Epoxidation of cyclohexene with tert-butyl hydroperoxide catalyzed by mixed oxide V2O5–TiO2

Article abstract of DOI:10.1002/jccs.201800014

TiO₂ and 20 wt% V₂O₅–TiO₂ catalysts were prepared by the sol–gel route and calcined at 500 °C. The mixed oxide presented the crystalline structures of TiO₂ anatase and V₂O₅ Shcherbinaite phases, with a BET (Brunauer–Emmett–Teller) surface area of 19 m²/g. The catalytic material was tested for the epoxidation of cyclohexene by tert-butyl hydroperoxide at 80 °C. The activity and selectivity were investigated as a function of the reaction time as well as the amounts of the catalyst and solvent. The reaction followed second-order kinetics, and the best catalytic performance was observed after 6 hr of reaction time, with 150 mg of catalyst in n-heptane solvent. The epoxidation selectivity reached 76% at 48% conversion. The catalyst remained stable after two cycles.

Full text of DOI:10.1002/jccs.201800014

Received: 11 January 2018
Revised: 19 May 2018
Accepted: 21 June 2018
DOI: 10.1002/jccs.201800014
A R T I C L E
Epoxidation of cyclohexene with tert-butyl hydroperoxide
catalyzed by mixed oxide V2O5–TiO2
Driss Lahcene1 | Abderrahim Choukchou-Braham2
1Laboratoire de chimie et sciences de
TiO2 and 20 wt% V2O5–TiO2 catalysts were prepared by the sol–gel route and cal-
cined at 500 C. The mixed oxide presented the crystalline structures of TiO2 ana-
l'environnement, Facultés de sciences exact,
ꢀ
Université TAHRI Mohamed de Béchar, Bechar,
Algeria
tase and V2O5 Shcherbinaite phases, with a BET (Brunauer–Emmett–Teller)
2Laboratoire de Catalyse et Synthèse en Chimie
surface area of 19 m2/g. The catalytic material was tested for the epoxidation of
Organique, Université de Tlemcen, Tlemcen,
ꢀ
cyclohexene by tert-butyl hydroperoxide at 80 C. The activity and selectivity
Algeria
were investigated as a function of the reaction time as well as the amounts of the
Correspondence
Driss Lahcene, Laboratoire de chimie et sciences
de l’environnement, Facultés de sciences exact,
Université TAHRI Mohamed de Béchar, BP
417 Route Kenadsa Bechar 08000, Algeria.
Email: drissino@yahoo.fr
catalyst and solvent. The reaction followed second-order kinetics, and the best cata-
lytic performance was observed after 6 hr of reaction time, with 150 mg of catalyst
in n-heptane solvent. The epoxidation selectivity reached 76% at 48% conversion.
The catalyst remained stable after two cycles.
KEYWORDS
epoxidation of cyclohexene and selectivity, mixed oxide, sol–gel, V2O5–TiO2
epoxidation of cyclohexene. High-valent early transition
metals, such as titanium (IV) and vanadium (V), have been
1
| INTRODUCTION
One of today's industrial routes for the formation of simple
epoxides is the chlorohydrin process, where alkenes react
with chlorine in the presence of sodium hydroxide. The for-
mation of epoxides via metal-catalyzed oxidation of alkenes
represents the most elegant and environmentally friendly
method for the production of this compound class.[1,2] Inno-
vation and improvement in catalytic epoxidation methods,
where molecular oxygen, hydrogen peroxide, or alkyl hydro-
peroxides are employed as the terminal oxidants, are highly
desirable.[3,4] Hence, from the environmental and economic
points of view, molecular oxygen and hydrogen peroxide
should be the preferred oxidants, considering their high
active oxygen content and the fact that there are no waste
products; only water is formed. However, one of the major
limitations when using molecular oxygen and hydrogen per-
oxide as terminal oxidants for the formation of epoxides is
the poor product selectivity obtained through these pro-
cesses.[5] Valderruten et al.[6] and Bellifa et al.[7] showed that
mixed oxides produced by the sol–gel method are the most
efficient and selective catalysts of this type of solids for the
shown to efficiently catalyze the epoxidation of alkenes in
homogeneous catalysis.[8] The most preferred oxidants using
these catalysts are various alkyl hydroperoxides, such as the
tert-butyl hydroperoxide (TBHP) or ethylbenzene hydroper-
oxide (EBHP). Amelioration the catalytic activity and selec-
tivity for the epoxidation of cyclohexene with cumene
hydroperoxide (CHP) as oxidant. In addition, the high sur-
face area mesoporous silicas (MCM-41 and SBA-15) are
more effective than amorphous silica as supports for these
catalysts. Supporting TiSi3 on the SBA-15 affords highly
active cyclohexene epoxidation catalysts (0.25–1.77 wt% Ti
loading), providing turnover frequencies (TOFs) of
500–1,500 hr−1 after 1 hr (TOFs are reduced by about half
after calcination). These results demonstrate that oxygen-rich
siloxide complexes of titanium are useful as precursors to
supported epoxidation catalysts.[9] Though titanium has been
used in several new applications of heterogeneous catalysis, it
is not the case for vanadium. Indeed, the development of the
solid titanium (IV)-silicate (TS-1) catalyst by chemists at Eni-
chem[10] represents a breakthrough for epoxidation reactions.
© 2018 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2018;1–7.
http://www.jccs.wiley-vch.de
1

2
LAHCENE AND CHOUKCHOU-BRAHAM
Catalytic liquid-phase epoxidation of cyclohexene is a com-
3500
3000
2500
2000
1500
1000
500
Intensity (count s-1)
mercially important reaction that is used to produce cyclohex-
ene oxide, which is an essential organic intermediate in the
production of fine chemicals. Moreover, the production of
epoxides paves the way to the development of mild and green
chemical processes for the synthesis of adipic acid, which is
the raw material used in the production of nylon 6,6.[11,12] The
use of solid catalysts for cyclohexene epoxidation, using TBHP
as oxidant, has been reported, with the formation of
2-cyclohexene-1-one, 2-cyclohexene-1-ol, and trans-cyclohex-
ane-1,2-diol, besides cyclohexene oxide.[3,13–17]
*
: Anatase TiO
*
¤
2
: Shcherbinaite V O
2
5
20%V2O5-TiO2
*
*
*
*
¤
*
*
¤
¤
*
*
*
¤
*
¤
Sasidharan et al.[18] studied the regioselective epoxida-
tion of different types of double bonds located within the
cyclic and acyclic parts of bulky olefins using large-pore
titanium silicate Ti-β in the presence of dilute aqueous H2O2
as oxidant under mild liquid-phase conditions. Their experi-
mental results revealed that the epoxidation tendency of vari-
ous bulky olefins with different positional and/or geometric
isomers over Ti- β follows the order: terminal –C C– > ring
–C C– ≈ bicyclic ring –C C– > allylic C−H bond.
TiO2
0
10
20
30
40
50
60
70
80
2 theta /°
FIGURE 1 X-ray diffraction (XRD) patterns of TiO2 and 20%V2O5–TiO2
catalysts
Many recent studies have shown that the V2O5–TiO2 cat-
alyst can be used for the selective oxidation of saturated and
unsaturated hydrocarbons such as cyclohexane, benzene,
and o-xylene.[19–22] To our knowledge, no study using the
V2O5–TiO2 system for cyclohexene epoxidation has been
reported so far.
After a preliminary paper on the sol–gel synthesis and
characterization of various V2O5–TiO2 mixed oxides,[23–25]
the preparation and catalytic activity of 20 wt% V2O5–TiO2
catalysts are described here. The prepared catalyst was char-
acterized by X-ray diffraction (XRD) and nitrogen physi-
sorption (specific surface area (SBET), pore size, and pore
volume) in order to understand its behavior and performance
as a solid catalyst for the epoxidation of cyclohexane, using
TBHP as oxidizer. Furthermore, the kinetics, catalyst stabil-
ity, catalyst mass, and the solvent effects on the epoxidation
reaction were studied.
ꢀ
500 C (not shown), indicating that vanadium oxide was
present earlier in a highly dispersed manner. The quantitative
composition was estimated from the intensity of the most
intense diffraction peaks, and the I/Icor factor was deduced
from the corresponding powder diffraction files (1.60, (001)
peak for V2O5; 3.30, (101) peak for anatase); the mass per-
centage of V2O5 is about 10%, i.e., half the expected value,
thus showing that an important part of vanadium (about
10 wt% V2O5) was not present in the crystalline form.
Therefore, the possibility of a partial substitution of
Ti(IV) by V(IV) in the anatase structure cannot be ruled out;
the initial oxidation number of vanadium introduced during
the preparation procedure is IV. The average crystallite sizes
of both phases are given in Table 1. V2O5 presented a
slightly higher size (33 nm) compared to anatase (27 nm).
The specific surface area showed a significant decrease
when vanadium oxide was introduced into titanium oxide
(40 and 19 m2/g, respectively, for TiO2 and V2O5–TiO2)
(Table 1), which is not in line with the variation of the tita-
nia’s crystallite size. A simple cubic model, with six free
faces, gave, as expected, higher values of the surface area;
the calculated value for TiO2 agrees with the experimental
one (64 vs. 40 m2/g), whereas the mixed oxide displays a
larger difference (57 vs. 19 m2/g). The pore volume and
mean pore size data are found to be in line with the classical
mesoporous cylindrical model (Table 1).
2
| RESULTS AND DISCUSSION
2.1 | Sample characterization
The results of XRD analysis of TiO2 and 20 wt%V2O5–TiO2
samples are shown in Figure 1. Typical diffraction peaks
characteristic of TiO2 anatase crystalline phase (ICDD-PDF
21–1272) and V2O5 Shcherbinaite crystalline phase (ICDD-
PDF 041–1426) were observed. No rutile phase was
detected in these oxides. These results are in line with the
recently published synthesis of sulfated mixed vanadium
oxide (25 wt% V2O5–TiO2/SO42−) prepared by the sol–gel
route and calcined at 773 K[26]; both anatase (TiO2) and
Our data can be usefully compared to recent published
results; a close value of the surface area (22 m2/g) was found
for sulfated 1% V2O5–TiO2 prepared by sol–gel procedure
[27]
ꢀ
and calcined at the same temperature (500 C).
Rodella
et al.[25] prepared V2O5/TiO2 catalysts using ammonium
2
Shcherbinaite (V2O5) were present when the wt% of SO4
−
vanadate as the vanadium precursor and V2O5 mass loading
up to 9%. After calcination at 450 C, the surface area was
was <0.3. In this study, the crystalline vanadia phase
ꢀ
appeared only when the calcination temperature reached

LAHCENE AND CHOUKCHOU-BRAHAM
3
TABLE 1 XRD crystallite size, N2 physisorption data, cubic crystallite model, and cylindrical pore model
Sample
XRD mean size/nm
24
SBET/m2ꢂg−1
40
SXRDa/m2.g−1
Pore volume/cm3ꢂg−1
0.093
Pore size/nm
Cylindrical pore modelb
TiO2
64
57
9.0
30
3,900
4,100
20%V2O5–TiO2
27 (TiO2)
19
0.14
33 (V2O5)
a
SXRD: Calculated from the mean size and a cubic model with six free faces.
SBET.(pore size)/(pore volume) (calculated value with the same units: 4,000).
b
found to be 87 m2/g; no separate vanadium oxide phase
could be seen by XRD, which is in good agreement with our
results. Bellifa et al.[22] prepared 20 wt%V2O5–TiO2 directly
fromꢀ V2O5 by an acidic sol–gel route; after calcination at
300 C under oxygen flow, the specific surface area was
found to be 27 m2/g; the presence of crystalline V2O5 oxide
could be observed from the diffractogram besides the ana-
tase and rutile phases. In a more recent paper, Debecker
et al.[19] used a non-hydrolytic sol–gel method where TiCl4
and VOCl3 were employed as oxide precursors in diꢀisopro-
pyl ether. The final calcination temperature was 500 C and
the V2O5 mass percentage was increased up to 10% (specific
surface area 71 m2/g); again, no separate vanadium oxide
phase could be observed.
besides a low formation of epoxide and oxidation products. In
the presence of V2O5–TiO2, the conversion and epoxide selec-
tivity increase to 46 and 79%, respectively. Despite the diffi-
culty in analyzing quantitatively the remaining TBHP by
iodine titration under the reaction conditions, the conversion
data are in good agreement with the disappearance of one
TBHP molecule for each cyclohexene molecule, as expected
for the formation of epoxides (Table 2). The cyclohexene con-
version and the yield of products versus time in presence of
150 mg of V2O5–TiO2 catalyst are presented in Figure 2.
2.2.2
| Influence of the catalyst mass
Cyclohexene conversion and the product selectivity were deter-
ꢀ
mined at 80 C for different masses of the mixed-oxide catalyst
(10, 25, 100, 150, and 250 mg). The results are presented in
Table 3, and the kinetic data are shown in Figure 3. The con-
version percentage increases as the mass is increased from
25 to 100 mg; the same remark can be made for the selectivity
in epoxide. Then, the conversion remains stable for the catalyst
mass of 250 mg, while the selectivity changes; it drops in
epoxide but rises mainly in C6 one and C6 diol products.
Higher cyclohexene conversion (48%) and epoxide selectivity
(76%) were observed for 150 mg of the catalyst. More experi-
mental work is needed in order to explain these results.
2.2 | Catalytic tests
2.2.1
| Preliminary tests
The oxidation of cyclohexane using TBHP was investigated at
temperatures 70 and 80 C (Table 2). Cyclohexene was oxi-
dized into cyclohexene oxide (C6 epoxide), cyclohexenol (C6
enol), cyclohexenone (C6 enone), cyclohexanone (C6 one), and
trans-1,2-cyclohexanediol (C6 trans) (Scheme. 1). The catalytic
performances of both catalysts in terms of cyclohexene conver-
ꢀ
ꢀ
sion and epoxide selectivity are presented in Table 2. At 70 C,
the conversion is 10% and the selectivity to cyclohexenol is
100%, in the absence or presence of TiO2, which means that
titania here has no influence. The mixed-oxide catalyst leads to
a significant increase in cyclohexene conversion (38%) and
epoxide selectivity (74%). The very low level of cyclohexenol
selectivity (6%) and the presence of the other oxidation prod-
ucts agree with the presence ofꢀa catalytic transformation of C6
enol as a side-reaction. At 80 C, the cyclohexene conversion
increases slightly for a blank test and in the presence of TiO2
(13 and 14%); the cyclohexenol selectivity remains high,
2.2.3
| Kinetics of reaction
The results obtained for 150 mg of catalyst are considered to
determine the reaction order and the rate constant; this corre-
sponds to the highest conversion (56%) after 10 hr. The rate
equation may be written as follows[28]
:
α
β
Rate = k½C6 eneꢁ ½TBHPꢁ = −d½C6 eneꢁ=dðtÞ,
where [C6 ene] and [TBHP] represent the cyclohexene and
TBHP concentrations, respectively, α and β are the
TABLE 2 Cyclohexene oxidation at two temperatures
aSelectivity/%
Temperature/ꢀC
Sample
bCyclohexene conversion/%
TBHP conversion/%
Epoxide
C6 enol
100
100
6
C6 enone
C6 one
trans-C6 diol
70
Blank test
TiO2
10
10
38
13
14
46
—
10
35
10
12
41
0
0
0
0
7
2
4
8
0
0
2
0
0
2
0
0
20%V2O5–TiO2
Blank test
TiO2
74
6
11
4
80
88
12
79
78
6
20%V2O5–TiO2
2
9
a
Epoxide: cyclohexene epoxide; C6 enol: 2-cyclohexenol; C6 enone: 2-cyclohexenone; C6 one: cyclohexanone; trans-C6 diol: trans-1,2-cyclohexanediol.
Reaction conditions: 3 mL cyclohexene; 25 mL heptane; 5 mL TBHP/decane; 100 mg catalyst; 6 hr.
b

4
LAHCENE AND CHOUKCHOU-BRAHAM
OH
OH
50
40
30
20
10
0
Conversion of cyclohexene /%
O
V2O5-TiO2
TBHP 5.5 mol.L -1 in decane
80 °C, 0.1 g , 6 h
OH
O
O
10 mg
25 mg
100 mg
150 mg
250 mg
SCHEME 1 Products identified during the oxidation of cyclohexene
by TBHP
Time /min
0
50 100 150 200 250 300 350 400
C6 enol
C6 enone
C6 one
5
C6 ene
FIGURE 3 Cyclohexene conversion versus time for different 20%V2O5–
C6 epox
TiO2 catalyst masses: temperature 80 ꢀC
50
40
30
20
10
0
order dependence of the oxidation reaction. The rate con-
stant k is equal to 2.14 × 10−3 L mol−1 min−1. Analysis of
the same data for a first-order reaction kinetics leads to a sig-
nificantly lower correlation coefficient (R = 0.97886, figure
not shown).
4
3
2
1
2.2.4
| Solvent effect
The selection of the solvent is an important step in the reac-
tion design. In order to identify suitable alternative solvents,
it is interesting to have a classification system so that sol-
vents with similar properties can be readily identified.[29] All
solvents should have properties that fulfill some specific
requirements related to the environment, safety, and
health.[30]
0
400
0
50
100
150
200
250
300
350
Time / min
FIGURE 2 Cyclohexene conversion and product yield versus time in the
presence of 150 mg of 20%V2O5–TiO2: temperature 80 ꢀC
Classification schemes have been proposed on the basis
of different properties such as the dipole moment, dielectric
constant, solubility, and polarity.[31] Table 4 shows the prop-
erties of the tested solvents. The behavior of cyclohexene
oxidation by TBHP in various solvents is very strikingly dif-
respective kinetic reaction orders, and k is the second-order
rate constant. Considering the classical assumption α = 1
and β = 1, and taking into account the close initial concen-
trations of cyclohexene and TBHP, integration leads to the
following equation:
ꢀ
ferent, as can be seen in Table 5 (80 C, 100 mg of catalyst).
Acetic acid gives the best conversion (52%) after 6 hr, fol-
lowed by heptane (46%) and acetonitrile (37%), whereas
propan-2-ol is only slightly better than the blank test (14%).
The selectivity to epoxide is the highest for the nonpolar sol-
vent n-heptane; it decreases to 50% in the two polar solvents
acetonitrile and propan-2-ol. It can easily be noted that the
1=½C6 eneꢁ = kt + 1=½C6 eneꢁt = 0
:
A plot of 1/[C6 ene] versus time is displayed in Figure 4
for a time range extending from 20 min to 10 hr. The
observed linear relationship is in agreement with the second-
TABLE 3 Cyclohexene oxidation with different catalyst masses on 20%V2O5–TiO2
aSelectivity/%
Catalyst mass/mg
bCyclohexene conversion/%
Epoxide
C6 enol
C6 enone
C6 one
trans-C6 diol
10
28
37
46
48
40
72
76
79
76
60
14
8
8
6
0
0
2
2
6
25
9
7
100
150
250
2
9
8
2
10
13
10
17
4
a
Epoxide: cyclohexene epoxide; C6 enol: 2-cyclohexenol; C6 enone: 2-cyclohexenone; C6 one: cyclohexanone; trans-C6 diol: trans-1,2-cyclohexanediol.
Reaction conditions: 3 mL cyclohexene; 25 mL heptane; 5 mL TBHP/decane; 80 ꢀC; 6 hr.
b

LAHCENE AND CHOUKCHOU-BRAHAM
5
vanadium have oxidation power. In the presence of heptane,
they promote the oxidation reaction of cyclohexene with an
epoxide selectivity.[17,37] The epoxidation of cyclohexane
with TBHP and H2O2 on Tiβ-1 catalyst has been studied
using CH3OH as solvent. It has been shown that TBHP is
more beneficial to the selective production of epoxide than
H2O2. It is also assumed that a similar mechanism is opera-
tive for the epoxidation of cyclic alkenes with H2O2 and
TBHP as oxidants. Obviously, the transition state involving
Ti–OOR and cyclic alkenes must be much bulkier than that
that relating to Ti–OOH and alkenes. This characteristic sig-
nificantly retards the reaction rate of cyclic alkenes with
TBHP, further decreasing the possibility of acid-catalyzed
ring-opening secondary reaction of the epoxide molecule.[38]
2.8
1/[cyclohexene]
2.6
2.4
2.2
2
R = 0.99015
k = 2.14 x 10-3 L mol-1 min-1
1.8
1.6
1.4
1.2
Time /min
400 500 600
0
100
200
300
FIGURE 4 Pseudo-second-order kinetics of cyclohexene oxidation with
150 mg of 20%V2O5–TiO2 catalyst at 80 ꢀC
2.2.5
| Recyclability of the reactions
Reutilization is one of the greatest advantages of heteroge-
neous catalysts; it can provide useful information about the
intercalation process and catalytic stability during the suc-
cessive catalytic cycles. The solid catalyst was recovered by
filtration and dried in open air. After the first cycle, conver-
sion decreased from 46 to 39% during the second cycle, and
then remained stable (38% for the third cycle, Table 5). The
selectivity showed slight changes only. These results suggest
that the catalyst is stable during the catalytic reaction and is
thus suitable for recycling.
second major product is not the same for the two solvents; it
is cyclohexanone in acetonitrile and cyclohexenol in propa-
nol. One can thus see that acetonitrile promotes the classical
enol–cetone transformation. In acetic acid, the major product
is cyclohexanol, and the absence of epoxide is in agreement
with the rapid transformation into trans-1,2 cyclohexanediol
because epoxides are unstable in acid solvents. Epoxides can
be cleaved in a regio- and stereo-selective manner under
neutral conditions, with alcohols and acetic acid.[32] The
conversion values are high in the presence of acetic acid and
some vanadium species (V2O5); this may be due to the for-
mation of stable peracids (peroxyacetic), which promote the
oxidation of hydrocarbons.[33]A high conversion is observed
in the case of acetonitrile (37%) with good epoxide selectiv-
ity (52%). The selectivity to epoxide obtained with acetoni-
trile as solvent results from the decreasing acidity, probably
due to the coordination of acetonitrile through the nitrogen
atom, leading to a decrease in the extent of the acid-
catalyzed secondary reaction.[34] It is widely reported in the
literature that the best solvent for oxidation is acetonitrile,
which is a polar aprotic solvent.[35] Acetonitrile was more
suitable for the epoxidation of cyclohexene on TS-1 than
methanol because the reaction occurred mainly on the hydro-
philic external surface.[36] In our case, heptane gives the best
activity and selectivity, which means that there is an interac-
tion between heptane as solvent and the vanadium species
(V2O5). Catalysts based on metals such as chromium and
3
| CONCLUSIONS
The mixed oxide 20 wt% V2O5–TiO2 was prepared by the
sol–gel method. Structural (XRD) and textural analyses
(nitrogen physisorption) showed that V2O5–TiO2 has the
crystalline structure of the anatase phase, and the introduc-
tion of vanadium oxide decreases the specific surface area.
Only half of the introduced vanadium was found as the
minor crystalline phase V2O5, whereas the second half was
well dispersed. This mixed oxide has proven to be an effi-
cient catalyst for the selective epoxidation of cyclohexene by
TBHP. Cyclohexene conversion was higher than 50%, and
the maximum selectivity (79%) for epoxidation of cyclohex-
ꢀ
ene was observed at the temperature of 80 C in n-heptane.
The oxidation reaction was shown to follow second-order
kinetics.
TABLE 4 Properties of the solvents
c
N
Solvent designation
Nonpolar aprotic
Polar aprotic
Solvent
Ta
98
82
μ
b (debye)
0
εr
1.92
37.5
ET
Polarity of constant
boi
n-Heptane
Acetonitrile
Acetic acid
Propanol-2
0.012
0.460
0.648
0.546
—
3.45
1.68
1.59
192.28
214.02
203.15
Polar aprotic
118
82
6.15
Polar aprotic
19.92
a
b
c
Boiling point.
Dipole moment (1 debye = 3,336 × 10−30 C m).
Dielectric constant at 20 ꢀC.

6
LAHCENE AND CHOUKCHOU-BRAHAM
TABLE 5 Effect of solvent and number of cycles on cyclohexene oxidation
aSelectivity (%)
Solvent
bConversion (%)
TBHP (%)
Epoxide
C6 enol
C6 enone
C6 one
trans-C6 diol
Heptane cycle 1
Heptane cycle 2
Heptane cycle 3
Acetonitrile
46
39
38
37
52
14
41
35
35
30
95
10
79
76
74
52
0
2
9
8
2
6
8
6
4
9
11
10
6
6
0
9
29
9
0
Acetic acid
46
28
39
0
Propan-2-ol
51
14
7
a
Epoxide: cyclohexene epoxide; C6 enol: 2-cyclohexenol; C6 enone: 2-cyclohexenone; C6 one: cyclohexanone; trans-C6 diol: trans-1,2-cyclohexanediol.
Reaction conditions: 3 mL cyclohexene; 25 mL solvent; 5 mL TBHP/decane, 80 ꢀC, 100 mg catalyst, 6 hr.
b
4
|
EXPERIMENTAL
references listed in the ICDD database. The average crys-
tallite size was estimated using the Scherrer law.
4.1 | Catalyst preparation
4.2 | Catalytic activity evaluation
4.1.1
| Starting materials
Cyclohexene oxidation reactions were carried out in a
Titanium tetrabutoxide (Ti[OC4H9]4, Aldrich, 97%), vanadyl
acetylacetonate (VO[C5H7O2]2, Merck), propan-2-ol (99,5%,
Merck), acetic acid (Prolabo, 100%), cyclohexene (Aldrich,
98%), heptane (Fluka), and tertiobutylhydroperoxide solution
(Aldrich, 5.5 mol/L in decane) were used in the experiments.
100-mL, three-neck flask placed in
a temperature-
equilibrated water bath and equipped with a reflux con-
denser. A mixture containing 5 mL of TBHP in decane
(27.3 mmol), 3 mL of cyclohexene (28.9 mmol), 25 mL of
the solvent (heptane, acetonitrile, acetic acid or propan-2-ol),
and 10–250 mg of the catalyst was prepared, and then mag-
4.1.2
| Synthesis of TiO2
ꢀ
netically stirred under atmospheric pressure at 70 or 80 C
Titanium butoxide (24.29 g, 0.0714 mol) and 0.50 mL of
acetic acid (9.0 mmol) were dissolved in 50 mL of propan-
2-ol, and the resulting mixture was stirred for 15 min. The
white gel formed after the addition of 50 mL of H2O was
with a speed of 460 rpm for 6–10 hr. The reaction mixture
was analyzed by gas chromatography (GC) by taking ali-
quots (0.2 mL) at different reaction times. Before injection
into the chromatograph, the aliquots were treated with
100 mg triphenylphosphine (TPP) in 1 mL hexane (mini-
mum mol ratio TPP/TBHP = 3) to remove the remaining
TBHP. A volume of 0.50 μL was injected into a Varian GC-
450 gas chromatograph equipped with a CP-wax-52 B
(25 m × 0.32 μm × 1.2 μm) column; a flame ionization
detector (FID) was also used. The consumption of TBHP
was determined by iodometric titration.
ꢀ
ꢀ
dried at 60 C overnight, then at 120 C for another night,
ꢀ
and finally calcined at 500 C for 4 hr under static air in a
muffle furnace (heating rate of 5 ꢀC/min).
4.1.3
| Synthesis of 20 wt% V2O5–TiO2
The mixed oxide was prepared by the acid-catalyzed sol–gel
method[39] using 3.499 g (0.0132 mol) of vanadyl acetylace-
tonate dissolved in water under stirring for 15 min. Then a
mixture containing titanium butoxide (20.45 g, 0.0601 mol),
acetic acid (0.50 mL, 9 mmol), and propan-2-ol (50 mL)
was added into the first solution while stirring. The obtained
green gel was first dried and then calcined, as previously
done for TiO2.
ACKNOWLEDGMENTS
The authors would like to thank the staff at the Institute of
Chemistry of Mediums and Materials, University of Poitiers
(UoP, France). They would also like to thank the Algerian
Ministry of Higher Education and Scientific Research for the
fellowship funding at UoP.
4.1.4
| Catalyst characterization
The surface area, pore size, and pore volume were deter-
mined using nitrogen adsorption at 77 K, on a Micromeri-
tics Tristar 3000 apparatus, after heat pretreatment under
ORCID
Driss Lahcene
http://orcid.org/0000-0001-8701-906X
ꢀ
vacuum for 6 hr at a temperature of 250 C. The XRD
measurements were carried out on a Bruker D5005 powder
diffractometer for an angle 2θ ranging from 10 to 80ꢀ at a
rate of 0.02ꢀ s−1, using a monochromatized Cu Kα radia-
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How to cite this article: Lahcene D, Choukchou-
Braham A. Epoxidation of cyclohexene with tert-
butyl hydroperoxide catalyzed by mixed oxide V2O5–
TiO2. J Chin Chem Soc. 2018;1–7. https://doi.org/10.
1002/jccs.201800014
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