AFTER-EFFECT IN THE OXIDATION OF HYDROQUINONE PHOTOINDUCED BY COBALT AZIDE COMPLEX

The mechanism of the oxidation of hydroquinone (QH(2)) photoinduced by the azide complex has been studied in aqueous acidic solution. Such a n oxidation is shown to proceed selectively through an electron transf er reaction producing the semiquinone radical. 1,4-Benzoquinone (Q) ap pears to be the primary product in the presence and in the absence of oxygen. The ratios [Co(II)](form)/[QH(2)](disap) and [Q](form)/[QH(2)] (disap) are found to be equal to 2 and 1, respectively. This fits well with the disproportionation of the semiquinone radical. The resulting quinone is unstable in acidic medium and reacts with the azide anion (N-3(-)) to generate azidohydroquinone and azidobenzoquinone. An overa ll mechanism describing the photochemical and the dark reaction has be en established. (C) 1997 Elsevier Science S.A.