Silica chloride as a mild and efficient reagent for acetylation of alcohols

Article abstract of DOI:10.1080/10426500390228684

A variety of alcohols underwent acetylation with acetic anhydride in the presence of silica chloride. All reactions were performed at room temperature and under completely heterogeneous conditions in good to high yields.

Full text of DOI:10.1080/10426500390228684

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Phosphorus, Sulfur, and Silicon and the Related
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Silica Chloride as a Mild and Efficient Reagent for
Acetylation of Alcohols
Farhad Shirini a , Mohammad Ali Zolfigol b & Mahroo Khaleghi a
a Guilan University, Rasht, Iran
b Bu-Ali Sina University, Hamadan, Iran
Published online: 23 Aug 2006.
To cite this article: Farhad Shirini , Mohammad Ali Zolfigol & Mahroo Khaleghi (2003): Silica Chloride as a Mild and Efficient
Reagent for Acetylation of Alcohols, Phosphorus, Sulfur, and Silicon and the Related Elements, 178:9, 1999-2002
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Phosphorus, Sulfur, and Silicon, 178:1999–2002, 2003
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ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500390228684
SILICA CHLORIDE AS A MILD AND EFFICIENT
REAGENT FOR ACETYLATION OF ALCOHOLS
Farhad Shirini,a Mohammad Ali Zolfigol,b
and Mahroo Khaleghia
Guilan University, Rashta and Bu-Ali Sina University,
Hamadan, Iranb
(Received February 18, 2003)
A variety of alcohols underwent acetylation with acetic anhydride in
the presence of silica chloride. All reactions were performed at room
temperature and under completely heterogeneous conditions in good to
high yields.
Keywords: Acetylation; alcohol; esterification; heterogeneous condi-
tions; silica chloride
Functional group protection and deprotection is important in synthetic
organic chemistry.1 Among protecting groups for alcohols, the esters
are the most important with acetate being the simplest and easiest of
all. Acetylation2 most commonly is performed using3,4 reagents such as
acetic anhydride or acetyl chloride in the presence of triethyl amine or
pyridine as a catalyst.5 4-(Dimethylamino)pyridine (DMAP) is known
to increase the rate of acetylation when used as a cocatalyst.6
Tributylphosphine has been introduced as a less basic catalyst for
acetylation of alcohols.7 In addition to the above catalysts, protic or
Lewis acids,8–14 or some times solid acid catalysts15–17 are known to cat-
alyze the acetylation of alcohols with acid anhydrides. Recently, scan-
dium triflate has been used for the efficient acetylation of alcohols.18
Most recently, the use of bismuth as a milder acetylation catalyst
than scandium triflate has been reported.19 However most of the re-
ported methods suffer from one or more of the following disadvantages:
long rection time, vigorous reaction conditions, the occurance of side
We appreciate the financial support of this work by the Guilan University Research
Council.
Address correspondence to Farhad Shirini, Department of Chemistry, Faculty of Sci-
ence, Guilan University, Rasht, Iran. E-mail: shirini@guilan.ac.ir
1999

2000
F. Shirini et al.
reactions, unavailability of the reagents, as well as poor yields of the
desired product. Thus, there still is a demand to develop new and mild
methods for the acetylation of alcohols in the presence of inexpensive
and bench top reagents.
Silica chloride has been used as a mild and efficient reagent for
a number of organic reactions.20–22 In this article we disclose a new
method for the acetylation of alcohols using acetic anhydride in the
presence of silica chloride in n-hexane (Scheme 1).
(CH3CO)2O, silica chloride
ROH
−→ ROCOCH3
n-hexane, r.t., 5–30 min.
SCHEME 1
As shown in Table I, primary and secondary alcohols are acety-
lated with acetic anhydride in excellent yields in the presence of silica
chloride (entries 1–15). Dihydroxy compounds are converted into the
corresponding diacetates efficiently (entry 16). Interestingly, hindered
TABLE I Acetylation of Alcohols Using Ac2O in the Presence of Silica
Chloridea
Entry
Substrate
Product
C6H5CH2 OAc
2-BrC6H4CH2 OAc
4-MeOC6H4CH2 OAc
4-ClC6H4CH2 OAc
Time (min.) Yield %b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
C6H5CH2 OH
5
5
90
86
85
85
90
85
92
88
85
85
80
85
82
80
86
82c,d
85
80
2-BrC6H4CH2 OH
4-MeOC6H4CH2 OH
4-ClC6H4CH2 OH
4-(Me)3CC6H4CH2 OH 4-(Me)3CC6H4CH2 OAc
3-NO2C6H4CH2 OH
C6H5CH(OH)CH3
C6H5CH(OH)C6H5
C6H5CH CHCH2 OH
C6H5CH2CH(OH)CH3 C6H5CH2CH(OAc)CH3
C6H5CH2CH2CH2 OH C6H5CH2CH2CH2 OAc
Cyclohexanol
1-octanol
5
5
3
5
5
15
5
10
5
5
3-NO2C6H4CH2 OAc
C6H5CH(OAc)CH3
C6H5CH(OAc)C6H5
C6H5CH CHCH2 OAc
Cyclohexyl acetate
1-octyl acetate
1-butyl acetate
(−) menthyl acetate
C6H5CH(OAc)CH2OAc
tert.butyl acetate
2
1-butanol
10
10
12
30
10
(−) menthol
C6H5CH(OH)CH2OH
tert.butyl alcohol
1-methylcyclohexanol
1-methylcyclohexyl acetate
aProducts were characterized by their physical constants, comparison with authentic
samples and IR and NMR spectroscopy.
bIsolated yield.
cYield refers to isolated pure diacetate.
d2.5 mmol of acetic anhydride was used.

Esterification
2001
tertiary alcohols such as tert-butyl alcohol and 1-methylcyclohexanol
(entries 17 and 18) also are acetylated in excellent yields in the pres-
ence of this reagent. The acetylation reactions were performed under
mild and completely heterogeneous conditions at room temperature and
take place with good to high yields.
In conclusion, we have shown that silica chloride is a very efficient
and versatile reagent for acetylation of alcohols. One of the advantages
of this method is that even hindered substrates can be acetylated in high
yields under mild reaction conditions. The actual role of silica chloride
is not clear and this subject is under investigation in our laboratory.
EXPERIMENTAL
General Procedure for Acetylation of Alcohols Using
Ac2O in the Presence of Silica Chloride23
A mixture of alcohol (1 mmol), acetic anhydride (1.5 mmol), and silica
chloride (0.1 g) in n-hexane (3 mL) was stirred at room temperature
for the specified time. The progress of the reaction was monitored by
TLC or GC. After completion of the reaction, the solvent was evaporated
and water was added (10 mL). The mixture was extracted with CH2Cl2
(2 × 15 mL). The organic layer was separated, washed with saturated
NaHCO3 (2 × 10 mL) and water (10 mL), and dried over anhydrous
MgSO4. Evaporation of the solvent followed by column chromatography
on silica gel afforded the pure acetate.
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