Question

Predict the major product $ P $ in the following sequence of reactions:
(i) HBr, benzoyl peroxide 
(ii) KCN 
(iii) Na(Hg), $C_{2}H_{5}OH$

• A. $C_6H_5-CH_2-CH_3$
• B. $C_6H_5-CH_2-NH_2$
• C. $C_6H_5-CH_2-CN$
• D. $C_6H_5-NH_2$

Hint:

In the presence of KCN, alkyl halides undergo nucleophilic substitution to form nitriles, which is a common reaction. The subsequent step does not affect the nitrile in this case.

Answer 1

The Correct Option is C

The sequence of reactions involves the following steps:

Step (i) HBr, benzoyl peroxide: This is a free radical halogenation reaction, where the alkyl group on the benzene ring undergoes bromination at the benzylic position due to the formation of free radicals, resulting in the product \( C_6H_5-CH_2Br \) (benzyl bromide).

Step (ii) KCN: The next step is the nucleophilic substitution of the bromine atom by the cyanide ion (CN^-), leading to the formation of \( C_6H_5-CH_2-CN \) (benzyl cyanide).

Step (iii) Na(Hg), C₂H₅OH: This is a reduction reaction (Clemmensen reduction), which typically reduces a carbonyl group (in this case, the nitrile group) to a methylene group (–CH₂–). However, since there is no carbonyl group here, this reaction doesn't affect the cyanide group. Hence, the major product remains as \(C_6H_5-CH_2-CN \).

Thus, the major product is \( C_6H_5-CH_2-CN \), and the correct answer is (3).