1,1,1-Trichloroethane
Solvent, now banned for ozone depletion
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Related on Lably
Through Solvent, Montreal Protocol and Hydrogen chloride
Production
1,1,1-Trichloroethane was first reported by Henri Victor Regnault in 1840. Industrially, it 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 (68–122 °F) to produce 1,1-dichloroethane:
- H2C=CHCl + HCl → CH3CHCl2
This reaction is catalyzed by a variety of Lewis acids, mainly aluminium chloride, iron(III) chloride, or zinc chloride. 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 is produced from the reaction of 1,1-dichloroethene and hydrogen chloride in the presence of an iron(III) chloride catalyst:
- CH2=CCl2 + HCl → CH3CCl3
It is sold with stabilizers because it is unstable with respect to dehydrochlorination and attacks some metals. Stabilizers comprise up to 8% of the formulation, including acid scavengers (epoxides, amines) and complexants. One discontinued product contained only 1,4-dioxane (2%±1%), while another chemical supplier included 2.5% 1,4-dioxane, 0.47% 1,2-butylene oxide, and 0.35% nitromethane as stabilizers.
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Uses
1,1,1-Trichloroethane is an excellent solvent for many organic compounds and one of the least toxic of the chlorinated hydrocarbons. It is generally considered non-polar, but owing to the good polarizability of the chlorine atoms, it is a superior solvent for organic compounds that do not dissolve well in hydrocarbons such as hexane. Prior to the Montreal Protocol, it was widely used for cleaning metal parts and circuit boards, as a photoresist solvent in the electronics industry, as an aerosol propellant, as a cutting fluid additive, and as a solvent for inks, paints, adhesives, and other coatings.
It was used to dry-clean leather and suede. Use in dry-cleaning remained until the 1980s. It was used as an insecticidal fumigant.
It was also the standard cleaner for photographic film. Other commonly available solvents damage emulsion and base (acetone will dissolve triacetate base on most films), and thus are not suitable for this application. The standard replacement, Forane 141 is much less effective, and tends to leave a residue. It was also used as a thinner in correction fluid products such as liquid paper.
Many of its applications previously used carbon tetrachloride (which was banned in US consumer products in 1970). In turn, 1,1,1-trichloroethane itself is now being replaced by other solvents in the laboratory. Phase-out of 1,1,1-Trichloroethane due to ozone depletion lead to a resurgence of the use of trichloroethylene in metal degreasing.
Methyl chloroform was also used as a veterinary anthelmintic.
Early anaesthetic research
1,1,1-Trichloroethane was one of the volatile organochlorides that have been tried as alternatives to chloroform in anaesthesia. In the 1880s, it was found to be a safe and strong substitute for chloroform but its production was too expensive and difficult for the era.
In 1880, 1,1,1-trichloroethane was suggested as an anaesthetic. It was first referred to as methyl-chloroform in the same year. At the time, the narcotic effects of chloral hydrate were owed to a hypothetical metabolic pathway to chloroform in "alkaline blood". Trichloroethane was studied for its structural similarity to chloral and potential anaesthetic effects. However, trichloroethane did not exhibit any conversion to chloroform in laboratory experiments. The 1,1,2-Trichloroethane (vinyl trichloride) isomer, which lacked a trichloromethyl group, exhibited anaesthetic effects even stronger than the 1,1,1 isomer.
Safety
Although not as toxic as many similar compounds, inhaled or ingested 1,1,1-trichloroethane acts as a central nervous system depressant and can cause decrease in reaction times and dexterity as well as impaired balance and abnormal EEG at lower concentrations, throat irritation, and in sufficiently high concentrations, death.
The International Agency for Research on Cancer places 1,1,1-trichloroethane in Group 2A as a probable carcinogen.
Atmospheric concentration
1,1,1-Trichloroethane is a fairly potent greenhouse gas with a 100-year global warming potential of 169 relative to carbon dioxide. This is nonetheless less than a tenth that of carbon tetrachloride — which it replaced as a solvent — due to its relatively short atmospheric lifetime of about 5 years.
The Montreal Protocol targeted 1,1,1-trichloroethane as a compound responsible for ozone depletion and banned its use beginning in 1996. Since then, its manufacture and use have been phased out throughout most of the world, and its atmospheric concentration has declined substantially.