Tetrachloroethylene

Tetrachloroethylene
Names
IUPAC name
Tetrachloroethene
Other names
Perchloroethene; Perchloroethylene; Perc; PCE
Identifiers
127-18-4 YesY
ChEBI CHEBI:17300 N
ChEMBL ChEMBL114062 YesY
ChemSpider 13837281 YesY
EC Number 204-825-9
Jmol 3D image Interactive graph
KEGG C06789 YesY
RTECS number KX3850000
UNII TJ904HH8SN YesY
UN number 1897
Properties
C2Cl4
Molar mass 165.82 g·mol−1
Appearance Clear, colorless liquid
Odor mild, chloroform-like[1]
Density 1.622 g/cm3
Melting point −19 °C (−2 °F; 254 K)
Boiling point 121.1 °C (250.0 °F; 394.2 K)
0.15 g/L (25 °C)
Vapor pressure 14 mmHg (20°C)[1]
Viscosity 0.89 cP at 25 °C
Hazards
Main hazards Harmful (Xn),
Dangerous for
the environment (N)
Safety data sheet See: data page
External MSDS
R-phrases R40 R51/53
S-phrases S23 S36/37 S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
0
2
0
Flash point Not flammable
Lethal dose or concentration (LD, LC):
4000 ppm (rat, 4 hr)
5200 ppm (mouse, 4 hr)
4964 ppm (rat, 8 hr)[2]
US health exposure limits (NIOSH):
TWA 100 ppm
C 200 ppm (for 5 minutes in any 3-hour period), with a maximum peak of 300 ppm[1]
Ca Minimize workplace exposure concentrations.[1]
Ca [150 ppm][1]
Related compounds
Related Related organohalides
 Tetrabromoethylene
Tetraiodoethylene
Related compounds
 Trichloroethylene
Dichloroethene
Tetrachloroethane
Supplementary data page
Refractive index (n),
Dielectric constant (εr), etc.
Thermodynamic
data
 Phase behaviour
solid–liquid–gas
UV, IR, NMR, MS
N verify (what is YesYN ?)
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.[3]

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.[3] 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 a 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).[4] By 1993, the volume produced in the United States had dropped to 123,000 metric tons (271 million lb).[5]

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.[6]

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.[7] Like many chlorinated hydrocarbons, tetrachloroethylene is a central nervous system depressant and can enter the body through respiratory or dermal exposure.[8] 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.[9]

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.[10] Also, tetrachloroethylene has been shown to cause liver tumors in mice and kidney tumors in male rats.[11]

At temperatures over 315 °C (599 °F), such as in welding, tetrachloroethylene can be oxidized into phosgene, an extremely poisonous gas.[12] Therefore, tetrachloroethylene should not be used near welding operations, flames, or hot surfaces.[13]

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.[14]

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.[15][16] 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.[17]

References

  1. 1 2 3 4 5 "NIOSH Pocket Guide to Chemical Hazards #0599". National Institute for Occupational Safety and Health (NIOSH).
  2. ↑ "Tetrachloroethylene". Immediately Dangerous to Life and Health. National Institute for Occupational Safety and Health (NIOSH).
  3. 1 2 M. Rossberg et al. "Chlorinated Hydrocarbons" in Ullmann’s Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2
  4. ↑ "Assessment of Hazardous Waste Practices: Organic Chemicals, Pesticides and Explosives Industries" prebpublication issue for EPA Libraries and Solid Waste Management Agencies under contract # 68-01-2919, USEPA 1976
  5. ↑ "Toxicological Profile For Tetrachloroethylene" (PDF). Atlanta, GA: Agency for Toxic Substances and Disease Registry. September 1997. p. 174. Retrieved 2012-09-16. citing C&EN, 1994, Facts and Figures for the Chemical Industry, Chemical and Engineering News, July 4, 1994.
  6. ↑ Young, M.D.; et al. (1960). "The Comparative Efficacy of Bephenium Hydroxynaphthoate and Tetrachloroethylene against Hookworm and other Parasites of Man". American Journal of Tropical Medicine and Hygiene 9 (5): 488–491. PMID 13787477.
  7. ↑ IARC monograph. Tetrachloroethylene, Vol. 63, p. 159. Last Updated May 20, 1997. Last retrieved June 22, 2007.
  8. ↑ Control of Exposure to Perchloroethylene in Commercial Drycleaning. Hazard Controls: Publication 97-157. National Institute for Occupational Safety and Health.
  9. ↑ http://www.arb.ca.gov/toxics/dryclean/alternativesolvts_e.pdf
  10. ↑ Industrial Solvent Linked to Increased Risk of Parkinson's Disease
  11. ↑ "Solvents: the hazardous chemicals to avoid in everyday life - Meds News". Meds News. Retrieved 2016-01-22.
  12. ↑ Medical Management Guidelines for Tetrachloroethylene
  13. ↑ Working safely with tetrachloroethylene
  14. ↑ "SCOEL recommendations". 2011-04-22. Retrieved 2011-04-22.
  15. ↑ Ryoo, D., Shim, H., Arenghi, F. L. G., Barbieri, P., Wood T. K. (2001). "Tetrachloroethylene, Trichloroethylene, and Chlorinated Phenols Induce Toluene-o-xylene Monooxoygenase Activity in Pseudomonas Stutzeri OX1". Appl Microbiol Biotechnol 56 (3–4): 545–549. doi:10.1007/s002530100675.
  16. ↑ Deckard, L. A., Wills, J. C., Rivers, D. B. (1994). "Evidence for aerobic degradation of tetrachloroethylene by bacterial isolate". Biotechnol. Lett. 16 (11): 1221–1224. doi:10.1007/BF01020855.
  17. ↑ Watts P. (2006). Concise International Chemical Assessment Document 68: TETRACHLOROETHENE, World Health Organization

Further reading

External links

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