Carbon tetrachloride


Carbon tetrachloride, also known by many other names is an organic compound with the chemical formula CCl4. It is a colourless liquid with a "sweet" smell that can be detected at low levels. It has practically no flammability at lower temperatures. It was formerly widely used in fire extinguishers, as a precursor to refrigerants and as a cleaning agent, but has since been phased out because of toxicity 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.

History and synthesis

Carbon tetrachloride was originally synthesized by the French chemist Henri Victor Regnault in 1839 by the reaction of chloroform with chlorine, but now it is mainly produced from methane:
The production often utilizes by-products of other chlorination reactions, such as from 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:
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. In 1992, production in the U.S./Europe/Japan was estimated at 720,000 tonnes.

Properties

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 somewhat volatile, giving off vapors with a smell characteristic of other chlorinated solvents, somewhat similar to the tetrachloroethylene smell reminiscent of dry cleaners' shops.
Solid tetrachloromethane has two polymorphs: crystalline II below −47.5 °C 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, β = 111°.
With a specific gravity greater than 1, carbon tetrachloride will be present as a dense nonaqueous phase liquid if sufficient quantities are spilled in the environment.

Uses

In organic chemistry, carbon tetrachloride serves as a source of chlorine in the Appel reaction.
One specialty use of carbon tetrachloride is in stamp collecting, to reveal watermarks on postage stamps without damaging them. A small amount of the liquid is placed on the back of a stamp, sitting in a black glass or obsidian tray. The letters or design of the watermark can then be seen clearly.

Historic uses

Carbon tetrachloride was widely used as a dry cleaning solvent, as a refrigerant, and in lava lamps. In case of the latter, carbon tetrachloride is a key ingredient that adds weight to the otherwise buoyant wax.

Solvent

It once was a popular solvent in organic chemistry, but, because of its adverse health effects, it is rarely used today. It is sometimes useful as a solvent for infrared spectroscopy, because there are no significant absorption bands > 1600 cm−1. Because carbon tetrachloride does not have any hydrogen atoms, it was historically used in proton NMR spectroscopy. In addition to being toxic, its dissolving power is low. Its use in NMR spectroscopy has been largely superseded by deuterated solvents. Use of carbon tetrachloride in determination of oil has been replaced by various other solvents, such as tetrachloroethylene. Because it has no C–H bonds, carbon tetrachloride does not easily undergo free-radical reactions. It is a useful solvent for halogenations either by the elemental halogen or by a halogenation reagent such as N-bromosuccinimide.

Fire suppression

In 1910, the Pyrene Manufacturing Company of Delaware filed a patent to use carbon tetrachloride to extinguish fires. The liquid was vaporized by the heat of combustion and extinguished flames, an early form of gaseous fire suppression. At the time it was believed the gas simply displaced oxygen in the area near the fire, but later research found that the gas actually inhibits the chemical chain reaction of the combustion process.
In 1911, Pyrene patented a small, portable extinguisher that used the chemical. The extinguisher consisted of a brass bottle with an integrated handpump that was used to expel a jet of liquid toward the fire. As the container was unpressurized, it could easily be refilled after use. Carbon tetrachloride was suitable for liquid and electrical fires and the extinguishers were often carried on aircraft or motor vehicles.
In the first half of the 20th century, another common fire extinguisher was a single-use, sealed glass globe known as a "fire grenade", filled with either carbon tetrachloride or salt water. The bulb could be thrown at the base of the flames to quench the fire. The carbon tetrachloride type could also be installed in a spring-loaded wall fixture with a solder-based restraint. When the solder melted by high heat, the spring would either break the globe or launch it out of the bracket, allowing the extinguishing agent to be automatically dispersed into the fire. A well-known brand was the "Red Comet", which was variously manufactured with other fire-fighting equipment in the Denver, Colorado area by the Red Comet Manufacturing Company from its founding in 1919 until manufacturing operations were closed in the early 1980s.

Refrigerants

Prior to the Montreal Protocol, large quantities of carbon tetrachloride were used to produce the chlorofluorocarbon refrigerants R-11 and R-12. However, these refrigerants play a role in ozone depletion and have been phased out. Carbon tetrachloride is still used to manufacture less destructive refrigerants. Carbon tetrachloride made from heavy chlorine-37 has been used in the detection of neutrinos.

Safety

Carbon tetrachloride is one of the most potent hepatotoxins, so much so that it is widely used in scientific research to evaluate hepatoprotective agents. Exposure to high concentrations of carbon tetrachloride can affect the central nervous system and degenerate the liver and kidneys, and prolonged exposure may lead to coma or death. Chronic exposure to carbon tetrachloride can cause liver and kidney damage and could result in cancer. See safety data sheets.
The effects of carbon tetrachloride on human health and the environment have been assessed under REACH in 2012 in the context of the substance evaluation by France. Thereafter, further information has been requested from the registrants. Later this decision was reversed.
In 2008, a study of common cleaning products found the presence of carbon tetrachloride in "very high concentrations" 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. CCl4 has an atmospheric lifetime of 85 years.
At high temperatures in air, it decomposes or burns to produce poisonous phosgene.