Cobalt polyoxometalate, CoW12O405- as a new reusable catalyst for the direct, fast, and efficient acetylation of alcohols and phenols under solventless conditions

Article abstract of DOI:10.1081/SCC-120002695

Alcohols and phenols were efficiently acetylated with acetic anhydride without solvent in the presence of 0.01 molar equiv. of cobalt polyoxometalate (CoW₁₂O₄₀^5-).

Full text of DOI:10.1081/SCC-120002695

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COBALT POLYOXOMETALATE, AS A NEW REUSABLE
CATALYST FOR THE DIRECT, FAST, AND EFFICIENT
ACETYLATION OF ALCOHOLS AND PHENOLS UNDER
SOLVENTLESS CONDITIONS
M. H. Habibi a , S. Tangestaninejad a , V. Mirkhani a & B. Yadollahi a
a Chemistry Department , Isfahan University , Isfahan, 81745-117, Iran
Published online: 16 Aug 2006.
To cite this article: M. H. Habibi , S. Tangestaninejad , V. Mirkhani & B. Yadollahi (2002) COBALT POLYOXOMETALATE,
AS A NEW REUSABLE CATALYST FOR THE DIRECT, FAST, AND EFFICIENT ACETYLATION OF ALCOHOLS AND PHENOLS UNDER
SOLVENTLESS CONDITIONS, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 32:6, 863-867, DOI: 10.1081/SCC-120002695
To link to this article: http://dx.doi.org/10.1081/SCC-120002695
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SYNTHETIC COMMUNICATIONS, 32(6), 863–867 (2002)
COBALT POLYOXOMETALATE,
CoW12O54À0 AS A NEW REUSABLE
CATALYST FOR THE DIRECT, FAST,
AND EFFICIENT ACETYLATION
OF ALCOHOLS AND PHENOLS
UNDER SOLVENTLESS
CONDITIONS
*
M. H. Habibi, S. Tangestaninejad,
V. Mirkhani, and B. Yadollahi
Chemistry Department, Isfahan University,
Isfahan 81745-117, Iran
ABSTRACT
Alcohols and phenols were efficiently acetylated with acetic
anhydride without solvent in the presence of 0.01 molar equiv.
of cobalt polyoxometalate (CoW12O540À).
The base catalyzed acylation of alcohols, phenols, amines and thiols by
acetic anhydride or acyl chloride is an established procedure in organic
synthesis.1 Some procedures have also been developed wherein Lewis acid
catalysts COCl2,2 Sc(OTf )3,3 TMSOTf,4 Bu3P,5 TaCl5,6 montmorillonite
*Corresponding author. Fax: þ98-311-6689732; E-mail: habibi@sci.ui.ac.ir
863
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

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864
HABIBI ET AL.
K-10 and KSF,7 4-(dimethylamino) pyridine (DMAP), 4-pyrrolidino-
pyridine (PPY),8 Cu(OTf )2,9 etc.10 have been used for acyl transfer reac-
tions in alcohols. Moreover, silica gel-supported sodium hydrogen
sulfate has been used for the selective monoacetylation of unsymmetrical
diols.11
Polyoxometalates have been proven to be good catalysts in various
oxidations. They are applied in bulk or supported forms, and both homo-
geneous and heterogeneous catalysis are possible. Due to their acidic
and redox properties, heteropoly compounds (heteropoly acids and salts)
are useful and versatile catalysts in a number of transformations.12 In
this research we present a cobalt polyoxometalate (K5CoW12O40Á3H2O)13
as an efficient, selective and reusable catalyst for direct acetylation of alco-
hols and phenols under solvent-free and room temperature conditions
(scheme).
Scheme.
The reaction of alcohol or phenol (1 mmol) with acetic anhydride
(2 ml) and cobalt polyoxometalate (K5CoW12O40Á3H2O) (0.01 mmol) was
performed at room temperature for a few minutes. High to excellent
yields were observed in all cases (Tables 1, 2). This method tolerates other
functionalities such as nitro, halides, ketones and methoxy groups. In addi-
tion, we found that cobalt polyoxometalate, K5CoW12O40Á3H2O, can be
reused several times without loss of activity, simply by filtering the catalyst,
washing with acetone, drying and immediately reusing. Acetylation yield of
benzyl alcohol promoted by the recovered catalyst for four times remained
99% and after seven times was about 95%. Cobalt polyoxometalate
(CoW12O54À0 ) shows good catalytic activity, which is independent of the
different polarities of the reactions.
Typical procedure: Alcohols or phenols (1 mmol) and acetic anhydride
(2 ml) were placed in a two-necked flask with stirring. After a few minute
cobalt polyoxometalate (K5CoW12O40Á3H2O) (0.01 mmol, 32 mg) was added
and the mixture stirred for the appropriate time (see Tables 1, 2) at room
temperature.

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ACETYLATION WITHOUT SOLVENT
865
Table 1. Esterification of Alcohols with Ac2O in the Presence of
K5CoW12O40ꢀ3H2Oa
Time
(min)
Yieldb
(%)
Entry
Alcohols
C6H5CH2OH
Esters
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
C6H5CH2OAc
1
10
1
3
1
1
1
1
1
3
3
30
5
2
99
92
99
96
99
99
99
99
p-CH3OC6H4CH2OH
m-CH3OC6H4CH2OH
o-CH3OC6H4CH2OH
p-O2NC6H4CH2OH
m-O2NC6H4CH2OH
o-O2NC6H4CH2OH
p-ClC6H4CH2OH
p-BrC6H4CH2OH
C6H5CH2CH2CH2OH
C6H5CH2CH2OH
C6H5CH(OH)CH3
C6H5COCH(OH)C6H5
C6H5CHCHCH2OH
a-Tetralol
p-CH3OC6H4CH2OAc
m-CH3OC6H4CH2OAc
o-CH3OC6H4CH2OAc
p-O2NC6H4CH2OAc
m-O2NC6H4CH2OAc
o-O2NC6H4CH2OAc
p-ClC6H4CH2OAc
p-BrC6H4CH2OAc
C6H5CH2CH2CH2OAc
C6H5CH2CH2OAc
C6H5CH(OAc)CH3
C6H5COCH(OAc)C6H5
C6H5CHCHCH2OAc
a-Tetralylacetate
99
100
98
94
94c
96
10
5
100
97
C6H11OH
(cyclohexanol)
C6H11OAc
17
18
19
20
21
22
(À)-Menthol
(À)-Menthylacetate
Adamantanylacetate
(C6H5)3COAc
CH3(CH2)6CH2OAc
CH3(CH2)5CH2OAc
CH3(CH2)3CH-
7
40
45
4
5
8
98
90
91
96
95
100
Adamantanol
(C6H5)3COH
CH3(CH2)6CH2OH
CH3(CH2)5CH2OH
CH3(CH2)3CH-
(C2H5)CH2OH
CH3(CH2)3CH2OH
CH3(CH2)2CH2OH
(C2H5)CH2OAc
CH3(CH2)3CH2OAc
CH3(CH2)2CH2OAc
23
24
5
10
97
93
aAll of the products were characterized by comparison of their physical and spectral
data with those of authentic samples.
bGC yields.
cIsolated yield.
After completion of reaction (monitored by GC or TLC) ether was
added and the catalyst filtered off with a layer of silica gel. The reaction
mixture was washed with a 10% aqueous solution of NaHCO3, and after
separation, organic solution dried with Na2SO4. After evaporation of the
solvent, products could be purified by flash chromatography.