Question:
Which of the following organic compounds will give Lucas test immediately?
Which of the following organic compounds will give Lucas test immediately?
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Remember that tertiary alcohols react quickly with PCl₅ to form a white precipitate, while primary and secondary alcohols do not show immediate reactions.
Updated On: May 31, 2026
- 2-Methylpropan-2-ol
- Propan-1-ol
- Propan-2-ol
- Ethanol
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The Correct Option is A
Solution and Explanation
Step 1: Concept
The Lucas test is used to distinguish between primary, secondary, and tertiary alcohols. In this test, an alcohol reacts with phosphorus pentachloride (PCl₅) in a chloroform solution. Primary alcohols do not show any immediate reaction, secondary alcohols react slowly, while tertiary alcohols react quickly to form a white precipitate of the alkyl chloride.
Step 2: Meaning
The Lucas test is particularly useful for identifying the type of alcohol (primary, secondary, or tertiary) by observing the rate and nature of the reaction with PCl₅ in chloroform. Immediate reaction indicates a tertiary alcohol.
Step 3: Analysis
Option A: 2-Methylpropan-2-ol This is a tertiary alcohol because it has three alkyl groups attached to the carbon atom that carries the hydroxyl group (-OH). Tertiary alcohols react quickly with PCl₅, showing an immediate reaction. Option B: Propan-1-ol This is a primary alcohol as it only has one alkyl group attached to the carbon carrying the -OH. Primary alcohols do not show any immediate reaction in the Lucas test. Option C: Propan-2-ol This is a secondary alcohol because it has two alkyl groups attached to the carbon with the -OH. Secondary alcohols react slowly, not immediately, with PCl₅. Option D: Ethanol Ethanol is also a primary alcohol (same as propan-1-ol). Like propan-1-ol, it does not show any immediate reaction in the Lucas test.
Step 4: Conclusion
The compound that will give an immediate reaction in the Lucas test is 2-methylpropan-2-ol, which is a tertiary alcohol. Final Answer: (A)
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