Hydrogen cyanide

Properties

General
Chemical name	Hydrogen cyanide
Chemical formula	HCN (H-C≡N:)
Appearance	Colorless liquid and gas
CAS number	74-90-8
Physical
Molecular mass	27.03 g/mol
Melting point	-13 °C
Boiling point	26 °C
Density	0.687 g/ml (liquid)
Solubility	Miscible with water
Thermochemistry
ΔfH0gas	135.14 kJ/mol
ΔfH0liquid	109 kJ/mol
ΔfH0solid	100 kJ/mol
S0gas, 1 bar	201.82 J/mol·K
S0liquid, 1 bar	113.01 J/mol·K
S0solid	? J/mol·K
Safety
Ingestion	Extremely toxic. Early symptoms include nausea, vomiting and abdominal pain.
Inhalation	Extremely dangerous. Early symptoms include slow breathing rate, irritation.
Skin	Poisoning is thought to be possible through the skin.
Eyes	Dilated pupils are a symptom of poisoning.
More info	Hazardous Chemical Database
Except where noted, all data was produced under conditions of standard temperature and pressure.

Hydrogen cyanide is a chemical compound with chemical formula H-C≡N. A solution of hydrogen cyanide in water is called hydrocyanic acid or prussic acid. Pure hydrogen cyanide is a colorless, very poisonous, and highly volatile liquid that boils sligthly above room temperature at 26 °C, thereby generating hydrogen cyanide gas. Hydrogen cyanide has a faint, bitter, almond-like odor that some people are unable to smell due to a genetic trait. Hydrogen cyanide is weakly acidic and partly converts to the cyanide ion CN^– in aqueous solution, resulting in a colorless volatile liquid with the typical hydrogen cyanide odor. The salts of hydrogen cyanide are known as cyanides.

Hydrogen cyanide is produced in large quantities all over the world by the chemical industry where it is used in tempering steel, dyeing, explosives, engraving, the production of acrylic resin plastic, and other organic chemical products. It can be produced by reacting a cyanide salt with a strong acid, or directly from ammonia and carbon monoxide.

Fruits that have a pit, such as cherries or apricots, often contain small quantities of hydrogen cyanide in the pit. Bitter almonds, from which almond oil and flavoring is made, also contain hydrogen cyanide. Hydrogen cyanide is contained in the exhaust of vehicles, in tobacco smoke, and in the smoke of burning nitrogen-containing plastics.

An HCN concentration of 300 parts per million of air will kill a human within a few minutes. The toxicity is caused by the cyanide ion. The mechanism of this toxicity, and the uses of the poison, are described on the cyanide page. Hydrogen cyanide (under the brand name Zyklon B) was perhaps most infamously employed by the Nazi regime in Germany as a method of mass-execution.

Hydrogen cyanide forms a foul tasting compound when it combines with tobacco smoke. For this reason, some chemists choose to have a lit cigarette in their mouth while they are working with it, as they receive an early warning against possible cyanide poisoning.

Hydrogen cyanide gas in air is explosive at concentrations over 56,000 ppm.

Reactions

1. hydrogen cyanide + ketone or aldehyde → cyanohydrin