cycloxydim and tetrachloroisophthalonitrile

The possible reaction mechanisms for the experimentally observed hydrogen transfer between the herbicide cycloxydim (CD) and the triplet fungicide chlorothalonil (CT) were identified with density functional theory (DFT) and time-dependent density function theory (TDDFT) computations. Excited energy transfer (EET) calculations indicate that reactants for intermolecular hydrogen transfer were formed via energy transfer from triplet CT to ground state CD. Three possible reaction pathways after EET were identified, and hydrogen transfer from the hydroxyl group on the cyclohexane ring of CD to CT exhibited the lowest energy barrier. Natural population analysis (NPA) along the reaction pathways has confirmed that the pathways involved either electron transfer induced proton transfer or coupled electron-proton transfer, leading to different potential energy profiles. Electrostatic potential (ESP) study substantiated the reaction mechanisms in different pathways. This study suggests an explanation for the accelerated photodegradation of CD by CT and provides a pipeline for future studies of photoinduced intermolecular hydrogen transfer.

Topics: Cyclohexanes; Electron Transport; Hydrogen; Nitriles; Photochemical Processes; Pyrans; Quantum Theory; Static Electricity

Photolysis is a known dissipation pathway of pesticides on leaves just after their spraying. This pathway may be affected by the residues of other pesticides. To illustrate this idea, this study investigated the mutual effect of two pesticides (chlorothalonil and cycloxydim) under simulated solar light. Cycloxydim was added at the agricultural rate (200 g ha(-1)) and chlorothalonil at 1.3-10% of the rate (20-150 g ha(-1)). These compounds were studied either pure or in their commercial formulation. Both analytical and kinetic data show that chlorothalonil significantly accelerates the decay of cycloxydim on wax films, promoting its oxidation, even at the lowest tested dose. Conversely, cycloxydim does not affect the fate of chlorothalonil. Moreover, the detection of oxidized forms of wax alkanes in the extracts demonstrates that chlorothalonil may have also a degrading effect on the leaves' constituents under the action of solar light.

Topics: Cyclohexanes; Fungicides, Industrial; Herbicides; Kinetics; Light; Nitriles; Oxidation-Reduction; Pesticide Residues; Photolysis; Pyrans; Waxes