Question

The compound which reacts fastest with Lucas reagent is:

• A. butan-1-ol
• B. butan-2-ol
• C. 2-methyl propan-1-ol
• D. 2-methyl propan-2-ol

Answer 1

Answer: (D)

Lucas reagent (anhydrous $ZnC{l}_2+conc.HCl$ ) is used to distinguish between primary, secondary and tertiary alcohols. It reacts with $3{}^{\circ }$ -alcohol readily giving white turbidity, with $2{}^{\circ }$ -alcohol it gives turbidity after 1-2 minutes. While with $1{}^{\circ }$ -alcohol, it reacts only on heating. Hence, it will react with 2-methyl propanal-2-ol fastest. $\underset{\text{2-}\text{methyl}\text{propanol-2}}{C{H}_3--\underset{C{H}_3}{\stackrel{C{H}_3}{\underset{|}{\stackrel{|}{C}}}}--OH}\stackrel{ZnC{l}_2/conc.HCl}{\to }$ $\underset{\text{white}\text{turbidity}\text{(immediately)}}{C{H}_3--\underset{C{H}_3}{\stackrel{C{H}_3}{\underset{|}{\stackrel{|}{C}}}}--Cl+H_{2}O}$