SHORT COMMUNICATION
DOI: 10.1002/ejoc.200801176
Iron-Catalyzed One-Pot Oxidative Esterification of Aldehydes
Xiao-Feng Wu[a] and Christophe Darcel*[a]
Keywords: Iron / Esterification / Aldehydes / Homogeneous catalysis / Oxidation
A highly efficient, mild, and simple protocol for Fe(ClO4)3·
xH2O-catalyzed oxidative esterification of aldehydes was de-
veloped. Several aromatic and aliphatic aldehydes reacted
with simple primary and secondary alcohols, used as the sol-
vent, smoothly in the presence of an iron salt catalyst
(10 mol-%) and hydroperoxide (4 equiv.) as an oxidant to
generate the corresponding esters in good to excellent yields.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
friendly ones. Despite the fact that the coordination chemis-
try of iron was widely developed in the past decades, it is
really surprising that until lately, iron was underrepresented
in the field of homogeneous catalysis relative to the other
transition metals. However, the last few years have seen a
rise in the use of iron as a catalyst, and very efficient pro-
cesses that are now able to compete with other metal-
catalyzed ones have emerged in the carbon–carbon bond-
formation, hydrosilylation, oxidation, and even hydrogena-
tion areas.[16]
Introduction
The development of synthetic strategies towards esters
has attracted the interest of chemists for more than 100
years due to the significance and omnipresence of these
compounds. The most common strategy for the preparation
of carboxylic acid ester derivatives under mild conditions
usually involves the stoichiometric activation of the parent
acid as an acyl halide, anhydride, or activated ester (in situ
or otherwise) amenable to subsequent nucleophilic substitu-
tion.[1] An interesting and potentially valuable alternative
transformation in which there has been a recent resurgence
in interest is the oxidative esterification of aldehydes under
mild conditions.[2] These one-pot conventional methods re-
ported require the use of stoichiometric heavy-metal oxi-
dants such as KMnO4,[3] CrO3,[4] hydrogen peroxide,[5]
ozone,[6a] oxone,[6b] N-iodosuccinimide,[7] or expensive
transition-metal catalysts such as vanadium,[8a] rhenium,[8b]
silver,[9] palladium,[10] ruthenium,[11] rhodium,[12] copper,[13]
titanium,[14] iridium,[15] and so on. From a viewpoint of
green chemistry, this transition-metal-catalyzed oxidative
esterification is expected to be a versatile procedure directly
giving esters from aldehydes and alcohols. In the environ-
mental context of today, one of the challenging issues for
chemists is to develop cost-effective, green, mild, and
efficient catalytic routes that minimize hazardous waste. In
contrast, many catalysts are derived from heavy or rare
metals and their toxicity and prohibitive prices can consti-
tute severe drawbacks for large-scale applications. In con-
trast, iron is one of the most abundant metals on the earth,
and one of the most inexpensive and environmentally
We disclose herein an oxidative esterification of a variety
of aldehydes with simple alcohols as solvents in the pres-
ence of a catalytic amount of Fe(ClO4)3·xH2O in combina-
tion with H2O2 as oxidant at room temperature in air.
Results and Discussion
In the initial attempts to improve this iron-catalyzed oxi-
dative esterification of aldehydes, benzaldehyde (1a) was
chosen as a test substrate to optimize the reaction condi-
tions (Scheme 1). An ethanol solution of 1a was allowed to
react with H2O2 (4 equiv.) at room temperature in the pres-
ence of a catalytic amount of iron salt (10 mol-%). It may
be pointed out that the hydroperoxide water solution must
be added slowly at 0 °C over 4 h to avoid the formation of
the corresponding benzoic acid. After stirring for a period
of one additional hour at 0 °C, and 15 h at room tempera-
ture, the reaction afforded the ester product. We then car-
ried out extensive investigations to define the best reaction
conditions, and Table 1 lists representative data obtained
for the oxidative esterification with various commercially
available iron(II) and iron(III) salts.
[a] UMR 6226 CNRS-Université de Rennes 1 “Sciences Chimiques
de Rennes”, Equipe “Catalyse et Organométalliques”, Campus
de Beaulieu, Bat 10C,
First of all, iron salts such as Fe(OAc)2, Fe(acac)2, or
Fe(acac)3 were not able to promote any oxidative esterifica-
tion reaction under our standard conditions (Table 1, En-
tries 1–3). By employing commercially available, classical
anhydrous or hydrated FeCl2 and FeCl3 precursors as a cat-
alyst, only moderate isolated yields were obtained (20–45%)
Avenue du Général Leclerc, 35042 Rennes Cedex, France
Fax: +33-2-23236939
E-mail: christophe.darcel@univ-rennes1.fr
Supporting information for this article is available on the
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Eur. J. Org. Chem. 2009, 1144–1147