K4[Fe(CN)6] + 3HNO3 → NO2 + HCN + K2[Fe(H2O)(CN)5] + 2KNO3
Potassium hexacyanoferrate(II) react with nitric acid to produce nitric oxide, hydrogen cyanide, pentacyanoaquaferrate(III) potassium and potassium nitrate. Nitric acid - concentrated solution. The reaction takes place in a boiling solution.