REDOX POTENTIALS OF THE AZIDE AND DITHIOCYANATE RADICALS

We have measured the midpoint potentials of the two redox couples azidyl radical/azide and dithiocyanate radical anion/thiocyanate. The two-pulse radiolytically determined potentials were obtained with use of the same reference couple, tris(bipyridine)ruthenium(III)/tris(bipyridine)ruthenium(II), and by both kinetic and equilibrium protocols. On the basis of the equilibrium constants measured for the reactions between the inorganic radicals and the ruthenium complex, the calculated Em′ at 25°C for azidyl radical/azide is 1.33 ± 0.01 V (NHE) and for dithiocyanate radical/thiocyanate, 1.29 ± 0.01 V (NHE). The observed kinetics for the one-electron oxidation of azide by the dibromide radical anion suggests that an intermediate monomeric neutral bromide radical species may be the actual oxidizing species. © 1990 American Chemical Society.