Iso-cyanic Acids and Salts

Iso-cyanic Acid.—If hydrocyanic acid is analogous to hydrochloric acid we should expect an oxygen acid to be obtained from it analogous to hypochlorous acid. 

An acid of this composition is known but it has been shown to have another constitution, viz., H—N=C = O, and is iso-cyanic acid though it is often called cyanic acid. It is an odorous, unstable liquid. We have already discussed (p. 73) the alkyl derivatives of these two acids. 

Thus while isomeric derivatives are known corresponding to two isomeric acids only one acid is known and this one has the structure of the iso-cyanic acid. When we study the salts obtained from this iso-cyanic acid we find, unlike the alkyl derivatives, that they are known in only one form but strangely enough in the form of the cyanic acid, e.g, K—O—C=N, potassium cyanate. 

Potassium Cyanate.—When iso-cyanic acid is neutralized with potassium hydroxide, potassium cyanate is obtained. Potassium cyanate is also obtained when potassitun cyanide is oxidized by means of lead oxide or potassium bichromate. 

Ammonium Cyanate.— The corresponding ammonium salt, viz., ammonium cyanate, NH4OCN, may be easily prepared from the potassium cyanate by treating a solution of the latter with the calculated amount of ammonium sulphate. This compound is of especial interest because on evaporation of the water solution to dryness a rearrangement takes place and urea is formed (p. 429). Ammonium cyanate is also formed when iso-cyanic acid is neutralized with ammonia. 

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