Question

Lucas reagent, used to distinguish between primary, secondary, and tertiary alcohols, is a mixture of:

• A. Conc. HCl + anhydrous ZnCl$_2$
• B. Conc. HNO$_3$ + AgNO$_3$
• C. Pd + BaSO$_4$
• D. NH$_4$OH + AgNO$_3$

Hint:

Lucas Test Summary: Tertiary alcohol → Immediate turbidity
Secondary alcohol → Turbidity after few minutes
Primary alcohol → No turbidity at room temperature

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The Lucas test is a chemical test used to differentiate among primary, secondary, and tertiary alcohols. It is based on the difference in reactivity of these alcohols with hydrogen halides via an $S_N1$ mechanism.
Step 2: Detailed Explanation:
1. The Reagent: Lucas reagent consists of a solution of anhydrous zinc chloride ($ZnCl_2$) in concentrated hydrochloric acid ($HCl$).
2. The Reaction: Alcohols are converted to alkyl chlorides. Since alkyl chlorides are insoluble in the reagent, they form a cloudy turbidity or separate layer.
3. Reactivity: - Tertiary alcohols: React immediately, showing turbidity instantly. - Secondary alcohols: React within 5–10 minutes. - Primary alcohols: Do not react at room temperature (turbidity only appears upon heating).
4. Other Options: (C) is Lindlar's catalyst, and (D) is Tollen's reagent.
Step 3: Final Answer
Lucas reagent is a mixture of Conc. HCl and anhydrous ZnCl₂.