Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
Department of Chemistry and iClimate, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark.
Environ Sci Technol. 2020 Jun 16;54(12):7136-7145. doi: 10.1021/acs.est.0c01090. Epub 2020 May 22.
With stricter regulation of atmospheric volatile organic compounds (VOCs) originating from fossil fuel-based vehicles and industries, the use of volatile chemical products (VCPs) and the transformation mechanism of VCPs have become increasingly important to quantify air quality. Volatile methylsiloxanes (VMS) are an important class of VCPs and high-production chemicals. Using quantum chemical calculations and kinetics modeling, we investigated the reaction mechanism of peroxy radicals of VMS, which are key intermediates in determining the atmospheric chemistry of VMS. L2-RSiCHO and D3-RSiCHO derived from hexamethyldisiloxane and hexamethylcyclotrisiloxane, respectively, were selected as representative model systems. The results indicated that L2-RSiCHO and D3-RSiCHO follow a novel Si-C-O rearrangement-driven autoxidation mechanism, leading to the formation of low volatile silanols and high yield of formaldehyde at low NO/HO conditions. At high NO/HO conditions, L2-RSiCHO and D3-RSiCHO react with NO/HO to form organic nitrate, hydroperoxide, and active alkoxy radicals. The alkoxy radicals further follow a Si-C-O rearrangement step to finally form formate esters. The novel Si-C-O rearrangement mechanism of both peroxy and alkoxy radicals are supported by available experimental studies on the oxidation of VMS. Notably, the high yield of formaldehyde is estimated to significantly contribute to formaldehyde pollution in the indoor environment, especially during indoor cleaning.
随着对源自化石燃料车辆和工业的大气挥发性有机化合物 (VOCs) 的更严格监管，挥发性化学产品 (VCPs) 的使用和 VCPs 的转化机制对于量化空气质量变得越来越重要。挥发性甲基硅氧烷 (VMS) 是一类重要的 VCPs 和高产量化学品。使用量子化学计算和动力学建模，我们研究了 VMS 过氧自由基的反应机制，这是决定 VMS 大气化学的关键中间体。分别来自六甲基二硅氧烷和六甲基环三硅氧烷的 L2-RSiCHO 和 D3-RSiCHO 被选为代表性模型体系。结果表明，L2-RSiCHO 和 D3-RSiCHO 遵循一种新颖的 Si-C-O 重排驱动的自动氧化机制，导致低挥发性硅醇的形成和低 NO/HO 条件下甲醛的高产率。在高 NO/HO 条件下，L2-RSiCHO 和 D3-RSiCHO 与 NO/HO 反应形成有机硝酸盐、过氧化物和活性烷氧基自由基。烷氧基自由基进一步遵循 Si-C-O 重排步骤，最终形成甲酸盐酯。过氧和烷氧基自由基的新颖 Si-C-O 重排机制得到了 VMS 氧化的现有实验研究的支持。值得注意的是，甲醛的高产率估计会对室内环境中的甲醛污染，特别是室内清洁期间的甲醛污染产生重大影响。
