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 reaction sequence proceeds as follows:

Step (i) HBr, benzoyl peroxide: This is a free radical bromination of the benzylic position on the alkyl group of the benzene ring, forming \( C_6H_5-CH_2Br \) (benzyl bromide).

Step (ii) KCN: Nucleophilic substitution replaces the bromine atom with a cyanide ion (CN^-), yielding \( C_6H_5-CH_2-CN \) (benzyl cyanide).

Step (iii) Na(Hg), C₂H₅OH: This is a reduction reaction. The Clemmensen reduction typically converts carbonyls to methylene groups. As no carbonyl group is present, the cyanide group is unaffected. Therefore, the primary product remains \(C_6H_5-CH_2-CN \).

Consequently, the principal product is \( C_6H_5-CH_2-CN \), and option (3) is correct.