Tetrachloroethylene

Tetrachloroethylene
Tetrachloroethylene	Tetrachloroethylene
IUPAC name tetrachloroethene
Other names perchloroethene, perchloroethylene, perc, PCE
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number	127-18-4 Y
EC number	204-825-9
UN number	1897
RTECS number	KX3850000
SMILES
style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula	C2Cl4
Molar mass	165.8 g/mol
Appearance	Clear, colorless liquid
Density	1.622 g/cm3, liquid
Melting point	−19 °C (254 K)
Boiling point	121.1 °C (394 K)
Solubility in water	0.015 g/100 ml (20 °C)
Viscosity	0.89 cP at 25 °C
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
MSDS	External MSDS
R-phrases	40-51/53
S-phrases	23-36/37-61
NFPA 704	75px 0 2 0
Flash point	Not flammable
style="background: #F8EABA; text-align: center;" colspan="2" | Related compounds
Related Related Haloforms	tetrabromoethylene tetraiodoethylene
Related compounds	trichloroethylene dichloroethene tetrachloroethane
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Tetrachloroethylene, also known under its systematic name tetrachloroethene and many other names, is a chlorocarbon with the formula Cl₂C=CCl₂. It is a colourless liquid widely used for dry cleaning of fabrics, hence it is sometimes called "dry-cleaning fluid." It has a sweet odor detectable by most people at a concentration of 1 part per million (1 ppm). Worldwide production was about 1 megatonne in 1985.

Production

Michael Faraday first synthesized tetrachloroethene in 1821 by thermal decomposition of hexachloroethane.

C₂Cl₆ → C₂Cl₄ + Cl₂

Most tetrachloroethene is produced by high temperature chlorinolysis of light hydrocarbons. The method is related to Faraday's discovery since hexachloroethane is generated and thermally decomposes. Side products include carbon tetrachloride, hydrogen chloride, and hexachlorobutadiene.

Several other methods have been developed. When 1,2-dichloroethane is heated to 400 °C with chlorine, tetrachloroethene is produced by the chemical reaction:

ClCH₂CH₂Cl + 3 Cl₂ → Cl₂C=CCl₂ + 4 HCl

This reaction can be catalyzed by a mixture of potassium chloride and aluminium chloride or by activated carbon. Trichloroethylene is a major byproduct, which is separated by distillation.

Uses

Tetrachloroethylene is an excellent solvent for organic materials. Otherwise it is volatile, highly stable, and nonflammable. For these reasons, it is widely used in dry cleaning. Usually as a mixture with other chlorocarbons, it is also used to degrease metal parts in the automotive and other metalworking industries. It appears in a few consumer products including paint strippers and spot removers.

Historical applications

Tetrachloroethene was once extensively used as an intermediate in the manufacture of HFC-134a and related refrigerants. In the early 20th century, tetrachloroethene was used for the treatment for hookworm infestation.

Health and safety

The International Agency for Research on Cancer has classified tetrachloroethene as a Group 2A carcinogen, which means that it is probably carcinogenic to humans. Like many chlorinated hydrocarbons, tetrachloroethene is a central nervous system depressant and can enter the body through respiratory or dermal exposure. Tetrachloroethene dissolves fats from the skin, potentially resulting in skin irritation.

Tetrachloroethene is a common soil contaminant. Because of the mobility of PCE in groundwater, its toxicity at low levels, and its density (which causes it to sink below the water table), cleanup activities are more difficult than for oil spills. Recent research has focused on the in place remediation of soil and ground water pollution by tetrachloroethylene. Instead of excavation or extraction for above-ground treatment or disposal, tetrachloroethylene contamination has been successfully remediated by chemical treatment or bioremediation. Bioremediation has been successful under anaerobic conditions by reductive dechlorination by Dehalococcoides sp. and under aerobic conditions by cometabolism by Pseudomonas sp.

Animal studies and a study of 99 twins by Dr. Samuel Goldman and researchers at the Parkinson's Institute in Sunnyvale, California determined there is a "lot of circumstantial evidence" that exposure to Tetrachloroethlene increases the risk of developing Parkinson's disease ninefold. Larger population studies are planned.

Testing for exposure

Tetrachloroethene exposure can be evaluated by a breath test, analogous to breath-alcohol measurements. Because it is stored in the body's fat and slowly released into the bloodstream, tetrachloroethene can be detected in the breath for weeks following a heavy exposure. Tetrachloroethylene and trichloroacetic acid (TCA), a breakdown product of tetrachloroethene, can be detected in the blood.

Environmental contamination

It has been estimated that about 85% of tetrachloroethylene is released into the atmosphere; OECD models assumed 90% release into the air and 10% to water. Based on these models, its distribution in the environment is estimated to be in the air (76.39% - 99.69%), water (0.23% - 23.2%), soil (0.06-7%), with the remainder in the sediment and biota. Estimates of lifetime in the atmosphere vary, but a 1987 survey estimated the lifetime in the air has been estimated at about 2 months in the Southern Hemisphere and 5-6 months in the Northern Hemisphere. Degradation products observed in a laboratory include phosgene, trichloroacetyl chloride, hydrogen chloride, carbon dioxide, and carbon monoxide. In water, tetrachloroethylene is degraded very slowly by hydrolysis, and it is persistent under aerobic conditions. It is degraded through reductive dechlorination under anaerobic conditions, with the degradation products including trichloroethene, dichloroethene, vinyl chloride, ethene, and ethane.

Further reading

• "Toxicological Profile for Tetrachloroethene". Agency for Toxic Substances and Disease Registry. 1997. 

• Doherty, R.E. (2000). "A History of the Production and Use of Carbon Tetrachloride, Tetrachloroethylene, Trichloroethylene and 1,1,1-Trichloroethane in the United States: Part 1 - Historical Background; Carbon Tetrachloride and Tetrachloroethylene". Journal of Environmental Forensics. 1: 69–81. doi:10.1006/enfo.2000.0010. 

External links

• ATSDR Case Studies in Environmental Medicine: Tetrachloroethylene Toxicity U.S. Department of Health and Human Services
• Australian National Pollutant Inventory (NPI) page
• "Toxic Fumes May Have Made Gunman Snap", by Julian Kesner, New York Daily News, April 20, 2007.bg:Тетрахлороетен

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