Mechanism of OH-initiated atmospheric photooxidation of the organophosphorus insecticide (C2H5O)3PS

O,O,O-triethyl phosphorothioate ((C2H5O)3PS, TEPT) is a widely used organophosphorus insecticide. TEPT may be released into the atmosphere where it can undergo transport and chemical transformations, which include reactions with OH radicals, NO3 radicals and O3. The mechanism of the atmospheric reactions of TEPT has not been fully understood due to the short-lifetime of its oxidized radical intermediates, and the extreme difficulty in detection of these species experimentally. In this work, we carried out molecular orbital theory calculations for the OH radical-initiated atmospheric photooxidation of TEPT. The profile of the potential energy surface was constructed, and the possible channels involved in the reaction are discussed. The theoretical study shows that OH addition to the PS bond and H abstractions from the CH3CH2O moiety are energetically favorable reaction pathways. The dominant products TEP and SO2 arise from the secondary reactions, the reactions of OH-TEPT adducts with O2. The experimentally uncertain dominant product with molecular weight 170 is mostly due to (C2H5O)2P(S)OH and not (C2H5O)2P(O)SH.