Hexachlorocyclopentadiene

Hexachlorocyclopentadiene (HCCPD), also known as C-56, Graphlox, and HRS 1655, is an organochlorine compound with the formula C5Cl6. It is a precursor to pesticides, flame retardants, and dyes. It is a colourless liquid, although commercial samples appear lemon-yellow liquid sometimes with a bluish vapour. Many of its derivatives proved to be highly controversial, as studies showed them to be persistent organic pollutants. An estimated 270,000 tons were produced until 1976, and smaller amounts continue to be produced today. Two prominent manufacturers are Velsicol Chemical Corporation in the US and by Jiangsu Anpon Electrochemicals Co. in China. Hexachlorocyclopentadiene is prepared by chlorination of cyclopentadiene to give 1,1,2,3,4,5-octachlorocyclopentane, which in a second step undergoes dehydrochlorination: The first procedure uses alkaline hypochlorite and after fractional distillation has a yield of about 75%, the other 25% consists of lower chlorinated cyclopentadienes. The second process uses thermal dechlorination, which occurs at 470-480 °C and gives a yield higher than 90%. Therefore, the first process is easier to perform, but the second gives a more pure product. C5H6 + 6 Cl2 → C5H2Cl8 + 4 HCl C5H2Cl8 → C5Cl6 + 2 HCl Besides manufacturers that produce the chemical for scientific synthesis and reference, there are two companies that produce HCCPD for industrial use: Velsicol Chemical LLC in the United States and Jiangsu Anpon Electrochemicals Co. in China. The first produces the chemical on a large scale to be used for producing rubber adherents, flame retardants and pesticides. Velsicol knows the dangers of handling HCCPD and therefore requires its buyers to go through a strict review and educational program on the storage, use and disposal of the chemical. The company also provides safety data sheets and a handling guide on its website, and delivers the chemical to purchasers all over the world. Of the Chinese company less is known.