Dodecatungstophosphoric acid (H3PW12O40): A novel and efficient recyclable catalyst for synthesis of 1,1-diacetates from aromatic aldehydes in solvent-free system and their deprotection

Article abstract of DOI:10.1080/00397910600907282

A facile and efficient method for the formation of 1,1-diacetates from a variety of aldehydes in the presence of a catalytic amount of H ₃PW₁₂O₄₀ and acetic anhydride was achieved in good yields at room temperature. The deprotection of the resulting acylals is achieved using the same catalyst in acetone. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910600907282

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Dodecatungstophosphoric Acid (H3PW12O40):
A Novel and Efficient Recyclable Catalyst for
Synthesis of 1,1‐Diacetates from Aromatic
Aldehydes in Solvent‐Free System and Their
Deprotection
Majid M. Heravi a , Fatemeh Derikvand a & Fatemeh F. Bamoharram b
a Department of Chemistry, School of Science, Azzahra University, Vanak,
Tehran, Iran
b Department of Chemistry, Azad University of Mashhad, Mashad, Iran
Version of record first published: 24 Nov 2006.
To cite this article: Majid M. Heravi , Fatemeh Derikvand & Fatemeh F. Bamoharram (2006):
Dodecatungstophosphoric Acid (H3PW12O40): A Novel and Efficient Recyclable Catalyst for Synthesis
of 1,1‐Diacetates from Aromatic Aldehydes in Solvent‐Free System and Their Deprotection, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:21,
3109-3115
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Synthetic Communicationsw, 36: 3109–3115, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600907282
Dodecatungstophosphoric Acid
(H3PW12O40): A Novel and Efficient
Recyclable Catalyst for Synthesis of
1,1-Diacetates from Aromatic Aldehydes
in Solvent-Free System and Their
Deprotection
Majid M. Heravi and Fatemeh Derikvand
Department of Chemistry, School of Science, Azzahra University, Vanak,
Tehran, Iran
Fatemeh F. Bamoharram
Department of Chemistry, Azad University of Mashhad, Mashad, Iran
Abstract: A facile and efficient method for the formation of 1,1-diacetates from a
variety of aldehydes in the presence of a catalytic amount of H3PW12O40 and acetic
anhydride was achieved in good yields at room temperature. The deprotection of the
resulting acylals is achieved using the same catalyst in acetone.
Keywords: Acylals, dodecatungstophosphoric acid, 1,1-diacetate, heteropolyacid,
H3PW12O40, Keggin-type heteropolyacid
1,1-Diacetates are suitable protecting groups for aldehydes because of their
stability and easy conversion into parent aldehydes.[1–3] In addition they
can be converted into other useful functional groups by reaction with appro-
priate nucleophiles[4] and used as carbonyl surrogates for asymmetric
synthesis.[5] The synthesis of optical aldehydes by lipase-catalyzed resolution
of the corresponding 1,1-diacetates has been reported.[6] They are also
Received in Poland March 8, 2006
Address correspondence to Majid M. Heravi, Department of Chemistry, School of
Science, Azzahra University, Vanak, Tehran, Iran. E-mail: mmh1331@yahoo.com
3109

3110
M. M. Heravi, F. Derikvand, and F. F. Bamoharram
important building blocks in the synthesis of dienes for the Diels–Alder cyclo-
addition reaction.[7] Acetic anhydride is the most used commonly reagent for
acylal formation, and a long list of catalysts is available for this reaction,
including H2NSO3H,[8] (NH4)2Ce(NO3)6,[9] ZrCl4,[10] AlPW12O40,[11]
Zn(BF4)2,[12] InCl3,[13] NBS,[14] PCl3,[15] and several inorganic heterogeneous
catalysts such as Nafion-H,[16] Zeolites,[17] and Montmorillonite.[18]
The use of solid acid catalysts has received considerable attention in
different areas of organic synthesis, because of their environmental compat-
ibility, reusability, greater selectivity, experimental simplicity, low cost, and
ease of isolation of the products.
Heteropolyacids (HPAs) have many advantages that make them economi-
cally and environmentally attractive in both academic and industrial signifi-
cance; they are useful acid and oxidation catalysts in various reactions
because their catalytic features can be varied at a molecular level.[19] HPAs
possess superacidity and a remarkable stability both in solution and in solid
state.[20] Many typical acid-catalyzed reactions are effective in the presence
of a suitable heteropolyacid.[21–24]
In continuation of our program to develop reactions in ecofriendly con-
ditions[21–25] and our interest in the synthesis of 1,1-diacetates,[26,27] in this
communication we report an efficient and convenient procedure for the prep-
aration of 1,1-diacetates from aromatic aldehydes and their deprotection
catalyzed by dodecatungstophosphoric acid (H3PW12O40).
When an appropriate aldehyde was stirred with acetic anhydride in the
presence of a catalytic amount of H3PW12O40 at room temperature, the corre-
sponding 1,1-diacetate was obtained in excellent yield (Scheme 1). The results
are shown in Table 1.
By using this catalyst, benzaldehyde, aromatic aldehydes containing
electron-withdrawing or electron-donating groups, and cinamaldehyde gave
the corresponding 1,1-diacetate in almost quantitative yields in short
reaction times (5–60 min). It is noteworthy to mention that this catalyst is
not suitable for the preparation of acylals from aldehydes carrying amino
groups such as 4-N,N-dimethylaminobenzaldehyde and ketones. To show
the high selectivity of the method, we studied competitive reactions for
acylation of aldehydes in the presence of ketones using H3PW12O40 as
catalyst. Ketones such as acetophenone did not produce any acylal under
the same condition (Table 1, entry 10); this suggested that chemoselective pro-
tection of aldehydes in the presence of ketones could be achieved with this
process (Scheme 2).
Scheme 1.

Dodecatungstophosphoric Acid
3111
Table 1. Synthesis of 1,1-diacetates using a catalytic amount of H3PW12O40
Mp(8C)
Time Yield
(min) (%)a
Entry
Substrate
Benzaldehyde
Found
Reported[lit]
1
2
4
5
98
97
99
98
97
99
98
99
93
0
44
81–81
70
44–45[2]
81–82[3]
70–71[31]
64–65[32]
81–82[33]
90[34]
4-Methyl-benzaldehyde
2-Methoxy-benzaldehyde
4-Methoxy-benzaldehyde
4-Chloro-benzaldehyde
2-Nitro-benzaldehyde
3-Nitro-benzaldehyde
4-Nitro-benzaldehyde
Cinamaldehyde
3
4
4
15
9
63–64
81
89
5
6
20
20
60
5
7
65–66
125–126 125–126[32]
64–66[32]
8
9
87–86
—
—
84–86[2]
10
11
Acetophenone
4-N,N-Dimethyl-benzaldehyde
12 h
12 h
—
—
0
aYields were analyzed by GC.
A few methods are reported in the literature for the conversion of acylals
to the corresponding aldehydes.[28–30] We use this catalyst in the deprotection
of 1,1-diacetates to the corresponding aldehydes by treatment of acylals with a
catalytic amount of H3PW12O40 in acetone as solvent. Under this condition,
aldehydes were obtained in quantitative yields (Scheme 1). The results are
shown in Table 2.
In conclusion, we established a facile, mild, and efficient method for
preparation of 1,1-diacetates from aromatic aldehydes and acetic anhydride
at room temperature and deprotection of the obtained acylals to the
corresponding aldehydes in acetone in the presence of H3PW12O40 in high
yields. Some of the major advantages of this procedure are operational
simplicity, high yields, short reaction times, and high selectivity. In
addition, as a nonhygroscopic, noncorrosive, and water-stable compound,
the handling of H3PW12O40 is easy, which makes this catalyst suitable for
the large-scale operation.
HPAs are not soluble in organic reactions, and they could be separated by
a simple filtration. The filtered catalyst was washed with diethyl ether and
reused. The results of the first experiment and our subsequent experiment
were almost consistent in yield for the synthesis of 1,1-diacetate from benzal-
dehyde (Entry 1, Table 1). The obtained results are comparable with those
Scheme 2.

3112
M. M. Heravi, F. Derikvand, and F. F. Bamoharram
Table 2. Deprotection of acylals catalyzed by H3PW12O40
Entry
R
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
Phenyl-
4-Me-Phenyl-
30
5
95
98
95
98
94
99
97
94
94
2-Metoxy-Phenyl-
4-Metoxy-phenyl-
4-Chloro-Phenyl-
2-Nitro-phenyl-
3-Nitro-phenyl-
4-Nitro-Phenyl-
Cinamyl-
15
5
15
40a
15a
40a
15
aThe reaction was carried out in refluxing acetone.
reported using AlPW12O40, but it should be noted that H3PW12O40 is the
precursor of AlPW12O40.
EXPERIMENTAL
All products were known and characterized by comparison of their physical
and spectral data with those reported.[2,3,31–34]
Preparation of 1,1-Diacetate: General Procedure
A mixture of an appropriate aldehyde (5.0 mmol), acetic anhydride
(15.00 mmol), and HPA (0.5 mol%) was stirred at room temperature for the
indicated time (Table 1). The progress of the reaction was monitored by thin-
layer chromatoarphy (TLC) using petroleum ether–ethyl acetate as eluent.
After completion of the reaction, diethyl ether (5 mL) was added to the
mixture, and the catalyst was filtered off. The catalyst was washed with
diethyl ether (5 mL), and then the filtrate was washed with 5% HCl (10 mL),
5% NaHCO3 (10 mL), and brine (10 mL) successively and dried over
MgSO4. The solvent was evaporated under reduced pressure to yield the pure
product. The filtered catalyst was washed with diethyl ether and reused.
Deprotection of Acylals: General Procedure
A mixture of acylal (1 mmol) and HPA (0.4 mol%) was stirred in acetone
(5 mL) at room temperature for the indicated time (Table 1). For the acylal
with electron-drawing groups, the mixture was refluxed. The progress of the
reaction was monitored by TLC using petroleum ether–ethyl acetate as

Dodecatungstophosphoric Acid
3113
eluent. After completion of the reaction, the catalyst was filtered off and
washed with diethyl ether. The combined organic layer was washed with
5% NaHCO3 (10 mL) and brine (10 mL) and dried over MgSO4. The
solvent was evaporated under reduced pressure to yield the product. The
filtered catalyst was washed with diethyl ether and reused.
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