Doubt by khadijah

What is the difference between acidic KMnO4 and basic KMnO4 and where is it used?

Answers

Answer by Rishikant Pandey

Permanganate as oxidizing agent works most efficiently in acidic solution, because it is reduced to the greatest extent in this medium, from oxidation state +VII in MnO4MnOX4X− to +II in Mn2+MnX2+.

8H++MnO4+5e  Mn2++4H2O8HX++MnOX4X−+5eX−⟶  MnX2++4HX2O

Therefore, the number of electrons transferred from oxidized species per mole KMnO4KMnOX4 (5 electrons) is the largest, and the least amount of KMnO4KMnOX4 is needed for the reaction with a certain amount of alcohol. This makes oxidation in acidic medium the best choice for economic reasons.

The oxidation in neutral medium is less efficient, as manganese(VII) is only reduced to manganese(IV), yielding insoluble MnO2MnOX2 as a byproduct which needs to be removed from the reaction mixture during purification of the desired product (carboxylic acid).

2H2O+MnO4+3e  MnO2+4OH2HX2O+MnOX4X−+3eX−⟶  MnOX2↓+4OHX−

Oxidation in strongly alkaline medium is least efficient in terms of transferred electrons per mole permanganate, as the latter is only reduced to manganate(VI).

MnO4+e  MnO42MnOX4X−+eX−⟶  MnOX4X2−

However, when the reaction is done under these conditions, a higher reaction speed and selectivity can be achieved, presumably because the alcohol will react more readily with MnO4MnOX4X− when deprotonated. Nevertheless, oxidation in acidic medium can be preferred for reasons stated above and substrates which are sensitive to strong bases.