Question

Primary, secondary and tertiary alcohols can be distinguished by :

• A. Lucas test
• B. Fehling’s test
• C. Tollens’ test
• D. Hinsberg’s test

Hint:

The Lucas test works on the principle of carbocation stability: \( 3^\circ \gt 2^\circ \gt 1^\circ \).
Remember that tertiary alcohols react "instantly," secondary "slowly," and primary "not at all" at room temperature.
Victor Meyer's test is another chemical method to distinguish these alcohols based on color changes (Red, Blue, Colorless).

Answer 1

The Correct Option is A

Concept:

• Distinction tests rely on the different rates of reactivity of primary (\( 1^\circ \)), secondary (\( 2^\circ \)), and tertiary (\( 3^\circ \)) functional groups with a specific reagent.

• For alcohols, the stability of the intermediate carbocation determines the speed of the reaction with halogen acids.
Step 1: Understanding the Lucas Reagent
Lucas reagent is a mixture of concentrated Hydrochloric acid \( (\text{HCl}) \) and anhydrous Zinc Chloride \( (\text{ZnCl}_2) \).
The reaction involves the substitution of the hydroxyl \( (-\text{OH}) \) group with a chlorine \( (-\text{Cl}) \) atom to form an alkyl chloride.

Step 2: Observing the reaction rates
Alkyl chlorides are insoluble in water and produce cloudiness or turbidity in the solution.
1. Tertiary alcohols react immediately, showing turbidity instantly at room temperature.
2. Secondary alcohols react within 5 to 10 minutes to show turbidity.
3. Primary alcohols do not produce turbidity at room temperature; it only appears upon heating.

Step 3: Evaluating other options
Fehling's and Tollens' tests are used to identify aldehydes.
Hinsberg's test is used to distinguish between primary, secondary, and tertiary amines.