What Is Trichloroethylene (TCE)?
Trichloroethylene (TCE, CAS 79-01-6, molecular formula C2HCl3) is a clear, colorless, volatile liquid with a sweet, chloroform-like odor. It is a powerful chlorinated solvent for oils, greases, waxes and many organic compounds, which made it one of the most widely used industrial degreasers of the 20th century. Today, because of its toxicity, its use is strictly controlled and in many regions being phased out.
Key Properties
| Property | Value |
|---|---|
| CAS number | 79-01-6 |
| Molecular formula | C2HCl3 |
| Molecular weight | 131.39 g/mol |
| Boiling point | 87.2 C |
| Melting point | -84.8 C |
| Flash point | None under normal conditions (non-flammable liquid) |
| Vapor density | About 4.5 (air = 1) |
| Water solubility | Low, about 0.1 g/100 mL |
| UN number | 1710, Class 6.1 (toxic) |
Main Applications
Metal degreasing: vapor degreasing and cold cleaning of steel, aluminum and copper parts in automotive, aerospace and electronics manufacturing.
Adhesives and coatings: solvent in glues, sealants, paints and paint removers.
Extraction: recovers oils, fats and waxes from natural materials.
Chemical intermediate: historically used to produce fluorochemicals such as HFC-134a and PVC; these routes are declining under regulation.
Household and many professional uses have been banned or restricted in the EU and the US because of the health risks described below.
Health and Environmental Hazards
The International Agency for Research on Cancer (IARC) classifies trichloroethylene as Group 1, carcinogenic to humans. It is associated with kidney cancer and with increased risk of liver cancer and non-Hodgkin lymphoma. TCE also harms the central nervous system (dizziness, headache, unconsciousness at high vapor levels), can cause cardiac arrhythmias, and repeated exposure damages the kidneys, liver, immune system and male reproductive system. Exposure during pregnancy may harm the unborn child. Environmentally, TCE is a volatile organic compound; spills and improper disposal contaminate soil and groundwater, where it persists for decades.
Regulations and Compliance
In the EU, TCE is subject to REACH restrictions (Annex XVII entry 75, amended by Commission Regulation (EU) 2024/1328), which prohibit supply to the general public and ban most professional and consumer uses with limited derogations. In the United States, the EPA issued a TSCA section 6(a) risk management rule for TCE in December 2024, banning most consumer and commercial uses and phasing out remaining uses such as vapor degreasing. Many other jurisdictions apply occupational exposure limits (OELs) and groundwater standards. Buyers and users must verify the current legislation in their country and confirm that their intended application is permitted.
Alternatives to TCE
For metal cleaning, aqueous and semi-aqueous cleaners, modified alcohol solvents, hydrocarbon solvents and other chlorinated-free formulations can replace TCE in most processes. Any substitution should be validated for the specific soil and substrate, and the alternative's own SDS and exposure limits must be reviewed.
Frequently Asked Questions
Q: What is trichloroethylene used for?
Mainly industrial metal degreasing, adhesives and extraction solvent; many uses are now restricted by regulation.
Q: What is the CAS number of trichloroethylene?
TCE has CAS number 79-01-6, molecular formula C2HCl3, molecular weight 131.39 g/mol and a boiling point of 87.2 C.
Q: What are the key physical properties of TCE?
TCE is a clear, colorless, volatile liquid with a sweet chloroform-like odor, low water solubility (about 0.1 g/100 mL) and a vapor density about 4.5 times that of air, so its vapors accumulate near the floor in poorly ventilated areas.
Q: What regulations restrict TCE in the EU and the United States?
In the EU, TCE falls under REACH Annex XVII entry 75 as amended by Commission Regulation (EU) 2024/1328, prohibiting supply to the general public and most professional and consumer uses; in the United States, the EPA issued a TSCA section 6(a) rule in December 2024 banning most consumer and commercial uses and phasing out remaining uses such as vapor degreasing.
Q: What environmental problems are associated with TCE?
TCE is a volatile organic compound, and spills or improper disposal contaminate soil and groundwater, where it can persist for decades; many jurisdictions therefore apply occupational exposure limits and groundwater standards.
Q: Why is TCE effective for vapor degreasing?
TCE boils at 87.2 C, and in vapor degreasing the hot solvent vapor condenses on cooler metal parts, dissolving oils and greases and carrying them away, leaving a clean, dry surface; this process is now strictly regulated because of the health risks.