Carbon tetrachloride, also known by many other names (see Table) is the organic compound with the formula CCl4. It is a reagent in synthetic chemistry and was formerly widely used in fire extinguishers and as a precursor to refrigerants. It is a colorless liquid with a "sweet" smell that can be detected at low levels.
Both carbon tetrachloride and tetrachloromethane are acceptable names under IUPAC nomenclature. Colloquially, it is called "carbon tet".
Carbon tetrachloride was originally synthesised in 1839 by reaction of chloroform with chlorine, from the french chemist Henri Victor Regnault, but now it is mainly synthesized from methane:chlorination reactions, such as the syntheses of dichloromethane and chloroform. Higher chlorocarbons are also subjected to "chlorinolysis:"
Prior to the 1950s, carbon tetrachloride was manufactured by the chlorination of carbon disulfide at 105 to 130 °C:
Solid tetrachloromethane has 2 polymorphs: crystalline II below -47.5 °C (225.6 K) and crystalline I above -47.5 °C.
In the early 20th century, carbon tetrachloride was widely used as a dry cleaning solvent, as a refrigerant and put in lava lamps. Small, carbon tetrachloride fire extinguishers were widely used and took the form of a brass bottle with a hand pump to expel the liquid.
However, once it became apparent that carbon tetrachloride exposure had severe adverse health effects, safer alternatives such as tetrachloroethylene were found for these applications, and its use in these roles declined from about 1940 onward. Carbon tetrachloride persisted as a pesticide to kill insects in stored grain, but in 1970, it was banned in consumer products in the United States.
One specialty use of "carbon tet" was by stamp collectors to reveal watermarks on the backs of postage stamps. A small amount of the liquid was placed on the back of a stamp sitting in a black glass or obsidian tray. The letters or design of the watermark could then be clearly detected.
Prior to the Montreal Protocol, large quantities of carbon tetrachloride were used to produce the freon refrigerants R-11 (trichlorofluoromethane) and R-12 (dichlorodifluoromethane). However, these refrigerants are now believed to play a role in ozone depletion and have been phased out. Carbon tetrachloride is still used to manufacture less destructive refrigerants.
Carbon tetrachloride has also been used in the detection of neutrinos. Carbon tetrachloride is one of the most potent hepatotoxins (toxic to the liver), and is widely used in scientific research to evaluate hepatoprotective agents 7,8
Because it has no C-H bonds, carbon tetrachloride does not easily undergo free-radical reactions. Hence it is a useful solvent for halogenations either by the elemental halogen, or by a halogenation reagent such as N-bromosuccinimide.
In 2008, a study of common cleaning products found the presence of carbon tetrachloride in "very high concentrations" (up to 101 mg m−3) as a result of manufacturers' mixing of surfactants or soap with sodium hypochlorite.
Carbon tetrachloride is also both ozone-depleting and a greenhouse gas. However, since 1992 its atmospheric concentrations have been in decline for the reasons described above (see also the atmospheric time-series figure).