Free radical induced oxidation of the azo dye Acid Yellow 9

The kinetics and mechanism of the free radical oxidation of the azo dye, Acid Yellow 9, by sulfate radical anions and hydroxyl radicals have been studied using pulse radiolysis and product analysis. Sulfate radicals react via one electron oxidation, generating the dye radical cation, which has an absorption maximum centered on 470 nm. In basic solutions, the radical cation mainly undergoes deprotonation to yield the aminyl radical which has a strong absorption with a maximum centered on 370 nm, and the pK(a) for the radical cation is 5.5. Formation of a sulfated product, 1, is indicative of a coupling reaction between the radical cation and sulfate radical anions. Studies also indicate that the hydroxyl radicals react with the dye by both electron transfer as well as by adduct formation.