Question

Baeyer’s reagent is :

• A. Acidic potassium permanganate solution
• B. Acidic potassium dichromate solution
• C. Cold, dilute, aqueous solution of potassium permanganate
• D. Hot, concentrated solution of potassium permanganate

Answer 1

The Correct Option is C

Baeyer's reagent is a commonly used reagent in organic chemistry to test for unsaturation, such as alkenes and alkynes. Here is a step-by-step explanation of the correct answer:

1. Understanding Baeyer's Reagent: Baeyer's reagent is specifically a cold, dilute, aqueous solution of potassium permanganate (KMnO₄). It is not used in concentrated form and is never hot when applied for the test.
2. Reaction Mechanism: In the presence of unsaturated compounds such as alkenes, the purple color of KMnO₄ fades to brown due to the formation of manganese dioxide (MnO₂), indicating a positive test.
3. Why Cold and Dilute? A cold and dilute solution is chosen because it ensures controlled oxidation of the double bonds without over-oxidation of alcohols or other functional groups.
4. Rule Out Other Options:
   • Acidic potassium permanganate solution: This is used for different oxidation processes, not for the detection of unsaturation.
   • Acidic potassium dichromate solution: Used in oxidation reactions primarily for alcohols, not typically applicable for Baeyer's test.
   • Hot, concentrated solution of potassium permanganate: Causes vigorous and uncontrolled reactions, unsuitable for assessing unsaturation.

Thus, the correct answer is the cold, dilute, aqueous solution of potassium permanganate, utilized for its selectivity and gentleness in detecting unsaturation by the change in color. This makes it an effective qualitative test in organic chemistry.