A mild and efficient method for esterification and transesterification catalyzed by iodine

Article abstract of DOI:10.1016/S0040-4039(01)02235-3

Iodine, was found to be a practical and useful Lewis acid catalyst for the esterification of carboxylic acids with alcohols. The high catalytic activity of iodine can be used for the transesterification of esters by different alcohols including tertiary alcohols and sterically hindered primary and secondary alcohols. The method presented is especially effective for simultaneous esterification and transesterification reactions.

Full text of DOI:10.1016/S0040-4039(01)02235-3

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 879–882
A mild and efficient method for esterification and
transesterification catalyzed by iodine†
K. Ramalinga, P. Vijayalakshmi and T. N. B. Kaimal*
Lipid Science & Technology, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Received 1 October 2001; revised 12 November 2001; accepted 22 November 2001
Abstract—Iodine, was found to be a practical and useful Lewis acid catalyst for the esterification of carboxylic acids with alcohols.
The high catalytic activity of iodine can be used for the transesterification of esters by different alcohols including tertiary alcohols
and sterically hindered primary and secondary alcohols. The method presented is especially effective for simultaneous esterifica-
tion and transesterification reactions. © 2002 Published by Elsevier Science Ltd.
Esterification of carboxylic acids and transesterification
of esters have wide academic as well as industrial
applications. A number of useful and reliable esterifica-
tion methods catalyzed by a variety of acids, ion
exchange resins, zeolites, solid acid catalysts, etc., have
been reported in the literature.1–11 Recent developments
include variation and improvements of well established
procedures and the discovery and application of new
reagents. Transesterifications are catalyzed by alkali
metal hydroxides and alkoxides in appropriate alcohols
and also by tin, calcium or titanium compounds.12
Environmental considerations limit the applicability of
many, otherwise useful catalysts commercially. There
are not many reagents available for commercial appli-
cations that can accomplish both esterification and
transesterification reactions under mild conditions.
Recent methods are those using diphenyl ammonium
triflate and a clay catalyst.13 During the course of our
search for a facile, practical and versatile catalyst for
simultaneous esterification and transesterification reac-
tions for the preparation of methyl esters as biodiesel
from low grade vegetable oils, we observed that granu-
lar iodine can accomplish both reactions in a highly
efficient manner. Reagents based on iodine reported in
recent years for transesterification reactions are indium
triodide,14 iodotrimethyl silane–iodine,15 etc.
To our knowledge, reports with molecular iodine alone
have not appeared so far. Here we wish to report our
results on reactions involving iodine/alcohol for their
usefulness in esterification, transesterification and
simultaneous esterification and transesterification reac-
tions (Scheme 1).
In a typical experimental procedure, the ester or acid
was refluxed or heated to a certain predetermined tem-
perature with the desired alcohol in the presence of
iodine. The reaction was monitored either by TLC or
GC and after completion, the excess alcohol was
removed and the residue was extracted with ether. The
ether extract, after being washed with sodium thiosul-
fate and subsequently with distilled water, was evapo-
rated to furnish the product. The esterification of
Scheme 1.
Keywords: esterification; transesterification; iodine.
* Corresponding author. Fax: +91-40-7193370; e-mail: kaimal@rediffmail.com
† IICT communication No. 01/09/12.
0040-4039/02/$ - see front matter © 2002 Published by Elsevier Science Ltd.
PII: S0040-4039(01)02235-3

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K. Ramalinga et al. / Tetrahedron Letters 43 (2002) 879–882
different acids such as saturated, unsaturated, hydroxy
and dicarboxylic acids with a variety of alcohols pro-
ceeded in high yields and the results are summarized in
Table 1. It was found that the esterification reaction
proceeds smoothly with primary, secondary and ter-
tiary aliphatic alcohols with the reactivity of the alco-
hols decreasing in the order primary>secondary>
tertiary. The yields of the products also showed a trend
in the same order as that of the reactivity. Esters of
tertiary alcohols which are otherwise difficult to prepare
are obtained in moderate yields (entry 12) but required
longer reaction times and increased amounts of cata-
lyst. In cases where a carboxylic acid group is directly
attached to an aromatic ring, such as benzoic acid,
there was no reaction. Wax esters, i.e. esters of long
chain carboxylic acids with long chain alcohols, which
are generally prepared via acyl chlorides, are also easily
prepared by this method. Butyl lactate, a valuable
intermediate for the production of butyl acrylate, is
prepared in an efficient manner by esterification of
commercial lactic acid (88%) with butanol even in the
presence of high amounts of water (12%) in the lactic
acid. Although esterification reactions are highly sensi-
tive to the presence of trace amounts of moisture, the
reaction catalyzed by iodine appears tolerant of high
amounts of water in the reaction system.
The results obtained in transesterification reactions are
summarized in Table 2. Transformations of esters from
lower to higher homologues and vice versa were
Table 1. Esterification of carboxylic acids with alcohols using iodine

K. Ramalinga et al. / Tetrahedron Letters 43 (2002) 879–882
881
Table 2. Transesterification of carboxylic acid esters with alcohols using iodine
achieved efficiently using this procedure. Transesterifica-
tion of a methyl ester to a t-butyl ester (entry 11) which
is normally problematic is achieved with this reagent but
transesterification with benzyl alcohol did not proceed.
While esterification of benzoic acid was not achieved
with this reagent, the transesterification of methyl ben-
zoate to butyl benzoate was accomplished with ease.
protocol described in this communication Jatropha cur-
cas seed oil containing 5–10% of free fatty acids could
be converted to methyl esters in a one-step reaction
(Table 2, entry 19).
The present procedure with iodine/alcohol provides a
very efficient method for esterification and transesterifi-
cation reactions. The notable advantages of this method
are: operational simplicity, the ready availability and
non-toxic nature of the reagent, general applicability,
mild reaction conditions and high yields. While esterifi-
cation and transesterification reactions are highly sensi-
tive to moisture, special precautions need not be taken
to exclude moisture or air from the system with
this catalyst. With the reported method, simultaneous
esterification and transesterification reactions can be
Vegetable oils were smoothly transesterified with
methanol (Table 2, entries 16 to 19). These esters are
presently gaining prominence as biodiesel. Vegetable
oils containing free carboxylic acids are conventionally
converted to esters in two steps: first, the free carboxylic
acids are converted to esters in the presence of an acid
catalyst and in the second step, the acylglycerols are
transesterified employing a basic catalyst. Using the

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K. Ramalinga et al. / Tetrahedron Letters 43 (2002) 879–882
carried out in a highly efficient manner. Very few
catalysts are known which catalyze esterification and
transesterification reactions and iodine is one such cata-
lyst which accomplishes both.
These procedures were followed for the esterification
and transesterification of all the substrates listed in
Tables 1 and 2. All the products are known compounds
and are easily identified by comparison of their physical
properties with those of authentic samples.16
Experimental
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General: The carboxylic acids and carboxylic esters
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alcohols were distilled before use. Iodine (LOBA Chem,
India) crystals was used as obtained.
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General procedure for simultaneous esterification and
transesterification: Jatropha oil (5 g), methanol (10 ml)
and iodine (50 mg), were refluxed for the specified time.
The progress of the reaction was monitored by TLC.
After the reaction, excess alcohol was removed under
reduced pressure and the residue was extracted with
diethyl ether. The ether extract was washed with a
solution of sodium thiosulfate and subsequently with
distilled water, dried over anhydrous sodium sulfate
and concentrated in vacuo to yield the crude product,
which was purified by column chromatography (hex-
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