Tetrafluoroethylene: Chlorodifluoromethane Pyrolysed in a Silver Tube at 700 °C

Tetrafluoroethylene (CF2=CF2) is the gas that polymerises to PTFE. Heat alone makes it: du Pont's Downing, Benning and McHarness (US 2,551,573, 1951) passed chlorodifluoromethane through a silver tube held at about 700 °C. Hydrogen chloride splits off and the fragments join up. In their example 28 % of the gas reacted in one pass, and 83 % of that became tetrafluoroethylene; the rest of the feed comes through unchanged. The picture: our diagram.