Angewandte
Communications
Chemie
Heterogeneous Catalysts
An Efficient Iron(III)-Catalyzed Aerobic Oxidation of Aldehydes in
Water for the Green Preparation of Carboxylic Acids
Han Yu+, Shi Ru+, Guoyong Dai+, Yongyan Zhai, Hualin Lin, Sheng Han,* and Yongge Wei*
Abstract: The first example of a heterogeneous iron(III)-
catalyzed aerobic oxidation of aldehydes in water was
developed. This method utilizes 1 atmosphere of oxygen as
the sole oxidant, proceeds under extremely mild aqueous
conditions, and covers a wide range of various functionalized
aldehydes. Chromatography is generally not necessary for
product purification. Its operational simplicity, gram-scale
oxidation, and the ability to successively reuse the catalyst,
make this new methodology environmentally benign and cost
effective. The generality of this methodology gives it the
potential to be used on an industrial scale.
Oxidation is one of the most fundamental reactions in
nature with the oxidation of aldehydes to carboxylic acids
being one of the most well-known and most frequently used
methodologies.[1] Although carboxylic acids are readily
obtained in the laboratory by oxidation of the corresponding
aldehydes, highly efficient and environmentally benign trans-
formations of aldehydes into carboxylic acids still remain
challenging.[2] Even today, the majority of these oxidation
reactions require stoichiometric amounts of hazardous oxi-
dants such as KMnO4,[3] CrO3,[4] KHSO5,[5] KIO4,[6] etc., and
often take place in harmful solvents (Figure 1a). Thus,
environmentally benign oxidization protocols are greatly
desired. Molecular oxygen possesses a number of advantages
over other oxidants, and reactions that use molecular oxygen
have a high atom economy and produce water as the only
byproduct. However, catalytic oxidations of aldehydes into
carboxylic acids with molecular oxygen as a terminal oxidant
remain scarce. The limited number of catalysts available for
the direct activation of molecular oxygen and the need for
rare and expensive noble metals as catalysts restricts its
use.[7–10] Moreover, most of the systems reported so far require
Figure 1. Oxidation of aldehydes into carboxylic acids.
the use of expensive metals, ligands that are not commercially
available, and aerobic catalyst systems than cannot be
recycled, thus leading to prohibitively expensive costs for
practical application.[11–13] Therefore, the use of inexpensive
and earth-abundant transition-metal catalyst systems, which
employ molecular oxygen as a terminal oxidant, are highly
desired. The natural abundance of water and its inherently
greener characteristics compared to common organic sol-
vents, makes it extremely attractive for the development of
more environmentally benign reactions.[14] Recently, catalytic
aerobic oxidation methodology has received a great deal of
attention because of its high efficiency and operational
simplicity. For example, Li et al.[2] reported the first example
of a homogeneous silver- or copper-catalyzed aerobic oxida-
tion in water, successfully oxidizing various aldehydes into
carboxylic acids with almost 100% conversion under mild
reaction conditions (Figure 1b). Nevertheless, such method-
ologies are uncommon and the organic ligands employed in
these reactions are susceptible to oxidative self-degradation
and limits their usefulness.
[*] Dr. H. Yu,[+] S. Ru,[+] G. Dai,[+] Y. Zhai, Dr. H. Lin, Prof. S. Han
School of Chemical and Environmental Engineering
Shanghai Institute of Technology
Polyoxometalates (POMs),[15] a large class of structurally
well-defined anionic molecular metal-oxygen clusters with
more-stable thermal and oxidative redox properties than
organometallic complexes, have been used extensively as
efficient catalysts in a number of oxidation reactions because
of both their resistance towards oxidation and compatibility
with various oxygen sources.[16] In particular, POMs are
commonly used as soluble molecular oxide supporters to
assist metal ions for homogeneous catalysis. In this respect,
Anderson-structured POMs[17] are very important since they
consist of a single metal atom supported by a polymolybdate
or polytungstate. This polymolybdate or polytungstate is
composed of six-edge sharing MO6 (M = W or Mo) octahedra
surrounding a central, edge-sharing metal heteroatom octa-
hedron (XO6) with six protons.
100 Haiquan Road, Shanghai 201418 (P.R. China)
E-mail: hansheng654321@sina.com
Dr. H. Yu,[+] Prof. Y. Wei
Key Lab of Organic Optoelectronics & Molecular Engineering
of Ministry of Education, Department of Chemistry
Tsinghua University, Beijing 100084 (P.R. China)
E-mail: yonggewei@tsinghua.edu.cn
Prof. Y. Wei
State Key Laboratory of Natural and Biomimetic Drugs
Peking University, Beijing 100191 (P.R. China)
E-mail: ygwei@pku.edu.cn
[+] These authors contributed equally to this work.
Supporting information for this article can be found under:
Angew. Chem. Int. Ed. 2017, 56, 1 – 6
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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