Skip to content
qorganica.es qorganica.comOrganic Chemistry made transparent Course map Español

SolutionsFriedel-Crafts Acylation

1. Acylations

Predict the outcome of the following reactions:

Benzene with AlCl₃ and isobutyryl chloride, fumaryl chloride, benzoyl chloride, maleyl chloride and glutaric anhydride
Products: isobutyrophenone; 1,4-diphenylbut-2-ene-1,4-dione; benzophenone; 1,4-naphthoquinone; 5-oxo-5-phenylpentanoic acid, with the mechanism of the anhydride opening

Fumaryl chloride (trans) acylates two benzene molecules; maleyl chloride (cis) has both acyl groups on the same side and acylates the same ring twice, closing 1,4-naphthoquinone. The cyclic anhydride opens and gives a keto acid.

2. No rearrangements

The reaction of 1-chloropropane with benzene catalyzed by AlCl3 gives isopropylbenzene and not propylbenzene. On the other hand, isobutyl chloride under the same conditions gives tert-butylbenzene instead of 1-phenyl-2-methylpropane. Why? How could propylbenzene and 1-phenyl-2-methylpropane be obtained?

1-Chloropropane and isobutyl chloride alkylate benzene with rearrangement to give isopropylbenzene and tert-butylbenzene
Acylation with propanoyl or isobutyryl chloride and reduction of the ketone: propylbenzene and isobutylbenzene

Primary carbocations rearrange to the more stable secondary or tertiary ones before reacting. Acyl cations, stabilized by the oxygen, do not rearrange: benzene is acylated and the ketone is then reduced to CH2 (Clemmensen, with Zn(Hg)/HCl, or Wolff-Kishner).

← Back to the exercises