Question

Butyne on oxidation with hot alkaline ${\text{KMn}}{{\text{O}}_{\text{4}}}$ gives:
A) ${\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{COOH}}$
B) ${\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{COOH}}$
C) ${\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{COOH}} + {\text{C}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}}$
D) ${\text{C}}{{\text{H}}_{\text{2}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{COOH}} + {\text{HCOOH}}$

Answer 1

Hint: In this reaction, alkaline potassium permanganate is used. We know that potassium permanganate is used for the displacement of carbon-carbon triple bonds.
Let us study the given reactions.
Complete answer:
Butyne on oxidation gives carboxylic acid.
In this reaction, alkaline potassium permanganate is used. We know that potassium permanganate is used for the displacement of carbon-carbon triple bonds.
The structure of butyne is ${\text{C}}{{\text{H}}_{\text{3}}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{C}} \equiv {\text{CH}}$.
The triple bond in butyne gets displaced on reaction with potassium permanganate and carboxylic acid is formed. The by-products of the reaction are carbon dioxide and water.
Thus, the oxidation reaction of butyne with hot alkaline potassium permanganate is as follows:
${\text{C}}{{\text{H}}_{\text{3}}} - {\text{C}}{{\text{H}}_{\text{2}}} - {\text{C}} \equiv {\text{CH}} + {\text{KMn}}{{\text{O}}_{\text{4}}} \to {\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{COOH}} + {\text{C}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}}$

Thus, the correct option is (C).

Additional Information: Butyne on oxidation with hot alkaline ${\text{KMn}}{{\text{O}}_{\text{4}}}$ gives propanoic acid alone with carbon dioxide gas. The reaction is used to confirm the presence of alkynes in the given sample. The carbon dioxide gas formed in the reaction turns lime water milky and confirms the presence of alkyne. The test is known as the test for unsaturation. Presence of alkenes in the given sample gives positive results for the test.

Note: Do not get confused between alkaline and acidified potassium permanganate. Acidified potassium permanganate reacts with alkenes or alkynes (unsaturated compounds) and oxidizes them to vicinal diols. Vicinal diols mean 1,2-diols. In vicinal diols, two hydroxyl functional groups are attached to adjacent carbon atoms. An acidified potassium permanganate solution is known as Baeyer’s reagent. Baeyer’s reagent is a stronger oxidising agent than alkaline potassium permanganate. Baeyer’s reagent can be used for the test of unsaturation. The colour of the solution changes from pink to brown If the given sample contains unsaturated compounds.