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

Reactions of (OH)-O-.,O.-,N-3(.) and SO4.- and e(aq)(-) radicals with furazan and its dimethyl and diamino derivatives were studied by radiation chemical methods, The (OH)-O-. 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 < 10(7), 3.5 x 10(8), 3.9 x 10(9) dm(3) mol(-1) s(-1), respectively. The transient absorption spectra measured in the (OH)-O-<bullet> 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 N-3(.) radical and was only 3,4-diaminofurazan found reactive with SO4.- (k = 3.6 x 10(9) dm(3) mol(-1) s(-1)). The rates of e(aq)(-) with all the three derivatives are diffusion controlled k = (0.8-1.9) x 10(10) dm(3) mol(-1) s(-1) and its reaction mechanism involves very fast protonation of the initially formed radical anions by water (k greater than or equal to 10(7) 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 x 10(4) and 1.5 x 10(5) s(-1) with furazan and 3,4-diaminofurazan, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.