JEE MainChemistryHaloalkanes and Haloarenes
Identify the correct sequence of reagents to convert propylbenzene into 2-bromo-1-phenylpropane.
Options
- A(i) Br ₂ , h (ii) Alc. KOH, (iii) HBr, R-O-O-R, h
- B(i) Br ₂ , h (ii) Alc. KOH, (iii) HBr
- C(i) Br ₂ , FeBr ₃ (ii) Alc. KOH, (iii) HBr, R-O-O-R, h
- D(i) Br ₂ , h (ii) Aq. KOH, (iii) HBr, R-O-O-R, h
Correct answer
A. (i) Br ₂ , h (ii) Alc. KOH, (iii) HBr, R-O-O-R, h
Step-by-step solution
The conversion of propylbenzene to 2-bromo-1-phenylpropane requires three steps: Step 1: Free radical halogenation of propylbenzene occurs at the most reactive benzylic position. C ₆ H ₅ -CH ₂ -CH ₂ -CH ₃ Br ₂, h C ₆ H ₅ -CH(Br)-CH ₂ -CH ₃ (1-bromo-1-phenylpropane) Step 2: Dehydrohalogenation (E2 elimination) to form a conjugated alkene. C ₆ H ₅ -CH(Br)-CH ₂ -CH ₃ Alc. KOH , C ₆ H ₅ -CH=CH-CH ₃ (1-phenylpropene) Step 3: Anti-Markovnikov addition of HBr via the peroxide effect. The bromine radical attacks C2 to form