Catalytic oxidations using cobalt(II) complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 297

Remarkably, primary C-H bonds are more reactive than the weaker
secondary C-H bonds or C-H bonds in to an alcohol functionality.
Under illumination by a 450 W high pressure mercury lamp at 30°C and
1 atm -chlorobenzaldehyde undergo oxidation by

molecular oxygen in the presence of Co(II) tetraphenylporphyrin,
Co(II)[ meso- tetra (benzoyloxy-phenyl)porphyrin] (CoTBCOPP) and Co(II)-
[

benzaldehyde and p

-tetra(benzenesulfonyloxy-phenyl)]porphyrin (CoTBSOPP) 109 . The
activity of the photocatalyst decreases in that order. An induction period in
uptake was observed and accelerates the oxidation. The proposed
reaction mechanism involves a free-radical chain process intiated by a
superoxocobalt(III) porphyrin species, which abstracts an H-atom from the
aldehyde, generating an radical. The latter participates in the following
propagation and termination steps:

meso

Initiation

Propagation

Termination