Gas-Phase reaction between CF2O and CF3C(O)OH: Characterization of CF3C(O)OC(O)F

Abstract

The thermal decomposition of trifluoroacetic acid and carbonyl fluoride (CF2O) has been extensively studied because of their importance in the oxidation of hydrochlorofluorocarbons in the atmosphere. We hitherto present the study of the thermal reaction between these two molecules. The reaction mechanism was studied using Fourier transform infrared spectroscopy in the temperature range of 513-573 K. The reaction proceeds homogeneously in the gas phase through the formation of a reaction intermediate, here characterized as CF3C(O)OC(O)F (detected for the first time in this work), the major final products being CF3C(O)F, HF, and CO2. We demonstrate that the reaction is first-order with respect to each reagent, second-order global and the mechanism consists of two steps, the first being the rate-determining one. The Ea = 110.1 ± 6.1 kJ mol-1 and A = (1.2 ± 0.2) × 10-12 cm3 molec-1 s-1 values were obtained from the experimental data. The low activation energy is explained by the hydrogen-bond interactions between the -OH group of the acid and the F atom of the CF2O. First-principles calculations at the G4MP2 level of theory were carried out to understand the dynamics of the decomposition. Thermodynamic activation values found for this reaction are as follows: Î"H⧧ = 105.6 ± 6.4 kJ mol-1, δS- = -88.6 ± 9.7 J mol-1 K-1, and δG = 153.7 ± 13.5 kJ mol-1. The comparison between theory and experimental results showed excellent similarities, thus strengthening the proposed mechanism.