Cyanocarbon
Cyanocarbons are a group of chemical compounds that contain several cyanide functional groups. Such substances generally are classified as organic compounds, since they are formally derived from hydrocarbons by replacing one or more hydrogen atoms with a cyanide group.[1] The parent member is C(CN)4 (tetracyanomethane, also known as carbon tetracyanide). Organic chemists often refer to cyanides as nitriles.
In general, cyanide is an electronegative substituent. Thus, for example, cyanide-substituted carboxylic acids tend to be stronger than the parents. The cyanide group can also stabilizes anions by delocalizing negative charge as revealed by resonance structures.
Definition and examples
Cyanocarbons are organic compounds bearing enough cyano functional groups to significantly alter their chemical properties.[1]
Important cyanocarbons:
- Tetracyanoethylene, which readily reduces to a stable anion, unlike most ethene derivatives
- Pentacyanocyclopentadiene, which forms a stable anion by ionization of the C-H bond.
- Tetracyanoethylene oxide, an electrophilic epoxide that undergoes ready scission of its C-C bond.
- Tetracyanoquinodimethane, C6H4-1,4-(C(CN)2)2, a powerful electron acceptor.
(NC)3CH. also known as cyanoform, is a hypothetical molecule that has thus far not been isolated as free acid. Dilute solutions of this acid have been prepared, however and its salts are well known. Cyanoform ranks as one of the most acidic of the carbon acids with an estimated pKa of -5.1 in water and measured pKa 5.1 in acetonitrile.[2]
Tricyanomethane
Tricyanomethane (NC)3CH is a hypothetical molecule that has thus far resisted all attempts at synthesis . It would rank as one of the most acidic of the carbon acids with an estimated Pka of -5. The reaction of sulfuric acid with sodium tricyanomethanide in water (a reaction first tried by H. Schmidtmann in 1896 with inconclusive results [3]) is reported to result in the formation of the hydrate (NC)3C-H3O+ or the formation of (Z)-3- amino-2-cyano-3-hydroxyacrylamide (H2N)(OH)C=C(CN)CONH2 depending on the precise conditions.[4] The reaction of HCl gas with sodium tricyanomethanide dissolved in THF is reported to yield 1-chloro-1-amino-2,2-dicyanoethylene ((NC)2C=C(NH2)Cl) and its tautomer.
References
- ↑ 1.0 1.1 Webster, Owen W. "Cyanocarbons: a classic example of discovery-driven research" Journal of Polymer Science, Part A: Polymer Chemistry 2001, volume, 40, pp. 210-221. doi:10.1002/pola.10087
- ↑ Raamat, E.; Kaupmees, K.; Ovsjannikov, G.; Trummal, A.; Kütt, A.; Saame, J.; Koppel, I.; Kaljurand, I.; Lipping, L.; Rodima, T.; Pihl, V.; Koppel, I. A.; Leito, I. "Acidities of strong neutral Brønsted acids in different media." J. Phys. Org. Chem. 2013, 26, 162-170. doi:10.1002/poc.2946
- ↑ Schmidtmann, H. (1896). "Ueber einige Derivate des Malonitrils". Berichte der deutschen chemischen Gesellschaft 29 (2): 1168. doi:10.1002/cber.18960290204.
- ↑ Šišak, Dubravka; McCusker, Lynne B.; Buckl, Andrea; Wuitschik, Georg; Wu, Yi-Lin; Schweizer, W. Bernd; Dunitz, Jack D. (2010). "The Search for Tricyanomethane (Cyanoform)". Chemistry - A European Journal 16 (24): n/a. doi:10.1002/chem.201000559. PMID 20480465.