Epoxidation of alkenes by an oxidovanadium(IV) tetradentate Schiff base complex as an efficient catalyst with tert-butyl hydroperoxide

Article abstract of DOI:10.1016/j.ica.2016.12.018

A new asymmetrical tetradentate N₂O₂Schiff base ligand was synthesized from 2-hydroxyacetophenon, 2-hydroxynaphthaldehyde and 1,2 phenylenediimine. The new oxidovanadium(IV) Schiff base complex, V^IVOL (L?=?N-2-hydroxyacetophenon-N′-2-hydroxynaphthaldehyde-1,2 phenylenediimine), was prepared by reaction of Schiff base ligand with vanadyl acetylacetonate. The Schiff base ligand (L) and the oxidovanadium(IV) complex were characterized by spectroscopic methods. The crystal structure of the complex was determined by the single crystal X-ray analysis. The complex crystallized in the orthorhombic system, having one V⁴⁺ion coordinating in an approximately square pyramidal N₂O₃geometry by two azomethine N atoms and phenolic oxygens from Schiff base ligand in a square plane and one oxygen atom in an apical position. Electrochemical properties of the complex were examined by means of cyclic voltammetry. The catalytic activity of the oxidovanadium(IV) Schiff base complex was tested in the epoxidation of cyclooctene.

Full text of DOI:10.1016/j.ica.2016.12.018

Accepted Manuscript
Epoxidation of alkenes by an oxidovanadium(IV) tetradentate Schiff base com-
plex as an efficient catalyst with tert-butyl hydroperoxide
Maryam Sedighipoor, Ali Hossein Kianfar, Wan Ahmad Kamil Mahmood,
Mohammad Hossein Azarian
PII:
S0020-1693(16)30792-7
http://dx.doi.org/10.1016/j.ica.2016.12.018
ICA 17380
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
5 November 2016
13 December 2016
18 December 2016
Please cite this article as: M. Sedighipoor, A. Hossein Kianfar, W. Ahmad Kamil Mahmood, M. Hossein Azarian,
Epoxidation of alkenes by an oxidovanadium(IV) tetradentate Schiff base complex as an efficient catalyst with
tert-butyl hydroperoxide, Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.12.018
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Epoxidation of alkenes by an oxidovanadium(IV) tetradentate Schiff
base complex as an efficient catalyst with tert-butyl hydroperoxide
b
Maryam Sedighipoora, Ali Hossein Kianfar1a, Wan Ahmad Kamil Mahmood and
Mohammad Hossein Azarianb
aDepartment of Chemistry, Isfahan University of Technology, Isfahan, Iran, 84156-83111
bSchool of Chemical Sciences, Universiti Sains Malaysia,11800 Minden, Penang, Malaysia
Abstract
A new asymmetrical tetradentate N2O2 Schiff base ligand was synthesized from 2-
hydroxyacetophenon, 2-hydroxynaphthaldehyde and 1,2 phenylenediimine. The new
oxidovanadium(IV) Schiff base complex, VIVOL (L = N-2-hydroxyacetophenon-N´-2-
hydroxynaphthaldehyde-1,2 phenylenediimine), was prepared by reaction of Schiff base ligand
with vanadyl acetylacetonate. The Schiff base ligand (L) and the oxidovanadium(IV) complex
were characterized by spectroscopic methods. The crystal structure of the complex was
determined by the single crystal X-ray analysis. The complex crystallized in the orthorhombic
system, having one V4+ ion coordinating in an approximately square pyramidal N2O3 geometry
by two azomethine N atoms and phenolic oxygens from Schiff base ligand in a square plane and
one oxygen atom in an apical position. Electrochemical properties of the complex were
examined by means of cyclic voltammetry. The catalytic activity of the oxidovanadium(IV)
Schiff base complex was tested in the epoxidation of cyclooctene.
1 Ali Hossein Kianfar, E-mail: akianfar@cc.iut.ac.ir
Tel : +98-31-33913251 Fax : +98-31-33912350
1

Keywords:
X-Ray crystallography, asymmetry, vanadium Schiff base complexes, electrochemistry, catalyst.
1. Introduction
In the Schiff base compounds which are among the privileged ligands, the carbonyl group of
ketone or aldehyde are replaced by an imine group due to simple one-pot condensation synthesis
in an alcoholic solvent. For more than a century, metal complexes of the Schiff base ligands have
been rigorously studied and used in different fields including biological research [1-6], chemical
analysis [7], non-linear optics [8], magneto chemistry [9], photo physical studies [10] and
catalysis [11].
In research studies, simple metal complexes related to different oxidants such as alkyl
hydroperoxides, H2O2 or O2 are used in order to imitate the metalloenzyme catalyzed oxidation
[12-14]. The oxidant is activated by the central metal and transfer the oxygen atom to substrate
from metal-oxo species [15-17].
Between transition metal complexes, use of vanadium complexes as oxidative catalysts is of
great interest and a number of intriguing -oxo-transfer reactions are derived by oxidovanadium
complexes of Schiff base compounds [18, 19]. Furthermore, the molecular oxygen for
oxygenation reactions can also be activated by vanadium complexes [20, 21].
In catalytic oxidation, the use of high valent vanadium is encouraged due to (a) the different
possible coordination numbers, (b) the easily interchangeable vanadium oxidation states (where
+4 and +5 are the most stable ones under aerobic conditions), (c) the Lewis acid character of the
vanadium centers and (d) the high affinity of the metal toward oxygen [22-24].
2

Since epoxides are the key starting materials for a wide variety of products, the epoxidation of
alkenes is considered to be one of the most widely studied reactions in organic chemistry. An
area of strong research activity is the catalytic epoxidation of olefins by transition metal
complexes [25, 26]. In recent years the structural study, synthesis and catalytic activity of
oxidovanadium Schiff base complexes in oxidation of different organic substrates are described
in a great number of publications [27-29]. The central metal is surrounded by N2O2 coordination
environment. In this work, in order to investigate the catalytic activity of oxidovanadium Schiff
base complex as catalyst, we synthesized a new asymmetrical tetradentate Schiff base ligand and
1
its metal complex“Scheme 1”characterized by FT-IR, H NMR and UV-Vis spectroscopies.
Subsequently, the crystal structure of this new oxidovanadium (IV) Schiff base complex is also
determined by X-ray crystallography. We also reported catalytic epoxidation of cyclooctene,
cyclohexene, 1-octene, styrene, indene and norbornene in CHCl3 using tert-butyl hydroperoxide
as oxidant. Electrochemical behavior of VIVO complex also have been investigated. The
oxidation potential of VIVO complex was measured by cyclic voltammetry.
2. Experimental
2.1 Chemicals and apparatus
All chemicals and solvents were purchased from commercial sources without any further
purification. Fourier Transform Infrared (FTIR) spectra of the synthesized samples were
recorded on a FT-IR JASCO 680 spectrophotometer in the range of 4000-400 cm−1 with
potassium bromide pellets. The UV-Vis spectra were obtained by a UV-Vis JASCO model V-
570 spectrophotometer in the 800-200 nm range. The 1HNMR spectrum was recorded in DMSO-
3

d6 on Bruker-500 MHz and elemental analysis was performed using a CHN-O-Heraeus
elemental analyzer.
The electrochemical experiments were carried out using a potentiostat/galvanostat Autolab
Model PGSTAT-302N and NOVA 1.7 software coupled with a Pentium (IV) personal computer.
A glassy carbon electrode was used as a working electrode (metrohm glassy carbon, 0.0314
cm2). An Ag/AgCl/KCl 3.0M and platinum wire were used as reference and counter respectively.
Voltammetric measurements were performed at room temperature in DMF solution with 0.1 M
tetrabutylammonium perchlorate as the supporting electrolyte. The X-ray single crystal structure
analysis was obtained by using Bruker SMART APEX II-2009 CCD area detector
diffractometer. Determination of products from the catalytic testing was carried out using gas
chromatographic (GC) technique. Reaction mixture was analyzed by 6890N Technologies from
Agilent Company with FID detector and N2 as the carrier gas. Column chromatography with
28.5 m length, 320 µm inner diameter and 0.25 µm thickness (the HP+5 types) was used.
2.2 Procedures for synthesis of the tridentate Schiff base ligand
The tridentate Schiff base ligand used in this research was prepared as previously reported
[30] by condensation between 2-Hydroxyacetophenone and 1, 2-phenylenediamine (1:1mmol
ratio) in 20 mL methanol as a solvent. The solution was refluxed for 3h and then the solvent was
evaporated under the reduced pressure. Water was added to the precipitate for dissolving
phenylenediamine. The resulting yellow solid was collected and washed with water and then
recrystallized from methanol.
2.3. General procedure for Synthesis of the unsymmetrical tetradentate Schiff base ligand
4

2-hydroxynaphthaldehyde 1 mmol was added to a solution of tridentate Schiff base ligand 1
mmol disolved in 10 mL methanol. The solution was stirred for 3h. The resulting yellow
precipitate of Schiff base ligand was separated by vacuum filtration, washed with cold methanol
and dried in vacuum desiccator.
Anal, calc. for C25H20N2O2: C, 78.94; H, 5.26; N, 7.36%. Found; C, 78.12; H, 5.02; N, 7.29%.
1
FT-IR (KBr cm-1) νmax: 1617 (C=N), 1482 (C=C), 1192 (C-O). H NMR (DMSO-d6, δ, ppm):
2.3 (s, 3H, CH3), 6.8-8.5 (m, 14H, Ar-H), 9.7 (s, 1H, HC=N), 14.1 (s, 1H, OH) and 15.3 (s, 1H,
OH). UV-Vis, λmax (nm) (ε,M-1cm-1) (Ethanol): 474 (8466), 454 (11333), 390 (12666), 338
(19333), 264 (45333), 232 (73333).
2.4. Synthesis of the vanadyl Schiff base complex
The methanolic solution (10 mL) of tetradentate Schiff base ligand (1mmol) was added to
10mL of a methanolic solution of VO(acac)2 (1mmol). The yellow color of solution turned to
dark green immediately and the reaction mixture was stirred and refluxed for 1h. As a result, a
green precipitate was formed which after filtration and washing with methanol recrystallized
from ether and dichloromethane.
Anal, calc. for C25H18N2VO3: C, 67.42; H, 4.04; N, 6.29%. Found; C, 64.96; H, 3.90; N, 6.01%.
FT-IR (KBr cm-1) νmax: 1617, 1599 (C=N), 1529 (C=C), 1202 (C-O), 978 (V=O). UV-Vis, λmax
(nm) (ε,M-1cm-1) (Ethanol): 451 (17692), 402(18461), 362 (20000), 316 (18461), 246 (50769),
221 (47692).
2.5. X-Ray Crystallography Analysis of the vanadyl Schiff base complex
5

By using graphite monochromated Mo-Kα radiation, the X-ray diffraction measurements were
collected on a STOE IPDS-2T diffractometer. For the purpose of collecting data, the black
crystal vanadyl complex with a dimension of 0.16 × 0.39 × 0.39 mm was chosen and mounted on
a glass fiber. Using least-squares refinement of diffraction data from 9695 unique reflections,
cell constants and an orientation matrix for data collection were gained.
In a series of ω scans in 1° oscillations and integrated using the Stoe X-AREA software
package, data were obtained at a temperature of 100(2) K to a maximum 2θ value of 60.3°. The
numerical absorption coefficient (µ) for Mo-Kα radiation is 0.710 mm-1.
numerical absorption correction was applied using X-RED and X-SHAPE softwares [31]. The
data were modified for Lorentz and polarization effects. Direct methods were used to solve the
structure [32] and different Fourier maps and full-matrix least-squares refinement against F2,
were performed using anisotropic displacement parameters [33]. All of hydrogen atoms were
placed by difference Fourier map and then refined isotropically. Atomic factors were from
International Tables for X-ray Crystallography. All purification were performed using the X-
STEP32 crystallographic software package [34].
The experimental details, crystal data, and refinement results were summarized in Table 1 for
vanadyl complexs. It is notable that, the asymmetric unit also contains solvents molecules, which
could not be modeled. Therefore, the diffraction contribution of the solvent molecules was
removed by the subroutine SQUEEZE in PLATON.
3. Results and discussion
3.1 FT-IR characterization
6

Several bands are observed within the FT-IR spectra of free Schiff base ligand and it’s
complex. The FT-IR spectrum of ligand shows a sharp band in the 1617 cm-1, related to the
stretching vibration frequency of imine. In the Shiff base complex, coordination of Schiff base
ligand to vanadyl ion causes a decrease in the C=N bond order and it’s vibration frequency shifts
to a lower frequency [35, 36] and is shown in 1599 cm-1. The exhibition of the sharp band in the
978 cm-1, corresponding to the V=O stretching vibration is the characteristic of the FT-IR
spectrum of vanadyl complex. The appearance of this particular band in this region indicates the
formation of vanadyl Schiff base complex.
3.2. Electronic spectra
In the sections 2.3 and 2.4, the UV-Vis spectral data in ethanol are listed. All the bands which
are lower than 400 nm are related to π → π* transition of aromatic ring within the Schiff base
ligand at 232-390 nm and the complex at 221-362 nm (Fig 1). The bonds at 454 and the shoulder
at 474 belong to the Schiff base ligand are attributed to π → π* transition related to azomethine
group [30, 37, 38]. It has to be noted that these transitions in the vanadyl complex take place at
451 and 402 nm.
3.3. 1H NMR spectra
1
The HNMR data of the asymmetrical tetradentate Schiff base ligand is presented in section
2.3. The single peak at about 2.3 ppm, is related to the hydrogens of methyl. However, in the
range of 6.88-8.50 ppm, the aromatic hydrogens are observed. The imine hydrogen is assigned at
9.70 ppm. At 14.12 and 15.35 ppm, the phenolic hydrogens of 2-hydroxyacetophenone and 2-
7

1
hydroxy naphthaldehyde are found, respectively. The H NMR techniques confirmed the
structure of synthesized ligand as well.
3.4 Description of the molecular structure of the vanadyl complex
The structure of the vanadyl complex with the atom–numbering scheme is presented in Fig 2.
The crystallographic data shows that the vanadium (IV) ion, in the five-coordinated geometry is
surrounded by two oxygen and two nitrogen atoms from Schiff base ligand and oxo ligand. The
geometry around the vanadium(IV) ion is distorted squre-pyramidal, as indicated by the unequal
metal-ligand bond distances and angles: i.e. V-N1 = 2.075(3), V-N2 = 2.041(3), V-O1 =
1.916(3), V-O2 = 1.926(2), V-O3 = 1.604(2) Å and O3-V-O1, O3-V-O2, O3-V-N2, O2-V-N1,
O1-V-N2, O3-V-N1, O1-V-N1, O2-V-N2, N2-V1-N1, O1-V-O2 angles are distributed in the
range of 111.59(13)°, 110.83(11)°, 106.90(13)°, 146.67(11)°, 141.25(11)°, 102.06(11)°,
88.65(11)°, 86.29(11)°, 79.06(11)° and 84.31(10)°, respectively. All distances and angles in
vanadyl complex are in agreement with the same distances in other vanadium (IV) complexes
[39-42]. Crystal data and experimental details are listed in Table 1 and 2. The structure of the
noted complex is identified by X-ray diffraction and crystallized in the Orthorhombic, space
group Pca2 (1).
3.5 Electrochemical investigation
The cyclic voltammetry of VOL complex is carried out in DMF solution at ambient
temperature.
The typical cyclic voltammogram of [VOL] complex in the potential range of 0.0 to 1.0 V (vs
Ag/AgCl) is shown in Fig 3. At about +0.50 V, an oxidation peak is observed. In a fully-
8

reversible one-electron step, [VOL] is oxidized to the mono cation [VOL]+. The electron is
separated from the nonbonding orbitals and the V(V) complex is created. Upon reversal of the
scan direction, the V(V) complex is reduced to V(IV) at lower potentials about 0.45 V. Multiple
scans result in nearly superposable cyclic voltammograms. Thereby showing that the five
coordinatione geometry is stable in both oxidation states, at least on the cyclic voltammetry time
scale. In the vanadyl Schiff base complex redox process is the one-electron transfer reaction. The
calculation for the formal potential (E1/2 (IV/V)) for the V(IV/V) redox couple is the average of
the cathodic (Epc) and anodic peak (Epa) which is equal to 0.47 V.
3.6 Catalytic epoxidation of olefins
The new synthesized vanadyl Schiff base complex VOL was examined in the epoxidation of
cyclooctene, cyclohexene, styrene, norbornene, 1-octene and indene in order to study it’s
catalytic activity.
In the epoxidation of cyclooctene, different parameters i.e. the effect of type of oxidants, quantity
of them, solvent and catalyst quantity were tested. The vanadyl Schiff base complex in the
epoxidation of cyclooctene and the result of it’s catalytic activity in different solvent with the
presence of tert-butylhydroperoxide (TBHP) is shown in Fig. 4 and Table 3. It is evident that the
catalytic activity of vanadyl Schiff base complex in CH3Cl and CH2Cl2, with low coordination
ability, is greater than CH3CN, C3H6O and CH3OH with high coordination ability [43]. Different
reactions were used in order to gain the suitable oxidant in the epoxidation of cyclooctene (Table
4). High yield was gained in the presence of TBHP in CHCl3. By altering the amount of oxidant,
the reaction was also studied (Table 5). Two mmol of oxidant offered the maximum epoxidation
yield among the 0.5, 0.75, 1, 2 and 2.5 mmol of TBHP. The quantity of Schiff base complex also
9

checked on the epoxidation of cyclooctene (Table 6). In the presence of TBHP, different quantity
of Schiff base complex (0.005, 0.01 and 0.02 mmol) were used in the epoxidation of cyclooctene
in the CHCl3 and the maximum epoxidation yield was made by 0.01 mmol of complex.
Our further investigation concerned the oxidation of cyclohexene, styrene, norbornene, 1-
octene and indene. In a typical experiment, a mixture of 0.01 mmol vanadyl Schiff base
complex, freshly distilled CH3Cl (3 mL), 1 mmol freshly distilled olefin and 2 mmol of TBHP
was refluxed at 50ºC for several times. The reaction products were monitored at periodic time
using gas chromatography. By using homogeneous catalyst, the product distributions in the
oxidation of olefins were shown in Table 7.
The same results were obtained from catalytic activities of some five coordination
oxidovanadium (IV) Schiff base complexes with tetradentate N2O2 or tridentate NO2 ligands in
cyclooctene epoxidation reaction [44-46]. The results showed that the cyclooctene epoxidation
reaction with TBHP had higher conversion than H2O2 [44]. The catalytic activities of two
oxovanadium (IV) Schiff base complexs in cyclooctene epoxidation reaction with chloroform,
acetonitrile and dichloromethane were investigated by Rayati and showed that the highest
conversion obtained in the chloroform [46]. In summary based on the reported results and also
present work, the high epoxidation yield by oxidovanadium Schiff base complexes was
obtainedin in the presence of TBHP in CHCl3.
Furthermore, the mechanistic aspects of the epoxidation reaction of alkenes were reviewed.
The proposed mechanism of epoxidation reaction by oxidovanadium (IV) Schiff base complex in
the presence of TBHP was showed in Scheme 2 [47]. The observed result confirmed that the first
step of mechanism involves the oxidation of vanadium (IV) Schiff base complex with TBHP and
the interaction of this complex with TBHP resulted in vanadium (V) species [48]. In the next
10

step involves the transfer of TBHP proton to the terminal oxygen atom of Vanadyl group and
coordination of t-BuOO‾ to vanadium (V) as a Lewis acidic metal center and resulted in
formation of the oxidoperoxidovanadium (V) intermediate.
4. Conclusions
In the present research, as a part of our progressing studies on the catalyst, we demonstrated
the synthesis and characterization of new oxidovanadium Schiff base complex (IV). The
elemental analysis (CHN), UV-Vis and FT-IR spectroscopy showed that the vanadyl complex
was synthesized succesfully. The single crystal X-ray analysis showed that V(IV) placed in a
distorted five coordinated square pyramidal N2O3 geometry. Fuethermore, the catalytic activity
of this complex was tested in epoxidation of alkenes such as cyclooctene, cyclohexene, styrene,
norbornene, 1-octene and indene using tert-butyl hydroperoxide as oxygen source in chloroform.
Based on the results, the vanadyl Schiff base complex was very active in epoxidation of alkenes
in optimized conditions. Moreover, electrochemical behavior of VIVO complex was also
investigated.
4. Supplementary material
CCDC No. 1513755 contains the supplementary crystallographic data for VIVOL (L = N-2-
hydroxyacetophenon-N´-2-hydroxynaphthaldehyde-1,2 phenylenediimine),. These data can be
obtained at www.ccdc.cam.ac.uk/deposit {or from the Cambridge Crystallographic Data Center
12, Union Road Cambridge CB2 1EZ, UK; Fax: (internet) +44-1223/336-033; E. mail:
deposit@ccdc.cam.ac.uk).
11

5. Acknowledgements
We wish to express our gratitude to the Research Affairs Division Isfahan University of
Technology (IUT), Isfahan, for partial financial support.
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Scheme 1. The structure of Schiff base ligand and its complex.
16

Scheme 2. The proposed mechanism for the epoxidation of alkenes by the oxovanadium
Schiff base complex in the presence of TBHP.
17

Fig. 1. Electronic spectra of Schiff base ligand (a) and [VO(L)] Complex (b, dashed line).
18

Fig. 2. The labeled diagram of [VO(L)] Complex showing 50% probability thermal ellipsoids.
19

Fig. 3. Cyclic voltamogram of [VO(L)] Complex in DMF at room temperature and Scan rate:
100 mv/s.
20

Fig. 4. The catalytic epoxidation of cyclooctene in different solvent in the presence of TBHP
by the vanadyl Schiff base complex in the reflux condition..Reaction condition: (3 ml) solvent, (1
mmol) cyclooctene, (2 mmol) oxidant and (0.01 mmol) Vanadyl Schiff base complex.
21

Table 1. Crystallographic and structure refinements data for [VO (L)] Complex.
Compound
(A)
Formula
C25H18N2O3V
445.35
Formula weight
Temperature /K
Wavelength λ /Å
Crystal system
Space Group
100(2)
0.710
Orthorhombic
Pca2(1)
Crystal size /mm3
0.16 × 0.39 ×
0.39
a /Å
7.8551(7)
25.291(2)
22.775(2)
90
b /Å
c /Å
α /°
β /°
90
γ /°
90
Density (calc.) /g cm-1
θ ranges for data collection
F(000)
1.308
0.805-25.99
1832
Absorption coefficient
Index ranges
0.466
-9 ≤ h ≤ 9
22

-31 ≤ k ≤ 31
-28 ≤ l ≤ 28
8887
Reflections collected
Parameters, restrains
561, 1
a
Final R1, wR2 (Obs. data)
0.0355 , 0.0918
0.0394 , 0.0890
1.021
a
Final R1, wR2 (All data)
Goodness of fit on F2 (S)
2
2 2
2 2 1
a R1 = Σ||Fo|-|Fc||/Σ|Fo|, wR2 = [Σ(w(Fo -Fc ) )/Σw(Fo ) ]
23

Table 2. Selected bond distances (Å) and bond angles (°) for [VO (L)] Complex.
Bond distances
Bond angels
O3-V1-O1
V1-N1
2.075(3)
2.041(3)
1.916(3)
1.926(2)
1.604(2)
1.335(4)
1.308(4)
1.315(4)
1.414(4)
1.419(4)
1.319(4)
111.59(13)
110.83(11)
84.31(10)
106.90(13)
141.25(11)
86.29(11)
102.06(11)
88.65(11)
146.67(11)
79.06(11)
V1-N2
V1-O1
V1-O2
V1-O3
O1-C1
O2-C24
N1-C7
N2-C13
N1-C8
N2-C14
O3-V1-O2
O1-V1-O2
O3-V1-N2
O1-V1-N2
O2-V1-N2
O3-V1-N1
O1-V1-N1
O2-V1-N1
N2-V1-N1
24

Table 3. The solvent effect on the catalytic epoxidation of cyclooctene in the presence of
TBHP by the vanadyl Schiff base complex in the reflux conditiona.
Solvent
Time (min)
120
Yield(٪)
acetone
1
methanol
120
2
acetonitrile
120
7
1, 2 dichloroethane
1, 2 dichloromethane
chloroform
120
14
43
93
120
120
a
Reaction condition: (3 ml) solvent, (1 mmol) cyclooctene, (2 mmol) TBHP and (0.01 mmol)
Vanadyl Schiff base complex.
25

Table 4. Epoxidation of cyclooctene in CHCl3 as solvent in the presence of different oxidant
by the Vanadyl Schiff base complex in the reflux conditiona.
Solvent
oxidante
-
Time(min)
120
Yield(٪)
chloroform
No
reaction
chloroform
chloroform
chloroform
chloroform
Sodium periodate
120
120
120
120
2
H2O2
UHP
10
41
93
TBHP
a
Reaction condition: (3 ml) chloroform, (1 mmol) cyclooctene, (2 mmol) oxidant and
(0.01 mmol) Vanadyl Schiff base complex.
26

Table 5. The effect of the amount of the oxidant in the epoxidation of cyclooctene in CHCl3
as solvent in the presence of TBHP by the Vanadyl Schiff base complex in the reflux conditiona.
Run
1
mmol of oxidante
Time(min)
120
Yield(٪)
0.5
0.75
1
80
10
4
2
120
3
120
4
2
120
93
20
5
2.5
120
a
Reaction condition: (3 ml) chloroform, (1 mmol) cyclooctene, (0.01 mmol) Vanadyl Schiff
base complex and (0.5, 0.75, 1, 2 and 2.5 mmol) oxidant.
27

Table 6. The effect of the amount of the Vanadyl Schiff base complex in the epoxidation of
cyclooctene in CHCl3 as solvent in the presence of TBHP complex in the reflux conditiona.
Run
1
mmol of catalyst
Time(min)
120
Yield(٪)
0
3
2
0.005
0.01
0.02
120
30
93
35
3
120
4
120
a
Reaction condition: (3 ml) chloroform, (1 mmol) cyclooctene, (0.01 mmol) Vanadyl Schiff
base complex and (0.5, 0.75, 1, 2 and 2.5 mmol) oxidant.
28

Table 7. Epoxidation of alkenes in CHCl3 as solvent in the presence of TBHP by the Vanadyl
Schiff base complex in the reflux condition a.
Entry
1
Alkene
Time(min)
Yield(٪)
120
93
2
3
480
360
85
76
4
5
120
480
60
50
6
480
40
a
Reaction condition: (3 ml) chloroform, (1 mmol) alkene, (0.01 mmol) Vanadyl Schiff base
complex and 2 mmol TBHP.
29