NOVEL CATALYSIS OF HYDROQUINONE AUTOXIDATION WITH NITROGEN-OXIDES

An efficient catalytic method is described for the preparative conversion of hydroquinones to quinones with dioxygen under mild conditions. The use of the gaseous nitrogen oxide (NOx) catalyst allows a simple workup procedure for the isolation of quinones in essentially quantitative yields by merely removing the low-boiling solvent dichloromethane in vacuo. The mechanism of the catalytic autoxidation of hydroquinones is ascribed to the critical role of nitrosonium (NO+) in the one-electron oxidation of hydroquinone, followed by the reoxidation of the reduced nitric oxide (NO) with dioxygen. An extensive series of complex interchanges among various NOx species in nitrogen-(V), -(IV), -(III), and -(II) oxidation states, coupled with stepwise oxidation of hydroquinone via a successive series of one-electron/proton transfers, form the critical components of the catalytic cycle.