Question

Which of the following reagents could be used to distinguish between prop-2-en-1-ol and propan-1-ol?

• A. Lucas reagent
• B. $ZnC{l}_{2}andconc.HCl$
• C. A Cr(VI) reagent like $H_{2}Cr{O}_4$
• D. Benzene

Answer 1

Answer: (A), (B)

$ZnC{l}_{2}andconc.HCl$

Both alcohols will effect a change in colour with Cr (VI) reagents. So that option is ruled out.

Lucas reagent is anhydrous $ZnC{l}_{2}dissolvedinconc.HCl$. At room temperature, it is extremely slow to react with primary alcohols like propan-1-ol.
So no oily layer is observed. But like tertiary alcohols, allyl alcohols give a positive Lucas test very quickly so an oily layer is observed in seconds.