hydrocyanic acid

References

hydrocyanic acid

chemical compound

Also known as: prussic acid

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

June 29, 2026

Quick Summary

Hydrocyanic acid, also known as hydrogen cyanide (HCN), is a highly volatile, colorless, and extremely poisonous liquid. It is also a poisonous weak acid when dissolved in water. Hydrogen cyanide has a characteristic odor of bitter almonds.123

This compound is highly toxic because it inhibits cellular oxidative processes. Exposure to even small amounts can be fatal, acting rapidly to cause symptoms like dizziness, nausea, and loss of consciousness.41

Hydrogen cyanide and its compounds have various industrial applications, including fumigation, case hardening of iron and steel, electroplating, and ore concentration. It is also a key component in the production of acrylonitrile, which is used to make acrylic fibers, synthetic rubber, and plastics. In nature, substances that can yield cyanide are found in certain plant seeds.514

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

5 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

cereal processing
Cassava
Their prussic acid level must be reduced to safe limits by boiling; the duration of boiling depends on the variety of the leaves. Cassava leaves are a popular vegetable in Africa, and the tuber also is used in meal for animal feed.
Read More
Their prussic acid level must be reduced to safe limits by boiling; the duration of boiling depends on the variety of the leaves. Cassava leaves are a popular vegetable in Africa, and the tuber also is used in meal for animal feed.
Read More

hydrogen cyanide
…cyanide in water is called hydrocyanic acid, or prussic acid. It was discovered in 1782 by a Swedish chemist, Carl Wilhelm Scheele, who prepared it from the pigment Prussian blue. Hydrogen cyanide and its compounds are used for many chemical processes, including fumigation, the case hardening of iron and steel,…
Read More
…cyanide in water is called hydrocyanic acid, or prussic acid. It was discovered in 1782 by a Swedish chemist, Carl Wilhelm Scheele, who prepared it from the pigment Prussian blue. Hydrogen cyanide and its compounds are used for many chemical processes, including fumigation, the case hardening of iron and steel,…
Read More

molecular cloud
Composition
…and its isomer HCN (hydrocyanic acid); in ordinary terrestrial conditions there is plenty of energy to allow the nitrogen and carbon atoms in HNC to exchange positions and produce HCN, by far the preferred species for equilibrium chemistry. In the cold clouds, however, not enough energy exists for the…
Read More
…and its isomer HCN (hydrocyanic acid); in ordinary terrestrial conditions there is plenty of energy to allow the nitrogen and carbon atoms in HNC to exchange positions and produce HCN, by far the preferred species for equilibrium chemistry. In the cold clouds, however, not enough energy exists for the…
Read More

chemical compound
Acids
…dissolved in water are called hydrocyanic and hydrosulfuric acids, respectively.
Read More
…dissolved in water are called hydrocyanic and hydrosulfuric acids, respectively.
Read More