The Oxidation of 2,4,6-Trimethylphenol with Molecular Oxygen Catalyzed by a Copper(II)-Oxime or Copper(II)-Amine System

Article abstract of DOI:10.1246/bcsj.66.251

2,4,6-Trimethylphenol (1a) was selectively oxidized to 3,5-dimethyl-4-hydroxybenzaldehyde (2a) by molecular oxygen in the presence of a copper(II) chloride-oxime or copper(II) chloride-amine catalyst in alcohol at ambient temperature.When an acid was present in the catalyst system, the formation of both 2,6-dimethyl-p-benzoquinone (3) and a formaldehyde dialkyl acetal was accelerated.It is likely that 2a is produced by way of the formation of a quinonemethide intermediate, followed by a repeated 1,6-addition of alcohol on the intermediate to form a 4-(alkoxymethyl)-2,6-dimethylphenol (5a), and then 3,5-dimethyl-4-hydroxybenzaldehyde dialkyl acetal, which would be hydrolyzed to 2a.When the reaction time was shortened, 5a was isolated in good yield.Oxidations of the other p-methyl-substituted phenols were also examined using the present oxidation system.