Question

Which of the following hydrocarbons can decolorize the alkaline potassium permanganate solution?

• A. ${\mathrm{C}}_2{\mathrm{H}}_6$
• B. ${\mathrm{C}}_3{\mathrm{H}}_8$
• C. ${\mathrm{C}}_5{\mathrm{H}}_{12}$
• D. ${\mathrm{C}}_3{\mathrm{H}}_6$

Answer 1

The correct option is D

${\mathrm{C}}_3{\mathrm{H}}_6$

The explanation for correct option

(D):

• An unsaturated organic compound decolorizes the pink color of potassium permanganate when treated with Baeyer's reagent, an aqueous solution of alkaline Potassium Permanganate $\left({\mathrm{KMnO}}_4\right)$.
• The purple color of alkaline ${\mathrm{KMnO}}_4$ solution changes to brown due to the formation of ${\mathrm{MnO}}_2$.

• Cold dilute neutral or alkaline ${\mathrm{KMnO}}_4$ solution quickly oxidizes alkenes to yield vicinal or $1,2-$glycol.
• ${\mathrm{C}}_3{\mathrm{H}}_6$ is an unsaturated hydrocarbon (an alkene) as it satisfies the general formula of alkene ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$.
• ${\mathrm{C}}_3{\mathrm{H}}_6$ (Propene) reacts with alkaline ${\mathrm{KMnO}}_4$ solution and decolorizes it.
• The reaction is as follows:

Explanation for the incorrect options

(A) ${\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{6}}$:

• The general formula of alkane is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$. ${\mathrm{C}}_2{\mathrm{H}}_6$ (Ethane) is an alkane.
• Due to the presence of saturation, ${\mathrm{C}}_2{\mathrm{H}}_6$ do not decolorize the alkaline ${\mathrm{KMnO}}_4$ solution.

(B) ${\mathbf{C}}_{\mathbf{3}}{\mathbf{H}}_{\mathbf{8}}$:

• The general formula of alkane is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$. ${\mathrm{C}}_3{\mathrm{H}}_8$ (Propane) is an alkane.
• Due to the presence of saturation, ${\mathrm{C}}_3{\mathrm{H}}_8$ do not decolorize the alkaline ${\mathrm{KMnO}}_4$ solution.

(C) ${\mathbf{C}}_{\mathbf{5}}{\mathbf{H}}_{\mathbf{12}}$:

• The general formula of alkane is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+2}$. ${\mathrm{C}}_5{\mathrm{H}}_{12}$ (Pentane) is an alkane.
• Due to the presence of saturation, ${\mathrm{C}}_5{\mathrm{H}}_{12}$ do not decolorize the alkaline ${\mathrm{KMnO}}_4$ solution.

Therefore, the correct option is (D). ${\mathbf{C}}_{\mathbf{3}}{\mathbf{H}}_{\mathbf{6}}$ can decolorize the alkaline Potassium Permanganate solution.