Cyanogen is the chemical compound with the formula2. 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. Certain
derivatives of cyanogen are also called "cyanogen" even though they contain only
one CN group. For example cyanogen bromide has the formula NCBr.
Cyanogen is the anhydride of oxamide: H2NC(O)C(O)NH2 → NCCN + 2 H2O
although oxamide is manufactured from cyanogen by hydrolysis:
NCCN + 2 H2O → H2NC(O)C(O)NH2 Preparation
Cyanogen is typically generated from cyanide compounds. One laboratory method
entails thermal decomposition of mercuric cyanide:
2 Hg(CN)2 →2 + Hg2(CN)2 Alternatively, one can combine solutions
of copper(II) salts sulfate) with cyanides, an unstable copper(II) cyanide
is formed which rapidly decomposes into copper(I) cyanide and cyanogen.
2 CuSO4 + 4 KCN →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.
Paracyanogen Paracyanogen 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 300-500 °C in the presence of trace
impurities. Paracyanogen can also be converted back to cyanogen by heating to
800 °C. 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 pi conjugation.
History 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
and γεννάω, 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
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. Cyanogen is a highly toxic compound, and
in 1910 a spectroscopic analysis of Halley's Comet found cyanogen in the
comet's tail. This 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.
Safety Like other inorganic 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 mg.
Inhalation of 900 ppm over a period of 10 min is considered lethal.
Cyanogen produces the second hottest known natural flame with a temperature
of over 4525 °C when it burns in oxygen. See also
Pseudohalogen References
External links National Pollutant Inventory - Cyanide
compounds fact sheet PhysOrg.com
CDC - NIOSH Pocket Guide to Chemical Hazards