Acetalization of aldehydes and ketones over H4[SiW 12O40] and H4[SiW12O 40]/SiO2

Article abstract of DOI:10.1039/c4cy00021h

H₄[SiW₁₂O₄₀] (H-SiW₁₂) is demonstrated to be able to efficiently catalyze the acetalization of aldehydes and ketones with ethylene glycol and 1,3-propanediol. Nevertheless, the possible leaching and the recycling of H-SiW₁₂ are two major disadvantages that largely restrict its further application in industry. Moreover, H ₄[SiW₁₂O₄₀] tends to deactivate strong proton sites due to the small surface area of 10 m² g^-1. Due to interactions with surface silanol groups, the proton sites of polyoxometalates (POMs) on SiO₂ are less susceptible to deactivation. As such, immobilization of H₄[SiW₁₂O₄₀] onto SiO ₂ leads to the heterogeneous catalyst H₄[SiW ₁₂O₄₀]/SiO₂ (H-SiW₁₂/SiO ₂), which can catalyze the acetalization of aldehydes and ketones with ethylene glycol and 1,3-propanediol selectively and efficiently without the need of a drying agent. The acetalization process can proceed smoothly at a relatively low temperature under solvent-free conditions. The catalyst of H ₄[SiW₁₂O₄₀]/SiO₂ can be recycled at least ten times without an obvious decrease in its catalytic activity. As far as we know, the TONs of the H-SiW₁₂/SiO₂-catalyzed acetalization of cyclohexanone with ethylene glycol, and benzaldehyde with 1,3-propanediol are the highest reported so far.

Full text of DOI:10.1039/c4cy00021h

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Table of Content:
Highly Selective and Efficient Acetalization of Aldehydes and Ketones Catalyzed
by Heterogeneous Catalyst of H
4
[SiW12O40]/SiO
2
Shen Zhao, Yueqing Jia and Yu-Fei Song*
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing
1
00029, P. R. China.
4
It has been demonstrated that H [SiW12O40] (H-SiW12) is able to catalyze the acetalization
of aldehydes and ketones with ethylene glycol and 1,3-propanediol efficiently.
Nevertheless, the possible leaching and the recycling of H-SiW12 restrict its further
application. The immobilization of H
4
[SiW12
O
40] onto SiO
2
leads to the heterogeneous
catalyst of H 40]/SiO (H-SiW12/SiO
4
[SiW12
O
2
2
), which can catalyze acetalization of
aldehydes and ketones with ethylene glycol and 1,3-propanediol selectively and
efficiently without drying agents. The acetalization process can proceed smoothly at
relative low temperature under solvent-free conditions. Moreover, H
be recycled at least ten times without obvious decrease of catalytic activity. The TONs of
H-SiW12/SiO -catalyzed acetalization of cyclohexanone with ethylene glycol, and
4 2
[SiW12O40]/SiO can
2
benzaldehyde with 1,3-propanediol are the highest one reported so far.
Keywords: polyoxometalates, acetalization, Brónsted acid, immobilization

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ARTICLE
Acetalization of Aldehydes and Ketones over
H [SiW O ] and H [SiW O ]/SiO
4
12 40
4
12 40
2
Cite this: DOI: 10.1039/x0xx00000x
Shen Zhao,† Yueqing Jia,† Yu-Fei Song*
Received
Accepted
4
The H [SiW12O40] (H-SiW12) is demonstrated to be able to catalyze the acetalization of
aldehydes and ketones with ethylene glycol and 1,3-propanediol efficiently. Nevertheless, the
possible leaching and the recycling of H-SiW12 are two major disadvantages that large restrict
DOI: 10.1039/x0xx00000x
its further application in industry. Moreover, H
4
[SiW12
O
40] tends to deactivate strong proton
sites due to the small surface area of 10 m ·g . Due to the interactions with surface silanol
groups, the proton sites of polyoxometalates (POMs) on SiO are less susceptible to deactivate.
As such, immobilization of H 40] onto SiO leads to the heterogeneous catalyst of
40]/SiO (H-SiW12/SiO ), which can catalyze acetalization of aldehydes and ketones
www.rsc.org/
2
-1
2
4
[SiW12
O
2
H
4
[SiW12
O
2
2
with ethylene glycol and 1,3-propanediol selectively and efficiently without drying agents. The
acetalization process can proceed smoothly at relative low temperature under solvent-free
conditions. The catalyst of H
4
[SiW12
O
40]/SiO
2
can be recycled at least ten times without obvious
-catalyzed
decrease of catalytic activity. As far as we know, the TONs of H-SiW12/SiO
2
acetalization of cyclohexanone with ethylene glycol, and benzaldehyde with 1,3-propanediol
are the highest one reported so far.
1
. Introduction
much higher catalytic activities compared to conventional
catalysts, such as mineral acids, ion-exchange resins, mixed
oxides, zeolites, etc. Unlike the network structure of zeolites
and metal oxides, POMs possess the discrete ionic structures,
which endow POMs extremely high proton mobility and a
Acetalization of aldehydes and ketones with alcohols or diols is
a widely used approach in pharmaceutical industries such as
drug design and carbohydrate chemistry etc, the currently
used catalysts for acetalization of aldehydes and ketones
include HCl, tri-fluoroacetic acid (TFA) and p-toluenesulfonic
1
-3
“pseudo-liquid phase”. On top of that, POMs are thermally and
oxidatively stable compared with commonly used organic
4
5,6
7-9
acid (p-TSA) , solid acids, functionalized silica,
polymers,
acidic
2
1-26
ligands.
As such, POMs are superior candidates as acid
1
0,11
12
13-16
Lewis
acids,
metal
catalysts,
catalysts for acetalization.
1
7
18
organocatalysts, and kaolintic clay . However, the reported
catalytic systems show the following disadvantages and
potential technological and environmental problems, which, in
the long run, cannot meet the green and sustainable requirement
because that (1) the used inorganic acids such as H SO , HCl,
p-toluenesulfonate etc are corrosive; (2) the excess of amount
of drying agents such as silical gel, montmorillonite and
molecular sieve etc are needed; and (3) the selectivity is usually
poor. As such, it is significant to develop reusable,
environmental-benign, selective and efficient green catalysts
without drying agents.
Polyoxometalates (POMs) are a large family of anionic
metal-oxides of V, Mo, W and Nb etc. POMs have
demonstrated to be attractive acid catalysts
hydration,
isomerization,
In this paper, the Keggin cluster of H [SiW O ] (H-SiW )
4
12 40
12
has been developed to catalyze acetalization of aldehydes and
ketones under solvent-free conditions. Selective and efficient
acetalization of aldehydes and ketones can be achieved by H-
SiW12 without drying agents under mild conditions.
2
4
Furthermore, the immobilization of H-SiW12 onto SiO results
2
in the formation of the heterogeneous catalyst of H-
38
SiW /SiO ,
which have shown selective and efficient
1
2
2
acetalization of aldehydes and ketones. In addition, H-
SiW /SiO is truly heterogeneous and can be recycled at least
1
2
2
ten times without obvious decrease of catalytic activity, and the
recycled catalyst of H-SiW /SiO remains its structure and
1
2
2
composition.
2
1-26
for
31,32
2
7,28
29,30
esterification,
saccharification
acetoxylation,
and cycloaddition etc,
2. Experimental Section
3
3,34
35,36
37
due to the stronger acidity, Keggin POMs generally exhibit
2
.1. Chemicals
This journal is © The Royal Society of Chemistry 2014
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Cyclohexanone (99%), 2-adamantanone (98%), hexanal (99%), In a typical experiment, 1 mmol aldehyde or ketone, 1.5 mmol
heptanal (99%), octanal (98%), nonanal (99%), decanal (96%), ethylene glycol or 1,3-propanediol and H-SiW /SiO (0.225
1
2
2
cyclohexanecarboxaldehyde (98%), benzaldehyde (98%), 2- μmol H-SiW ) as catalyst were placed in a 20 ml glass bottle at
1
2
o
methylbenzaldehyde (98%), 3-methylbenzaldehyde (97%), 4- 60 C and the reaction mixture was kept stirring vigorously.
methylbenzaldehyde (98%), 2-methoxybenzaldehyde (98%), 3- The reaction was effectively quenched after 6 hours. The
methoxybenzaldehyde (98%), 4-methoxybenzaldehyde (98%), resulting oily products were extracted by diethyl ether,
1
2
-chlorobenzaldehyde (97%), 3-chlorobenzaldehyde (97%), 4- analyzed by GC, and identified by H-NMR. The yields were
chlorobenzaldehyde (98%), 2-bromobenzaldehyde (98%), 3- determined by reference standards. After completion of the
bromobenzaldehyde (97%), 4-bromobenzaldehyde (99%), 2- reaction, H-SiW /SiO were recovered by centrifugation,
1
2
2
nitrobenzaldehyde (98%), 3-nitrobenzaldehyde (99%), 4- washed with acetone, and dried in air.
nitrobenzaldehyde (99%), ethylene glycol (99%), 1,3-
propanediol (99%), and all solvents were purchased from Alfa 3. Results and Discussion
Aesar. Analytical silicotungstic acid (H SiW O ) was
4
12 40
3
.1. Catalysis of H-SiW12
obtained from Energy Chemical in Shanghai. Silica gel (SiO2,
pore size: 6 nm, particle size: 40-63 μm) was purchased from
Sigma Aldrich. All the chemicals and solvents were used
without further purification.
Table 1. The effect of different catalysts on acetalization of cyclohexanone
with ethylene glycol at 25 C under solvent-free condition.
o
a
Entry
Catalyst
H-SiW12
K-PW11
K-SiW11
Yield(%)
92
2
.2. Measurements
1
2
3
4
5
6
7
8
9
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
<0.1
Powder X-ray diffraction (XRD) patterns were recorded on a
Rigaku XRD-6000 diffractometer under the following
conditions: 40 kV, 30 mA, Cu Kα radiation (λ = 0.154 nm).
Fourier transform infrared (FT-IR) spectra were recorded on a
Bruker Vector 22 infrared spectrometer using KBr pellet
method. Inductively coupled plasma-atomic emission
spectroscopy (ICP-AES) analysis was performed using a
Shimadzu ICPS-7500 spectrometer. BET measurements were
performed at 77 K on a Quantachrome Autosorb-1C analyzer.
Na-A-PW
Na-B-PW
Na-SiW
K-W
K-La(PW11
K-Ce(PW11
Na WO
Na SiO
Na HPO
NaH PO
WO
None
9
9
9
2
)
)
2
2
1
1
0
1
2
4
2
3
12
2
4
4
1
1
1
3
4
5
2
o
3
The samples were degassed at 110 C for 6 hours before the
measurements. Solid state NMR measurements were carried out
on a Bruker Avance 300 M solid-state spectrometer equipped
a
Reaction conditions: cyclohexanone (1 mmol), catalyst (5.5 mol% based on
o
W to cyclohexanone), ethylene glycol (1.5 mmol), 25 C, 6 hours. Yields
with
a
commercial
7
mm MAS NMR probe. X-ray were determined by GC analysis using reference standard. Assignments of
1
photoelectron spectroscopy (XPS) measurements were corresponding products were analyzed by H-NMR.
performed with mono-chromatized Al Kα exciting X-radiation
As the first trial, the acetalization of cyclohexanone with
ethylene glycol catalyzed by H-SiW12 has been carried out
under solvent-free conditions. It is found that good yield of
(
PHI Quantera SXM). Temperature-programmed desorption of
ammonia (NH -TPD) was performed using Auto Chem. II 2920
3
equipment. The corresponding acetals and ketals were analyzed
by Agilent 7820A gas chromatography (GC) system using a 30
m 5% phenylmethyl silicone capillary column with an ID of
9
2% with excellent selectivity of above 99.9% can be obtained
o
in 6 hours at 25 C (Table 1, Entry 1). Contrast experiments
under the same conditions suggest that the lacunary Keggin
clusters of K [PW O ] (K-PW ), K [SiW O ] (K-SiW ),
0.32 mm and 0.25 µm coating (HP-5). Yields were determined
7
11 39
11
8
11 39
11
by GC analysis using reference standards. Assignments of the
1
Na H[A-PW O ] (Na-A-PW ), Na H[B-PW O ] (Na-B-PW )
8 9 34 9 8 9 34 9
corresponding acetals and ketals were analyzed by H-NMR
and Na [SiW O ] (Na-SiW ) are not effective (Entries 2-6)
10
9
34
9
spectra recorded on a Bruker 400 MHz NMR spectrometer.
for
such
acetalization.
Furthermore,
the
2
.3. Synthesis of H-SiW /SiO
K [{WO(O ) (H O)} (μ-O)]∙2H O (K-W ) is not effective too
1
2
2
2
2 2
2
2
2
2
(
Entry
7).
The
lanthanide-containing
POMs
of
H SiW O (1 g) was dissolved in 50 ml H O, which was
4
12 40
2
K [La(PW O ) ] (K-La(PW ) ) and K [Ce(PW O ) ] (K-
Ce(PW ) ), involving Lewis-acid center of La and Ce , have
11 2
not shown any catalytic activities (Entries 8-9). In addition,
Na WO , Na SiO , Na HPO , NaH PO and WO3 are not
effective either (Entries 10-14). The reaction hardly proceeds in
the absence of the catalyst (Entry 15). The above experimental
results clearly indicate that the Brónsted-acid catalyst of H-
SiW12 is selective and effective for acetalization of
cyclohexanone. On the basis of the first trial, it is reasonable to
1
1
11 39 2
11 2
11
11 39 2
3+
added to SiO (10g) suspended in 50 ml H O. The resulting
2
2
3
+
o
mixture was stirred at 25 C overnight and H O was evaporated
2
under vacuum. The obtained H-SiW /SiO was dried under
1
2
2
2
4
2
3
2
4
2
4
reduced pressure overnight. ICP analysis showed that the 9.0
wt.% H SiW O on the SiO support. The specific surface
4
12 40
2
2
-1
area determined by BET method is 324 m ·g . The average
pore diameter and the single-point total pore volume are 6.6 nm
and 0.67 cm ·g , respectively.
3
-1
2
.4. Procedure for the acetalization of aldehydes and ketones
2
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extend the substrates towards a wide range of aldehydes and
ketones.
(3)
ln k  (ln A E ) / RT
a
As shown in Table 2 and Table S5, H-SiW12 can realize
selective and efficient acetalization of various aldehydes and
ketones with ethylene glycol or 1,3-propanediol, and all the
corresponding acetals and ketals can be afforded in good yields
with excellent selectivity of all above 99.9%.
The acetalization of 2-methylbenzaldehyde with ethylene
glycol using H-SiW12 as catalyst has been performed, and it is
o
noted that the yield is quite low at 25 C under solvent-free
conditions. As such, the effect of temperature (denoted as T) on
The above results reveal that H-SiW12 can catalyze the
acetalization of various aldehydes and ketones with ethylene
glycol and 1,3-propanediol selectively and efficiently. However,
the ICP analysis of reaction filtrate after acetalization of
benzaldehyde with 1,3-propanediol catalyzed by H-SiW12
reveal the contents of Si and W are 0.04 and 0.49 ppm,
respectively (Table S7). The ICP results clearly show that H-
SiW12 is partly dissolved in reaction mixture during the
catalytic reaction, which means the H-SiW12 is leaching during
the reaction. Therefore, the leaching of H-SiW12 and the
Figure 1. Effect of temperature on acetalization of cyclohexanone and 2-
methylbenzaldehyde with ethylene glycol (A) and the plot lnk(T) vs (-1/T).
Reaction conditions: cyclohexanone or 2-methylbenzaldehyde (1 mmol), H-SiW12 recycling of H-SiW12 are potential problems for its further
(
0.25 mol% to cyclohexanone or 2-methylbenzaldehyde), ethylene glycol (1.5
27
application. Moreover, H-SiW12 tends to deactivate strong
mmol), 6 hours.
2
-1
proton sites due to the small surface area of 10 m ·g . In this
regard, SiO2 is the ideal support for H-SiW12 for its large
surface area and inertness towards Keggin POMs. Due to the
interaction with surface silanol groups, the proton sites of
are less susceptible to deactivate. As such,
2
immobilization of H-SiW12 onto SiO leads to the formation of
acetalization is explored. As shown in Figure 1A, for 2-
methylbenzaldehyde, the yield increases from 49% to 81%
upon increasing T from 25 to 60 C, and the yield remains
unchanged by further increase T from 60 to 70 C. For
cyclohexanone, the yield remains almost the same upon
o
2
6
o
POMs/SiO
2
3
8
o
heterogeneous catalyst of H-SiW12/SiO .
2
increasing T from 25 to 70 C. In order to explain the catalytic
results in detail, the kinetic parameters for acetalization of
cyclohexanone and 2-methylbenzaldehyde with ethylene glycol catalyzed by H-SiW12 at 60 C under solvent-free conditions.
Table 2. Acetalization of various aldehydes and ketones with ethylene glycol
o
a
catalyzed by H-SiW12 have been calculated. In addition, the
Entry
Donor
Acceptor
Product
Yield(%)
o
yield and ln(C /C ) are plotted against reaction time at 25 C, 40
t
o
0
o
o
o
C, 50 C, 60 C and 70 C (Fig S1 and S2), in which C and C
0
t
1
2
3
4
5
6
7
8
9
X = H
X = H
73
81
73
95
90
80
93
85
89
are concentrations of cyclohexanone ketal or 2-
methylbenzaldehyde acetal at initial time (t =0) and time t,
respectively. The linear fit of data reveals the pseudo-first-
order kinetics for acetalization of cyclohexanone and 2-
methylbenzaldehyde with ethylene glycol at different
temperatures. Figure 1B shows the plot of lnk(T) vs (-1/T). The
X = 2-Me
X = 3-Me
X = 2-Cl
X = 3-Cl
X = 4-Cl
X = 2-Br
X = 3-Br
X = 4-Br
X = 2-Me
X = 3-Me
X = 2-Cl
X = 3-Cl
X = 4-Cl
X = 2-Br
X = 3-Br
X = 4-Br
calculated activation energy (E ) by Arrhenius equation for
a
1
0
X = 2-NO
X = 3-NO2
X = 4-NO
2
X = 2-NO
X = 3-NO2
X = 4-NO
2
93
94
>99.9
acetalization of cyclohexanone and 2-methylbenzaldehyde with
11
-
1
1
2
2
2
ethylene glycol are 3.3 and 15.9 kJ∙mol , respectively. The E
a
for acetalization of cyclohexanone with ethylene glycol is much
lower than that for that of 2-methylbenzaldehyde with ethylene
glycol. The above result can explain the differences between
acetalization of cyclohexanone and 2-methylbenzaldehyde with
ethylene glycol at different temperatures. Furthermore, the
1
1
15
1
1
3
4
R = n-C
R = n-C
R = n-C H
R = n-C
R = n-C
5
6
H
H
11
13
15
17
19
R = n-C
R = n-C
R = n-C H
R = n-C
R = n-C
5
6
H
H
11
13
15
17
19
>99.9
98
99
99
98
7
7
6
7
8
H
H
8
H
H
9
9
yields and E for acetalization of various substrates with
a
1
8
97
99
ethylene glycol catalyzed by H-SiW have been summarized in
1
2
o
Table S4. The yields at 60 C are much higher than that at 25
1
9
o
C in most cases. Therefore, the acetalization of various
aldehydes and ketones with ethylene glycol and 1,3-
propanediol has been performed at 60 C in order to achieve
good yields using H-SiW12 as catalyst.
a
o
Reaction conditions: substrate (1 mmol), H-SiW12 (0.25 mol% to substrate),
o
ethylene glycol (1.5 mmol), 60 C, 6 hours. Yields were determined by GC
analysis using reference standards. Assignments of corresponding products
were analyzed by H-NMR.
1

dC / dt  kCt (1)
t
ln(C / C )  kt (2)
t
o
3
.2. Characterization of H-SiW /SiO
12 2
This journal is © The Royal Society of Chemistry 2014
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Table 3. BET and NH
3
-TPD results of H-SiW12/SiO
2
, SiO
2
and H-SiW12.
2
-1
3
-1
-1 a
Entry
Catalyst
SiO
fresh H-SiW12/SiO
reused H-SiW12/SiO
H-SiW12
Surface Area (m ∙g )
Pore Volume (cm ·g )
Pore Size (nm)
3
Total Acidity (mmol NH ·gcat )
1
2
3
4
2
490
324
322
9
0.82
0.67
0.66
6.6
6.6
6.5
0.4
-
2
0.42
0.41
0.44
2
0.026
a
3 3
The amount of acid sites were calculated by quantifying the desorbed NH from NH -TPD.
XPS spectra corresponding to W core levels of the H-
SiW /SiO and H-SiW are shown in Fig 3A. The binding
1
2
2
12
energy of W4f7/2 and W4f5/2 are 36.4 and 38.1 eV for H-
SiW /SiO , and 36.2 and 37.8 eV for H-SiW . XPS spectra
1
2
2
12
corresponding to Si core levels of the H-SiW /SiO and SiO
2
1
2
2
are shown in Fig 3B. The Si2p peak at 101.2 eV in the H-SiW12
is so weak that the Si2p peak of H-SiW12 will be overlapped by
the Si2p peak of SiO in the H-SiW /SiO as only 9.0 wt. % H-
2
12
2
SiW12 has been immobilized onto SiO . Therefore, the Si2p
2
peak in the H-SiW /SiO comes from SiO not from H-SiW .
1
2
2
2
12
The binding energy of Si2p is 103.1 eV in H-SiW /SiO , and
1
2
2
1
02.8 eV in SiO . The above results reveal that the binding
2
energy of W4f7/2 and W4f5/2 in the H-SiW /SiO are higher
12
2
than those of the H-SiW , and the binding energy of Si2p in
29
12
2 2
Figure 2. Si CP/MAS NMR spectra of H-SiW12/SiO , SiO and H-SiW12.
the H-SiW /SiO is higher than those of the SiO . These results
1
2
2
2
confirm the presence of the hydrogen bonding interactions
ICP analysis of H-SiW /SiO shows 9.0 wt.% H SiW O on
the SiO2 support (Table S1). Powder XRD pattern of H-
1
2
2
4
12 40
between the hydroxyl groups on SiO support and the oxygen
2
atoms of the H-SiW12 in the H-SiW /SiO .
12
2
SiW /SiO reveals the characteristic peak of H-SiW at 2θ =
1
o
2
2
12
8
.46 , which reveals that the structure of H-SiW12 remains
unchanged after being immobilized onto the SiO support (Fig
2
S3A). The weak resonance compared with that of the H-SiW12
is due to the fact that only 9.0 wt. % H-SiW12 has been
immobilized onto SiO . FT-IR spectrum of H-SiW shows four
2
12
characteristic peaks of W-O stretching bands at 934, 891, 790,
-
1
-
and 715 cm , which have shifted to 935, 893, 792, and 716 cm
1
in the corresponding FT-IR spectrum of H-SiW /SiO ,
1
2
2
respectively (Fig S3B). These shifts reveal the presence of the
hydrogen bonding interactions between the hydroxyl groups on
the surface of SiO support and the oxygen atoms of the H-
2
SiW .
1
2
2
9
As shown in Fig 3, the Si CP/MAS NMR spectrum of H-
SiW /SiO exhibits two resonances at -102.8 and -111.9 ppm,
1
2
2
3
4
which correspond to (SiO) SiOH (Q ) and Si(OSi) (Q ). At the
same time, SiO also exhibits Q and Q peaks at -101.5 and
3
4
3
4
2
4
1
10.8 ppm. It should be noted that the Q peak is the main peak
2
9
in the Si CP/MAS NMR spectrum of H-SiW /SiO , whereas
the Q peak is the main peak in the Si CP/MAS NMR
1
2
2
3
29
spectrum of SiO . Such differences can be explained by the fact
2
that H-SiW1 is bound to SiO through the hydrogen bonding
2
2
3
9
29
interactions. The Si CP/MAS NMR spectrum of H-SiW12
shows one peak at -84.9 ppm, while that of H-SiW /SiO at -
1
2
2
8
6.0 ppm. The weak resonance compared with that of the H- Figure 3. XPS spectra of H-SiW /SiO , SiO and H-SiW .
12 2 2 12
SiW12 is due to the fact that only 9.0 wt. % H-SiW12 has been
immobilized onto SiO . The peak shift is due to the hydrogen
BET measurements have been performed on H-SiW /SiO ,
12 2
2
bonding interactions between the hydroxyl groups on SiO2 SiO and H-SiW , and the specific surface area, pore volume,
2
12
support and the oxygen atoms of the H-SiW .
and pore diameters are presented in Table 3. The samples of H-
1
2
4
| Catal. Sci. Technol., 2014, 00, 1-8
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Page 6 of 9
Catalysis Science & Technology
SiW /SiO and SiO2 display a type IV isotherm with H1 3.3. Catalysis of H-SiW /SiO
2
ARTICLE
1
2
2
12
4
0
hysteresis (Fig S4A). The SiO exhibits a maximum pore
diameter of 6.6 nm and surface area of 490 m ∙g . The H-
2
Acetalization of various aldehydes and ketones with ethylene
2
-1
o
glycol by H-SiW /SiO at 60 C has been investigated under
1
2
2
SiW /SiO remains the pore diameter of 6.6 nm and a decrease
1
2
2
solvent-free conditions. All the corresponding acetals and ketals
can be afforded in good yields with excellent selectivity of
above 99%. For example, benzaldehyde can be converted to the
corresponding acetal in the yield of 73% (Table 4, Entry 1).
2
-1
in surface area of 324 m ∙g . The above results reveal that the
immobilization of H-SiW12 onto SiO affects the surface area
2
and pore distribution of SiO . However, the surface area of H-
2
2
-1
SiW /SiO (324 m ∙g ) is much larger than that of H-SiW
12
1
2
2
2
Methyl-substituted
aromatic
aldehydes
including
2-
-1
(
10 m ∙g ), which can reduce the deactivation of strong proton
sites.
The above catalytic results reveal that the strong acidity of
methylbenzaldehyde and 3-methylbenzaldehyde can be
converted to the corresponding acetals in the yields of 81% and
73%, respectively (Entries 2-3). For cholor-, bromo- or nitro-
H-SiW12 plays a significant role in acetalization of aldehydes
and ketones with ethylene glycol and 1,3-propanediol.
Therefore, the acidity of the H-SiW /SiO is expected to play a
substituted aldehydes, good yields in the range of 80~99.9%
can be achieved (Entries 4-12). The above results reveal that
acetalization of aromatic aldehydes with electron-drawing
groups (cholor-, bromo- or nitro- substituted aldehydes) gives
higher yields than those of aromatic aldehydes with electron-
1
2
2
key role in determining the catalytic performance in
acetalization of aldehydes and ketones with diols. As such,
temperature-programmed desorption of ammonia (NH -TPD)
3
drawing
groups
(2-methylbenzaldehyde
and
3-
demonstrate that the H-SiW /SiO and H-SiW exhibit a main
1
2
2
12
methylbenzaldehyde). The reason is that the protonation of
carbonyl groups in electron-drawing substituted aromatic
aldehydes is easier and more completely than that in electron-
donating one. The above results confirm that the protonation of
carbonyl group is essential for acetalization.
For aliphatic aldehydes, acetalization of alkyl aldehydes
leads to excellent yields of >98% (Entries 13-17). Acetalization
of cyclohexanecarboxaldehyde proceeds efficiently with yield
of 97% (Entry 18). In terms of 2-admantanone, excellent yield
of 99% can be obtained (Entry 19).
o
NH desorption peak at 454.2 C in Fig S5, which corresponds
to the NH molecules adsorbed on strong acid sites of Keggin.
3
4
1
3
The total acidity of the H-SiW /SiO and H-SiW determined
1
2
2
12
by NH -TPD are summarized in Table 3. The results reveal that
3
not only H-SiW12 but also H-SiW /SiO can provide strong
12
2
acidity to promote acetalization of aldehydes and ketones with
diols.
Table 4. Acetalization of various aldehydes and ketones with ethylene glycol
o
catalyzed by heterogeneous catalyst of H-SiW12/SiO
free conditions.
2
at 60 C under solvent-
a
As shown in Table S6, H-SiW /SiO can realize selective
1
2
2
b
and efficient acetalization of various aldehydes and ketones
with 1,3-propanediol, and all the corresponding acetals and
ketals can be afforded in good yields with excellent selectivity
of all above 99.9%.
Entry
Donor
Acceptor
Product
Yield(%)
1
2
3
4
5
6
7
8
9
X = H
X = H
73(70)
81(76)
73(69)
95(91)
90(85)
80(74)
93(90)
85(81)
89(86)
93(91)
94(89)
X = 2-Me
X = 3-Me
X = 2-Cl
X = 3-Cl
X = 4-Cl
X = 2-Br
X = 3-Br
X = 4-Br
X = 2-Me
X = 3-Me
X = 2-Cl
X = 3-Cl
X = 4-Cl
X = 2-Br
X = 3-Br
X = 4-Br
Though acetalization of benzaldehyde with ethylene glycol
over heterogeneous catalyst of [Hmim] PW O has been
3
12 40
reported with the high yield of 97%, the turnover number (TON)
6
is only 111 (Table 5, Entry 4) , which is much lower than that
of H-SiW /SiO (TON = 3243, benzaldehyde: ethylene glycol:
1
2
2
H-SiW12 = 4443: 6664: 1). Furthermore, the reaction condition
of [Hmim] PW O is environmental-unfriendly using toluene
1
1
1
0
1
2
X = 2-NO
X = 3-NO
X = 4-NO
2
X = 2-NO
X = 3-NO
X = 4-NO
2
2
2
2
2
3
12 40
o
>99.9(98)
as solvent at 110 C. In contrast, when H-SiW /SiO is applied
1
2
2
as catalyst, although acetalization of cyclohexanone with
ethylene glycol (cyclohexanone: ethylene glycol: H-SiW12
6000: 54000: 1) proceeds in 83% yield, it is worth noting that
=
1
1
1
1
1
3
4
5
6
7
R = n-C
R = n-C
R = n-C
R = n-C
R = n-C
5
6
7
8
9
H
H
H
H
H
11
13
15
17
19
R = n-C
R = n-C
R = n-C
R = n-C
R = n-C
5
6
7
8
9
H
H
H
H
H
11
13
15
17
19
>99.9(99)
98(96)
99(97)
99(95)
98(94)
3
o
the reaction is carried out under solvent-free conditions at 60 C
and the TON can reach as high as 29880 (Table 5, Entry 1).
The TON for H-SiW /SiO -catalyzed acetalization of
1
2
2
1
8
97(92)
cyclohexanone with ethylene glycol is the highest one reported
7
so far, when compared with those of SO H-FSM , SC-34-
3
1
9
99(94)
1
4
9
15
16
SO H , M-ZrPO , Bi(OTf) ∙4H O , tin(IV) phosphate and
3
3
2
2
0
m-SZ (Table 5, Entries 5-10).
a
2
Reaction conditions: substrate (1 mmol), H-SiW12/SiO (0.0225 mol% to
substrate), ethylene glycol (1.5 mmol), 60 C, 6 hours. Yields were
determined by GC analysis using reference standards. Assignments of
corresponding products were analyzed by H-NMR. The values in
parentheses are the isolated yields.
o
It is worth noting that the acetalization of benzaldehyde with
1,3-propanediol proceeds efficiently in 85% yield with H-
SiW /SiO (benzaldehyde: H-SiW = 36000: 54000: 1) under
1
b
1
2
2
12
solvent-free conditions (Table 5, Entry 2). The turnover number
(
TON) can reach as high as 30600. As far as we know, the
This journal is © The Royal Society of Chemistry 2014
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ARTICLE
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Catalysis Science & Technology
Table 5. Comparison of yields and TONs for the acetalization catalyzed by different catalysts.
o
a
Entry
1
Catalyst
Substrate
Alcohol
ethylene
glycol
Solvent
none
Temp.( C)
Time(h)
6
Yield(%)
83
TON
Ref.
this
work
this
H-SiW12/SiO
2
cyclohexanone
60
60
29800
1
,3-
2
3
4
5
6
7
8
9
H-SiW12/SiO
2
benzaldehyde
benzaldehyde
benzaldehyde
cyclohexanone
cyclohexanone
cyclohexanone
cyclohexaone
cyclohexanone
none
none
6
24
2
85
94
97
93
98
98
82
68
30600
-
propanediol
1,3-
propanediol
ethylene
glycol
ethylene
glycol
ethylene
glycol
ethylene
glycol
ethylene
glycol
ethylene
glycol
work
b
mPMF
25
11
6
[Hmim]
3
PW12
O
40
toluene
toluene
none
reflux
reflux
120
90
111
930
666
-
c
3
SO H-FSM
10
2
7
d
M-ZrPO
SC-34-SO
Bi(OTf) ∙4H
tin(IV) phosphate
14
9
e
3
H
cyclohexane
toluene
toluene
5
3
2
O
110
110
4
82
15
16
3
59
1
1
0
1
Al(OTf)
IL
3
4-methoxybenzaldehyde
2-chlorobenzaldehyde
methanol
methanol
none
none
25
25
1
24
98
96
98
19
13
10
f
fluorous hydrazine-
1
1
1
2
3
4
3-phenylpropionaldehyde
benzaldehyde
methanol
none
none
none
25
30
25
1
88
97
98
18
388
-
17
8
1
,2-bis(carbothioate)
g
IL-silica-polymer
methanol
ethylene
glycol
0.6
h
m-SZ
cyclohexanone
0.25
20
a
b
c
TON (turnover number) = mole of corresponding product/ mole of catalyst used; mPMF: mesoporous poly-melamine-formaldehyde; SO
3
H-FSM: propyl-
d
e
sulfonic acid-functionalized FSM-16 mesoporous silica; M-ZrPO: mesoporous zirconium oxophosphate; mesoporous silica SBA-15 with sulfonic acid (-
h
f
g
3
SO H) groups; aprotic imidazolium ionic liquid; IL-silica-polymer: silica-polymer core–shell microspheres with imidazolium-styrene copolymer shells; m-
SZ: mesoporous sulfated zirconia.
TON for H-SiW /SiO -catalyzed acetalization of benzaldehyde SiW12 and H-SiW /SiO has been proposed as follows: (1) the
1
2
2
12
2
with 1,3-propanediol is the highest among previously reported carbonyl group of aldehyde or ketone can be protonated by H-
values. At the same time, the reaction time is much shorter than SiW ; (2) the nucleophilic addition to the protonated carbonyl
1
2
1
1
that of mPMF (Table 5, Entry 3).
group with one of the hydroxyl groups of diol leads to the
To confirm the catalysis of H-SiW /SiO is truly corresponding hemiacetal or hemiketal; (3) the intermolecular
1
2
2
heterogeneous, acetalization of benzaldehyde with 1,3- addition of hemiacetal or hemiketa results in the corresponding
propanediol has been carried out using H-SiW /SiO as acetal or ketal (Figure S4).
1
2
2
o
catalyst at 60 C under solvent-free conditions. When the yield
reaches about 50%, the solid POM catalyst of H-SiW /SiO is 4. Conclusions
1
2
2
removed from the reaction mixture by filtration and the reaction
is allowed to proceed with the filtrate under the same conditions.
No additional corresponding acetal is obtained even re-adding
To summarize, immobilization of H-SiW12 onto SiO leads to
2
the formation of the heterogeneous catalyst of H-SiW /SiO .
1
2
2
2
9
The Si CP/MAS NMR and XPS results confirm the presence
of the hydrogen bonding interactions between the hydroxyl
groups on SiO and the oxygen atoms of the H-SiW . The
1,3-propanediol. Furthermore, the ICP analysis of reaction
filtrate after acetalization of benzaldehyde with 1,3-propanediol
catalyzed by H-SiW12 reveal the contents of Si and W are both
below 0.01 ppm, respectively (Table S8). The ICP results
2
12
2
-1
surface area of H-SiW /SiO (324 m ∙g ) is much larger than
1
2
2
2
-1
that of H-SiW12 (10 m ∙g ). The hydrogen bonding interactions
and the largely enhanced surface area can reduce the
deactivation of strong proton sites.
clearly show that H-SiW12 on SiO is not dissolved in reaction
2
mixture during the catalytic reaction, which means the H-
SiW /SiO is not leaching during the reaction. These results
1
2
2
The heterogeneous catalyst of H-SiW /SiO can realize
1
2
2
rule out the contribution of Si and W species leached into the
reaction solution for the observed catalytic results. Similar
catalytic results can be achieved with H-SiW /SiO as catalyst
selective and efficient acetalization of various aldehydes and
ketones with ethylene glycol and 1,3-propanediol under
1
2
2
o
solvent-free conditions at 60 C. Taking the acetalization of
in the acetalization of cylclohexanone with ethylene glycol
under solvent-free conditions. The reason is that the interaction
with SiO can stabilize H-SiW . Therefore, the catalysis is
benzaldehyde with 1,3-propanediol as an example, the catalytic
reaction proceeds efficiently in 85% yield (benzaldehyde: 1,3-
propanediol: H-SiW12 = 36000: 54000: 1) under solvent-free
conditions with the TON of 30600, which is the highest one
reported so far. The H-SiW /SiO can be recycled at least ten
2
12
truly heterogeneous.
The mechanism of acetalization of aldehydes and ketones
with diols (ethylene glycol or 1,3-propanediol) catalyzed by H-
1
2
2
6
| Catal. Sci. Technol., 2014, 00, 1-8
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Page 8 of 9
Catalysis Science & Technology
ARTICLE
2
Figure 4. The H-SiW12/SiO -recycling and reusing experiments of the acetalization of benzaldehyde with 1,3-propanediol.
C. Yokoyama, Catal. Commun., 2009, 11, 227-231.
L. Fang, K. Zhang, L. Chen and P. Wu, Chin. J. Cata., 2013, 34
32-941.
times without decrease of catalytic activity. The recycled H-
SiW /SiO remains its structure and composition. The
9
,
1
2
2
9
reusability, selectivity and efficiency of H-SiW /SiO provide 10 L. Myles, R. Gore, M. Špulák, N. Gathergood and S. J. Connon,
1
2
2
Green Chem., 2010, 12, 1157-1162.
M. Tan, L. Gu, N. Li, J. Y. Ying and Y. Zhang, Green Chem., 2013,
15, 1127-1132.
J. S. Swenton, R. M. Blankenship and R. Sanitra, J. Am. Chem.
Soc., 1975, 97, 4941-4947.
D. B. G. Williams and M. G. Lawton, Green Chem., 2008, 10, 914-
great potential for their application in industry.
1
1
1
1
2
3
Acknowledgements
This research was supported by the National Science
Foundation of China (21222104), the Fundamental Research
9
17.
Funds for the Central Universities (RC1302) and the Program 14 Z. Miao, L. Xu, H. Song, H. Zhao and L. Chou, Catal. Sci.
Technol., 2013, , 1942-1954.
for Changjiang Scholars and Innovative Research Team in
3
University. Song appreciates the financial support by Key 15 N. M. Leonard, M. C. Oswald, D. A. Freiberg, B. A. Nattier, R. C.
Smith and R. S. Mohan, J. Org. Chem., 2002, 67, 5202-5207.
S. M. Patel, U. V. Chudasama and P. A. Ganesphure, J. Mol. Catal.
A: Chem., 2003, 194, 267-271.
Laboratory of Polyoxometalates Science of Ministry of
Education, China.
1
6
1
7
Y .W. Zhu, W. B. Yi and C. Cai, New J. Chem., 2013, 37, 890-892.
Notes and references
18 D. E. Ponde, V. H. Desphande, V. J. Bulbule, A. Sudalai and A. S.
Gajare, J. Org. Chem., 1998, 63, 1058-1063.
State Key Laboratory of Chemical Resource Engineering
Beijing University of Chemical Technology
Beijing 100029, P. R. China
Tel/Fax: (+86)10-64431832
E-mail: songyufei@hotmail.com or songyf@mail.buct.edu.cn
1
2
9
0
A. J. Showler and P. A. Darley, Chem. Rev., 1967, 67, 427-440.
A. Sinhamahapatra, N. Sutradhar, M. Ghosh, H. C. Bajaj and A. B.
Panda, Appl. Catal. A: Gen., 2011, 402, 87-93.
Special issue on “polyoxometalates”, Guest Editor, C. L. Hill,
Chem. Rev., 1998, 98, 1-390.
2
2
1
2
†
They have the same contribution
L. Cronin and A. Müller, Chem. Soc. Rev., 2012, 41, 7333-7334.
Electronic Supplementary Information (ESI) available: The 23 Y. F. Song and R. Tsunashima, Chem. Soc. Rev., 2012, 41, 7384-
7
402.
D. L. Long, R. Tsunashima and L. Cronin, Angew. Chem., 2010,
22, 1780-1803; Angew. Chem. Int. Ed., 2010, 49, 1736-1758.
characterization and catalytic results of H-SiW12 and H-SiW12/SiO
DOI: 10.1039/b000000x/
2
. See
2
2
4
5
1
D. L. Long, E. Burkholder and L. Cronin, Chem. Soc. Rev., 2007,
126, 117-123.
1
2
D. M. Clode, Chem. Rev., 1979, 79, 491-513.
K. Bauer, D. Garbe and H. Surburg, Common Fragrances and 26 I. V. Kozhevnikov, Catalysis by Polyoxometalates, Wiley,
Flavor Materials: Preparation and Uses, Wiley, New York, 4th
edn, 2001.
P. G. M. Wuts and T. W. Greene, Greene’s Protective Groups in
Organic Synthesis, Wiley, New York, 4th edn, 2007.
F. A. J. Meskens, Synthesis, 1981, 501-522.
Chichester, 2002.
27 T. Okuhara, N. Mizuno and M. Misono, Adv. Catal., 1996, 41, 113-
252
28 K. A. da Silva, I. V. Kozhevnikov and E. V. Gusevskaya, J. Mol.
Catal. A: Chem., 2003, 192, 129-134.
3
4
5
6
S. A. Patwardhan and S. Dev, Synthesis, 1974, 348-349.
Y. Dai, B. Li, H. Quan and C. Lü, Chin. Chem. Lett., 2010, 21, 678-
29 Y. Leng, J. Wang, D. Zhu, X. Ren, H. Ge and L. Shen, Angew.
Chem., 2009, 121, 174-177; Angew. Chem. Int. Ed., 2009, 48, 168-
171.
6
81.
7
8
K. Shimizu, E. Hayashi, T. Hatamachi, T. Kodama, T. Higuchi, A. 30
Satsuma and Y. Kitayama, J. Catal., 2005, 231, 131-138.
Y. Yamada, K. Qiao, Q. Bao, D. Tomida, D. Nagao, M. Konno and 31 E. J. L. Lana, K. A. da Silva Rocha, I. V. Kozhevnikov and E. V.
A. L. P. de Meireles, K. A. da Silva Rocha, I. V. Kozhevnikov and
E. V. Gusevskaya, Appl. Catal. A: Gen., 2011, 409-410, 82-86.
Gusevskaya, J. Mol. Catal. A: Chem., 2006, 243, 258-263.
This journal is © The Royal Society of Chemistry 2014
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View Article Online
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Catalysis Science & Technology
3
3
3
3
3
3
2
3
4
5
6
7
K. A. da Silva Rocha, N. V. S. Rodrigues, I. V. Kozhevnikov and E.
V. Gusevskaya, Appl. Catal. A: Gen., 2010, 374, 87-94.
K. A. da Silva Rocha, J. L. Hoehne and E. V. Gusevskaya, Chem.
Eur. J., 2008, 14, 6166-6172.
V. V. Costa, K. A. da Silva Rocha, I. V. Kozhevnikov and E. V.
Gusevskaya, Catal. Sci. Technol., 2013, 3, 244-250.
K. Shimizu, H. Furukawa, N. Kobayashi, Y. Itaya and A. Satsuma,
Green Chem., 2009, 11, 390-396.
Y. Ogasawara, S. Itagaki, K. Yamaguchi and N. Mizuno,
ChemSusChem, 2011, 4, 519-525.
V. V. Costa, K. A. da Silva Rocha, R. A. Mesquita, E. F.
Kozhevnikova, I. V. Kozhevnikov and E. V. Gusevskaya,
ChemCatChem, 2013,
A. M. Alexander and R. Neumann, ChemSusChem, 2011,
48.
Y. Qiao, H. Li, L. Hua, L. Orzechowski, K. Yan, B. Feng, Z. Pan,
N. Theyssen, W. Leither and Z. Hou, ChemPlusChem, 2012, 77
128-1138.
5, 3022-3026.
3
3
8
9
4, 346-
3
,
1
4
4
0
1
K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A.
Pierotti, J. Rouquerol and T. Siemieniewska, Pure Appl. Chem.,
1
985, 57, 603-620.
M. Sun, J. Zhang, Q. Zhang, Y. Wang and H. Wan, Chem. Comm.,
009, 5174-5176.
2
8
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