[sahy-an-uh-juhn, -jen]
cyanogen, NCCN, colorless, flammable, extremely poisonous gas with a characteristic odor somewhat like that of hydrogen cyanide. It melts at -35°C;, boils at -21°C;, and is soluble in water, ethanol, or ether. It is chemically very active.

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 is far less oxidizing). The two cyano groups are bonded together at their carbon atoms: N≡C−C≡N, although other isomers have been detected. Certain derivatives of cyanogen are also called “cyanogen” even though they contain only one CN group. For example Cyanogen bromide is the compound with the structure NCBr.

Cyanogen is the anhydride of oxamide:

H2NC(O)C(O)NH2 → NCCN + 2 H2O


Cyanogen is typically generated from cyanide compounds. One laboratory method entails thermal decomposition of mercuric cyanide:
2 Hg(CN)2 → (CN)2 + 2 HgCN
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 made 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 (N2) and acetylene (C2H2) are made to react by an electrical spark or discharge.


Cyanogen has a long history and was probably first generated by Carl Scheele around 1782 in the course of his studies of hydrogen cyanide. The first confirmed synthesis was reported 1802, when it was used to make what we now know as cyanogen chloride. It attained importance with the growth of the fertilizer industry in the late nineteenth century and is still an important intermediate in the production of many fertilizers. It is also used as a stabilizer in the production of nitrocellulose.


Like other inorganic cyanides, cyanogen is very toxic, as it undergoes reduction to cyanide, which binds more strongly than oxygen to 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.

Cyanogen produces the second hottest known natural flame (after Carbon subnitride) with a temperature of over 4525°C (8180°F) when it burns in oxygen.

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