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.
REFERENCEAkhmotov, N. S. Neorganicheskaia khimiia, 2nd ed. Moscow, 1975.
B. A. POPOVKIN