Carbon tetrachloride
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General |
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| Name | Carbon tetrachloride |
| Synonyms | benziform, carbon chloride, methane tetrachloride, perchloromethane , tetrachloromethane |
| Chemical formula | CCl4 |
| Appearance | Colourless liquid |
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Physical |
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| Formula weight | 153.8 amu |
| Melting point | 250 K (-23 °C) |
| Boiling point | 350 K (77 °C) |
| Density | 1.6 ×103 g/cm3 |
| Solubility | 0.08 g in 100g water |
| Dipole moment | 0.0 D |
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| ΔfH0gas | -95.5 kJ/mol |
| ΔfH0liquid | -128 kJ/mol |
| ΔfH0solid | -130.5 kJ/mol |
| S0gas, 1 bar | ? J/mol·K |
| S0liquid, 1 bar | 216 J/mol·K |
| S0solid | ? J/mol·K |
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Safety | |
| Ingestion | Very dangerous, long term exposure can cause brain damage. |
| Inhalation | As for ingestion. |
| Skin | May cause irritation. |
| Eyes | May cause irritation. |
| More info | Hazardous Chemical Database (http://ull.chemistry.uakron.edu/erd/chemicals/7/6262.html) |
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SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references </font> | |
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Production
Most carbon tetrachloride is produced by reacting carbon disulfide with chlorine. At 105-130°C, these chemicals react to produce carbon tetrachloride according to the chemical equation
A smaller quantity of carbon tetrachloride is produced as a byproduct in the synthesis of methylene chloride and chloroform.
Chemistry
In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral geometry, joined to a carbon atom in the center by single covalent bonds. This symmetrical configuration results in the molecule having no net dipole moment. Therefore, carbon tetrachloride is a non-polar solvent, best at dissolving other non-polar compounds. It is somewhat volatile, giving off vapors having a smell characteristic of other chlorinated solvents, somewhat similar to the perchloroethylene smell reminiscent of some dry cleaner 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 solvent for non-polar samples. Because of its the health risks, its use as a solvent, etc. 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. However, carbon tetrachloride is still used to manufacture less destructive refrigerants.
Carbon tetrachloride has also been used in the detection of neutrinos.
Carbon tetrachloride, like chloroform, is a useful source of chlorine in the Appel reaction.
Health effects
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.
See also
de:Tetrachlormethan es:Tetracloruro de carbono fr:Tétrachlorure de carbone nl:Tetrachloormethaan
ja:四塩化炭素