DEGRADATION OF METHYLANTHRANILATE BY H2O2/UV: EFFECT OF INORGANIC ANIONS AND DERIVED RADICALS

We show that methyl anthranilate (MA) undergoes direct photolysis under UVC and UVB irradiation, but its photodegradation is considerably accelerated in the presence of H2O2. Hydrogen peroxide acts as a source of hydroxyl radicals (·OH) under photochemical conditions and yields MA hydroxyderivatives. The trend of MA degradation rate vs. H2O2 concentration reaches a plateau because of the combined effects of absorption saturation and ·OH scavenging by H2O2. The addition of chloride ions causes ·OH scavenging and production of Cl2·- as the most likely reactive species, which reacts with MA with second-order rate constant = (4.0±0.3)×108 M-1 s-1. The reaction between Cl2·- and MA appears to be more selective than the ·OH process in the presence of H2O2. Because Cl2·- undergoes more limited scavenging by H2O2 compared to ·OH, added chloride enhances the MA photodegradation at high H2O2 concentration. A similar effect might be expected with carbonate that scavenges ·OH to produce CO3·- ( = (3.1±0.2)×108 M-1 s-1), but carbonate considerably inhibits the photodegradation of MA. A possible explanation is that the elevated pH of the carbonate solutions causes H2O2 to partially occur as HO2-, which reacts very quickly with either ·OH or CO3·- to produce O2·-. The latter may be involved in the reduction of the partially oxidised MA back to the initial substrate, thereby inhibiting MA degradation. Fast MA transformation is also observed in the presence of persulfate/UV, which yields SO4·- that reacts effectively with MA ( = (5.6±0.4)×109 M-1 s-1).