Carbon Halide

any of the compounds of carbon with the halogens. Carbon halides are usually regarded as derivatives of hydrocarbons, in which hydrogen has been wholly replaced by a halogen.

The simplest carbon halides are tetrahalides of the general formula CX₄. These compounds have a tetrahedral structure, with the C—F, C—Cl, C—Br, and C—I bond lengths equal to, respectively, 1.36, 1.76, 1.94, and 2.12 angstroms and bond energies equal to, respectively, 487, 340, 285, and 214 kilojoules per mole (or 116, 81, 68, and 51 kilocalories per mole). Under ordinary conditions, CF₄ is a gas with a boiling point of – 128°C; CC1₄is a liquid with a melting point of – 22.9°C and a boiling point of 76.8°C; and CBr₄ and CI₄ are solids with melting points of 93.7°C and 171°C, respectively. All the tetrahalides, virtually insoluble in water, are soluble in organic solvents.

The stability of CX₄ compounds decreases with decreasing bond energy, and the chemical reactivity increases in moving from fluorine to iodine. The compounds CF₄ and CC1₄ are stable when heated and when exposed to air, light, or acids. CI₄ readily decomposes upon heating. Only CF₄ can be obtained by a direct reaction of its constituent elements. One of the methods for the synthesis of CC1₄ and CBr₄ is the reaction of CS₂ with the corresponding halogens. CI₄ is obtained from the reaction of CC1₄ with the iodides of aluminum, bismuth, and other metals.

Carbon tetrachloride has the greatest importance among the carbon tetrahalides. Mixed carbon halides are also known, for example, CC1F₃, CBr₂Cl₂, and C₂Br₂F₄. Many carbon halides are widely used in various industries. For example, difluorodi-chloromethane (CC1₂F₂) and trichlorofluoromethane (CC1₃F) are used as coolants in refrigerators (Freons); tetrafluoroethylene (C₂F₄) and trifluorochloroethylene (C₂C1F₃) are used as monomers in the production of fluoroplastics; hexachloroethane (C₂CI₆) serves as a camphor substitute; and certain carbon halides containing fluorine and chlorine are components of synthetic oils.