Tetrachloroethylene (original) (raw)

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Chemical compound in very wide use

Tetrachloroethylene

TetrachloroethyleneTetrachloroethylene TetrachloroethyleneTetrachloroethylene Carbon, C Chlorine, Cl
Names
Preferred IUPAC name Tetrachloroethene
Other namesCarbon bichloride; Carbon dichloride (Carboneum Dichloratum); Ethylene tetrachloride; Perchlor; Perchloroethene; Perchloroethylene;
Identifiers
CAS Number 127-18-4 checkY
3D model (JSmol) Interactive image
Abbreviations PCE; Perc; Per
Beilstein Reference 1304635
ChEBI CHEBI:17300 ☒N
ChEMBL ChEMBL114062 checkY
ChemSpider 13837281 checkY
ECHA InfoCard 100.004.388 Edit this at Wikidata
EC Number 204-825-9
Gmelin Reference 101142
KEGG C06789 checkY
PubChem CID 31373
RTECS number KX3850000
UNII TJ904HH8SN checkY
UN number 1897
CompTox Dashboard (EPA) DTXSID2021319 Edit this at Wikidata
InChI InChI=1S/C2Cl4/c3-1(4)2(5)6 checkYKey: CYTYCFOTNPOANT-UHFFFAOYSA-N checkYInChI=1/C2Cl4/c3-1(4)2(5)6Key: CYTYCFOTNPOANT-UHFFFAOYAO
SMILES ClC(Cl)=C(Cl)Cl
Properties
Chemical formula C2Cl4
Molar mass 165.82 g/mol
Appearance Clear, very refractive, colorless liquid
Odor Mild, sharp and sweetish[1]
Density 1.622 g/cm3
Melting point −22.0 to −22.7 °C (−7.6 to −8.9 °F; 251.2 to 250.5 K)
Boiling point 121.1 °C (250.0 °F; 394.2 K)
Solubility in water 0.15 g/L (25 °C)
Vapor pressure 14 mmHg (20 °C)[1]
Magnetic susceptibility (χ) −81.6·10−6 cm3/mol
Refractive index (_n_D) 1.505
Viscosity 0.89 cP at 25 °C
Hazards
Occupational safety and health (OHS/OSH):
Main hazards Inhalation of vapours can cause anaesthesia and respiratory irritation. Causes irritation in contact with skin and eyes with no residual injury.
GHS labelling:
Pictograms GHS08: Health hazardGHS09: Environmental hazard
Signal word Warning
Hazard statements H351, H411
Precautionary statements P201, P202, P273, P281, P308+P313, P391, P405, P501
NFPA 704 (fire diamond) [5] NFPA 704 four-colored diamond 2 0 0
Flash point Not flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose) 3420 mg/kg (oral, rat)[2]2629 mg/kg (oral, rat), >10000 mg/kg (dermal, rat)[3]
LC50 (median concentration) 4000 ppm (rat, 4 hr)5200 ppm (mouse, 4 hr)4964 ppm (rat, 8 hr)[4]
NIOSH (US health exposure limits):
PEL (Permissible) TWA 100 ppmC 200 ppm (for 5 minutes in any 3-hour period), with a maximum peak of 300 ppm[1]
REL (Recommended) Ca Minimize workplace exposure concentrations.[1]
IDLH (Immediate danger) Ca [150 ppm][1]
Safety data sheet (SDS) External MSDS
Related compounds
Related analogous organohalides Tetrafluoroethylene TetrabromoethyleneTetraiodoethylene
Related compounds TrichloroethyleneDichloroethylene1,1,2,2-TetrachloroethaneCarbon tetrachloride
Supplementary data page
Tetrachloroethylene (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 ?) Infobox references

Chemical compound

Tetrachloroethylene, also known as perchloroethylene[a] 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.[6]

Tetrachloroethylene is regarded as a toxic substance, a human health hazard, and an environmental hazard.[5][7] 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.[8]

History and production

[edit]

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.[_non-primary source needed_] 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)".[9]

Tetrachloroethylene can be made by passing chloroform vapour through a red-hot tube, the side products include hexachlorobenzene and hexachloroethane, as reported in 1886.[10]

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.[11] 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.[11]

Although in very small amounts, tetrachloroethylene occurs naturally in volcanoes along with trichloroethylene.[12]

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.[13]

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

[edit]

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.[14][15] 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.[16]Tetrachloroethylene treatment has played a vital role in eradicating hookworms in the United States and abroad.[_citation needed_] Hall's innovation was considered a breakthrough in medicine.[_citation needed_] It was given orally as a liquid or in capsules along with magnesium sulfate to get rid of the Necator americanus parasite in humans.[17]

Chemical properties and reactions

[edit]

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.[11] 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.[18]

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.[11]

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:[19]

C2Cl4 + Cl2 → C2Cl6

CFC-113 is produced by the reaction of tetrachloroethylene with chlorine and HF in the presence of antimony pentafluoride:[20]

C2Cl4 + 3 HF + Cl2 → CClF2CCl2F + 3 HCl

Tetrachlorodinitroethane can be obtained by nitration of tetrachloroethylene with fuming nitric acid (conc. HNO3 rich in nitrogen oxides) or nitrogen tetroxide:[21]

Cl2CCCl2 + N2O4 → NO2Cl2CCCl2NO2

The preparation of this crystalline solid compound from Tetrachloroethylene and nitrogen tetroxide was first described by Hermann Kolbe in 1869.[21]

Thermal decomposition

[edit]

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.[22]

Tetrachloroethylene is considered to be a toxin.[7] It is identified as a health hazard and environmental hazard.[5] Exposure to tetrachloroethylene, especially over a long term, may harm the nervous system, other organs, and increase the risk of getting cancer.[8] It may also have effects on pregnancy and the fetus.[8]

Reports of human injury are uncommon despite its wide usage in dry cleaning and degreasing.[23] Although limited by its low volatility, tetrachloroethylene has potent anaesthetic effects upon inhalation.[8][24] The risk depends on whether exposure is over minutes or hours, or over years.[8]

Despite the advantages of tetrachloroethylene, cancer research and government environmental agencies have called for its replacement from widespread commercial use.[8] It is described as a possible neurotoxicant, liver and kidney toxicant and reproductive and developmental toxicant (...) a potential occupational carcinogen.[7][8][25] 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.[11]

Tetrachloroethylene's biological half-life is approximately 3 days.[26] 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.[27][26]

Tetrachloroethylene can harm the nervous system, cause developmental deficits in children, impair vision, and increase the risk of psychiatric diagnoses.[7][28][29]

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.[30]: 32

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.[30]: 326 [31]: § 4.2.1.3 [32]: 237

Several modes of action are hypothesized for the carcinogenicity of tetrachloroethylene in humans, though existing data is insufficient for adequate characterization.[31]: § 4.2.4, § 4.3.4 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,[33][34] which suggests a potential for hepatocellular damage through the formation of reactive intermediates from glutathione conjugates during metabolization.[30]: 328 [32]: 10, 189–193 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.[31]: § 4.10.3 [32]: 172–178

Testing for exposure

[edit]

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.[35] 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.[36]

In principle, tetrachloroethylene contamination can be remediated by chemical treatment. Chemical treatment involves reducing metals such as iron powder.[37]

Bioremediation usually entails reductive dechlorination under anaerobic conditions by Dehalococcoides spp.[38] Under aerobic conditions, degradation may occur via co-metabolism by Pseudomonas sp.[39] Products of biological reductive dechlorination include trichloroethylene, _cis_-1,2-dichloroethylene, vinyl chloride, ethylene and chloride.

  1. ^ Previously spelt as perchlorethylene

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