Hydrogen cyanide
|
General |
|
|---|---|
| Name | Hydrogen cyanide |
| Chemical formula | HCN |
| Appearance | Colourless liquid |
|
Physical |
|
| Formula weight | 27.0 amu |
| Melting point | 260 K (-13 °C) |
| Boiling point | 299 K (26 °C) |
| Density | 0.7 ×103 kg/m3 |
| Solubility | very soluble |
|
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 |
|
SI units were used where possible. Unless otherwise stated, standard conditions were used. | |
Hydrogen cyanide, also known as formonitrile, is the chemical compound with chemical formula HCN (with the carbon atom (C) being triple bonded to the nitrogen atom (N)).
Hydrogen cyanide is highly poisonous. It is colorless and has a faint, bitter, almond-like odor. Some people are unable to smell cyanide at all, due to a genetic trait. The melting point is at -14°C and the boiling point is at 26°C.
Hydrogen cyanide is weakly acidic and partly converts to the cyanide ion CN– in aqueous solution. Such a solution is called hydrocyanic acid or prussic acid. It is a colorless volatile liquid with a peach-blossom 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 plastics.
An HCN concentration of 300 parts per million of air will kill a human in 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 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
- hydrogen cyanide + ketone or aldehyde → cyanohydrin
History
During World War II, prussic acid (hydrocyanic acid) was used by the Nazis under its commercial name, Zyklon-B, as a means of executing Jewish and other concentration camp prisoners as part of the "Final Solution".