Pulse radiolysis study on one-electron oxidation of 1-naphthylamine-4-sulphonic acid in aqueous solutions

Abstract

Reactions of 1-naphthylamine-1-sulphonic acid (NASA) with hydroxyl radicals and oneelectron oxidants such as N3, Br2- and Cl2- radicals have been studied at various pHs using pulse radiolysis technique. Rate constants for the reaction of N3 and Br2-. radicals with NASA at neutral pH were found to be 5 × 109 and 4 × 108 dm3 mol-1 s-1 respectively. These reactions led to the formation of a cation radical (semi-oxidized species). OH radical reaction with NASA (k = 7.2 × 109 dm3 mol-1 s-1) at neutral pH gave a mixture of species, namely, a semi-oxidized species as well as an adduct species. Cl2-. radicals reacted with NASA rather slowly (k = 7 × 107 dm3 mol-1 s-1) at pH 1 to give the semioxidised species. However, even at pH 1, OH radical reaction with NASA gave a mixture containing semi-oxidized as well as an adduct species. The OH-adduct species having λmax at 340 nm decays at acidic pHs to give semi-oxidized species having λmax at 370 nm. Electron adduct of NASA was found to be a strong reducing radical.