The State Agriculture Ministry Laboratory of Quality & Safety Risk Assessment for Tobacco, Tobacco Research Institute, Chinese Academy of Agricultural Sciences, Qingdao 266101, China.
Environ Sci Process Impacts. 2018 May 23;20(5):790-797. doi: 10.1039/c8em00024g.
Quinclorac, a widely used herbicide in agriculture, has been recognized as an emerging environmental pollutant owing to its long persistence and potential risk to humans. However, no related information is available on the degradation of quinclorac by employing oxidants. Herein, the reactivity of quinclorac with permanganate was systematically investigated in water by combining experimental and computational approaches. The reaction followed overall second-order kinetics pointing to a bimolecular rate-limiting step. The second-order rate constant was found to be 3.47 × 10-3 M-1 s-1 at 25 °C, which was independent of pH over the range from 5 to 9 and was dependent on temperature over the range from 19 to 35 °C. The initial product was identified by UPLC-Q-TOF-MS to be mono-hydroxylated quinclorac, which was more susceptible to further oxidation. The result could be supported by the complete simulation of the reaction process in DFT calculations, indicating the [3 + 2] cycloaddition oxidation of the benzene ring in the rate-limiting step. The plausible mechanism was then proposed, accompanied by the analysis of the HOMO indicating the hydroxylation position and of the ESP suggesting a more electron-rich moiety. Considering the high effectiveness and low toxicity, permanganate oxidation was considered to be a very promising technique for removing quinclorac from aquatic environments.
百草枯，一种在农业中广泛使用的除草剂，由于其持久性和对人类的潜在风险，已被认为是一种新兴的环境污染物。然而，关于氧化剂降解百草枯的相关信息还没有。在此，通过实验和计算相结合的方法，系统地研究了锰酸钾与百草枯在水中的反应性。反应遵循总体二级动力学，表明这是一个双分子速率限制步骤。在 25°C 下，发现二级速率常数为 3.47×10-3 M-1 s-1，在 pH 值为 5 到 9 之间是独立的，并且在 19 到 35°C 之间随温度变化而变化。通过 UPLC-Q-TOF-MS 鉴定初始产物为单羟基化百草枯，它更容易进一步氧化。该结果可以通过 DFT 计算中对反应过程的完全模拟得到支持，表明在速率限制步骤中存在苯环的[3 + 2]环加成氧化。然后提出了可能的机制，并分析了 HOMO 表明了羟基化位置和 ESP 表明了一个更富电子的部分。考虑到高功效和低毒性，锰酸钾氧化被认为是一种很有前途的技术，可以从水生环境中去除百草枯。
