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The organic compound 1,1,1-trichloroethane, also known as methyl chloroform, is a chloroalkane. This colourless, sweet-smelling liquid was once produced industrially in large quantities for use as a solvent.[4] It is regulated by the Montreal Protocol as an ozone-depleting substance and its use is being rapidly phased out.

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 to produce 1,1-dichloroethane:

CH2=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 of 1,1,1-trichloroethane 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

1,1,1-Trichloroethane 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.

Uses

1,1,1-Trichloroethane is generally considered a non-polar solvent. 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. It 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 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. 1,1,1-Trichloroethane is also used as an insecticidal fumigant.

It was also the standard cleaner for photographic film (movie/slide/negatives, etc.). 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. 1,1,1-Trichloroethane was 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.[5]

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 ethanol intoxication, including dizziness, confusion, and, in sufficiently high concentrations, unconsciousness and death.[6] Fatal poisonings and illnesses linked to intentional inhalation of trichloroethane have been reported.[7][8][9][10] The removal of the chemical from correction fluid commenced due to Proposition 65 declaring it hazardous and toxic.[11][12]

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).

Atmospheric concentration

1,1,1-Trichloroethane timeseries at various latitudes.

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 have been phased out throughout most of the world. Its atmospheric presence has declined rapidly due to its relatively short lifetime of about 5 years.[13]

References

  1. ^ a b c d e f g NIOSH Pocket Guide to Chemical Hazards. "#0404". National Institute for Occupational Safety and Health (NIOSH).
  2. ^ "International Programme On Chemical Safety, Environmental Health Criteria 136". World Health Organization, Geneva. 1990. Retrieved 2017-12-25.
  3. ^ a b "Methyl chloroform". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  4. ^ Manfred Rossberg, Wilhelm Lendle, Gerhard Pfleiderer, Adolf Tögel, Eberhard-Ludwig Dreher, Ernst Langer, Heinz Rassaerts, Peter Kleinschmidt, Heinz Strack, Richard Cook, Uwe Beck, Karl-August Lipper, Theodore R. Torkelson, Eckhard Löser, Klaus K. Beutel, Trevor Mann "Chlorinated Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2.
  5. ^ Use of Ozone Depleting Substances in Laboratories. TemaNord 516/2003 Archived 2008-02-27 at the Wayback Machine
  6. ^ Toxicological Profile for 1,1,1-Trichloroethane Archived 2008-05-09 at the Wayback Machine, Agency for Toxic Substances and Disease Registry (ATSDR). 2006
  7. ^ King, Gregory S.; Smialek, John E.; Troutman, William G. (15 March 1985). "Sudden Death in Adolescents Resulting From the Inhalation of Typewriter Correction Fluid". JAMA: The Journal of the American Medical Association. 253 (11): 1604–1606. doi:10.1001/jama.253.11.1604. PMID 3974043. Archived from the original on 2013-02-23. Retrieved 2010-01-05. We describe four cases of sudden death in adolescents associated with recreational sniffing of typewriter correction fluid occurring during the period 1979 through mid-1984.
  8. ^ D'costa, DF; Gunasekera, NP (August 1990). "Fatal cerebral oedema following trichloroethane abuse". Journal of the Royal Society of Medicine. 83 (8): 533–534. doi:10.1177/014107689008300823. PMC 1292788. PMID 2231588.
  9. ^ Winekab, Charles L.; Wahba, Wagdy W.; Huston, Robert; Rozin, Leon (6 June 1997). "Fatal inhalation of 1,1,1-trichloroethane". Forensic Science International. 87 (2): 161–165. doi:10.1016/S0379-0738(97)00040-6. PMID 9237378. A 13-year-old male was found dead in the woods subsequent to 1,1,1-trichloroethane (TCE) inhalation.
  10. ^ Wodka, Richard M.; Jeong, Erwin W. S. (1 January 1989). "Cardiac Effects of Inhaled Typewriter Correction Fluid". Annals of Internal Medicine. 110 (1): 91–92. doi:10.7326/0003-4819-110-1-91_2. PMID 2908837. Archived from the original on 2013-04-14. Retrieved 2010-01-05.
  11. ^ Paddock, Richard C. (29 September 1989). "Gillette Agrees to Remove Toxics From Its Paper Correction Fluid". Los Angeles Times. Sacramento. Archived from the original on 15 July 2012. Retrieved 5 January 2010.
  12. ^ Estrin, Norman F.; Akerson, James M. (2000). "Proposition 65". Cosmetic regulation in a competitive environment. New York, New York: Marcel Dekker. p. 138. ISBN 0-8247-7516-3. Retrieved 5 January 2010. Gillette agreed to reformulate the product so that it would not pose a risk requiring a Proposition 65 warning
  13. ^ "Chapter 8, Table 8.A.1". AR5 Climate Change 2013: The Physical Science Basis. p. 733.

Further reading

  • 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". Environmental Forensics. 1 (2): 83–93. doi:10.1006/enfo.2000.0011. S2CID 97370778.