Question

In the preparation of ethylchloride by the reaction
$C{H}_{3}C{H}_{2}OH+HCl\underset{ZnC{l}_2}{\overset{\text{anhydrous}}{\to }}C{H}_{3}C{H}_{2}Cl+H_{2}O$
the major reason for using anhydrous $ZnC{l}_2$ as a catalyst is that

• A. it absorbs water formed in the reaction and drives the equilibrium to the right
• B. it coordinates with the product $C{H}_{3}C{H}_{2}Cl$ and drives the reaction to the right
• C. it assist in forming the nucleohile $C{1}^{-}$ from HCl
• D. it coordinates with oxygen of ethyl alcohol and increase the leaving ability of the -OH group

Answer 1

The correct option is D it coordinates with oxygen of ethyl alcohol and increase the leaving ability of the -OH group

Lucas reagent reacts with alcohols to form precipitates of alkyl halides.
$ZnC{l}_2$ is a Lewis acid so oxygen of -OH forms coordinate bond with Zn or in other words complexes with zinc.
Oxygen acquires a positive charge and Zn acquires a negative charge. Thus, oxygen becomes a good leaving group and the reaction progresses in the forward reaction. At last chloride ion as a nucleophile attack the carbocation to form alkylhalide.
Hence coorect option is d.
First step in Lucas test reaction​ is acid-base reaction with $ZnC{l}_2$