A new and efficient procedure for the production of 1,1-diacetate from corresponding aldehydes promoted by silica chromate (SiO2-O-CrO 2-O-SiO2)

Article abstract of DOI:10.1080/10426507.2010.503208

Chemical Equation Presented A wide range of aromatic aldehydes has been selectively converted to 1,1-diacetates using silica chromate (SiO ₂-O-CrO₂-O-SiO₂) under solvent-free conditions at room temperature in moderate to good yields. This protocol is mild and efficient compared to other reported methods. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426507.2010.503208

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Phosphorus, Sulfur, and Silicon and the
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A New and Efficient Procedure for
the Production of 1,1-Diacetate from
Corresponding Aldehydes Promoted by
Silica Chromate (SiO2-O-CrO2-O-SiO2)
Abdolhamid Bamoniri a , Arash Ghorbani-Choghamarani b & Bi Bi
Fatemeh Mirjalili c
a Department of Chemistry, College of Science , University of
Kashan , Kashan, Islamic Republic of Iran
b Department of Chemistry, Faculty of Science , Ilam University ,
Ilam, Islamic Republic of Iran
c Department of Chemistry, College of Science , Yazd University ,
Yazd, Islamic Republic of Iran
Published online: 19 Feb 2011.
To cite this article: Abdolhamid Bamoniri , Arash Ghorbani-Choghamarani & Bi Bi Fatemeh Mirjalili
(2011) A New and Efficient Procedure for the Production of 1,1-Diacetate from Corresponding
Aldehydes Promoted by Silica Chromate (SiO2-O-CrO2-O-SiO2), Phosphorus, Sulfur, and Silicon and the
Related Elements, 186:2, 381-388, DOI: 10.1080/10426507.2010.503208
To link to this article: http://dx.doi.org/10.1080/10426507.2010.503208
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Phosphorus, Sulfur, and Silicon, 186:381–388, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.503208
A NEW AND EFFICIENT PROCEDURE FOR THE
PRODUCTION OF 1,1-DIACETATE FROM
CORRESPONDING ALDEHYDES PROMOTED BY SILICA
CHROMATE (SiO2-O-CrO2-O-SiO2)
Abdolhamid Bamoniri,1 Arash Ghorbani-Choghamarani,2
and Bi Bi Fatemeh Mirjalili3
1Department of Chemistry, College of Science, University of Kashan, Kashan,
Islamic Republic of Iran
2Department of Chemistry, Faculty of Science, Ilam University, Ilam,
Islamic Republic of Iran
3Department of Chemistry, College of Science, Yazd University, Yazd,
Islamic Republic of Iran
GRAPHICAL ABSTRACT
O
O
SiO2
OCrO
SiO2
OAc
C
O
Ar
H
Ar
H
Ac2O, Solvent-Free
rt
OAc
Abstract A wide range of aromatic aldehydes has been selectively converted to 1,1-diacetates
using silica chromate (SiO2 CrO2 SiO2) under solvent-free conditions at room tem-
O
O
perature in moderate to good yields. This protocol is mild and efficient compared to other
reported methods.
Keywords Aldehydes; 1,1-diacetates; silica chromate; solvent-free
INTRODUCTION
Selective protection and deprotection of carbonyl groups are essential steps in syn-
thetic organic chemistry.1 1,1-Diacetates are synthetically useful protecting groups for
carbonyl compounds due to their stability and also important building blocks for the syn-
thesis of dienes in Diels–Alder reactions.2,3 Additionally, the (1,1-diacetate) functionality
can be converted into other functional groups by reaction with appropriate nucleophiles.4,5
Received 7 April 2010; accepted 16 June 2010.
Financial support for this work by the research facilities of Kashan University and Ilam University is
gratefully acknowledged.
Address correspondence to Abdolhamid Bamoniri, Department of Chemistry, College of Science, Uni-
versity of Kashan, Kashan, Islamic Republic of Iran. E-mail: bamoniri@kashanu.ac.ir and Arash Ghorbani-
Choghamarani, Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran.
E-mail: arashghch58@yahoo.com
381

382
A. BAMONIRI ET AL.
These 1,1-diacetates have several synthetic and industrial applications and are
used as cross-linking reagents6 in cellulose and the cotton industry, and are also used
as stain bleaching agents.7 Usually, 1,1-diacetates are prepared from aldehydes and
acetic anhydride in the presence of strong proton acids or Lewis acids as catalyst, such
as RuCl3.xH2O,7 P2O5/montmorillonite K10,8 zinc(II) perchlorate,9 BiCl3,10 methylim-
idazolium hydrogen sulphate,11 sodium hydrogen sulfate,12 PVC-FeCl3,13 Zr(HSO4)4,14
Cu(NO3)2.3H2O,15 Caro’s acid supported on silica gel,16 SO42−/SnO2,17 copper(II) tetraflu-
oroborate,18 [NO+Crown- H(NO3)2−],19 SbCl3,20 and NbCl5.21 However, some of the re-
ported procedures require the use of harsh conditions, long reaction times, formation of
byproducts, laborious work-up, and poor yields of the target products.
RESULTS AND DISCUSSION
In continuation of our investigation on the silica-based reagents,22–26 we found that
silica gel reacts with dichloro chromium oxide to give silica chromate, and it has been used
in some organic reactions such as oxidation of 1,4-dihydropyridines,27 regeneration of car-
bonyl compounds from oximes,28 oxidation of alcohols, and deprotection of trimethylsilyl
ethers.29 Silica chromate as a nontoxic and efficient reagent can be easily obtained by the
reaction of dichloro chromium oxide with silica gel (Scheme 1).
O
SiO2
OH
+ ClCrO2Cl
2
SiO2
SiO2
+
OCrO
O
2 HCl
Scheme 1
To investigate the scope and limitation of silica chromate, we decided to apply this
reagent for the preparation of 1,1-diacetates. Initially, the results of the preparation of 1,1-
diacetoxy-1-(3-nitrophenyl)-methane (as typical example) as a function of the amounts of
silica chromate were investigated and listed in Table 1. As the results show, the optimal
amount of silica chromate to convert aldehydes to the corresponding 1,1-diacetates is 0.25 g.
In order to investigate the solvent effect on the outcome of the reaction, different
solvents were applied for the preparation of 1,1-diacetoxy-1-(3-nitrophenyl)-methane; the
Table 1 Conversion of 3-nitrobenzaldehyde to the corresponding 1,1-diacetate using acetic anhydride and dif-
ferent amounts of silica chromate (SiO2
O CrO2 O
SiO2)a
Entry
Silica chromate (g)
Time (min)
Yield (%)b
1
2
3
4
5
6
7
0.05
0.1
0.15
0.2
0.25
0.3
0.35
50
45
40
35
30
30
25
60
70
75
80
90
90
92
aMolar ratio of reagents: aldehyde/acetic anhydride (1 mmol/1 mmol).
bIsolated yield.

PRODUCTION OF 1,1-DIACETATE FROM ALDEHYDES
383
Table 2 Conversion of 3-nitrobenzaldehyde to the corresponding 1,1-diacetate using acetic anhydride and silica
chromate (SiO2
Entry
O CrO2 O
SiO2) in different solvents at room temperaturea
Solvent
Time (min)
Yield (%)b
1
2
3
4
5
6
7
Acetonitrile
Water
Ethyl acetate
Dichloromethane
Cyclohexane
Ethanol
100
120
150
100
120
110
30
75
40
45
70
50
40
90
Solvent-Free
aMolar ratio of reagents: aldehyde/acetic anhydride (1 mmol/1 mmol).
bIsolated yield.
results are summarized in Table 2. The protection of 3-nitrobenzaldehyde was performed
using a mixture containing 3-nitrobenzaldehyde (1 mmol), acetic anhydride (1 mmol), and
silica chromate (0.25 g) at room temperature. It was observed that the solvent-free condition
is the most effective media, so it was used in all further reactions.
Consequently, we decided to apply a new heterogeneous protocol for the selective
protection of a wide range of aromatic aldehydes (1) to the corresponding 1,1-diacetates
(2) via combination of acetic anhydride and silica chromate under solvent-free conditions
at room temperature (Scheme 2 and Table 3).
O
OAc
SiO2-O-CrO2-O-SiO2
+ Ac O
H
Ar
2
Ar
C
H
Solvent-Free
rt
OAc
1
2
Scheme 2
1,1-Diacetate products were prepared easily by mixing an aldehyde, acetic anhy-
dride, and silica chromate, then stirring this mixture under solvent-free conditions at room
temperature. The pure product can be easily isolated from the reaction media by washing
the reaction mixture with diethyl ether, simple filtration, and evaporation of the solvent.
As the results of Table 3 show, the reaction rate for the aromatic rings with electron-
withdrawing groups is more than the aromatic rings with electron-donating groups.
The described method for the preparation of 1,1-diacetates has interesting and excel-
lent selectivity. To show the chemoselectivity of the described system, some competitive
reactions were designed (Scheme 3).
To the best of our knowledge, silica chromate is the first example of a silica-
chromium–based oxidant with covalent linkages. Thus, we hoped that the silica chromate
(SiO2 O CrO2 O SiO2) would be superior to the previously reported chromium-based
oxidants30–32 because (i) toxic chromium cations could be collected from the reaction mix-
ture easily; (ii) work up is very simple, and pure products are obtained solely by filtration
and removing of solvent; and (iii) there is no need for any chelating agents such as pyridine
in pyridinium chlorochromate (PCC). In conclusion, in this article we have developed a
simple and efficient procedure for the chemoselective preparation of 1,1-diacetates using

384
A. BAMONIRI ET AL.
Table 3 Preparation of 1,1-diacetatesvia combination of aldehydes, silica chromate (SiO2
O
CrO2
O
SiO2)
and acetic anhydride under solvent-free conditions at room temperaturea
Time
(min)
Yield
(%)b
Mp (◦C)
found
Mp (◦C)
reported
Entry
1
Substrate
Product
Ref.
(36)
30
85
84–86
85–86
2
3
30
95
64–66
65–67
(11)
(11)
30
90
124
124–126
4
5
40
40
85
90
51–52
81–83
52–53
81–82
(11)
(11)
6
7
8
20
20
20
85
80
85
68–70
Gummy
80–82
—
—
—
—
80–82
(11)
9
45
75
64–66
65–66
(11)
10
11
75
50
75
80
100–102
87–89
101–102
89–90
(11)
(11)

PRODUCTION OF 1,1-DIACETATE FROM ALDEHYDES
385
Table 3 Preparation of 1,1-diacetatesvia combination of aldehydes, silica chromate (SiO2
and acetic anhydride under solvent-free conditions at room temperaturea (Continued)
O
CrO2
O
SiO2)
Time
(min)
Yield
(%)b
Mp (◦C)
found
Mp (◦C)
reported
Entry
12
Substrate
Product
Ref.
—
50
50
80
75
118–120
78–79
—
13
—
—
14
15
100
100
70
70
108–109
103–105
107–108
—
(11)
—
16
17
120
600
80
65
89–91
90–92
—
(35)
—
Gummy
18
19
30
20
85
85
80–81
84–86
(11)
(36)
104–106
105–106
20
20
90
98–100
99–100
(36)
aMolar ratio of reagents: aldehyde/silica chromate/acetic anhydride for entries 1–9, 11–15, and 17–20
(1 mmol/0.25 g/1 mmol); for entries 10 and 16 (1 mmol/0.25 g/2 mmol).
bIsolated yield.
silica chromate (SiO2 O CrO2 O SiO2) under mild and solvent-free conditions with
moderate to good yields.
EXPERIMENTAL
Chemicals were purchased from Fluka, Merck, and Aldrich chemical companies.
The oxidation products were characterized by comparison of their spectral (IR, 1H NMR,
or 13C NMR) and physical data with authentic samples.

386
A. BAMONIRI ET AL.
O
O
Ac2O (1 mmol)
SiO2-O-CrO2-O-SiO2
OAc
OAc
+
Ph
H
Ph
CH3
Ph
C
H
+ Ph
C
CH3
Solvent-Free
30 min, rt
OAc
OAc
100 %
0 %
CHO
OMe
CH(OAc)2
CHO
CH(OAc)2
Ac2O (1 mmol)
SiO2-O-CrO2-O-SiO2
+
+
Solvent-Free
30 min, rt
OMe
NO2
NO2
0 %
100 %
Scheme 3
Preparation of Silica Chromate
A 500-mL suction flask was used. It was equipped with a constant pressure dropping
funnel containing dichloro chromium oxide (23.2 g, 0.15 mol) and a gas inlet tube for
conducting HCl gas over an adsorbing solution, i.e., water. It was charged with silica gel
(100 g). Dichloro chromium oxide was added dropwise over a period of 20 min at room
temperature. HCl gas evolved from the reaction vessel immediately (Scheme 1). After the
addition was complete, the mixture was shaken for 90 min. A brown solid (silica chromate)
was obtained quantitatively.29
Typical Procedure: Preparation of 1,1-Diacetoxy-1-(3-methylphenyl)-
methane
In a round bottom flask, 3-methylbenzaldehyde (0.120 g, 1 mmol), acetic anhydride
(0.102 g, 1 mmol), and silica chromate (1 mmol) were added. The mixture was stirred at
room temperature for 20 min. The progress of the reaction was monitored by TLC using
n-hexane and ethyl acetate (7:3) as an eluent. After completion of the reaction, diethyl ether
was added to the mixture and filtered. The organic layer was washed with saturated NaHCO3
(2 × 25 mL) and water (30 mL). The organic phase was dried over anhydrous Na2SO4,
filtered, and the solvent was evaporated to give the pure 1,1-diacetoxy-1-(3-methylphenyl)-
methane in 80% yield (0.177 g); colorless gummy oil; 1H NMR (400 MHz, CDCl3): δ =
7.46 (s, 1H), 7.12 (m, 3H), 7.01 (s, 1H), 2.19 (s, 3H), 1.93 (s, 6H) ppm; IR (KBr): v¯ =
2926, 1757, 1609, 1490, 1370, 1242, 1205, 791 cm−1
.
1,1-Diacetoxy-1-(2-methylphenyl)-methane. Colorless oil; 1H NMR
(400 MHz, CDCl3): δ = 7.64 (s, 1H), 7.31 (d, 1H, J = 8 Hz), 7.05 (m, 3H), 2.26 (s, 3H)
1.93 (s, 6H) ppm; IR (KBr): v¯ = 3100, 2890, 1750, 1619, 1442, 1371, 1247, 1215, 972,
967, 768 cm−1
.
1,1-Diacetoxy-1-(2,4-dichlorophenyl)-methane. Crystalline white solid, mp
1
118–120◦C; H NMR (400 MHz, CDCl3): δ = 7.07–7.32 (m, 3H), 1.95 (s, 6H) ppm; IR
(KBr): v¯ = 3010, 2883, 1751, 1609, 1373, 1196, 1017, 890 cm−1
.

PRODUCTION OF 1,1-DIACETATE FROM ALDEHYDES
387
1,1-Diacetoxy-1-(2,3-dichlorophenyl)-methane. Crystalline white solid, mp
78–79◦C; 1H NMR (400 MHz, CDCl3): δ = 7.72 (s, 1H), 7.07–7.59 (m, 3H), 1.95 (s, 6H)
ppm; IR (KBr): v¯ = 3012, 2893, 1748, 1429, 1375, 1219, 1031, 780 cm−1
.
1,1-Diacetoxy-1-(2,3-dimethoxyphenyl)-methane. Crystalline white solid,
1
mp 103–105◦C H NMR (400 MHz, CDCl3): δ = 7.78 (s, 1H), 6.75–6.91 (m, 3H), 3.70
(s, 6H), 3.67 (s, 6H), 1.91 (s, 6H) ppm; IR (KBr): v¯ = 2938, 1753, 1602, 1488, 1452,
1369,1242, 1208, 1054, 1018, 964, 804 cm−1
.
1,1-Diacetoxy-1-(4-N,N-dimethylaminophenyl)-methane. Colorless gum-
my oil; 1H NMR (400 MHz, CDCl3): δ = 7.48 (s,), 6.94–7.26 (m, 4H), 2.12 (s, 6H) 1.93
(s, 6H) ppm; IR (KBr): v¯ = 3021, 2989, 1761, 1602, 1448, 1372, 1203, 1059, 1011, 805,
698 cm−1
.
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