6Na[Fe(CO)4H] + 9H2SO4 + 6MnO2 → 2[Fe3(CO)12] + 6MnSO4 + 3Na2SO4 + 12H2O
Sodium hydroxotetracarbonylferrate(0) react with sulfuric acid and manganese(IV) oxide to produce dodekacarbonyltriiron, manganese(II) sulfate, sodium sulfate and water. Sulfuric acid - 50% solution.