A pulse radiolysis study of salicylic acid and 5-sulpho-salicylic acid in aqueous solutions

Reactions of H, OH, eaq- and some one-electron oxidants have been studied with salicylic acid and 5-sulpho-salicylic acid in aqueous solutions. Rate constants for the reaction of eaq- with these compounds were of the order of 109 dm3 mol−1 s−1 and this reaction led to the formation of reducing radicals which could transfer electron to methyl viologen. Other one-electron reductants were not able to reduce these compounds. OH radicals reacted with these compounds by addition pathway with very high rate constants (>1010 dm3 mol−1 s−1) while O− radical anions could oxidize these molecules to give phenoxyl type of radicals. Amongst the one-electron oxidants, only N3 and SO4− could oxidize salicylic acid while 5-sulpho-salicylic acid could be oxidized only by SO4− radicals indicating that while one-electron reduction potential for semi-oxidized SA may be<1.33 V vs. NHE (the Eo1 for N3 radical), it is more than 1.33 V vs. NHE for semi-oxidized SSA species.