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OH
OH
Au/graphite (1 mol%)
HO
OH
HO
OH
O
2
, H
2
O, NaOH, 60°C
O
d
n
4
r
4
n
g
|
6
Scheme 10.3 Glycerol oxidation to glyceric acid.
deposited on carbon nanotubes. Such nanohybrid structures were able to
convert benzylic alcohol selectively to benzoic acid when employing toluene-
water (1 : 1) as solvent, while the reaction afforded benzaldehyde selectively
when THF was employed. Upon addition of H
2
O to the reaction mixture,
benzaldehyde was further oxidized into benzoic acid in 99% yield.
11
10.5 Oxidation of Propargyl Alcohols
Vanadium is certainly the metal of choice for oxidizing secondary propargyl
alcohols to the corresponding ketones, as widely discussed in Chapter 6. The
use of 1 mol% VO(acac)
2
in acetonitrile at 80 1C oxidized a variety of
propargyl alcohols, including aryl, vinyl, alkynyl and aliphatic substrates
(see also Chapter 6, Scheme 6.16).
12
General procedure for the oxidation of propargylic alcohols.
12b
To a solution
of VO(acac)
2
(2.65 mg, 0.01 mmol) in acetonitrile (1.5 mL) in a 10 mL two-
necked round-bottomed flask was added MS 3Å (500 mg, powder). Next, a
solution of propargylic alcohol (1 mmol) in acetonitrile (0.5 mL) was
added and the resulting mixture was stirred. Oxygen gas was then
introduced into the flask from an O
2
balloon under atmospheric pressure
and the mixture was stirred vigorously for 3 h at 80 1C under oxygen. The
mixture was then cooled to room temperature and MS 3Å was separated
by filtration through a glass filter. The amount of the product was
determined by GLC analysis. For isolation of the product, the solvent was
evaporated and the residue was purified by column chromatography
(Merck silica gel 60; hexane-ethyl acetate as eluent).
.
A practical synthetic procedure for the conversion of propargyl alcohol to
propionaldehyde on a fairly large scale (56 g) was also reported recently by
Liu and Ma employing Fe(NO
3
)
3
9H
2
O, TEMPO and NaCl as catalysts, with
oxygen at room temperature in p-xylene.
13
Further details can be found in
Chapter 6.
10.6 Nanoparticles Preparation
Palladium and gold catalysts have been found particularly active in the form
of nanoparticles. The general routes to nanocluster/nanoparticle synthesis
involve chemical reduction of transition metal salts with a reducing agent in
the presence of a stabilizer for the metal. The resulting stabilized metal
nanoclusters dispersed in solution can be used as catalysts as such or
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