Oxidation of ortho- and para-aminobenzoic acid. A pulse radiolysis- and gamma radiolysis study

The oxidation of anthranilic acid (ortho-aminobenzoic acid, ANA) and para-aminobenzoic acid (PABA) by •OH, N3• and O•− in basic solution was studied by pulse radiolysis. The kinetic and spectroscopic characteristics of the intermediate transients were determined. For ANA the site attack of the OH radicals was established to be ∼50% on the -NH2 moiety and ∼50% on the aromatic ring with an overall rate constant k(•OH+ANA)=(5.5×109) dm3 mol−1 s−1. The rate constant of PABA was k(•OH+PABA)=8×109 dm3 mol−1 s−1. The OH-adducts of both compounds showed a first order decay of 0.8×105 and 1.2×105 s−1, respectively, whereby the corresponding anilino-radicals were formed. The rate constant of ANA with solvated electrons was k(e−aq+ANA)=2.9×109 dm3 mol−1 s−1. The radiation induced decomposition of both substrates was studied by gamma radiolysis as a function of the absorbed dose. They exhibited a distinct radiation resistance, the initial degradation yields were ∼0.16 μmol J−1, i.e. only 28% of the •OH radicals contributed to their decomposition. The hydroxylation process was of minor importance, the yield of hydroxylated aminobenzoic acids was≤0.01 μmol J−1.