Catalytic oxidations using ruthenium porphyrins - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 47

electrophilic oxygen; thus 1,3,5-trimethoxybenzene was oxidized to 2,6-
dimethoxy- p -quinone with 97% yield, the total turnover reaching 33,000.
Oxidation of m -dimethoxybenzene gave 2-methoxy- p -quinone (74%), while
o -dimethoxybenzene yielded the corresponding p -quinone in only 11%
yield, and p -dimethoxybenzene was not oxidized at all; the chemoselectivity
of these reactions is clear. Similarly, oxidation of 2,3',4,4'- or 2,2',4,5'-
tetramethoxy-1,1'-biphenyl resulted in 2-methoxy-5-(3,4-dimethoxyphenyl)-
and 2-methoxy-5-(2,5-dimethoxyphenyl)- p -quinones in 77 and 46% yields,
respectively (Fig. 24). Oxidation of naphthalene and phenanthrene yielded
1,4-naphthoquinone (29%) and 9,10-phenanthroquinone (40%), respectively;
benzene was not oxidized. The nature of the catalytic Ru-oxo species
involved was considered uncertain (see Section 3.3.). The intermediate
phenol formed in the first step was isolated in the m -dimethoxy system, and
the second stage involved loss of MeOH. An experiment
showed that at least one ketonic O-atom of the p -quinone originated from the
pyridine oxide.

3.6 Oxidative-dehydrogenation of alcohols

at 1 mM concentrations in benzene catalyzes
aerobic oxidative-dehydrogenation of 2-propanol to acetone 65,74,167,168 ,
benzylalcohols to the corresponding benzaldehydes 65,167,168 , and various
benzhydrols (solid substrates, where X = F, H, MeO) to
the corresponding benzophenones 169 , and in each system water is the co-
product, but the turnovers are small. After 24 h under 1 atm air at 50°C, for
substrates typically at ~0.2 M, 6 turnovers were observed for 2-propanol, and
50

for a maximum 23 was seen (after 45 h) for ( p-