Unimolecular decomposition of acetyl peroxy radical: a potential source of tropospheric ketene

Tailoring the mechanistic pathways and kinetics of OH-addition reaction of sulfoxaflor and its ecotoxicity assessment

Sulfoxaflor is one of the widely used insecticides in agricultural lands to protect crops from insects. Due to its persistent nature, sulfoxaflor is identified as an environmental pollutant. In the present work, the mechanism and kinetics of sulfoxaflor degradation initiated by OH radical addition reaction are studied by using quantum chemical calculations. In the gas phase, the OH addition reaction at the C4 position of sulfoxaflor is found to be the favorable reaction pathway. The rate constant for the initial OH-addition reaction has been studied using canonical variational transition state theory (CVT) over the temperature range of 200-350 K. The initially formed sulfoxaflor-OH adduct intermediate transforms by reacting with O₂, H₂O, HO₂, and NO_x (x = 1-2) radicals. The excited-state calculation performed for the stationary points shows that the intermediates formed along the reaction pathway are easily photolyzed in normal sunlight. The toxicity assessment result shows that sulfoxaflor and few of its degradation products are harmful and toxic. The acidification potential of sulfoxaflor was found to be one, which shows its contribution to acid rain. This study gives an in-depth understanding of the mechanism, kinetics, and risk assessment of sulfoxaflor in the environment and aquatic system.

Autoxidation of Formaldehyde with Oxygen-A Comparison of Reaction Channels

The autoxidation of formaldehyde through initiation by triplet oxygen is studied via two initial steps: (1) H-atom abstraction and (2) ³O₂ addition reaction. The reaction energy profiles show that the reactions are thermodynamically and kinetically demanding. A comparison of the pathways of these initial reactions and the search for a less energy-demanding pathway is presented. The presence of a Brønsted acid has no effect on the energetics of the reaction, while the presence of a single water molecule catalyst enhances the initial reactions. The H-atom abstraction reaction from formaldehyde results in formyl and hydroperoxy radicals. These radicals on further reaction with the second equivalent of ³O₂ lead to a CO + 2HO₂ product channel. The ³O₂ addition reaction to formaldehyde results in a triplet biradical intermediate which further leads to performic acid, the precursor in the synthesis of carboxylic acids from aldehydes. In the presence of water molecules, performic acid is formed in a single kinetic step, and this leads to a CO₂ + OH + HO₂ product channel upon subsequent reaction with ³O₂ in a thermodynamically favorable reaction. The results show that the less established ³O₂ addition reaction to aldehydes is a viable route for autoxidation in the absence of purpose-built initiators, in addition to the well-established H-atom abstraction route.

Mechanism, Kinetics, and Ecotoxicity Assessment of ·OH-Initiated Oxidation Reactions of Sulfoxaflor

The ·OH-initiated reaction mechanism and kinetics of sulfoxaflor were investigated by using electronic structure calculations. The possible hydrogen atom and cyano group abstraction reaction pathways were studied, and the calculated thermochemical parameters show that the hydrogen atom abstraction from the C7 carbon atom is the more favorable reaction pathway. The subsequent reactions for the favorable intermediate (I4) with other atmospheric reactive species, such as O₂, H₂O, HO₂·, and NO_x· (x = 1, 2), were studied in detail. The products identified from the subsequent reactions could contribute to secondary organic aerosol (SOA) formation in the atmosphere. The intermediates and products formed from the initial and subsequent reactions are equally as toxic as the parent sulfoxaflor. At 298 K, the rate constant calculated for the formation of the favorable intermediate I4 is 2.54 × 10^-12 cm³ molecule^-1 s^-1, which shows that the lifetime of sulfoxaflor is 54 h. The excited-state calculation performed through time-dependent density functional theory shows that the photolysis of the title molecule is unlikely in the atmosphere. The global warming potentials (GWPs) for different time horizons, photochemical ozone creation potential (POCP), and ecotoxicity analysis were also studied for the insecticide sulfoxaflor.