Oxidative dealkylation of hydroquinone ethers with nitrogen dioxide in the convenient preparation of quinones

Abstract

Various hydroquinone dialkyl ethers (R₂Q) are effectively converted by nitrogen dioxide into the corresponding quinone (Q) and alkyl nitrite (RONO) in dichloromethane at room temperature or below. The preparative procedure for the isolation of crystalline quinones in quantitative yield merely involves the convenient removal of the low boiling solvent in vacuo. Isotopic labelling studies demonstrate that the oxidative dealkylation proceeds via alkoxy scission of the labile cation radical (R₂Q˙⁺) formed via the oxidation of the hydroquinone ether by nitrogen dioxide (as the disproportionated ion pair NO ⁺N₃^–). The electron-transfer mechanism is confirmed by the spectral observation of R₂Q˙⁺(identified by the isolation of the crystalline salt R₂Q˙⁺ SbCl₆^–) and its rapid conversion into quinone and alkyl nitrite by combination with nitrate (NO₃^–) and nitric oxide (NO).