Baeyer rehearsal
The Baeyer sample , named after Adolf von Baeyer , is a qualitative method in analytical chemistry to detect unsaturated hydrocarbon compounds , especially alkenes .
execution
The substance to be examined is mixed with the Baeyer reagent, consisting of sodium carbonate and potassium permanganate solution. If the purple solution is already discolored in the cold and a brown precipitate is formed, this is evidence of unsaturated hydrocarbons. The color change is the result of a redox reaction in which, with the cleavage of a carbon-carbon double bond , manganese dioxide and a manganate (VI) as well as a diol are formed:
The Baeyer sample initially produces a manganate (V) (MnO 3 - ). This disproportionates to manganese (IV) oxide and manganate (VI) (MnO 4 2− ). For compounds that are insoluble in water, an alcoholic permanganate solution can also be used. If the Baeyer test is carried out with an acetic acid potassium permanganate solution, the detection also consists of a discoloration of the purple solution.
The Baeyer sample, however, not only shows a positive reaction to alkenes . Alkynes and a number of other classes of compounds are also oxidized by potassium permanganate. So also give aldehydes , formic acid and its esters , phenol - and aniline derivatives and mercaptans and thioethers a positive test.
The oxidation of alkynes with potassium permanganate is confusing. Depending on the choice of reaction conditions are formed
- Carboxylic acids (use of aqueous potassium permanganate solution)
- α- diketones (anhydrous dichloromethane solution that is oxidized with solid potassium permanganate under phase transfer conditions )
- α-Diketones and other oxidation products (dichloromethane solution, which is oxidized with aqueous potassium permanganate under phase transfer conditions)
Web links
Reaction scheme of the Baeyer sample
Individual evidence
- ^ Siegfried Hauptmann : Organische Chemie , 2nd edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig 1985, ISBN 3-342-00280-8 , p. 235 and p. 241.
- ↑ The Baeyer sample - evidence of alkenes. Contribution to Prof. Blum's educational server for chemistry.
- ^ Brockhaus ABC Chemie, VEB FA Brockhaus Verlag, Leipzig 1965, p. 153.
- ↑ http://www.chemistry.ccsu.edu/glagovich/teaching/316/qualanal/tests/baeyertest.html .
- ↑ Donald G. Lee and Victor S. Chang: Oxidation of Hydrocarbons. 9. The Oxidation of Alkynes by Potassium Permanganate , Journal of Organic Chemistry 44 , 1979, pp. 2726-2730.