We have carried out a computational study on the reactivity of catechol (1,2-dihydroxybenzene) towards superoxide radical anion (O₂˙⁻) in water, N,N-dimethylformamide (DMF), pentyl ethanoate (PEA) and vacuum using density functional theory and the coupled cluster method. Five reaction mechanisms were studied: (i) sequential proton transfer followed by hydrogen atom transfer (PT-HT), (ii) sequential hydrogen atom transfer followed by proton transfer (HT-PT), (iii) single electron transfer (SET), (iv) radical adduct formation (RAF) and (v) concerted double proton-transfer electron-transfer (denoted as global reaction, GR). Our results show that catechol and superoxide do not react via a sequential reaction mechanism (initial PT, initial HAT or SET). Instead, the reaction proceeds via a concerted double proton-transfer electron-transfer mechanism yielding hydrogen peroxide and catechol radical anion. The protons are transferred asynchronously between the σ orbitals of the catechol oxygen atoms to superoxide, while the electron is transferred between oxygen π orbitals in the same direction. The calculated rate constants in aqueous media agree with the experimental values reported in the literature. This suggests that the mechanism proposed in this work is adequate to describe this reaction. In addition, our results show that the reaction exhibits a large tunneling effect.

中文翻译：

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儿茶酚和超氧自由基阴离子之间的协同双质子转移电子转移

我们已经进行了计算研究上儿茶酚（1,2-二羟基苯）朝向超氧阴离子自由基（O的反应₂ ˙ ^- ）的水，Ñ，Ñ二甲基甲酰胺（DMF），戊基乙（PEA）和真空用密度功能理论和耦合聚类方法。研究了五种反应机理：（i）依次进行质子转移，然后进行氢原子转移（PT-HT），（ii）依次进行氢原子转移，然后进行质子转移（HT-PT），（iii）单电子转移（SET）， （iv）自由基加合物的形成（RAF）和（v）一致的双质子转移电子转移（表示为全局反应GR）。我们的结果表明，邻苯二酚和超氧化物不会通过顺序反应机制（初始PT，初始HAT或SET）。相反，该反应通过一致的双质子转移电子转移机理进行，产生过氧化氢和邻苯二酚自由基阴离子。质子在邻苯二酚氧原子的σ轨道之间向超氧化物异步转移，而电子在氧π轨道之间以相同方向转移。在水介质中计算出的速率常数与文献报道的实验值一致。这表明在这项工作中提出的机制足以描述这种反应。另外，我们的结果表明该反应表现出大的隧穿效应。