From the pyrolytic products of polytrifluorochloroethylene a perhaloolefin,C₄Cl₂F₆(b.p.70°),was isolated.Oxidation of the olefin afforded a perhalopropionic acid[(C₂Cl₂F₃) COOH] which was degraded through the Curtius degradation to give fluorodi-chloroacetic acid.Pyrolysis of the sodium salt of the perhalopropionic acid in ethylene glycol yielded trifluorochloroethylene and 1,1,2-trifluoro-2,2-dichloroethane,the structure of the latter was established by its infrared and proton magnetic resonance spectra.Consequently,the structure of the propionic acid is CCl₂F-CF₂- COOH,and the olefin,CCl₂F-CF₂-CF=CF₂.