Catalysis Communications
Short Communication
Oxidative esterification of alcohols and aldehydes using supported iron
oxide nanoparticle catalysts
a,
b
b
Fatemeh Rajabi ⁎, Rick A.D. Arancon , Rafael Luque
a
Department of Science, Payame Noor University, P.O. Box: 19395-4697, Tehran, Iran
Departamento de Quimica Organica, Universidad de Córdoba, Edificio Marie Curie (C-3), Ctra Nnal IV-A, Km 396, E14014 Cordoba, Spain
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 July 2014
Received in revised form 8 September 2014
Accepted 12 September 2014
Available online 22 September 2014
The synthesis of esters has become an important industrial methodology over the past years because of the role
that they serve in the chemical industry. In this study, we present the use of a novel catalyst for the direct
conversion of aldehydes into esters. The yields obtained using supported iron oxide nanoparticle catalysts
(FeNP) are very high (N90%). The catalyst is also shown to be very stable as shown by the recyclability study
(up to 11 times).
©
2014 Published by Elsevier B.V.
Keywords:
Supported iron oxide nanoparticles
Oxidative esterification
Room temperature catalysis
1
. Introduction
The current movement towards more sustainable fuels has urged
used cannot be recovered and recycled, making the entire process not so
cost effective. Recently, heterogeneous catalysts have been proposed for
these reactions [13].
scientific research to also move towards greener and more efficient
catalytic systems for synthesis. One organic reaction which has gained
popularity in the recent years is the synthesis of esters either from
carboxylic acids or from aldehydes. For carboxylic acid starting sub-
strates, methyl esters are commonly produced via base/acid homoge-
neous catalysis [1]. For esterification reactions involving carboxylic
acids, heterogeneous catalysis had also been used [2]. Most heteroge-
neous catalysts present are acidic in nature and have the ability to
perform simultaneous esterification and transesterification reactions.
One example is the use of metal oxides of aluminum and zinc for the
conversion of soybean oil into methyl esters [3] reaching very high
yields up to 89%. Tin oxide, one of the catalysts under investigation,
was shown to be relatively stable (~10 times of re-use without activa-
In this work, we report the use of supported iron oxide nanoparticles
(FeNP) for the oxidative esterification of various aldehyde substrates.
The use of FeNP is especially industrially attractive because of the
benign nature of iron and the good catalytic activity of nanoparticles.
In this work, we were able to produce esters with very high yields
using a stable and recyclable FeNP catalyst.
2. Experimental
The catalyst was prepared according to a previously established
protocol [14]. The characteristics of the FeNP materials used herein are
almost identical to those previously reported [14], including those after
reaction/reuses and so will not be included in this contribution. NMR
spectra of representative structures can be found in the Supplementary
information.
tion). Similar studies had also been reported with CaO [4], ZnO–La
2 3
O
[5], sulfated zirconia [6], and sulfated carbon [7,8]. Another route for
this synthesis is via direct oxidation of an aldehyde in the presence of
an alcohol to produce an ester. In the past, this organic reaction is
usually performed using a ruthenium catalyst [9], vanadium oxide [10,
2.1. Oxidative reactions
1
1], and copper [12]. The primary mechanism of the reaction involves
the formation of the hemiacetal intermediate upon reaction with the
alcohol — this reaction is mediated by the presence of the metal acting
as a Lewis acid that chelates with the carbonyl oxygen. These reactions
have been reported to be efficient, however, the time to produce a
decent ester yield is usually very high. Also, the homogeneous catalysts
FeNP (0.01 mmol, 10 mol%) was added to a solution of aldehyde
(1 mmol) in 2 mL of ethanol or methanol. Then 2 mmol of 33% H O
2 2
was slowly added under constant stirring and the reaction was further
left at room temperature for 20 h. The reaction progress was monitored
by thin layer chromatography (TLC). After filtration of the supported
iron catalyst, the solvent was removed under vacuum and the residue
was purified by column chromatography using the solvent system
hexane/ethyl acetate at a ratio 9:1. The purified fractions were then
⁎
566-7367/© 2014 Published by Elsevier B.V.
1