Nanocasted Cs salt of phosphomolybdic acid: A new system for selective oxidation of alcohols

Article abstract of DOI:10.1080/15533174.2011.617347

Since the discovery of many types of mesoporous silicas, such as SBA-15, KIT-6, FDU-12, and SBA-16, porous crystalline transition metal oxides have been synthesized using the mesoporous silicas as hard templates. The authors have used 2D hexagonal SBA-15 silicas as hard templates for the nanofabrication of Cs_2.5H_0.5PMo₁₂O₄₀ (CsHPMo) salt nanocrystal. The oxidation of alcohols occurs effectively and selectively with H₂O₂ as the oxidant. CsHPMo salt nanocrystal was used as the catalyst.

Full text of DOI:10.1080/15533174.2011.617347

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Nanocasted Cs Salt of Phosphomolybdic Acid: A New
System for Selective Oxidation of Alcohols
a b
a b
a b
Razieh Fazaeli
, Hamid Aliyan
& Mohammad Reza Poorgholam
a
Department of Chemistry , Shahreza Branch, Islamic Azad University , I. R. Iran
Razi Chemistry Research Center, Shahreza Branch, Islamic Azad University , I. R. Iran
b
Accepted author version posted online: 11 Apr 2012.Published online: 11 Jul 2012.
To cite this article: Razieh Fazaeli , Hamid Aliyan & Mohammad Reza Poorgholam (2012) Nanocasted Cs Salt of
Phosphomolybdic Acid: A New System for Selective Oxidation of Alcohols, Synthesis and Reactivity in Inorganic, Metal-
Organic, and Nano-Metal Chemistry, 42:6, 805-810
To link to this article: http://dx.doi.org/10.1080/15533174.2011.617347
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:805–810, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.617347
Nanocasted Cs Salt of Phosphomolybdic Acid: A New
System for Selective Oxidation of Alcohols
1
,2
1,2
1,2
Razieh Fazaeli, Hamid Aliyan, and Mohammad Reza Poorgholam
1
Department of Chemistry, Shahreza Branch, Islamic Azad University, I. R. Iran
Razi Chemistry Research Center, Shahreza Branch, Islamic Azad University, I. R. Iran
2
[
4]
important for industries related with fine chemicals, including
Since the discovery of many types of mesoporous silicas, such as flavors, pharmaceuticals, and food industries.[5]
SBA-15, KIT-6, FDU-12, and SBA-16, porous crystalline transition
metal oxides have been synthesized using the mesoporous silicas as
thesis owing to easy workup procedures, easy filtration, and
hard templates. The authors have used 2D hexagonal SBA-15 sili-
Solid HPAs have attracted much attention in organic syn-
minimization of cost and waste generation due to reuse and
cas as hard templates for the nanofabrication of Cs2.5
CsHPMo) salt nanocrystal. The oxidation of alcohols occurs ef-
fectively and selectively with H as the oxidant. CsHPMo salt
nanocrystal was used as the catalyst.
H0.5PMo12O
40
recycling of the catalysts.[
6]
(
2
O
2
Oxidation of alcohols into the corresponding aldehydes and
ketones is one of the most fundamental transformations in or-
ganic synthesis. Usually the oxidation of benzylic alcohols has
been carried out using oxidants such as vanadium polyoxomet-
Keywords green chemistry, heteropoly acids, HPAs, mesoporous
silica SBA-15, nanocasting
[7]
alate [(C6H5CH2)(CH3)3N]3[H3V10O28]3H2O, Mn(OAC)3/
[
8]
9]
catalytic 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ),
ceric ammonium nitrate (CAN)/Br o¨ nsted acidic ionic liquid,
and supported platinum by iron oxide.
[
INTRODUCTION
[10]
The synthesis of porous materials has attracted and still at-
tracts intensive attention, and significant advances have been
made with respect to structural, compositional, and morpholog-
ical control. Porous materials are normally classified into three
types by pore diameter (i.e. microporous [below 2 nm], meso-
porous [2–50 nm], and macroporous [exceeding 50 nm]).[1] The
fabrication of porous materials, especially the creation of meso-
porous materials, has been extensively investigated over the last
years. Template methods, which imply a more or less direct
replication of the pore system from the template, seem to be one
of the most promising synthetic pathways to create porous ma-
terials, especially if materials with ordered porosity are the goal.
The principle of the nanocasting pathway with hard template,
which involves three main steps: (a) formation of the template,
In recent years, replacement of toxic oxidants in organic re-
actions has become of high priority in environmentally benign
chemistry. Among other reagents, hydrogen peroxide is a cheap
and easily available oxidizing reagent, and it is considered as
the most desirable oxidant in terms of environmentally pro-
moted oxidation of benzylic alcohols have been reported. As
part of a continuing effort to understand catalytic properties of
[11–14]
HPAs,
herein we studied the H2O2 /Cs2.5H0.5PMo12O40
[
2]
(CsHPMo) salt nanocrystal system for the aerobic oxidative of
alcohols (Scheme 1).
(b) the casting step, and (c) removal of the template. Clearly,
a three-dimensional pore network is necessary in the template
to create a stable replica. In addition, the templates should be
easily and completely removed to obtain the true replicas.[ In
3]
recent decades, uses of heteropoly acids (HPAs) as catalysts for EXPERIMENTAL
fine organic synthetic processes have been developed and are
All materials were commercial reagent grade. Infrared
−1
spectra (400–4000 cm ) were recorded from KBr pellets
on a Nicolet Impact 400 D spectrometer (Sahreza Branch,
Islamic Azad University). Reaction courses and product mix-
tures were monitored by thin-layer chromatography. The X-
ray powdered diffraction patterns were performed on a Bruker-
D8 advance with automatic control (Central Laboratory of the
University of Isfahen X-ray Lab). The patterns were run with
Received 9 December 2010; accepted 21 August 2011.
The authors gratefully thank Islamic Azad University, Shahreza
Branch, for financial support.
Address correspondence to Razieh Fazaeli, Department of Chem-
istry, Shahreza Branch, Islamic Azad University, 86145–311, I. R. Iran.
E-mail: fazaeli@iaush.ac.ir
805

806
R. FAZAELI ET AL.
◦
◦
1
00 C for 48 h after stirring at 40 C for 16 h. The product was
◦
filtered off and dried at 800 C for 10 h (Figure 1).
CsHPMo/SBA
The CsHPMo was inserted in the SBA-15 silica matrix by
the two-step reaction deposition method. The parent CsHPMo
sample was obtained by dispersing the surfactant free SBA-15
(0.5 g) in 10 mL of n-propanol followed by an addition of 0.20 g
of cesium carbonate (Aldrich). The contents were stirred for 4 h,
filtered, and dried under vacuum. The dry solids were treated
FIG. 1. Ordered mesoporous silica (SBA-15 material). (a) High-resolution for 12 h with a solution containing an excess of H PMo O
3
12 40
FESEM image of the pore structure of SBA-15; (b) representation of the pore
arrangement.
dissolved in n-propanol under continuous stirring, after which
they were filtered and washed with an excess of n-propanol.
The resulting solids were dried at 383 K for 2 h and calcined at
5
73 K for another 2 h (Figure 2).
monochromatic Cu Kα (1.5406 Å) radiation with a scan rate of
◦
−1
2
min . The micrographs were recorded using a SEM (HI-
CsHPMo Nanoparticles
TACHI COM-S-4200, Tarbiat Hodares University) operated at
an accelerating voltage of 30 kV. Transmission electron mi-
croscopy (TEM) images were recorded digitally with a Gatan
slow-scan charge-coupled device camera on a JEOL 2011 elec-
tron microscope operating at 200 kV (Shiraz University).
The silica matrix was gradually removed from the CsH-
PMo/SBA materials by a treatment with HF. CsHPMo/SBA
composite 0.50 g were continuously stirred in 20 mL of an
aqueous HF solution for 3 h at room temperature (Figure 2). The
solid was recovered by decantation after centrifugation (7000
rpm). The water addition/centrifugation sequence was repeated
three times and finally the material was evacuated at 333 K.
SBA-15
SBA-15 was first synthesized by Zhao et al.[15] in 1998, us-
ing amphiphilic triblock copolymers, EO20PO70EO20 (Pluronic
P123), as template. In a typical synthesis, 1.00 g of P123 was
dissolved in a mixture of HCl/H2O (30.00 g of 2 M HCl to 7.50 g
H2O). After dissolution 2.08 g of TEOS or 1.96 g of sodium
silicate was added. The slurry was hydrothermally treated at
Oxidation of Benzylic Alcohols, General Procedure
A 25-mL round-bottomed flask with 5 mL of CH3CN
equipped with a magnetic stirrer and reflux condenser was
charged with 0.02 mmol catalyst and 5 mmol aqueous hydro-
gen peroxide (30%). The mixture was stirred and then 1 mmol
FIG. 2. (a) Preparation of the CsHPMo/SBA-15; (b) preparation of the CsHPMo nanoparticles.

CS NANOCASTED SALTS OF PMO
807
FIG. 3. FTIR spectra of Cs2.5H0.5PMo12O40.
◦
alcohol was added. The biphasic mixture was stirred at 90 C for tion or silica gel column chromatography (hexane/ethyl acetate,
the required time. Progress of the reaction was followed by the 10/1).
aliquots withdrawn directly from the reaction mixture analyzed
by GC using internal standard. After completion of the reaction,
the mixture was treated with a 10% sodium hydrogen sulfite
solution to decompose the unreacted hydrogen peroxide and
RESULTS AND DISCUSSION
Physicochemical Characterization
then with 10% sodium hydroxide. The product was extracted
Figure 3 shows the FTIR spectra of the Cs2.5H0.5PMo12O40.
with n-butyl-ether. The pure product was obtained by distilla- From the FTIR spectra, it was found that for 110 C dried
◦
TABLE 1
Chemical composition of parent CsHPMo/SBA-15 and its nanocast
Cs/Mo12
ICP
SiO2 removed (%)
Entry
Sample
EDX
AA
NAA
EDX
AA
ICP
NAA
1
2
CsHPMo/SBA-15
CsHPMo (nanocast)
2.41
2.46
2.43
2.38
2.5 ± 0.08
2.4 ± 0.03
2.5 ± 0.05
2.4 ± 0.01
0
0
0
0
98.02
98.10
98 ± 0.05
98 ± 0.01
FIG. 4. XRD patterns of Cs2.5H0.5PMo12O40.

808
R. FAZAELI ET AL.
samples the Keggin bands are observed at 1098, 960, 903,
−1
and 806 cm for Cs2.5H0.5PMo12O40. These were assigned to
νas(P–Oa), νas(Mo–Oa), νas(Mo–O–Mo), and νas(Mo–Oc–Mo),
respectively.[
16]
Figure 4 shows the XRD pattern of Cs2.5H0.5PMo12O40 dried
◦
at 110 C. It can be observed that Cs2.5H0.5PMo12O40 nanoparti-
cles are crystalline. Thus, the removal of the silica matrix does
not affect the crystal structure. The wide amorphous halo cen-
◦
tered at 2θ = 23 in the spectra of SBA-15 silica in as-prepared
composite[ completely disappeared for Cs2.5H0.5PMo12O40
17]
nanocasted material.
The as-prepared CsHPMo particles have been found to be
high purity by EDX measurements. EDX results (Figure 5)
indicated that the as-prepared samples contain Cs, Mo, P, and
O elements. The percentage of silica matrix removed from the
CsHPMo/SBA composite is about 98%. The good distribution of
all elements analyzed is in agreement with the atomic adsorption
analysis, neutron activation analysis (NAA), and ICP results
with deviation in the range of ± 0.09 (Table 1). These analyses
FIG. 5. (a) EDX measurements carried out during SEM observations; (b) SEM
micrographs of the sample Cs2.5H0.5PMo12O40 nanoparticles.
TABLE 2
a
Oxidation of benzylic alcohols with H2O2 catalyzed by CsHPMo nanocrystals in CH3CN at reflux conditions
CsHPMo- nanocrystal
ArCH OH
ArCHO
a-t
2
H O , CH CN, reflux
2
2
3
2
1
a-t
Ar
Entry
Substrate (1)
Product (2)
Time (min)
Yield (%)b,c
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
C6H5
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
70
90
85
90
50
85
78
90
50
80
95
90
95
90
100
85
78
100
82
95
98
95
87
82
95
90
92
75
92
90
90
92
87
85
87
90
87
90
75
82
4-NO2-C6H4
3-NO2-C6H4
2-NO2-C6H4
4-HO-C6H4
2-HO-C6H4
4-Cl-C6H4
2-Cl-C6H4
4-MeO-C6H4
3-MeO-C6H4
4-F-C6H4
1
1
1
1
1
1
1
1
1
1
2
4-Br-C6H4
4-Me-C6H4
3-Me-C6H4
2-NH2-C6H4
2-Thienyl
2-Me-C6H4
2-Pyridyl
s
t
1-phenyl ethanol
C6H5CH2CH2
s
t
a
2 2 3
Reaction conditions: benzyl alcohol derivatives (1 mmol), H O (5 mmol), CsHPMo (2 mol %), CH CN (5 mL).
Isolated yield.
All products were identified by comparison with authentic sample (mp, IR, NMR).
b
c

CS NANOCASTED SALTS OF PMO
809
FIG. 6. TEM micrographs of CsHPMo nanocast.
indicate the value of Cs/Mo12 ratio is 2.5, which agrees well alcohols were converted in to their corresponding aldehydes in
with calculated formula, Cs2.5H0.5PMo12O40.
good isolated yields within 50 and 90 min.
The SEM picture of CsHPMo is shown in Figure 5. CsHPMo
Heterocyclic alcohols, 2-thiophenemethanol, and 2-
exhibited nearly the dense aggregate of rock-like morphology. pyridinemethanol were oxidized to the corresponding aldehy-
There is no definite shape shown for any particles but the edges des in high yields. No oxidation was observed with S and
appear to be spherical with diameters about 43 nm. The isolated N hetero atoms. In addition, a mixture of primary and sec-
primary 10–20 nm nanoparticles of CsHPMo were also detected ondary alcohols was next subjected to oxidation. When ben-
at TEM micrographs (Figure 6).
zyl alcohol and 1-phenylethanol were allowed to react, the
former oxidized to benzaldehyde in 93% yield and the lat-
ter gave acetophenone in <7% yield. This clearly reveals
Oxidation of Benzylic Alcohols
In the catalytic reactions the choice of solvent is crucial. The that this method can be applied for the chemoselective oxi-
influence of the various solvents on the yield of the reaction was dation of primary hydroxyl groups in the presence of secondary
investigated using of benzyl alcohol as the substrate. From these alcohols.
studies it was deduced that CH3CN to be the most favorable
The recovery and reusability of the catalyst has been inves-
solvent. To study the scope of this procedure the oxidation of tigated. We have noticed that after the addition of CHCl3 to the
other alcohols was next studied (Table 2, entries 2–20). All reaction mixture, this catalyst can be easily recovered quantita-
benzylic alcohols having electron-donating and withdrawing tively by simple filtration. The wet catalyst was recycled (the
groups in the aromatic ring that is 4-methoxy and 4-nitro benzyl nature of the recovered catalysts has been followed by NAA,

810
R. FAZAELI ET AL.
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5
6
7
a
after 70 min
Run
Yield (%)
1
2
3
4
98
98
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55
2
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2
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(
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1
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