- Formula
- Chemical structure
- Applications
- Medicine and veterinary
- Water treatment
- Preservation of fruits
- Action on fire
- Redox titrant
- Reagent in organic synthesis
- Historical uses
- How is it done?
- Properties
- Decomposition
- Oxidizing power
- References
The potassium permanganate (KMnO 4) is an inorganic compound consisting of manganese - metal transition group 7 (VIIB) -, oxygen and potassium. It is a deep purple vitreous solid. Its aqueous solutions are also dark purple; these solutions become less violet as they are diluted in larger amounts of water.
KMnO 4 then begins to undergo reductions (gain electrons) in a succession of colors in the following order: purple> blue> green> yellow> colorless (with brown precipitate of MnO 2). This reaction demonstrates an important property of potassium permanganate: it is a very strong oxidizing agent.
Formula
Its chemical formula is KMnO 4; that is, for each K + cation there is an MnO 4 anion - interacting with this
Chemical structure
The upper image represents the crystalline structure of KMnO 4, which is of the orthorhombic type. The purple spheres correspond to the K + cations, while the tetrahedron formed by the four red spheres and the bluish sphere correspond to the MnO 4 - anion.
Why does the anion have a tetrahedral geometry? Your Lewis structure answers this question. The dotted lines mean that the double bonds are resonating between Mn and O. In order to adopt this structure, the metal center must have an sp 3 hybridization.
Since manganese lacks unshared pairs of electrons, the Mn-O bonds are not pushed into the same plane. Likewise, the negative charge is distributed among the four oxygen atoms, being responsible for the orientation of the K + cations within the crystalline arrangements.
Applications
Medicine and veterinary
Due to its bactericidal action, it is used in numerous diseases and conditions that cause skin lesions, such as: fungal foot infections, impetigo, superficial wounds, dermatitis and tropical ulcers.
Due to its harmful action, potassium permanganate should be used at low concentrations (1: 10,000), which limits the effectiveness of its action.
It is also used to treat fish parasites in aquariums that cause gill infections and skin ulcers.
Water treatment
It is a chemical regenerant used to remove iron, magnesium and hydrogen sulfide (with an unpleasant odor) from water, and can be used to purify wastewater.
Iron and magnesium precipitate as their water-insoluble oxides. In addition, it helps to remove the rust present in the pipes.
Preservation of fruits
Potassium permanganate removes by oxidation the ethylene generated in the banana during its storage, allowing it to remain unripe for more than 4 weeks, even at room temperature.
In Africa they use it to soak vegetables, in order to neutralize and eliminate any bacterial agents present.
Action on fire
Potassium permanganate is used to limit the spread of fires. Based on the ability of permanganate to start fire, it is used to create firefighting in forest fires.
Redox titrant
In analytical chemistry, its standardized aqueous solutions are used as an oxidizing titrant in redox determinations.
Reagent in organic synthesis
It serves to convert alkenes into diols; that is, two OH groups are added to the C = C double bond. The following chemical equation:
Likewise, in sulfuric acid solution with chromic acid (H 2 CrO 4) it is used for the oxidation of primary alcohols (R-OH) to carboxylic acids (R-COOH or RCO 2 H).
Its oxidizing power is strong enough to oxidize the primary or secondary alkyl groups of aromatic compounds, "carboxyllating" them; that is, transforming the R side chain (eg, a CH 3) into a COOH group.
Historical uses
It was part of the powders used as a flash in photography or to initiate the thermite reaction.
It was used in the Second World War for camouflage of white horses during the day. For this they used manganese dioxide (MnO 2), which is brown in color; in this way they went unnoticed.
How is it done?
The mineral pyrolusite contains manganese dioxide (MnO 2) and potassium carbonate (CaCO 3).
In 1659 the chemist Johann R. Glauber melted the mineral and dissolved it in water, observing the appearance of a green coloration in the solution, which later changed to violet and finally to red. This last color corresponded to the generation of potassium permanganate.
In the middle of the 19th century, Henry Condy was looking for an antiseptic product and initially treated pyrolusite with NaOH and later with KOH, producing the so-called Condy crystals; that is, potassium permanganate.
Potassium permanganate is produced industrially from manganese dioxide present in the mineral pyrolusite. The MnO 2 present in the mineral reacts with potassium hydroxide and is subsequently heated in the presence of oxygen.
2 MnO 2 + 4 KOH + O 2 => 2 K 2 MnO 4 + 2 H 2 O
Potassium manganate (K 2 MnO 4) is converted to potassium permanganate by electrolytic oxidation in an alkaline medium.
2 K 2 MnO 4 + 2 H 2 O => 2 KMnO 4 + 2 KOH + H 2
In another reaction to produce potassium permanganate, potassium manganate is reacted with CO 2, accelerating the disproportionation process:
3 K 2 MnO 4 + 2 CO 2 => 2 KMnO 4 + MnO 2 + K 2 CO 3
Due to the generation of MnO 2 (manganese dioxide) the process is unfavorable, having to generate KOH from K 2 CO 3.
Properties
It is a purple crystalline solid that melts at 240 ºC, which has a density of 2.7 g / mL, and a molecular weight of approximately 158 g / mol.
It is poorly soluble in water (6.4 g / 100 ml at 20 ºC), which indicates that water molecules do not solvate to a large extent MnO 4 - ions, because perhaps their tetrahedral geometries require a lot of water to its dissolution. Similarly, it can also be dissolved in methyl alcohol, acetone, acetic acid, and pyridine.
Decomposition
It decomposes at 240 ºC, releasing oxygen:
2KMnO 4 => K 2 MnO 4 + MnO 2 + O 2
It can undergo decomposition by the action of alcohol and other organic solvents, as well as by the action of strong acids and reducing agents.
Oxidizing power
In this salt, manganese exhibits its highest oxidation state (+7), or what is equal, to the maximum number of electrons that it can lose ionically. In turn, the electron configuration of manganese is 3 d 5 4 s 2; therefore, in potassium permanganate the entire valence shell of the manganese atom is "empty."
So the manganese atom has the natural tendency to gain electrons; that is, to be reduced to other oxidation states in alkaline or acidic media. This is the explanation why KMnO 4 is a powerful oxidizing agent.
References
- Wikipedia. (2018). Potassium permanganate. Retrieved on April 13, 2018, from: en.wikipedia.org
- F. Albert Cotton and Geoffrey Wilkinson, FRS. (1980). Advanced Inorganic Chemistry. Editorial Limusa, México, 2nd edition, pages 437-452.
- Robin Wasserman. (August 14, 2017). Medical Uses for Potassium Permanganate. Retrieved on April 13, 2018, from: livestrong.com
- Clark D. (September 30, 2014). The 3 Ultimate Uses Of Potassium Permanganate. Retrieved on April 13, 2018, from: technology.org
- James H. Pohl, Ali Ansary, Irey RK (1988). Modular Thermodynamics, Vol. 5, Evaluation of changes in properties. Ediciones Ciencia y Técnica, SA México, Editorial Limusa, pages 273-280.
- JM Medialdea, C. Arnáiz and E. Díaz. Potassium permanganate: a powerful and versatile oxidant. Department of Chemical and Environmental Engineering. University School of Seville.
- Hasan Zulic. (October 27, 2009). Biological Wastewater Treatment.. Retrieved on April 13, 2018, from: es.wikipedia.org
- Adam Rędzikowski. (March 12, 2015). Simple potassium permanganate.. Retrieved on April 13, 2018, from: commons.wikimedia.org