Zeinali Nassim, Oluwoye Ibukun, Altarawneh Mohammednoor K, Almatarneh Mansour H, Dlugogorski Bogdan Z
Discipline of Chemistry and Physics, College of Science, Health, Engineering and Education, Murdoch University, Murdoch, WA 6150, Australia.
Chemical Engineering Department, UAE University, Al-Ain 15551, United Arab Emirates.
ACS Omega. 2019 Aug 14;4(9):14040-14048. doi: 10.1021/acsomega.9b01825. eCollection 2019 Aug 27.
Monoterpenes represent a class of hydrocarbons consisting of two isoprene units. Like many other terpenes, monoterpenes emerge mainly from vegetation, indicating their significance in both atmospheric chemistry and pharmaceutical and food industries. The atmospheric recycling of monoterpenes constitutes a major source of secondary organic aerosols. Therefore, this contribution focuses on the mechanism and kinetics of atmospheric oxidation of five dominant monoterpenes (i.e., limonene, α-pinene, β-pinene, sabinene, and camphene) by singlet oxygen. The reactions are initiated via the ene-type addition of singlet oxygen (O Δ) to the electron-rich double bond, progressing favorably through the concerted reaction mechanisms. The physical analyses of the frontier molecular orbitals agree well with the thermodynamic properties of the selected reagents, and the computed reaction rate parameters. The reactivity of monoterpenes with O Δ follows the order of α-pinene > sabinene > limonene > β-pinene > camphene, i.e., α-pinene and camphene retain the highest and lowest reactivity toward singlet oxygen, with rate expressions of () (M s) = 1.13 × 10 exp(-48(kJ)/(K)) and 6.93 × 10 exp(-139(kJ)/(K)), respectively. The effect of solvent on the primary reaction pathways triggers a slight reduction in energy, ranging between 12 and 34 kJ/mol.
单萜类化合物是一类由两个异戊二烯单元组成的碳氢化合物。与许多其他萜类化合物一样，单萜类化合物主要来源于植被，这表明它们在大气化学以及制药和食品工业中都具有重要意义。单萜类化合物在大气中的循环是二次有机气溶胶的主要来源之一。因此，本论文聚焦于单线态氧对五种主要单萜类化合物（即柠檬烯、α-蒎烯、β-蒎烯、桧烯和莰烯）进行大气氧化的机理和动力学。反应通过单线态氧（OΔ）对富电子双键的烯型加成引发，通过协同反应机理顺利进行。前沿分子轨道的物理分析与所选试剂的热力学性质以及计算得到的反应速率参数吻合良好。单萜类化合物与OΔ的反应活性顺序为α-蒎烯 > 桧烯 > 柠檬烯 > β-蒎烯 > 莰烯，即α-蒎烯和莰烯对单线态氧的反应活性最高和最低，其速率表达式分别为() (M s) = 1.13 × 10 exp(-48(kJ)/(K)) 和6.93 × 10 exp(-139(kJ)/(K))。溶剂对主要反应途径的影响会使能量略有降低，降低幅度在每摩尔反应12至34千焦之间。
