Tetracyanoethylene

Structural formula
General
Surname	Tetracyanoethylene
other names	TCNE Ethene tetracarbonitrile Percyanoethene
Molecular formula	C 6 N 4
Brief description	pure: colorless, commercially available: beige to yellowish mass
External identifiers / databases
CAS number 670-54-2 EC number 211-578-0 ECHA InfoCard 100.010.527 PubChem 12635 Wikidata Q413864
properties
Molar mass	128.09 g · mol -1
Physical state	firmly
density	1.35 g cm −3
Melting point	201-202 ° C
boiling point	223 ° C
solubility	hydrolyzed in water soluble in dichloromethane
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 300-312 + 332 P: 264-280-301 + 310
Toxicological data	5 mg kg −1 ( LD 50 ,  rat ,  oral )
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Tetracyanoethylene - also abbreviated TCNE ( T etra C ya N o E thylen) - is a hygroscopic organic compound from the group of nitriles and has a flat, even structure.

Presentation and reactions

Tetracyanoethylene is produced by bromination of malonic acid dinitrile in the presence of potassium bromide , a potassium bromide complex being obtained which is then dehalogenated with copper powder in the heat .

${\displaystyle \mathrm {4\ H_{2}C(CN)_{2}\ {\xrightarrow[{H_{2}O,\ \Delta }]{8\ Br_{2},\ KBr}}\ KBr+[Br_{2}C(CN)_{2}]_{4}} }$

${\displaystyle \mathrm {KBr+[Br_{2}C(CN)_{2}]_{4}\ {\xrightarrow[{-KBr,\ CuBr_{2}}]{Cu,\ \Delta }}\ (CN)_{2}C=C(CN)_{2}} }$

Oxidation of tetracyanoethylene with hydrogen peroxide leads to the corresponding epoxide , which has unusual chemical properties for an epoxide.

${\displaystyle \mathrm {(CN)_{2}C=C(CN)_{2}\ {\xrightarrow[{-4\ bis\ 10\ ^{\circ }C}]{H_{2}O_{2},\ CH_{3}CN}}\ (CN)_{2}C{\frac {\diagup O\diagdown }{}}C(CN)_{2}} }$

properties

Tetracyanoethylene sublimes at 130–140 ° C and 0.133 hPa.

TCNE is often used as an electron acceptor . Cyano groups have low energy * orbitals, and the presence of four such groups, whose systems are linked (conjugated) by the central C = C double bond, makes an excellent electron acceptor. TCNE reacts with iodides to form the radical anion . ${\displaystyle \pi }$ ${\displaystyle \pi }$

${\displaystyle \mathrm {(CN)_{2}C=C(CN)_{2}+I^{-}\ {\xrightarrow {}}\ [(CN)_{2}C=C(CN)_{2}]^{-}+{\dfrac {1}{2}}I_{2}} }$

use

Because of the planarity of the molecule and its ability to accept electrons easily, TCNE has also been used to make a number of organic superconductors - usually as one-electron oxidants for an organic electron donor. Such charge transfer complexes are sometimes called Bechgaard salts .

safety

TCNE hydrolyzes in water and in humid air to form very toxic hydrocyanic acid . Appropriate precautionary measures should be observed when handling the substance.

Individual evidence

1. ↑ ^{a b c d} R. A. Carboni: Tetracyanoethylene In: Organic Syntheses . 39, 1959, p. 64, doi : 10.15227 / orgsyn.039.0064 ; Coll. Vol. 4, 1963, p. 877 ( PDF ).
2. ↑ ^{a b c d e} data sheet tetracyanoethylene (PDF) from Merck , accessed on April 24, 2011.
3. ↑ ^{a b} W. J. Linn: Tetracyanoethylene Oxide In: Organic Syntheses . 49, 1969, p. 103, doi : 10.15227 / orgsyn.049.0103 ; Coll. Vol. 5, 1973, p. 1007 ( PDF ).
4. ↑ ^{a b} Datasheet Tetracyanoethylene from Sigma-Aldrich , accessed on November 3, 2016 ( PDF ).
5. ^ The Merck Index . An Encyclopaedia of Chemicals, Drugs and Biologicals , 14th Edition, 2006, ISBN 978-0-911910-00-1 , p. 1582.