Theoretical investigation on the mechanism and kinetics of the OH'-initiated atmospheric degradation of p-chloroaniline via OH'-addition and hydrogen abstraction pathways

Atmospheric oxidative degradation of p-chloroaniline (PCA) initiated by OH' has been studied theoretically at the M06-2X/aug-cc-pVTZ and CBS-QB3//M06-2X/aug-cc-pVTZ levels, coupled with kinetic calculations using the RRKM/ZCT method over the temperature range of 250-350 K. The calculations exhibit that the OH' addition and hydrogen atom abstraction pathways are thermodynamically favorable. RRKM results revealed that the atmospheric oxidation of PCA is dominated by OH addition to the C1 and C2 atoms and hydrogen atom abstraction from amino group. The individual and overall rate coefficients of PCA reaction triggered by OH' at 1 bar are negatively linear dependent on the temperature and their values are consistent with the experimental data. RRKM calculations also show that the transition state theory approximation for estimation of rate coefficients at ambient pressure breaks down and very high pressures are essential to be valid. The atmospheric lifetime at the benchmark CBS-QB3 level is smaller than 2 days.