Hussein Aqeel A, Al-Hadedi Azzam A M, Mahrath Alaa J, Moustafa Gamal A I, Almalki Faisal A, Alqahtani Alaa, Shityakov Sergey, Algazally Moaed E
Faculty of Dentistry, University of Al-Ameed, Karbala PO Box 198, Iraq.
Department of Chemistry, University of Southampton, Southampton, Hampshire SO17 1BJ, UK.
R Soc Open Sci. 2020 Feb 5;7(2):191568. doi: 10.1098/rsos.191568. eCollection 2020 Feb.
A computational study on Pinnick oxidation of aldehydes into carboxylic acids using density functional theory (DFT) calculations has been evaluated with the (SMD)-M06-2X/aug-pVDZ level of theory, leading to an important understanding of the reaction mechanism that agrees with the experimental observations and explaining the substantial role of acid in driving the reaction. The DFT results elucidated that the first reaction step (FRS) proceeds in a manner where chlorous acid reacts with the aldehyde group through a distorted six-membered ring transition state to give a hydroxyallyl chlorite intermediate that undergoes a pericyclic fragmentation to release the carboxylic acid as a second reaction step (SRS). H NMR experiments and simulations showed that hydrogen bonding between carbonyl and -butanol is unlikely to occur. Additionally, it was found that the FRS is a rate-determining and thermoneutral step, whereas SRS is highly exergonic with a low energetic barrier due to the Cl(III) → Cl(II) reduction. Frontier molecular orbital analysis, intrinsic reaction coordinate, molecular dynamics and distortion/interaction analysis further supported the proposed mechanism.
利用密度泛函理论（DFT）计算对醛类通过平尼克氧化反应转化为羧酸进行了一项计算研究，该研究采用了（SMD）-M06-2X/aug-pVDZ理论水平，从而对反应机理有了重要认识，这与实验观察结果相符，并解释了酸在驱动反应中所起的重要作用。DFT结果表明，第一步反应（FRS）的进行方式是，亚氯酸通过扭曲的六元环过渡态与醛基反应，生成羟基烯丙基亚氯酸酯中间体，该中间体经历周环断裂，作为第二步反应（SRS）释放出羧酸。1H NMR实验和模拟表明，羰基与叔丁醇之间不太可能形成氢键。此外，还发现FRS是一个速率决定且热中性的步骤，而由于Cl（III）→Cl（II）还原，SRS具有很高的放能性且能量势垒较低。前线分子轨道分析、内禀反应坐标、分子动力学和畸变/相互作用分析进一步支持了所提出的机理。
