Question

Lucas reagent gives immediate turbidity with:

• A. Ethanol
• B. Propan-1-ol
• C. Propan-2-ol
• D. tert-Butyl alcohol

Hint:

Lucas reagent test: \[ 3^\circ \text{ alcohol } \rightarrow \text{Immediate turbidity} \] \[ 2^\circ \text{ alcohol } \rightarrow \text{Slow turbidity} \] \[ 1^\circ \text{ alcohol } \rightarrow \text{No turbidity at room temperature} \]

Answer 1

The Correct Option is D

Concept: Lucas reagent is a mixture of: \[ \text{Conc. HCl + Anhydrous ZnCl}_2 \] It is used to distinguish primary, secondary and tertiary alcohols.

• Tertiary alcohols react immediately.
• Secondary alcohols react within few minutes.
• Primary alcohols react very slowly.

Turbidity appears due to formation of insoluble alkyl chlorides.

Step 1: Understand reactivity order. Tertiary alcohols form highly stable tertiary carbocations. Hence substitution reaction occurs rapidly through \(S_N1\) mechanism. \[ 3^\circ > 2^\circ > 1^\circ \]

Step 2: Identify tertiary alcohol. Among the given compounds: \[ \text{tert-Butyl alcohol} \] is a tertiary alcohol.

Step 3: Conclusion. Therefore it gives immediate turbidity with Lucas reagent. \[ \boxed{\text{tert-Butyl alcohol}} \]