Tetrachlorethylene

Structural formula
General
Surname	Tetrachlorethylene
other names	Tetrachlorethylene By Ethylene tetrachloride Perchlorethylene Perchlorethylene (PCE)
Molecular formula	C 2 Cl 4
Brief description	colorless, chlorine-like smelling liquid
External identifiers / databases
CAS number 127-18-4 EC number 204-825-9 ECHA InfoCard 100.004.388 PubChem 31373 Wikidata Q410772
properties
Molar mass	165.83 g mol −1
Physical state	liquid
density	1.62 g cm −3 (20 ° C)
Melting point	−22 ° C
boiling point	121 ° C
Vapor pressure	19.4 h Pa (20 ° C) 32.5 hPa (30 ° C) 52.5 hPa (40 ° C) 82.4 hPa (50 ° C)
solubility	very bad in water (160 mg l −1 at 20 ° C) mixable with most org. Solvents
Refractive index	1.5059
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary Caution H and P phrases H: 315-317-319-336-351-411 P: 273-280-304 + 340 + 312-333 + 313-337 + 313-391
MAK	not awarded because of suspected carcinogenic effects Switzerland: 50 ml m −3 or 345 mg m −3
Toxicological data	2630 mg kg −1 ( LD 50 ,  rat ,  oral )
Thermodynamic properties
ΔH f 0	−50.6 kJ / mol
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Tetrachlorethylene (common name perchlorethylene , perchlorine , PER , PCE ) is a colorless, non-flammable volatile liquid whose vapors are much heavier than air. It can be formally derived from ethene , in which all four hydrogen atoms have been replaced by chlorine atoms, so it is one of the highly volatile chlorinated hydrocarbons . Tetrachlorethylene dissolves polyolefins and chemically related plastics and makes them soft and opaque.

Due to its widespread use in industry and trade (especially in chemical cleaning ) and high environmental mobility, tetrachlorethylene is one of the main contaminants of groundwater.

Extraction and presentation

Michael Faraday first synthesized tetrachloroethene in 1821 by the thermal decomposition of hexachloroethane .

${\displaystyle \mathrm {C_{2}Cl_{6}\ \longrightarrow C_{2}Cl_{4}\ +\ Cl_{2}} }$

Today tetrachlorethylene is mostly produced by high-temperature chlorolysis of light hydrocarbons, the method being similar to that used by Faraday. By-products of the reaction are tetrachloromethane , hydrogen chloride and hexachlorobutadiene .

Several other methods have been developed. So the reaction of 1,2-dichloroethane at 400 ° C with chlorine :

${\displaystyle \mathrm {ClCH_{2}CH_{2}Cl+3\ Cl_{2}\rightarrow Cl_{2}C{\mathord {=}}CCl_{2}+4\ HCl} }$

The reaction is carried out with a mixture of potassium chloride and aluminum chloride as a catalyst. The trichloroethene formed as a by-product is separated off by distillation .

properties

Tetrachlorethylene is a colorless liquid that boils at 121 ° C under normal pressure . The enthalpy of vaporization at the boiling point is 34.68 kJ mol ⁻¹ . According to Antoine, the vapor pressure function results from log ₁₀ (P) = A− (B / (T + C)) (P in bar, T in K) with A = 4.18056, B = 1440.819 and C = −49.171 in the temperature range from 301 to 380.8 K. In the solid phase there are two polymorphic crystal forms. The crystal form II changes into the crystal form I at −63.15 ° C with a heat of transformation of 0.82 kJ mol ⁻¹ . This then melts at −22.35 ° C with a melting enthalpy of 10.88 kJ mol ⁻¹ . The miscibility with water is limited. As the temperature rises, the solubility of tetrachloroethene in water or the solubility of water in tetrachloroethene rises.

Solubilities between tetrachlorethylene and water
temperature	° C	0	9.5	19.5	31.1	40.0	50.1	61.3	71.0	80.2	91.8
Tetrachlorethylene in water	in%	0.0273	0.0270	0.0286	0.0221	0.0213	0.0273	0.0304	0.0377	0.0380	0.0523
Water in tetrachlorethylene	in%	0.0045	0.0054	0.0075	0.0091	0.0104	0.0117	0.0142	0.0205	0.0214	0.0245

use

Tetrachlorethylene is produced on an industrial scale. In the picture a tank container with tetrachlorethylene on a freight wagon .

Tetrachlorethylene is a solvent that is used in the textile , film , optical and metal industries . Because of its high fat dissolving power it is used there as a degreasing agent. In optical production, lenses and prisms are cleaned by cementing or wringing with tetrachlorethylene (also manually) before they are connected to optical elements . The systems in use today have several flood tanks and the option of steam degreasing (condensation of solvent vapor on the parts to be cleaned) so that a practically grease-free surface is obtained. The solvent is processed internally by distillation. Since chlorinated hydrocarbons tend to undergo autocatalytic decomposition (formation of hydrogen chloride) when acid is introduced, tetrachlorethylene is offered for metal cleaning with special stabilizers (amines, epoxides).

Textile care symbol: cleaning with perchlorethylene

Another important area of ​​application is dry cleaning . This is where the “P” (“perchlorethylene”) on the care symbol on the textile labels comes from.

Tetrachlorethylene found an unusual use in the 1960s in the Homestake experiment , a pioneering experiment in elementary particle physics . Here 615 t of the substance was stored in a gold mine in order to find the neutrino, which has been postulated for a long time but is very difficult to detect, with the help of a nuclear reaction .

In the rendering industry tetrachloroethene is no longer used today.

safety instructions

Tetrachlorethylene is classified as a category three carcinogenic hazardous substance . Chronic ingestion leads to liver and kidney damage. It is suspected of being toxic to reproduction and carcinogenic .

The IARC classified tetrachlorethylene as likely carcinogenic in 2014.

Tetrachlorethylene decomposes through light, moisture and heat (decomposition temperature: from 150 ° C). It uses u. a. releases a number of dangerous decomposition products, such as B. hydrogen chloride , phosgene , chlorine , polychlorinated dibenzodioxins (PCDD) or polychlorinated dibenzofurans (PCDF).

Tetrachlorethylene reacts with a number of other chemicals (especially with metals and metal compounds), sometimes very violently, and this can lead to strong heat development and even an explosion. This can also produce or release dangerous products and vapors.

Tetrachlorethylene as a hazardous substance

The use of tetrachloroethene can cause workplace pollution in the metal industry and in dry cleaning . Pollution of residents in the vicinity of companies that work with tetrachlorethylene, for which a limit value of 0.1 mg per cubic meter of indoor air applies, and the accumulation of tetrachlorethylene in groundwater are the most common environmental pollution. The reference method for determining pollution in the vicinity of tetrachlorethylene emitters are room air analyzes with the help of so-called passive collectors that work according to the diffusion principle. The average tetrachlorethylene exposure in rural regions is less than 1 µg per cubic meter of air and in urban areas between 2 and 5 µg per cubic meter of air, which corresponds to 1/100 of the limit value.

The state of the art for some time has been use in closed systems, the air emissions of which are minimized by various measures such as vacuum and activated carbon filters in the exhaust air. However, the operation of such systems in old buildings with beamed ceilings is still critical. It is partly for these reasons that dry-cleaners are switching to non-halogenated hydrocarbon solvents (i.e. hydrocarbons in which no hydrogen atom is replaced by one of the halogens fluorine , chlorine or bromine ).

Soil contamination by tetrachlorethylene is recorded in the contaminated site register.

According to the German Drinking Water Ordinance, a limit value of 10 µg per liter for the sum of trichloroethene and tetrachloroethene is specified for drinking water .

In 2012, tetrachlorethylene was included in the EU's ongoing action plan ( CoRAP ) in accordance with Regulation (EC) No. 1907/2006 (REACH) as part of substance evaluation . The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. The reasons for the uptake of tetrachloroethene were concerns about its classification as a CMR substance, high (aggregated) tonnage and widespread use, as well as the dangers arising from a possible assignment to the group of PBT / vPvB substances. The re-evaluation took place from 2013 and was carried out by Latvia . A final report was then published.

Web links

• Substance dossier at the Institute for Occupational Safety and Health of the German Social Accident Insurance
• Use of PER in chemical cleaning
• Concise International Chemical Assessment Document (CICAD) for tetrachloroethene

Individual evidence

1. ↑ ^{a b c d} Entry on tetrachlorethylene. In: Römpp Online . Georg Thieme Verlag, accessed on March 26, 2014.
2. ↑ ^{a b c d e f g h i j k l} Entry on tetrachlorethylene in the GESTIS substance database of the IFA , accessed on November 13, 2017(JavaScript required) .
3. ↑ Entry on tetrachlorethylene in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on August 3, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
4. ↑ Schweizerische Unfallversicherungsanstalt (Suva): Limit values ​​- current MAK and BAT values (search for 127-18-4 or tetrachlorethylene ), accessed on November 2, 2015.
5. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-21.
6. ↑ Silke Granzow: Isolation and characterization of a new tetrachlorethylene dechlorinating strictly anaerobic bacterium. Herbert Utz Verlag, 1998, ISBN 3-89675-388-6 .
7. ^ M. Rossberg et al .: Chlorinated Hydrocarbons. In: Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim 2006. doi : 10.1002 / 14356007.a06_233.pub2
8. ^ V. Majer, V. Svoboda: Enthalpies of Vaporization of Organic Compounds: A Critical Review and Data Compilation. Blackwell Scientific Publications, Oxford 1985, p. 300.
9. ↑ J. Polak, S. Murakami, VT Lam, Benson, George C .: Excess enthalpy, volume, and Gibbs free energy of cyclopentane-tetrachlorethylene mixtures at 25.deg. In: J. Chem. Eng. Data . 15, 1970, pp. 323-328, doi: 10.1021 / je60045a041 .
10. ^ NV Novoselova, IB Rabinovich, L. Ya. Tsvetkova, EM Moseeva, AG Babinkov: Heat capacity and thermodynamic functions of tetrachlorethylene. In: Zhur. Fiz. Khim. 60, 1986, pp. 1627-1630.
11. ↑ ES Domalski, ED Hearing: Heat Capacities and Entropies of Organic Compounds in the Condensed phase. Volume III. In: J. Phys. Chem. Ref. Data . 25, 1996, p. 1, doi: 10.1063 / 1.555985 .
12. ^ ^{A b} R. M. Stephenson: Mutual Solubilities: Water-Ketones, Water-Ethers, and Water-Gasoline-Alcohols. In: J. Chem. Eng. Data . 37, 1992, pp. 80-95, doi: 10.1021 / je00005a024 .
13. ↑ Lothar Oberauer, Michael Wurm: Astrophysics with neutrinos . (PDF; 1.1 MB). In: Stars and Space. February 2010, pp. 30-38.
14. ↑ inFranken.de: Still chemical degreaser in the groundwater (environmental damage caused by an animal body recycling facility operated with PER).
15. ↑ Reinhard Matissek, Gabriele Steiner, Markus Fischer: Food analysis. Springer, Berlin 2010, ISBN 978-3-540-92204-9 , p. 334.
16. ↑ IARC Monograph 106 - Tetrachlorethylene, 2014
17. ↑ Section 15 of the Ordinance on Limiting Emissions of Volatile Halogenated Organic Compounds .
18. ↑ Innenraumanalytik.at: Leaflet - Tetrachlorethylene (PDF; 15 kB).
19. ↑ Umweltlexikon-aktuell.de: "Tetrachlorethylene"
20. ↑ Air pollution control with dry cleaning. ( Memento of the original from March 1, 2010 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Environment portal on Berlin.de, accessed on December 9, 2010. 
21. ↑ Text of Annex 2 (to Section 6, Paragraph 2) of the Drinking Water Ordinance .
22. ^ European Chemicals Agency (ECHA): Substance Evaluation Report and Conclusion Document .
23. ↑ Community rolling action plan ( CoRAP ) of the European Chemicals Agency (ECHA): Tetrachlorethylene , accessed on March 26, 2019.