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Interstellar Medium
The cyanide radical CNꞏ has been identified in interstellar space. The cyanide radical (called
cyanogen) is used to measure the temperature of interstellar gas clouds.

Pyrolysis and Combustion Product
Hydrogen cyanide is produced by the combustion or pyrolysis of certain materials under oxygen-
deficient conditions. For example, it can be detected in the exhaust of internal combustion engines
and tobacco smoke. Certain plastics, especially those derived from acrylonitrile, release hydrogen
cyanide when heated or burnt.

Coordination Chemistry
The cyanide anion is a ligand for many transition metals. The high affinities of metals for this anion
can be attributed to its negative charge, compactness, and ability to engage in π-bonding.

Well-known complexes include:
 hexacyanides [M(CN) 6 ]3− (M = Ti, V, Cr, Mn, Fe, Co), which are octahedral in shape;
 the tetracyanides, [M(CN) 4 ]2− (M = Ni, Pd, Pt), which are square planar in their geometry;
 the dicyanides [M(CN) 2 ]− (M = Cu, Ag, Au), which are linear in geometry.

The dye Prussian blue was first accidentally made around 1706, by heating substances containing
iron and carbon and nitrogen. Prussian blue consists of an iron-containing compound called
"ferrocyanide" ({Fe(CN) 6 ]4-) meaning "blue substance with iron", from Latin ferrum = "iron" and
Greek kyanos = "(dark) blue”. Prussian blue is the deep-blue pigment used in the making of
blueprints.

The enzymes called hydrogenases contain cyanide ligands attached to iron in their active sites.
The biosynthesis of cyanide in the [NiFe]-hydrogenases proceeds from carbamoylphosphate,
which converts to cysteinyl thiocyanate, the CN− donor.

Organic Derivatives
Because of the cyanide anion's high nucleophilicity, cyano groups are readily introduced into
organic molecules by displacement of a halide group (e.g., the chloride on methyl chloride). In
general, organic cyanides are called nitriles. Thus, CH 3 CN can be called methyl cyanide but more
commonly is referred to as acetonitrile. In organic synthesis, cyanide is a C-1 synthon; i.e., it can
be used to lengthen a carbon chain by one, while retaining the ability to be functionalized.
RX + CN− → RCN + X− (nucleophilic substitution) followed by

1. RCN + 2 H 2 O → RCOOH + NH 3 (hydrolysis under reflux with mineral acid catalyst), or


2. 2 RCN + LiAlH 4 + (second step) 4 H 2 O → 2 RCH 2 NH 2 + LiAl(OH) 4 (under reflux in dry ether,
   followed by addition of H 2 O)

Manufacture
The principal process used to manufacture cyanides is the Andrussow process in which gaseous
hydrogen cyanide is produced from methane and ammonia in the presence of oxygen and a
platinum catalyst.

2 CH 4 + 2 NH 3 + 3 O 2 → 2 HCN + 6 H 2 O

Gaseous hydrogen cyanide may be dissolved in aqueous sodium hydroxide solution to produce
sodium cyanide.