What Is Trichloroethylene?
Trichloroethylene is an organic compound where the three hydrogen atoms in ethylene are substituted by chlorine atoms.
Also known as trilene or trichlene, it appears as a clear, colorless liquid at room temperature.
Due to its toxicity, the International Agency for Research on Cancer (IARC) classifies its carcinogenicity as Group 1 (carcinogenic to humans).
Uses of Trichloroethylene
Trichloroethylene finds primary usage in degreasing and cleaning metal and electronic parts, owing to its ability to dissolve oils, greases, and lubricants. It serves as a solvent in adhesives to dissolve rubber and resins, and in the industrial manufacture of dyes and paints.
Furthermore, it acts as a raw material for synthesizing CFC substitutes and is involved in CFC gas production.
Trichloroethylene is utilized in dry cleaning to remove oil from clothing, wool, and leather items unsuitable for water washing. Additionally, it serves as a standard concentration solution for comparison in water quality measurements, albeit in limited quantities.
Properties of Trichloroethylene
Trichloroethylene has a boiling point of 86.7°C, a melting point of -86.4°C, and an ignition point of 420°C. It is nonflammable and volatile at room temperature, emitting a sweet odor reminiscent of chloroform.
It is highly soluble in various organic solvents such as ethanol, diethyl ether, and chloroform. However, it exhibits instability in the presence of metals, especially over prolonged periods and at elevated temperatures. Commercially available trichloroethylene often includes additives to address this issue.
Structure of Trichloroethylene
Trichloroethylene is an organochlorine compound in which three hydrogen atoms of ethylene are substituted by chlorine atoms. Organochlorine compounds entail chlorine bonded to a carbon-containing compound.
Its chemical formula is C2HCl3, with a density of 1.46g/cm3 at 20°C.
Other Information on Trichloroethylene
1. Synthesis of Trichloroethylene Using Acetylene
Before the early 1970s, trichloroethylene was synthesized from acetylene through a two-step reaction. Chlorine reacts with acetylene at 90°C, with an iron (III) chloride catalyst yielding 1,1,2,2-tetrachloroethane.
Subsequently, trichloroethylene can be synthesized from 1,1,2,2-tetrachloroethane by reacting it with aqueous calcium hydroxide. The former is synthesized by gas-phase heating of 1,1,2,2-tetrachloroethane to 300-500°C using catalysts like calcium chloride or barium chloride.
2. Trichloroethylene Synthesis Using Ethylene
Presently, most trichloroethylene is produced from ethylene. The chlorination of ethylene with iron (III) chloride as a catalyst yields 1,2-dichloroethane.
Heating chlorine with 1,2-dichloroethane to around 400°C results in trichloroethylene. Catalysts such as a mixture of aluminum chloride and potassium chloride or porous carbon can be employed for the chlorination of 1,2-dichloroethane. Depending on chlorine concentration, tetrachloroethylene may be a byproduct, separable by distillation.
3. Trichloroethylene Hazards
Inhalation or direct contact with trichloroethylene vapor can induce poisoning symptoms like headache, dizziness, and vomiting. It poses risks of liver and kidney damage.
Highly toxic to humans, trichloroethylene, when released into the environment, is insoluble in water, leading to soil and groundwater contamination issues. Consequently, strict regulations govern its handling.