Question

Which of the following would not give 2-phenylbutane as the major product in a Friedel-Crafts alkylation reaction with benzene?

• A. 1-butene + HF
• B. 2-butanol + $H_{2}S{O}_4$
• C. Butanoylchloride + $AlC{l}_3$ then $\text{Zn-Hg/HCl}$
• D. Butyl chloride + $AlC{l}_3$

Answer 1

Answer: (C)

The Friedal - crafts alkylation reaction will give propyl phenyl ketone which on further Clemmenson’s reduction will give butyl benzene.

${\text{C}}_{\text{6}}{\text{H}}_{\text{6}}\text{+}{\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{COCl}\stackrel{{\text{AlCl}}_{\text{3}}}{\to }{\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{COCH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{3}}\stackrel{\text{Zn-Hg/HCl}}{\to }\underset{\text{Butylbenzene}}{{\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{3}}}$

Rest other will give 2-phenylbutane as in them rearrangement of carbocation is possible.