Question

When hydrochloric acid gas is treated with propene in presence of benzoyl peroxide, it gives

• A. 2-chloropropane
• B. alkyl chloride
• C. no reaction
• D. n-propyl chloride

Answer 1

The Correct Option is A

To solve this question, we need to consider the chemical reaction between hydrochloric acid (HCl) gas and propene in the presence of benzoyl peroxide.

Concept: This reaction involves an addition mechanism where the Markovnikov rule and anti-Markovnikov rule in organic chemistry guide the process.

1. Propene (CH₂=CH-CH₃) is an alkene, and when subjected to an addition reaction with HCl, the H⁺ from HCl adds to one carbon of the double bond, and the Cl^- adds to the other.
2. The presence of benzoyl peroxide initiates a radical mechanism. Typically, benzoyl peroxide is a free radical initiator that can lead to anti-Markovnikov addition, but in the presence of HCl without free radicals derived from peroxides like hydrogen peroxide or UV light, it usually adheres to the common ionic addition pathway.
3. In a regular ionic mechanism (Markovnikov addition), the H⁺ ion from HCl adds to the less substituted carbon atom of the double bond in propene (CH₂=CH-CH₃), leading to a more stable carbocation on the more substituted carbon atom.
4. Thus, the Cl^- ion then adds to this carbocation, producing 2-chloropropane (CH₃-CHCl-CH₃).

Explanation of Options:

• 2-chloropropane: As explained, this is the product of the Markovnikov addition of HCl to propene in the presence of benzoyl peroxide.
• Alkyl chloride: This is a general term and not specific; hence it is not the correct specific answer.
• No reaction: This is incorrect as the reaction actually proceeds as detailed.
• n-propyl chloride: This would be the product if Cl added in an anti-Markovnikov fashion without the intervention of typical peroxide mechanisms.

Conclusion: The presence of benzoyl peroxide does not alter the course of a typical ionic addition of HCl to alkenes, resulting in the formation of 2-chloropropane, following the Markovnikov addition pathway.