Question

What is Lucas reagent? Distinguish primary secondary and tertiary alcohol using Lucas reagent.

Answer 1

Solution of $ZnC{l}_2$ in conc. $HCl$ is known as Lucas reagent.
Application : It is used to differentiate primary, secondary and tertiary alcohols.
On adding the alcohol to Lucas reagent, a tertiary alcohol reacts immediately forming a ppt of alkyl chloride. If the ppt. appears after few minutes, the alcohols is secondary. If no ppt, is obtained in cold the alcohol is primary.

$RC{H}_{2}OH\underset{AnhydrousZnCl,}{\overset{Con.HCl}{\to }}NoReaction$

$1^o$ Alcohol (At room temperature)

$R_{2}CHOH\underset{AnhydrousZnCl,}{\overset{Con.HCl}{\to }}{R}_{2}CgCl\downarrow +H_{2}O$

$2^o$ Alcohol (After 5 minute)

$R_{3}CHOH\underset{AnhydrousZnCl,}{\overset{Con.HCl}{\to }}{R}_{3}CCl\downarrow +H_{2}O$