A simple and fast method for protection of aldehydes as 1,1-diacetates using cerium(IV) sulfate as an efficient and reusable inorganic catalyst

Article abstract of DOI:10.1080/15533174.2011.591346

A simple, green, and very fast method for protection of aryl aldehydes as 1,1-diacetates promoted by cerium(IV) sulfate tetrahydrate, Ce(SO ₄)₂·4H₂O, as a novel inorganic solid acid catalyst at room temperature and under solvent-free conditions is described. The present methodology offers several advantages, such as a simple procedure with an easy workup, very short reaction times, high yields, and the absence of any volatile and hazardous organic solvents. Copyright Taylor & Francis Group, LLC.

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A Simple and Fast Method for Protection of
Aldehydes as 1,1-Diacetates Using Cerium(IV) Sulfate
as an Efficient and Reusable Inorganic Catalyst
a
a
a
Elahe Saburi , Abolghasem Davoodnia & Niloofar Tavakoli-Hoseini
a
Department of Chemistry, Mashhad Branch , Islamic Azad University , Mashhad, Iran
Published online: 07 Nov 2011.
To cite this article: Elahe Saburi , Abolghasem Davoodnia & Niloofar Tavakoli-Hoseini (2011) A Simple and Fast
Method for Protection of Aldehydes as 1,1-Diacetates Using Cerium(IV) Sulfate as an Efficient and Reusable Inorganic
Catalyst, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:9, 1063-1066, DOI:
10.1080/15533174.2011.591346
To link to this article: http://dx.doi.org/10.1080/15533174.2011.591346
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 41:1063–1066, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.591346
A Simple and Fast Method for Protection of Aldehydes as
1
,1-Diacetates Using Cerium(IV) Sulfate as an Efficient and
Reusable Inorganic Catalyst
Elahe Saburi, Abolghasem Davoodnia, and Niloofar Tavakoli-Hoseini
Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran
temperature, long reaction times, moisture sensitivity, and high
A simple, green, and very fast method for protection of aryl alde- cost of the catalyst. These limitations prompted us toward fur-
hydes as 1,1-diacetates promoted by cerium(IV) sulfate tetrahy- ther investigation in search of a new catalyst, which will carry
drate, Ce(SO
4
)
2
·4H
2
O, as a novel inorganic solid acid catalyst at
out the protection of aldehydes as 1,1-diacetates under a simpler
experimental setup and eco-friendly conditions.
room temperature and under solvent-free conditions is described.
The present methodology offers several advantages, such as a sim-
ple procedure with an easy workup, very short reaction times,
high yields, and the absence of any volatile and hazardous organic of products separation, recycling of the catalyst, and environ-
solvents.
Using solid acid catalysts has some advantages, such as ease
mental acceptability, as compared to liquid acid catalyst.[ In
20]
recent years, cerium(IV) salts have attracted considerable at-
Keywords acetic anhydride, aldehydes, cerium(IV) sulfate, 1,1- tention. These compounds have been widely applied in many
diacetates, protection
reactions in organic chemistry, such as synthesis of acetamido
[21]
phenols by Ce(SO4)2,
conversion of oximes into aldehydes
and ketones by cerium(IV) salts,[ one-pot synthesis of 3-
22]
INTRODUCTION
[23]
acylisoxazoles using cerium(IV) ammonium nitrate, and syn-
Protection and deprotection of functional groups are in-
dispensable ingredients of the synthesis of polyfunctional
compounds. The carbonyl group is one of the most versatile
functional groups in organic synthesis and its protection is nec-
essary in the manipulation of organic molecules with multiple
functional groups.[ 1,1-Diacetates (acylals) are synthetically
thesis of carboxylic esters from alkenes using Ce(SO4)2·4H2O
in carboxylic acids.[ To the best of our knowledge there are
no examples on the use of cerium(IV) sulfate as catalyst for
protection of aldehydes as 1,1-diacetates.
24]
In continuation of our previous works on the applications
of reusable catalysts in the synthesis of organic compounds,[
herein we report an efficient, mild, and very fast procedure for
conversion of aryl aldehydes to the corresponding 1,1-diacetates
in the presence of acetic anhydride and catalytic amount of
Ce(SO4)2·4H2O (Scheme 1). The reactions are easily carried
out at room temperature under solvent-free conditions.
1]
25]
useful protecting groups for carbonyl compounds due to their
stability and easy conversion into parent aldehydes.[
2,3]
The
diacetates of α,β-unsaturated aldehydes are important start-
ing materials for Diels–Alder reactions and also are useful
[
4,5]
intermediate in industry.
Moreover, the acylal functional-
ity can be converted into other functional groups by reaction
[
6,7]
with appropriate nucleophiles.
Protection of aldehydes as
1
,1-diacetates using acetic anhydride has been reported in the
[
8]
presence of several catalysts such as sulfuric acid, Montmoril-
lonite K-10, InBr3, LiClO4, Sc(OTf)3, Cu(OTf)2,
I2,
acidic ionic liquid, Nafion-H, and Cu(BF4)2. Although
some of these methods have convenient protocols with good to
high yields, majority of these methods suffer from at least one of
the following disadvantages: use of halogenated solvents, high
[
9]
[10]
[11]
[12]
[13]
[
14]
[15]
[16]
Bi(NO2)3,
silica-bonded S-sulfonic acid, Brønsted
[
17]
[18]
[19]
SCH. 1. Protection of aryl aldehydes as 1,1-diacetates.
EXPERIMENTAL
Chemicals and Apparatus
Received 11 March 2011; accepted 22 April 2011.
All chemicals were available commercially and used without
additional purification. Melting points were recorded on an elec-
trothermal type 9100 melting point apparatus. The infrared (IR)
Address correspondence to Abolghasem Davoodnia, Department
of Chemistry, School of Sciences, Mashhad Branch, Islamic Azad
University, Mashhad, Iran. E-mail: adavoodnia@mshdiau.ac.ir
1063

1064
E. SABURI ET AL.
TABLE 1
a
Effect of Ce(SO4)2·4H2O amount and molar ratio of reagents on the model reaction
Entry
Catalyst (mol%)
Molar ratio of Ac2O:4-O2NC6H4CHO
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
None
1
1
1
3
3
3
5
5
2 : 1
1 : 1
2 : 1
3 : 1
1 : 1
2 : 1
3 : 1
1 : 1
1.5 : 1
2 : 1
3 : 1
1 : 1
2 : 1
3 : 1
1 : 1
2 : 1
3 : 1
30
10
2
2
10
1
1
10
5
< 1
< 1
10
< 1
< 1
10
< 1
< 1
None
27
42
41
36
69
70
44
61
93
93
45
93
93
45
94
94
1
1
1
1
1
1
1
1
5
5
10
10
10
15
15
15
a
Acetic anhydride and 4-nitrobenzaldehyde at room temperature under neat conditions.
Isolated yields.
b
spectra were obtained using a 4300 Shimadzu spectrophotome- tection of aldehydes as 1,1-diacetates under solvent-free condi-
1
ter as KBr disks. The H-nuclear magnetic resonance (NMR; tions.
4
5
00 and 500 MHz) spectra were recorded on a Bruker 400 and
00 spectrometer.
To find the optimal conditions, the protection of 4-
nitrobenzaldehyde was selected as a model. Therefore, a mix-
ture of 4-nitrobenzaldehyde, and acetic anhydride was stirred at
room temperature under various reaction conditions.
General Procedure for Protection of Aryl Aldehydes as
1
,1-Diacetates
The efficiency of the reaction is affected mainly by the
amount of Ce(SO4)2·4H2O and the molar ratio of acetic anhy-
dride to 4-nitrobenzaldehyde (Table 1). No product was obtained
in the absence of the catalyst (entry 1), indicating that the catalyst
is necessary for the reaction. Increasing the amount of the cat-
alyst increased the yield of the product 3i. The optimal amount
of Ce(SO4)2·4H2O was 5 mol% based on 4-nitrobenzaldehyde
To a solution of an aryl aldehyde (2 mmol) and freshly dis-
tilled acetic anhydride (4 mmol), Ce(SO4)2·4H2O (0.10 mmol,
0.04 g, 5 mol% base on aryl aldehyde) was added and the re-
action mixture was stirred at room temperature. After a few
seconds or minutes a solid was formed. Hot ethanol was added
to the reaction mixture. The catalyst insoluble in with hot ethanol
and separated by filtration. The product was collected from the
filtrate after cooling to room temperature and recrystallized from
ethanol to give compounds 3a–i in high yields.
(entry 10); increasing the amount of the catalyst beyond this
value did not increase the yield noticeably (entries 13 and
TABLE 2
Effect of solvent on the model reaction
RESULTS AND DISCUSSION
a
Solvent-free conditions are especially important for provid-
ing an eco-friendly system. One advantage of solvent-free reac- Entry Solvent
tions, in comparison to the reaction in molecular solvents, is that
the compounds formed are often sufficiently pure to circumvent
extensive purification using chromatography.
On the other hand, the use of heterogeneous inorganic cat-
alysts presented itself as a remarkable technique toward envi-
ronmentally clean synthesis of organic compounds. Therefore,
due to the increasing demand in modern organic processes for
Temperature ( C) Time (h) Yield (%)b
◦
1
2
3
4
5
EtOH
Reflux
Reflux
Reflux
Reflux
3
3
3
3
76
60
81
86
93
MeOH
CH2Cl2
CH3CN
Solvent-free Room temperature <1 min
a4-Nitrobenzaldehyde (2 mmol), acetic anhydride (4 mmol), and
avoiding expensive purification, we decided to investigate the Ce(SO ) ·4H O (0.1 mmol, 0.04 g, 5 mol%).
4
2
2
b
efficiency of cerium(IV) sulfate as solid acid catalyst for pro-
Isolated yields.

PROTECTION OF ALDEHYDES USING CERIUM(IV) SULFATE
1065
16). The effect of different molar ratio of acetic anhydride:4- of 5 mol% of the catalyst. As shown in Table 2, in comparison
nitrobenzaldehyde on this reaction was also examined. The re- with neat conditions, the reaction times were longer and the
sults are shown in Table 1. It can be seen that with the increase yields were lower.
of the molar ratio of acetic anhydride:4-nitrobenzaldehyde from
Encouraged by this success, we extended the reaction of
1:1 to 2:1, the yield of the product 3i increased. However, when acetic anhydride with a range of other aromatic aldehydes
the molar ratio increased from 2:1 to 3:1, the yield had no under the optimized reaction conditions. As shown in Table
obvious increase. Therefore, the optimal molar ratio of acetic 3, different aromatic aldehydes are converted successfully to
anhydride:4-nitrobenzaldehyde was 2:1 (entry 10).
the corresponding 1,1-diacetates in solvent-free conditions at
Furthermore, the reaction was carried out in different solvents room temperature in high yield and very short reaction time.
including EtOH, MeOH, CH2Cl2, and CH3CN in the presence The type of aromatic aldehyde had no significant effect on
TABLE 3
a
Ce(SO4)2 catalyzed protection of aryl aldehydes as 1,1-diacetates 3a–i
◦
Melting point ( C)
Entry
1
Ar
Productb
Time (min)
Yields (%)c
94
Found
91–94
Reported
93–95
Reference
[17]
4-BrC6H4
< 1
2
2-ClC6H4
2
91
51–54
51–52
[17]
3
4
5
4-ClC6H4
4-FC6H4
< 1
3
93
92
89
80–82
53–55
96–98
81–82
51–53
[17]
[16]
[17]
2-HOC6H4
5
101–103
6
7
8
4-HOC6H4
4-MeC6H4
3-NO2C6H4
5
2
90
90
93
92–93
78–80
64–66
90–92
80–82
65–67
[17]
[17]
[17]
< 1
9
4-NO2C6H4
< 1
93
125–127
124–126
[17]
a
Aryl aldehyde (2 mmol), acetic anhydride (4 mmol), and Ce(SO
4
)
2
·4H
2
O (0.1 mmol, 0.04 g, 5 mol%) at room tempterature.
b
All the products were characterized by IR spectral data and comparision of their melting points with those of authentic samples. Also, the
1
structures of some products were confirmed by H-NMR spectral data.
c
Isolated yields.

1066
E. SABURI ET AL.
4
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the reaction time and yield. When 2-hydroxybenzaldehyde
1
2. Aggarwal, V.K.; Fonquerna, S.; Vennal, G.P. Synlett. 1998, 849.
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563.
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anism for this reaction using Brønsted acidic ionic liquid as
catalyst has been shown by Hajipour et al.
Reusability of the catalyst was also investigated. For this
1
5. Aggen, D.H.; Arnold, J.N.; Hayes, P.D.; Smoter, N.J.; Mohan, R.S. Tetra-
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[
17]
1
purpose, the same model reaction was again studied under op- 17. Hajipour, A.R.; Khazdooz, L.; Ruoho, A.E. Catal. Commun. 2008, 9,
8
9.
timized conditions. After the completion of the reaction, hot
ethanol was added. The catalyst was separated by simple filtra-
tion, dried at 50 C under vacuum for 2 h, and reused for a similar
reaction. As shown in Figure 1, the catalyst could be used at least
five times with only slight reduction in its catalytic activity.
1
1
2
8. Olah, G.A.; Mehrotra, A.K. Synthesis 1982, 962.
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conditions. The catalyst can be reused after a simple workup,
with only slight reduction in the catalytic activity. High to excel-
lent yields, ease of workup, mild reaction conditions, very short
reaction times, and environmentally friendly procedure without
use of any solvent are features of this new procedure.
2
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