Tetrachloroethylene oxide

Tetrachloroethylene oxide, perchloroethylene oxide (PCEO) or tetrachlorooxirane, is the perchlorinated analogue of ethylene oxide and a proposed metabolite of tetrachloroethylene. It is a halogenated epoxide with the formula C2Cl4O. Tetrachloroethylene oxide is fairly stable but rearranges to trichloroacetyl chloride at higher temperatures.

It is metabolised to trichloroacetyl chloride which is hydrolysed to trichloroacetic acid.

Production
Tetrachloroethylene oxide was first synthesised by the English chemist Frederick William Kirkbride in 1940, by exposing a mixture of oxygen and chlorine in tetrachloroethylene to UV light. Tetrachloroethylene oxide can be obtained by the direct oxidation of tetrachloroethylene under UV light.

Reactions
Unlike most epoxides, PCEO does not polymerise.

PCEO reacts with methanol, with mercury(II) chloride as the catalyst, giving methyl trichloroacetate and hydrogen chloride:
 * C2Cl4O + CH3OH -> CH3O(CO)CCl3 + HCl

PCEO reacts with methanolic potassium hydroxide to give potassium oxalate. It is slowly decomposed by dilute acid or base solutions, giving off carbon monoxide, carbon dioxide and hydrogen chloride which was possibly from the further decomposition of the intermediate oxalyl chloride.