A variety of alpha -hydroxyketones were efficiently oxidized to alpha -diketones in near quantitative yields with molecular oxygen, under alkaline conditions, using cobalt phthalocyaninetetrasulphonamide as catalyst. Acyloins in general were found to less reactive than benzoins and required high pH for their oxidation. Among the benzoins, those substituted with electron donating groups were found to be more reactive and required lesser reaction time for their oxidation.