Chlorodifluoromethane, thermal decomposition

Difluorocarbene can be generated by high-temperature reaction of chlorodifluoromethane in the production of tetrafluoroethylene (TFE) (equation 48). Another method of in situ generation of the carbene is thermal decomposition of... 

Pyrolysis of hexafluoropropylene oxide generates difluorocarbene for cyclo-propanation reactions, as does the action of heat on chlorodifluoromethane. Halogenocarbenes formed in the thermal decomposition of polyhalogenomethanes at 500—650°C can be trapped by cyclopentene and cyclohexene. The primary adducts are unstable under these conditions, suffering dehydrohalogenation to halogeno-benzenes and cycloheptadienes, respectively. ... 

Kinetic studies on the static gas-phase thermal decomposition of the halogenomethanes CHFgCI (temperature range 434—S23 °C, initial reactant pressure 100—500 Torr) and CHF (437—515 C, 20—250 Torr) have established that the initial mechanistic step is a-eliraination of HX (X = Cl or Br) leading to difluorocarbene release, a reaction that has been put to preparative use in the synthesis of gem-difiuorocyclopropylsilanes [via flow copyrolysis of vinylchlorosilanes with chlorodifluoromethane at 485— 505 C (see p. 197)]. Fluoro-carbenes, -carbenoids, or -carbenoid complexes have also featured in several other pieces of work on the synthesis of halogenocyclopropanes [for example, see Schemes 29, 30 (olefins used... 

One of the best-known thermal reactions of fluorine compounds is the pyrolysis of chlorodifluoromethane to tetrafluoroethylene as used in the production of Teflon polymer. This reaction was described by Park et in 1947, and Nor-ton" in 1957 reported an activation energy of 49 kcal.mole for the decomposition over silica at 425-525 °C. More recently, Gozzo and Patrick have made a kinetic study of the process using a helium flow system at 670-750 °C with a surface conditioned platinum tubular reactor. HCl is found to retard the raction and the following mechanism has been proposed... 

There are a number of ways to prepare HFP. Excellent hexafluoropropylene yields from the thermal degradation of heptafluorobutyrate (CF3CF2CF2COONa) have been reported.Cracking of tetrafluoroethylene in a stainless steel tube at 700-800°C under vacuum is an efficient route for the production of HFP. TFE conversions up to 72% and HFP yields of 82% have been reportedf lP Octa-fluorocyclobutane (TFE dimer), octafluoroisobutylene, and some polymer are the major side products of cracking. The presence of a small amount (3-10%) of chlorodifluoromethane stops the formation of poly-mer.P lThermal decomposition of PTFE under 20 ton-vacuum at 860°C yields 58% hexafluoropropylene. 1... 

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