Permanganate

Permanganate anion

Permanganates (also tetraoxomanganates (VII) ) are salts with the single negatively charged anion MnO ₄ ^- .

structure

Permanganate are derived from the constant only in dilute aqueous solution permanganic with the molecular formula HMnO ₄ from. Permanganic acid can be concentrated up to about 20% in a vacuum. It is a strong acid with a pKa value of −2.25. A very pure solution of permanganic acid can be obtained, among other things, by adding dropwise the underlying anhydride manganese (VII) oxide with the empirical formula Mn ₂ O ₇ to a large amount of well-cooled water.

Salts

Important salts are:

• Potassium permanganate KMnO ₄
• Calcium permanganate Ca (MnO ₄ ) ₂
• Rubidium permanganate RbMnO ₄
• Magnesium permanganate Mg (MnO ₄ ) ₂
• Silver permanganate AgMnO ₄

properties

The permanganates are water-soluble and form violet solutions, the best known is potassium permanganate . They are strong oxidizing agents . With their help, for example, alkenes can be converted into ketones or carboxylic acids via the corresponding glycols , formic and oxalic acids into carbon dioxide and aldehydes into carboxylic acids. A typical reaction of permanganate as an oxidizing agent is the oxidation of concentrated hydrochloric acid to chlorine gas , whereby the permanganate itself is reduced to manganese (II):

${\displaystyle {\ce {2MnO4- + 10Cl- + 16H3O+ -> 2Mn^{2}+ + 5Cl2 ^ + 24H2O}}}$

Iron (II) sulphate solution reacts with permanganate solution in acid to form manganese (II) and iron (III) salts, in basic to manganese (IV) oxide ( manganese dioxide ).

In analysis , permanganates are used for redox titrations , see manganometry .

use

Permanganates are also used to purify organic liquids, exhaust air and wastewater in the pharmaceutical and chemical industries . In the paraffin oxidation permanganates were used as catalysts used. In organic synthesis, potassium permanganate is reacted with alkenes to form cyclic manganate esters. The work-up gives cis -1,2-diols:

Individual evidence

1. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1618.
2. ^ Gmelin's Handbook of Inorganic Chemistry; Volume Manganese C2.
3. ↑ G. Wietzel: Production of synthetic fatty acids by oxidation of paraffinic hydrocarbons with molecular oxygen. In: Chemical Engineering Science. 3, 1954, pp. 17-IN4, doi : 10.1016 / S0009-2509 (54) 80003-0 .
4. ↑ Joachim Buddrus, Bernd Schmidt: Fundamentals of Organic Chemistry , 5th Edition, de Gruyter Verlag, Berlin, 2015, p. 186, ISBN 978-3-11-030559-3 .

Web links

Wikibooks: Internship Inorganic Chemistry / Permanganate  - Learning and teaching materials

• Video demonstration of various experiments with potassium permanganate