Chemistry Reference
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Molybdenum- and tungsten-containing heteropolyanions are also
effective catalysts for alcohol oxidations with
91-96
. For example,
or in combination with cetylpyridinium chloride as
a phase transfer agent, were shown by Ishii and coworkers
90-94
to be effective
catalysts for alcohol oxidations with
in a biphasic, chloroform/water
system.
Methyltrioxorhenium (MTO) also catalyzes the oxidation of alcohols
with
via
a peroxometal pathway
97,98
. Primary benzylic and secondary
aliphatic alcohols afforded the corresponding aldehydes and ketones,
respectively, albeit using two equivalents of In the presence of
bromide ion the rate was increased by a factor 1,000
98
. In this case the active
oxidant may be hypobromite (HOBr), formed by MTO-catalyzed oxidation
of bromide ion by
Molybdenum
99-102
and vanadium compounds
103
have also been widely
investigated as catalysts for the oxidation of alcohols with
tert
-butyl
hydroperoxide (TBHP) as the oxidant. With the former a peroxometal
pathway is involved while with the latter an oxovanadium(V) intermediate is
the active oxidant. As with the systems described above, these
systems exhibit a preference for the oxidation of secondary hydroxyl
functionalities over primary ones. In contrast, zirconyl acetate,
catalyzes the selective oxidation of primary alcohol moieties with TBHP
(Reaction 29)
104
.
Polymer-supported tetrabromooxomolybdate(V) was claimed to be a
heterogeneous catalyst for alcohol oxidations with TBHP
102
. However, it
seems likely that molybdenum is leached from the surface and the observed
catalysis may be, at least partially, homogeneous in nature. The same applies
to Cr(III) and Ce(IV) catalysts supported on a perfluorinated sulfonic acid
resin (Nafion
®
K) which catalyze the oxidation of alcohols with TBHP
105
.
Similarly, vanadium-pillared montmorillonite clay (V-PILC)
106
and a
zeolite-encapsulated vanadium picolinate complex
107
were shown to catalyze
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