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Tetracyanoethylene
Organic compound with formula C2(CN)4 From Wikipedia, the free encyclopedia
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Tetracyanoethylene (TCNE) is organic compound with the formula C2(CN)4. It is a colorless solid, although samples are often off-white. It is an important member of the cyanocarbons.
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Synthesis and reactions
TCNE is prepared by brominating malononitrile in the presence of potassium bromide to give the KBr-complex, and dehalogenating with copper.[1]
Oxidation of TCNE with hydrogen peroxide gives the corresponding epoxide, which has unusual properties.[2]
In the presence of base, TCNE reacts with malononitrile to give salts of pentacyanopropenide:[3]
- C2(CN)4 + CH2(CN)2 → [(NC)2C=C(CN)−C(CN)2]− + CN− + 2 H+
Redox chemistry
TCNE is 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 at −0.27 V vs ferrocene/ferrocenium:[4]
- C2(CN)4 + e− → [C2(CN)4]−
Because of its ability to accept an electron, TCNE has been used to prepare numerous charge-transfer salts[5] and magnetic molecular materials.
The central C=C distance in TCNE is 135 pm.[6] Upon reduction, this bond elongates to 141–145 pm, depending on the counterion.[7]
Safety
TCNE hydrolyzes in moist air to give hydrogen cyanide and should be handled accordingly.[1]
References
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