Hydroxyl radical induced oxidation of 3-methoxy-4-hydroxy cinnamic acid (ferulic acid)

Hydroxyl radical reaction of 3-methoxy-4-hydroxy cinnamic acid (ferulic acid) produced the ·OH-radical adducts. A part of these radical adducts undergo water elimination to finally yield phenoxyl radicals and the process was found to be base catalysed. Phenoxyl radical of ferulic acid was further identified by following its reaction with more specific oxidising radicals, e.g. azide (N₃·) and Cl·₂^- in the pH range from 2.5 to 9. The phenoxyl radicals produced by one-electron oxidation did not possess any pK_a in this pH range. The one-electron reduction potential for the formation of the phenoxyl radical was determined after achieving electron transfer equilibrium between the two couples involving the phenoxyl radical/phenol and phenothiazine radical cation/phenothiazine. Scavenging ability of the phenol toward NO·₂ radical was evaluated.