气相和水相中氯代酚与单线态氧反应机理的研究

Theoretical study of the reaction of chlorophenols with 1O2 in gas phase and aqueous solutions

用密度泛函理论分别研究气相和水相中的6种氯代酚(2-CP,3-CP,4-CP,2,4-DCP,2,4,6-TCP和PCP)与单线态氧的反应机理。在B3LYP/6-31+G(d,p)水平上,将可能路径上的反应复合物、过渡态和产物分别全优化几何结构和计算频率,通过内禀反应坐标(IRC)的方法验证反应路径,并在B3LYP/6-311+(2df,p)水平上计算单点能。采用极化统一模型(PCM)法探索溶剂效应。结果,不论气相还是水相,1,3加成生成1个烯丙基氢过氧化物和1,4加成生成1个酮类氢过氧化物,在热力学上均是可行的,但是在动力学上前者的能垒比后者更低,是优先路径。热力学更支持在水相中反应,而动力学则相反。能垒随氯代数量的增多而升高。

Theoretical study of the reactions between singlet oxygen and chlorophenols is an important aspect in understanding the reaction mechanism of the dye-sensitized photodegradation. With the intention of finding certain predictors to be used for the determination of the most probable reaction path and estimating the dye sensitized photodegradation rates of chlorophenols, the reactions of 1O2 with six chorophenols （CPs）, including 2-CP, 3-CP, 4-CP, 2,4-DCP, 2,4,6-TCP and PCP, was investigated by using the density functional theory. Results suggested that 1,3-addition to a double bond connected to a hydrogen-carrying group, resulting in the formation of allylic hydroperoxides, and 1,4-addition to chlorophenols to form of hydroperoxide ketoues are thermodynamically more likely to take place. Furthermore, the reaction barrier of the former one is lower than that of later one, which tends to conclude that 1,3-addition to a double bond connected to a hydrogen-carrying group to form allylic hydroperoxides is the most likely route. When the solvent effect was considered via polarizable continuum model （PCM） computations, reactions are thermodynamically more likely to take place in presence of water, but the reaction barriers increased. Also it was observed that with the increase of chlorine substitutions, the reactions become less exergonic and dynamically less favorable due to the increase in reaction barriers.