Pulse radiolysis of solutions of sodium tetraphenylborate

Pulse radiolysis of solutions of sodium tetraphenylborate (NaBPh₄) indicates that the absorption observed in organic amides with λ_max in the range 650-725 nm is not due to Na^-, an electron adduct to BPh₄^-, a triplet excited state, or a proton-donating solvent cation. Experiments in aqueous solution are described in which the reactions of selected radicals with NaBPh₄ are studied. One-electron oxidation of NaBPh₄ by N₃^•- radicals yields a species, assumed to be BPh₄^•, with absorption maxima at 335 and 800 nm. A similar spectrum is observed on pulse radiolysis of solutions of NaBPh₄ in tetramethylurea (TMU), but the long-wavelength absorption is shifted to 725 nm. The formation of an oxidizing radical in irradiated TMU was confirmed by the observation of I₂^•- on pulse radiolysis of solutions of KI in this solvent. Pulse radiolysis of solution of NaBPh₄ and KI in TMU demonstrated that these solutes compete for the oxidizing intermediate.