Cyanides are among the most acutely toxic of all industrial chemicals and are produced in large quantities and used in many different applications. However, they cause few serious accidents or deaths. This is partly because the word cyanide is synonymous with a highly poisonous substance and a certain amount of care in handling is thereby ensured. The cyanides and nitriles are a disparate group of substances characterized by the presence of a cyanide ([BOND]C[TRIPLE BOND]N) group in their molecular structure. The cyanide group consists of a carbon bonded to a nitrogen. In those cases where the cyanide group is readily available, toxicity is likely to have similarity to hydrogen cyanide (HCN). The chemical and physical characteristics of the compound will affect the potential availability of the cyanide group and therefore, the hazards associated with different chemical species.
For purposes of the toxicologist, cyanides and nitriles can be classified into groups based on their common properties. Group 1, inorganic cyanides, includes hydrogen cyanide, cyanogen, and simple salts such as sodium, potassium, calcium, and ammonium cyanide of hydrogen cyanide that dissociate readily to release CN−1 ions. Group 2 includes halogenated compounds such as cyanogen chloride or bromide. Group 3 comprises simple and complex salts such as cobalt cyanide trihydrate, cupric and cuprous cyanide, silver cyanide, and ferricyanide and ferrocyanide salts of hydrogen cyanide that do not dissociate readily to release CN−1 ions. Group 4, organic cyanides, includes cyanide glycosides produced by plants such as amygdalin and linamarin. Group 5, nitriles, have a general structure R-CNO, and include compounds such as acetonitrile (methyl cyanide), acrylonitrile, and isobutyronitrile.