Tetrachloroethylene - Misplaced Pages

Tetrachloroethylene, also known as perchloroethylene or under the systematic name tetrachloroethene, and abbreviations such as perc (or PERC), and PCE, is a chlorocarbon with the formula Cl₂C=CCl₂. It is a non-flammable, stable, colorless and heavy liquid widely used for dry cleaning of fabrics. It also has its uses as an effective automotive brake cleaner. It has a mild sweet, sharp odor, detectable by most people at a concentration of 50 ppm.

Tetrachloroethylene is regarded as a toxic substance, a human health hazard, and an environmental hazard. In 2020, the United States Environmental Protection Agency stated that "tetrachloroethylene exposure may harm the nervous system, liver, kidneys, and reproductive system, and may be harmful to unborn children", and reported that numerous toxicology agencies regard it as a carcinogen.

History and production

French chemist Henri Victor Regnault first synthesized tetrachloroethylene in 1839 by thermal decomposition of hexachloroethane following Michael Faraday's 1820 synthesis of protochloride of carbon (carbon tetrachloride).

C₂Cl₆ → C₂Cl₄ + Cl₂

Faraday was previously falsely credited for the synthesis of tetrachloroethylene, which in reality, was carbon tetrachloride. While trying to make Faraday's "protochloride of carbon", Regnault found that his compound was different from Faraday's. Victor Regnault stated "According to Faraday, the chloride of carbon boiled around 70 °C (158 °F) to 77 °C (171 °F) degrees Celsius but mine did not begin to boil until 120 °C (248 °F)".

Tetrachloroethylene can be made by passing chloroform vapour through a red-hot tube, the side products include hexachlorobenzene and hexachloroethane, as reported in 1886.

Most tetrachloroethylene is produced by high-temperature chlorinolysis of light hydrocarbons. The method is related to Faraday's method 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:

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.

Worldwide production was about 1 million metric tons (980,000 long tons; 1,100,000 short tons) in 1985.

Although in very small amounts, tetrachloroethylene occurs naturally in volcanoes along with trichloroethylene.

Uses

Tetrachloroethylene is an excellent nonpolar solvent for organic materials. Additionally, it is volatile, highly stable (easily recycled) and nonflammable, and has low toxicity. For these reasons, it has been widely used in dry cleaning worldwide since the 1930s. The chemist Sylvia Stoesser (1901–1991) had suggested tetrachloroethylene to be used in dry cleaning as an alternative to highly flammable dry cleaning solvents such as naphtha.

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, aerosol preparations and spot removers.

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 of hookworm infestation. In 1925, American veterinarian Maurice Crowther Hall (1881–1938), working on anthelmintics, demonstrated the effectiveness of tetrachloroethylene in the treatment of ancylostomiasis caused by hookworm infestation in humans and animals. Before Hall tested tetrachloroethylene on himself, in 1921 he discovered the powerful effect of carbon tetrachloride on intestinal parasites and was nominated for the Nobel Prize in Physiology or Medicine, but a few years later he found tetrachloroethylene to be more effective and safer. Tetrachloroethylene treatment has played a vital role in eradicating hookworms in the United States and abroad. Hall's innovation was considered a breakthrough in medicine. It was given orally as a liquid or in capsules along with magnesium sulfate to get rid of the Necator americanus parasite in humans.

Chemical properties and reactions

Tetrachloroethylene is a derivative of ethylene with all hydrogens replaced by chlorine. 14.49% of the molecular weight of tetrachloroethylene consists of carbon and the remaining 85.5% is chlorine. It is the most stable compound among all chlorinated derivatives of ethane and ethylene. It is resistant to hydrolysis and less corrosive than other chlorinated solvents. It does not tend to polymerise like fluorine analogue tetrafluoroethylene, C₂F₄.

Tetrachloroethylene may react violently with alkali or alkaline earth metals, alkalis (sodium hydroxide and potassium hydroxide), nitric acid, beryllium, barium and aluminium.

Oxidation

Oxidation of tetrachloroethylene by ultraviolet radiation in air produces trichloroacetyl chloride and phosgene:

4 C₂Cl₄ + 3 O₂ → 2 CCl₃COCl + 4 COCl₂

This reaction can be halted by using amines and phenols (usually N-methylpyrrole and N-methylmorpholine) as stabilisers. But the reaction can be done intentionally to produce trichloroacetyl chloride.

Chlorination

Hexachloroethane is formed when tetrachloroethylene reacts with chlorine at 50–80 °C in the presence of a small amount of iron(III) chloride (0.1%) as a catalyst:

C₂Cl₄ + Cl₂ → C₂Cl₆

CFC-113 is produced by the reaction of tetrachloroethylene with chlorine and HF in the presence of antimony pentafluoride:

C₂Cl₄ + 3 HF + Cl₂ → CClF₂CCl₂F + 3 HCl

Nitration

Tetrachlorodinitroethane can be obtained by nitration of tetrachloroethylene with fuming nitric acid (conc. HNO₃ rich in nitrogen oxides) or nitrogen tetroxide:

Cl₂CCCl₂ + N₂O₄ → NO₂Cl₂CCCl₂NO₂

The preparation of this crystalline solid compound from Tetrachloroethylene and nitrogen tetroxide was first described by Hermann Kolbe in 1869.

Thermal decomposition

Tetrachloroethylene begins to thermally decompose at 400 °C, decomposition accelerates around 600 °C, and completely decomposes at 800 °C. Organic decomposition products identified were trichlorobutene, 1,3-dichloro-2-propanone, tetrachlorobutadiene, dichlorocyclopentane, dichloropentene, methyl trichloroacetate, tetrachloroacetone, tetrachloropropene, trichlorocyclopentane, trichloropentene, hexachloroethane, pentachloropropene, hexachloropropene, hexachlorobutadiene.

Health and safety

Tetrachloroethylene is considered to be a toxin. It is identified as a health hazard and environmental hazard. Exposure to tetrachloroethylene, especially over a long term, may harm the nervous system, other organs, and increase the risk of getting cancer. It may also have effects on pregnancy and the fetus.

Reports of human injury are uncommon despite its wide usage in dry cleaning and degreasing. Although limited by its low volatility, tetrachloroethylene has potent anaesthetic effects upon inhalation. The risk depends on whether exposure is over minutes or hours, or over years.

Despite the advantages of tetrachloroethylene, cancer research and government environmental agencies have called for its replacement from widespread commercial use. It is described as a possible neurotoxicant, liver and kidney toxicant and reproductive and developmental toxicant (...) a potential occupational carcinogen. On the other hand, dry cleaning industry emphasizes minimal risk because modern machinery use closed systems to avoid any vapour escape and to optimize recycling.

Metabolism

Tetrachloroethylene's biological half-life is approximately 3 days. About 98% of the inhaled tetrachloroethylene is exhaled unchanged and only about 1–3% is metabolised to tetrachloroethylene oxide which rapidly isomerises into trichloroacetyl chloride. Trichloroacetyl chloride hydrolyses to trichloroacetic acid.

Neurotoxicity

Tetrachloroethylene can harm the nervous system, cause developmental deficits in children, impair vision, and increase the risk of psychiatric diagnoses.

Carcinogenicity

Tetrachloroethylene has been classified as "Group 2A: Probably Carcinogenic" by the International Agency for Research on Cancer (IARC) due to sufficient evidence in experimental animals and limited evidence in humans for non-Hodgkin lymphoma, urinary bladder cancers, and cancers of the esophagus and cervix.

Evidence from cohort and case-controlled epidemiologic studies demonstrates a positive association between cumulative exposures to tetrachloroethylene and the prevalence of bladder cancer, non-Hodgkin lymphoma, and multiple myeloma in adults. Some limited evidence of increased prevalence of kidney, lung, liver, and breast cancers with exposure to tetrachloroethylene has been found in epidemiologic research, but data quality limitations have produced variable results across studies.

Several modes of action are hypothesized for the carcinogenicity of tetrachloroethylene in humans, though existing data is insufficient for adequate characterization. Markers of oxidative metabolism of tetrachloroethylene and increased prevalence of abnormal hepatic sonographs have been observed in dry-cleaners and laundry workers exposed to tetrachloroethylene, which suggests a potential for hepatocellular damage through the formation of reactive intermediates from glutathione conjugates during metabolization. Although most genotoxicity assays of tetrachloroethylene produced negative findings for genotoxicity and mutagenicity, modest genotoxic effects and mutagenic effects have been identified under certain metabolic activation conditions, and several of tetrachloroethylene's metabolites have been shown to be mutagenic.

Testing for exposure

Tetrachloroethylene exposure can be evaluated by a breath test, analogous to breath-alcohol measurements. Also, for acute exposures, tetrachloroethylene in expired air can be measured. Tetrachloroethylene can be detected in the breath for weeks following a heavy exposure. Tetrachloroethylene and its metabolite trichloroacetic acid, can be detected in the blood.

In the European Union, 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.

Remediation and degradation

In principle, tetrachloroethylene contamination can be remediated by chemical treatment. Chemical treatment involves reducing metals such as iron powder.

Bioremediation usually entails reductive dechlorination under anaerobic conditions by Dehalococcoides spp. Under aerobic conditions, degradation may occur via co-metabolism by Pseudomonas sp. Products of biological reductive dechlorination include trichloroethylene, cis-1,2-dichloroethylene, vinyl chloride, ethylene and chloride.

Explanatory notes

Previously spelt as perchlorethylene

References

^ NIOSH Pocket Guide to Chemical Hazards. "#0599". National Institute for Occupational Safety and Health (NIOSH).
Sigma Aldrich Tetrachloroethylene MSDS
Fischer Scientific Tetrachloroethylene MSDS
"Tetrachloroethylene". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
^ "Compound Summary: Tetrachloroethylene". PubChem, US National Library of Medicine. 21 September 2024. Retrieved 24 September 2024.
Browning, Ethel (1953). "Perchloroethylene". Toxicity of Industrial Organic Solvents. Chemical Publishing. pp. 182–185.
^ US Agency for Toxic Substances and Disease Registry (June 2019). "Toxicological Profile for Tetrachloroethylene". US National Library of Medicine. Retrieved 23 September 2024.
^ "Public Health Statement for Tetrachloroethylene (PERC)". US Environmental Protection Agency. 22 June 2020. Retrieved 23 September 2024.
V. Regnault (1839) "Sur les chlorures de carbone CCl et CCl" (On the chlorides of carbon CCl and CCl), Annales de Chimie et de Physique, vol. 70, pages 104–107. Reprinted in German as: V. Regnault (1839). "Ueber die Chlorverbindungen des Kohlenstoffs, C2Cl2 und CCl2". Annalen der Pharmacie. 30 (3): 350–352. doi:10.1002/jlac.18390300310.
W. Ramsay and S. Young, Jahres-Bericht über die Leistungen der chemischen Technologie, 1886, p. 628
^ Rossberg, M.; Lendle, W.; Pfleiderer, G.; Tögel, A.; Dreher, E.-L.; Langer, E.; Rassaerts, H.; Kleinschmidt, P.; Strack, H.; Cook, R.; Beck, U.; Lipper, K.-A.; Torkelson, T.R.; Löser, E.; Beutel, K.K.; Mann, T. "Chlorinated Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a06_233.pub2. ISBN 978-3527306732.
Gribble, G. W. (1996). "Naturally occurring organohalogen compounds – A comprehensive survey". Progress in the Chemistry of Organic Natural Products. 68 (10): 1–423. doi:10.1021/np50088a001. PMID 8795309.
Amos, J. Lawrence (1990). "Chlorinated solvents". In Boundy, Ray H.; Amos, J. Lawrence (eds.). A History of the Dow Chemical Physics Lab : the freedom to be creative. New York and Basel: Marcel Dekker, Inc. pp. 71–79.
Young, M.D.; Jeffery, G.M.; Morehouse, W.G.; Freed, J.E.; Johnson, R.S. (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. doi:10.4269/ajtmh.1960.9.488. PMID 13787477. S2CID 19521345.
"Clinical Aspects and Treatment of the More Common Intestinal Parasites of Man (TB-33)". Veterans Administration Technical Bulletin 1946 & 1947. 10: 1–14. 1948.
"Maurice C. Hall". United States National Agricultural Library. Special Collections.
Davison, Forrest Ramon (1940). "Tetrachlorethylene". Synopsis of materia medica, toxicology, and pharmacology for students and practitioners of medicine. p. 181.
Pohanish, Richard P., ed. (2012). "Tetrachloroethylene". Sittig's Handbook of Toxic and Hazardous Chemical Carcinogens (6th ed.). Elsevier. p. 2520. ISBN 978-1-4377-7870-0.
Oshin LA, Промышленные хлорорганические продукты (Promyshlennyye khlororganicheskie produkty). 1978.
Knunyatsya IL. Химическая энциклопедия (Khimicheskaya Entsiklopediya). 1992. ISBN 5-85270-039-8
^ Argo, W. L.; James, E. M.; Donnelly, J. L. (November 1919). "Tetrachlordinitroethane". The Journal of Physical Chemistry. 23 (8): 578–585. doi:10.1021/j150197a004.
Yasuhara, Akio (April 1993). "Thermal decomposition of tetrachloroethylene". Chemosphere. 26 (8): 1507–1512. Bibcode:1993Chmsp..26.1507Y. doi:10.1016/0045-6535(93)90218-T. S2CID 94961581.
Dreher, E.-L.; Torkelson, T. R.; Beutel, K. K. (19 November 2014). "Chlorethanes and Chloroethylenes; In: Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Verlag: Wiley. doi:10.1002/14356007.o06_o01. ISBN 9783527306732.
Foot, Ellen B.; Apgar, Virginia; Bishop, Kingsley (May 1943). "Tetrachlorethylene as an Anesthetic Agent". Anesthesiology. 4 (3): 283–292. doi:10.1097/00000542-194305000-00009. S2CID 70969652.
Ceballos, Diana M.; Fellows, Katie M.; Evans, Ashley E.; Janulewicz, Patricia A.; Lee, Eun Gyung; Whittaker, Stephen G. (2021). "Perchloroethylene and Dry Cleaning: It's Time to Move the Industry to Safer Alternatives". Frontiers in Public Health. 9: 638082. doi:10.3389/fpubh.2021.638082. PMC 7973082. PMID 33748070. S2CID 232116380.
^ Shane S. Que Hee, ed. (1993). "Biological Exposure Indices". Biological Monitoring: An Introduction. John Wiley & Sons. p. 470. ISBN 978-0-471-29083-4.
Toxicological Profile for Tetrachloroethylene: Draft. (1995). U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry.
Grandjean P, Landrigan PJ (March 2014). "Neurobehavioural effects of developmental toxicity". The Lancet. Neurology. 13 (3): 330–8. doi:10.1016/S1474-4422(13)70278-3. PMC 4418502. PMID 24556010.
Aschengrau A, Janulewicz PA, White RF, et al. (2016). "Long-term Neurotoxic Effects of Early-life Exposure to Tetrachloroethylene-contaminated Drinking Water". Annals of Global Health. 82 (1): 169–79. doi:10.1016/j.aogh.2016.01.013. PMC 4916338. PMID 27325074.
^ "Trichloroethylene, Tetrachloroethylene, and Some Other Chlorinated Agents (IARC Monograph, Volume 106, 2014)". publications.iarc.fr/. Retrieved 23 September 2024.
^ "Tetrachloroethylene (Perchloroethylene) (United States Environmental Protection Agency, Integrated Risk Information System [IRIS] Toxicological Review, 2012)". iris.epa.gov/. Retrieved 23 September 2024.
^ "Toxicological Profile for Tetrachloroethylene (United States Agency for Toxic Substances and Disease Registry, 2019)" (PDF). www.atsdr.cdc.gov/. Retrieved 23 September 2024.
Brodkin, CA; Daniell, W; Checkoway, H; Echeverria, D; Johnson, J; Wang, K; Sohaey, R; Green, D; Redlich, C; Gretch, D (1995). "Hepatic ultrasonic changes in workers exposed to perchloroethylene". Occupational and Environmental Medicine. 52 (10): 679–685. doi:10.1136/oem.52.10.679. PMC 1128334. PMID 7489059.
Gennari, P; Naldi, M; Motta, R; Nucci, MC; Giacomini, C; Violante, FS; Raffi, GB (1992). "gamma-Glutamyltransferase isoenzyme pattern in workers exposed to tetrachloroethylene". American Journal of Industrial Medicine. 21 (5): 661–671. doi:10.1002/ajim.4700210506. PMID 1351699.
"Tetrachloroethylene Toxicity: Section 3.1. Evaluation and Diagnosis". Agency for Toxic Substances and Disease Registry. 9 February 2021. Retrieved 2 March 2023.
"SCOEL recommendations". 22 April 2011. Retrieved 22 April 2011.
Campbell, Timothy J.; Burris, David R.; Roberts, A. Lynn; Wells, J. Raymond (October 2009). "Trichloroethylene and tetrachloroethylene reduction in a metallic iron–water-vapor batch system". Environmental Toxicology and Chemistry. 16 (4): 625–630. doi:10.1002/etc.5620160404. S2CID 94525849.
Ghattas, Ann-Kathrin; Fischer, Ferdinand; Wick, Arne; Ternes, Thomas A. (2017). "Anaerobic biodegradation of (Emerging) organic contaminants in the aquatic environment". Water Research. 116: 268–295. Bibcode:2017WatRe.116..268G. doi:10.1016/j.watres.2017.02.001. PMID 28347952. S2CID 205698959.
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. PMID 11549035. S2CID 23770815.