Kinetics and mechanism of ozone addition to tetrafluoroethylene and hexafluoropropylene

The DSC method was used to study the low-temperature (77-280 K) ozonolysis of perfluoroleflns, tetrafluoroethylene (TFE) and hexafluoropropylene (HFP), in the direct interaction with ozone in the absence of solvents and oxygen. The values of activation energy (E-a/kJ mol(-1)), rate constants (k/L (mol s)(-1)), and the Arrhenius equation were obtained: for TFE k = 1.2 center dot 10(6)exp[(-42.0 +/- 2)/(RT)] at T = 150-165 K and for HFP k = 1.2 center dot 10(3)exp[(-39.9 +/- 2)/(RT)] at T = 170-190 K. The quantum chemical calculation for the addition of ozone to TFE and HFP via the mechanisms of concerted (Criegee mechanism) and nonconcerted (DeMore mechanism) addition was performed at the UB2PLYP/aug-cc-pVDZ level. The ozonolysis of TFE proceeds via the DeMore mechanism, whereas both mechanisms contribute certainly to the reaction of HFP ozonolysis.