Pergamon Tetrahedron Letters 41 (2000) 1439–1442
TETRAHEDRON
LETTERS
Hydrogen peroxide oxidation of aldehydes to carboxylic acids:
an organic solvent-, halide- and metal-free procedure
Kazuhiko Sato, Mamoru Hyodo, Junko Takagi, Masao Aoki and Ryoji Noyori
*
Department of Chemistry and Research Center for Materials Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan
Received 8 November 1999; revised 29 November 1999; accepted 1 December 1999
Abstract
Aqueous hydrogen peroxide oxidizes aldehydes to carboxylic acids under aqueous/organic biphasic conditions
without affecting olefinic or alcoholic functions © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: aldehydes; Baeyer–Villiger reaction; carboxylic acids; hydrogen peroxide; oxidation; quaternary ammonium salts.
Despite the growing awareness of the need for ‘green chemistry’, many chemists still use environmen-
tally unacceptable reagents or unnecessarily sophisticated conditions for the oxidation of aldehydes.
1–3
Certain aldehydes can be oxidized to carboxylic acids with 3–60% aqueous H
2
O
2
without organic
solvents or metallic catalysts. Here we propose a very simple procedure which is suitable for medium
and large scale reactions.
Ignoring the ability of aqueous H
2
O
2
to oxidize aldehydes, tremendous efforts have been made to
develop metal-based catalysts
4
and inorganic
5
or organic promoters
6
for the oxidation of aldehydes. In
1941, Späth found that H
2
O
2
reacts with dodecanal to form a perhydrate, which decomposes slowly at
120°C to give dodecanoic acid.
7
Since then aqueous H
2
O
2
has been considered to have a weak ability to
oxidize aldehydes. Some benzaldehyde derivatives can be converted to methyl benzoates with 31% H
2
O
2
in methanol containing 38 mol% H
2
SO
4
,
8
and a patent claimed that 35% H
2
O
2
in dioxane containing HBr
oxidizes aldehydes to carboxylic acids.
9
However, the general capability of H
2
O
2
to oxidize aldehydes
to carboxylic acids has not yet been reported explicitly in academic literature. During our recent study
of the alcohol dehydrogenation reaction,
10
we found that the oxidation of some aliphatic and aromatic
aldehydes with H
2
O
2
proceeds under aqueous/organic biphasic conditions without organic solvents,
halides, or metal catalysts (Scheme 1). The reaction is catalyzed simply by an acid. Thus, when a mixture
of octanal, 30% H
2
O
2
, and [CH
3
(n-C
8
H
17
)
3
N]HSO
4
(QHSO
4
) in a 200:220:1 molar ratio was heated at
90°C for 2 h with magnetic stirring at 1000 rpm, octanoic acid was obtained with a yield of 82%. Without
stirring under otherwise identical conditions, the yield was lowered to 73%. The reaction at 70°C gave the
carboxylic acid with a yield of only 4%. When a biphasic mixture of octanal and 30% H
2
O
2
was stirred
at 1000 rpm at 90°C without the acidic quaternary ammonium salt, octanoic acid was produced in a yield
*
Corresponding author.
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(99)02310-2
tetl 16238