Tetracyanoethylene

Tetracyanoethylene (TCNE) is an organic compound consisting of ethylene with the four hydrogen atom replaced with cyano groups. It is an important member of the cyanocarbons.

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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 linked (conjugated) to the central C=C double bond, gives rise to an excellent acceptor. Thus, treatment of TCNE with iodide salts gives the radical anion:

C₂(CN)₄ + I^- → [C₂(CN)₄]^- + 0.5 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 salt.

Synthesis and reactions

TCNE is prepared from malononitrile^[1]

Oxidation of TCNE with hydrogen peroxide gives the corresponding epoxide, which has unusual properties.^[2]

Safety

TCNE is a source of HCN and should be handled accordingly.

References

1. ^ ^{a b} Carboni, R. A. "Tetracyanoethylene" Organic Syntheses, Collected Volume 4, p.877 (1963)
2. ^ Linn, W. J. "Tetracyanoethylene Oxide" Organic Syntheses, Collected Volume 5, p.1007 (1973).