Hydrogen Cyanide - Production and Synthesis

Production and Synthesis

Hydrogen cyanide forms in at least limited amounts from many combinations of hydrogen, carbon, and ammonia. Hydrogen cyanide is currently produced in great quantities by several processes, as well as being a recovered waste product from the manufacture of acrylonitrile. In the year 2000, 732,552 tons were produced in the US.

The most important process is the Andrussow oxidation invented by Leonid Andrussow at IG Farben in which methane and ammonia react in the presence of oxygen at about 1200 °C over a platinum catalyst:

2 CH₄ + 2 NH₃ + 3 O₂ → 2 HCN + 6 H₂O

The energy needed for the reaction is provided by the partial oxidation of methane and ammonia.

Of lesser importance is the Degussa process (BMA process) in which no oxygen is added and the energy must be transferred indirectly through the reactor wall:

CH₄ + NH₃ → HCN + 3H₂

This reaction is akin to steam reforming, the reaction of methane and water to give carbon monoxide and hydrogen.

In the Shawinigan Process, hydrocarbons, e.g. propane, are reacted with ammonia:

C₃H₈ + 3 NH₃ → 3 HCN + 7 H₂

When heated strongly, formamide decomposes to hydrogen cyanide and water vapor:

CH(O)NH₂ → HCN + H₂O

In the laboratory, small amounts of HCN are produced by the addition of acids to cyanide salts of alkali metals:

H+ + NaCN → HCN + Na+

This reaction is sometimes the basis of accidental poisonings because the acid converts a nonvolatile cyanide salt into the gaseous HCN.