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
Names
Preferred IUPAC name Ethenetetracarbonitrile
Other names TCNE
Identifiers
CAS Number	670-54-2 Y
3D model (JSmol)	Interactive image
ChemSpider	12114 Y
ECHA InfoCard	100.010.527
PubChem CID	12635
UNII	C592309ECU Y
CompTox Dashboard (EPA)	DTXSID7049425
InChI InChI=1S/C6N4/c7-1-5(2-8)6(3-9)4-10 Y Key: NLDYACGHTUPAQU-UHFFFAOYSA-N Y InChI=1/C6N4/c7-1-5(2-8)6(3-9)4-10 Key: NLDYACGHTUPAQU-UHFFFAOYAN
SMILES N#CC(C#N)=C(C#N)C#N
Properties
Chemical formula	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). Y verify (what is YN ?) 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.