| General |
|
|---|---|
| Name | Tetrachloroethylene |
| Chemical formula | Cl2C=CCl2 |
| Appearance | Colorless liquid |
| Physical |
|
| Formula weight | 131.4 amu |
| Melting point | 254 K (-19 °C) |
| Boiling point | 420 K (147 °C) |
| Density | 1.63 ×103 kg/m3 (liquid) |
| Solubility | insoluble in water |
| Thermochemistry |
|
| ΔfH0gas | ? kJ/mol |
| ΔfH0liquid | ? kJ/mol |
| ΔfH0solid | ? kJ/mol |
| S0gas, 1 bar | ? J/mol·K |
| S0liquid, 1 bar | ? J/mol·K |
| S0solid | ? J/mol·K |
| Safety |
|
| Ingestion | May cause nausea, vomiting. May damage liver and kidneys. May cause symptoms like for inhalation. |
| Inhalation | May irritate mucous membranes. Can cause headache, dizziness, stupor, unconsciousness. |
| Skin | May cause skin irritation, severe burns. |
| Eyes | May cause severe irritation |
| More info | Hazardous Chemical Database (http://ull.chemistry.uakron.edu/erd/chemicals/8/7139.html) |
| SI units were used where possible. Unless otherwise stated, standard conditions were used. |
|
Tetrachloroethylene Cl2C=CCl2 is a manufactured chemical that is widely used for the dry cleaning of fabrics and for metal-degreasing. It is also used to make other chemicals and is used in some consumer products.
Other names for tetrachloroethylene include perchloroethylene, PCE, and tetrachloroethene. It is a nonflammable liquid at room temperature. It evaporates easily into the air and has a sharp, sweet odor. Most people can smell tetrachloroethylene when it is present in the air at a level of 1 part tetrachloroethylene per million parts of air (1 ppm) or more, although some can smell it at even lower levels.
Michael Faraday first synthesized tetrachloroethylene in 1821 by heating hexachloroethane until it decomposed into tetrachloroethylene and chlorine.
Production
Most tetrachloroethylene is produced ethylene via 1,2-dichloroethane. When 1,2-dichloroethane is heated to 400°C with chlorine, tetrachloroethylene can result from the chemical reaction
- ClCH2CH2Cl + 3 Cl2 → Cl2C=CCl2 + 4 HCl
This reaction can be catalyzed by a mixture of potassium chloride and aluminum chloride, or by activated carbon. Trichloroethylene is a major byproduct of the reaction, and since both are salable commercial chemicals, typical industrial practice is to collect both products and then separate them by distillation.
A somewhat smaller amount of tetrachlorethylene is made from a mixture of partially chlorinated light hydrocarbons that would other be hazardous waste products of several chemical processes. When these compounds are heated in the presence of excess chlorine, they are converted to a mixture of tetrachloroethylene, carbon tetrachloride, and hydrogen chloride.
Uses
Most applications of tetrachloroethylene use it for its solvent properties. Most organic materials dissolve in tetrachloroethylene. It is the most widely used solvent in dry cleaning. It is also used to degrease metal parts in the automotive and other metalworking industries. It appears in a few consumer products including paint strippers and spot removers.
Until the early 1990s, tetrachloroethylene was also heavily used in the manufacture of freon refrigerants, especially the freons R-113, R-114, and R-115. Since 1996, these chemicals have been banned in most of the world under the terms of the Montreal Protocol, and so tetrachloroethylene is no longer used for this purpose.
Health effects
Like many chlorinated hydrocarbons, tetrachloroethylene is a central nervous system depressant, and inhaling its vapors (particularly in closed, poorly ventilated areas) can cause dizziness, headache, sleepiness, confusion, nausea, difficulty in speaking and walking, unconsciousness, and death.
After repeated or extended skin contact, tetrachloroethylene may dissolve fats from the skin, resulting in severe skin irritation. These symptoms occur almost entirely in work (or hobby) environments where people have been accidentally exposed to high concentrations or have intentionally used tetrachloroethylene to get a "high."
In industry, most workers are exposed to levels lower than those causing obvious nervous system effects. The health effects of breathing in air or drinking water with low levels of tetrachloroethylene are not known.
Results from some studies suggest that women who work in dry cleaning industries where exposures to tetrachloroethylene can be quite high may have more menstrual problems and spontaneous abortions than women who are not exposed. However, it is not known if tetrachloroethylene was responsible for these problems because other possible causes were not considered.
Results of animal studies, conducted with amounts much higher than those that most people are exposed to, show that tetrachloroethylene can cause liver and kidney damage. Exposure to very high levels of tetrachloroethylene can be toxic to the unborn pups of pregnant rats and mice. Changes in behavior were observed in the offspring of rats that breathed high levels of the chemical while they were pregnant.
Testing for TCE
One way of testing for tetrachloroethylene exposure is to measure the amount of the chemical in the breath, much the same way breath-alcohol measurements are used to determine the amount of alcohol in the blood.
Because it is stored in the body's fat and slowly released into the bloodstream, tetrachloroethylene can be detected in the breath for weeks following a heavy exposure.
Tetrachloroethylene and trichloroacetic acid (TCA), a breakdown product of tetrachloroethylene, can be detected in the blood. These tests are relatively simple to perform. These tests aren't available at most doctors' offices, but can be performed at special laboratories that have the right equipment.
Because exposure to other chemicals can produce the same breakdown products in the urine and blood, the tests for breakdown products cannot determine if you have been exposed to tetrachloroethylene or the other chemicals.