Dioxomolybdenum(VI) complex immobilized on ascorbic acid coated TiO2 nanoparticles catalyzed heterogeneous oxidation of olefins and sulfides

Article abstract of DOI:10.1039/c4gc01398k

Addition of MoO₂ (acac)₂ to TiO₂ coated with ascorbic acid (AA) under ultrasonic agitation resulted in a nanohybrid (TiO₂/AA/MoO₂) with size ranging between 20-25 nm. The structural and morphological characterization of the as-prepared nanohybrid was carried out by different techniques such as XRD, FT-IR, TGA and transmission electron microscopy (TEM). The catalytic performance of the TiO₂/AA/MoO₂ nanocomplex in the heterogeneous oxidation of olefins and sulfides using H₂O₂ in ethanol as a safe solvent was exploited. Our results clearly demonstrated the efficiency, selectivity and oxidative stability of the heterogeneous nanocatalyst providing its effective reusability and removing by-products. The catalytic activity of the TiO₂/AA/MoO₂ nanocomplex was strikingly different from other nanometer sized metal oxides such as m-ZrO₂, MoO₃, Fe₃O₄ and TiO₂, as well as their nanocomposites such as TiO₂/AA, ZrO₂/AA/MoO₂, MoO₃/AA/MoO₂ and Fe₃O₄/AA/MoO₂.

Full text of DOI:10.1039/c4gc01398k

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Page 1 of 25
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Graphical Abstract
Dioxomolybdenum(VI) Complex Immobilized on Ascorbic acid
Coated TiO Nanoparticles Catalyzed Heterogeneous Oxidation of
Olefins and Sulfides
Maasoumeh Jafarpour ,
Ghahramaninezhad, and Fahimeh feizpour.
2
*
*
Abdolreza
Rezaeifard ,
Mahboube

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Dioxomolybdenum(VI) Complex Immobilized on Ascorbic
acid Coated TiO Nanoparticles Catalyzed
2
Heterogeneous Oxidation of Olefins and Sulfides
*
*
Maasoumeh Jafarpour, Abdolreza Rezaeifard , Mahboube Ghahramaninezhad,
Fahimeh Feizpour
Catalysis Research Laboratory, Department of Chemistry, Faculty of Science,
University of Birjand, Birjand, 97179ꢀ414 Iran
Abstract: Addition of MoO
2 2 2
(acac) to TiO coated with ascorbic acid (AA) under
ultrasonic agitation resulted a nanohybrid (TiO /AA/MoO ) with size ranging between
2
2
2
0–25 nm. The structural and morphological characterization of asꢀprepared
nanohybrid was carried out by different techniques such as XRD, FTꢀIR, TGA and
transmission electron microscopy (TEM). The catalytic performance of
TiO
2
/AA/MoO
2
nanocomplex in the heterogeneous oxidation of olefins and sulfides
using H
2
O
2
in ethanol as a safe solvent was exploited. Our results demonstrated well
the efficiency, selectivity and oxidative stability of heterogeneous nanocatalyst
providing its effective reusability and removing byꢀproducts. The catalytic activity of
2 2
TiO /AA/MoO nanocomplex was strikingly different from another nanometer sized
metal oxides such as mꢀZrO , MoO , Fe O and TiO , as well as their nanocomposites
2
3
3
4
2
such as TiO
2
/AA, ZrO
2
/AA/MoO
2
, MoO
3
2 3 4 2
/AA/MoO and Fe O /AA/MoO .
Keywords: Nano titanium oxide, ascorbic acid, surface modification, nanooxometales,
nanocomposites.
*
Corresponding Authors: Tel: +98 561 2502516; Fax: +98 561 2502515.
Eꢀmail: mjafarpour@birjand.ac.ir (M. Jafarpour) rrezaeifard@birjand.ac.ir (A.
Rezaeifard) ; rrezaeifard@gmail.com
1

Page 3 of 25
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Introduction
In recent years, heterogenization of homogeneous catalysts has attracted many
attentions due to combining the best properties of both homogeneous and
1
heterogeneous catalysts. Among the various approaches for immobilizing soluble
catalysts, the covalent attachment has been the most frequently used strategy as the
resulted heterogeneous catalysts have good stabilities during the course of catalytic
reactions. The stable covalent bonds experience no leaching from the support and thus
provide an efficient approach to prepare site isolated catalysts.
Epoxides, as precious precursors in organic synthesis, can be easily obtained from
2
alkenes by the use of strong organic oxidants (mꢀCPBA, NaClO), or smoother
3
oxidants (THBP, H
2
O
2
), with the assistance of metalꢀbased catalysts (Fe, Mn, Re,
3
, 4
Mo, V, W). Among these metals, molybdenum attracts most of the attention.
The enthusiasm shown in the coordination chemistry of molybdenum followed the
discovery of molybdenum in a number of redox enzymes, such as aldehyde oxidase,
5
sulphite oxidase, xanthine oxidase, nitrate reductase and nitrogenase.
Dioxomolybdenum (VI)–complexes are important catalysts as well as catalystꢀ
6
precursors for oxygenꢀtransferꢀreactions in chemical and biological systems.
Considerable efforts devoted to the preparation and investigation of catalytic
properties of dioxomolybdenum complexes under both homogeneous and
7
heterogeneous conditions is a testimony to show that they are valuable catalysts.
Most of the investigated processes are performed in chlorinated solvents with catalyst
loadings as high as 1% Mo. Solvent recovery requires extra efforts and costs that
could be eliminated by the application of greener processes.
In the aim of developing cleaner processes and in continuation of our ongoing
8
research on catalytic activity of Mo catalysts, in this work, we incorporated simple
and easily available MoO
ultrasonic agitation to obtain a novel heterogeneous molybdenum nanocatalyst for the
oxidation of olefins and sulfides using H in ethanol as a safe solvent. The catalyst
2 2 2
(acac) to ascorbic acidꢀcoated TiO nanoparticles under
2
O
2
showed high thermal and oxidation stability and desired activity and selectivity in the
oxidation of olefins and sulfides using hydrogen peroxide as industrially and
environmentally important oxidant (Scheme 1). The additional advantage of this
catalytic system is facile and efficient reusability of the solid catalyst at the end of
reaction.
2

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2 2
Scheme 1. Catalytic activity of TiO /AA/MoO nanocomplex in oxidation of olefins and sulfides
Results and discussion
Synthesis and characterization of catalyst
At the first step of this investigation, TiO
2
nanoparticles of approximately 18ꢀ20 nm
8
f
diameters were prepared by the PC sol–gel method (Scheme 2). The particles were
subsequently coated with ascorbic acid layer followed by complexation with MoO2
2
(acac) to yield the corresponding supported cisꢀdioxomolybdenum nanocomplex
(Scheme 3). Inductively coupled plasma atomic emission (ICP) analysis revealed that
the contents of supported Mo was 2.78 wt%. Therefore, each gram of heterogeneous
catalyst contains 29 µmol Mo or MoO
2
group.
T iC l
0 .0 5 m ol)
3
(
D isso lvin g in
2
H O & e than ol (1:1)
E thy lene G lyc ol
0.15 m ol)
C itr ic acid
( 0.15 m o l)
(
M ixing b y Son icate
a t 45° C f or 15 m in
R ef luxing at 12 0 °C
f or 8 h
S low h eating at 90 ° C
f or 6 h
H eating directly on ho t
p late a t 150 ° C f or 6 h
A nne allin g at 60 0 °C
f or 3 h
2
Scheme. 2. The flow chart of preparation of nano TiO by solꢀgel process.
3

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Scheme 3. Schematic representation of the procedure for the fabrication of TiO /AA/MoO
2
2
nanocomplex
The spectral and analysis data confirmed successful synthesis of title nanocatalyst.
The XRD pattern of TiO nanoparticles exhibited two different phases of TiO such as
2
2
anatase (tetragonal, a = b= 3.782 A⁰, c =9.502 A⁰) and rutile (tetragonal, a = b= 4.584
9
A⁰, c = 2.953 A⁰) (Fig.1). The strong diffraction peaks observed at 2θ = 25, 38, 48,
5
4, 55, 63, 69, 70, 75 were assigned to the (101), (004), (200), (105), (211), (204),
116), (220), (215) reflection planes of tetragonal crystal of anatase TiO , respectively
JCPDs No. 21ꢀ1272). The other diffraction peaks observed at 2θ = 27, 35, 41, 56
(
(
2
10
were assigned to the (110), (101), (111), (220) reflection planes of tetragonal crystal
11
of rutile TiO
estimated to be 20 nm according to the Debye sherrer formula (D=Kλ/βCosθ ). It is
well known that TiO containing both the rutile and anatase phases exhibit higher
photocatalytic activity in visible light than either pure phase alone.
2
respectively (JCPDS No. 21ꢀ1276). The size of particles were
2
1
2
Fig. 1. XRD pattern of nano TiO
2
(Anatase)
(Rutile)
The FTꢀIR spectrum of TiO nanoparticles (Fig. 2a) reveals the presence of major
2
ꢀ1
bands at 450–775 cm which are attributed to the stretching vibrations of TiꢀO group.
4

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−
1
It can be observed that there are broad peaks at 3400 and 1638 cm , which
1
3
correspond to the surface adsorbed water and hydroxyl groups. Fig.2b confirms the
successful fabrication of TiO /AA composite particle. orthoꢀsubstituted hydroxyl
groups of furan ring binding to AA act as bidentate ligands to attach to surface Ti
2
14
atoms forming chelateꢀtype coordination in desired complexes. The appearance of
ꢀ1
peaks in the range of 927 and 1010 cm rationalized to CꢀO stretching vibration of
15
ꢀ1
TiꢀOꢀC. The strong peak at 1320 cm corresponding to the (O–H) enediol for the
free acid disappeared in the spectra of the complexes showing the coordination of the
16
O
C3 and OC2 atoms to the Ti atoms.
Apparently, AA coating on the surface of TiO
2
particles contributes to the decrease of
the number of ꢀOH on TiO
2
surface. The vibration absorption at low frequencies, such
ꢀ1
as that observed at 720 cm , shows the existence of the nanoTiO
nanocomposite.
2 2
core in TiO /AA
Comparison of the FTꢀIR spectra of TiO
those of TiO and TiO /AA composite supports the formation of the respective
composite since significant spectral changes are observed. It revealed the presence of
2 2
/AA/MoO nanocomplex (Fig. 2c) with
2
2
ꢀ1
major bands at 500ꢀ750 cm which are attributed to the stretching vibrations of TiꢀO
group and the symmetric and asymmetric stretching vibrations of the cisꢀMoO at
00ꢀ950 (Fig. 2c).
2
8
Fig. 2. FTꢀIR spectra of (a) nano TiO
2 2
(b) TiO /AA nanocomposite (c)
TiO /AA/MoO nanocomplex
2
2
5

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Transmission electron microscopy (TEM) observations clearly revealed spherical
nanoparticles of TiO and TiO /AA/MoO composite with size ranging between 18ꢀ20
2
2
2
nm and 20ꢀ25, respectively (Fig. 3).
.
Fig.3. TEM (A) nano TiO
2
2 2
(B) TiO /AA/MoO nanocomplex
Thermal behavior of the synthesized amorphous powder dried at 150 ºC was analyzed
through TGA (Thermogravimetric analysis) from ambient temperature to 800 °C. The
results showed that 600 °C was an optimum calcination temperature for the
2
synthesized of TiO nanopowders (Fig. 4).
100
80
60
40
20
0
100
200
300
400
500
600
700
800
0
Temperature( C)
Fig.4 The TGA of TiO powder
2
2 2
The TGA curve of TiO /AA/MoO nanocomplex (Fig. 5) demonstrates its degradation
at 817 °C, which indicates the high thermostability of the catalyst. The organic parts
decomposed completely at 877 °C.
6

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2 2
Fig. 5. The TGA of TiO /AA/MoO nanocomplex
2 2
Catalytic activity of TiO /AA/MoO nanocomplex
Epoxidation of olefins with H
2
O
2
Preliminary experiments were initiated with oxidation of cyclooctene (1 mmol) using
(2 mmol) as a model reaction under neat conditions which did not proceed in
2 2
H O
the absence of catalyst under different conditions. To find optimum reaction
conditions, the influence of different factors that may affect the conversion and
selectivity of the cyclooctene epoxidation was investigated.
A systematic examination on the solvent nature was performed in various solvents
such as chloroform, dichloroethane (DCE), acetonitrile, methanol, ethanol and water
using 0.03 mol% of TiO /AA/MoO nanocomposite catalyst (Fig. 6) at different
2
2
temperatures (Fig. 7). The best yield and conversion rate were obtained in ethanol at
0 °C.
7
7

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Fig. 6. The screening of solvent nature (1 mL) on oxidation of cyclooctene (1 mmol) using H
mmol) catalyzed by TiO /AA/MoO nanocomplex (0.03 mol% ) at 70˚C except for solvents having
lower b.p which performed at reflux temperature.
2 2
O (2
2
2
Fig. 7. The screening of temperature on oxidation of cyclooctene (1 mmol) using H
2 2
O (2 mmol)
/
EtOH (1 mL) catalyzed by TiO /AA/MoO nanocomplex (0.03 mol%) after 6h
2
2
The reaction was further optimized with respect to catalyst (Fig. 8) and oxidant
amount (Fig. 9). It was observed that full conversion of cyclooctene required 0.03 mol
%
2 2
of nanocatalyst and two equivalents of H O within 6 h and an increase in any of
these ratios did not affect noticeably the reaction rate.
2 2
Fig.8. The screening of catalyst amount on the epoxidation of cyclooctene (1 mmol) using H O (2 mmol)
/
EtOH (1 mL) catalyzed by TiO /AA/MoO nanocomplex at 70°C
2 2
8

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Fig. 9. The screening of H
1 mL) catalyzed by TiO
2
O
2
amount on the epoxidation of cyclooctene (1 mmol) in EtOH
/AA/MoO nanocomplex (0.03 mol%) at 70°C after 6 h
(
2
2
To evaluate the oxidizing potential of other common oxidants, cyclooctene was
®
subjected to the oxidation protocol using TBHP, NaIO
4
and Oxone under the
catalytic influence of TiO /AA/MoO nanocomposite in ethanol at 70°C (Fig. 10).
2
2
Only small amounts of the oxidation products were observed.
Fig. 10. The screening of different oxidants ( 2 mmol) on oxidation of cyclooctene (1 mmol)
in EtOH (1 mL) catalyzed by TiO /AA/MoO nanocomposite (0.03 mol%) at 70°C after 6 h.
2 2
Under the optimized conditions (10000:20000:3 molar ratio for olefin/
/catalyst in ethanol at 70°C), cyclooctene converted completely within 6 h and
5% of the corresponding epoxide was secured as the sole product.
Moreover, prolonged reaction resulted for cyclooctene oxidation when the
TiO /AA/MoO nanocomplex was replaced by another nanooxometals such as
MoO , Fe and TiO , as well as their nanocomposites such as TiO /AA,
2 2
H O
9
2
2
30
3
, mꢀZrO
2
3
O
4
2
2
9

Page 11 of 25
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2 2 3 2 3 4 2
ZrO /AA/MoO , MoO /AA/MoO and Fe O /AA/MoO under the same conditions.
Photocatalytic properties of TiO at the core of title nanocomplex may be an
2
acceptable reason for great improvement of catalytic activity (Fig. 11). To support this
claim oxidation of αꢀmethyl styrene and diphenyl sulfide under UV light, room light
lamps as well as in dark were investigated (Table 1). Accelerated reactions under light
radiation particularly UV light demonstrated the photocatalytic activity of TiO
on the oxidation efficiency of TiO /AA/MoO nanocomplex.
2
core
2
2
2 2
Fig. 11. The comparison of catalytic activity of TiO /AA/MoO nanocomplex with other
nanooxometals and nanocomposites in the epoxidation of cyclooctene (1 mmol) in EtOH (1
mL) at 70°C after 6h
Table 1. The screening of photocatalytic activity of TiO
2
/AA/MoO
2
nanocomplex in
a
the oxidation of αꢀmethyl styrene and diphenyl sulfide using H O in EtOH
2
2
Substrate
Condition
Product ( Selectivity % )
Conversion% (Time)
100 (10 h)
room light
lamps
α ꢀMethyl styrene oxide (75)
α ꢀMethyl styrene oxide (70)
UV light
darkness
100 (8 h)
α ꢀMethyl styrene oxide (60)
100 (12 h)
1
0

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S
S
room light
lamps
Diphenyl sulfoxide (90)
80 (30 min)
UV light
Diphenyl sulfoxide (90)
Diphenyl sulfoxide (90)
80 (20 min)
50 (45min)
S
darkness
a
The molar ratio of substrate/ oxidant /catalyst was 10000:20000:3. The reactions were run under air at 70 °C
Considering the results presented in Fig. 11 and Table 1 the catalytic activity of
TiO /AA/MoO nanocomplex can be related to Lewis acid catalyst activity of Mo(VI)
centers combined with photocatalytic activity of TiO core which also acts as
support. It is noteworthy that one of the most widely used methods to provide the
2
2
7c, 17
2
18
2
selectivity is encapsulation of TiO particles into substances.
In order to establish the general applicability of the method, various olefins were
subjected to the oxidation protocol under the catalytic influence of TiO /AA/MoO
2
2
nanocomplex (Table 2).
Several useful features of this catalytic method can be seen in Table 2. Different
olefins were generally good substrates for this catalyst. It led to high conversions of
cyclooctene, norbornene and cyclohexenes with the formation of the corresponding
epoxides as sole products (entries 1–4).
It is worth to mention that cyclic olefin conjugated with phenyl ring produced
exclusively the pertinent epoxide, albeit with low yield (entry 5).
When terminal C=C double bond was conjugated with aromatic ring, the major
product was the corresponding epoxide and the related carbonyl compound was
achieved as byproduct resulting from a ringꢀopening reaction of styrene oxide
derivatives (entries 6ꢀ8).
The chemoselectivity of the procedure was notable. The catalyst was able to oxidize
2
ꢀcyclohxeneꢀ1ꢀol as an allylic alcohol to the related unsaturated carbonyl compound
in high yield and selectivity (entry 9).
1
1

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Table 2. Oxidation of alkenes using H
2
O
2
2 2
catalyzed by TiO /AA/MoO nanocomplex
a
in EtOH.
Conversion %
Isolated yield%)
b
Selectivity
Entry
Alkene
Product
b
Time (h)
6
(
%
O
1
90 (82)
95 (85)
100 (95)
100
100
100
O
2
3
6
6
O
1
2
4
5
100
100
O
9
0 (83)
15
24
16
O
O
7
5
6
100 (93)
O
H
25
O
7
2
5
5
7
100 (94)
O
10
1
2

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O
8
1
5
5
Cl
8
9
80 (72)
20
O
Cl
H
Cl
OH
O
100
12
100
a
b
2 2
The molar ratio of substrate/ H O /catalyst was 10000:20000:3. The reactions were run under air at 70 °C. The products were
19
1
identified by H NMR or by comparison with authentic samples retention times of GC analysis.
Oxidation of sulfides to sulfoxides
To extend the generality and scope of the present methodology, oxidation of sulfides
was investigated. Oxidation of thioanisole using 2.0 equivalents of H
2 2
O in the
presence of 0.03 mol% of TiO /AA/MoO nanocomposite in ethanol produced the
2
2
related sulfoxide as the sole product in excellent yield within 30 min. Accordingly,
different sulfides were subjected to the reaction system in the presence of title
nanocatalyst (Table 3). The results given in Table 3 illustrate the high efficiency of
this protocol for the oxidation of structurally different sulfides. All substrates could be
smoothly converted into sulfoxides with excellent conversion rates, and excellent
selectivities were obtained under mild conditions.
The chemoselectivity of the method is noteworthy, as exemplified by sulfide
containing hydroxyl group (Table 3, entry 3) or C=C double bond (Table 3, entries 2,
6
). While, the sulfide oxidized completely, the alcohol and olefin moieties remained
intact. In addition, dibenzyl sulfide (Table 3, entry 4) was selectively oxidized to its
corresponding sulfoxide without formation of any benzylic oxidation byproducts.
1
3

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Table 3. Oxidation of sulfides using H
2
O
2
2 2
in ethanol catalyzed by TiO /AA/MoO
a
nanocomplex.
Conversion%
b
Entry
Substrate
Sulfoxide Selectivity%
(
Isolated yield%)
S
1
100 (96)
100
S
c
2
3
100 (95)
100 (96)
90
S
100
OH
S
c
4
5
6
80(72)
80 (73)
100 (96)
95
S
c
90
S
100
c
9
0 (80)
95
7
8
S
100 (96)
100
S
a
The reactions were run at 70°C and the molar ratio of sulfide: H O : catalyst was 10000:20000:3 in 1
2
2
b
ml ethanol within 30 min. The products were identified by comparison with authentic
samples. The remainder is the related sulfone.
2
0 c
Recovery of catalyst
The good/excellent yields of epoxides and sulfoxides obtained using these new
catalytic methods demonstrated the high stability and catalytic activity of prepared
1
4

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2 2
TiO /AA/MoO nanocomplex. This was further supported by evaluation of the
recovery potential of the catalyst in the oxidation of both olefins and sulfides under
different conditions mentioned in tables 2 and 3.
Recovery of TiO /AA/MoO nanocomplex catalyst was easy and efficient. The
2
2
catalyst was recovered by centrifuging and decantation of the reaction mixture. It was
then washed with ethanol as safe solvents, dried under vacuum, and used directly for
next round of reaction without further purification. The ease of recovery, combined
2 2
with the intrinsic stability of the TiO /AA/MoO nanocomplex, allows the catalyst to
be recovered efficiently over at least five times in the oxidation of olefins and sulfides
under different conditions used in this study (Fig. 12).
Fig. 12. Recycling of the catalytic system for oxidation of cyclooctene (left) and thioanisole
(
right) using H O2 by TiO /AA/MoO nanocomplex at 70°C according to procedures
2 2 2
mentioned in experimental section
The comparison of FTꢀIR and TEM images of used TiO
Fig. 13) with fresh one showed that the structure, size and morphology of the catalyst
remained almost intact after five times recovering.
2 2
/AA/MoO nanocomplex
(
1
5

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Fig. 13. (Left) FTꢀIR spectra of fresh TiO
the oxidation of cyclooctene; (Right) TEM image of TiO
in the oxidation of cyclooctene
2
/AA/MoO
2
nanocomplex (A) and after 5 times reuses (B) in
2
/AA/MoO nanocomplex after 5 times reuses
2
Table 4 shows the merit of this operationally simple catalytic protocol for epoxidation
of cyclooctene as a model substrate in comparison with the other catalysts in terms of
oxygen source, conversion rate, catalyst loading and especially, conditions used in the
reactions.
Table 4. The comparison of catalytic activity of TiO
other catalysts in the epoxidation of cyclooctene
2
/AA/MoO
2
nanocomplex with
Conversion
catalyst
Time
(h)
Entry
Cata
l
yst
Conditions
Ref
(%)
amount
0.03 mol %
“
Ethanol/
H
2
O
2
2
TiO /AA/MoO nanocomplex
(70 °C)
2
2
1
2
6
100
0
a
Ethanol/ H O
2
mꢀZrO
2
(70 °C)
6
b
Ethanol/
H
2
O
2
2
2
(70 °C)
3
4
5
TiO
2
“
“
“
6
6
6
45
53
71
b
b
b
Ethanol/ H O
2
(70 °C)
3 4
Fe O
Ethanol/
2
H O
(70 °C)
MoO
3
1
6

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Ethanol/ H O
2
2
2
2
2
(70 °C)
6
7
8
9
TiO
2
/AA
“
“
“
6
6
6
62
64
71
b
b
b
Ethanol/
2
H O
(70 °C)
3 4 2
Fe O /AA/MoO
Ethanol/ H O
2
(70 °C)
3 2
MoO /AA/MoO
Ethanol/
2
H O
(
70 °C)
ZrO
2
/AA/MoO
2
“
6
5
0
b
dititaniumꢀcontaining 19ꢀ
tungstodiarsenate(III)
CH
H
3
CN/
10
0.002 M
2
O
2
70
[21]
o
(
50 C)
CH CN/
Mn(II)/ Pyridineꢀ2ꢀ
carboxylic Acid
3
0
.01 mol%
5 mM
1
1
2
H
2
O
2
0.5ꢀ2
1
95
77
[22]
[23]
o
(
0ꢀ25 C)
CH CN/ PAA
[
Ga(phen)
2
Cl
2
]Cl
3
1
o
(
0 C)
c
Mn–TMTACN
Mn
CH
H
3
CN/
IV,IV
[
2(ꢁꢀO)(ꢁꢀ
13
2+
0.1 mol %
2
O
2
1
71
[24]
RCO
2
)
2
(TMTACN)
2
]
o
(
0 C)
[
pꢀ
EtOAc/ H
o
2 2
O
1
4
5
C
5
H
5
N(CH
2
)
15CH
3
]
3
[PW
4
O
32
]
30 mg
0.1 g
1
6
98
91
[25]
[26]
(
65 C)
Toluene/
TBHP
o
Ti−Fe
Ti−Fe
3
3
O
4
4
@MCMꢀ41
1
(
80 C)
CH CN/
3
O
@MCMꢀ41
1
1
1
6
7
8
0.1 g
H
2
O
2
6
24
5
24
25
[27]
[27]
[28]
o
(
80 C)
nPr
CH
H
3
CN/
O
2
[
Fe(BMIP )2](OTf)2
0.1 mol %
2
(r.t)
Manganese complexes of
(tmtacn)
CH
H
3
CN/
d
0.3 mM
2
O
2
54
o
(
0 C)
t
Bis(ꢁꢀhydroxo) bridged diꢀ
3
CH CN/ BuO
e
1.67 mM
19
vanadium
H/ H
2
O
2
24
93
[29]
o
(
20 C)
polyoxotungstate
S.F / H
o
2
O
2
+
−
20
21
22
Na
9
[SbW
9
O
33] [MTCA] Cl
0.09 mmol
0.007 mmol
100 mg
6
10
4
97
94
[30]
[31]
[32]
(
60 C)
f
CH
3
CN/H
NaIO
r.t)
DMF/NaHCO
/ H
r.t)
CH CN/
2
O/
Mn (TMPyP)ꢀNaX
4
(
Mnꢀbetaꢀ1
Mn ꢀexchanged zeolites
2
+
3
2
O
2
13.5
(
3
2 2
NH TiO ꢀSiO
2
3
4
50 mg
H
2
O
2
6
67
89
[33]
[34]
o
(
60 C)
[
MnL(OTf)
2
]
CH
3
CN/ PAA
over
3min
2
0.5 mol %
o
(
0 C)
a
This work
1
7

Page 19 of 25
Green Chemistry
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DOI: 10.1039/C4GC01398K
b
c
Unpublished results. The experiments were performed under the same conditions in our laboratory.
Manganese complexes of 1,4,7ꢀtrimethylꢀ1,4,7ꢀtriazacyclononane, in present of trichloroacetic acid
d
diol selectivity
e
f
4ꢀ
2 2 10 2
The Kegginꢀtype diꢀvanadiumꢀsubstituted silicotungstate [γꢀ1,2ꢀH SiV W O40] with the {VOꢀ(ꢁꢀH) ꢀVO}core.
Host (nanocavity of zeoliteꢀ X)–guest (manganese (III)tetrakis[4ꢀNꢀmethylpyridinum]porphyrin)
Therefore, title methodologies are cost effective and industrially important because of
reusing of catalyst and using H as environmentally oxidants especially in ethanol
2
O
2
as a safe reaction media. These advantages for high yielding oxidation methods
offered ready scalability. For example the use of a semi scaleꢀup procedure (10 mmol)
for epoxidation of cyclooctene and oxidation of thioanisole in the presence of
2 2
TiO /AA/MoO nanocomplex led to isolation of the related epoxide and sulfoxide in
9
5 and 96% yield, respectively.
Conclusions
2
In conclusion, ascorbic acid coated TiO nanoparticles provided a favored solid
support for heterogenization of dioxomolybdenum(VI) centers under ultrasonic
agitation producing a novel nanohybrid (TiO /AA/MoO ) with size ranging between
0ꢀ25 nm. TiO /AA/MoO nanocomplex demonstrated desired activity and selectivity
in the epoxidation of olefins and oxidation of sulfides to sulfoxides using H as an
2
2
2
2
2
2
O
2
environmentally benign oxidant in ethanol as a green solvent. These favorable
characteristics for a heterogeneous catalytic system, along with the easy and safe
workup procedure and excellent reusability of the catalyst, are environmentally
benign and costꢀeffective. Thus, our method possesses high generality which makes it
suitable for industrial goals.
Experimental
General remarks
All chemicals were purchased from Merck and Fluka Chemical Companies. Powder
Xꢀray diffraction (XRD) was performed on a Bruker D8ꢀadvance Xꢀray
diffractometer with Cu Kα (λ = 1.54178 Å) radiation. The FTꢀIR spectra were
recorded on NICOLET system. Raman spectra were recorded on a Bruker senterra
ꢀ1
(
2009) model with spectral range 200ꢀ3500 cm and laser wavenumber 785 nm.
1
8

Green Chemistry
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DOI: 10.1039/C4GC01398K
Thermogravimetric analysis (TGA) of nanopowders was performed in air by
Shimadzu 50. TEM images were obtained by TEM instrumentation (Philips CM 10).
Progresses of the reactions were monitored by TLC using silicaꢀgel SIL G/UV 254
plates and also by GCꢀFID on a Shimadzu GCꢀ16A instrument using a 25 m CBP1ꢀ
S25 (0.32 mm ID, 0.5 µm coating) capillary column. NMR spectra were recorded on
a Brucker Avance DPX 250 and 400 MHz instruments.
Fabrication of TiO
2
nanoparticles
(0.05 mol) in a mixture of doubleꢀdistilled water and absolute
To a solution of TiCl
3
ethanol (1:1) was added citric acid (0.15 mol) and ethylene glycol (0.15 mol)
subsequently. The resulting mixture was dissolved at 45 ºC under ultrasound for 15
min to give a clear violet solution. The solution was refluxed at 120 ºC for 8 h which
turned into a metalꢀcitrate homogeneous complex with a little color change from clear
violet to blackꢀviolet. After cooling down, in order to bring about the required
chemical reactions for the development of polymerization and evaporation of the
solvent, the sol was further slowly heated at 90 ºC for 6 h in an open bath until a beige
wet gel was obtained. During continuous heating at this temperature, the
polymerization between citric acid, ethylene glycol and complexes is developed and
ultimately sol became more viscous as a wet gel. In the final step of solꢀgel process,
the wet gel was fully dried by direct heating on the hot plate at 150 ºC for 6 h. The
resultant production was a black powder. Then it was calcined in a furnace at 600 ºC
2
for 3 h at a rate of 5 ºC/min. Finally TiO nanoparticles with a white color were
obtained (Scheme 2).
Preparation of TiO /AA nanocomposite particles
2
2
To 1.0 g TiO particles was gradually added 10.0 ml of 0.01 M ascorbic acid in water
over a period of 20 min at room temperature under ultrasonic agitation. Then, the
reaction mixture was stirred at room temperature for 8 h. Afterwards, the product was
1
9

Page 21 of 25
Green Chemistry
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DOI: 10.1039/C4GC01398K
2
centrifuged and washed by distilled water. Finally, TiO /AA nanocomposite was
obtained after drying for 4 h at 100 °C.
Preparation of TiO
2 2
/AA/MoO nanocomplex
To 0.2 g of TiO /AA nanocomposite was gradually added 1.0 mmol MoO (acac)
2
2 2
dissolved in ethanol over a period of 20 min at room temperature under ultrasonic
agitation. Then, the asꢀobtained mixture was refluxed for 12 h. Afterwards, the
product was centrifuged and washed by ethanol. Finally, TiO
nanocomplex was obtained after drying for 12 h at 80 °C (Scheme 2).
2 2
/AA/MoO
General procedure for catalytic oxidation of olefins
To a mixture of olefin (1.0 mmol) and TiO
2
/AA/MoO
2
nanocomplex (0.03 mol%,
0
.01 g) in ethanol (1.0 mL) was added 30% H O
2 2
(2.0 mmol), and the reaction
mixture was stirred in air at 70 °C for the required time. The reaction progress was
monitored by GC, and the yields of the products were determined by GC and NMR
2 2
analysis. After the completion of the reaction, TiO /AA/MoO nanocomplex (solid
phase) was separated by centrifuging followed by decantation (3×5 mL ethanol).
Then, desired product (liquid phase) was extracted by plate chromatography eluted
1
with nꢀhexane/EtOAc (10/1). Assignments of products were made by IR, H NMR
and MS spectral data in comparison with authentic samples.
General procedure for oxidation of sulfides
To a mixture of the sulfide (1.0 mmol) and TiO
2 2
/AA/MoO nanocomplex (0.03
mol%, 0.01 g) in ethanol (1.0 mL) was added H O (2.0 mmol), and the reaction
2
2
mixture was stirred in air at 70 °C for 30 min. The reaction progress was monitored
by TLC, and the yields of the products were determined by GC analysis. After the
2 2
completion of the reaction, TiO /AA/MoO nanocomplex (solid phase) was separated
by centrifuging followed by decantation (3×5 mL ethanol). Then desired product
(liquid phase) was extracted by plate chromatography eluted with nꢀhexane/EtOAc
1
(
10/3). Assignments of products were made by IR, H NMR and MS spectral data in
comparison with authentic samples.
Reusability of catalyst
To a mixture of the cyclooctene (10.0 mmol) and TiO
2
/AA/MoO
(20.0 mmol), and the reaction
mixture was stirred in air at 70 °C for 4 h. After completion of the reaction,
TiO /AA/MoO nanocomplex was separated by centrifuging followed by decantation
2
nanocomplex (0.3
2 2
mol %, 0.1 g) in ethanol (10.0 mL) was added H O
2
2
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0

Green Chemistry
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DOI: 10.1039/C4GC01398K
2 2
(3×5 ml ethanol). The isolated solid phase (TiO /AA/MoO nanocomplex ) was dried
under reduced pressure and reused for next runs. Catalyst recovery was also
2 2
investigated in the oxidation of sulfides with H O in ethanol according to the above
mentioned procedure.
Acknowledgements
Support for this work by Research Council of University of Birjand is highly
appreciated.
References
:
1
a) J. Y. Ying, C. P. Mehnert, M. S. Wong, Angew. Chem. Int. Edit. 1999, 38,
6–77; b) D. Trong, D. DesplantierꢀGiscard, C. Danumah, S. Kaliaguine,
5
Appl. Catal. A: Gen. 2001, 222, 299–357; c) D. E. De Vos, M. Dams, B.F.
Sels, P.A. Jacobs, Chem. Rev. 2002, 102, 3615–3640. d) M. H. Valkenberg,
W. F. Holderich, Catal. Rev. 2002, 44, 321. e) A. Choplin, F. Quignard,
Coordin. Chem. Rev. 1998, 178–180, 1679–1702; f) M. MasteriꢀFarahani, F.
Farzaneh, M. Ghandi, J. Mol. Catal. A: Chem. 2003, 192, 103–111.
A. Corma, I. Dominguez, A. Domenech, V. Fornes, C. J. GomezꢀGarcia, T.
Rodenas, M. J. Sabater, J. Catal. 2009, 265, 238–244.
2
3
a) P. M. Reis, C. A. Gamelas, J. A. Brito, N. Saffon, M. Gomez, B. Royo, Eur.
J. Inorg. Chem. 2011, 5, 666–673; b) C. Dinoi, M. Ciclosi, E. Manoury, L.
Maron, L. Perrin, R. Poli, Chem. Eur. J. 2010, 16, 9572–9584; c) C. Cordelle,
D. Agustin, J. C. Daran, R. Poli, Inorg. Chim. Acta 2010, 364, 144–149.
a) R. Sanz, M. R. Pedrosa, Curr. Org. Chem. 2009, 6, 239–263; b) F.E. Kühn,
A. M. Santos, M. Abrantes, Chem. Rev. 2006, 106, 2455–2475.
4
5
6
R. C. Bray, Enzymes 1975, 12, 299.
a) R. Hille, Eur. J. Inorg. Chem. 2006, 1913−1926; b) M. J. Romao, Dalton
Trans. 2009, 4053−4068; c) M. J. Romao, M. Archer, I. Moura, J. J. G.
Moura, J. LeGall, R. Engh, M. Schneider, P. Hof, R. Huber, Science 1995,
2
70, 1170−1176; d) R. Hille, Arch. Biochem. Biophys. 2005, 433, 107−116.
a) M. MasteriꢀFarahani, F. Farzaneh, M. Ghandi, J. Mol. Catal. A: Chem.
006, 248, 53–60; b) M. MasteriꢀFarahani, F. Farzaneh, M. Ghandi, Catal.
7
2
Commun. 2007, 8, 6–10; c) M. Amini, M. M. Haghdoost, M. Bagherzadeh,
Coordin. Chem. Rev., 2013, 257, 1093ꢀ1121; d) M. MasteriꢀFarahani, J. Mol.
Catal. A: chem. 2010, 316, 45–51; e) C.D. Nunes, M. Pillinger, A.A. Valente,
2
1

Page 23 of 25
Green Chemistry
View Article Online
DOI: 10.1039/C4GC01398K
A.D. Lopes, I.S. Goncalves, Inorg. Chem. Commun. 2003, 6, 1228–1233; f)
M. Jia, W.R. Thiel, Chem. Commun. 2002, 2392–2393
8
a) A. Rezaeifard, I. Sheikhshoaie, N. Monadi, H. StoeckliꢀEvans, Eur. J.
Inorg. Chem. 2010, 799–806; b) I. Sheikhshoaie, A. Rezaeifard, N. Monadi ,
S. Kaafi, Polyhedron 2009, 28, 733–738; c) A. Rezaeifard, I. Sheikhshoaie,
N. Monadi, M. Alipour, Polyhedron 2010, 29, 2703–2709; d) A. Rezaeifard,
M. Jafarpour, H. Raissi, M. Alipour, H. StoeckliꢀEvans, Z. Anorg. Allg. Chem.
2012, 638, 1023–1030; e) A. Rezaeifard, R. Haddad, M. Jafarpour, M.
Hakimi, J. Am. Chem. Soc. 2013, 135, 10036ꢀ10039; f) M. Jafarpour, A.
Rezaeifard, M. Ghahramaninezhad, T. Tabibi, New J. Chem., 2013, 37, 2087ꢀ
2
095; g) M. Jafarpour, M. Ghahramaninezhad, A. Rezaeifard, RSC Adv.,
014, 4, 1601–1608; h) M. Jafarpour, M. Ghahramaninezhad, A. Rezaeifard,
2
New J. Chem., 2014, 38, 2917ꢀ2926.
9
a) G. V. Samsonov, The Oxide Handbook, IFI/Plenum Press, New York,
1982; b) U. Diebold, Surface Science Reports 2003, 48, 53ꢀ229.
10
11
12
13
H. Peng, X. Wang, G. Li, H. Pang, X. Chen, Mater Lett. 2010, 64, 1898ꢀ1901.
M. Ye, Z. Chen, W. Wang, L. Zhen, J. Shen, Mater Lett. 2008, 62, 3404ꢀ3406.
G. S. Mital, T. Manoj, Chinese Sci. Bull., 2011, 56, 1639ꢀ1657.
a) S.C. Pillai, P.P. Periyat, R. George, D.E. McCormack, M.K. Seery, H.
Hayden, J Colreavy, D. Corr, S.J. Hinder, J. Phys. Chem. C 2007, 111, 1605–
1611; b) J. Yang, J. Zhang, L.W. Zhu, S.Y. Chen, Y.M. Zhang, Y. Tang,
Y.L. Zhu, Y.W. Li, , J. Hazard. Mater. B 2006, 137, 958ꢀ952.
1
4
5
T. Rajh, J. M. Nedeljkovic, M.C. Thurnauer, J. Phys. Chem. B 1999, 103,
3
515.
Y. Ou, J.D. Lin, H.M. Zou, D.W. Liao, J. Mol. Catal. A: Chem. 2005, 241,
9–64.
1
5
1
6
7
D. A. Köse, B. ZümreogluꢀKaran, New J. Chem., 2009, 33, 1874–1881.
1
a) A. O. Chong, K. B. Sharpless, J. Org. Chem. 1977, 42, 1587; b) S. Patai,
in: S.Patai (Ed.), The Chemistry of Peroxides, Wiley,Chichester,1983; c) R.
Sheldon, Metal-catalyzed Oxidations of Organic Compounds 1981; d) J.
nd
Kochi, Academic Press; J. E. Backvall, Modern Oxidation Methods, 2 ed.;
WileyꢀVCH: Weinheim, Germany, 2010; e) H. Srour, P. Le Maux, S.
Chevance, G. Simonneaux, Coord. Chem. Rev. 2013, 257, 3030ꢀ3050.
2
2

Green Chemistry
Page 24 of 25
View Article Online
DOI: 10.1039/C4GC01398K
1
8
a) S. Ikeda, Y. Kowata, K. Ikeue, M. Matsumura, B. Ohtani, Appl. Catal. A
Gen. 2004, 265, 69; b) K. Inumaru, T. Kasahara, M. Yasui, S. Yamanaka,
Chem. Commun. 2005, 2131; c) J. Seok Lee, K. Hwan You, Ch. Beum Park.
Chem Phys Chem 2005, 6, 714 – 718; d) K. Raghava Reddy, V. G Gomes, M.
Hassan, Materials Research Express 2014, 1, 015012; e) U. Diebold, Surface
Science Reports 2003, 48, 53ꢀ229.
1
9
a) A. Rezaeifard, M. Jafarpour, A. Naeimi, S. Kaafi, Catal. Commun. 2011,
12, 761ꢀ765; b) A. Rezaeifard, M. Jafarpour, A. Naeimi, K. Mohammadi, J.
Mol. Catal. A: Chem. 2012, 357, 141ꢀ147; c) Y. Ding, W. Zhao, H. Hua, B.
Ma, Green Chem., 2008, 10, 910ꢀ913; d) E. G. Ankudey, H. F. Olivo, T. L.
Peeples, Green Chem., 2006, 8, 923ꢀ926; e) F. Bruyneel, C. Letondor, B.
Bastürk, A. Gualandi, A. Pordea, H. StoeckliꢀEvans, R. Neier, Adv. Synth.
Catal. 2012, 354, 428ꢀ440.
2
0
a) F. Rajabi, S. Naserian, A. Primo, R. Luque, Adv. Synth. Catal. 2011, 353,
2
060ꢀ2066; b) L. Xu, J. Cheng, M. L. Trudel, J. Org. Chem. 2003, 68, 5388ꢀ
391; c) J. M. Samanen, E. Brandeis, J. Org. Chem. 1988, 53, 561ꢀ569; d) M.
5
H. Ali, G. J. Bohnert, Synth. Commun. 1998, 28, 2983ꢀ2998.
2
1
2
B.G. Donoeva, T. A. Trubitsina, N. S. Antonova, J. J. Carbó, J. M. Poblet, Gh.
AlꢀKadamany, U. Kortz, O. A. Kholdeeva, Eur. J. Inorg. Chem. 2010, 5312–
5317.
2
J. Dong, P. Saisaha, T. G. Meinds, P. L. Alsters, E. G. Ijpeij, R. P. van
Summeren, B. Mao, M. FananasꢀMastral, J. W. de Boer, R. Hage, B. L.
Feringa, W. R. Browne, ACS Catal. 2012, 2, 1087−1096.
2
3
4
W. Jiang, J. D. Gorden, C. R. Goldsmith, Inorg. Chem. 2012, 51, 2725−2727.
P. Saisaha, Jo. W. de Boerb, W. R. Browne, Chem. Soc. Rev. 2013, 42, 2059ꢀ
2
2074.
2
5
6
Y. Ding, W. Zhao, H. Hua, B. Ma, Green Chem, 2008, 10, 910–913.
2
A. Jha, Ch. R. Patil, A. C. Garade, Ch. V. Rode, Ind. Eng. Chem. Res. 2013,
52, 9803−9811.
2
7
8
M. A. H. Moelands, S. Nijsse, E. Folkertsma, Bas. de Bruin, M. Lutz, A. L.
Spek, R. J. M. Klein Gebbink, Inorg. Chem. 2013, 52, 7394ꢀ7410.
N. J. Schoenfeldt, Zh. Ni, A. W. Korinda, R. J. Meyer, J. M. Notestein, J. Am.
Chem. Soc. 2011, 133, 18684–18695.
2
2
3

Page 25 of 25
Green Chemistry
View Article Online
DOI: 10.1039/C4GC01398K
2
9
N. Mizunoa,Y. Nakagawa, K. Yamaguchi, J. Mol. Catal. A: Chem, 2006, 251,
86–290.
2
3
0
1
R. H. Ingle, N. K. Kala Raj. J. Mol. Catal. A: Chem, 2008, 294, 8–13.
M. Moghadam, Sh.Tangestaninejad, V. Mirkhani, I. MohammadpoorꢀBaltork,
M. Moosavifar, J. Mol. Catal. A: Chem. 2009, 302, 68–75.
3
32
33
34
B. Qi, X.ꢀH. Lu, D. Zhou, Q.ꢀH. Xia, Z.ꢀR. Tang, S.ꢀY. Fang, T. Pang, Y.ꢀL.
Dong, J. Mol. Catal. A: Chem. 2010, 322, 73–79.
A. M. Cojocariua, P. H, Mutin, E. Dumitriu, F. Fajula, A. Viouxc, V. Hulea,
Appl. Catal. B: Environmental 2010, 97, 407–413.
G. De Faveri, G. Ilyashenko, M. Watkinson, Chem. Soc. Rev., 2011, 40, 1722–
1760.
2
4