DFT Insight into the Kinetics and Mechanism of the OH.‐Initiated Atmospheric Oxidation of Catechol: OH. Addition and Hydrogen Abstraction Pathways

• Published in: ChemistrySelect (Weinheim) 2021-04, Vol.6 (16), p.3875-3883
• Main Authors: Rahbar, Ali, Zahedi, Ehsan, Aghaie, Hossein, Giahi, Masoud, Zare, Karim
• Format: Article
• Language: English
• Subjects: Catechol; Hydroxyl radical; Kinetics; Mechanism; Oxidation
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.202100524

Gas phase oxidation of catechol with hydroxyl radical is expected as dominant atmospheric removal process. The mechanism and kinetics of OH.‐initiated atmospheric oxidation of catechol was investigated theoretically by employing of M06‐2X/aug‐cc‐pVTZ level of theory at 300 K and 760 Torr by considering of OH. addition and H‐atom ion reactions. Oxidation of catechol begins with reversible formation of pre‐reactive molecular complex and its conversion to products in unimolecular manner. Fall‐off pressure expression indicated that canonical transition state theory breaks down to estimate rate constant at 760 Torr. RRKM unimolecular rates were corrected for basis set superposition error and quantum tunneling effects. RRKM bimolecular rates for OH. addition and H‐atom ion pathways at 300 K and 760 Torr were about 10−12 cm3 molecule−1 s−1. The RRKM bimolecular rate for oxidation of catechol triggered by OH. at 300 K and 760 Torr was 9.45×10−12 cm3 molecule−1 s−1 and its temperature dependence over 200–400 K can be expressed by the lnk=(2929.8/T)+(5.82×10−16), indicating that reaction rate is negatively dependent on the temperature. H‐atom ion from the hydroxy group at the C2 position and addition of OH. onto the C2 atom are the most favorable processes. Evolution of branching ratios demonstrate that the OH.‐initiated oxidation of catechol is not essentially selective process. The kinetics and mechanism of the gas phase oxidation of catechol initiated by hydroxyl radical have been studied theoretically. The RRKM bimolecular rate at 300 K and 760 Torr was 9.45×10−12 cm3 molecule−1 s−1 and its temperature dependence over 200–400 K was lnk=(2929.8/T)+(5.82×10−16), indicating that reaction rate is negatively dependent on the temperature.