Carbon Tetrachloride

Carbon tetrachloride is known by many other names (Tetrachloromethane, Carbon tet, benziform, Methane tetrachloride, Tetrasol, Freon 10, etc.).  Both carbon tetrachloride and tetrachloromethane are acceptable names under international naming conventions.  Colloquially, it is called "carbon tet".  Its chemical formula is 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.

The production of carbon tetrachloride has steeply declined since the 1980s due to environmental concerns and the decreased demand for CFCs, which were derived from carbon tetrachloride.

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.

In the early 20th century, carbon tetrachloride was widely used as a dry cleaning solvent, as a refrigerant, and in fire extinguishers. 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 is one of the most potent hepatotoxins (substances toxic to the liver), and is widely used in scientific research to evaluate hepatoprotective agents (substances that protect the liver).

Carbon tetrachloride has practically no flammability at lower temperatures. Under high temperatures in air, it forms poisonous phosgene.  Carbon tetrachloride is used as a solvent in synthetic chemistry research, but because of its adverse health effects, it is no longer commonly used, and chemists generally try to substitute it with other solvents.

Safety
Exposure to high concentrations of carbon tetrachloride (including vapor) can affect the central nervous system, destroy the liver and kidneys and may result (after prolonged exposure) in coma and even death.  Chronic exposure to carbon tetrachloride can cause liver and kidney damage and could result in cancer.

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.