Silica chloride/wet SiO2 as a novel heterogeneous system for the deprotection of acetals under mild conditions

Article abstract of DOI:10.1080/714040981

A combination of silica chloride and wet SiO₂ was used as an effective deacetalizating agent for the conversion of acetals to their corresponding carbonyl derivatives under mild and heterogeneous condition.

Full text of DOI:10.1080/714040981

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Phosphorus, Sulfur, and Silicon and the Related
Elements
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Silica Chloride/Wet SiO2 as a Novel Heterogeneous
System for the Deprotection of Acetals Under Mild
Conditions
BiBi Fatemeh Mirjalili a , Ali Pourjavadi b , Mohammad Ali Zolfigol c & Abdolhamid Bamoniri d
a Yazd University, Yazd, Iran
b Sharif University of Technology, Tehran, Iran
c Bu-Ali Sina University, Hamadan, Iran
d Kashan University, Kashan, Iran
Published online: 18 Jun 2010.
To cite this article: BiBi Fatemeh Mirjalili , Ali Pourjavadi , Mohammad Ali Zolfigol & Abdolhamid Bamoniri (2003) Silica
Chloride/Wet SiO2 as a Novel Heterogeneous System for the Deprotection of Acetals Under Mild Conditions, Phosphorus,
Sulfur, and Silicon and the Related Elements, 178:12, 2667-2670, DOI: 10.1080/714040981
To link to this article: http://dx.doi.org/10.1080/714040981
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Phosphorus, Sulfur, and Silicon, 178:2667–2670, 2003
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Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500390248402
SILICA CHLORIDE/WET SiO2 AS A NOVEL
HETEROGENEOUS SYSTEM FOR
THE DEPROTECTION OF ACETALS UNDER
MILD CONDITIONS
BiBi Fatemeh Mirjalili,a Ali Pourjavadi,b
Mohammad Ali Zolfigol,c and Abdolhamid Bamonirid
Yazd University, Yazd, Iran;a Sharif University of Technology,
Tehran, Iran;b Bu-Ali Sina University, Hamadan, Iran;c
and Kashan University, Kashan, Irand
A combination of silica chloride and wet SiO2 was used as an effective
deacetalizating agent for the conversion of acetals to their correspond-
ing carbonyl derivatives under mild and heterogeneous condition.
Keywords: Deacetalization; silica chloride
There is current general interest in heterogeneous systems because
of the importance such systems have in industry and in developing
technologies.1 In continuation of our studies on the application of het-
erogeneous systems2 we found that silica chloride3,4 (I) is an excellent
source for generation of HCl. It is interesting to note that the addition
of wet SiO2 to the reaction mixture containing silica chloride generates
HCl in situ (Scheme 1). Therefore, we used it for a different purposes.4
We also were interested in using reagent (I) for the conversion of ac-
etals to their corresponding carbonyl derivatives. We report on a simple
SCHEME 1
Financial support for this work by Research Affairs, Yazd University, Yazd, Iran and
Bu-Ali Sina University, Hamadan, Iran, is gratefully acknowledged.
Address correspondence to Mohammad Ali Zolfigol, Department of Chemistry, Bu-Ali
Sina University, PO Box 4135, Hamadan 65174, Iran. E-mail: Zolfi@basu.ac.ir
2667

2668
B. F. Mirjalili et al.
method for the effective conversion of acetals to their corresponding car-
bonyl derivatives under mild and heterogeneous condition. (Scheme 2
and Table I).
SCHEME 2
Acetals are widely used as protecting groups in organic synthe-
sis and, as a consequence, many methods have been examined for
both their formation and removal.6,7 Typically, deprotection of acetals
requires the use of protic8 or Lewis acids,9 iodotrimethylsilane,10 cobalt,
or manganese salts in the presence of air or O2,11 pyridinium tosylate,12
montmorillonite K10,13 ceric ammonium nitrate (CAN),14 etc.
We hoped that the silica chloride (I)/wet SiO2 system would be a su-
perior proton source to all of the reported acidic solid supports or acidic
resins such as polystyrene sulfonic acid and Nafion-H15 for running
reactions under heterogeneous conditions. Here, we report on a conve-
nient method for the deacetalization of acetals by using silica chloride
(I) and wet SiO2 (II) under heterogeneous conditions (Scheme 2).
Different types of acetals (I) were subjected to the deacetalization
reaction in the presence of silica chloride and wet SiO2 (60% w/w) under
mild and heterogeneous condition with quantitative yields. we used
toluene as a solvent at 60–70◦C. The results of deacetalization were
shown in Table I.
In conclusion, a cost-effective and easy procedure for the effective
conversion of acetals to their corresponding carbonyl derivatives has
been achieved. The low cost and availability of the reagents, easy pro-
cedure, and work-up make this method attractive for organic chemists.
EXPERIMENTAL SECTION
General
Chemicals such as carbonyl compounds, ethylene glycol, thionyl chlo-
ride, and silica gel were purchased from the chemicals companies Fluka,
Merck, and Aldrich. Acetals and 5-norbornene-2,2-dimethyl-1-ol were
synthesized according to the our previously reported procedure.6 Sil-
ica chloride was synthesized according to the reported procedure.3,4

Deacetalization
2669
TABLE I Deprotection of Acetals by Silica Chloride (I) and Wet SiO2 (II) in
Toluene at 60–70◦C
Substrate(mmol)
I(g)/II(g)
/
Time
(min)
Entry
Substrate
Yield(%)
85a
Product
0.25/0.4/0.5
0.25/0.3/0.5
90
60
1a
92a
94
1b
1c
0.25/0.3/0.5
60
0.25/0.35/0.5
0.25/0.3/0.5
90
60
80a
75a
1d
1e
0.25/0.3/0.5
60
90
1f
0.25/0.3/0.5
0.25/0.4/0.6
60
70
92
92
1g
1h
0.25/0.4/0.5
45
95
1i
1j
0.25/0.45/0.5
0.25/0.45/0.5
0.25/0.4/0.5
60
80
60
90
93
90
1k
1l
0.25/0.4/0.5
0.25/0.4/0.5
0.25/0.45/0.5
90
60
70
82a
92
1m
1n
10
93
aThe isolated yields are based on weight of 2,4-Dinitro phenyl hydrazone derivative.

2670
B. F. Mirjalili et al.
The deacetalization products were characterized by comparison of their
1
spectral (IR, H-NMR), TLC, and physical data with that of authentic
samples.
Deacetalization of (1i) to the Corresponding Aldehyde
(2i). A Typical Procedure
A mixture of 1i (0.07 g, 0.25 mmol), silica chloride (I) (0.4 g) and wet
SiO2 (II) (60% w/w, 0.5 g) in toluene (3 mL) was heated at 60–70◦C
for 45 min. Then the solvent was removed under reduced pressure. By
addition of ethanol and water, 4-nitrobenzaldehyde (2i) was obtained
in quantitative yield.
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