Potassium ferrocyanide trihyrate

Preparation

Potassium hexacyanoferrate(II), K4Fe(CN)6·3H20, is obtained commercially from gasworks spent oxide (which contains Prussian blue) by treatment with lime and subsequent treatment of the solution with a soluble potassium salt ; the less soluble potassium hexacyanoferrate(II) can be crystallized from this mixture. In the laboratory it is readily prepared by treating aqueous iron(II) sulphate with an excess of potassium cyanide ; the initially precipitated iron(II) cyanide dissolves upon boiling in the excess of potassium cyanide solution and the ferrocyanide crystallizes on cooling.

Purification Methods

The anhydrous salt is prepared by drying at 110o over P2O5 in a vacuum desiccator. To obtain the trihydrate, it is necessary to equilibrate the salt in a desiccator over a saturated aqueous solution of sucrose and NaCl. It can also be precipitated from a saturated solution at 0o by adding an equal volume of cold 95% EtOH, setting aside for several hours, then centrifuge and wash with cold 95% EtOH. It is finally sucked air dry with water-pump vacuum. The anhydrous salt is obtained by drying the hydrate in a platinum boat at 90o in a slow stream of N2 [Loftfield & Swift J Am Chem Soc 60 3083 1938].

Structure and conformation

The trihydrate is diamagnetic and dimorphic existing in monoclinic (pseudotetragonal) and tetragonal forms. Its infrared spectrum in solution shows a single ν(C≡ N) at 2044 cm-1, but in the solid state a large number of bands are observed160; ν(Fe-C) occurs at 416cm-1. White, anhydrous K4Fe(CN)6 is obtained by dehydrating the trihydrate at 100°.

General Description

Potassium hexacyanoferrate(II) trihydrate, commonly known as potassium ferrocyanide, is a commonly used anticaking agent. Its cytotoxic and genotoxic effect has been evaluated. The growth of chemical garden in aqueous potassium hexacyanoferrate solution droplets on a superhydrophobic surface has been reported. The inhibition efficiency of potassium ferrocyanide in phosphoric acid solution against the corrosion of mild steel has been investigated.