Coumarins are important chemical precursors for the synthesis of anticoagulants used as human medicines as well as rodenticides. Environmental discharge of these coumarin derivatives, commonly known as 4-hydroxycoumarins, is therefore a major concern. Advanced oxidative processes (AOP) are radical reactions of toxic contaminants with environmental free radicals, ideally leading to less toxic products. Therefore, the study of these processes is of key importance for a better understanding of the chemical transformations and long term environmental effect of toxic discharges. Here the AOP of the unsubstituted 4-Hydroxycoumarin (4HC), the parent compound of the drugs and pesticides, is studied with HO˙ radical in aqueous and lipidic environments, using quantum chemical methods. Two reaction steps were modelled by considering the fundamental radical reactions of phenolic compounds as established before. Particular attention is paid to the reactions in aqueous environment. Thermodynamic and kinetic calculations were performed, assessing the likelihood and contribution of each possible reaction path to yield the most likely products. Previous works on AOP of 4HC neglected the deprotonation of the acidic moiety and the diffusion limits of the solvent. Here these points are addressed, predicting a different set of intermediate and final products. Toxicity tests predict that the main products are less toxic than 4HC. Our results demonstrate the importance of aqueous environment in the chemical fate of toxins in the environment.

中文翻译：

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4-羟基香豆素与环境中羟基自由基的反应：去质子化和扩散效应

香豆素是合成用作人类药物和杀鼠剂的抗凝血剂的重要化学前体。因此，通常称为 4-羟基香豆素的这些香豆素衍生物的环境排放是一个主要问题。高级氧化过程 (AOP) 是有毒污染物与环境自由基的自由基反应，理想情况下会产生毒性较低的产品。因此，研究这些过程对于更好地了解有毒排放的化学转化和长期环境影响至关重要。这里未取代的 4-羟基香豆素 ( 4HC)的 AOP)，药物和农药的母体化合物，使用量子化学方法在水和脂质环境中用 H2O2 自由基进行研究。通过考虑之前建立的酚类化合物的基本自由基反应，对两个反应步骤进行建模。特别关注水性环境中的反应。进行了热力学和动力学计算，评估了每种可能的反应路径产生最可能的产物的可能性和贡献。以前关于4HC 的AOP 的工作忽略了酸性部分的去质子化和溶剂的扩散限制。在这里解决了这些问题，预测了一组不同的中间产品和最终产品。毒性试验预测主要产品毒性低于4HC. 我们的结果证明了水环境在环境中毒素的化学归宿中的重要性。