Potassium ferrocyanide

  • Potassium hexacyanoferrate ( II)
  • Potassium ferrocyanide
  • Yellow prussiate of potash
  • Yellow potash
  • Ferrozin
  • E 536

Yellowish crystals

Fixed

1.85 g · cm -3 ( anhydrous)

At about 70 ° C of the trihydrate releases water of crystallization

Decomposition before reaching the boiling point

Readily soluble in water: 337 g · l-1 (20 ° C)

Template: Infobox chemical / molecular formula search available

Kaliumhexacyanidoferrat ( II) is a salt having the structural formula K 4 [Fe (CN ) 6]. It is also known as potassium ferrocyanide, yellow prussiate of potash or yellow potash. It still often finds the designation of potassium hexacyanoferrate (II ) according to the IUPAC nomenclature older. It is well water and acetone, insoluble in ethanol and ether. In contrast to Kaliumhexacyanidoferrat (III) the aqueous solution of Kaliumhexacyanidoferrat (II) does not show any fluorescence.

Origin of the name

The name of prussiate of potash comes from the presentation by alchemists. They heated blood with bone, horn and other proteinaceous substances in the presence of iron filings and potash. The residue was leached with water. It then crystallized, depending on how much air is allowed when heated, a yellow ( yellow prussiate of potash ) or red salt ( red prussiate of potash ) from.

Production

Is produced Kaliumhexacyanidoferrat (II ) from an iron (II ) salt solution and potassium cyanide. It then contains water of crystallisation and is as K4 [Fe (CN ) 6] · 3H2O ( Kaliumhexacyanidoferrat (II) trihydrate) available. Above 60 ° C there is the crystal water again and goes into a colorless powder over, at 100 ° C it is anhydrous.

Under normal conditions, however, the Hexacyanidoferrat (II) ion is a stable complex, it is therefore intended to be non-toxic.

Use

In the analysis for detecting the salt of iron ( III) ions is used. In solution, obtained upon addition of FeIII ions initially soluble Prussian blue, K [ FeIIIFeII (CN ) 6], due to an excess precipitates insoluble Prussian blue, FeIII [ FeIIIFeII (CN) 6 ] 3 These reactions are used for the detection of iron (III ) ions:

From Kaliumhexacyanidoferrat (II ) can be prepared by oxidation with hydrogen peroxide Kaliumhexacyanidoferrat (III).

In the food industry is used as Kaliumhexacyanidoferrat release agent and stabilizer. However, it may only be used in small amounts in foods, as can form hydrogen cyanide when heated or when exposed to acids. It's 536 approved exclusively for use in salt and salt substitutes as a flow in the EU as a food additive called E.

Kaliumhexacyanidoferrat is also used for case hardening of otherwise poorly hardenable steels. Kaliumhexacyanidoferrat becomes liquid upon contact with the red hot workpiece and returns its carbon from the workpiece. The surface is carburized and thus curable.

Others

In nature Kaliumhexacyanidoferrat (II ) occurs as the rare mineral Kafehydrocyanit.

CAS registry number Dangerous Substances Directive (67/548/EEC) Stabilizer (chemistry)
6775
de