Potassium hexacyanidoferrate (II)

Structural formula
General
Surname	Potassium hexacyanidoferrate (II)
other names	Potassium hexacyanoferrate (II) Potassium hexacyanidoferrate (4−) Potassium ferrocyanide Yellow blood liquor salt Yellow potash Ferrozine E  536
Molecular formula	K 4 [Fe (CN) 6 ]
Brief description	yellowish crystals
External identifiers / databases
CAS number 13943-58-3 (anhydrous) 14459-95-1 (trihydrate) EC number 237-722-2 ECHA InfoCard 100.034.279 PubChem 9605257 ChemSpider 20162028 Wikidata Q422017
properties
Molar mass	368.34 g mol −1 (anhydrous)
Physical state	firmly
density	1.85 g cm −3 (anhydrous)
Melting point	at approx. 70 ° C, the trihydrate releases water of crystallization
boiling point	Decomposes before boiling point is reached
solubility	easily in water (337 g l −1 at 20 ° C, anhydrous) easily in water (289 g l −1 at 20 ° C, trihydrate)
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: 412 P: 273
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Potassium hexacyanidoferrate (II) is a salt with the constitutional formula K ₄ [Fe (CN) ₆ ]. It is also known as potassium ferrocyanide , yellow blood liquor salt, or yellow potash . The name potassium hexacyanoferrate (II) is still often found according to the older IUPAC nomenclature . It is good in water and acetone , not soluble in ethanol and diethyl ether .

origin of the name

The name blood liquor salt comes from the way it is represented 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. Then, depending on how much air was allowed in during heating, a yellow (yellow blood liquor salt) or red salt ( red blood liquor salt ) crystallized out.

Manufacturing

Potassium hexacyanidoferrate (II) is produced from an iron (II) salt solution and potassium cyanide . It then contains water of crystallization and is present as K ₄ [Fe (CN) ₆ ] · 3H ₂ O (potassium hexacyanidoferrate (II) trihydrate). Above 60 ° C the water of crystallization is released again and turns into a colorless powder, at 100 ° C it is anhydrous.

Under normal conditions, however, the hexacyanidoferrate (II) ion is a stable complex and is therefore non-toxic.

${\displaystyle \mathrm {Fe^{2+}+6CN^{-}\rightleftharpoons [Fe(CN)_{6}]^{4-}} \quad \quad K_{A}=\mathrm {\frac {[[Fe(CN)_{6}]^{4-}]}{[Fe^{2+}]\cdot [CN^{-}]^{6}}} =10^{35}}$

use

Potassium hexacyanidoferrate (II)

In the analysis , the salt is used for the detection of iron (III) ions. In solution, when Fe ^III ions are added, soluble Prussian blue , K [Fe ^III Fe ^II (CN) ₆ ], is initially obtained ; an excess precipitates insoluble Prussian blue, Fe ^III [Fe ^III Fe ^II (CN) ₆ ] ₃ . These reactions are used to detect iron (III) ions:

${\displaystyle \mathrm {4\ Fe^{3+}+3\ [Fe^{+II}(CN)_{6}]^{4-}\longrightarrow {Fe^{+III}[Fe^{+III}Fe^{+II}(CN)_{6}]}_{3}} }$

Potassium hexacyanidoferrate (II) can be produced by oxidation with hydrogen peroxide or chlorine, potassium hexacyanidoferrate (III) .

In the food industry, potassium hexacyanidoferrate is used as a release agent and stabilizer . However, it may only be used in small quantities in food, as hydrogen cyanide can form when heated or when exposed to acids . It is approved in the EU as a food additive with the designation E 536 exclusively for use in table salt and table salt substitute as a trickle aid .

Potassium hexacyanidoferrate is also used for case hardening of otherwise poorly hardenable steels. Potassium hexacyanidoferrate becomes liquid when it comes into contact with the red-hot workpiece and releases its carbon to the workpiece. The surface is carburized and hardened.

Others

Potassium hexacyanidoferrate (II) occurs naturally as the very rare mineral cafehydrocyanite .

It was first made in 1752 by Pierre-Joseph Macquer from Berlin blue and caustic potash and, conversely, was often used to produce Berlin blue.

See also

• Potassium hexacyanidoferrate (III) (red blood liquor salt)
• Cyanide

Individual evidence

1. ↑ Erbslöh.com Ferrozin ( Memento of the original from February 18, 2017 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
2. ↑ Entry on E 536: Potassium ferrocyanide in the European database for food additives, accessed on June 27, 2020.
3. ↑ ^{a b c d e f g h} Entry on potassium hexacyanoferrate (II) in the GESTIS substance database of the IFA , accessed on May 17, 2017(JavaScript required) .
4. ↑ Seilnacht: Potassium hexacyanoferrate (II) trihydrate.

Web links

• Data sheet potassium hexacyanidoferrate (II) (PDF) from Carl Roth , accessed on 2014-03-31.