Catalytic oxidations using cobalt(II) complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 298

Step (26) differs from what the authors have proposed. The effect of light
is assigned to generation of free radicals, which act as initiators and shorten
the induction period.
The oxidation of alkylaryl sulfides with dioxygen/2,2-dimethypropanal is
catalyzed by Co(II)-tetraarylporphyrin and a perfluoroalkyl-substituted
Co(II)-phthalocyanine in a fluorous organic biphasic system 110 . Sulfoxide
was generally obtained as the main product, together with variable quantities
of sulfone (0-100%), depending on the nature of the substrate. The reaction
probably proceeds through a free-radical oxidative process initiated by the
Co(II)-porphyrin. The catalysts used are decomposed under the free-radical
reaction conditions.

6. OXIDATION WITH COBALT(II) PHTHALOCYANINES

The interaction of cobalt(II) phthalocyanine with ammonia and dioxygen
has been studied by ESR spectroscopy. Both 1:1 and 1:2 adducts with are
formed. The phthalocyanine ring is oxidized to a cation radical when the
binunlear adduct is formed 111 .
Cobalt(II) phthalocyanines are efficient oxidation catalysts 112 . They have
been used for the oxidation of ascorbic acid 113 , cysteine 114 , mercapto-
ethanol 115 , hydrazine 116 , hydroxylamine 117 and sulfite 118 .
In pyridine solution the nitroso derivative PcCoNO can be converted
under an atmosphere (50 atm) to the nitrito derivative which

oxidizes triphenylphosphine or 1-octene by O-atom transfer 119,120 .
The tetra- tert -butylphthalocyanine complex of cobalt(II)
catalyzes the oxidation of styrene to 1-phenylethanol with at room
temperature in the presence of (Figure 39). The analogous
reactions with the Mn(III) and Fe(III) complexes are inhibited by the free-
radical scavenger TEMPO, indicating a free-radical mechnism. The lack of
inhibition of the cobalt(II)-catalyzed oxygenation points to the involvement
of a intermediate. The zinc complex is catalytically inactive.
In the presence of water-soluble cobalt phthalocyaninetetra(sodium
sulfonate) (CoPcTS), 3,4-dimethoxybenzyl alcohol (a lignin model) is cata-
lytically oxidized by dioxygen to 3,4-dimethoxy-benzaldehyde 123-127 . Typical
reaction conditions are 1 atm and 85°C, 12 hours at pH 11, yield
100%.The product yield decreases with decreasing pH; it is 84% at pH 10
and 18% at pH 8. A cationic latex particles had little effect on the yield or
rate of oxidations. PcTS complexes of Fe(II), Cu(II) and Ni(II) gave less
than 1% yield under comparable conditions.