Cyanogen is the chemical compound with the formula (CN)2. It is a colorless, toxic gas with a pungent odor. The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups – analogous to diatomic halogen molecules, such as Cl2, but far less oxidizing. The two cyano groups are bonded together at their carbon atoms: N≡C−C≡N, although other isomers have been detected. The name is also used for the CN radical, and hence is used for compounds such as cyanogen bromide (NCBr).
|Preferred IUPAC name|
|Systematic IUPAC name|
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||52.034 g/mol|
|Density||950 mg mL−1 (at −21 °C)|
|Melting point||−28 °C (−18 °F; 245 K)|
|Boiling point||−21.1 °C; −6.1 °F; 252.0 K|
|45 g/100 mL (at 20 °C)|
|Solubility||soluble in ethanol, ethyl ether|
|Vapor pressure||5.1 atm (21 °C)|
|1.9 μmol Pa−1 kg−1|
Refractive index (nD)
|1.327 (18 °C)|
|241.57 J K−1 mol−1|
Std enthalpy of
|309.07 kJ mol−1|
Std enthalpy of
|−1.0978–−1.0942 MJ mol−1|
|Main hazards||forms cyanide in the body; flammable|
|Safety data sheet||inchem.org|
|R-phrases (outdated)||R12, R23, R50/53|
|S-phrases (outdated)||(S1/2), S16, S33, S45, S63|
|NFPA 704 (fire diamond)|
|NIOSH (US health exposure limits):|
|TWA 10 ppm (20 mg/m3)|
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
- H2NC(O)C(O)NH2 → NCCN + 2 H2O
- NCCN + 2 H2O → H2NC(O)C(O)NH2
Cyanogen is typically generated from cyanide compounds. One laboratory method entails thermal decomposition of mercuric cyanide:
- 2 Hg(CN)2 → (CN)2 + Hg2(CN)2
Alternatively, one can combine solutions of copper(II) salts (such as copper(II) sulfate) with cyanides, an unstable copper(II) cyanide is formed which rapidly decomposes into copper(I) cyanide and cyanogen.
- 2 CuSO4 + 4 KCN → (CN)2 + 2 CuCN + 2 K2SO4
Industrially, it is created by the oxidation of hydrogen cyanide, usually using chlorine over an activated silicon dioxide catalyst or nitrogen dioxide over a copper salt. It is also formed when nitrogen and acetylene are reacted by an electrical spark or discharge.
Cyanogen is NCCN. There are less stable isomers in which the order of the atoms differs. Isocyanogen (or cyanoisocyanogen) is NCNC, diisocyanogen is CNNC, and diazodicarbon is CCNN.
Paracyanogen is a polymer of cyanogen. It can be best prepared by heating mercuric cyanide. It can also be prepared by heating silver cyanide, silver cyanate, cyanogen iodide or cyanuric iodide. It can also be prepared by the polymerization of cyanogen at 300 to 500 °C (572 to 932 °F) in the presence of trace impurities. Paracyanogen can also be converted back to cyanogen by heating to 800 °C (1,470 °F). Based on experimental evidence, the structure of this polymeric material is thought to be rather irregular, with most of the carbon atoms being of sp2 type and localized domains of π conjugation.
Cyanogen was first synthesized in 1815 by Joseph Louis Gay-Lussac, who determined its empirical formula and named it. Gay-Lussac coined the word "cyanogène" from the Greek words κυανός (kyanos, blue) and γεννάω (gennao, I create), because cyanide was first isolated by the Swedish chemist Carl Wilhelm Scheele from the pigment "Prussian blue". By the 1850s, cyanogen soap was used by photographers to remove silver stains from their hands. It attained importance with the growth of the fertilizer industry in the late 19th century and remains an important intermediate in the production of many fertilizers. It is also used as a stabilizer in the production of nitrocellulose.
In 1910 a spectroscopic analysis of Halley's Comet found cyanogen in the comet's tail, which led to public fear that the Earth would be poisoned as it passed through the tail. Because of the extremely diffuse nature of the tail, there was no effect when the planet passed through it.
Like other cyanides, cyanogen is very toxic, as it readily undergoes reduction to cyanide, which poisons the cytochrome c oxidase complex, thus interrupting the mitochondrial electron transfer chain. Cyanogen gas is an irritant to the eyes and respiratory system. Inhalation can lead to headache, dizziness, rapid pulse, nausea, vomiting, loss of consciousness, convulsions, and death, depending on exposure. Lethal dose through inhalation typically ranges from 100 to 150 milligrams (1.5 to 2.3 grains). Inhalation of 900 ppm over a period of 10 minutes is considered lethal.
Cyanogen produces the second-hottest-known natural flame (after carbon subnitride) with a temperature of over 4,525 °C (8,177 °F) when it burns in oxygen.
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- NIOSH Pocket Guide to Chemical Hazards. Department of Health and Human Services, Centers for Disease Control, National Institute for Occupational Safety & Health. September 2007. p. 82.
- The Merck Index (10th ed.). Rahway, NJ: Merck & Co. 1983. p. 385.
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- Bircumshaw, L. L.; F. M. Tayler; D. H. Whiffen (1954). "Paracyanogen: its formation and properties. Part I". J. Chem. Soc.: 931–935. doi:10.1039/JR9540000931.
- Maya, Leon (1993). "Paracyanogen Reexamined". Journal of Polymer Science Part A (Submitted manuscript). 31 (10): 2595–2600. Bibcode:1993JPoSA..31.2595M. doi:10.1002/pola.1993.080311020.
- Gay-Lussac, J. L. (1815). "Recherches sur l'acide prussique". Annales de Chimie. 95: 136–231. Gay-Lussac names cyanogen on p. 163.
- Crookes, William, ed. (1859). "Photographic News: A Weekly Record of the Process of the Photography": 11. Cite journal requires
- Comet's Poisonous Tail.
- Halley's Comet 100 years ago.
- Muir, G. D., ed. (1971). Hazards in the Chemical Laboratory. London: The Royal Institute of Chemistry.
- Ledgard, Jared (2006). A Laboratory History of Chemical Warfare Agents. Lulu.com. ISBN 978-0615136455. p. 82.
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- J. B. Conway; R. H. Wilson Jr.; A. V. Grosse (1953). "THE TEMPERATURE OF THE CYANOGEN-OXYGEN FLAME". Journal of the American Chemical Society. 75 (2): 499. doi:10.1021/ja01098a517.
|Wikimedia Commons has media related to cyanogen.|
|Wikisource has the text of the 1911 Encyclopædia Britannica article Cyanogen.|
- National Pollutant Inventory - Cyanide compounds fact sheet
- CDC - NIOSH Pocket Guide to Chemical Hazards