Efficient synthesis of aromatic carboxylic acids from aryl ketones in ionic liquid

Article abstract of DOI:10.1080/00397910500503611

Conversion of aryl ketones to the corresponding aromatic carboxylic acids has been achieved using sequential treatment of HDNIB and urea-hydrogen peroxide in [bmim]BF₄ ionic liquid. Copyright Taylor & Francis Group, LLC.

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Efficient Synthesis of Aromatic Carboxylic
Acids from Aryl Ketones in Ionic Liquid
a
a
Jong Chan Lee & Jang Mi Lee
a
Department of Chemistry, Chung‐Ang University, Seoul, South Korea
Version of record first published: 16 Aug 2006.
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Acids from Aryl Ketones in Ionic Liquid, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 36:8, 1071-1074
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Synthetic Communications , 36: 1071–1074, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500503611
Efficient Synthesis of Aromatic Carboxylic
Acids from Aryl Ketones in Ionic Liquid
Jong Chan Lee and Jang Mi Lee
Department of Chemistry, Chung-Ang University, Seoul, South Korea
Abstract: Conversion of aryl ketones to the corresponding aromatic carboxylic acids
has been achieved using sequential treatment of HDNIB and urea–hydrogen peroxide
in [bmim]BF ionic liquid.
4
Keywords: Carboxylic acids, ionic liquid, ketones, peroxide
The oxidative carbon–carbon cleavage reaction of aryl ketones to aromatic
carboxylic acids is a fundamental reaction in organic synthesis. In general,
oxidative degradation reactions of aryl ketones are generally conducted in
strong acidic or basic conditions. A number of oxidative reagents have been
developed for the carbon–carbon cleavage reaction of aryl ketones in acidic
[
1]
[2]
systems such as Mn(NO ) /Co(NO )
Re O /tert-butyl hydroperoxide,
2 7
3
2
3 2,
[3]
and sodium nitrite/pyridinium poly(hydrogen fluoride). The reported
reagent systems utilizing basic conditions for the oxidative degradation of
[
4]
[5]
aryl ketones include KOH/DMF, NaClO/b-cyclodextrin, tert-BuOK/
[
6]
[7]
1
,3-dinitrobenzene,
and tert-BuOK/sodium percarbonate.
There are
only a few literature methods that are conducted in neutral reaction conditions
for the conversion of ketones to the corresponding carboxylic acids. Examples
[8]
of these methods utilize pentafluoroiodobenzene bis(trifluoroacetate) and
[9]
N-bromophthalimide/mercuric(II) acetate.
Recently, we have found an efficient route, occurring under neutral
conditions, for the oxidation of aryl ketones into the carboxylic acids using
initial reaction of aryl ketones with [hydroxy(2,4-dinitrobenzenesulfonyloxy)
iodo]benzene (HDNIB) in acetonitrile, followed by the reaction with
Received in Japan August 25, 2005
Address correspondence to Jong Chan Lee, Department of Chemistry, Chung-Ang
University, Seoul 156-756, South Korea. Fax: þ82-2-825-4736; E-mail: jclee@cau.ac.kr
1
071

1
072
J. C. Lee and J. M. Lee
Scheme 1.
[10]
tetrabutylammonium (meta)periodate in refluxing 1,4-dioxane.
However,
the necessary switching of the reaction solvents during the reaction
procedure makes this protocol rather inconvenient for practical applications.
Therefore, it would be very desirable to develop the oxidative degradation
reactions of aryl ketones occurring under a single solvent in one-pot con-
ditions. We envisioned that a HDNIB/urea–hydrogen peroxide addition
[11]
compound (UHP) combination in ionic liquid
could behave in a way
similar to the HDNIB/tetrabutylammonium (meta)periodate system. After
examination of the usefulness of HDNIB/UHP oxidation system, we have
newly found that the sequential treatment of aryl ketones with HDNIB and
UHP in 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim]BF , success-
4
fully afforded the corresponding aromatic carboxylic acids (Scheme 1).
Treatment of a-[(2,4-dinitrobenzene)sulfonyloxy] ketone intermediates,
preformed via the reaction of ketones with HDNIB for 1 h at 608C in
[
bmim]BF with UHP, afforded the corresponding carboxylic acids in high
4
yields. The results are summarized in Table 1. As shown in Table 1, both
aryl methyl ketones and aryl methylene ketones were oxidized equally well
Table 1. Oxidative conversion of aryl ketones to carboxylic acids
a
Entry
Substrate
Product
Yield (%)
1
2
3
4
5
6
7
8
9
Acetophenone
Benzoic acid
85
78
78
80
76
66
80
76
78
75
78
67
4-Methylacetophenone
4-Bromoacetophenone
4-Chloroacetophenone
4-Fluoroacetophenone
4-Nitroacetophenone
Propiophenone
4-Methylbenzoic acid
4-Bromobenzoic acid
4-Chorobenzoic acid
4-Fluorobenzoic acid
4-Nitrobenzoic acid
Benzoic acid
4-Methylpropiophenone
4-Bromopropiophenone
4-Chloropropiophenone
4-Fluoropropiophenone
Butyrophenone
4-Methylbenzoic acid
4-Bromobenzoic acid
4-Chlorobenzoic acid
4-Fluorobenzoic acid
Benzoic acid
1
1
1
0
1
2
a
Isolated yield.

Synthesis of Aromatic Carboxylic Acids
1073
in high yields. The yields of the carboxylic acids obtained in this study are
[10]
always superior to the previous results obtained using HDNIB/Bu NIO .
4
4
Replacement of UHP by the Bu NIO at the present reaction conditions
4
4
gave much lower yields of the carboxylic acids. The use of conventional
organic solvents (CH Cl and CH CN) instead of the [bmim]BF gave the
2
2
3
4
negligible formation of the carboxylic acid at the present reaction conditions.
Presumably, the oxidative cleavage reactions occurred via well-known
a-hydoxyperoxo ketones formed by the reaction of a-[(2,4-dinitrobenzene)-
[1]
sulfonyloxy] ketone intermediates with UHP.
In summary, we have developed a new and efficient method for the
oxidative degradation reaction of aryl ketones to the corresponding aromatic
carboxylic acids by the treatment with HDNIB and UHP in [bmim]BF4
ionic liquid.
EXPERIMENTAL
The 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4) was
obtained from Fluka. The HDNIB was prepared by following the method
[
10]
presented in the literature.
General Procedure for Oxidative Cleavage Reaction
of Aryl Ketones
HDNIB (0.562 g, 1.2 mmol) was added to a solution of ketones (1.0 mmol) in
[
bmim]BF (1 mL). The mixture was stirred for 1 h at 608C. UHP (0.141 g,
4
1
.5 mmol) was added to the solution, and the reaction continued for an
additional 2–6 h. After completion of the reaction, the product was
extracted with diethyl ether (30 mL) and washed with aqueous 10% sodium
carbonate solution (2 ꢀ 20 mL). The aqueous layer was neutralized with
dilute hydrogen chloride, and the product was extracted with diethyl ether
(
2 ꢀ 25 mL). The organic layer was dried over sodium sulfate and evaporated
to give the desired carboxylic acid.
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