Question

Lucas test is used to differentiate and categorize primary, secondary and tertiary alcohols using a solution of anhydrous zinc chloride in concentrated hydrochloric acid. This solution is commonly referred to as “Lucas Reagent”.

Which alcohol reacts fastest and by what mechanism?

• A. Tertiary alcohol by $S_{N}1$
• B. Secondary alcohol by $S_{N}2$
• C. Tertiary alcohol by $S_{N}2$
• D. Secondary alcohol by $S_{N}1$

Answer 1

The correct option is A Tertiary alcohol by $S_{N}1$

The difference between primary, secondary and tertiary alcohol can be distinguished by Lucas test on the basis of their reactivity with Lucas reagent.
Generally, reaction takes place via $S_{N}1$ mechanism.
$\text{Rate of}{S}_{N}1\text{reaction}\propto \text{Stability of carbocation formed}$
Therefore, the order of reactivity of alcohols with Lucas reagent is $3^{\circ }>2^{\circ }>1^{\circ }$.