Kinetic Study of the Gas-Phase Reactions of Nitrate Radicals with Methoxyphenol Compounds: Experimental and Theoretical Approaches

详细信息    查看全文

• 作者：Amélie Lauraguais ; Atallah El Zein ; Cécile Coeur ; Emil Obeid ; Andy Cassez ; Marie-Thérèse Rayez ; Jean-Claude Rayez
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：May 5, 2016
• 年：2016
• 卷：120
• 期：17
• 页码：2691-2699
• 全文大小：459K
• 年卷期：0
• ISSN：1520-5215

文摘

The gas-phase reactions of five methoxyphenols (three disubstituted and two trisubstituted) with nitrate radicals were studied in an 8000 L atmospheric simulation chamber at atmospheric pressure and 294 ± 2 K. The NO₃ rate constants were investigated with the relative kinetic method using PTR–ToF–MS and GC-FID to measure the concentrations of the organic compounds. The rate constants (in units of cm³ molecule^–1 s^–1) determined were: 2-methoxyphenol (guaiacol; 2-MP), k_(2-MP) = (2.69 ± 0.57 × 10^–11; 3-methoxyphenol (3-MP), k_(3-MP) = (1.15 ± 0.21) × 10^–11; 4-methoxyphenol (4-MP), k_(4-MP) = (13.75 ± 7.97) × 10^–11; 2-methoxy-4-methylphenol, k_(2-M-4-MeP) = (8.41 ± 5.58) × 10^–11 and 2,6-dimethoxyphenol (syringol; 2,6-DMP), k_(2,6-DMP) = (15.84 ± 8.10) × 10^–11. The NO₃ rate constants of the studied methoxyphenols are compared with those of other substituted aromatics, and the differences in the reactivity are construed regarding the substituents (type, number and position) on the aromatic ring. This study was also supplemented by a theoretical approach of the methoxyphenol reactions with nitrate radicals. The upper limits of the NO₃ overall rate constants calculated were in the same order of magnitude than those experimentally determined. Theoretical calculations of the minimum energies of the adducts formed from the reaction of NO₃ radicals with the methoxyphenols were also performed using a DFT approach (M06-2X/6-31G(d,p)). The results indicate that the NO₃ addition reactions on the aromatic ring of the methoxyphenols are exothermic, with energy values ranging between −13 and −21 kcal mol^–1, depending on the environment of the carbon on which the oxygen atom of NO₃ is attached. These energy values allowed identifying the most suitable carbon sites for the NO₃ addition on the aromatic ring of the methoxyphenols: at the exception of the 3-MP, the NO₃ ipso-addition to the hydroxyl group is one of the favored sites for all the studies compounds.