Trichloroethylene Defined

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From Wikipedia, the free encyclopedia



Trichloroethylene

trichloroethene

Identifiers
Abbreviations TCE
CAS number 79-01-6 Yes
PubChem 6575
ChemSpider 13837280 Yes
UNII 290YE8AR51 Yes
EC number 201-61-04
KEGG C06790 Yes
ChEBI CHEBI:16602
ChEMBL CHEMBL279816 Yes
RTECS number KX4550000
ATC code N01AB05
Jmol-3D images Image 1
Image 2
Properties
Molecular formula C2HCl3
Molar mass 131.39 g mol−1
Appearance Colorless liquid
Density 1.46 g/cm3 (20 °C)
Melting point −73 °C, 200 K, -99 °F
Boiling point 87.2 °C, 360 K, 189 °F ([1])
Solubility in water 1.280 g/L[1]
Solubility ether, ethanol, chloroform
Refractive index (nD) 1.4777 at 19.8 °C
Hazards
MSDS External MSDS
Main hazards Harmful if swallowed or inhaled
Autoignition
temperature
420 °C

 The chemical compound trichloroethylene (C2HCl3) is a chlorinated hydrocarbon commonly used as an industrial solvent. It is a clear non-flammable liquid with a sweet smell. It should not be confused with the similar 1,1,1-trichloroethane, which is commonly known as chlorothene.

 The IUPAC name is trichloroethene. Industrial abbreviations include TCE, trichlor, Trike, Tricky and tri. It has been sold under a variety of trade names. Under the trade names Trimar and Trilene, trichloroethylene was used as a volatile anesthetic and as an inhaled obstetrical analgesic in millions of patients.

 History

 Pioneered by Imperial Chemical Industries in Britain, its development was hailed as an anesthetic revolution. Originally thought to possess less hepatotoxicity than chloroform, and without the unpleasant pungency and flammability of ether, TCE use was nonetheless soon found to have several pitfalls. These included promotion of cardiac arrhythmias, low volatility and high solubility preventing quick anesthetic induction, reactions with soda lime used in carbon dioxide absorbing systems, prolonged neurologic dysfunction when used with soda lime, and evidence of hepatotoxicity as had been found with chloroform.

 The introduction of halothane in 1956 greatly diminished the use of TCE as a general anesthetic. TCE was still used as an inhalation analgesic in childbirth given by self-administration. Fetal toxicity and concerns for carcinogenic potential of TCE led to its abandonment in developed countries by the 1980s.

 Due to concerns about its toxicity, the use of trichloroethylene in the food and pharmaceutical industries has been banned in much of the world since the 1970s. Legislation has forced the substitution of trichloroethylene in many processes in Europe as the chemical was classified as a carcinogen carrying an R45 risk phrase. Many degreasing chemical alternatives are being promoted such as Ensolv and Leksol; however, each of these is based on n-propyl bromide which carries an R60 risk phrase and they would not be a legally acceptable substitute.

 Groundwater contamination by TCE has become an important environmental concern for human exposure.

 In 2005 it was announced by the USEPA (the United States Environmental Protection Agency) that the agency had completed its Final Health Assessment for Trichloroethylene and released a list of new TCE toxicity values. The results of the study have formally characterized the chemical as a human carcinogen and a non-carcinogenic health hazard. A 2011 toxicological review performed by the EPA continues to list trichloroethylene as a known carcinogen.[2]

 Production

Prior to the early 1970s, most trichloroethylene was produced in a two-step process from acetylene. First, acetylene was treated with chlorine using a ferric chloride catalyst at 90 °C to produce 1,1,2,2-tetrachloroethane according to the chemical equation:  HC≡CH + 2 Cl2Cl2CHCHCl2

The 1,1,2,2-tetrachloroethane is then dehydrochlorinated to give trichloroethylene. This can either be accomplished with an aqueous solution of calcium hydroxide: 2 Cl2CHCHCl2 + Ca(OH)2 → 2 ClCH=CCl2 + CaCl2 + 2 H2O

or in the vapor phase by heating it to 300-500°C on a barium chloride or calcium chloride catalyst: Cl2CHCHCl2 → ClCH=CCl2 + HCl

Today, however, most trichloroethylene is produced from ethylene. First, ethylene is chlorinated over a ferric chloride catalyst to produce 1,2-dichloroethane. :
CH2=CH2 + Cl2ClCH2CH2Cl

When heated to around 400 °C with additional chlorine, 1,2-dichloroethane is converted to trichloroethylene: ClCH2CH2Cl + 2 Cl2 → ClCH=CCl2 + 3 HCl

 This reaction can be catalyzed by a variety of substances. The most commonly used catalyst is a mixture of potassium chloride and aluminum chloride. However, various forms of porous carbon can also be used. This reaction produces tetrachloroethylene as a byproduct, and depending on the amount of chlorine fed to the reaction, tetrachloroethylene can even be the major product. Typically, trichloroethylene and tetrachloroethylene are collected together and then separated by distillation.

 Uses

 Trichloroethylene is an effective solvent for a variety of organic materials.

 When it was first widely produced in the 1920s, trichloroethylene’s major use was to extract vegetable oils from plant materials such as soy, coconut, and palm. Other uses in the food industry included coffee decaffeination and the preparation of flavoring extracts from hops and spices. It has also been used for drying out the last bit of water for production of 100% ethanol.

 From the 1930s through the 1970s, both in Europe and North America, trichloroethylene was used as a volatile anesthetic almost invariably administered with nitrous oxide. Marketed in the UK by ICI under the trade name Trilene it was coloured blue (with a dye called waxolene blue) to avoid confusion with the similar smelling chloroform. TCE replaced earlier anesthetics chloroform and ether in the 1940s, but was itself replaced in the 1960s in developed countries with the introduction of halothane, which allowed much faster induction and recovery times. Trilene was also used as a potent inhaled analgesic, mainly during childbirth. It was used with halothane in the Tri-service field anaesthetic apparatus used by the UK armed forces under field conditions. As of 2000, however, TCE was still in use as an anesthetic in Africa.[3]

 It has also been used as a dry cleaning solvent, although replaced in the 1950s by tetrachloroethylene (also known as perchloroethylene), except for spot cleaning where it was used until the years 2000.

 Trichloroethylene was marketed as ‘Ecco 1500 Anti-Static Film Cleaner and Conditioner’ until 2009, for use in automatic movie film cleaning machines, and for manual cleaning with lint-free wipes.

 Perhaps the greatest use of TCE has been as a degreaser for metal parts. The demand for TCE as a degreaser began to decline in the 1950s in favor of the less toxic 1,1,1-trichloroethane. However, 1,1,1-trichloroethane production has been phased out in most of the world under the terms of the Montreal Protocol, and as a result trichloroethylene has experienced some resurgence in use as a degreaser.

 TCE has also been used in the United States to clean kerosene-fueled rocket engines (TCE was not used to clean hydrogen-fueled engines such as the Space Shuttle Main Engine). During static firing, the RP-1 fuel would leave hydrocarbon deposits and vapors in the engine. These deposits had to be flushed from the engine to avoid the possibility of explosion during engine handling and future firing. TCE was used to flush the engine’s fuel system immediately before and after each test firing. The flushing procedure involved pumping TCE through the engine’s fuel system and letting the solvent overflow for a period ranging from several seconds to 30–35 minutes, depending upon the engine. For some engines, the engine’s gas generator and LOX dome were also flushed with TCE prior to test firing.[4][5] The F-1 rocket engine had its LOX dome, gas generator, and thrust chamber fuel jacket flushed with TCE during launch preparations.[5]

 TCE is also used in the manufacture of a range of fluorocarbon refrigerants[6] such as 1,1,1,2-Tetrafluoroethane more commonly known as HFC 134a

 Chemical instability

 Despite its widespread use as a metal degreaser, trichloroethylene itself is unstable in the presence of metal over prolonged exposure. As early as 1961 this phenomenon was recognized by the manufacturing industry, when stabilizing additives were added in the commercial formulation. Since the reactive instability is accentuated by higher temperatures, the search for stabilizing additives was conducted by heating trichloroethylene to its boiling point in a reflux condenser and observing decomposition. The first widely used stabilizing additive was dioxane; however, its use was patented by Dow Chemical Company and could not be used by other manufacturers. Considerable research took place in the 1960s to develop alternative stabilizers for trichloroethylene. Other chemical stabilizers include ketones such as methyl ethyl ketone.

 Physiological effects

 When inhaled, trichloroethylene produces central nervous system depression resulting in general anesthesia. Its high blood solubility results in a less desirable slower induction of anesthesia. At low concentrations it is relatively non-irritating to the respiratory tract. Higher concentrations result in tachypnea. Many types of cardiac arrhythmias can occur and are exacerbated by epinephrine (adrenaline). It was noted in the 1940s that TCE reacted with carbon dioxide (CO2) absorbing systems (soda lime) to produce dichloroacetylene and phosgene.[7] Cranial nerve dysfunction (especially the fifth cranial nerve) was common when TCE anesthesia was given using CO2 absorbing systems. These nerve deficits could last for months. Occasionally facial numbness was permanent. Muscle relaxation with TCE anesthesia sufficient for surgery was poor. For these reasons as well as problems with hepatotoxicity, TCE lost popularity in North America and Europe to more potent anesthestics such as halothane by the 1960s.[8]

 The symptoms of acute non-medical exposure are similar to those of alcohol intoxication, beginning with headache, dizziness, and confusion and progressing with increasing exposure to unconsciousness.[9] Respiratory and circulatory depression can result in death.

 Much of what is known about the human health effects of trichloroethylene is based on occupational exposures. Beyond the effects to the central nervous system, workplace exposure to trichloroethylene has been associated with toxic effects in the liver and kidney.[9] Over time, occupational exposure limits on trichloroethylene have tightened, resulting in more stringent ventilation controls and personal protective equipment use by workers.

 Research from Cancer bioassays performed by the National Cancer Institute (later the National Toxicology Program) showed that exposure to trichloroethylene is carcinogenic in animals, producing liver cancer in mice, and kidney cancer in rats.[9][10] Research published in 1994 examined the incidence of leukemia and non-Hodgkin lymphoma in populations exposed to TCE in their drinking water.[11]

 The National Toxicology Program’s 11th Report on Carcinogens categorizes trichloroethylene as “reasonably anticipated to be a human carcinogen”, based on limited evidence of carcinogenicity from studies in humans and sufficient evidence of carcinogenicity from studies in experimental animals.[12]

 One recent review of the epidemiology of kidney cancer rated cigarette smoking and obesity as more important risk factors for kidney cancer than exposure to solvents such as trichloroethylene.[13] In contrast, the most recent overall assessment of human health risks associated with trichloroethylene states, “[t]here is concordance between animal and human studies, which supports the conclusion that trichloroethylene is a potential kidney carcinogen”.[14] The evidence appears to be less certain at this time regarding the relationship between humans and liver cancer observed in mice, with the NAS suggesting that low-level exposure might not represent a significant liver cancer risk in the general population.

 Recent studies in laboratory animals and observations in human populations suggest that exposure to trichloroethylene might be associated with congenital heart defects[15][16][17][18][19] While it is not clear what levels of exposure are associated with cardiac defects in humans, there is consistency between the cardiac defects observed in studies of communities exposed to trichloroethylene contamination in groundwater, and the effects observed in laboratory animals. A study published in August 2008, has demonstrated effects of TCE on human mitochondria. The article questions whether this might impact female reproductive function. [20]

 Occupational exposure to TCE was reported to correlate with development of symptoms of Parkinson’s Disease in three laboratory workers.[21] A retrospective twin study of pairs discordant for Parkinson’s showed a six-fold increase in Parkinson’s risk associated with TCE workplace exposure.[22]

 The health risks of trichloroethylene have been studied extensively. The U.S. Environmental Protection Agency (EPA) sponsored a “state of the science” review of the health effects associated with exposure to trichloroethylene.[23] The National Academy of Sciences concluded that evidence on the carcinogenic risk and other potential health hazards from exposure to TCE has strengthened since EPA released their toxicological assessment of TCE, and encourages federal agencies to finalize the risk assessment for TCE using currently available information, so that risk management decisions for this chemical can be expedited.[14]

 In Europe, the Scientific Committee on Occupational Exposure Limit Values (SCOEL) recommends for trichloroethylene an occupational exposure limit (8h time-weighted average) of 10 ppm and a short-term exposure limit (15 min) of 30 ppm.[24]

 Human exposure

 Some are exposed to TCE through contaminated drinking water. With a specific gravity greater than 1, trichloroethene can be present as a dense nonaqueous phase liquid if sufficient quantities are spilled in the environment. Another significant source of vapor exposure in Superfund sites that had contaminated groundwater, such as the Twin Cities Army Ammunition Plant, was by showering. TCE readily volatilizes out of hot water and into the air. Long, hot showers would then volatilize more TCE into the air. In a home closed tightly to conserve the cost of heating and cooling, these vapors would then recirculate.

 The first known report of TCE in groundwater was given in 1949 by two English public chemists who described two separate instances of well contamination by industrial releases of TCE.[25] Based on available federal and state surveys, between 9% to 34% of the drinking water supply sources tested in the U.S. may have some TCE contamination, though EPA has reported that most water supplies are in compliance with the maximum contaminant level (MCL) of 5 ppb.[26] In addition, a growing concern in recent years at sites with TCE contamination in soil or groundwater has been vapor intrusion in buildings, which has resulted in indoor air exposures, such is in a recent case in the McCook Field Neighborhood of Dayton, Ohio.[27] Trichloroethylene has been detected in 852 Superfund sites across the United States,[28] according to the Agency for Toxic Substances and Disease Registry (ATSDR). Under the Safe Drinking Water Act of 1974, and as amended[29] annual water quality testing is required for all public drinking water distributors. The EPA’S current guidelines for TCE can be found here. It should be noted that the EPA’s table of “TCE Releases to Ground” is dated 1987 to 1993, thereby omitting one of the largest Superfund cleanup sites in the nation, the NIBW in Scottsdale, Arizona. The TCE “released” here occurred prior to its appearance in the municipal drinking wells in 1982.[30]

 References

^ abTrichloroethylene in the ChemIDplus database

  1. ^ United States Environmental Protection Agency (September 2011). EPA635 (R-09/011F). http://www.epa.gov/iris/toxreviews/0199tr/0199tr.pdf.
  2. ^ P. Fenton (2000). “Volatile Anaesthetic Agents”. Retrieved 2012-02-11.
  3. ^The Use of Trichloroethylene at NASA’s SSFL Sites
  4. ^ abF-1 Rocket Engine Operating Instructions
  5. ^http://www.nd.edu/~enviro/design/r134a.pdf
  6. ^ Orkin, F. K. (1986) Anesthesia Systems (Chapter 5). In R. D. Miller (Ed.), Anesthesia (second edition). New York, NY: Churchill Livingstone.
  7. ^ Stevens, W.C. and Kingston H. G. G. (1989) Inhalation Anesthesia (Chapter 11). In P. G. Barash et al. (Eds.) Clinical Anesthesia. Philadelphia, PA: Lippincott.
  8. ^ abchttp://www.epa.gov/ttn/atw/hlthef/tri-ethy.html
  9. ^http://www.atsdr.cdc.gov/toxprofiles/phs19.html
  10. ^ New Jersey Department of Health, Environmental Health Services, Trenton, NJ 08625 USA.
  11. ^http://ntp.niehs.nih.gov/index.cfm?objectid=72016262-BDB7-CEBA-FA60E922B18C2540/
  12. ^Elsevier
  13. ^ abAssessing the Human Health Risks of Trichloroethylene: Key Scientific Issues
  14. ^ J Am Coll Cardiol. 1990 Jul;16(1):155-64.
  15. ^ J Am Coll Cardiol. 1993 May;21(6):1466-72
  16. ^ Toxicol Sci. 2000 Jan;53(1):109-17
  17. ^ Birth Defects Res A Clin Mol Teratol. 2003 Jul;67(7):488-95
  18. ^ Environ Health Perspect. 2006 Jun;114(6):842-7
  19. ^ Xu F, Papanayotou I, Putt DA, Wang J, Lash LH (August 2008). “Role of mitochondrial dysfunction in cellular responses to S-(1,2-dichlorovinyl)-L-cysteine in primary cultures of human proximal tubular cells”. Biochem. Pharmacol.76 (4): 552–67. doi:10.1016/j.bcp.2008.05.016. PMC2593897. PMID18602084.
  20. ^ Gash, DM; etal. (2008). “Trichloroethylene: Parkinsonism and complex 1 mitochondrial neurotoxicity”. Ann Neurol63 (2): 184–92. doi:10.1080/17482960802351029. PMID18792848. Retrieved 11 February 2012.
  21. ^ Goldman, S. M.; etal. (14 NOV 2011). “Solvent exposures and parkinson disease risk in twins”. Annals of Neurology. doi:10.1002/ana.22629. Retrieved 11 February 2012.
  22. ^EHP Supplement: Volume 108 (Supplement 2) May 2000
  23. ^“SCOEL recommendations”. 2011-04-22. Retrieved 2011-04-22.
  24. ^ Lyne, F.A. and T. McLachlan, “Contamination of water by trichloroethylene,” The Analyst, 74, p. 513, 1949.
  25. ^[1] EPA – Consumer Factsheet on: TRICHLOROETHYLENE
  26. ^ EPA Long-Term Study Begins http://www.epa.gov/Region5/sites/behr/pdfs/behr-factsheet-200809.pdf Behr-Dayton Thermal Systems VOC Plume Site
  27. ^ATSDR – ToxFAQs: Trichloroethylene (TCE)
  28. ^http://www.epa.gov/safewater/sdwa/
  29. ^http://yosemite.epa.gov/r9/sfund/r9sfdocw.nsf/webdisplay/oid-3a4364e2a3ab3c7688256de9006819f2?OpenDocument

 

Further reading

U.S. EPA: Trichloroethylene—TCE information website – U.S. Environmental Protection Agency—EPA.
Euro Chlor: Q&A on TrichloroethyleneEuro Chlor, European Chlorinated Solvent Association—ESCA, World Chlorine Council.
ATSDR – Case Studies in Environmental Medicine: Trichloroethylene ToxicityAgency for Toxic Substances and Disease Registry—ATSDR, of the U.S. Department of Health and Human Services(public domain)
NAS: Assessing Human Health Risks of Trichloroethylene – Key Scientific Issues – U.S. National Academy of Sciences—NAS.
U.S. NIH: Eleventh Report on Carcinogens: Trichloroethylene Monograph – U.S. National Institutes of Health—NIH.
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