Kinetics and mechanism of the gas-phase reaction of the hydroxyl radical with meta-aminotoluene compound

Abstract

Context: An ab initio investigation into the potential energy landscape of the meta-aminotoluene + ^•OH reaction has been conducted in this study. The calculated results reveal that the reaction channel leading to the product (NHC₆H₄CH₃ + H₂O) prevails under the 300-1700 K temperature range, while the reaction path forming the product (NH₂C₆H₄CH₂ + H₂O) dominates in the higher-temperature region (T ≥ 1800 K). Within the specified temperature range, the product branching ratio for the former declines from 48 to 30%, while the latter shows an increase, reaching 29%. The overall second-order rate constants of the titled reaction obtained at the pressure 760 Torr (N₂) can be illustrated by the modified Arrhenius expression of k_total = 1.46 × 10^-13 T^0.58 exp[(-0.759 kcal.mol^-1)/RT] cm³ molecule^-1 s^-1 and k_total = 1.86 × 10^-22 T^3.24 exp[(-5.086 kcal.mol^-1)/RT] cm³ molecule^-1 s^-1, covering the temperature range of T = 300-600 K and T > 600 K, respectively. The total rate constant at the ambient conditions in this work, 1.43 × 10^-11 cm³ molecule^-1 s^-1, has been found to be roughly one order of magnitude lower than the available experimental data, ~ 1.2 × 10^-10 cm³ molecule^-1 s^-1, measured by Atkinson et al., Rinke et al., and Witte et al., or the theoretical value, 4.4 × 10^-10 cm³ molecule^-1 s^-1, and calculated by Abdel-Rahman and co-workers for the aniline + ^•OH reaction.

Methods: The structures of reactants, transition states, intermediate states, and products of the meta-aminotoluene + ^•OH reaction are calculated with the aug-cc-pVTZ basis set and the methods DFT/B3LYP and CCSD(T). The rate constants and branching ratios in the 300-2000 K temperature range are calculated with the statistical theoretical TST and RRKM master equation computations including tunneling corrections, with potential energy surface constructed by the CCSD(T)//B3LYP/aug-cc-pVTZ approach.

Keywords: Hydroxyl radical; Meta-aminotoluene; NH2C6H4CH3; RRKM; TST.