Thermal decomposition of FC(O)OCH₃ and FC(O)OCH₂CH₃

Abstract

The thermal decomposition of methyl and ethyl formates has been extensively studied due to their importance in the oxidation of several fuels, pesticidal properties and their presence in interstellar space. We hitherto present the study of the thermal decomposition of methyl and ethyl fluoroformates, which could help in the elucidation of the reaction mechanisms. The reaction mechanisms were studied using FTIR spectroscopy in the temperature range of 453-733 K in the presence of different pressures of N2 as bath gas. For FC(O)OCH3 two different channels were observed; the unimolecular decomposition which is favored at higher temperatures and has a rate constant kFC(O)OCH3 = (5.3 ± 0.5) × 1015 exp[-(246 ± 10 kJ mol-1/RT)] (in units of s-1) and a bimolecular channel with a rate constant kFC(O)OCH3 = (1.6 ± 0.5) × 1011 exp[-(148 ± 10 kJ mol-1/RT)] (in units of s-1 (mol L)-1). However for ethyl formate, only direct elimination of CO2, HF and ethylene operates. The rate constants of the homogeneous first-order process fit the Arrhenius equation kFC(O)OCH2CH3 = (2.06 ± 0.09) × 1013 exp[-(169 ± 6 kJ mol-1/RT)] (in units of s-1). The difference between the mechanisms of the two fluoroformates relies on the stabilization of a six-centered transition state that only exists for ethyl formate. First principles calculations for the different channels were carried out to understand the dynamics of the decomposition.

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

“…The theoretical energy barrier for TS1–6 is (114 ± 5) kJ mol –1 , where we considered the hydrogen-bond interaction between the two reagents (Figure S3) as the error in the definition of the ZPE. The stability of six-center structures over the four-center ones is well-known for this kind of processes, , and in our case, the stability is ≈100 kJ mol –1 (depending on the method used). The energies along the IRC for the two pathways calculated at the B3LYP level of theory are plotted in Figure .…”

“…Carbonyl fluoride (CF 2 O) and trifluoroacetic acid (TFA) could account for almost a third of the inorganic fluorinated compounds in the atmosphere, − and it is expected that their concentrations will increase in the future. − This is due to the current widespread use of replacements, that is, hydrofluorocarbons and hydrofluoroethers, as well as the past use of chlorofluorocarbons. − Though their concentrations are still far from becoming an environmental problem (its mutual reaction has not yet become an environmental issue), the reaction is of interest from the point of view of fluorine as well as physical chemistry. It affords a new fluorooxygenated compound to be synthesized and characterized and allows fundamental kinetic parameters to be known.…”