What is cyanide

Cyanide are salts and other compounds of hydrogen cyanide (Hydrogen cyanide, HCN). In organic chemistry, cyanides with the general formula R-C≡N are an outdated, but still common name for Nitriles. The name cyanide is derived from the Greek κυανός (blue) and comes from the extraction of iron hexacyanoferrate (Berlin blue), a not very stable pigment with a blue color.


The salt-like cyanides contain the cyanide anion [C≡N], the organic cyanides have the functional group -C≡N. Water-soluble cyanides are partially hydrolyzed in moist air and smell like hydrocyanic acid.

Easy connections

All alkali and alkaline earth salts of cyanides are highly toxic and easily soluble in water, such as potassium cyanide (cyanide). The toxicity of these salts is due to the release of hydrogen cyanide when it reacts with the hydrochloric acid of the stomach:

KCN + HCl → HCN + KCl

Potassium cyanide is an important component in electroplating.

Complex compounds (cyano compounds)

The cyanide anion is very reactive and often forms very stable compounds with other metals (apart from alkali and alkaline earth metals), e.g. with iron. In many cases a new anion is formed, which consists of a metal and a fixed number (often four or six) cyanide building blocks. The metal forms the center and is surrounded by the cyanide ions (e.g. [Fe (CN)6]4-). A type of connection has formed which is known as a complex. A salt can form with cations (e.g. K4[Fe (CN)6], Potassium hexacyanoferrate (II), the so-called yellow blood liquor salt). In many complex compounds, the cyanide is so tightly bound that it has lost its toxicity (reactivity). However, hydrogen cyanide can be released, for example, by adding hot, dilute sulfuric acid, so it must be handled with a certain degree of caution. Concentrated sulfuric acid does not release hydrogen cyanide as it oxidizes the hydrogen cyanide immediately. Analytically, however, no cyanide can be directly detected in aqueous solutions of the complexes.

Use of complex compounds in the food industry

In the food industry, the cyano complexes sodium ferrocyanide (E 535, sodium hexacyanoferrate (II)), potassium ferrocyanide (E 536, potassium hexacyanoferrate (II)) and calcium ferrocyanide (E 538, calcium hexacyanoferrate (II)) are used as food additives. The salts are approved in small quantities as artificial flow aids, release agents and stabilizers for table salt and table salt substitutes.

Poisonous effect

The mechanism of cyanide poisoning occurs through the inhibition of the enzyme cytochrome c oxidase in the respiratory chain. Antidotes: 4-dimethylaminophenol hydrochloride (4-DMAP), sodium thiosulfate, hydroxocobalamin (vitamin B12a) = cyanokit, amyl nitrite.


The qualitative chemical detection of cyanides is done with Fe3+-Ions in hydrochloric acid solution after reaction with ammonium polysulphide. This creates the deep red colored iron thiocyanate Fe (SCN)3. However, it must be noted that this detection does not work in the presence of Fe (II) because of the formation of Prussian blue, a complex of Fe (II) with hexacyanoferrate (III) as ligand.

Categories: Fabric Group | Cyanide | Pseudohalogen