Trichloroethylene

Properties

General
Name	Trichloroethylene
Chemical formula	ClCH=CCl2
Appearance	Colorless liquid
Physical
Formula weight	131.4 amu
Melting point	200 K (-73 °C)
Boiling point	360 K (87 °C)
Density	1.46 ×103 kg/m3 (liquid)
Solubility	insoluble in water
Thermochemistry
ΔfH0gas	-7.78 kJ/mol
ΔfH0liquid	-42.3 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, stomach irritation. Inhaling vapors from stomach into lungs causes symptoms like those of inhalation.
Inhalation	Can cause dizziness, drowsiness, confusion, unconsciousness, and cardiac failure. May irritate mucous membranes.
Skin	May cause skin irritation. Prolonged exposure may lead to chronic irritation.
Eyes	May cause burning senation, watering.
More info	Hazardous Chemicals Database
SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references

The chemical compound trichloroethylene is a chlorinated hydrocarbon commonly used as an industrial solvent. It is a clear nonflammable liquid with a sweet smell.

Its IUPAC name is trichloroethene. In industry, it is informally referred to by the abbreviations TCE and tri, and it is sold under a variety of trade names.

Production

Prior to the early 1970's, 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 either be accomplished with an aqueous solution of caclium hydroxide

Cl₂CHCHCl₂ + Ca(OH)₂ → ClCH=CCl₂ + CaCl₂

or in the vapor phase by heating it to 300-500°C on a barium chloride or calcium chloride catalyst

Cl₂CHCHCl₂ → ClCH=CCl₂ + HCl

Today, however, 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.

Uses

Trichloroethylene is a good solvent for a variety of organic materials. When it was first widely produced in the 1920's, 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 and the preparation of flavoring extracts from hops and spices. It was also used as a dry cleaning solvent, although tetrachloroethylene surpassed it in this role in the 1950's.

Due to concerns about its toxicity, the use of trichloroethylene in the food and pharmaceutical industries has been banned in much of the world since the 1970's.

For most of its history, trichloroethylene has been widely used as a degreaser for metal parts. In the late 1950's, the demand for trichloroethylene as a degreaser began to decline 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, and as a result trichloroethylene has experienced a resurgence in use.

Health effects

When inhaled, trichloroethylene depresses the central nervous system. It symptoms are similar to those of intoxication, beginning with headache, dizziness, and confusion and progressing with increasing exposure to unconsciousness and death. Caution should be exercised anywhere a high concentration of trichloroethylene vapors may be present, because it quickly desensitizes the nose to its scent, and it is possible to unknowingly inhale harmful or even lethal amounts of the vapor.

The long-term effects of trichloroethylene on human beings is unknown. In animal studies, chronic trichloroethylene exposure has produced liver cancer in mice, but not in rats. Studies on its effects on reproduction in animals have been similarly inconsistent, and so no conclusive statements about its ability to cause birth defects in humans can be made.