A Simple and Efficient Procedure for Transesterification Catalyzed by Indium Triiodide

Full text of DOI:10.1021/jo980157y

J . Org. Chem. 1998, 63, 6027-6028
6027
A Sim p le a n d Efficien t P r oced u r e for
Sch em e 1
Tr a n sester ifica tion Ca ta lyzed by In d iu m
Tr iiod id e
Brindaban C. Ranu,* Pinak Dutta, and
Arunkanti Sarkar
The ether extract, after being washed with sodium
thiosulfate and brine, was evaporated to furnish the
product.
Department of Organic Chemistry, Indian Association
for the Cultivation of Science,
A wide range of structurally varied carboxylic esters
including open-chain, cyclic, and aromatic ones under-
went transesterification with a variety of alcohols by this
procedure. The results are summarized in Table 1. The
reaction proceeds smoothly with primary (methanol,
ethanol, and benzyl alcohol), secondary (2-propanol), as
well as tertiary alcohols (tert-butyl alcohol), although
transesterification with tert-butyl alcohol and benzyl
alcohol have been carried out under sonication. Conver-
sions from methyl ester to higher homologues and from
higher esters to lower homologues are achieved with
uniform efficiency by this procedure. Particularly, trans-
formation of menthyl ester to methyl ester (entries 12
and 13), which is very difficult to accomplish by other
methods, indicates the efficacy of this reagent. Trans-
esterification to tert-butyl ester (entries 5 and 6), which
is often problematic in acid-catalyzed reactions, is also
realized by this reagent. This procedure is also suitable
for transesterification of a chiral ester without any
racemization (entries 14 and 15). Several functional
groups such as double bond (entries 16, 17, 22, and 23),
nitro (entry 21), methoxyl (entries 20 and 23), and
hydroxyl (entries 14 and 15) remain unaffected under the
present reaction conditions.
J adavpur, Calcutta 700 032, India
Received J anuary 29, 1998
Transesterification is an important reaction which has
wide applications1 in academic as well as industrial
research. Thus, a number of procedures catalyzed by a
variety of protic and Lewis acids, organic and inorganic
1
,2
bases, enzymes, and antibodies have been developed.
Surprisingly, in all these reports although there are many
examples of transesterification of esters to the corre-
sponding analogues with higher alcohol moieties, ex-
amples of reverse transformations are not adequately
included. During the course of our recent investigation
we sought a transesterification of a menthyl ester to
methyl or ethyl ester. However, our attempts with
r
several reported reagents including AlCl
3
and Ti(OPr )
4
failed to produce a satisfactory result. Moreover, some
of these reagents, particularly organotin compounds, are
highly toxic. Thus, we felt the necessity of an efficient
transesterification procedure with general applicability
involving simple operations and a nontoxic reagent.
3
4
The reactions involving indium metal and its halides
have been the subject of current interest because of their
great potential in organic synthesis. During our recent
endeavor with indium-mediated reactions we have ob-
served a very significant effect of indium triiodide in the
transesterification process. This prompted us to initiate
3
a systematic investigation on InI -catalyzed transesteri-
Although the reaction proceeds well with a catalytic
amount (0.3-0.5 equiv) of indium triiodide, the reactions
are quite slow. However, reaction times are substantially
5
3
reduced when 1.5 equiv of InI is used. The reactions
are, in general, very clean giving very high yields, and
no side product has been isolated. The transesterification
of aliphatic esters is usually complete within 5-6 h, but
aromatic esters took longer (25-30 h).
In conclusion, the present procedure using indium
triiodide provides a very efficient method for transesteri-
fication. The notable advantages of this method are: (a)
operational simplicity; (b) easy availability and nontoxic
nature of the reagent; (c) general applicability; (d) mild
reaction conditions (tolerance to several sensitive func-
tionalities during transesterification), and (e) high yield.
We believe this will present a better and more practical
alternative to the existing methodologies and will find
useful applications in organic synthesis.
fication reactions, and herein we wish to disclose our
results (Scheme 1)
In a typical experimental procedure, the ester was
6
heated under reflux in a desired alcohol in the presence
of indium triiodide, prepared in situ by stirring indium
metal and iodine in that particular alcohol at room
temperature for half an hour. The reaction was moni-
tored by TLC, and after completion, excess alcohol was
stripped off and the residue was extracted with ether.
(
1) (a) Fujita, T.; Tanaka, M.; Norimine, Y.; Suemune, H. J . Org.
Chem. 1997, 62, 3824. (b) Shapiro, G.; Marzi, M. J . Org. Chem. 1997,
2, 7096.
6
(
(
2) Otera, J . Chem. Rev. 1993, 93, 1447, and references therein.
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X.-R. Tetrahedron Lett. 1997, 38, 3465.
4
(
Gen er a l. The carboxylic esters are obtained commercially
or prepared from the corresponding acids by a standard method.
The esters and alcohols are distilled before use. Indium metal
Ingot, SRL, India) was cut into small slices and used directly
without any treatment. Iodine crystal was used as obtained
commercially.
(
(
1
Gen er a l P r oced u r e for Tr a n sester ifica tion . Rep r esen -
ta tive P r oced u r e. Methyl phenyl acetate (150 mg, 1 mmol)
(
5) Ranu, B. C.; Majee, A. J . Chem. Soc., Chem. Commun. 1997,
225.
6) The alcohol was taken in excess for a clean and smooth reaction.
1
was heated at reflux with a solution of indium triiodide in
(
7
2
-propanol, prepared in situ by stirring indium metal slices (173
The use of just 1 equiv of alcohol leads to charring, and the reactions
are messy. The presence of a cosolvent such as benzene also fails to
provide a satisfactory result.
mg, 1.5 mmol) and iodine (571 mg, 2.25 mmol) in dry 2-propanol
(6 mL) at room temperature (25 °C) for half an hour. After the
S0022-3263(98)00157-1 CCC: $15.00 © 1998 American Chemical Society
Published on Web 08/01/1998

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028 J . Org. Chem., Vol. 63, No. 17, 1998
Notes
Ta ble 1. In I3-Ca ta lyzed Tr a n sester ifica tion
a
Yields refer to those of pure isolated products, fully characterized by spectral data. b The reaction was carried out under sonication.
reaction was over (6 h, monitored by TLC) excess alcohol was
distilled off at reduced pressure and the residue was extracted
with ether. The ether extract was washed successively with a
(entry 10) which were carried out under sonication in an
ultrasonic cleaner (J ulabo, Germany).
All the products are known compounds and are easily identi-
fied by comparison of their spectra with those of authentic
samples.8
2 4
solution of sodium thiosulfate, brine, and dried Na SO . Evapo-
ration of ether produced the crude product which was purified
by column chromatography over silica gel to furnish pure
isopropyl phenyl acetate (oil, 160 mg, 90%) which is in full
agreement with spectral data of an authentic sample.
This procedure is followed for transesterification of all the
substrates included in Table 1, except those of methyl phenyl
acetate (entry 5) and methyl phenyl propionate (entry 6) with
tert-butyl alcohol and methyl phenyl acetate with benzyl alcohol
Ack n ow led gm en t. We are pleased to acknowledge
the financial support from CSIR, New Delhi [Grant No.
0
1(1504)/98] for this investigation.
J O980157Y
(
8) Pouchert, C. J . The Aldrich Library of NMR Spectra, 2nd ed.;
(7) Han, Y.; Huang, Y.-Z. Tetrahedron Lett. 1995, 36, 7277.
Aldrich Chemical Co., Inc.: Milwaukee, 1983; Vols. 1 and 2.