Fluorochromate-catalyzed periodic acid oxidation of alcohols and aldehydes

Article abstract of DOI:10.1016/j.jfluchem.2005.07.012

Preparation of aldehydes and ketones from alcohols, and carboxylic acids from alcohols and aldehydes using pyridinium fluorochromate (PFC) as a catalyst and H₅IO₆ as the terminal oxidant is described here.

Full text of DOI:10.1016/j.jfluchem.2005.07.012

Journal of Fluorine Chemistry 126 (2005) 1356–1360
www.elsevier.com/locate/fluor
Fluorochromate-catalyzed periodic acid oxidation
of alcohols and aldehydes
*
Mo Hunsen
Department of Chemistry, Kenyon College, Tomsich Hall, Gambier OH 43022, USA
Received 28 June 2005; received in revised form 15 July 2005; accepted 15 July 2005
Available online 24 August 2005
Abstract
Preparation of aldehydes and ketones from alcohols, and carboxylic acids from alcohols and aldehydes using pyridinium fluorochromate
PFC) as a catalyst and H IO as the terminal oxidant is described here.
2005 Elsevier B.V. All rights reserved.
(
5
6
#
Keywords: Oxidation; Alcohols; Catalysis; Pyridinium fluorochromate (PFC); Carboxylic acids; Periodic acid; Aldehydes; Ketones
1
. Introduction
Recently, several groups have reported chromium-
catalyzed oxidations. Preparation of aldehydes and ketones
in a chromium(III)-catalyzed periodic acid oxidation is
reported [13a]. Oxidation of (homo-) allylic and (homo-)
propargylic alcohols to ketones and carboxylic acids is
achieved using Na Cr O /NaIO [13b]. A CrO -catalyzed
Oxidation, one the most fundamental reactions in
synthetic organic chemistry, has been the subject of
numerous studies [1,2]. Fluorochromates [3] and chlor-
ochromates [4] are two of the most favored reagents for
oxidation of organic substrates, particularly alcohols, under
2
2
7
4
3
[14] periodic acid oxidation of primary alcohols to
carboxylic acids that works very well for electron poor
benzylic alcohols is also reported. However, the CrO3-
catalyzed oxidation gives complex mixtures when it comes
to electron rich benzylic and homobenzylic alcohols. It also
gives lower yields for benzylic alcohols and fails for allylic
and propargylic alcohols. Our group have recently shown
that pyridinium chlorochromate (PCC) can be used
catalytically to oxidize alcohols to aldehydes and ketones
using the recyclable periodic acid as the co-oxidant [15a].
We have also shown that carboxylic acids can be prepared in
a PCC-catalyzed oxidation [15b].
mild conditions. Unlike CrO , halochromates have a long
3
shelf life and better solubility in organic solvents. However,
the carcinogenicity of chromium in combination with the
requirement of more than a stoichiometric amount of the
above reagents to complete the reaction is a significant
problem especially for large-scale industrial applications. In
light of this, there is a need for environmentally friendlier
oxidation reactions that retain the power of chromium
oxidations. In addition to fluorochromates and chlorochro-
mates, the Swern and co-workers [5] and Dess and Martin
[
6] oxidations are commonly used for preparation of
aldehydes and ketones. Current methods for direct conver-
sion of primary alcohols to carboxylic acids include RuCl3/
NaIO [7], CrO /H SO [8], TEMPO/NaClO [9], Na WO /
Various fluorochromates [3] have been shown to be mild
yet powerful oxidants. In an effort to show that fluorochro-
mates can be used catalytically instead of stoichiometrically
for mild oxidations and to further study the generality of
halochromate-catalyzed oxidations using Periodic acid as
the terminal oxidant, we have investigated pyridinium
fluorochromate (PFC) catalyzed oxidations. We report
herein a PFC-catalyzed oxidation of alcohols to aldehydes
4
3
2
4
2
4
H O [10], and TEMPO/NaClO in solution [11] and solid
2
2
2
[
12] phase.
*
Tel.: +740 427 5091; fax: +740 427 5731.
E-mail address: hunsenm@kenyon.edu.
0022-1139/$ – see front matter # 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2005.07.012

M. Hunsen / Journal of Fluorine Chemistry 126 (2005) 1356–1360
1357
moderate to excellent yields. An attempt to oxidize
cinnamyl alcohol resulted in the formation of a mixture
of products (data not shown). Oxidation of 1-naphthalene-
methanol (entry 5) gave the aldehyde with out oxidation of
the naphthalene ring unlike the CrO /H IO oxidation [16].
Scheme 1.
3
5
6
We hypothesize that the PFC/periodic acid combination
may form fluorochromatoperiodate (FCP), [17] possibly a
more powerful oxidizing agent than the fluorochromate
(
Scheme 2) that can accomplish oxidations not possible by
PFC alone. We further hypothesize that the covalently
attached fluoride ion may be facilitating the regeneration of
the catalyst. No addition of water was required in contrast to
the CrO /H IO [14] oxidation.
3
5
6
Next, we investigated the preparation of carboxylic acids
directly from primary alcohols using PFC/H IO . We used
5
6
only a catalytic (2 mol%) amount of pyridinium fluoro-
chromate and 2.2 equivalent of the co-oxidant, H IO , for a
5
6
clean and quantitative conversion of primary alcohols to
carboxylic acids (Scheme 3). As shown in Table 2, various
primary alcohols were directly oxidized with PFC/H IO to
5
6
give the corresponding carboxylic acids in quantitative
yields. Benzylic (entries 1, 4–6), aliphatic (entries 2, 9 and
10) as well as homobenzylic (entries 3 and 7) alcohols were
Scheme 2.
oxidized smoothly in a short amount of time. Both electron
poor (entries 5 and 6) as well as electron rich (entry 1) benzyl
alcohols were also quantitatively oxidized with out any
problem. The electron rich homobenzylic alcohol (entry 7)
was also oxidized effortlessly. It is worth mentioning that
and ketones, and alcohols and aldehydes to carboxylic acids
using only 2 mol% of pyridinium fluorochromate and
stoichiometric amounts of the co-oxidant, H IO , in
unlike the CrO catalyzed [14] oxidation, the PFC-catalyzed
3
5
6
acetonitrile (Schemes 1–4).
oxidation works very well for benzylic alcohols as well as
for electron rich benzylic and homobenzylic alcohols. The
naphthalene ring (entry 8) did not get oxidized under the
above mentioned reaction conditions. It is noteworthy that in
a control experiment where the reaction was repeated under
the same conditions but in the absence of PFC, no oxidation
of benzyl alcohol to benzaldehyde or benzoic acid was
observed. We hypothesize that the mechanism may involve
oxidation of the hydrates of the aldehydes that would form
2
. Results and discussion
First, we investigated the preparation of aldehydes and
ketones. Various alcohols were oxidized with PFC/H IO to
5
6
give the corresponding aldehydes and ketones mostly in
quantitative yields and the results are shown in Table 1.
Benzylic 28 alcohols (entries 3 and 4) were oxidized
smoothly to give the ketones in a short amount of time. The
aliphatic (entry 2) and homobenzylic (entry 1) 28 alcohols
were also oxidized cleanly to the corresponding ketones
with out any problems. Benzyl alcohols (entries 6–8) were
oxidized effortlessly to give the corresponding aldehydes in
under the reaction condition (with the H
generate the carboxylic acids.
O byproduct) to
2
Lastly, we investigated the oxidation of aldehydes to
carboxylic acids (Scheme 4). Aldehydes were oxidized in a
shorter amount of time and the clean carboxylic acids were
obtained quantitatively. The procedure for the oxidation of
aldehydes to carboxylic acids was the same as the one for the
direct conversion of primary alcohols to carboxylic acids
except for the use of 1.1 equivalent of periodic acid and the
shorter reaction time (90 min). As shown in Table 3,
aliphatic aldehydes (entries 1 and 2) were oxidized cleanly.
Benzaldehyde (entry 3) as well as electron rich (entries 4 and
Scheme 3.
7), and electron poor (entries 5, 6, 8, and 9) benzaldehydes
were also oxidized effortlessly to deliver the corresponding
carboxylic acids quantitatively.
In conclusion, we have shown for the first time that
fluorochromates efficiently catalyze the oxidation of
alcohols to aldehydes and ketones, and alcohols and
Scheme 4.

1358
M. Hunsen / Journal of Fluorine Chemistry 126 (2005) 1356–1360
Table 1
Oxidation of alcohols to aldehydes and ketones with PFC/H
a
5
IO
6
b
Entry
1
Substrate
Product
Yield (%)
9
9
2
3
95
9
9
9
6
7
8
4
5
6
7
6
9
7
0
8
5
3
a
5 6
The reactions were conducted in acetonitrile using 1.05 equivalent of H IO and 2 mol% PFC at 0 8C for 2 h. The products were characterized by
comparing their NMR spectra with those reported by Aldrich and with authentic samples.
b
Isolated yield.
aldehydes to directly to carboxylic acids using periodic acid
as the terminal oxidant in moderate to excellent yields in a
short amount of time. The protocols described in this work
represent greener alternatives to the stoichiometric fluor-
ochromate oxidations.
100 mL ethyl acetate and washed with 1:1 brine:water,
saturated aq. Na SO solution, and brine, respectively, dried
over anhydrous Na SO and concentrated to give the ketone.
2
3
2
4
The crude product was purified by silica gel flash
chromatography (hexanes:ethyl acetate, 8:1) to yield
0.67 g (99%) of phenyl acetone.
3
. Experimental
3.2. Representative procedure for preparation of
carboxylic acids: synthesis of p-methyl benzoic acid
(Table 2, entry 1)
3.1. Representative procedure for preparation of
aldehydes and ketones: synthesis of phenylacetone
(Table 1, entry 1)
To 40 mL of acetonitrile was added 2.50 g (11 mmol) of
H IO and stirred vigorously at r.t. for 15 min. p-Methyl
5
6
To 40 mL of acetonitrile was added 1.20 g (5.2 mmol) of
H IO and stirred vigorously at r.t. for 15 min. 3-Phenyl-2-
benzyl alcohol (0.61 g, 5 mmol) was then added (in ice-
bath) followed by addition of 22 mg (2 mol%) PFC in 10 mL
acetonitrile (in two portions) and the reaction mixture was
stirred for 3 h. The reaction mixture was then diluted with
100 mL ethyl acetate and washed with 1:1 brine:water,
5
6
propanol (0.69 g, 5 mmol) was then added (in ice-bath)
followed by addition of 22 mg (2.0 mol%) PFC in 10 mL
acetonitrile (in two portions) and the reaction mixture was
stirred for 2 h. The reaction mixture was then diluted with
saturated aq. NaHSO solution, and brine, respectively, dried
3

M. Hunsen / Journal of Fluorine Chemistry 126 (2005) 1356–1360
1359
Table 3 (Continued )
Table 2
Direct oxidation of 18 alcohols to carboxylic acids with PFC/H
a
5
IO
6
Entry
6
Substrate
Product
Yield (%)
98
Entry
Substrate
Product
Yield
%)
(
1
9
8
7
8
9
9
9
2
2
3
99
98
4
5
95
9
98
9
9
9
9
8
8
a
The reactions were conducted in acetonitrile using 1.1 equivalent of
and 2 mol% PFC for 1.5 h at 0 8C. The products were characterized
by comparing their NMR spectra with those reported by Aldrich and with
6
7
8
H
5
IO
6
authentic samples.
over anhydrous Na SO and concentrated to give the
2
4
carboxylic acid (0.65 g, 96% yield).
Acknowledgment
9
9
9
6
MH thanks Kenyon College for the generous start up
fund.
9
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1
0
99
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