Zhang Tianqi, von Gunten Urs
School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015, Switzerland.
School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015, Switzerland; Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf CH-8600, Switzerland.
Water Res. 2023 Aug 15;242:120131. doi: 10.1016/j.watres.2023.120131. Epub 2023 May 25.
Amides are common constituents in natural organic matter and synthetic chemicals. In this study, we investigated kinetics and mechanisms of the reactions of chlorine with seven amides, including acetamide, N-methylformamide, N-methylacetamide, benzamide, N-methylbenzamide, N-propylbenzamide, and N-(benzoylglycyl)glycine amide. Apparent second-order rate constants for the reactions of the amides with chlorine at pH 8 are in the range of 5.8 × 10 - 1.8 Ms and activation energies in the range of 62-88 kJ/mol. The second-order rate constants for the reactions of chlorine with different amides decrease with increasing electron donor character of the substituents on the amide-N and N-carbonyl-C in the amide structures. Hypochlorite (OCl) dominates the reactions of chlorine with amides yielding N-chloramides with species-specific second-order rate constants in the range of 7.3 × 10 - 2.3 Ms. Kinetic model simulations suggest that N-chlorinated primary amides further react with HOCl with second-order rate constants in the order of 10 Ms. The chlorination products of amides, N-chloramides are reactive towards phenolic compounds, forming chlorinated phenols via electrophilic aromatic substitution (phenol and resorcinol) and quinone via electron transfer (hydroquinone). Meanwhile, N-chloramides were recycled to the parent amides. At neutral pH, apparent second-order rate constants for the reactions between phenols and N-chloramides are in the order of 10-0.1 Ms, comparable to those with chloramine. The findings of this study improve the understanding of the fate of amides and chlorine during chlorination processes.
酰胺是天然有机物和合成化学品中的常见成分。在本研究中，我们研究了氯与七种酰胺反应的动力学和机理，这七种酰胺包括乙酰胺、N-甲基甲酰胺、N-甲基乙酰胺、苯甲酰胺、N-甲基苯甲酰胺、N-丙基苯甲酰胺和N-(苯甲酰甘氨酰)甘氨酸酰胺。在pH为8时，酰胺与氯反应的表观二级速率常数在5.8×10⁻¹.⁸ M⁻¹s⁻¹范围内，活化能在62 - 88 kJ/mol范围内。氯与不同酰胺反应的二级速率常数随着酰胺结构中酰胺-N和N-羰基-C上取代基给电子特性的增加而降低。次氯酸盐（OCl）主导氯与酰胺的反应，生成N-氯代酰胺，其物种特异性二级速率常数在7.3×10⁻².³ M⁻¹s⁻¹范围内。动力学模型模拟表明，N-氯代伯酰胺进一步与HOCl反应，二级速率常数约为10 M⁻¹s⁻¹。酰胺的氯化产物N-氯代酰胺对酚类化合物具有反应性，通过亲电芳香取代（苯酚和间苯二酚）形成氯代酚，通过电子转移（对苯二酚）形成醌。同时，N-氯代酰胺会再循环为母体酰胺。在中性pH下，酚类与N-氯代酰胺之间反应的表观二级速率常数约为10⁻⁰.¹ M⁻¹s⁻¹，与它们和氯胺反应的速率常数相当。本研究的结果有助于增进对氯化过程中酰胺和氯去向的理解。
