A DFT study on the addition and abstraction reactions of thiourea with hydroxyl radical

摘要

The thiourea + (OH)-O-center dot hydrogen atom transfer mechanism has been investigated theoretically for the first time. The objectives of the study have been to elucidate the nature of the reaction species, energetic, geometric, electronic and reaction kinetic properties for the reaction. The study has been performed with the DFT/BHHLYP, DFT/omega B97X-D and DFT/M06-2X methods, by using the 6-311++G(3df, 2p) basis set. The study has been performed in vacuo and in aqueous media. The results of the study indicate that the (OH)-O-center dot addition mechanism is thermodynamically favored to the direct H-atom abstraction mechanism. The activation energy is dependent on the media; it is higher in water solution than in vacuo. The direct H-atom abstraction mechanism is kinetically favored with respect to the (OH)-O-center dot addition mechanism in both media, suggesting that the reaction of thiourea with (OH)-O-center dot most likely proceeds through this mechanism. In water solution, the estimated apparent rate constant is close to the experimentally determined value. The spin density distribution on the thiyl is delocalized throughout the S-C-N region. The bond dissociation enthalpy is overestimated, with respect to experimentally available data, but suggests that H-atom transfer is easier in non-polar medium than in polar medium.