Question

Which of the following alcohols reacts most readily with Lucas reagent?

• A. $C{H}_{3}C{H}_{2}C{H}_{2}OH$
• B. $(C{H}_3{)}_{2}CHOH$
• C. $(C{H}_3{)}_{3}COH$
• D. $C{H}_{3}C{H}_{2}OH$

Answer 1

The correct option is C $(C{H}_3{)}_{3}COH$

Lucas reagent is a mixture of conc HCl and anhydrous zinc chloride. The reactivity of alcohols towards Lucas reagent follows the order: tertiary > secondary > primary.

The reaction of alcohol with Lucas reagent $(\text{conc.}HCl+\text{anhyd.}ZnC{l}_2)$ is mostly $S_{N}1$ reaction and the rate of reaction is directly proportional to the stability of carbocation formed in the reaction.
Since, $3^o$ alcohol forms $3^o$ carbocation (most stable) hence, it will react fastest by $S_{N}1$ reaction.

When a tertiary alcohol, reacts with Lucas reagent, an oily layer (turbidity) is formed immediately.
When a secondary alcohol, reacts with Lucas reagent, a precipitate is formed after 10 to 15 minutes.
When a primary alcohol is treated with Lucas reagent, no reaction is observed at room temperature.
Hence, the correct answer is option (c).