Triple oxidations of some polyhydric phenols by cerium(IV) in acid solutions as observed by electron spin resonance spectroscopy

Abstract

A hitherto unobserved radical species has now been obtained from the oxidation of pyrogallol (1,2,3-trihydroxy-benzene) by Ce^IV in acid solution. Evidence is presented which indicates that this ‘new’ radical differs from the semiquinone radical from pyrogallol only by having two fewer electrons, and therefore comes from three consecutive one-electron oxidations. Analogous reactions occur with purpurogallin (2,3,4,6-tetrahydroxy-5H-benzocyclohepten-5-one) and with juglone(5-hydroxy-1,4-naphthoquinone). Where there is symmetry, it is clear that the two adjacent molecule orbitals, which may contain the odd electron, depending on whether there has been one-or three-electron oxidation overall, have opposite symmetries.