Host (nanocavity of zeolite-Y)-guest (molybdophosphoric acid) nanocomposite materials: An efficient catalyst for solvent-free synthesis and deprotection of 1,l-diacetates

Article abstract of DOI:10.1016/j.crci.2011.03.004

In the present work, a mild and efficient method has been developed for the synthesis of acylals from aldehydes with acetic anhydride in the presence of molybdophosphoric acid encapsulated into dealuminated zeolite Y (MPA-DAZY) as a catalyst under solvent-free conditions at 45-55 °C in good to excellent yield. The deprotection of acylals has also been attained using this catalyst in acetonitrile. The catalyst was reused several times without efficient loss of its catalytic activity.

Full text of DOI:10.1016/j.crci.2011.03.004

C. R. Chimie 14 (2011) 953–956
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Full paper/M e´ moire
Host (nanocavity of zeolite-Y)–guest (molybdophosphoric acid)
nanocomposite materials: An efficient catalyst for solvent-free
synthesis and deprotection of 1,l-diacetates
a,
b
b
Maryam Moosavifar *, Shahram Tangestaninejad , Majid Moghadam ,
b
b
Valiollah Mirkhani , Iraj Mohammadpoor-Baltork
a
Department of Chemistry, Faculty of Science, University of Maragheh, 55181-83111 Maragheh, Iran
Department of Chemistry, Catalysis Division, University of Isfahan, 81746-73441 Isfahan, Iran
b
A R T I C L E I N F O
A B S T R A C T
Article history:
In the present work, a mild and efficient method has been developed for the synthesis of
acylals from aldehydes with acetic anhydride in the presence of molybdophosphoric acid
encapsulated into dealuminated zeolite Y (MPA-DAZY) as a catalyst under solvent-free
conditions at 45–55 8C in good to excellent yield. The deprotection of acylals has also been
attained using this catalyst in acetonitrile. The catalyst was reused several times without
efficient loss of its catalytic activity.
Received 23 January 2011
Accepted after revision 16 March 2011
Available online 12 May 2011
Keywords:
MPA-DAZY
Protection
Deprotection
ß 2011 Published by Elsevier Masson SAS on behalf of Acad e´ mie des sciences.
1
,1-diacetates
Solvent-free
1
. Introduction
ferrous sulfate [9], PCl
13], sulfated zirconia [14], montmorillonite clay [15],
expansive graphite [16], aluminum dodecatungstopho-
sphate [17], Well–Dawson acid (H 62 .24H O) [18]
zeolite HSZ-360 [19], Cu(OTf) [20], Sc(OTf) [21], Bi(OTf)
[22], Zn(BF [23], Bi(NO .5H O [24] and ZrCl [25] which
are alsoefficientforthisconversion. However,manyofthese
methodologies have drawbacks, and involve strongly acidic
conditions, corrosive reagents, long reaction times, high
temperature and high toxicity. Recently, solvent-free
reactions were developed because of their ecological and
3 3
[10], FeCl [11], NBS [12], Nafion-H
[
Protection of functional groups plays an important role
in multi-step synthesis of natural products. However,
selective protection and deprotection of carbonyl groups
are substantial steps in synthetic organic chemistry [1].
Acylals (1,1-diacetates) are appropriate candidates to this
aim due to their stability in basic and neutral reaction
media as well as in aqueous acids [2]. Meanwhile, gem-
6 2 18
P W O
2
2
3
3
)
4 2
)
3 3
2
4
diacetates derived from
a,b-unsaturated aldehydes are
useful as dienes for Diels–Alder cycloaddition reactions.
Moreover, acylals are used as cross linking reagents for
cellulose in cotton [3].
Several methods have been used for the synthesis of 1,1-
diacetates from strong acids including sulfuric acid [4],
methane sulfuric acid [5], sulfamic acid [6], Lewis acids as
lithium bromide [7], aluminum chloride [8], anhydrous
low-cost advantages. Some of these catalysts are P
2
O
5
/Al
/SnO [28],
bromodimethylsulfonium bromide [29], solid lithium
perchlorate [30], [bmim]BF [31], [Hmim]HSO [32] zirco-
2 3
O
2À
[26], dodecamolybdophoshporic acid [27], SO
4
2
4
4
nium sulfophenyl phosphonate [19] and Zeolite Y [33].
In this article, we report a new and efficient method for
solvent-free conversion of aromatic aldehydes to their
corresponding 1,1-diacetates with acetic anhydride and
their deprotection in acetonitrile using encapsulated
*
Corresponding author.
molybdophosphoric acid in dealuminated
(MPA-DAZY) as a reusable catalyst (Scheme 1).
Y zeolite
E-mail addresses: m.moosavifar@maragheh.ac.ir,
maryam_moosavifar@yahoo.com (M. Moosavifar).
1
631-0748/$ – see front matter ß 2011 Published by Elsevier Masson SAS on behalf of Acad e´ mie des sciences.
doi:10.1016/j.crci.2011.03.004

9
54
M. Moosavifar et al. / C. R. Chimie 14 (2011) 953–956
MPA-DAZY
CHO
o
Solvent-free, 45-55 C
CH(OAc)2
(
CH CO) O
3 2
+
MPA-DAZY
R
CH CN, Reflux
3
R
Scheme 1. Synthesis of 1,1-diacetates under solvent-free conditions and their deprotection in acetonitrile using encapsulated molybdophosphoric acid in
dealuminated Y zeolite (MPA-DAZY).
2
. Experimental
filtered. The organic layer was washed with NaHCO
3
(10%,
2
 5 ml) and dried over Na
2
SO . The organic solvent was
4
All solventsand reagentswereofthecommercialreagent
evaporated to produce the crude aldehyde. The residue
was purified by plate chromatography (n-hexane/ether
4:1) to give the corresponding aldehyde.
grade and obtained from Merck or Fluka. All of reaction
mixtures were monitored by TLC. Melting points were
recorded on a Barnstead Electrothermal 9200 apparatus,
and are uncorrected. The NaY-zeolite was purchased from
Sigma-Aldrich Chemical Company. The framework of NaY-
zeolite contains aluminum atoms are basic and therefore,
increase the decomposition of MPAs, or disturb the
formation of MPA into the supercages of zeolite. Therefore,
the modified DAZY (dealuminated zeolite Y) as support, was
prepared by hydrothermal treatment [34]. Dealumination
ofNaY zeolite notonly improvesthe zeolitestabilitybutalso
yields a secondary pore system in zeolite matrix for
deposition of the large MPA species [35]. Therefore, zeolite
Y was dealuminated. The method reported by Mukai was
3. Results and discussion
3.1. Catalytic performance in the protection of aldehydes
The MPA-DAZY catalyst was synthesized and charac-
terized by infrared spectroscopy (FT-IR), X-ray diffraction
(XRD), differential thermal gravimetry (DTG) and atomic
absorption spectroscopic (AAS) techniques. The content of
MPA in the synthesized sample, obtained by dissolving a
small amount of the washed catalyst in hydrofluoric acid
and hot concentrated hydrochloric acid, was determined
by atomic absorption spectroscopy (AAS) [37].
3
used for the synthesis of H PMo12O40 encapsulated into
dealuminated zeolite (MPA-DAZY) [36,37]. All products
were known compounds and identified by comparing their
physical data by their authentic samples.
The results showed that the catalyst loading was about
0.043 mmol/g of encapsulated catalyst. The reaction of
aldehydes with acetic anhydride in the presence of MPA-
DAZY produces the correponding 1,1-diacetates (Scheme
1). First, the amount of catalyst was optimized in the
reaction of 3-nitrobenzaldehyde with acetic anhydride.
The results showed that highest yield was obtained with
250 mg (0.01 mmol) of catalyst (Table 1). For optimization
of the reaction media, the same reaction was performed in
2.1. General procedure for the preparation of 1,1-diacetates
In a round bottom flask equipped with a magnetic
stirrer, aldehyde (1 mmol), acetic anhydride (3 mmol) and
catalyst (250 mg, 0.01 mmol) were mixed and stirred at
4
5–55 8C for an appropriate time. The progress of the
reaction was monitored by TLC (ethyl acetate/n-hexane
:1). After the reaction was completed, saturated NaHCO
5 ml) was added and the catalyst was filtered. The product
was extracted with diethyl ether (2 Â 15 ml) and the
etherates were dried over Na SO . The solvent was
evaporated to give the corresponding 1,1-diacetate.
Table 1
7
(
3
Optimization of the catalyst amount in the reaction of 3-nitrobenzalde-
a
hyde with acetic anhydride under solvent-free conditions after 1 h.
b
Entry
Catalyst amount (mg)
Yield (%)
2
4
1
2
3
4
100
40
65
84
95
150
200
2.2. Catalyst recovery and reuse
250 (0.01 mmol of MPA)
a
Reaction conditions: 3-nitrobenzaldehyde (1 mmol), acetic anhy-
The reusability of catalyst also was investigated in the
dride (3 mmol).
Isolated yield.
multiple sequential reaction of 3-nitrobenzaldehyde as a
model substrate. At the end of each reaction, the catalyst
was filtered, activated by washing with ethyl acetate and
drying at 120 8C for 3 h, and reused with fresh aldehyde
and acetic anhydride.
b
Table 2
The effect of solvent on the protection of 3-nitrobenzaldehyde with acetic
a
anhydride catalyzed by MPA-DAZY after 1 h.
b
Entry
Solvent
Yield (%)
2.3. General procedure for the deprotection of 1,1-diacetates
1
2
3
4
5
CH
CH
CH
CH
3
3
3
2
CN
44
35
40
25
95
COCH
OH
3
In a typical procedure, 1,1-diacetates (1 mmol) in
acetonitrile (3 ml) and MPA-DAZY (500 mg, 0.02 mmol)
were mixed and refluxed for an appropriate time. The
progress of reaction was monitored by TLC (ethyl acetate/
n-hexane 7:1). After completion of the reaction, the
reaction mixture was diluted with ethyl acetate and
Cl
2
Solvent-free
a
Reaction conditions: 3-nitrobenzaldehyde (1 mmol), acetic anhy-
dride (3 mmol), catalyst (250 mg, 0.01 mmol).
b
Isolated yield.

M. Moosavifar et al. / C. R. Chimie 14 (2011) 953–956
955
Table 3
Synthesis of 1,1-diacetates with anhydride acetic catalyzed by MPA-DAZY under solvent-free conditions and their deprotection in acetonitrile.
a
Entry
Substrate
Product
Protection
Time (min)
90
Deprotection
b
b
Yield (%)
Reported
Yield (%)
Time (h)
4
1
80
52–53 [19]
45
O
OAc
OAc
H
H
Cl
O
Cl
2
98
70
64–65 [26]
75
4
OAc
OAc
Cl
Cl
3
4
98
95
75
60
103 [38]
75
90
4
4
O
OAc
OAc
H
H
OH
O
OH
OAc
65–66 [39]
OAc
NO 2
NO2
5
6
95
92
85
127 [26]
60
76
4
4
O
O
OAc
OAc
H
H
O N
O N
2
2
110
81–82 [26]
OAc
OAc
H C
3
H C
3
7
8
9
90
98
85
70
75
85
82–83 [39]
70–71 [40]
82–83 [41]
40
70
80
4
4
4
O
OAc
OAc
H
MeO
MeO
O
OAc
OAc
OMe
H
OMe
O
OAc
OAc
H
Cl
Cl
a
Reaction conditions: aldehyde (1 mmol), Ac
Isolated yield.
2
O (3 mmol) catalyst (250 mg, 0.01 mmol).
b

9
56
M. Moosavifar et al. / C. R. Chimie 14 (2011) 953–956
Table 4
The results obtained in the reusability of MPA-DAZY and the amount of
AAS). The results showed that Mo catalyst is leached from
zeolite and therefore, the yield decreased (Table 4).
molybdenum leached in the reaction of 3-nitrobenzaldehyde with Ac
2
O
a
under solvent-free conditions after 1 h.
4. Conclusion
b
c
Run
Yield (%)
Mo leached (%)
1
2
3
4
95
87
80
76
3
4
5
1
In summery, in this paper we reported a mild and
efficient protocol for the protection of aldehydes with
acetic anhydride under solvent-free conditions and 1,1-
diacetates were obtained in good to excellent yield. This
catalytic system was also used for deprotection of 1,1-
diacetates refluxing acetonitrile. The advantages of this
catalytic system are high catalytic activity, environmen-
tally benign nature of the reaction and reusability of the
catalyst.
a
Reaction condition: 3-nitrobenzaldehyde (1 mmol), acetic anhydride
(
3 mmol).
b
Isolated yield.
c
Determined by atomic absorption spectroscopy.
different solvents and also under solvent-free conditions.
When the reaction was performed in solvent, the progress
of the reaction was lower in comparison with solvent-free
conditions. Therefore, the solvent-free conditions was used
for the conversion of aldehydes to their corresponding 1,1-
diacetates (Table 2). The amount of acetic anhydride was
also optimized and the best result was obtained with a 3:1
molar ratio of acetic anhydride: aldehyde.
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