Question

Baeyer's reagent is:
(A)- aqueous bromine solution
(B)- neutral permanganate solution
(C)- acidified permanganate solution
(D)- alkaline potassium permanganate solution

Answer 1

Hint: Baeyer's reagent is a very strong oxidizing agent. It gives pink or purple colour in solution. It reacts with unsaturated compounds like alkenes and alkynes. Unsaturation in compounds is detected by change in its colour from pink to brown.


Complete step by step solution:
Potassium permanganate is a soluble in water and gives purple coloured solution.
It acts as a very strong oxidizing agent in acidic medium and a mild oxidizing agent in alkaline and neutral solution.
alkaline solution of potassium permanganate ($KMn{{O}_{4}}$) is known as Bayer’s reagent. It reacts with organic compounds containing $-C=C-$ or $-C\equiv C-$ and oxidizes them to vicinal diols, i.e. 1.2-diols.
For example, when ethylene is treated with an alkaline solution of $KMn{{O}_{4}}$, the colour of the solution fades on the formation of ethylene glycol.
     \[{{H}_{2}}C=C{{H}_{2}}+{{H}_{2}}O+\left[ O \right]\xrightarrow{\text{Bayer }\!\!'\!\!\text{ s reagent}}C{{H}_{2}}(OH)-C{{H}_{2}}(OH)\]
The reaction involves the oxidation of alkenes to diols and reduction of $KMn{{O}_{4}}$ to$Mn{{O}_{2}}$ which is brown in colour. Change in oxidation state of potassium permanganate in alkaline medium is shown below:
     \[\overset{+7}{\mathop{Mn}}\,O_{4}^{-}+2{{H}_{2}}O+3{{e}^{-}}\to \overset{+4}{\mathop{Mn}}\,{{O}_{2}}+4O{{H}^{-}}\]
     \[2KMn{{O}_{4}}+{{H}_{2}}O\to 2KOH+2Mn{{O}_{2}}+3\left[ O \right]\]


Additional information: Aqueous bromine solution is known as bromine water. Bromine is a volatile liquid and soluble in water. Solution of bromine in water is called bromine water. It is a yellow coloured liquid mixture used in qualitative analysis of compounds. Alkenes react with bromine water to form additional compounds whereas alkanes do not.


Note: Do not get confused between the options. Potassium permanganate acts as an oxidizing agent in neutral, acid and alkaline solutions. However, acidified solution of potassium permanganate is a stronger oxidizing agent than Bayer’s solution.