Tetraiodoethylene

Tetraiodoethylene (TIE), or diiodoform, is the periodinated analogue of ethylene with the chemical formula C2I4. It is a decomposition product of carbon tetraiodide and diiodoacetylene. It is an odourless yellow crystalline solid that is soluble in benzene and chloroform, and insoluble in water. It has been used as an antiseptic and a component in pesticide and fungicide formulations.

Tetraiodoethylene reacts with ethylamine to give ethylamine di-tetraiodoethylene, EtNH2.(C2I4)2, and ethylaminetetraiodoethylene. Tetraiodoethylene and iodine pentafluoride yield iodopentafluoroethane.

Tetraiodoethylene turns brown and emits a "characteristic" odour due to decomposition when exposed to light.

History
Tetraiodoethylene was discovered by Baeyer in 1885. It was proposed as an antiseptic under the name Diiodoform, in 1893 by M. L. Maquenne and Taine. It was an alternative to iodoform which has a strong and persistent odour that caused difficulties for physicians in private practices.

Synthesis
Tetraiodoethylene can be made by the iodination of calcium carbide:
 * CaC2 + 3I2 -> C2I4 + CaI2

Diiodoacetylene is a byproduct of the reaction which can later be iodinated to TIE.

The action of aqueous solution of potassium hydroxide and iodine on barium carbide in chloroform or benzene can also give TIE. Another synthesis involves mixing separate solutions of diiodoacetylene and iodine in carbon disulphide. Tetraiodoethylene would be left as a residue after carbon disulphide was evaporated.