JEE MainChemistryHaloalkanes and Haloarenes
Which of the following sequences of reagents is most suitable for the conversion of p -xylene (1,4-dimethylbenzene) into 2-(p-tolyl)acetic acid?
Options
- A(i) Cl ₂/h (1 eq) (ii) KCN (iii) H ₃ O ^+/
- B(i) Cl ₂/ FeCl ₃ (1 eq) (ii) KCN (iii) H ₃ O ^+/
- C(i) Cl ₂/h (1 eq) (ii) AgCN (iii) H ₃ O ^+/
- D(i) KMnO ₄/ H ^+ (ii) SOCl ₂ (iii) KCN
Correct answer
A. (i) Cl ₂/h (1 eq) (ii) KCN (iii) H ₃ O ^+/
Step-by-step solution
To convert p -xylene to 2-(p-tolyl)acetic acid, one methyl group must be converted into a - CH ₂ COOH group. Step 1: Free-radical halogenation of the benzylic position using Cl ₂/h (1 eq) gives 1-(chloromethyl)-4-methylbenzene. (Using Cl ₂/ FeCl ₃ would incorrectly lead to electrophilic aromatic substitution on the ring). Step 2: Nucleophilic substitution with KCN replaces the chlorine atom with a cyanide group, forming 2-(p-tolyl)acetonitrile. (Using AgCN would yield an isocyanide instead). Step 3: Acidic hydrolys