含氮消毒副产物形成机制及其前体识别的理论研究

Nitrogenous disinfection by-products (N-DBPs) have become the focus in drinking water safety field mainly due to their high toxicities and high detection rates. However, there are three problems in the research of N-DBPs, i.e., the lacks of understanding of the formation mechanisms and their precursors as well as the limited research methods, which result in the difficulty to control N-DBPs formation. Therefore, this project intends to take three typical N-DBPs as the research objects and use quantum chemistry calculations, statistical analysis and experimental verification as research methods. The formation mechanisms of N-DBPs in the complex substrates during chlorination and chloramination will be firstly systematically investigated, the structure-activity relationship of precursors and their N-DBPs formation potentials will be studied to establish a prediction model of N-DBPs precursors and put forward an environmentally friendly and economical precursor recognition method based on the theoretical study, finally this method will be applied into identify the precursors with high formation potential and then establish the precursor library of N-DBPs. The implementation of the project can not only enrich the understanding about the formation mechanisms of N-DBPs and extend the ways for precursor recognition with the theoretical significance, but also provide theoretical guidance and technical support for the development of water treatment process as well as wastewater discharge management and standard establishment of N-DBPs. It is of great value for the maintenance of human health and the sustainable development of chemical and related industries.

含氮消毒副产物(N-DBPs)因其高毒性及高检出率已成为饮用水安全保障领域关注的焦点。目前N-DBPs的研究存在对其形成机制了解不足、前体认识匮乏以及研究手段有限的三方面问题，导致难以从源头控制其形成。本项目以三类代表性的N-DBPs化合物为研究对象，运用量化计算、统计分析和实验验证研究手段，首先系统研究氯和氯氨消毒处理水中基于复杂基底的N-DBPs形成机制，探讨N-DBPs前体与其生成势的构效关系，在此基础上建立前体预测模型，提出一种基于理论计算的“环保且节约”的N-DBPs前体识别方法，最后应用该方法识别高活性前体，创建N-DBPs前体库。项目的实施既可以加强对N-DBPs形成机制的认识，扩展其前体识别的手段，具有重要的理论意义；也为开发防控N-DBPs形成的水处理工艺提供理论指导，为污废水的排放管理及相关标准的制定提供技术支撑，对人类健康的维护和化工等产业的可持续性发展具有重要价值。

本项目完成了对以强致癌性的N-亚硝基二甲胺（NDMA）、三氯硝基甲烷（TCNM）和二氯乙腈（DCAN）为代表的三类含氮消毒副产物（N-DBPs）在氯（胺）化下形成机理的研究。研究发现三级胺在氯胺化下生成NDMA包括亲核取代、胺基和过氧自由基及N-亚硝基阳离子的形成和NDMA的释放五个过程，而且发现NDMA释放过程的活化自由能（∆G≠）值与NDMA的产率密切相关。对于∆G≠值大于30 和小于20 kcal/mol的叔胺，其NDMA产率分别 <3％ 和 >25％，而且发现∆G≠值本质上与ONN(Me)2-R+键的解离能有关，可以将解离能作为前体预测模型直接评估叔胺的NDMA产率。有关TCNM的形成，发现胺和氨基酸前体在氯化下分享共同的机制，包括N-氯化，亚胺化，β-C-醇化，α-C-氯化，N-硝化和脱醛过程，基于形成机制预测出了具有迄今最高TCNM转化率的前体，并在实验上得到了证实。有关腈的形成，在碱性条件或Cl/N＞2时，氨基酸会很快降解生成腈产物，而且发现α-C取代共轭吸电基团和N-terminal取代共轭供电基团会显著促进分子间β-E反应的发生，进而生成腈。乙醛在氯胺化下也可生成DCAN，经过亲核加成、异构化、脱水反应和HCl消除过程，其中脱水反应为控速步骤；乙酰胺和N-氯-乙酰胺可以分别以N-氯-甲醇胺和腈为前体的形成路径。深入探究乙醛α-H的取代效应发现，发现被供电基团和吸电基团取代的乙醛分别有利于腈和N-氯酰胺的形成，而共轭基团取代乙醛有利于腈和N-氯酰胺两种化合物的形成。此外，还揭示了臭氧化下肼和腙生成NDMA和预臭氧化提高胺生成TCNM以及N-DBPs形成中以氮原子为中心的SN2反应机理。本项目的研究充实了N-DBPs的形成机理，扩展了其前体的识别手段；为开发防控致癌性N-DBPs形成的水处理工艺提供了理论依据和技术支撑，对提高饮用水质量和维护人类健康具有重要价值。