Catalytic oxidative degradation of s-triazine and phenoxyalkanoic acid based herbicides with metalloporphyrins and hydrogen peroxide: Identification of two distinct reaction schemes

Abstract

Oxidative degradation of the herbicides atrazine ( 1), atraton ( 2), ametryn ( 3) and mecoprop ( 4), was carried out with hydrogen peroxide and metalloporphyrins as catalysts. Two different reaction conditions were studied, the first involving Mn(TDCPP)Cl in an aprotic solvent with buffer ( S-I), and the second using Fe(TPFPP)Cl in a protic solvent ( S-II). Reaction products were characterized, and based on these it is shown that there are two distinct reaction schemes. In the case of the S-I conditions, it is suggested that the s-triazines were oxidized through hydroxylation of the alkyl side chains followed by dealkylation, while S-II was ineffective for these reactions. In contrast, mecoprop, was oxidized with high efficiency by S-II, leading to decarboxylation and further oxidation, while in the presence of S-I, low substrate conversion was observed, and reaction resulted mainly from oxidation at the benzyl position. Sulfoxidation of ametryn was observed with both systems. The different reactivity shown by the two systems supports the involvement of different reactive species, which we assign to the oxo and hydroperoxy complexes. These routes show similarities with metabolic pathways, with the reactivity pattern of S-I analogous to the reported metabolism of these pollutants with cytochrome P450 enzymes, while S-II catalyses mecoprop decarboxylation via a similar pathway to that seen with peroxidase catalysed reactions.