14459-95-1

pale yellow solid

Potassium hexacyanoferrate(II) trihydrate may be used in the following processes:
Preparation of Carrez I solution.
Milk sample preparation for gold nanoparticles (AuNPs) based colorimetric detection of melamine.
Preparation of ferrocyanide/ferricyanide reaction, a redox pair solution for electrochemical testing.

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.

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].

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°.