Potassium ferrate

Potassium ferrate.
Names
	IUPAC name Potassium ferrate(VI)
	Other names Potassium ferrate; Dipotassium ferrate
Identifiers
CAS Number	39469-86-8;
3D model (JSmol)	Interactive image;
PubChem CID	53493006;
	InChI InChI=1S/Fe.2K.4O/q+6;2+1;4-2 Key: REKHNDAXGYXSBT-UHFFFAOYSA-N;
	SMILES [K+].[K+].[O-][Fe]([O-])(=O)=O;
Properties
Chemical formula	K2FeO4
Molar mass	198.0392 g/mol
Appearance	Dark purple solid
Density	2.829 g/cm3
Melting point	>198 °C (decomposes)
Solubility in water	soluble in 1M KOH
Solubility in other solvents[which?]	reacts with most solvents
Structure
Crystal structure	K2SO4 motif
Coordination geometry	Tetrahedral
Dipole moment	0 D
Hazards
	Occupational safety and health (OHS/OSH):
Main hazards	Oxidizer
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H272
Precautionary statements	P210, P220, P221, P280, P370+P378, P501
Flash point	non-combustible
Safety data sheet (SDS)	External SDS
Related compounds
Other anions	K2MnO4; K2CrO4; K2RuO4
Other cations	BaFeO4; Na2FeO4
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Potassium ferrate is the chemical compound with the formula K₂FeO₄. This purple salt is paramagnetic, and is a rare example of an iron(VI) compound. In most of its compounds, iron has the oxidation state +2 or +3 (Fe²⁺ or Fe³⁺). Reflecting its high oxidation state, FeO2−4 is a powerful oxidizing agent resembling chromate (CrO2−4) or manganate (MnO2−4).

Synthesis and structure

An aqueous solution of potassium ferrate(VI).

Georg Ernst Stahl (1660 – 1734) first discovered that the residue formed by igniting a mixture of potassium nitrate (saltpetre) and iron powder dissolved in water to give a purple solution. Edmond Frémy (1814 – 1894) later discovered that fusion of potassium hydroxide and iron(III) oxide in air produced a compound that was soluble in water:

8 KOH + 2 Fe₂O₃ + 3 O₂ → 4 K₂FeO₄ + 4 H₂O

The composition corresponded to that of potassium manganate or potassium chromate. In the laboratory, K₂FeO₄ is prepared by oxidizing an alkaline solution of an iron(III) salt with concentrated chlorine bleach:^[2]

3 ClO⁻ + 3 Fe(OH)₃(H₂O)₃ + 4 K⁺ + 4 OH⁻ → 3 Cl⁻ + 2 K₂FeO₄ + 11 H₂O

The salt is isostructural with K₂MnO₄, K₂SO₄, and K₂CrO₄. The solid consists of K⁺ and the tetrahedral FeO2−4 anion, with Fe-O distances of 1.66 Å.^[3] The poorly soluble barium salt, BaFeO₄, is also known.

Properties and applications

The main difficulty with the use of K₂FeO₄ is that it is often too reactive, as indicated by the fact that it decomposes in contact with water, especially in acidic water:^[4]

4 K₂FeO₄ + 4 H₂O → 3 O₂ + 2 Fe₂O₃ + 8 KOH

At high pH, aqueous solutions are stable. The deep purple solutions are similar in appearance to potassium permanganate (KMnO₄). It is a stronger oxidizing agent than the latter. As a dry solid, K₂FeO₄ is stable.

Because the side products of its redox reactions are rust-like iron oxides, K₂FeO₄ has been described as an "environmentally friendly" oxidant. It has been employed in waste-water treatment as an oxidant for organic contaminants and as a biocide. Conveniently, the resulting reaction product is iron(III) oxyhydroxide, an excellent flocculant. In organic synthesis, K₂FeO₄ oxidizes primary alcohols.^[5] In contrast, related oxidants such as chromates are considered environmentally hazardous.^[6]

K₂FeO₄ has also attracted attention as a potential cathode material in a "super iron battery."

Stabilised forms of potassium ferrate have been proposed for the removal of transuranic species, both dissolved and suspended, from aqueous solutions. Tonnage quantities were proposed to help remediate the effects of the Chernobyl disaster in Belarus. This new technique was successfully applied for the removal of a broad range of heavy metals.^{[citation needed]}

Work on the use of potassium ferrate precipitation of transuranics and heavy metals was carried out in the Laboratories of IC Technologies Inc. in partnership with ADC Laboratories, in 1987 though 1992. The removal of the transuranic species were done on samples from various Dept. of Energy nuclear sites in the USA.^{[citation needed]}

It has been proposed as a bleeding stopper for fresh wounds.^[7]^[8]

References

^ ^a ^b ^c ^d "Potassium Ferrate". American Elements. Retrieved June 13, 2019.
^ Schreyer, J. M.; Thompson, G. W.; Ockerman, L. T. (1953). "Potassium Ferrate(VI)" (PDF). In Bailar, John C. (ed.). Inorganic Syntheses. Vol. IV. pp. 164–168.
^ Hoppe, M. L.; Schlemper, E. O.; Murmann, R. K. "Structure of Dipotassium Ferrate(VI)" Acta Crystallographica 1982, volume B38, pp. 2237-2239. doi:10.1107/S0567740882008395.
^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
^ Green, J. R. "Potassium Ferrate" Encyclopedia of Reagents for Organic Synthesis 2001, John Wiley. doi:10.1002/047084289X.rp212.
^ Sharma, Virender K. (2002). "Potassium ferrate(VI): an environmentally friendly oxidant". Advances in Environmental Research. 6 (2): 143–156. doi:10.1016/s1093-0191(01)00119-8. ISSN 1093-0191.
^ "How WoundSeal Works". WoundSeal. 2016.
^ WO application 2014153566, John Hen; Talmadge Kelly Keene & Mark Travi, "Hemostatic device and method", published 2014-09-25, assigned to Biolife, LLC