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NEET CHEMISTRYHaloalkanes and HaloarenesEasy

Question

The -OH\text{-OH} group of an alcohol or the carboxylic acid can be replaced by -Cl\text{-Cl} using:

A

Hypochlorous acid

B

Chlorine

C

Hydrochloric acid

D

Phosphorous pentachloride

Step-by-Step Solution

The hydroxyl group (-OH\text{-OH}) of an alcohol or a carboxylic acid can be readily replaced by a chlorine atom (-Cl\text{-Cl}) upon reaction with phosphorus halides such as phosphorus pentachloride (PCl5\text{PCl}_5), phosphorus trichloride (PCl3\text{PCl}_3), or thionyl chloride (SOCl2\text{SOCl}_2) .

For example, the reaction with alcohols is given by: R-OH+PCl5R-Cl+POCl3+HCl\text{R-OH} + \text{PCl}_5 \rightarrow \text{R-Cl} + \text{POCl}_3 + \text{HCl} .

Similarly, carboxylic acids react with PCl5\text{PCl}_5 to form acyl chlorides (R-COCl\text{R-COCl}). While concentrated hydrochloric acid (HCl\text{HCl}) can replace the -OH\text{-OH} group of primary and secondary alcohols in the presence of a ZnCl2\text{ZnCl}_2 catalyst , it cannot replace the -OH\text{-OH} group of carboxylic acids. Therefore, phosphorous pentachloride is the correct general reagent for both.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Haloalkanes and Haloarenes. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYHaloalkanes and Haloarenestextohalcoholcarboxylicreplacedtextcl

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