Shock wave studies of the pyrolysis of fluorocarbon oxygenates. I. The thermal dissociation of C 3 F 6 O and CF 3 COF

HINTZER, K.; THALER, A.; COBOS, C. J.; TELLBACH, E.; SÖLTER, L.; TROE, J.

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Año: 2017 vol. 19 p. 3151 - 3158

1463-9076

The thermal decomposition of hexafluoropropylene oxide, C3F6O, to perfluoroacetyl fluoride, CF3COF, and CF2 has been studied in shock waves highly diluted in Ar between 630 and 1000 K. The measured rate constant k1 = 1.1 1014 exp(162(4) kJ mol1/RT) s1 agrees well with literature data and modelling results. Using the reaction as a precursor, equimolar mixtures of CF3COF and CF2 were further heated. Combining experimental observations with theoretical modelling (on the CBS-QB3 and G4MP2 ab initio composite levels), CF3COF is shown to dissociate on two channels, either leading to CF2 + COF2 or to CF3 + FCO. By monitoring the CF2 signals, the branching ratio was determinedbetween 1400 and 1900 K. The high pressure rate constants for the two channels were obtained from theoretical modelling as k5,N(CF3COF - CF2 + COF2) = 7.1 1014 exp(320 kJ mol1/RT) s1 and k6,N(CF3COF - CF3 + FCO) = 3.9 1015 exp(355 kJ mol1/RT) s1. The experimental results obtained at [Ar] E 5 106 mol cm3 were consistent with modelling results, showing that the reaction is in the falloff range of the unimolecular dissociation. The mechanism of secondary reactions following CF3COF dissociation has been analysed as well.