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Butanoic acid reacts with Red Phosphorus and Cl2 to give 2-chlorobutanoic acid. What type of reaction is this? CH3CH2CH2COOH + Red P + Cl2 -> CH3CH2CH(Cl)COOH

1. It is a Hell-Volhard-Zelinsky (HVZ) reaction
2. It is not a HVZ reaction
3. It is a simple substitution reaction only
4. It is an addition reaction

Correct answer: It is a Hell-Volhard-Zelinsky (HVZ) reaction

Solution

The reaction of a carboxylic acid with Cl2 in the presence of red phosphorus (or P + Cl2 generating PCl3) to give an alpha-chloro carboxylic acid is called the Hell-Volhard-Zelinsky (HVZ) reaction. Here butanoic acid is chlorinated at the alpha carbon to give 2-chlorobutanoic acid.

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