Q54 / 180 · COMEDK 2025 (10 May Shift 1) · Chemistry
Identify the final product $[Z]$ formed when Chlorobenzene undergoes the given series of reactions:
- Correct answerA
- B
- C
- D
Solution
The reaction sequence begins with the Friedel-Crafts alkylation of chlorobenzene with methyl chloride in the presence of anhydrous $AlCl_{3}$. Chlorobenzene is ortho/para directing, and the para-isomer is the major product due to steric hindrance at the ortho position. Thus, $[W]$ is 1-chloro-4-methylbenzene (p-chlorotoluene).
Next, $[W]$ reacts with $Cl_{2}$ in the presence of UV light. This is a free-radical substitution reaction that occurs at the benzylic position. Therefore, $[X]$ is 1-chloro-4-(chloromethyl)benzene (p-chlorobenzyl chloride).
Then, $[X]$ reacts with alcoholic $KCN$ and heat. This is a nucleophilic substitution reaction where the benzylic chloride is replaced by a cyanide group, yielding $[Y]$, which is 2-(4-chlorophenyl)acetonitrile.
Finally, the hydrolysis of the nitrile $[Y]$ with excess dilute $HCl$ converts the $-CN$ group into a carboxylic acid group $-COOH$. Thus, the final product $[Z]$ is 2-(4-chlorophenyl)acetic acid, which corresponds to the structure shown in the first option.
Answer:
Next, $[W]$ reacts with $Cl_{2}$ in the presence of UV light. This is a free-radical substitution reaction that occurs at the benzylic position. Therefore, $[X]$ is 1-chloro-4-(chloromethyl)benzene (p-chlorobenzyl chloride).
Then, $[X]$ reacts with alcoholic $KCN$ and heat. This is a nucleophilic substitution reaction where the benzylic chloride is replaced by a cyanide group, yielding $[Y]$, which is 2-(4-chlorophenyl)acetonitrile.
Finally, the hydrolysis of the nitrile $[Y]$ with excess dilute $HCl$ converts the $-CN$ group into a carboxylic acid group $-COOH$. Thus, the final product $[Z]$ is 2-(4-chlorophenyl)acetic acid, which corresponds to the structure shown in the first option.
Answer:
Hence, the correct answer is option: 'A'.