Tetracyanoethylene

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.

Tetracyanoethylene
tetracyanoethylene
tetracyanoethylene
Names
Preferred IUPAC name
Ethenetetracarbonitrile
Other names
TCNE
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.010.527
UNII
  • InChI=1S/C6N4/c7-1-5(2-8)6(3-9)4-10 checkY
    Key: NLDYACGHTUPAQU-UHFFFAOYSA-N checkY
  • InChI=1/C6N4/c7-1-5(2-8)6(3-9)4-10
    Key: NLDYACGHTUPAQU-UHFFFAOYAN
  • N#CC(C#N)=C(C#N)C#N
Properties
C2(CN)4
Molar mass 128.094 g·mol−1
Density 1.35 g/cm3
Melting point 199 °C (390 °F; 472 K)
Boiling point 130 to 140 °C (266 to 284 °F; 403 to 413 K) 0.1 mmHg (sublimes)[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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]

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
  1. Carboni, R. A. (1959). "Tetracyanoethylene". Organic Syntheses. 39: 64. doi:10.15227/orgsyn.039.0064.
  2. Linn, W. J. (1969). "Tetracyanoethylene Oxide". Organic Syntheses. 49: 103. doi:10.15227/orgsyn.049.0103.
  3. Middleton, W. J.; Wiley, D. W. (1961). "Tetramethylammonium 1,1,2,3,3-Pentacyanopropenide". Org. Synth. 41: 99. doi:10.15227/orgsyn.041.0099.
  4. Connelly, N. G.; Geiger, W. E. (1996). "Chemical Redox Agents for Organometallic Chemistry". Chemical Reviews. 96 (2): 877–910. doi:10.1021/cr940053x. PMID 11848774.
  5. Chittipeddi, Sailesh; Cromack, K. R.; Miller, Joel S.; Epstein, A. J. (1987-06-22). "Ferromagnetism in Molecular Decamethylferrocenium Tetracyanoethenide (DMeFc TCNE)". Physical Review Letters. 58 (25): 2695–2698. Bibcode:1987PhRvL..58.2695C. doi:10.1103/physrevlett.58.2695. ISSN 0031-9007. PMID 10034821.
  6. Becker, P.; Coppens, P.; Ross, F. K. (1973). "Valence electron distribution in cubic tetracyanoethylene by the combined use of x-ray and neutron diffraction". Journal of the American Chemical Society. 95 (23): 7604–7609. doi:10.1021/ja00804a010.
  7. Bock, H.; Ruppert, K. (1992). "Structures of charge-perturbed or sterically overcrowded molecules. 16. The cesium tetracyanoethylenide radical salt". Inorganic Chemistry. 31 (24): 5094–5099. doi:10.1021/ic00050a032.
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