Study of radiation chemical reactions of oxidising and reducing radicals with furazan derivatives

Abstract

Reactions of √ OH, O√^-, N₃√ and SO₄√ ^- and e_aq^- radicals with furazan and its dimethyl and diamino derivatives were studied by radiation chemical methods. The √ OH radical reaction is selective with the rates following the order furazan<3,4-dimethylfurazan (3,4-DMF)<3,4-diaminofurazan (3,4-DAF), the k values being <10⁷, 3.5 × 10⁸, 3.9 × 10⁹ dm³ mol^-1 s^-1, respectively. The transient absorption spectra measured in the √ OH radical reaction with 3,4-DMF and 3,4-DAF exhibited maxima at 270 and 290 nm, respectively, which are assigned to the benzylic and anilino type radicals. The same intermediates are also formed in the O √^- reaction by H abstraction. All three derivatives showed lack of reactivity with N₃ √ radical and was only 3,4-diaminofurazan found reactive with SO₄√ ^- (k=3.6 × 10⁹ dm³ mol^-1 s^-1). The rates of e_aq^- with all the three derivatives are diffusion controlled k=(0.8-1.9) × 10¹⁰ dm³ mol^-1 s^-1 and its reaction mechanism involves very fast protonation of the initially formed radical anions by water (k ≥ 10⁷ s^-1) followed by tautomerisation of the N-atom protonated C-centred radical to the C-atom protonated N-centred radical. The transformation is catalysed by OH^- and the rates for the spontaneous transformation in neutral solution are 5.4 × 10⁴ and 1.5 × 10⁵ s^-1 with furazan and 3,4-diaminofurazan, respectively.