Tetrachloroethylene

Tetrachloroethylene

Names
IUPAC name Tetrachloroethene
Other names Perchloroethene; Perchloroethylene; Perc; PCE
Identifiers
CAS Number	127-18-4 Y
ChEBI	CHEBI:17300 N
ChEMBL	ChEMBL114062 Y
ChemSpider	13837281 Y
EC Number	204-825-9
Jmol 3D model	Interactive image
KEGG	C06789 Y
RTECS number	KX3850000
UNII	TJ904HH8SN Y
UN number	1897
InChI InChI=1S/C2Cl4/c3-1(4)2(5)6 Y Key: CYTYCFOTNPOANT-UHFFFAOYSA-N Y InChI=1/C2Cl4/c3-1(4)2(5)6 Key: CYTYCFOTNPOANT-UHFFFAOYAO
SMILES Cl/C(Cl)=C(/Cl)Cl
Properties
Chemical formula	C2Cl4
Molar mass	165.82 g·mol−1
Appearance	Clear, colorless liquid
Odor	mild, chloroform-like
Density	1.622 g/cm3
Melting point	−19 °C (−2 °F; 254 K)
Boiling point	121.1 °C (250.0 °F; 394.2 K)
Solubility in water	0.15 g/L (25 °C)
Vapor pressure	14 mmHg (20°C)
Viscosity	0.89 cP at 25 °C
Vapor pressure	{{{value}}}
Related compounds
Related Related organohalides	Tetrabromoethylene Tetraiodoethylene
Related compounds	Trichloroethylene Dichloroethene Tetrachloroethane
Supplementary data page
Structure and properties	Refractive index (n), Dielectric constant (εr), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	UV, IR, NMR, MS
N verify (what is YN ?)
Infobox references

Tetrachloroethylene, also known under the systematic name tetrachloroethene, or perchloroethylene ("perc" or "PERC"), and many other names, is a chlorocarbon with the formula Cl₂C=CCl₂. It is a colorless 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 one million metric tons in 1985.

Production

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

C₂Cl₆ → C₂Cl₄ + Cl₂

Most tetrachloroethylene 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, tetrachloroethylene 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.

According to an United States Environmental Protection Agency (EPA) report of 1976, the quantity of tetrachloroethylene produced in the United States in the 1973 totaled 320,000 metric tons (706 million lb). By 1993, the volume produced in the United States had dropped to 123,000 metric tons (271 million lb).

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. It is also used to degrease metal parts in the automotive and other metalworking industries, usually as a mixture with other chlorocarbons. It appears in a few consumer products including paint strippers and spot removers.

It is used in neutrino detectors where a neutrino interacts with a neutron in the chlorine atom and converts it to a proton to form argon.

Historical applications

Tetrachloroethylene 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 tetrachloroethylene as a Group 2A carcinogen, which means that it is probably carcinogenic to humans. Like many chlorinated hydrocarbons, tetrachloroethylene is a central nervous system depressant and can enter the body through respiratory or dermal exposure. Tetrachloroethylene dissolves fats from the skin, potentially resulting in skin irritation.

Owing to tetrachloroethylene's toxicity and cancer risks, California's Air Resources Board banned the substance from use in new dry-cleaning machines in 2007, with older PCE-using machines shut down by mid-2010 and the use of all such machines discontinued in California by 2023.

Animal studies and a study of 99 twins showed there is a "lot of circumstantial evidence" that exposure to tetrachloroethylene increases the risk of developing Parkinson's disease ninefold. Larger population studies are planned.

At temperatures over 315 °C (599 °F), such as in welding, tetrachloroethylene can be oxidized into phosgene, an extremely poisonous gas. Therefore, tetrachloroethylene should not be used near welding operations, flames, or hot surfaces.

Testing for exposure

Tetrachloroethylene 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, tetrachloroethylene can be detected in the breath for weeks following a heavy exposure. Tetrachloroethylene and trichloroacetic acid (TCA), a breakdown product of tetrachloroethylene, can be detected in the blood.

In Europe, the Scientific Committee on Occupational Exposure Limits (SCOEL) recommends for tetrachloroethylene an occupational exposure limit (8 hour time-weighted average) of 20 ppm and a short-term exposure limit (15 min) of 40 ppm.

Environmental contamination

Tetrachloroethylene is a common soil contaminant. With a specific gravity greater than 1, tetrachloroethylene will be present as a dense nonaqueous phase liquid (DNAPL) if sufficient quantities are released. Because of its mobility 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 (which has a specific gravity less than 1). 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. Partial degradation daughter products include trichloroethylene, cis-1,2-dichloroethene and vinyl chloride; full degradation converts tetrachloroethylene to ethene and hydrogen chloride dissolved in water.

Estimates state that 85% of tetrachloroethylene produced is released into the atmosphere; while models from OECD assumed that 90% is released 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. Tetrachloroethylene is degraded by hydrolysis, and is also persistent under aerobic conditions. This compound is degraded by reductive dechlorination with anaerobic conditions present, with the degradation products such as trichloroethylene, dichloroethylene, vinyl chloride, ethylene, and ethane.

External links

• ATSDR Case Studies in Environmental Medicine: Tetrachloroethylene Toxicity U.S. Department of Health and Human Services
• Tetrachloroethylene (Perchloroethylene) 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.
• Sustainable uses and Industry recommendations