1,1,1-Trichloroethane

The chemical compound 1,1,1-trichloroethane is a chlorinated hydrocarbon that was until recently widely used as an industrial solvent. Other names for it include methyl chloroform, chlorothene, and the trade names Solvent 111 and Genklene (used by ICI).

1,1,1-trichloroethane was first produced by the French chemist Henri Victor Regnault in 1840. It was produced in large quantities by the chemical industry beginning in the mid-1950s and continuing through 1995. Today, it is banned by the Montreal Protocol.

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Production

Industrially, 1,1,1-trichloroethane is usually produced in a two-step process from vinyl chloride. In the first step, vinyl chloride reacts with hydrogen chloride at 20-50 °C to produce 1,1-dichloroethane. This reaction is catalyzed by one of aluminium chloride, iron(III) chloride, or zinc chloride. Its chemical equation is

CH₂=CHCl + HCl → CH₃CHCl₂

The 1,1-dichloroethane is then converted to 1,1,1-trichloroethane by reaction with chlorine under ultraviolet irradiation

CH₃CHCl₂ + Cl₂ → CH₃CCl₃ + HCl

This reaction proceeds at 80-90% yield, and the hydrogen chloride byproduct can be recycled to the first step in the process. The major side-product is the related compound 1,1,2-trichloroethane, from which the 1,1,1-trichloroethane can be separated by distillation.

A somewhat smaller amount of 1,1,1-trichloroethane is produced from the reaction of vinylidene chloride and hydrogen chloride in the presence of an iron(III) chloride catalyst:

CH₂=CCl₂ + HCl → CH₃CCl₃

Uses

1,1,1-trichloroethane is an excellent solvent for many organic materials and also one of the least toxic of the chlorinated hydrocarbons. Prior to the Montreal Protocol, it was used for cleaning metal parts and circuit boards, as a photoresist solvent in the electronics industry, as an aerosol propellant, and as a solvent for inks, paints, adhesives, and other coatings. It was also very effective at safely removing PVC from copper and silver coins that had been stored in PVC containers for several years. It was also the standard cleaner for photographic film (movie/slide/negatives, etc). It had the property of being able to clean almost anything off film, without softening or otherwise damaging the emulsion. Other commonly available solvents damage emulsion, and thus are not suitable for this application. The standard replacement, Forane 141 is much less effective, and tends to leave a residue. Many applications for 1,1,1-trichloroethane (including film cleaning) were previously done with carbon tetrachloride, which was banned in 1970.

The Montreal Protocol targeted 1,1,1-trichloroethane as one of those compounds responsible for ozone depletion and banned its use beginning in 1996. Since then, its manufacture and use has been phased out throughout most of the world.

1,1,1-trichloroethane is generally considered as a non-polar solvent, but since all three electronegative chlorine atoms lie on the same side of the molecule, it is slightly polar, making it a good solvent for organic matters that do not dissolve into totally non-polar substances such as hexane.

Safety

Although not as toxic as many similar compounds, inhaled or ingested 1,1,1-trichloroethane does act as a central nervous system depressant and can cause effects similar to those of intoxication, including dizziness, confusion, and in sufficiently high concentrations, unconsciousness and death.

Prolonged skin contact with the liquid can result in the removal of fats from the skin, resulting in chronic skin irritation.

Studies on laboratory animals have shown that 1,1,1-trichloroethane is not retained in the body for long periods of time. However, chronic exposure has been linked to abnormalities in the liver, kidneys, and heart. Pregnant women should avoid exposure, as the compound has been linked to birth defects in laboratory animals (see teratogenesis).

The substance is deadly to insects.

Cultural references

It is referenced in Chuck Palahniuk's novel "Choke" as the substance the protagonist's mother inhales in order to forget everything she knows.

References

Further reading

Agency for Toxic Substances and Disease Registry (ATSDR). 2006. Toxicological Profile for 1,1,1-Trichloroethane. link

Doherty, R.E. 2000. A History of the Production and Use of Carbon Tetrachloride, Tetrachloroethylene, Trichloroethylene and 1,1,1-Trichloroethane in the United States: Part 2 - Trichloroethylene and 1,1,1-Trichloroethane. Journal of Environmental Forensics (2000) 1, 83-93. link