0.009
0.009
0.009
0.009
0.009
0.009
0.009
0.009
0.006
0.003
0
2
1:2
3
1:3
4
1:4
5
1:5
6
1:10
1:10
1:10
1:10
1:10
1:10
1:10
1:10
1:10
1:10
1:10
7
8
9
10
11
12
13
14
15
16
28

Table 8.Reuse of the heterogeneous catalysts in the oxidation of
cyclooctene.
Run
Conversion (%)a Selectivity %
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
Cycle 6
Cycle 7
Cycle 8
100
100
100
100
97
100
100
100
100
100
100
100
100
95
94
91
aReaction conditions: catalyst(mmol):alkene:H2O2 is 1:50:500 at
55 °C for a 1-h reaction time.
29