Carbon tetrachloride

Carbon tetrachloride
General
Systematic name	Carbon tetrachloride Tetrachloromethane
Other names	benziform, carbon chloride, methane tetrachloride, perchloromethane
Molecular formula	CCl₄
SMILES	ClC(Cl)(Cl)Cl
Molar mass	153.82 g/mol
Appearance	colorless liquid
CAS number	^*
Properties
Density and phase	1.5842 g/ml, liquid
Solubility in water	0.08 g/100 ml (20 °C)
Melting point	−22.9 °C (250 K)
Boiling point	76.8 °C (350 K)
Viscosity	0.901 cP at 25 °C
Structure
Molecular shape	tetrahedral
Dipole moment	zero
Thermodynamic data
Std enthalpy change of formation Δ_fH^o_liquid	−128 kJ/mol
Standard molar entropy S^o_gas	216.4 J.K⁻¹.mol⁻¹
Hazards
MSDS	External MSDS
EU classification	Toxic (T) Carc. Cat. 3 Dangerous for the environment (N)
NFPA 704
R-phrases	, , , ,
S-phrases	, , , , ,
Flash point	non flammable
RTECS number	FG4900000
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related carbon tetrahalides	Tetrafluoromethane Tetrabromomethane Tetraiodomethane
Related chloromethanes	Chloromethane Dichloromethane Chloroform
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Chemical infobox

Carbon tetrachloride (CCl₄), also known as tetrachloromethane, is a synthetic chemical compound formerly widely used in fire extinguishers and refrigeration, but now largely abandoned due to its toxicity. At room temperature and pressure, it is a clear, colorless liquid with a "sweet" smell that can be detected at low levels.

Both carbon tetrachloride and tetrachloromethane are acceptable names under IUPAC nomenclature, depending on whether it is seen as an inorganic or an organic compound.

It is also called carbon chloride, methane tetrachloride, perchloromethane or benziform. Colloquially, it is called "carbon tet". Trade names include Benzinoform, Freon 10, Halon 104, Tetraform, and Tetrasol.

Production

Most carbon tetrachloride is produced by reacting carbon disulfide with chlorine. At 105 to 130 °C, these chemicals react to produce carbon tetrachloride according to the chemical equation

CS₂ + 3Cl₂ → CCl₄ + S₂Cl₂

A smaller quantity of carbon tetrachloride is produced as a byproduct in the synthesis of dichloromethane and chloroform in reaction:

CH₄ + 4Cl₂ → CCl₄ + 4HCl

Chemistry

In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a carbon atom, in the center, by single covalent bonds. This symmetrical geometry results in the molecule having no net dipole moment. Therefore, carbon tetrachloride is a non-polar solvent best suited to dissolving other non-polar compounds. It is somewhat volatile, giving off vapors having a smell characteristic of other chlorinated solvents, somewhat similar to the tetrachloroethylene smell reminiscent of dry cleaner's shops. Pure carbon tetrachloride has little or, practically, no flammability at lower temperatures. Because it has no hydrogen atoms it is sometimes useful as an ¹H NMR spectroscopy solvent for non-polar samples. Because of its health risks, its use as a solvent, particularly where human contact is usual, has been minimized in the past decades.

Uses

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 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.

Prior to the Montreal Protocol, large quantities of carbon tetrachloride were used to produce the freon refrigerants R-11 and R-12. However, these refrigerants are now believed to play a role in ozone depletion and have been phased out of use, though it is still used to manufacture less destructive refrigerants.

Carbon tetrachloride has also been used in the detection of neutrinos, and is a useful source of chlorine in the Appel reaction.

Safety

Exposure to high concentrations of carbon tetrachloride (including vapor) can affect the central nervous system, including the brain. Victims may feel intoxicated and experience headaches, dizziness, sleepiness, and nausea and vomiting. These effects may subside if exposure is stopped, but in severe cases, coma and even death can occur. Chronic exposure to carbon tetrachloride can cause liver and kidney damage. When exposed, the liver swells, and its cells can be damaged or destroyed. The risk of liver damage is greater when one is exposed to carbon tetrachloride while under the influence of alcohol. Kidneys may also be damaged, causing a buildup of wastes in the blood. If exposure is low and then stops, the liver and kidneys can repair the damaged cells and function normally again.

Chronic ingestion of carbon tetrachloride has been linked to liver cancer in animals. It is not known if breathing carbon tetrachloride vapors causes cancer in animals, or if carbon tetrachloride exposure causes cancer in humans. However, the US Department of Health and Human Services holds that carbon tetrachloride may reasonably be anticipated to be a human carcinogen.

There have been no studies in people on carbon tetrachloride's effects on reproduction or development, but studies in rats showed no adverse effects.

Several tests are available to measure the amount of carbon tetrachloride in a person's breath, blood, urine, and body tissues. Because carbon tetrachloride leaves the body quickly, the tests cannot tell you how much carbon tetrachloride the subject was exposed to if there is a substantial delay between exposure and testing.

Typical recommended limits are 0.005 parts of carbon tetrachloride per million parts of drinking water (0.005 ppm). Drinking water exposures should not exceed 0.3 ppm for adults and 0.07 ppm for children for long periods of time (7 years).

There are limits on how much carbon tetrachloride can be released from an industrial plant into waste-water and the outside air. A typical maximum concentration limit in workplace air is 10 ppm for an 8-hour workday over a 40-hour working week.

Repeated sub-toxic doses of carbon tetrachloride may allow an individual to build up a partial, short-term "immunity" to toxic doses. This may be related to induction of cytochrome P450 enzymes, and is linked to the phenomenon of hormesis.

External links

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Production

Chemistry

Uses

Safety

See also

External links