Friedel-Crafts acylation reaction using carboxylic acids as acylating agents

Dehydrative Friedel-Crafts acylation reaction of aromatic compounds with carboxylic acids as acylating agents was investigated in the presence of Lewis acid- or Bronsted acid-catalyst. Various metal triflates and bis(trifluoromethanesulfonyl)amides showed catalytic activity at high temperature, among which Eu(NTf2)(3) proved to be the most effective and efficiently catalyzed the acylation reaction of alkyl- and alkoxybenzenes with aliphatic and aromatic carboxylic acids at 250 degrees C. Bi(NTf2)(3) was more effective than Eu(NTf2)(3) at lower temperature, but proved to be hydrolyzed in the presence of a small amount of water to give HNTf2 and [Bi6O4(OH)(4)(H2O)(6])(NTf2)(6). The structure of the latter compound was confirmed by a single crystal X-ray analysis. Among five Bronsted acids, HOTf, HNTf2, HCTf3, TsOH, and Nafion (R) SAC-13, HNTf2 has proved to be the most efficient catalyst and more effective than Eu(NTf2)(3) for the acylation of p-xylene with heptanoic acid at 220 degrees C or lower temperature. HNTf2 catalyzed the acylation of anisole with carboxylic acids in high yields in refluxing toluene with azeotropic removal of water. (c) 2006 Elsevier Ltd. All rights reserved.