1,1,1-Trichloroéthane

The organic compound 1,1,1-trichloroethane, also known as methyl chloroform and chlorothene, is a chloroalkane with the chemical formula CH3CCl3. It is an isomer of 1,1,2-trichloroethane. This colorless, sweet-smelling liquid was once produced industrially in large quantities for use as a solvent. It is regulated by the Montreal Protocol as an ozone-depleting substance and its use is being rapidly phased out. 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: CH_2=CHCl + HCl → CH_3CHCl_2 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: CH_3CHCl_2 + Cl_2 → CH_3CCl_3 + 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: CH_2=CCl_2 + HCl → CH_3CCl_3 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. 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.