Today, most trichloroethylene is produced from ethylene. First, ethylene is chlorinated over a ferric chloride catalyst to produce 1,2-dichloroethane:
:CH=CH + Cl → ClCHCHCl
When heated to around 400 °C with additional chlorine, 1,2-dichloroethane is converted to trichloroethylene:
:ClCHCHCl + 2 Cl → ClCH=CCl + 3 HCl
This reaction can be catalyzed by a variety of substances. The most commonly used catalyst is a mixture of potassium chloride and aluminum chloride. However, various forms of porous carbon can also be used. This reaction produces tetrachloroethylene as a byproduct and depending on the amount of chlorine fed to the reaction, tetrachloroethylene can even be the major product. Typically, trichloroethylene and tetrachloroethylene are collected together and then separated by distillation.
Prior to the early 1970s, however, most trichloroethylene was produced in a two-step process from acetylene. First, acetylene was treated with chlorine using a ferric chloride catalyst at 90 °C to produce 1,1,2,2-tetrachloroethane according to the chemical equation:
:HC≡CH + 2 Cl → ClCHCHCl
The 1,1,2,2-tetrachloroethane is then dehydrochlorinated to give trichloroethylene. This can be accomplished either with an aqueous solution of calcium hydroxide:
:2 ClCHCHCl + Ca(OH) → 2 ClCH=CCl + CaCl + 2 HO
or in the vapor phase by heating it to 300–500 °C on a barium chloride or calcium chloride catalyst:
:ClCHCHCl → ClCH=CCl + HCl
Common impurities in reagent and technical grade TCE are methyl chloroform, carbon tetrachloride, ethylene dichloride, tetrachloroethanes, benzene and phenol. However, these compounds are present in very small amounts and do not possess any risk.