Hexachloroethane

Hexachloroethane (perchloroethane) is an organochlorine compound with the chemical formula (CCl3)2. It is a white or colorless solid at room temperature with a camphor-like odor. It has been used by the military in smoke compositions, such as base-eject smoke munitions (smoke grenades).

Hexachloroethane was discovered along with carbon tetrachloride by Michael Faraday in 1820. Faraday obtained it by chlorinating ethylene.

Manufacture
Chlorination of tetrachloroethylene at 100–140 °C with the presence of ferric chloride is the most commonly used commercial production method, however several other methods exist. A high purity form can be produced in a small scale by reacting chlorine together with barium carbide. In September 1997, it was reported as no longer being produced in the United States for commercial distribution, but was produced as a by-product of industrial chlorination process.

Applications
Hexachloroethane has been used in the formulation of extreme pressure lubricants. It has also been used as a chain transfer agent in the emulsion polymerization of propylene–tetrafluoroethylene copolymer. Hexachloroethane has been used as an anthelmintic in veterinary medicine, a rubber accelerator, a component of fungicidal and insecticidal formulations as well as a moth repellant and a plasticizer for cellulose esters.

Hexachloroethane has been used in the manufacture of degassing pellets to remove hydrogen gas bubbles from molten aluminum in aluminum foundries. This use, as well as similar uses in magnesium, is being phased out in the European Union.

Use as smoke agent
Smoke grenades, called hexachloroethane smoke or HC smoke, utilize a mixture containing roughly equal parts of hexachloroethane and zinc oxide and approximately 6% granular aluminium. These smokes are toxic, which is attributed to the production of zinc chloride (ZnCl2). According to Steinritz et al., "Due to  its potential pulmonary toxicity," zinc chloride producing smoke grenades "have been discharged from the armory of most western countries (...)."

Use as a riot control agent
Most documented uses of HC smoke as a riot control agent have occurred in the United States; its purchase towards that end has occurred in Milwaukee, Denver and Portland.

Federal Protective Services (FPS) and forces from the Department of Homeland Security are believed to have used HC smoke grenades against protesters during various protests in 2020. At the time, journalists photographed numerous smoke canisters labeled "HC", and measured unusually high levels of zinc and chloride in the area. However, FPS communications director Rob Sperling has denied the use of HC smoke, arguing that, of the two organizations, "FPS doesn't have any items that contain HC."

Toxicity
Hexachloroethane is not particularly toxic when taken orally, but is considered to be quite toxic by skin adsorption. The primary effect is depression of the central nervous system. The concentration that is immediately dangerous to life or health is 300 ppm and the permissible exposure limit according to the Occupational Safety and Health Administration is 1 ppm (skin). It is reasonably anticipated to be a carcinogen.