Trichloroethylene

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"Trichlor" redirects here. For the reagent also known as "trichlor", see trichloroisocyanuric acid. For Tri-clor, see chloropicrin.
Trichloroethylene

sample of Trichloroethylene
Names
Preferred IUPAC name
Trichloroethene
Other names
1-Chloro-2,2-dichloroethylene; 1,1-Dichloro-2-chloroethylene; Acetylene Trichloride; Anamenth; HCC-1120; TCE; Trethylene; Triclene; Tri; Trico; Trilene; Trimar
Identifiers
3D model (
JSmol
)
Abbreviations TCE
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.001.062 Edit this at Wikidata
EC Number
  • 201-167-4
KEGG
RTECS number
  • KX4550000
UNII
UN number 1710
  • InChI=1S/C2HCl3/c3-1-2(4)5/h1H checkY
    Key: XSTXAVWGXDQKEL-UHFFFAOYSA-N checkY
  • InChI=1/C2HCl3/c3-1-2(4)5/h1H
  • Cl\C=C(/Cl)Cl
  • Cl\C=C(/Cl)Cl
  • ClC=C(Cl)Cl
Properties
C2HCl3
Molar mass 131.38 g·mol−1
Appearance Colorless liquid
Odor pleasant, chloroform-like
Density 1.46 g/cm3 at 20 °C
Melting point −84.8 °C (−120.6 °F; 188.3 K)[5]
Boiling point 86.7 °C (188.1 °F; 359.8 K)[1]
1.280 g/L[1]
Solubility Ether, ethanol, chloroform
log P 2.26[2]
Vapor pressure 58 mmHg (0.076 atm) at 20 °C[3]
−65.8·10−6 cm3/mol
1.4777 at 19.8 °C
Viscosity 0.532 mPa·s[4]
Pharmacology
N01AB05 (WHO)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Acute exposure can cause dizziness and loss of consciousness, chronic exposure can increase cancer risk. Unstable in presence of light.
GHS labelling:
GHS08: Health hazard GHS07: Exclamation mark
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
1
0
420 °C (788 °F; 693 K)
Explosive limits
 8-10.5%[3]
Lethal dose or concentration (LD, LC):
4920 mg/kg (oral, rat), 29000 mg/kg (dermal, rabbit)[6]
8450 ppm (mouse, 4 hr)
26300 (rat, 1 hr)[7]
2900 ppm (human)
37,200 ppm (guinea pig, 40 min)
5952 ppm (cat, 2 hr)
8000 ppm (rat, 4 hr)
11,000 (rabbit)[7]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 100 ppm C 200 ppm 300 ppm (5-minute maximum peak in any 2 hours)[3]
REL (Recommended)
 Ca[3]
IDLH
(Immediate danger)
 Ca [1000 ppm][3]
Safety data sheet (SDS) Carl Roth
Legal status
  • BR: Class B1 (Psychoactive drugs)[8]
  • US: banned for medical use (1977)
Related compounds
Vinyl chloride
Tetrachloroethylene
Related compounds
 Chloroform
1,1,1-Trichloroethane
1,1,2-Trichloroethane
Supplementary data page
Trichloroethylene (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Trichloroethylene (TCE) is a

1,1,1-trichloroethane
, which is commonly known as chlorothene.

TCE is classified as a volatile organic compound.[9]

History

The earliest record of trichloroethylene synthesis dates back to 1836. It was obtained from the action of potassium hydroxide on 1,1,2,2-tetrachloroethane and 1,1,1,2-tetrachloroethane by Auguste Laurent and notated as C4HCl3 (then the atomic weight of carbon was thought to be the half of it really was). Laurent did not investigate the compound further.[10][11]

Trichloroethylene's discovery is widely attributed to E. Fischer who made it in 1864 via the reduction of hexachloroethane with hydrogen. Fischer investigated TCE and noted its boiling point as between 87 and 90 degrees Celsius.[12][13][14] Commercial production began in Germany, in 1920 and in the US in 1925.[15]

Pioneered by

University of Maryland, e.g., "Fluoromar" for fluroxene and "Vinamar" for ethyl vinyl ether".[16]

Cyprane handheld anaesthetic device for trichloroethylene, made in the UK, 1947. This device was designed for self-administration by the patient.

Originally thought to possess less

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 about the carcinogenic potential of TCE led to its abandonment in developed countries by the 1980s.

The use of trichloroethylene in the food and pharmaceutical industries has been banned in much of the world since the 1970s due to concerns about its toxicity. Legislation has forced the replacement of trichloroethylene in many processes in Europe as the chemical was classified as a carcinogen carrying an R45

n-propyl bromide
which carries an R60 risk phrase of May impair fertility, and would not be a legally acceptable substitute.

Production

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

CH2=CH2 + Cl2 → ClCH2CH2Cl

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.

Prior to the early 1970s, however, most trichloroethylene was produced in a two-step process from

catalyst at 90 °C to produce 1,1,2,2-tetrachloroethane according to the chemical equation
:

HC≡CH + 2 Cl2 → Cl2CHCHCl2

The 1,1,2,2-tetrachloroethane is then dehydrochlorinated to give trichloroethylene. This can be accomplished either 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

Common impurities in reagent and technical grade TCE are

ethylene dichloride, tetrachloroethanes, benzene and phenol. However, these compounds are present in very small amounts and do not possess any risk.[17]

Uses

Trichloroethylene is an effective

paint strippers. It is applied before plating, anodizing, and painting.[19]

When trichloroethylene was first widely produced in the 1920s, its major use was to extract

freezing point depressant in carbon tetrachloride fire extinguishers.[17]

Dehydrochlorination of trichloroethylene with potassium hydride gives dichloroacetylene.[20] Trichloroethylene is also a chain terminator for polyvinyl chloride.[17] Chlorination gives pentachloroethane
.

Anaesthesia

Bottle of trichloroethylene for anesthesia by ICI
Inhaler used for Trilene, 1961-1970
video icon Pain Relief in Childbirth (1954), a short film by Imperial Chemical Industries explaining the use of nitrous oxide and trichloroethylene anaesthesia systems for childbirth.

Trichloroethylene is a good analgesic at 0.35 to 0.5% concentrations.[21] Trichloroethylene was used in the treatment of trigeminal neuralgia beginning in 1916.[17]

From the 1940s through the 1980s, both in Europe and North America, trichloroethylene was used as a volatile anesthetic almost invariably administered with

waxoline blue in 1:200,000 concentration)[22] to avoid confusion with the similar-smelling chloroform. Trilene was stabilised with 0.01% thymol.[22]

TCE replaced earlier anesthetics chloroform and ether in the 1940s due to its lower toxicity than chloroform and being relatively non-flammable (unlike ether which is extremely flammable), but was itself replaced in the 1960s in developed countries with the introduction of halothane, which allowed much faster induction and recovery times and was considerably easier to administer. Trilene was also used as an inhaled analgesic, mainly during childbirth, often self-applied by the patient. Trichloroethylene was introduced for obstetrical anaesthesia in 1943, and used until the 1980s.[21] Its anaesthetic use was banned in the United States in 1977 but the anaesthetic use in the United Kingdom remained until the late 1980s.[17]

TCE was used with halothane in the tri-service field anaesthetic apparatus used by the UK armed forces under field conditions. As of 2000, TCE was still in use as an anesthetic in Africa.[23]

Trichloroethylene has been used in the production of halothane.[24]

Cleaning solvent

TCE has also been used as a dry cleaning solvent, although mostly replaced by tetrachloroethylene (also known as perchloroethylene), except for spot cleaning where it is still used under the trade name Picrin.[citation needed]

Perhaps the greatest use of TCE is as a degreaser for metal parts. It has been widely used in degreasing and cleaning since the 1920s because of its low cost, low flammability, low toxicity and high effectivity as a solvent. 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 due to its effect of ozone depletion. As a result, trichloroethylene has experienced some resurgence in use as a degreaser.[17]

Trichloroethylene is used to remove grease and lanolin from wool before weaving.[17]

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

F-1 rocket engine had its LOX dome, gas generator, and thrust chamber fuel jacket flushed with TCE during launch preparations.[26]

Refrigerants

TCE is also used in the manufacture of a range of fluorocarbon refrigerants

1,1,1,2-tetrafluoroethane
more commonly known as HFC 134a. TCE was also used in industrial refrigeration applications due to its high heat transfer capabilities and its low-temperature specification.

Safety

Chemical instability

Despite its widespread use as a metal

methyl ethyl ketone
.

DuPont's Triclene D, for degreasing metals (1946)
Ohio Chemical's Trimar, for anaesthesia (1952)
Two advertisements for trichloroethylene in two different uses, metal degreasing (1947) and anaesthesia (1952)

Physiological effects

When inhaled, trichloroethylene produces

Cranial nerve dysfunction (especially the fifth cranial nerve) was common when TCE anesthesia was given using CO2 absorbing systems. ] 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 anesthetics such as halothane by the 1960s.[34]

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.[35] Much of what is known about the chronic human health effects of trichloroethylene is based on occupational exposures. Besides the effects to the central nervous system, workplace exposure to trichloroethylene has been associated with toxic effects in the liver and kidney.[35] A history of long-term exposure to high concentrations of trichloroethylene is a suspected environmental risk of Parkinson's disease.[36]

Metabolism

Trichloroethylene is metabolised to trichloroepoxyethane (TCE oxide) which rapidly isomerises to

trichloromethane[38][40][41]
were also detected as minor metabolites of TCE.

Exposure and regulations

Main article: List of trichloroethylene-related incidents

With a

specific gravity greater than 1 (denser than water), trichloroethylene can be present as a dense non-aqueous phase liquid
(DNAPL) if sufficient quantities are spilt in the environment.

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.[42] Based on available federal and state surveys, between 9% and 34% of the drinking water supply sources tested in the US may have some TCE contamination, though EPA has reported that most water supplies comply with the maximum contaminant level (MCL) of 5 ppb.[43]

Generally, atmospheric levels of TCE are highest in areas of concentrated industry and population. Atmospheric levels tend to be lowest in rural and remote regions. Average TCE concentrations measured in air across the United States are generally between 0.01 ppb and 0.3 ppb, although mean levels as high as 3.4 ppb have been reported.[44] TCE levels in the low parts per billion range have been measured in food; however, levels as high as 140 ppb were measured in a few samples of food.[44] TCE levels above background have been found in homes undergoing renovation.[45]

Existing regulations in the United States and European Union

Until recent years[

tumors.[citation needed
]

State, federal, and international agencies classify trichloroethylene as a known or probable carcinogen. In 2014, the International Agency for Research on Cancer updated its classification of trichloroethylene to Group 1, indicating that sufficient evidence exists that it causes cancer of the kidney in humans as well as some evidence of cancer of the liver and non-Hodgkin's lymphoma.[46]

In the European Union, the Scientific Committee on Occupational Exposure Limit Values (SCOEL) recommends an exposure limit for workers exposed to trichloroethylene of 10 ppm (54.7 mg/m3) for 8-hour TWA and of 30 ppm (164.1 mg/m3) for STEL (15 minutes).[47]

Existing EU legislation aimed at protection of workers against risks to their health (including Chemical Agents Directive 98/24/EC[48] and Carcinogens Directive 2004/37/EC[49]) currently do not impose binding minimum requirements for controlling risks to workers' health during the use phase or throughout the life cycle of trichloroethylene.

In 2023, the United States

EPA, in October 2023 it "proposed to ban the manufacture (including import), processing, and distribution in commerce of TCE for all uses, with longer compliance time frames and workplace controls (including an exposure limit) for some processing and industrial and commercial uses until the prohibitions come into effect"[needs update] to protect everyone including bystanders from the harmful health effects of TCE.[53]

Remediation

Recent research has focused on the in-place remediation of trichloroethylene in soil and groundwater using potassium permanganate instead of removal for off-site treatment and disposal. Naturally occurring bacteria have been identified with the ability to degrade TCE. Dehalococcoides sp. degrade trichloroethylene by reductive dechlorination under anaerobic conditions. Under aerobic conditions, Pseudomonas fluorescens can co-metabolize TCE. Soil and groundwater contamination by TCE has also been successfully remediated by chemical treatment and extraction. The bacteria Nitrosomonas europaea can degrade a variety of halogenated compounds including trichloroethylene.[54] Toluene dioxygenase has been reported to be involved in TCE degradation by Pseudomonas putida.[55] In some cases, Xanthobacter autotrophicus can convert up to 51% of TCE to CO and CO2.[55]

Society and culture

drinking water
contamination from industrial discharge including trichloroethylene is a major concern for human health and has precipitated numerous incidents and lawsuits in the United States.

The 1995 non-fiction book

Anderson v. Cryovac) against following the increase in cancer cases after trichloroethylene pollution incidents and it was adapted to cinema in 1998
.

TCE has been used as a

recreational drug.[56] Common methods of taking trichloroethylene recreationally include inhalation from a rag (similar to taking an inhalational anaesthetic) and drinking.[57] Most TCE abusers were young people and workers who use the chemical in their workplace. The main reason for abuse is TCE's euphoriant and slight hallucinogenic effect.[57] Some workers had become addicted to TCE.[58]

References

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Further reading

External links

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