Question

Lucas test is very rapid with:

• A. 1° alcohol
• B. 2° alcohol
• C. 3° alcohol
• D. Phenol

Answer 1

The Correct Option is C

The Lucas test is a qualitative analysis technique used to differentiate between primary (1°), secondary (2°), and tertiary (3°) alcohols based on their reactivity with Lucas reagent (a mixture of concentrated hydrochloric acid and zinc chloride). This reaction is also applied to phenol but is primarily used to distinguish among alcohols.

Key Points about the Lucas Test:

• 3° Alcohols (tertiary): React immediately with Lucas reagent to form a cloudy solution at room temperature because the tertiary carbocation formed is stable and rapidly reacts to form the alkyl chloride.
• 2° Alcohols (secondary): React with Lucas reagent within 2 to 5 minutes to form a cloudy solution, indicating the formation of 2° haloalkane, as secondary carbocations are less stable than tertiary but more stable than primary.
• 1° Alcohols (primary): Do not react immediately. They require heating for a reaction to occur because primary carbocations are the least stable and hence harder to form.
• Phenol: Generally does not react with Lucas reagent due to the resonance stabilization of the phenolic oxygen, which prevents the formation of a carbocation.

Therefore, the Lucas test is very rapid with 3° alcohol, making option "3° alcohol" the correct answer in this context.

Conclusion: The correct answer is "3° alcohol" because tertiary alcohols react immediately with Lucas reagent at room temperature.