Arathala Parandaman, Musah Rabi A
Department of Chemistry, University at Albany-State University of New York, 1400 Washington Avenue, Albany, New York 12222, United States.
J Phys Chem A. 2024 Mar 21;128(11):2136-2149. doi: 10.1021/acs.jpca.3c07775. Epub 2024 Mar 11.
3-Methyl-2-butene-1-thiol ((CH)C═CH-CH-SH; MBT) is a recently identified volatile organosulfur compound emitted from and is purported to contribute to its skunky odor. To understand its environmental fate, hydroxyl radical (OH)-mediated oxidation of MBT was conducted using high-level quantum chemical and theoretical kinetic calculations. Three stable conformers were identified for the title molecule. Abstraction and addition pathways are possible for the MBT + OH radical reaction, and thus, potential energy surfaces involving H-abstraction and OH addition were computed at the CCSD(T)/aug-cc-pV(T+d)Z//M06-2X/aug-cc-pV(T+d)Z level of theory. The barrier height for the addition of the OH radical to a C atom of the alkene moiety, leading to the formation of a C-centered MBT-OH radical, was computed to be -4.1 kcal mol below the energy of the starting MBT + OH radical-separated reactants. This reaction was found to be dominant compared to other site-specific H-abstraction and addition paths. The kinetics of all the site-specific abstraction and addition reactions associated with the most stable MBT + OH radical reaction were assessed using the MESMER kinetic code between 200 and 320 K. Further, we considered the contributions from two other conformers of MBT to the overall reaction of MBT + OH radical. The estimated global rate coefficient for the oxidation of MBT with respect to its reactions with the OH radical was found to be 6.1 × 10 cm molecule s at 298 K and 1 atm pressure. The thermodynamic parameters and atmospheric implications of the MBT + OH reaction are discussed.
3-甲基-2-丁烯-1-硫醇（(CH)C═CH-CH-SH；MBT）是一种最近发现的从[具体来源未给出]排放的挥发性有机硫化合物，据称它会导致其产生臭鼬气味。为了解其环境归宿，使用高水平量子化学和理论动力学计算对MBT的羟基自由基（OH）介导的氧化反应进行了研究。确定了标题分子的三种稳定构象。MBT与OH自由基反应可能存在氢原子夺取和加成途径，因此，在CCSD(T)/aug-cc-pV(T+d)Z//M06-2X/aug-cc-pV(T+d)Z理论水平下计算了涉及氢原子夺取和OH加成的势能面。计算得出OH自由基加成到烯烃部分的一个碳原子上，导致形成以碳为中心的MBT-OH自由基的势垒高度比起始的MBT + OH自由基（分离的反应物）的能量低4.1千卡/摩尔。与其他位点特异性氢原子夺取和加成路径相比，该反应占主导地位。使用MESMER动力学代码在200至320 K之间评估了与最稳定的MBT + OH自由基反应相关的所有位点特异性夺取和加成反应的动力学。此外，我们考虑了MBT的另外两种构象对MBT + OH自由基整体反应的贡献。发现在298 K和1个大气压下，MBT与OH自由基反应的氧化反应的估计全局速率系数为6.1×10 cm分子·s。讨论了MBT + OH反应的热力学参数及其大气意义。
