Tetrachloroethylene

Tetrachloroethylene

Carbon, C   Chlorine, Cl
Names
Preferred IUPAC name Tetrachloroethene
Other names Carbon bichloride; Carbon dichloride (Carboneum Dichloratum); Dicarbon tetrachloride;[1] Ethylene tetrachloride; Perchlor; Perchloroethene; Perchloroethylene; Chlorethose[2]
Identifiers
CAS Number	127-18-4 Y
3D model (JSmol)	Interactive image
Abbreviations	PCE; Perc; Per
Beilstein Reference	1304635
ChEBI	CHEBI:17300 N
ChEMBL	ChEMBL114062 Y
ChemSpider	13837281 Y
ECHA InfoCard	100.004.388
EC Number	204-825-9
Gmelin Reference	101142
KEGG	C06789 Y
PubChem CID	31373
RTECS number	KX3850000
UNII	TJ904HH8SN Y
UN number	1897
CompTox Dashboard (EPA)	DTXSID2021319
InChI InChI=1S/C2Cl4/c3-1(4)2(5)6 Y Key: CYTYCFOTNPOANT-UHFFFAOYSA-N Y InChI=1/C2Cl4/c3-1(4)2(5)6 Key: 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[3]
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)[3]
Magnetic susceptibility (χ)	−81.6·10−6 cm3/mol
Refractive index (nD)	1.505
Viscosity	0.89 cP at 25 °C
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Mild skin and respiratory irritant
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H351, H411
Precautionary statements	P201, P202, P273, P281, P308+P313, P391, P405, P501
NFPA 704 (fire diamond)	[7] 2 0 0
Flash point	Not flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	3420 mg/kg (oral, rat)[4] 2629 mg/kg (oral, rat), >10000 mg/kg (dermal, rat)[5]
LC50 (median concentration)	4000 ppm (rat, 4 hr) 5200 ppm (mouse, 4 hr) 4964 ppm (rat, 8 hr)[6]
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 100 ppm C 200 ppm (for 5 minutes in any 3-hour period), with a maximum peak of 300 ppm[3]
REL (Recommended)	Ca Minimize workplace exposure concentrations.[3]
IDLH (Immediate danger)	Ca [150 ppm][3]
Safety data sheet (SDS)	External MSDS
Related compounds
Related analogous organohalides	Tetrafluoroethylene Tetrabromoethylene Tetraiodoethylene
Related compounds	Trichloroethylene Dichloroethylene 1,1,2,2-Tetrachloroethane Carbon 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 YN ?) Infobox references

Tetrachloroethylene, also known under the systematic name tetrachloroethene, or perchloroethylene,^[a] and abbreviations such as "perc" (or "PERC"), and "PCE", is a chlorocarbon with the formula Cl₂C=CCl₂. It is a colorless liquid widely used for dry cleaning of fabrics, hence it is sometimes called "dry-cleaning fluid". 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.^[8]

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) ".^[9]

A few years after its discovery, in the 1840s, Tetrachloroethylene was named Chlorethose by Auguste Laurent. The -ose ending was explained as the fourfold replacement of the hydrogens in ethylene. If only one atom of hydrogen was replaced, the word would end with -ase. By Laurent's logic, vinyl chloride would be named Chlorethase.^[10]

Tetrachloroethylene can be made by passing chloroform vapour through a red-hot tube, the side products include hexachlorobenzene and hexachloroethane, as reported in 1886.^[11]

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.^[12] 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 by the chemical reaction:

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.^[12]

Although in very small amounts, tetrachloroethylene occurs naturally in volcanoes along with trichloroethylene.^[13]

Uses

Tetrachloroethylene is an excellent nonpolar solvent for organic materials. Otherwise, it is volatile, highly stable 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) suggested Tetrachloroethylene to be used in dry cleaning as an alternative to highly flammable dry cleaning solvents such as naphtha.^[14]

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.^[15][16]

Health and safety

Tetrachloroethylene is much less toxic than other chlorinated solvents.^[8] The acute and chronic toxicity of tetrachloroethylene is moderate to low. Reports of human injury are uncommon despite its wide usage in dry cleaning and degreasing.^[17]

Despite the advantages of tetrachloroethylene, many^[who?] have called for its replacement from widespread commercial use. It has been described as a possible "neurotoxicant, liver and kidney toxicant and reproductive and developmental toxicant (...) a 'potential occupational carcinogen'".^{[18][better source needed]}

As an anthelmintic, tetrachloroethylene was given orally to approximately fifty thousand people between 1925 and 1943. The most severe side effects were nausea and vomiting due to the irritation of gastric tract. Most reported poisonings were manifestations of its narcotic effects.^[19]

Metabolism

Tetrachloroethylene's biological half-life is approximately 3 days.^[20] 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.^[21][20]

Carcinogenicity

Tetrachloroethylene has been classified as "probably carcinogenic to humans" (Group 2A) by the International Agency for Research on Cancer (IARC). There is a possibility that it is carcinogenic to humans in long-term exposure, but the evidence is limited since most of the evaluated dry-cleaners had heavy smoking and drinking habits which are known to cause multiple types of cancer.^[22] Epidemiological research has been conducted in the dry-cleaning industry because of the widespread use of tetrachloroethylene in the industry since 1960. The evidence demonstrates a positive association between tetrachloroethylene exposure, bladder cancer, non-Hodgkin lymphoma, and multiple myeloma in adults. A review of 109 occupational studies estimated a mean exposure of 59 ppm in dry-cleaning employees. Epidemiological evidence shows that exposure via ingestion or inhalation can increase tumor incidence.^[23] Exposure to tetrachloroethylene in a typical dry cleaning shop is considered far below the levels required to cause any risk.^[24]

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.^[25] 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 Europe, 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.^[26]

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.^[27] Under aerobic conditions, degradation may occur via cometabolism by Pseudomonas sp.^[28] Products of biological reductive dechlorination include trichloroethene, cis-1,2-dichloroethene, vinyl chloride, ethene and chloride.

Explanatory notes

References

Further reading

• "Toxicological Profile for Tetrachloroethene". Agency for Toxic Substances and Disease Registry. 1997.
• Doherty, R.E. (2000). "A History of the Production and Use of Carbon Tetrachloride, Tetrachloroethylene, Trichloroethylene and 1,1,1-Trichloroethane in the United States: Part 1 - Historical Background; Carbon Tetrachloride and Tetrachloroethylene". Environmental Forensics. 1 (2): 69–81. Bibcode:2000EnvFo...1...69D. doi:10.1006/enfo.2000.0010. S2CID 97680726.

External links

• ATSDR Case Studies in Environmental Medicine: Tetrachloroethylene Toxicity U.S. Department of Health and Human Services
• Tetrachloroethylene (Perchloroethylene) U.S. Department of Health and Human Services
• Australian National Pollutant Inventory (NPI) page
• Sustainable uses and Industry recommendations