Unexpected formation of oxygen-free products and nitrous acid from the ozonolysis of the neonicotinoid nitenpyram
Unexpected formation of oxygen-free products and nitrous acid from the ozonolysis of the neonicotinoid nitenpyram
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DOI：
10.1073/pnas.2002397117
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发表时间：
2020-05
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通讯作者：
Weihong Wang;M. J. Ezell;P. Lakey;K. Aregahegn;M. Shiraiwa;B. Finlayson‐Pitts
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作者：
Weihong Wang;M. J. Ezell;P. Lakey;K. Aregahegn;M. Shiraiwa;B. Finlayson‐Pitts
烟酰胺烯啶虫胺（NPM）广泛用于农业环境和动物跳蚤控制。这可能会在与空气污染物（如臭氧）接触时被氧化，形成与母体化合物相比具有不同毒性的新产物，但对反应动力学，产物和机制知之甚少。我们在这里表明，许多臭氧分解产物的NPM不含氧，尽管高度氧化的环境。了解这种不寻常的和以前未被认识的化学是至关重要的准确评估的环境命运和影响，这种类烟碱。我们还表明，亚硝酸，空气中的高活性羟基自由基的主要来源（但其来源是有争议的），也产生。烟碱类烯啶虫胺（NPM）是一种多功能硝基烯胺[（R1N）（R2N）C=CHNO2]农药。作为一种硝基烯烃，它在结构上类似于其他新兴的污染物，如药物雷尼替丁和尼扎替丁。由于臭氧是一种常见的大气氧化剂，这些化合物在与空气接触时可能被氧化，形成与母体化合物相比具有不同毒性的新产物。在这里，我们表明，NPM的固体薄膜的气相臭氧氧化产生意想不到的产品，其中大多数不含氧，尽管高度氧化反应物。另一个令人惊讶的发现是气相亚硝酸（HONO）的形成，这是一种已知是空气中高活性羟基自由基的主要光解源的物质。动力学多层模型的应用结果表明，反应不限于表面层，但在足够高的臭氧浓度，发生在整个膜。O3−NPM反应的速率常数为1 × 10−18 cm 3·s−1，薄膜中臭氧的扩散系数为9 × 10−10 cm 2·s−1。这些研究结果突出了多官能硝基烯胺的独特化学性质，并证明了这些化合物中单个部分的已知化学机制不能从简单的烯烃中推断出来。这对于指导对农药和药品的环境归宿和影响的评估以及为设计更好的未来替代品提供指导至关重要。
Significance The neonicotinoid nitenpyram (NPM) has widespread use in agricultural settings and for flea control in animals. This may be oxidized on contact with air pollutants such as ozone to form new products that have different toxicity compared to the parent compound, yet little is known of the reaction kinetics, products, and mechanisms. We show here that many of the ozonolysis products of NPM do not contain oxygen, despite the highly oxidizing environment. Understanding such unusual and previously unrecognized chemistry is critical for accurate assessment of the environmental fates and impacts of this neonicotinoid. We also show that nitrous acid, a major source of the highly reactive hydroxyl free radical in air (but whose sources are controversial), is also generated. The neonicotinoid nitenpyram (NPM) is a multifunctional nitroenamine [(R1N)(R2N)C=CHNO2] pesticide. As a nitroalkene, it is structurally similar to other emerging contaminants such as the pharmaceuticals ranitidine and nizatidine. Because ozone is a common atmospheric oxidant, such compounds may be oxidized on contact with air to form new products that have different toxicity compared to the parent compounds. Here we show that oxidation of thin solid films of NPM by gas-phase ozone produces unexpected products, the majority of which do not contain oxygen, despite the highly oxidizing reactant. A further surprising finding is the formation of gas-phase nitrous acid (HONO), a species known to be a major photolytic source of the highly reactive hydroxyl radical in air. The results of application of a kinetic multilayer model show that reaction was not restricted to the surface layers but, at sufficiently high ozone concentrations, occurred throughout the film. The rate constant derived for the O3−NPM reaction is 1 × 10−18 cm3⋅s−1, and the diffusion coefficient of ozone in the thin film is 9 × 10−10 cm2⋅s−1. These findings highlight the unique chemistry of multifunctional nitroenamines and demonstrate that known chemical mechanisms for individual moieties in such compounds cannot be extrapolated from simple alkenes. This is critical for guiding assessments of the environmental fates and impacts of pesticides and pharmaceuticals, and for providing guidance in designing better future alternatives.