Carbon Tetrafluoride, CF₄

Fluorine is the only halogen that will unite readily with carbon. Moissan has shown that in fluorine gas purified lampblack becomes incandescent, and wood-charcoal takes fire spontaneously, but that it is necessary to heat the denser forms of amorphous carbon to 50°-100° C. to induce combination; whilst graphite and gas-carbon react with fluorine only at a red heat, and diamond is unaffected at any temperature.

Carbon tetrafluoride results from the substitution of fluorine for hydrogen or halogen in methane or any of its halogen substitution products, but is best prepared by passing the vapour of carbon tetrachloride over silver fluoride heated in a metallic tube to 195°-200° C. Carbon tetrafluoride is a gas at ordinary temperatures and pressures; it is liquefied at 20° C. under four atmospheres, and at - 15° C. under one atmosphere pressure. It is slightly soluble in water, and very soluble in alcohol and ether; it reacts with the silica of heated glass, thus:

CF₄ + SiO₂ = CO₂ + SiF₄,

and with heated sodium forms fluoride with separation of carbon. It is absorbed by alcoholic potash, being gradually converted into a mixture of potassium fluoride and carbonate.

It is noteworthy that no complex acid, H₂CF₆, analogous to H₂SiF₆, has been described; and indeed that carbon tetrafluoride, like the tetrachloride, is unacted on by water.