Perthiocyanogen, HC₃N₃S₃

Perthiocyanogen, HC₃N₃S₃, is a yellow, amorphous powder, insoluble in water, alcohol, ether and concentrated sulphuric acid; it can be obtained by the action of chlorine or boiling dilute nitric acid on an aqueous solution of potassium thiocyanate. It is decomposed by heat according to the equation:

3HC₃N₃S₃ = 3CS₂ + 3S + H₃C₆N₉ (Mellone.)

With concentrated potassium hydroxide solution thiocyanic acid is obtained.