A facile method for promoting activities of vanadium-schiffbase complex anchored on organically modified MCM-41 in epoxidation reaction

Article abstract of DOI:10.1016/j.molcata.2010.03.028

A heterogeneous catalytic system (V-MCM-41) displays a most pronounced efficiency with NaHCO₃ as co-catalyst and H₂O₂ as oxidant in a CH₃CN medium at room temperature towards epoxidation reaction.

Full text of DOI:10.1016/j.molcata.2010.03.028

Journal of Molecular Catalysis A: Chemical 325 (2010) 40–47
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
A facile method for promoting activities of vanadium–schiffbase complex
anchored on organically modified MCM-41 in epoxidation reaction
K.M. Parida∗, Sudarshan Singha, P.C. Sahoo
Colloids and Materials Chemistry Department, Institute of Minerals & Materials Technology, Bhubaneswar-751013, Orissa, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An organic–inorganic hybrid heterogeneous catalyst (V-MCM-41) was synthesized by anchoring
vanadium–schiffbase complex on chloropropyl modified mesoporous silica (CP-MCM-41). Characteri-
zation of the functionalized ordered two-dimensional mesoporous material by powder X-ray diffraction
(XRD), N2 adsorption–desorption, CP-MAS NMR spectroscopy (13C and 29Si), Fourier transform infrared
spectroscopy (FT-IR), diffuse-reflectance UV–vis spectroscopy, demonstrate the successful grafting of
vanadium complex into the functionalized mesoporous silica. It is also observed that the mesostructure
has not been destroyed in multistep synthetic procedure. We have performed the epoxidation reaction
of various olefins using V-MCM-41 as the catalyst, hydrogen peroxide as the oxidant and sodium bicar-
bonate as the co-catalyst in acetonitrile solvent. The co-catalyst enhances the rate of reaction by many
folds. The reaction requires minimum amount of H2O2, short time period and most importantly occurs at
room temperature. The heterogeneous catalyst can be recovered easily and reused many times without
significant loss in catalytic activity and selectivity.
Received 15 February 2010
Received in revised form 17 March 2010
Accepted 23 March 2010
Available online 30 March 2010
Keywords:
Mesoporous silica
Immobilization
Vanadium complex
Schiffbase
Epoxidation
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
plex used in epoxidation taking tert-butylhydroperoxide as oxidant
[5]. Schiffbase complex bearing salen ligand represents one of the
The discovery of efficient method for catalytic epoxidation is an
important goal in synthetic chemistry as there is a growing interest
in using epoxide as building block in organic synthesis. Devel-
oping systems that achieve high selectivity using environmental
friendly conditions and inexpensive terminal oxidants remain as
an important challenge [1,2]. In this context, H2O2 is probably the
best ecological sustainable green terminal oxidant after dioxygen
as water is the only byproduct. In certain circumstances, it is better
than O2 in so far as O2–organic mixtures sometimes spontaneously
ignite. In actual epoxidation process, alkyl hydroperoxide is used as
oxidant. Since alkyl hydroperoxide is traditionally obtained by the
reaction of H2O2 and aliphatic acid or acid derivatives, the epoxida-
tion reaction in alkyl hydroperoxide generates a significant amount
of waste and co-products [3,4].
The use of transition metal complexes as catalyst has been
receiving increasing attention during past two decades due to many
reasons: (1) the requirement for the functionalization of lower
alkenes formed as byproducts in the manufacture of gasoline, (2)
the need for partial selective oxidation and (3) the preparation of
compounds with a specific spatial structure. The transition metal
complexes seem to fulfill some of these requirements. Vanadium
pentoxide was probably one of the first transition metal com-
effective catalytic systems for the epoxidation of olefins. Recently
vanadyl acetylacetonate grafting on to mesoporous silica used for
the epoxidation of geraniols has been reported by Jarris et al.
[6]. Transition metal schiffbase complexes (e.g., M = Mn2+, Ni2+
,
Fe3+, Co2+, and Cu2+) chemically anchored on Y zeolite (partially
modified by n-octadecyltrichlorosilane) have been applied to the
epoxidation of 1-octene [7]. However, these catalysts have very low
reactivity (conversion <3% after 24 h at 100 ◦C) despite high selec-
tivity to epoxide (96%). Busch et al. reported olefin epoxidation by
the hydrogen peroxide adduct of a novel non-heme manganese (IV)
complex, where they demonstrate the oxygen transfer by multiple
mechanisms [8]. The asymmetric epoxidation of olefins catalyzed
by the manganese–salen complexes developed by Jacobsen et al.
provides an easy approach to unfunctionalized epoxides [9].
Complex encapsulation and methodologies involving grafting
and tethering procedures have been shown several advantages
over method based on non-covalent interaction such as electro-
static, ␲–␲*, hydrophobic/hydrophilic interactions and hydrogen
bonds [10]. The heterogenization of homogeneous catalyst has
gained considerable interest over the last few decades; the most
attractive advantage is the easy separation of the product from
the catalyst without tedious experimental work-up. Mesoporous
silica is a kind of ideal support which possess high surface area
and ordered mesoporous channels [11,12]. This will be beneficial
to the enhancement of loading amounts and dispersion of catalytic
active sites. The preparation of organic–inorganic hybrid materi-
∗
Corresponding author. Tel.: +91 674 2581636×425; fax: +91 674 2581637.
E-mail address: paridakulamani@yahoo.com (K.M. Parida).
1381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.03.028

K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 325 (2010) 40–47
41
Scheme 1. Schematic representation of the formation of V-MCM-41 within the pore channels of MCM-41.
als is of growing interest [13–15]. In contrast to organic polymers,
2.2. Synthesis procedures
organic–inorganic hybrid materials do not swell or dissolve in
organic solvents. This type of material has many advantages over
most organic polymers because of their superior mechanical and
thermal stabilities. The surface fuctionalization of mesoporous sil-
ica with different organic groups has been reported in literature.
Both mesoporous and modified mesoporous silica have already
been used for several transition metal catalysts such as manganese,
copper, and titanium [16–18]. Obviously, the design of mesoporous
silica supported metal complex represents a rapidly growing field
that has significantly applied in industry.
Metal complex containing vanadium has been found to be an
efficient catalyst for the epoxidation of allylic alcohols but shows
relatively poor catalyst for olefin epoxidation. But here in, we are
very much delighted to report an efficient vanadium-based catalyst
which is found to be effective for the epoxidation of olefins. This
catalyst is in tandem with NaHCO3 and aqueous H2O2 in a CH3CN
medium at room temperature which display a most pronounced
efficiency (% yield, low catalyst loading and high selectivity) in
olefin oxidation.
2.2.1. Preparation of hybrid mesoporous material: chloro
functionalized MCM-41 (CP-MCM-41)
Parent silica MCM-41 was prepared by
a standard pro-
cedure [19]. Organic modified mesoporous silica with 3-
chloropropyltrimethoxysilane(3-CPTMS) (Scheme 1) was prepared
according to litreture [20], using C16H33N(CH3)3Br (CTAB) as
templete, tetraethylorthosilicate (TEOS) as silica precurser and 3-
CPTMS as organoalkoxysilane precurser. The mixture contained
CTAB/TEOS/CPTMS/NaOH/H2O (1.0:8.16:1.05:2.55:4857) based on
molar ratio. The mixture of CTAB (2.0 g, 5.49 mmol), 2.0 M of NaOH
(aq) (7.0 ml, 14.0 mmol) and H2O (480 g, 26.67 mmol) was heated
at 80 ◦C for 30 min to reach pH 12.3. To this clear solution, TEOS
(9.34 g, 44.8 mmol) and CPTMS (1.03 g, 5.75 mmol) were added
sequentially and rapidly via injection. Following the injection, a
white precipitation was observed after 3 min of stirring. The reac-
tion temperature was maintained at 80 ◦C for 2 h. The product was
isolated by hot filtration, washed with copious amount of water
and ethanol and dried under vacuum. To this dried product, an acid
extraction process was performed in a methanol (100 ml) mixture
of concentrated hydrochloric acid (1.0 ml) at 60 ◦C for 6 h. with
stirring. Resulting surfactant removed product was filtered and
washed with water and ethanol and dried under vacuum.
2. Experimental methods
2.1. Materials
2.2.2. Synthesis of schiffbase ligand
(3-Chloropropyl)
trimethoxysilane
(CPTMS),
tetraethyl
To an ethanolic solution of salicyldehyde (2.12 ml, 20 mmol) a
solution of diethylenetriamine (0.96 ml, 10 mmol) was added. The
resulting yellow colour solution was allowed to reflux for 2 h. The
excess of solvent was removed under vacuum and a dark yellow
oily product was obtained. In a silmillar manner various substituted
ligands were synthesized by taking substituted salicyldehydes.
orthosilicate Si(OC2H4)4 (TEOS), cetyl trimethylammonium-
bromide (CTAB), cyclohexene, styrene, norbornene, allylic alcohol,
1-octene, cyclooctene, crotylalcohol, VOSO4·H2O (Aldrich), sali-
cyldehyde, diethylene triamine (CDH), and acetonitrile (Across)
were used without further purification.

42
K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 325 (2010) 40–47
2.2.3. Synthesis of V-MCM-41
3. Results and discussion
To a suspension of freshly dried CP-MCM-41 (1 g) in 40 ml of
ethanol, a solution of 3.1 mmol of above prepared ligand in 10 ml
of ethanol was added and the resulting solution was refluxed for
10 h. The whole solution turned yellowish upon addition of lig-
and. The solid was separated, washed repeatedly with ethanol to
remove the unreacted ligand. VOSO4 (1.56 g, 6.2 mmol) was added
in 25 ml ethanol to this solid. The solution immediately turned light
green indicating immobilization of vanadium, and the final prod-
uct is abbreviated as V-MCM-41. Atomic absorption spectrometric
analysis showed vanadium content in the sample is ca. 0.32%.
3.1. Characterization of the heterogeneous catalyst
3.1.1. Powder X-ray diffraction
Fig. 1 shows the powder XRD patterns of MCM-41, CP-MCM-41
and V-MCM-41. In case of MCM-41 four diffraction peaks corre-
sponding to Miller indices (1 0 0), (1 1 0), (2 0 0), and (2 1 0) in the
range 2ꢀ = 2–8◦ imply that of typical hexagonal structure. However,
after organo-functionalization and metal complex loading there is a
slight decrease in intensity with broadening of corresponding peaks
indicating a slight disorder in the CP-MCM-41 and V-MCM-41. The
addition of organic group probably distorts the regular liquid crys-
talline array of the template and lowers the long-range order of the
MCM-41 mesostructure. This is evidenced by the steric effect that
becomes more significant when larger or more abundant organic
species are added. This is not interpreted as a severe loss of long
range ordering of the silica framework [21,22].
2.3. Physico-chemical characterizations
Powder X-ray diffraction (XRD) patterns of the samples were
obtained on Rigaku D/Max III VC diffractometer with Cu K␣
radiation at 40 kV and 40 mA in the range of 2ꢀ = 0–10◦. The scan-
ning rate was 2◦ min−1. Nitrogen adsorption–desorption isotherms
were measured at liquid nitrogen temperature using ASAP 2020
(Micromeritics). Before the measurement, the samples were out
gassed at 100 ◦C for 3 h to evacuate the physically adsorbed
moisture. Specific surface area was calculated using BET method.
Solid-state 13C and 29Si cross-polarization magic-angle spinning
NMR spectra were recorded at 100.58 and 79.46 MHz, respectively
using a Bruker Avance 400 MHz spectrometer.
3.1.2. N2 sorption studies
N2 adsorption–desorption isotherms of MCM-41, CP-MCM-41
and V-MCM-41 are given in Fig. 2. Analysis of N2 adsorption and
desorption data exhibit a typical type-IV isotherm (defined by
IUPAC) with a small hysteresis for neat MCM-41, CP-MCM-41 and
V-MCM-41, characteristic for a mesoporous structure. The relative
pressure at which pores are filled is shifted to a lower value for
modified samples in comparison to the parent materials, resulting
in decrease in BET specific surface area, pore volume and pore diam-
eter. The results are presented in Table 1. The nitrogen sorption
study exhibits that the BET surface area of MCM-41 is 1280 m2 g−1
and the mesopore volume is 1.19 cm3/g. The average pore diame-
tre is calculated to be 30.7 Å using the BJH method. All calculated
values are in agreement with those reported for good quality meso-
porous silica. CP-MCM-41 shows less N2 uptake (BET surface area
The FT-IR spectra of the samples were recorded using Var-
ian 800-FT-IR in KBr matrix in the range of 4000–400 cm−1
.
The coordination environments of the samples were examined
by diffuse-reflectance UV–vis spectroscopy. The spectra were
recorded in Varian-100 spectrophotometer in the wavelength
range of 200–800 nm in BaSO4 phase. The V loading in the catalyst
and in the leaching solution was determined by atomic absorption
spectroscopy (AAS) with a PerkinElmer Analysis 300 using acety-
lene (C2H2) flame.
2.4. Catalytic reaction
Catalytic test of the prepared heterogeneous catalyst (V-MCM-
41) was carried out in a 100 ml two-necked round bottom flask
fitted with a reflux condenser. An acetonitrile (10 ml) solution con-
taining a given substrate (10 mmol) and 0.05 g catalyst was taken.
To this NaHCO3 (2.5 mmol) and 30% H2O2 (30 mmol) were added.
Reaction was carried out at room temperature. To get an effec-
tive result, an aliquot of the reaction solution was withdrawn from
the reaction solution through the help of a syringe. The reaction
products were analyzed by off-line gas chromatography (Shimadzu
GC-2010) equipped with a capillary column (ZB-1, 30 m length
0.53 mm I.D. and 3.0 ␮ film thickness) using flame ionization detec-
tor (FID). The response factor is calculated by dividing initial mole
percent of olefins with initial area percent (olefin peak area from
GC). The unreacted moles of cycloalkene remained in the reaction
mixture were calculated by multiplying response factor with the
area percentage of the GC peak for olefins obtained after the reac-
tion.
The conversion and selectivity were calculated as follows:
ꢀ
ꢁ
initial mol% − final mol%
conversion (mol%) =
epoxide selectivity =
× 100
× 100
initial mol%
GC peak area of epoxide
GC peak area of all products
Fig. 1. XRD spectra of MCM-41, CP-MCM-41, and V-MCM-41.

K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 325 (2010) 40–47
43
Fig. 2. N2 adsorption–desorption isotherms of MCM-41, CP-MCM-41, and V-MCM-41.
983 m2 g−1) and pore volume 1.03 cm3/g and V-MCM-41 shows fur-
3.1.4. 29Si CP-MAS NMR studies
ther less N2 uptake (BET surface area 584 m2 g−1) and pore volume
0.68 cm3/g. We can conclude that complex modified samples pos-
sess lower pore volume and pore size distributions compared to
its parent materials. With an increase in bulkiness inside the pores,
the hysteresis occurred at lower P/P0 indicating the decrease of pore
size. This is a clear indication of immobilization of V complex inside
the pore channel of mesoporous silica [23].
The degree of functionalization, i.e. the covalent linkage
between the silanol groups and the organic moiety on the
mesostructured materials can be monitored by means of 29Si
CP-MAS NMR spectroscopy. The spectrum of MCM-41 [Fig. 3(g)]
generally exhibits three resonance peak at
ı
−110, −101,
and −92 corresponds to Q4 [siloxane, (SiO)4Si], Q3 [single
silanol,(SiO)3Si(OH)] and Q2 [geminal silanol,(SiO)2Si(OH)2] sites
of the silica framework, respectively. Covalent binding makes the
Q2 signal disappear, decrease Q3 and concomitantly increase the
Q4 intensity, which is due to consumption of isolated Si OH and
geminal silandiols during condensation process. Two resonance
peaks due to the Si environments of Q4 (ı = −110 ppm) and Q3
(ı = −102 ppm) can be seen in the organic group modified silica.
In addition to these two peaks, the sample displays two more
resonance peaks at ı = −68 ppm, assigned to T3 [C Si(OSi)3], and
at −57 ppm, attributed to T2 [C Si(OSi)2(OH)], respectively. The
existence T3 confirms that MCM-41 has been modified by organic
moieties [24,25]. The appearance of Q3 signal indicates the pres-
ence of some residual non-condensed OH groups attached to the
silicon atom. The 29Si CP-MAS NMR provides direct evidence that
the hybrid CP-MCM-41 sample consists of a highly condensed
siloxane network with organic group covalently bonded to the
mesoporous silica. These two peaks due to the Si atoms of different
environments in the organosilane CP-MCM-41 also revealed that
both synthesis process and surfactant-extraction treatment did not
cause cleavage of the Si C bonds.
3.1.3. 13C CP-MAS NMR studies
The 13C CP-MAS NMR spectrum of CPTMS functionalized MCM-
41 is shown in Fig. 3(a). The sharp peak at 10.4 ppm is ascribed to
the carbon atom bonded to silicon. The signal at 22.4 ppm corre-
sponds to methylene carbon and the peak around at 50 ppm can be
attributed to carbon atom attached to the chlorine atom. In case of
CP-MCM-41 one can observe three distinct peaks for thee differ-
ent carbon atoms. Three similar types of peaks are also observed
for V-MCM-41 in the range of 0–40 ppm. This may be due to par-
tial change in the environment after the replacement of chlorine
by nitrogen. The 13C CP-MAS NMR spectra of complex immobilized
MCM-41(3(b)) show peaks corresponding to aliphatic and aromatic
carbons of the schiffbase. Similar resonance shift are observed for
all functional group modified schiffbase complex in Fig. 3(c–f).
Table 1
Textural properties of parent MCM-41 and modified mesoporous samples from N2
isotherms at 77 K.
3.1.5. FT-IR studies
Samples
BET surface
area (m2 g−1
Pore volume
Pore
diameter (Å)
To establish the immobilization of vanadium complex inside the
pore of organically modified mesoporous silica is a difficult task.
However, in our experiment we have developed that IR has been
shown to be a powerful characterization in monitoring multistep-
assembly of the complex inside the mesoporous silica. Fig. 4 shows
)
(cm3 g−1
)
MCM-41
CP-MCM-41
V-MCM-41
1280
983
584
1.19
1.03
0.68
30.7
26.1
20.6

44
K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 325 (2010) 40–47
Fig. 4. FT-IR spectra of (a) MCM-41, (b) CP-MCM-41, (c) schiffbase ligand modified
CP-MCM-41, (d) V-MCM-41, and (e) V-MCM-41 after recycled.
the FT-IR spectra of (a) MCM-41, (b) CP-MCM-41, (c) schiffbase
ligand modified CP-MCM-41, (d) V-MCM-41, (e) V-MCM-41 after
recycled. The stretching vibration due to Si
O Si bond of par-
ent MCM-41 as well as in all modified samples appeared around
1050 cm−1 indicating that silica framework was not affected, which
is in accordance with the XRD result. A peak observed at 780 cm−1
is likely to be from the SiOCH2CH2CH2 group due to incomplete
hydrolysis of TEOS. Generally a weak band within ∼2900 appears
in case of organic group modified mesoporous silica due to C
H
stretching vibration. Upon functionalization with CPTMS a band
appeared around 2900 cm−1 due to asymmetric stretching vibra-
tion of C H bond in CH2 unit. In Fig 4(c) a band at 1640 cm−1
is due to characteristic of C N stretching in the ligand modified
organic–inorganic hybrid material. The intensity of that particular
bond decreased after metal loading and slightly shifted to lower fre-
quency due to coordination with vanadium. Again a band appeared
around 970 cm−1 due to stretching vibration of V O [26]. All these
data give a clear indication for the attachment of the metal complex
to the organic group modified MCM-41. In Fig 4(e), the stretching
vibrations do not change significantly, suggesting existence of all
the properties in the recycled catalyst.
3.1.6. UV–vis spectral studies
The UV–vis diffuse-reflectance spectra of vanadium schiffbase
anchored CP-MCM-41 are added in Fig. 5. It can be seen that a series
of characteristic bands of the schiffbase ligand immobilized MCM-
41 at 220, 260, 340 and 380 nm emerges in the spectra. The bands
can be attributed to a typical electronic transition of the aromatic
ring and
C
N
conjugated system in the schiffbase molecule. A
broad band is noticed at about 410 nm resulting from the ␲–␲*
electronic transition of the schiffbase. In case of V-MCM-41 an
additional broad band around 580 nm arises due to d–d electronic
transition of vanadium present in the complex. Similar types of
peaks are also exhibited in case of vanadium–schiffbase complex.
Appearance of all types of transition bands in the recycled catalyst
indicates the retention of all the properties.
Fig. 3. 13C CP-MAS NMR spectrum of (a) CP-MCM-41, (b) V-MCM-41, (c–f) different
functional group attach to ligand in V-MCM-41, 29Si CP-MAS NMR spectrum of (g)
MCM-41, and (h) CP-MCM-41
3.2. Catalytic epoxidation reaction
Control experiments were carried out using only H2O2 as oxi-
dant, but failed to produce the desired yield. Though H2O2 is an

K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 325 (2010) 40–47
45
Scheme 2. The possible reaction pathway comprising of path I and path II.
environmentally benign oxidant, but a disadvantage is that high
activation energy is required for the oxidation of many organic
compounds by using this oxidant. In contrast, the number of
organic, non-metal compounds capable of activating H2O2 for
epoxidation is limited [27]. Again, catalytic efficiency of H2O2
when it is used as sole oxidant is rather poor as compared to
tert-butylhydroperoxide and peracids in epoxidation reaction. This
is due to the poor leaving tendency of the hydroxide ion. How-
ever, higher conversion and epoxide selectivity can be achieved by
adding a small amount of NaHCO3 to the reaction medium. The
addition of NaHCO3 enhances the catalytic activity to many folds
due to the formation of peroxomonocarbonate species. A method
for activating hydrogen peroxide with bicarbonate was described
by Drago et al. [28]. Production of active peroxomonocarbonate
matically in Scheme 2. The catalytic−oxo–peroxo intermediate is
formed by the treatment of the HCO4 with the complex immobi-
lized MCM-41 (path I). Such a peroxo complex than oxidized olefin
(Path II) and itself revert back to oxo complex, which again react
with H2O2/NaHCO3 to regain its catalytic properties and so on. As
peroxomonocarbonate is a more reactive nucleophile compared to
H2O2 that accelerates the reaction leading to epoxidation.
HCO−3 + H2O2 ꢀ HCO− + H2O
4
By using 0.25 M of NaHCO3 we got maximum conversion.
Increase in concentration of bicarbonate increased the pH of
the reaction medium greater than 8, which would reduce the
efficiency towards epoxidation reaction. The catalytic epoxi-
dation of various olefins is summarized in Table 2. Though
the correlative literatures shows catalytic activity sequence
as cyclooctene > cyclohexene > styrene > 1-octene, opposite to our
observations (1-octane > cyclohexene > styrene > cyclooctene). This
may presumably be due to easy approach of active species (oxidant)
to 1-octene compared to cyclooctene which has a stained ring [29].
However there is marginally change in the yields between 1-octene
and cyclooctene. We have also carried out the reaction by using
H2O2 NaHCO3 in absence of V-MCM-41, but it showed negligible
conversion (2%). If the stirring is continued for a longer period of
time, conversion rate gradually decreases perhaps due to forma-
tion of diols. The ligand structure also influences the relative rates
of catalyst towards epoxidation reaction of different olefins [30].
A characteristic epoxidation reactivity profile can be measured for
each substitution under identical condition. Substituted aromatic
rings with various electron donating ( OMe, OH) and withdraw-
ing groups such as (–Br, –NO2) have been used in the ligand design
and catalytic epoxidation. We found practically no influence of the
substitution on the conversion as well as selectivity. These data
demonstrate the beneficial influence of designing a complex with
sufficiently large flexibility to allow the substrate–complex adduct
to adopt a spatial disposition similar to that in the homogeneous
phase. A ball-stick model representation of vanadium–schiffbase
complex is depicted in Fig. 6.
−
ion, HCO4 and its involvement in the reaction plays an impor-
−
tant role. The formation of HCO4 is an equilibrium process and
it takes only few minutes. Though vanadium (V) is found to be
a relatively poor catalyst for alkene epoxidation, the generation
of peroxomonocarbonate in this reaction medium totally changes
the reaction scenario. The mechanistic pathway is shown diagram-
The epoxidation reaction is markedly influenced by reaction
temperature. High yield of epoxide products were obtained at room
temperature especially for olefinic alcohol, i.e. for allylic alcohol
and cinnamyl alcohol. Olefin group is chemoselectively oxidized
Fig. 5. UV–vis spectra of (a) CP-MCM-41, (b) schiffbase ligand modified CP-MCM-41,
(c) V-MCM-41, (d) V-MCM-41 after recycled, and (e) vanadium–schiffbase complex.

46
K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 325 (2010) 40–47
Table 2
Details of the catalytic epoxidation of olefinic compounds.
Entry
Substrate
Product
Time (h)
Conversion (%)
Selectivity
Epoxide
Others
6
1
2
8
8
84
83
94
93
7
3
4
8
6
87
95
97
94
3
6
5
6
8
8
82
88
98
90
2
10
7
6
90
94
6
Reaction conditions: substrate 10 mmol, amount of catalyst 0.05 g, acetonitrile 10 ml, 2.5 mmol NaHCO3, 30 mmol H2O2, reaction occurred at room temperature.
to epoxide, alcohol groups remain unchanged. We employed the
epoxidation reaction of olefins at various temperatures in order to
check the exact effect of temperature on the reaction. Chemoselec-
tivity for olefinic alcohols is presumed to be lost as some undesired
product formation takes place at higher temperature. Besides epox-
ide, epoxy aldehyde is also formed to some extent. It is the alcoholic
group in the olefinic alcohol, which is activated at higher temper-
ature, i.e. around 70–80 ◦C. Also at higher temperature a part of
NaHCO3 is converted to Na2CO3, which will increase the pH of the
reaction and facilitates the higher decomposition of H2O2 [29].
in a biphasic solvent system. We have performed the reaction with
methylbenzene, dichloromethane, diethyl ether, ethyl acetate, or
pentane with acetonitrile in equimolar proportion which produced
no significant result. Presumably they may suppress the formation
−
of HCO4 which decreases the promotional effect.
In addition, the stability of the modified materials was stud-
ied by recycling the recovered catalyst. At the end of the reaction,
the solid catalyst was separated from the reaction solution, thor-
oughly washed with ethanol, dried at room temperature and reused
under similar reaction conditions. The reused catalyst showed a
slight lower catalytic activity in successive runs. These trends can
be interpreted by considering the leaching process, as it is more
important due to economic point of view. Probably, in fact leaching
is a particular problem for heterogeneous catalyst in liquid phase
reaction. To test if vanadium is leaching out of the catalyst, the reac-
tion mixture was filtered out after the reaction and was subjected
to atomic absorption spectroscopic analysis. The analysis showed
the absence of vanadium in the filtrate. Besides that the filtrate mix-
ture also did not show any catalytic activity towards epoxidation
reaction. These results indicate that the catalyst is regenerable and
reusable which has the advantage over the homogeneous counter-
part.
2NaHCO3 → Na2CO3 + CO2 + H2O
This will lead to reduce the yield by deactivating the reaction.
Several attempts were also made to effect the epoxidation reaction
4. Conclusions
Covalent functionalization of vanadium–schiffbase complex
onto the CP-MCM-41 was successfully achieved by a multi-
ple synthetic procedure. The presence of d (1 0 0) in the XRD
pattern confirmed the retention of hexagonal ordering even
after functionalization and metal complex loading. The effect of
vanadium–schiffbase complex loading on the physical properties
of MCM-41 (surface area and pore parameters) was explored by
nitrogen sorption. The progressive change with different modi-
fications on Type IV isotherm confirms that the immobilization
Fig. 6. Model representation of vanadium–schiffbase complex.

K.M. Parida et al. / Journal of Molecular Catalysis A: Chemical 325 (2010) 40–47
47
of vanadium–schiffbase complex causes pore narrowing, which
resulted in decrease in the mesoporosity of MCM-41. This is also
supported by a decrease in surface area, pore volume and pore
diameter of MCM-41. The 13C CP-MAS NMR spectra of the com-
plex immobilized sample shows all possible peaks corresponding
to both the aliphatic and aromatic carbon atoms. Solid-state 29Si
CP-MAS NMR showed that the organic group is successfully bonded
to mesoporous silica. FT-IR and diffuse-reflectance UV–vis spectra
confirmed the immobilization and retention of the surface proper-
ties of the catalyst after the catalytic reaction. The most interesting
features of the present work is the revealing of chemistry that dis-
play a most pronounced efficiency with NaHCO3 as co-catalyst and
H2O2 as oxidant in a CH3CN medium at room temperature. The
reaction suggests that nature of the catalyst and reaction medium
can influence the reaction. This method is green and economical
from environmental point of view. Repeated recycled study with-
out loss of activity shows the stability of V-MCM-41.
[5] E.S. Gould, R.R. Hiatt, K.C. Irwin, J. Am. Chem. Soc. 90 (1968) 4573–4579.
[6] B. Jarrais, C. Pereira, A.R. Silva, A.P. Carvalho, J. Pires, C. Freire, Polyhedron 28
(2009) 994–1000.
[7] S.I. Mostafa, S. Ikeda, B. Ohtani, J. Mol. Catal. A 225 (2005) 181–188.
[8] G. Yin, M. Buchalova, A.M. Danby, C.M. Perkins, D. Kitko, J.D. Carter, W.M.
Scheper, D.H. Busch, Inorg. Chem. 45 (2006) 3467–3474.
[9] W. Zhang, J.L. Loebach, S.R. Wilson, E.N. Jacobsen, J. Am. Chem. Soc. 112 (1990)
2801–2803.
[10] Q.-H. Fan, Y.-M. Li, A.S.C. Chan, Chem. Rev. 102 (2002) 3385–3466.
[11] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 (1992)
710–712.
[12] D.Y. Zhao, J.L. Feng, Q.S. Huo, N. Melosh, G.H. Fredrickson, B.F. Chmelka, G.D.
Stucky, Science 279 (1998) 548–552.
[13] A. Stein, B.J. Melde, R.C. Schroden, Adv. Mater. 12 (2000) 1403.
[14] S.-J. Bae, S.-W. Kim, T. Hyeon, B.-M. Kim, Chem. Commun. (2000) 31–32.
[15] D.D. Das, A. Sayari, Stud. Surf. Sci. Catal. 170 (2007) 1197–1204.
[16] D.E. de Vos, I.F.J. Vankelecom, P.A. Jacobs (Eds.), Chiral Catalyst Immobilisation
and Recycling, Wiley–VCH Verlag, Weinheim, 2000, p. p19.
[17] D.E. de Vos, M. Dams, B.F. Sels, P.A. Jacobs, Chem. Rev. 102 (2002) 3615–3640.
[18] Q.-H. Xia, H.-Q. Ge, C.-P. Ye, Z.-M. Liu, K.-X. Su, Chem. Rev. 105 (2005)
1603–1662.
[19] D. Brunel, Micropor. Mesopor. Mater. 27 (1999) 329–344.
[20] S. Huh, J.W. Wiench, J. Yoo, M. Pruski, W.S.-Y. Lin, Chem. Mater. 15 (2003) 4247.
[21] M. Kruk, M. Jaroniec, Y. Sakamoto, O. Terasaki, R. Ryoo, C.H. Ko, J. Phys. Chem.
104B (2000) 292–298.
Acknowledgements
[22] W. Hammond, E. Prouzet, S.D. Mohanti, T.J. Pinnaviam, Micropor. Mesopor.
Mater. 27 (1999) 19–25.
[23] H. Yang, G. Zhang, X. Hong, Y. Zhan, J. Mol. Catal. A: Chem. 210 (2004) 143–148.
[24] D. Jiang, Q. Yang, H. Wang, H. Chen, G. Zhu, J. Yang, C. Li, J. Catal. 239 (2006)
23–29.
[25] D. Jiang, Q. Yang, J. Yang, L. Zhang, G. Zhu, C. Li, Chem. Mater. 17 (2005)
6154–6160.
[26] R.A. Shiel, K. Venkatasubbaiah, C.W. Jones, Adv. Synth. Catal. 350 (2008)
2823–2834.
The authors are extremely thankful to Prof. B.K. Mishra, Director,
IMMT, Bhubaneswar 751013, Orissa, India, for his constant encour-
agement and permission to publish the paper. The authors are also
thankful to Department of Science and Technology, New Delhi for
financial support.
[27] W. Adam, C.R. Saha-Moller, P.A. Ganeshpure, Chem. Rev. 01 (2001) 3499–3548.
[28] R.S. Drago, K.M. Frank, Y.-C. Yang, G.W. Wagner, Proceedings of 1997 ERDEC
Scientific Conference on Chemical and Biological Defense Research, ERDEC,
1998.
[29] S.K. Maiti, S. Dinda, N. Gharah, R. Bhattacharyya, New J. Chem. 30 (2006)
479–489.
References
[1] B.S. Lane, K. Burgess, Chem. Rev. 103 (2003) 2457–2474.
[2] T. Katsuki, K.B. Sharpless, J. Am. Chem. Soc. 113 (1991) 7063–7064.
[3] R. Noyori, M. Aoki, K. Sato, Chem. Commun. (2003) 1986–1997.
[4] M.K. Tse, M. Klawonn, S. Bhor, C. Do1bler, G. Anilkumar, H. Hugl, W. Ma1gerlein,
M. Beller, Org. Lett. 7 (2005) 987–990.
[30] A. Murphy, A. Pace, T.D.P. Stack, Org. Lett. 6 (2004) 3119–3122.