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”.

The compound which reacts fastest with Lucas reagent at room temperature is:

• A. Butan-1-ol
• B. Butan-2-ol
• C. 2-Methylpropan-1-ol
• D. 2-Methylpropan-2-ol

Answer 1

The correct option is D 2-Methylpropan-2-ol

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 $3^{\circ }>2^{\circ }>1^{\circ }$.

Since 2-methylpropan-2-ol is a $3^{\circ }$ alcohol, it will react fastest with Lucas reagent.