Tetracyanoethylene

Tetracyanoethylene (TCNE) is organic compound with the formula C2(CN)4. It is a colorless solid. It is an important member of the cyanocarbons.

Synthesis and reactions
TCNE is prepared by brominating malononitrile in the presence of potassium bromide to give the KBr-complex, and dehalogenating with copper.

Oxidation of TCNE with hydrogen peroxide gives the corresponding epoxide, which has unusual properties.

Redox chemistry
TCNE is often used as an electron acceptor.  Cyano groups have low energy π* orbitals, and the presence of four such groups, with their π systems (conjugated) to the central C=C double bond, gives rise to an electrophilic alkene.  TCNE is reduced by iodide to give the radical anion:
C2(CN)4  +  I−  →  [C2(CN)4]−  +   I2
Because of its planarity and its ability to accept electrons, TCNE has been used to prepare numerous organic superconductors, usually by serving as a single electron oxidant of an organic electron donor.  Such charge-transfer salts are sometimes called Bechgaard salts.

Safety
TCNE hydrolyzes in moist air to give hydrogen cyanide and should be handled accordingly.

References

Category:Alkene derivatives
Category:Nitriles