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.

Cu-Catalyzed Hydrodehalogenation of Brominated Aromatic Pollutants in Aqueous Solution

The catalytic effect of copper in Devarda’s Al-Cu-Zn alloy (Dev. alloy) and sole metallic copper, copper salts and copper oxides in the coaction of NaBH4 within the hydrodehalogenation (HDH) of polybrominated phenols, such as the herbicide Bromoxynil in alkaline aqueous solution has been investigated. Namely, the hydrodebromination (HDB) activity of Dev. alloy/NaOH system has been compared to heterogeneous Cu-based catalysts using NaBH4 as a reductant. Differences in the solid-state structures of used Cu-based heterogeneous catalysts after the mentioned HDB process have been studied using the powder XRD and SEM techniques. It was found that some of the used copper-based catalysts are reusable and reasonably effective even at room temperature. Efficiency of the most promising copper-based reduction systems (Dev. alloy/NaOH and Cu-based catalysts/NaBH4) have been successfully tested within the HDB of industrially important brominated flame retardant tetrabromobisphenol A (TBBPA). Dev. alloy/NaOH and Cu-based catalyst generated in-situ within the CuSO4/NaBH4 produced were recognized as the most active HDB agents for complete debromination of both BRX and TBBPA.

Mechanism and kinetics of diuron oxidation by hydroxyl radical addition reaction

Diuron is a phenyl urea herbicide used to control weeds in agricultural lands. The degradation of diuron in the atmosphere takes place dominantly via reaction with OH radicals. In this work, the OH addition reaction of diuron has been studied by using density functional theory methods M06-2X, ωB97X-D and MPWB1K with 6-31G(d,p) basis set. The calculated thermochemical parameters show that OH addition reaction occurs favourably at C₂ position of diuron. The rate constant is calculated for the favourable initial reaction pathway by using canonical variational transition state theory with small curvature tunnelling (SCT) correction over the temperature range of 200-1000 K. The reaction of initially formed diuron-OH adduct intermediate with O₂ leads to the formation of peroxy radical intermediate. The reaction of peroxy radical intermediate with HO₂ and NO_x (x = 1, 2) radicals is studied in detail. The results obtained from time-dependent density functional theory (TDDFT) calculations show that the intermediates and products formed from oxidation of diuron can be easily photolyzed in the sunlight. This study provides thermodynamical and kinetic data for the atmospheric oxidation of diuron by OH radical addition reaction and demonstrates the atmospheric chemistry of diuron and its derivatives.

Atmospheric oxidation mechanism of OH-initiated reactions of diethyl ether – the fate of the 1-ethoxy ethoxy radical

The 1-ethoxy ethoxy radical resulting from the secondary peroxy chemistry in the oxidation of diethyl ether (DEE) by hydroxyl radical leads to the formation of ethyl formate in major quantities and ethyl acetate in minor quantities.