Primary Processes in the Reduction of 4-Nitroazobenzene. A Pulse Radiolysis Study in Alcoholic Solvents

Article abstract of DOI:10.1021/j100278a043

The transient species produced in the reactions of solvated electrons and α-hydroxyalkyl radicals with 4-nitroazobenzene have been studied by spectrophotometric pulse radiolysis in 2-propanol and methanol.Solvated electrons were found to react with rate constants of 1.6*10¹⁰ and 2.3*10¹⁰ M^-1 s^-1 in 2-propanol and methanol, respectively, giving the anion as primary product.The same species is produced by electron transfer from both alcohol radicals, with rate constants ca. 10⁹ M^-1 s^-1 for (CH3)2COH and ca. 6*10⁷ M^-1 s^-1 for CH2OH.Protonation of the anion is observed in the microsecond time scale, leading to the hydrazyl radical. pK values for the protolytic dissociation of this species are evaluated to be 14.8 and 12.3 in 2-propanol and methanol, respectively.Association of the hydrazyl with the starting compound is observed in 2-propanol.Complete reduction of the azo bond occurs by very efficient second-order disproportionation of hydrazyl and/or dimer radicals.