Aspects of the oxidation of naphthazarin as studied by pulse radiolysis

Abstract

The spectroscopic characteristics and kinetic parameters associated with the intermediates formed on reaction of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) with the oxidising radicals OH^˙, O^˙–, N^˙₃, Br^˙–₂, SO^˙–₄, ĊH₂CHO and ĊHCHO^– have been determined by pulse radiolysis. Although all these oxidants give some semioxidised naphthazarin, other species such as adducts may also be formed. SO^˙–₄, O^˙– and N^˙₃ in strong alkali appear to lead predominantly to semioxidised naphthazarin which exists in anionic form above pH 5. Possible mechanisms for the decay of the semioxidised radicals under various conditions are proposed.