Carbon Tetrachloride
Overview
Carbon tetrachloride (CAR-bun tet-ra-KLOR-ide) is a colorless, nonflammable liquid with a sweetish odor and a density 1.5 times that of water. The compound is classified as a halogenated hydrocarbon because all of the hydrogens in methane (CH4), a hydrocarbon, have been replaced by halogen atoms (chlorine, in this case). Carbon tetrachloride was first prepared in 1839 by German-born French chemist Henri Victor Regnault (1810–1878). Regnault made carbon tetrachloride by reacting chloroform (trichloromethane; CHCl3) with chlorine: CHCl3 + Cl2 → CCl4 + HCl.
Key Facts
Other Names:
Tetrachloromethane; perchloromethane
Formula:
CCl4
Elements:
Carbon, chlorine
Compound Type:
Halogenated hydrocarbon; alkyl chloride (organic)
State:
Liquid
Molecular Weight:
153.82 g/mol
Melting Point:
−22.62°C (−8.72°F)
Boiling Point:
76.8°C (170°F)
Solubility:
Insoluble in water; miscible with ethyl alcohol, ether, benzene, chloroform, and most other organic solvents
Until the mid-twentieth century, carbon tetrachloride had a number of important applications, including use as a dry cleaning fluid, a refrigerant, and an industrial and chemical solvent. It was also used in fire extinguishers. By the 1950s, however, evidence of the serious health hazards posed by carbon tetrachloride began to accumulate, and its use was dramatically cut. In 1970, the U.S. Food and Drug Administration banned its use in consumer products in the United States.
Production of carbon tetrachloride was not seriously affected in the long run by this ban, however, as a new use was found for the chemical: the manufacture of chlorofluorocarbons (CFCs). Between the 1930s and the 1970s, the chlorofluorocarbons were among the most successful and widely used of all synthetic organic compounds. They were used in a number of applications, including as refrigerants, blowing agents, solvents, and cleaning agents. They were also used in the production of a variety of organic compounds. In the 1950s and the 1960s, demand for carbon tetrachloride was increasing at a rate of about 10 percent a year in response to the demand for CFCs.
Eventually, that use of carbon tetrachloride was also lessened. Studies conducted by American chemists Mario Molina (1943–) and F. Sherwood Rowland (1927–) showed that CFCs were responsible for the destruction of the Earth's ozone layer, posing potentially serious health hazards to plants and animals living on the planet. In response to this discovery, the world's nations agreed to cut back on the production of CFCs and the compounds from which they are made. According to the Montreal Protocol on Substances That Deplete the Ozone Layer, adopted in 1987, the production of carbon tetrachloride for use as a raw material in the manufacture of CFCs was to be first reduced, and then banned entirely by the year 2000. As a result, the production of carbon tetrachloride and its use in modern society has diminished considerably.
How It Is Made
Carbon tetrachloride is now made by a method invented more than a century ago. Carbon disulfide (CS2) is treated with chlorine gas, producing sulfur monochloride (S2Cl2) and carbon tetrachloride: CS2 + 3Cl2 → CCl4 + S2Cl2.
Interesting Facts
- Before the ban imposed by the Montreal Protocol, more than 90 percent of the chloroform produced was used in the manufacture of chlorofluorocarbons.
- Although carbon tetrachloride was once used as a fire extinguisher, this use had its potential risks. When used on electrical fires, carbon tetrachloride can react with oxygen in the air to produce phosgene (CCl2O), a poisonous gas used by Germany armies during World War I (1914–1918).
- The carcinogenic effects of carbon tetrachloride are now thought to result from the fact that the compound is converted by enzymes in the body to phosgene, which then attack cells and genes, initiating the processes by which cancer develops.
- Researchers have discovered that the bacterium Shewanella oneidensis is capable of degrading carbon tetrachloride, suggesting a possible simple and safe way to clean up areas contaminated with the compound.
This process is very efficient because the sulfur monochloride can then be treated with additional carbon disulfide to produce more carbon tetrachloride: CS2 + 2S2Cl2 → CCl4 + 6S.
A relatively small amount of carbon tetrachloride is also made in the reaction between methane gas (CH4) and chlorine gas at temperatures of 250°C to 400°C (500°F to 750°F): CH4 + 4Cl2 → CCl4 + 4HCl.
Common Uses and Potential Hazards
The effect of bans on the production of carbon tetrachloride in recent decades has been dramatic. Production of the compound in the United States dropped from more than 50,000 metric tons (55,000 short tons) in 1989 to less than 2 metric (2.2 short tons) in 1998. The compound cannot be used in any consumer or household products and has only a limited number of industrial applications. In general, its use is restricted to those situations in which no satisfactory substitute has been found. Some of these uses include:
- Certain specific and limited types of refrigeration systems;
- Degreasing metals;
- The manufacture of certain electronic products;
- Additives for some kinds of gasoline;
- The recovery of tin from tin plating operations;
- The fumigation of limited types of grains;
- Solvents for a number of industrial operations.
The average person is likely to come into contact with carbon tetrachloride in one of three ways: by inhaling vapors of the compound, by ingesting (swallowing) the compound or any product in which it is an ingredient, and (to a lesser extent), through the skin. The primary health risks from exposure to carbon tetrachloride involve damage to the liver and kidneys and, at high doses, the central nervous system. Some symptoms associated with exposure to carbon tetrachloride include soreness of the liver or kidneys, nausea, headaches, drowsiness, and disorientation. Although strong evidence is lacking, the U.S. Environmental Protection Agency has labeled carbon tetrachloride as a probable carcinogen.
Words to Know
A chemical that causes cancer in humans or other animals. Able to be mixed; especially applies to the mixing of one liquid with another. A region of Earth's atmosphere that contains a large quantity of ozone, which absorbs some of the sun's radiation.For Further Information
"Carbon Tetrachloride." 11th Report on Carcinogens. National Toxicology Program. http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s029carb.pdf (accessed on December 29, 2005).
"Carbon Tetrachloride." International Programme on Chemical Safety. http://www.inchem.org/documents/ehc/ehc/ehc208.htm#Sub-SectionNumber:3.2.1 (accessed on December 29, 2005).
"Carbon Tetrachloride." Matheson Tri-Gas. http://www.matheson-trigas.com/msds/MAT04310.pdf (accessed on December 29, 2005).
"Carbon Tetrachloride." National Safety Council. http://www.nsc.org/library/chemical/carbonte.htm (accessed on December 29, 2005).
"Chemical Fact Sheet: Carbon Tetrachloride." Spectrum Laboratories. http://www.speclab.com/compound/c56235.htm (accessed on December 29, 2005).
See Also
Chloroform
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