Wang Weihong, Karimova Natalia V, Gerber R Benny, Finlayson-Pitts Barbara J
Department of Chemistry, University of California Irvine, Irvine, California 92697, United States.
The Institute of Chemistry and Fritz Haber Research Center, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
J Phys Chem A. 2025 Apr 10;129(14):3289-3299. doi: 10.1021/acs.jpca.5c00826. Epub 2025 Apr 1.
Benzothiazoles are in widespread use as components of, or precursors to, a variety of consumer and industrial products. This class of compounds encompasses the simplest molecule benzothiazole (BTH) in which a benzene ring is fused to a thiazole ring, as well as a series of derivatives which are commonly functionalized at the C2 position of the thiazole ring. The addition of groups at this position modifies the reactivity in ways that are not well-known. While the reactions of benzothiazoles in water have been the subject of investigation, in part for wastewater treatment applications, much less is known about their atmospheric reactions where gas phase oxidation by the OH radical is expected to dominate. We report here studies of the kinetics, products, and mechanism of reaction of 2-methylbenzothiazole (MeBTH) with OH in the gas phase using a combination of experiments and theory. Comparison to previous studies of the OH oxidation of BTH highlights the impact of substitution of a methyl group at the 2-position on the products and reactivity. Specifically, the rate constant at 298 K and 1 atm pressure for the MeBTH-OH reaction is (3.0 ± 0.4) × 10 cm molecule s (1σ), about 50% faster than that of BTH. In addition, attack of OH on the -CH group at the 2-position of the thiazole ring to form the aldehyde as the stable product becomes important, accounting for ∼ 33% of the overall reaction. Formation of the phenol-type products from attack on the benzene ring accounts for the remainder, with the experimental relative yields consistent with theoretical predictions based on energies of formation of the prereaction MeBTH···OH complex. The formation of the aldehyde product (2-CHO-BTH) involves a sequence of five distinct stages involving two oxygen molecules and one NO. Both processes involve a spin flip of unpaired electrons, which enables a transition between electronic states that is essential for the reaction to proceed. Using the room temperature rate constant, the estimated lifetimes of MeBTH in air range from about 9 h to 4 days over OH concentrations of 10 - 10 cm. Thus, this reaction represents a significant loss process for MeBTH in air both outdoors and indoors, and exposures and toxicity of both the parent MeBTH and its oxidation products need to be taken into account in assessments of its environmental fates.
苯并噻唑作为多种消费品和工业产品的成分或前体被广泛使用。这类化合物包括最简单的分子苯并噻唑（BTH），其中苯环与噻唑环稠合，以及一系列通常在噻唑环的C2位置官能化的衍生物。在该位置添加基团以尚不为人知的方式改变了反应活性。虽然苯并噻唑在水中的反应一直是研究的主题，部分原因是用于废水处理应用，但对于它们在大气中的反应知之甚少，在大气反应中，预计OH自由基的气相氧化起主导作用。我们在此报告使用实验和理论相结合的方法对2-甲基苯并噻唑（MeBTH）与气相中的OH的反应动力学、产物和机理的研究。与先前对BTH的OH氧化研究的比较突出了在2-位取代甲基对产物和反应活性的影响。具体而言，在298 K和1个大气压下，MeBTH与OH反应的速率常数为(3.0±0.4)×10 cm分子s（1σ），比BTH快约50%。此外，OH进攻噻唑环2-位的-CH基团形成醛作为稳定产物变得很重要，占总反应的约33%。进攻苯环形成酚类产物占其余部分，实验相对产率与基于预反应MeBTH···OH络合物形成能量计算的理论预测一致。醛产物（2-CHO-BTH）的形成涉及五个不同阶段，涉及两个氧分子和一个NO。这两个过程都涉及未成对电子的自旋翻转，这使得电子态之间的跃迁成为反应进行所必需的。使用室温速率常数，在OH浓度为10 - 10 cm的情况下，MeBTH在空气中的估计寿命范围从约9小时到4天。因此，该反应是MeBTH在户外和室内空气中的一个重要损失过程，在评估其环境归宿时需要考虑母体MeBTH及其氧化产物的暴露和毒性。
