Carbon tetrachloride

Carbon tetrachloride, also known by many other names (such as carbon tet for short and tetrachloromethane, also recognised by the IUPAC), is a chemical compound with the chemical formula CCl₄. It is a non-flammable, dense, colourless liquid with a chloroform-like sweet odour that can be detected at low levels. It was formerly widely used in fire extinguishers, as a precursor to refrigerants, an anthelmintic and a cleaning agent, but has since been phased out because of environmental and safety concerns. Exposure to high concentrations of carbon tetrachloride can affect the central nervous system and degenerate the liver and kidneys. Prolonged exposure can be fatal.

In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a central carbon atom by single covalent bonds. Because of this symmetric geometry, CCl₄ is non-polar. Methane gas has the same structure, making carbon tetrachloride a halomethane. As a solvent, it is well suited to dissolving other non-polar compounds such as fats and oils. It can also dissolve iodine. It is volatile, giving off vapors with an odor characteristic of other chlorinated solvents, somewhat similar to the tetrachloroethylene odor reminiscent of dry cleaners' shops.

Solid tetrachloromethane has two polymorphs: crystalline II below −47.5°C (225.6 K) and crystalline I above −47.5°C. At −47.3°C it has monoclinic crystal structure with space group C2/c and lattice constants a = 20.3, b = 11.6, c = 19.9 (.10⁻¹ nm), β = 111°.

With a specific gravity greater than 1, carbon tetrachloride will be present as a dense nonaqueous phase liquid if sufficient quantities are spilt in the environment.

Despite being generally inert, carbon tetrachloride can undergo various reactions. Hydrogen or an acid in the presence of an iron catalyst can reduce carbon tetrachloride to chloroform, dichloromethane, chloromethane and even methane. When its vapours are passed through a red-hot tube, carbon tetrachloride dechlorinates to tetrachloroethylene and hexachloroethane.

Carbon tetrachloride, when treated with HF, gives various compounds such as trichlorofluoromethane (R-11), dichlorodifluoromethane (R-12), chlorotrifluoromethane (R-13) and carbon tetrafluoride with HCl as the by-product:

This was once one of the main uses of carbon tetrachloride, as R-11 and R-12 were widely used as refrigerants.

An alcohol solution of potassium hydroxide decomposes it to potassium chloride and potassium carbonate in water: