Potassium ferrate
Encyclopedia
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, FeO42−
is a powerful oxidizing agent
.
K2FeO4 has attracted interest for applications in "green chemistry
" because the by-products of its use, iron oxides, are environmentally innocuous. In contrast, some related oxidants such as chromate
are considered environmentally hazardous. However, 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.
(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. The composition corresponded to that of potassium manganate
. In the laboratory, K2FeO4 is prepared by oxidizing an alkaline solution of an iron(III) salt with concentrated chlorine bleach.
The salt is isostructural with K2MnO4
, K2SO4
, and K2CrO4
. The solid consists of K+ and the tetrahedral FeO42− anion, with Fe-O distances of 1.66 Å. The poorly soluble barium salt, BaFeO4
, is also known.
, aqueous solutions are stable. The deep purple solutions are similar in appearance to potassium permanganate
. It is stronger oxidizing agent than the latter.
Because the side products of its redox reactions are rust-like iron oxides, K2FeO4 has been described as a "green 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 alcohol
s.
K2FeO4 has also attracted attention as a potential cathode
material in a "super iron battery
."
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
K2FeO4. This purple salt is paramagnetic, and is a rare example of an iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
(VI) compound. In most of its compounds, iron has the oxidation state +2 or +3 (Fe2+ or Fe3+). Reflecting its high oxidation state, FeO42−
Ferrate
In chemistry, ferrate refers either to the anion , in which iron is in the +6 oxidation state, or to a salt containing this anion. The term ferrate is often used to mean ferrate, although according to IUPAC naming conventions, it may also refer to other iron-containing oxyanions, such as ferrate...
is a powerful oxidizing agent
Oxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
.
K2FeO4 has attracted interest for applications in "green chemistry
Green chemistry
Green chemistry, also called sustainable chemistry, is a philosophy of chemical research and engineering that encourages the design of products and processes that minimize the use and generation of hazardous substances...
" because the by-products of its use, iron oxides, are environmentally innocuous. In contrast, some related oxidants such as chromate
Chromate
Chromate salts contain the chromate anion, CrO42−. Dichromate salts contain the dichromate anion, Cr2O72−. They are oxyanions of chromium in the oxidation state +6. They are moderately strong oxidizing agents.- Chemical properties :...
are considered environmentally hazardous. However, 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.
- 4 K2FeO4 + 4 H2O → 3 O2 + 2 Fe2O3 + 8 KOH
Synthesis and structure
Georg Ernst StahlGeorg Ernst Stahl
Georg Ernst Stahl was a German chemist and physician.He was born at Ansbach. Having graduated in medicine at the University of Jena in 1683, he became court physician to Duke Johann Ernst of Sachsen Weimar in 1687...
(1660 – 1734) first discovered that the residue formed by igniting a mixture of potassium nitrate
Potassium nitrate
Potassium nitrate is a chemical compound with the formula KNO3. It is an ionic salt of potassium ions K+ and nitrate ions NO3−.It occurs as a mineral niter and is a natural solid source of nitrogen. Its common names include saltpetre , from medieval Latin sal petræ: "stone salt" or possibly "Salt...
(saltpetre) and iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
powder dissolved in water to give a purple solution. Edmond Frémy
Edmond Fremy
Edmond Frémy was a French chemist. He is perhaps best known today for Frémy's salt, a strong oxidizing agent which he discovered in 1845...
(1814 – 1894) later discovered that fusion of potassium hydroxide
Potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
and iron(III) oxide in air produced a compound that was soluble in water. The composition corresponded to that of potassium manganate
Potassium manganate
Potassium manganate is the inorganic compound with the formula K2MnO4. This green-colored salt is an intermediate in the industrial synthesis of potassium permanganate , a common chemical...
. In the laboratory, K2FeO4 is prepared by oxidizing an alkaline solution of an iron(III) salt with concentrated chlorine bleach.
The salt is isostructural with K2MnO4
Potassium manganate
Potassium manganate is the inorganic compound with the formula K2MnO4. This green-colored salt is an intermediate in the industrial synthesis of potassium permanganate , a common chemical...
, K2SO4
Potassium sulfate
Potassium sulfate is a non-flammable white crystalline salt which is soluble in water...
, and K2CrO4
Potassium chromate
Potassium chromate is a yellow chemical indicator used for identifying concentrations of chloride ions in a salt solution with silver nitrate...
. The solid consists of K+ and the tetrahedral FeO42− anion, with Fe-O distances of 1.66 Å. The poorly soluble barium salt, BaFeO4
Barium ferrate
Barium ferrate is the chemical compound of formula BaFeO4. This compound contains iron in the +6 oxidation state. It is isostructural with BaSO4, and contains the tetrahedral [FeO4]2− anion.-Preparation and chemistry:...
, is also known.
Properties and applications
As a dry solid, K2FeO4 is stable. It decomposes with evolution of O2 in neutral water, and especially rapidly in acidic water. At high pHPH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
, aqueous solutions are stable. The deep purple solutions are similar in appearance to potassium permanganate
Potassium permanganate
Potassium permanganate is an inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO4− ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intensely purple solutions, the...
. It is stronger oxidizing agent than the latter.
Because the side products of its redox reactions are rust-like iron oxides, K2FeO4 has been described as a "green 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
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
, K2FeO4 oxidizes primary alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s.
K2FeO4 has also attracted attention as a potential cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
material in a "super iron battery
Super iron battery
The Super-iron battery is a new class of rechargeable electric battery."Super-iron" is a moniker for a special kind of ferrate salt...
."