Question

What is the function of anhydous $ZnC{l}_2$ in Lucas test for distinction between $1^o,2^o\text{and}{3}^o$ alcohols?

• A. act as nucleophile
• B. act as dehydrating agent
• C. act as lewis base
• D. act as lewis acid

Answer 1

The correct option is D act as lewis acid

Lucas reagent reacts with alcohols to form precipitates of alkyl halides.
$ZnC{l}_2$ is a Lewis acid due to the empty d orbitals of Zn. 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 direction. At last chloride ion as a nucleophile attack the carbocation to form alkylhalide.

Mechanism of Lucas test reaction​:
Acid-Base reaction with $ZnC{l}_2$
Attack of chloride ion