Question

Primary, secondary and tertiary alcohols can be distinguished by:
a.) Baeyer’s reagent
b.) Fehling’s solution
c.) Sulphuric acid
d.) Lucas reagent

Answer 1

Hint : We know that primary alcohol is alcohol in which the hydroxyl group is bonded to a primary carbon atom and similarly for other alcohols. To distinguish them we have to check which reactant reacts with which alcohol and with which not.

Complete step by step solution :
Here primary alcohol is attached with primary carbon, secondary alcohol is attached with secondary carbon and tertiary alcohol is attached with a tertiary carbon
The Lucas test of alcohol is a test for differentiation between primary, secondary, and tertiary alcohols. It is based on the difference in reactivity of the three classes of alcohols with hydrochloric acid via a${{S}_{N}}1$ reaction.

This test consists of treating alcohol with Lucas reagent, an equimolar mixture of conc. $HCl$ and anhydrous $ZnC{{l}_{2}}$ at room temperature, when turbidity due to the formation of insoluble alkyl chlorides is observed.
If turbidity appears immediately, the alcohol is tertiary:

${{R}_{3}}COH~\xrightarrow[+anhydrousZnC{{l}_{2}}]{conc.HCl}~{{R}_{3}}CCl~+{{H}_{2}}O$

If turbidity appears in five minutes, the alcohol is secondary:

${{R}_{2}}CHOH~\xrightarrow[+anhydrousZnC{{l}_{2}}]{conc.HCl}{{R}_{2}}CHCl~~\text{ }+\text{ }{{H}_{2}}O$

Primary alcohols do not react with Lucas reagent at room temperature and so, no turbidity is formed:

$RC{{H}_{2}}OH~\xrightarrow[+anhydrousZnC{{l}_{2}}]{conc.HCl}$no reaction.

So, the correct answer is “Option D”.

Note : Here ${{S}_{N}}1$ reaction takes place. So, you can check the reactivity of each alcohol by the order of reactivity for ${{S}_{N}}1$(nucleophilic substitution) reaction.