Metal ions and complexes in organic reactions. Part VI. A comparison of oxidants for 2,6-dimethylphenol

Abstract

Transition-metal compounds, with or without aqueous hydrogen peroxide or other oxidants, were compared for capacity to effect coupling and oxygenation of 2,6-dimethylphenol. para-Oxygenation, giving the benzoquinone, generally competed fairly strongly with oxidative coupling, which produced the dihydroxybiphenyl or the corresponding diphenoquinone; best yields of the benzoquinone were obtained with titanium salts in aqueous hydrogen peroxide. ortho-Oxygenation, giving the dimer of the hydroxy-dienone, occurred in four cases, and in best yield with molybdate or tungstate in aqueous hydrogen peroxide. Comparative oxidations were carried out with oxygen donors, mainly oxyhalide anions, in the absence of metal ions; these generally resulted in coupling, as well as ortho- or para-oxygenation.