Chloramination of Nitromethane: Incomplete Chlorination and Unexpected Substitution Reaction
Chloramination of Nitromethane: Incomplete Chlorination and Unexpected Substitution Reaction
复制标题
硝基甲烷的氯胺化：不完全氯化和意外的取代反应
DOI：
10.1021/acs.est.2c09821
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发表时间：
2023
影响因子：
11.4
通讯作者：
McCurry, Daniel L.
中科院分区：
文献类型：
--
作者：
Shi, Jiaming Lily;Kim, Euna;Cardosa, Georgia B.;McCurry, Daniel L.
臭氧通常用作饮用水回用处理列车的预消毒剂。硝基甲烷是一种普遍存在于废水中的臭氧副产物，也是臭氧化废水二次氯消毒过程中生成氯化苦的关键中间体。然而，许多公用事业公司已经从游离氯转向氯胺作为二级消毒剂。与游离氯不同，氯胺转化硝基甲烷的反应机理和动力学尚不清楚。本文研究了硝基甲烷氯胺化反应的动力学、反应机理和产物。预期的主要产物是氯化苦，因为通常认为氯胺的反应类似于游离氯，尽管比游离氯反应慢。在酸性、中性和碱性条件下观察到氯化苦的不同摩尔产率，令人惊讶的是，发现了氯化苦以外的转化产物。在碱性pH下检测到一氯硝基甲烷和二氯硝基甲烷，并且在中性pH下最初的质量平衡很差。来自一种新发现的途径，该途径涉及一氯胺作为亲核试剂而不是卤化剂通过推测的SN 2机制进行反应。该研究表明，硝基甲烷氯胺化，不像氯化，可能会产生一系列的产品，其形态是pH值和反应时间的函数。
Ozone is commonly used as a predisinfectant in potable water reuse treatment trains. Nitromethane was recently found as a ubiquitous ozone byproduct in wastewater, and the key intermediate toward chloropicrin during subsequent secondary disinfection of ozonated wastewater effluent with chlorine. However, many utilities have switched from free chlorine to chloramines as a secondary disinfectant. The reaction mechanism and kinetics of nitromethane transformation by chloramines, unlike those for free chlorine, are unknown. In this work, the kinetics, mechanism, and products of nitromethane chloramination were studied. The expected principal product was chloropicrin, because chloramines are commonly assumed to react similarly to, although more slowly than, free chlorine. Different molar yields of chloropicrin were observed under acidic, neutral, and basic conditions, and surprisingly, transformation products other than chloropicrin were found. Monochloronitromethane and dichloronitromethane were detected at basic pH, and the mass balance was initially poor at neutral pH. Much of the missing mass was later attributed to nitrate formation, from a newly identified pathway involving monochloramine reacting as a nucleophile rather than a halogenating agent, through a presumed SN2 mechanism. The study indicates that nitromethane chloramination, unlike chlorination, is likely to produce a range of products, whose speciation is a function of pH and reaction time.