Possible reaction pathways of selected organophosphorus and carbamate pesticides according to the DFT calculation method

Abstract

This research was carried out in order to analyse the reactions of three organophosphorus (OP) and three carbamate (CB) pesticides with the hydroxyl radical (.OH), and their degradation paths. The studied organophosphorus pesticides are Azamethiphos, Coumaphos, Temephos, and the carbamate pesticides are Methiocarb, Carbofuran, Pirimicarb. Initially, in the reactions, the initial geometries of the reactants were determined. Geometric optimisations were performed using the DFT/B3LYP/6-31G (d) basic set of Quantum Mechanical Density Functional Theory (DFT). For each molecule, degradation reaction mechanisms were tried to be clarified using the calculated energy values. Since the reactions of pesticides with .OH are essential in terms of both water treatment and atmospheric chemistry, energy values were calculated both at gaseous phase and aqueous phase by modelling the solvent effect. For each molecule, fragments were found out by analysing the bond lengths, bond angles, and energy values, and as a result, degradation paths were determined. © 2022 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria.