Degradation of Methyl 2-Aminobenzoate (Methyl Anthranilate) by H(2)O(2)/UV: Effect of Inorganic Anions and Derived Radicals

This study shows that methyl 2-aminobenzoate (also known as methyl anthranilate, hereafter MA) undergoes direct photolysis under UVC and UVB irradiation and that its photodegradation is further accelerated in the presence of H(2)O(2). Hydrogen peroxide acts as a source of hydroxyl radicals (·OH) under photochemical conditions and yields MA hydroxyderivatives. The trend of MA photodegradation rate vs. H(2)O(2) concentration reaches a plateau because of the combined effects of H(2)O(2) absorption saturation and ·OH scavenging by H(2)O(2). The addition of chloride ions causes scavenging of ·OH, yielding Cl(2)·(−) as the most likely reactive species, and it increases the MA photodegradation rate at high H(2)O(2) concentration values. The reaction between Cl(2)·(−) and MA, which has second-order rate constant [Formula: see text] = (4.0 ± 0.3) × 10(8) M(−1)·s(−1) (determined by laser flash photolysis), appears to be more selective than the ·OH process in the presence of H(2)O(2), because Cl(2)·(−) undergoes more limited scavenging by H(2)O(2) compared to ·OH. While the addition of carbonate causes ·OH scavenging to produce CO(3)·(−) ([Formula: see text] = (3.1 ± 0.2) × 10(8) M(−1)·s(−1)), carbonate considerably inhibits the photodegradation of MA. A possible explanation is that the elevated pH values of the carbonate solutions make H(2)O(2) to partially occur as HO(2)(−), which reacts very quickly with either ·OH or CO(3)·(−) to produce O(2)·(−). The superoxide anion could reduce partially oxidised MA back to the initial substrate, with consequent inhibition of MA photodegradation. Fast MA photodegradation is also observed in the presence of persulphate/UV, which yields SO(4)·(−) that reacts effectively with MA ([Formula: see text] = (5.6 ± 0.4) × 10(9) M(−1)·s(−1)). Irradiated H(2)O(2) is effective in photodegrading MA, but the resulting MA hydroxyderivatives are predicted to be about as toxic as the parent compound for aquatic organisms (most notably, fish and crustaceans).