Degradação do agrotóxico atrazina catalisada por porfirinas de manganês

Abstract

The extensive use of pesticides can lead to bioaccumulation and negatively affect the environment. An example of these substances is atrazine (ATZ), an herbicide of the triazine family, widely used in weed control worldwide, mainly in Brazil. Its large-scale use raises concerns because it is a very persistent substance for the environment. In addition, ATZ has toxicological potential for carcinogenesis, mutagenesis, and teratogenesis in different beings. In this study, the catalytic potential of second and third-generation manganese porphyrins was evaluated in ATZ degradation reactions, in homogeneous systems, using acetonitrile as solvent, under mild temperature and pressure. Different types of oxidants were used individually in the catalytic reactions, such as environmentally friendly oxidants (Oxone® and hydrogen peroxide), the iodosylbenzene (PhIO) commonly applied in systems with metalloporphyrins and its analog, iodobenzene diacetate (PhI(OAc)2). An axial coordination study for manganese porphyrins was also carried out using imidazole and ammonium acetate. They were studied to potentiate the catalytic reactions as a co-catalyst. The degree of ATZ degradation was determined using high-performance liquid chromatography. The best results were obtained using beta-brominated manganese porphyrins (third-generation) in the presence of the oxidants PhIO and PhI(OAc)2, yield ATZ degradation of 85% and 79%, respectively. The axial ligands use as cocatalysts did not prove to be advantageous in the studied systems. Reactions with radical inhibitors were performed to help the identification of possible reactive species generated in the reaction medium. In addition to the high valence species (Mn-oxo), the presence of hydroxyl radical, singlet oxygen, and other radicals was also proposed. The ATZ degradation products were analyzed by mass spectrometry; it was possible to observe the formation of the main metabolites described in the literature: deethylatrazine (DEA), desisopropylatrazine (DIA), and deethyldeisopropylatrazine (DAA).