Acetylation of alcohols with acetic anhydride promoted by N,N,N-trimethylanilinium tribromide

Article abstract of DOI:10.1134/S1070428013120026

A wide variety of alcohols were reacted with acetic anhydride at room temperature in the presence of a catalytic amount of N,N,N-trimethylanilinium tribromide to produce the corresponding alkyl acetates in good to excellent yields. Following this procedure, acetylation of primary, secondary, and tertiary alcohols has been performed under neutral conditions.

Full text of DOI:10.1134/S1070428013120026

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 12, pp. 1728–1730. © Pleiades Publishing, Ltd., 2013.
Acetylation of Alcohols with Acetic Anhydride
Promoted by N,N,N-Trimethylanilinium Tribromide
A. Ghorbani-Choghamarani, L. Shiri, and A. Rostami
Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
e-mail: arashghch58@yahoo.com; a.ghorbani@mail.ilam.ac.ir
Received December 25, 2012
Abstract—A wide variety of alcohols were reacted with acetic anhydride at room temperature in the presence
of a catalytic amount of N,N,N-trimethylanilinium tribromide to produce the corresponding alkyl acetates in
good to excellent yields. Following this procedure, acetylation of primary, secondary, and tertiary alcohols has
been performed under neutral conditions.
DOI: 10.1134/S1070428013120026
Acetylation of a hydroxy group is a frequently used
transformation in organic chemistry. Extensive studies
have been undertaken on acetylation due to its ex-
perimental simplicity and effectiveness [1]. Esters
represent an important class of intermediates which are
widely used in the synthesis of fine chemicals, drugs,
food preservatives, perfumes, plasticizers, and pharma-
ceuticals [2–6]. Many synthetic procedures for the
acylation of alcohols have been emerged in the recent
years, such as those utilizing acetic anhydride/1,3-di-
bromo-5,5-dimethylhydantoin and/or trichloroiso-
cyanuric acid [7], acetic acid/borated zirconia [8],
acetic anhydride/TaCl5 [9], acetic anhydride/Bi(OTf)3
[10], acetyl chloride/ZrOCl2·8H2O [11], acid chloride
or acid anhydride/ZnO [12], acetic anhydride/benzyl-
(triphenyl)phosphonium tribromide [13], acetic anhy-
dride or benzoic anhydride/N,N,N′,N′-tetramethyl-
ethane-1,2-diamine [14], acetyl chloride/CuO [15],
acetic anhydride/LiOTf [16], acetic anhydride/Zr(OTf)3
[17], etc. However, these procedures are limited by
some drawbacks, in particular formation of by-prod-
ucts, harsh reaction conditions, low yields, toxicity of
reactants, heavy metal contamination, long reaction
times, etc. Therefore, introducing an efficient, general,
mild, and new procedure is called for in order to
prepare alkyl acetates in the presence of an appropriate
catalyst.
Taking into account the above stated, in continua-
tion of our studies on the application of new reagents
and reagent systems for transformations of organic
functional group [18–25] we used N,N,N-trimethyl-
anilinium tribromide as an efficient, green, and versa-
tile catalyst for the acetylation of alcohols.
Initially, the reaction conditions were optimized
using 2-phenylethanol (Ii) as model substrate. Various
solvents were tested, and the results are listed in
Table 1. It is seen that acetone ensured the best results
in terms of reactivity, and this solvent was selected for
all other acetylation reactions. We thus performed
acetylation of primary, secondary, and tertiary alcohols
to produce the corresponding acetates using acetic
anhydride and a catalytic amount of N,N,N-trimethyl-
Table 1. Acetylation of 2-phenylethanol with acetic anhy-
dride in the presence of trimethyl(phenyl)ammonium tri-
bromidea
Solvent
Time, h
Yield,b %
Scheme 1.
Chloroform
Acetonitrile
Methylene chloride
Ethyl acetate
Acetone
23
24
93
Traces
89
Ac2O, Me3NPh Br3
ROH
ROAc
22
Ia–Ik
IIa–IIk
24
No reaction
91
R = 4-i-PrC6H4CH2 (a), 4-t-BuC6H4CH2 (b), 4-BrC6H4CH2 (c),
2,4-Cl2C6H4CH2 (d), 4-FC6H4CH2 (e), 3-FC6H4CH2 (f),
4-O2NC6H4CH2 (g), 2-ClC6H4CH2 (h), PhCH2CH2OH (i),
adamantan-2-yl (j), adamantan-1-yl (k).
50 min
a
Molar ratio substrate–catalyst–acetic anhydride 1:0.1:2.5.
Yield of the isolated compound.
b
1728

ACETYLATION OF ALCOHOLS WITH ACETIC ANHYDRIDE
1729
Table 2. Acetylation of alcohols with acetic anhydride in the presence of trimethyl(phenyl)ammonium tribromide in
acetone at room temperaturea
Substrate
Product
Reaction time, min
Yield,b %
Substrate
Product
Reaction time, min
Yield,b %
Ia
Ib
Ic
Id
Ie
If
IIa
IIb
IIc
IId
IIe
IIf
050
060
090
170
070
120
95
98
94
94
93
90
Ig
Ih
Ii
IIg
IIh
IIi
200
105
050
24 h
120
24 h
94
98
91
Ii
IIi
No reaction
98
Ij
IIj
IIk
Ik
c83c
a
b
c
Molar ratio substrate–catalyst–acetic anhydride 1 : 0.1 : 2.5.
Yield of the isolated compound.
The product was purified by short column chromatography.
anilinium tribromide in acetone under mild conditions
(Scheme 1, Table 2).
chloride (5×5 ml). The extract was dried over anhy-
drous Na2SO4 (1.5 g) and evaporated to obtain 0.202 g
(98%) of 4-tert-buthylbenzyl acetate (IIi).
Financial support for this work by the Ilam
University, Ilam, Iran, is gratefully acknowledged.
The reactions were easily carried out by mixing
1 mmol of alcohol, 0.1 mmol of N,N,N-trimethyl-
anilinium tribromide, and 2.5 mmol of acetic anhy-
dride in acetone, followed by stirring of the resulting
mixture at room temperature for appropriate time.
Finally, the reaction mixture was quenched with water,
and the product was isolated by extraction with methy-
lene chloride. No acetylation of 2-phenylethanol (Ii)
was observed for at least 24 h in the absence of
N,N,N-trimethylanilinium tribromide, whereas in the
presence of the catalyst the reaction was complete in
50 min (Table 2).
In summary, we have developed an efficient,
simple, and environmentally friendly procedure for the
acetylation of alcohols. Mild conditions, nontoxic
reactants, and easy reaction work-up are some of the
notable features of this protocol.
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