Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; State Agriculture Ministry Laboratory of Quality & Safety Risk Assessment for Tobacco, Tobacco Research Institute, Chinese Academy of Agricultural Sciences, Qingdao 266101, China.
Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Chemosphere. 2019 May;222:71-82. doi: 10.1016/j.chemosphere.2019.01.113. Epub 2019 Jan 22.
Permanganate is a versatile chemical oxidant, and has undergone a dramatic evolution toward deep insight into its reaction mechanism. However, the hydrogen abstraction of the NH bond by permanganate remains unclear. We studied the permanganate oxidation of the emerging micropollutant sulfamethoxazole in acidic aqueous solution. The reaction followed autocatalytic kinetics and demonstrated first-order with respect to each reactant. The presence of HMnO accelerated the reaction rate, which was four orders of magnitude higher than that of MnO. Based on the identified products, the rate-limiting step was determined to be simple NH bond oxidation by metal-oxo species permanganate. The mechanism was then studied computationally by density functional theory (DFT) using ammonia as the simplest model. Results showed that the NH bond oxidation by MnO (32.86 kcal/mol) was a concerted mechanism similar to that of CH bond oxidation, whereas HMnO oxidation of the NH bond (10.44 kcal/mol) was a stepwise electron-proton transfer. This reminds us that coordination of Brønsted acid could not only produce the stronger electrophile but also change the reaction mode by avoiding the bond cleavage in electron transfer process.
高锰酸盐是一种多功能的化学氧化剂，其反应机理的研究已经取得了显著的进展。然而，高锰酸盐对 NH 键的氢提取反应仍不清楚。我们研究了新兴的微污染物磺胺甲恶唑在酸性水溶液中被高锰酸盐氧化的反应。反应遵循自催化动力学，对每种反应物均表现为一级反应。HMnO 的存在加速了反应速率，其反应速率比 MnO 高四个数量级。基于鉴定出的产物，确定限速步骤为金属氧物种高锰酸盐对简单 NH 键的氧化。然后，我们使用密度泛函理论（DFT）方法，以氨作为最简单的模型，对该反应机制进行了计算研究。结果表明，MnO 对 NH 键的氧化（32.86 kcal/mol）是一种协同机制，类似于 CH 键的氧化，而 HMnO 对 NH 键的氧化（10.44 kcal/mol）是一种分步的电子-质子转移。这提醒我们，布朗斯台德酸的配位不仅可以产生更强的亲电试剂，而且可以通过避免电子转移过程中的键断裂来改变反应模式。
