Catalytic oxidations of alcohols - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 147

in combination with N-hydroxyphthalimide (NHPI) as
cocatalyst mediates the aerobic oxidation of primary and secondary alcohols,
to the corresponding carboxylic acids and ketones, respectively, e.g.
Reaction 20 83 .

By analogy with other oxidations mediated by the Co/NHPI catalyst
studied by Ishii and coworkers 84 , Reaction 20 probably involves a free
radical mechanism. We attribute the promoting effect of NHPI to its ability
to efficiently scavenge alkylperoxy radicals, suppressing the rate of
termination by combination of alkylperoxy radicals. The resulting PINO
radical subsequently abstracts a hydrogen atom from the bond of the

alcohol to propagate the autoxidation chain (Reactions 21-23).