Preparation and Uses of Baeyer's Reagent | Alkaline KMnO4

Alkaline potassium permanganate (KMnO4) solution is called as bayer's reagent. It is prepared by dissolving anhydrous sodium carbonate (Na2CO3) in a KMnO4 solution. Baeyer's reagent can oxidize alkenes and alkynes.


Uses of Bayer's Reagent in Organic Chemistry

It is used as a potent oxidizing agent and used in the qualitative organic analysis to test for the presence of unsaturated alkenes and alkyne groups. Baeyer's reagent interacts with alkene and alkyne, changing its pinkish-purple colour to brown colour (due to formation of manganese dioxide).




Preparation of Baeyer's Reagent

There are some conditions to be careful when baeyer's reagent is prepared for alkene oxidation to diol.

  • KMnO4 solution should be dilute.
  • Solution should be cold.

Steps of preparation of 1% alkaline potassium permanganate solution

  1. Dissolve 1 gram of solid KMnO4 in 100 ml of distilled water to produce a 1% potassium permanganate solution
  2. Add 10 grams of anhydrous sodium carbonate (NaCO3) to the KMnO4 solution and the stoppered bottle is shaken until fully dissolved and mixed. Sodium carbonate is weak alkaline compound. Therefore, solution will become slightly alkaline.
  3. Keep the solution in a dark, cool cupboard when not in use to maintain it fresh.


Oxidation of alkene and alkyne compounds by baeyer's reagent

Alkene compounds can be oxidized to diol and alkyne compounds can be oxidized to vicinal diketones or dialdehyde (Vic-diketones or 1,2-diketones) or, under more vigorous conditions, carboxylic acids.


Alkene and baeyer's reagent

Two -OH groups are attached to the carbon atoms in alkene group as in the figure.

alkene + KMnO4 in alkali medium

Alkynes and baeyer's reagent

Alkyne compounds can be oxidized to vicinal diketones or dialdehyde (Vic-diketones or 1,2-diketones) or, under more vigorous conditions, carboxylic acids by baeyer's reagent. More vigorous conditions can be made by increasing the alkalinity of the solution by adding potassium hydroxide (KOH). KOH is a strong alkali.

alkynne + KMnO4 in alkaliine medium




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Lewis structures

P2O5 lewis structure OH- lewis structure Ammonium ion (NH4+) lewis structure H2CO3 lewis structure