Catalytic oxidations of alcohols - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 148

7. CATALYTIC OXIDATION OF ALCOHOLS WITH
HYDROGEN PEROXIDE AND ALKYL HYDROPEROXIDES
In the aerobic oxidations discussed in the preceding sections the most
effective catalysts tend to be late transition elements, e.g. Ru and Pd, that
operate via oxometal or hydridometal mechanisms. In contrast, the most
effective catalysts with or as the oxidant tend to be early
transition metal ions with a d° configuration, e.g. Mo(VI), W(VI) and
Re(VII), that operate via peroxometal pathways. Ruthenium and palladium
are generally not effective with because they display high catalase
activity, i.e. they catalyze rapid decomposition of Early transition
elements, on the other hand, are generally poor catalysts for
decomposition.
One of the few examples of ruthenium-based systems is the
bromide combination reported by
Sasson and coworkers 85 . This system catalyzes the selective oxidation of a
variety of alcohols, at high (625:1) substrate:catalyst ratios, in an
aqueous/organic biphasic system. However, 3-6 equivalents of were
required, reflecting the propensity of ruthenium for catalyzing non-
productive decomposition of
Jacobsen and coworkers 86 showed, in 1979, that anionic
molybdenum(VI) and tungsten(VI) peroxo complexes are effective oxidants
for the stoichiometric oxidation of secondary alcohols to the corresponding
ketones. Subsequently, Trost and Masuyama 87 showed that ammonium
molybdate, (10m%), is able to catalyze the selective
oxidation of secondary alcohols, to the corresponding ketones, using
hydrogen peroxide in the presence of tetrabutylammonium chloride and a
stoichiometric amount of a base It is noteworthy that a more
hindered alcohol moiety was oxidized more rapidly than a less hindered one,
e.g. Reaction 24.
The above mentioned reactions were performed in a single phase using
tetrahydrofuran as solvent. Subsequently, the group of Di Furia and Modena