Trichloroethylene (TCE, IUPAC name: trichloroethene) is an organochloride with the formula C2HCl3, commonly used as an industrial degreaser. It is a clear, colourless, non-flammable, volatile liquid with a sweet chloroform-like pleasant mild smell and burning sweet taste. Trichloroethylene has been sold under a variety of trade names for various purposes. Under the trade names Trimar and Trilene, it was used as a volatile anesthetic and as an inhaled obstetrical analgesic in millions of patients. Industrial abbreviations include trichlor, Trike, Tricky and tri.
Trichloroethylene is heavier than water and insoluble in water, therefore it sinks under water when spilt which causes it to migrate downward through soil and aquifers. It settles at the bottom of aquifers and forms persistent subsurface contamination that is difficult to detect and remediate.
History The earliest trichloroethylene synthesis was reported by Auguste Laurent in 1836. Laurent obtained it from the action of potassium hydroxide on a mixture of 1,1,2,2-tetrachloroethane and 1,1,1,2-tetrachloroethane made from the chlorination of ethylene dichloride and notated it as (at the time, the atomic weight of carbon was thought to be half of what it really is). He named trichloroethylene chlorétherise but did not investigate the compound further as his sample seemed unstable.
E. Fischer obtained trichloroethylene in 1864 via the reduction of hexachloroethane with hydrogen. Fischer investigated the compound and noted its boiling point as between 87 and 90 degrees Celsius.
First industrial plant for producing trichloroethylene was opened in Jajce, Austria-Hungary (modern-day Bosnia) in 1908. Commercial production of trichloroethylene began in Germany, in 1920 and in the United States in 1925.
As early as 1920, trichloroethylene was reported to cause sickness and severe narcotic effects including sleepiness and fainting in exposed workers.
The use of trichloroethylene in the food and pharmaceutical industries has been banned in some parts of the world since the 1970s due to concerns about its toxicity.
Anaesthesia Trichloroethylene is a good analgesic at 0.35 to 0.5% concentrations. Trichloroethylene has a blood/gas coefficient of 9, oil/gas coefficient of 714, and a minimum alveolar concentration of 0.23% in humans. It was mainly used as a general anaesthetic for small procedures and inhaled obsterical analgesic on millions of patients.
Trichloroethylene was first used in the treatment of trigeminal neuralgia beginning in 1916 after the recommendation by the German neurologist Hermann Oppenheim in 1915. Trichloroethylene for use as an analgesic for neuralgia were sold under the trade names "Gemalgene", "Trethylene" and "Chlorylen" in the 1920s.
American pharmacologist Dennis Emerson Jackson used trichloroethylene on patients given by the inhaler he developed in 1933 and published the report in 1934. Jackson later published a larger report on applying trichloroethylene on 300 patients along with the researchers Cecil Striker, Samuel Goldblatt, Irwin S. Warm in 1935. English anaesthetist Christopher Langton Hewer introduced trichloroethylene for anaesthetic use in Britain, in 1941. Hewer found that Imperial Chemical Industries (ICI) was already producing purified medical-grade trichloroethylene in Britain under the trade name Trilene (from trichloroethylene). Trilene was the purest TCE in the market at the time and other TCE formulations had impurities that could be unsafe for inhalation. Hewer noted that ICI sold Trilene for external wound cleaning. Hewer claimed that TCE would not pose cardiac danger based on a small group of patients, and mentions a death occurring during a TCE-nitrous oxide anaesthesia.
Pioneered by ICI in Britain, its development was hailed as an anesthetic revolution. It was also sold as "Trimar" in the United States. The –mar suffix indicated study and development at the University of Maryland, e.g., "Fluoromar" for fluroxene and "Vinamar" for ethyl vinyl ether". From the 1940s through the 1980s, both in Europe and North America, trichloroethylene was used as a volatile anesthetic almost invariably administered with nitrous oxide. Marketed in the UK by Imperial Chemical Industries under the trade name Trilene it was coloured blue with a dye called waxoline blue in 1:200,000 concentrationCurrent Researches in Anesthesia & Analgesia. (1951). USA: International Anesthesia Research Society. p.278 to avoid confusion with the similar-smelling chloroform. Trilene was stabilised with 0.01% thymol. "Anamenth" was an early German anaesthetic trichloroethylene formulation which contained menthol as the stabiliser.
Trichloroethylene was also used as an inhaled analgesic, mainly during childbirth, often self-applied by the patient. It was introduced for obstetrical anaesthesia in 1943, and used until the 1980s. Self-administration of trichloroethylene by the patient was common for obstetrical use with specialised devices that required little supervision by the medical staff. When used in analgesic doses, it did not affect the uterine muscles during labour. Other analgesic uses included dental operations, superficial plastic and orthopedic surgeries and other small procedures that did not require muscle relaxation.
Triservice Anaesthetic Apparatus (TSAA) is a portable draw-over vapouriser originally designed for trichloroethylene and halothane using ambient air as the carrier gas for the anaesthetic vapour. It was designed by Ivan Houghton for military/field use in 1981. It used trichloroethylene for its analgesic properties and halothane for main general anaesthesia.
Originally thought to possess less hepatotoxicity than chloroform, and without the unpleasant pungency and flammability of ether, TCE replaced earlier anesthetics chloroform and ether in the 1940s. TCE use was nonetheless soon found to have several pitfalls. These included promotion of cardiac arrhythmias, sensitivity to catecholamines in the heart, low volatility and high solubility preventing quick anesthetic induction, prolonged neurologic dysfunction from the reaction with soda lime used in carbon dioxide absorbing systems, and evidence of hepatotoxicity as had been found with chloroform, although the hepatotoxic effects (such as central necrosis and acute yellow atrophy) were reported to be temporary.Carl E. Wasmuth "Complications of Anesthesia" in Anesthesiology by Forty American Authors by Donald E. Hale (1955), pages 148-149 Alkali components of carbon dioxide absorbers reacted with trichloroethylene and released dichloroacetylene, a neurotoxin and a nephrotoxin. Most of the trichloroethylene toxicity cases were due to its breakdown into dichloroacetylene from the reaction with the soda lime, rather than trichloroethylene itself. Dichloroacetylene poisoning was common and often fatal during trichloroethylene anaesthesia if soda lime was used. Patients exposed to dichloroacetylene showed symptoms such as nausea, vomiting, loss of apetite, headache, facial nervous and muscular issues, and formation of herpes-like lesions on the face. Formation of dichloroacetylene lead to fatal encephalopathies and cranial nerve palsies. The muscle relaxant effect of trichloroethylene was inefficient for surgery.
The introduction of halothane in 1956 greatly diminished the use of TCE as a general anesthetic in the 1960s, as halothane allowed much faster induction and recovery times and was considerably easier to administer. Trichloroethylene has also been used in the production of halothane.
Anaesthetic use of trichloroethylene was banned in the United States in 1977 but the use in the United Kingdom remained until the late 1980s (especially for childbirth). Concerns about the carcinogenic potential of TCE led to its abandonment in developed countries by the 1980s and ICI had ceased medical grade TCE production by 1984. TCE was still in use as an anesthetic in some African countries as of 2000, and in Malawi and Nepal as of 2005.
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 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 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 methyl chloroform, carbon tetrachloride, ethylene dichloride, tetrachloroethanes, benzene and phenol. However, these compounds are present in very small amounts and do not possess any risk.
Uses Trichloroethylene is an effective solvent for a variety of organic materials. It is mainly used for cleaning. Trichloroethylene is an active ingredient (solvent) in various printing ink, varnish and industrial paint formulations. Other uses include dyeing and finishing operations, adhesive formulations, rubber processing, adhesives, lacquers, and paint strippers. It is applied before plating, anodizing, and painting.
When trichloroethylene was first widely produced in the 1920s, its 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 (removal of caffeine) and the preparation of flavoring extracts from hops and spices. TCE was used as a freezing point depressant in carbon tetrachloride fire extinguishers.
Trichloroethylene is also a chain terminator for polyvinyl chloride. Chlorination gives pentachloroethane.
Cleaning solvent Perhaps the greatest use of TCE is as a degreaser for metal parts. It has been widely used in degreasing and cleaning since the 1910s because of its low cost, low flammability, low toxicity, and high effectiveness 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 contribution to the ozone depletion. As a result, trichloroethylene has experienced some resurgence in use as a degreaser.
Trichloroethylene has been used as a dry cleaning solvent, although mostly replaced by tetrachloroethylene, except for spot cleaning – for grease and oil stains – where it is still often used under various tradenames. It was found unfavourable for dry cleaning because it tended to dissolve acetate dyes, which tetrachloroethylene did not. Trichloroethylene is used to remove grease and lanolin from wool before weaving.