Catalytic oxidations using cobalt(II) complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 270

with molecular oxygen and tert -butylhydroperoxide was investigated using
biomimetic Mn-, Fe- and Co-complexes as catalysts 19 . The catalytic activity
and product distribution were determined and compared with those observed
in the reactions of the well-known Co(salen) complex.
Supercritical is gaining importance as a reaction medium. The
oxidation of substituted phenols by O 2 has been studied in supercritical
using [{ N,N' -bis(3,5-di- tert -butylsalicylidene)-1,2-cyclohexanediaminato(2- )}-
cobalt(II)] as catalyst 20 Both oxidase and oxygenase activities are observed
with 2,6-di- tert -butylphenol as substrate at 70°C and 207 bar total pressure,
at an O 2 :phenol:catalyst ratio of 1500:20:1, and a methylimidazole to
catalyst ratio of 1.28. Total conversion to 2,6-di- tert- butyl-1,4-benzoquinone
and 3,5,3',5'-tetra- tert -butyl-4,4'-diphenoquinone took place in 21 h.

3.2 Oxidation of 3,5-di- tert -butylcatechol

Binuclear Co(II) complexes derived from 2,6-diformyl-4-methylphenol
and various aromatic monoamines have been prepared and investigated. 21
The Co(II) complexes have the composition where L represents
the organic ligand. The complexes are active catalysts in the oxidation of
3,5 - di -tert- butylcatechol.

3.3 Oxidation of lignin phenolics

Earlier work on the Co(salen)-catalyzed of p -substituted
phenols to p -benzoquinones 22,23 has been extended to include substrates that
serve as models for lignin phenolic subunits. Lignin is a renewable source
of carbon and its oxidation to p -benzoquinone derivatives would allow
conversion to useful intermediates. Certain p -substituted phenolics can be
oxidized to p -benzoquinones with dioxygen using the Co(salen) complexes
A and B in Figure 4 as catalysts 24 .