Abstract
Dehydrative Friedel–Crafts acylation reaction of aromatic compounds with carboxylic acids as acylating agents was investigated in the presence of Lewis acid- or Brønsted acid-catalyst. Various metal triflates and bis(trifluoromethanesulfonyl)amides showed catalytic activity at high temperature, among which Eu(NTf 2) 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 °C. Bi(NTf 2) 3 was more effective than Eu(NTf 2) 3 at lower temperature, but proved to be hydrolyzed in the presence of a small amount of water to give HNTf 2 and [Bi 6O 4(OH) 4(H 2O) 6](NTf 2) 6. The structure of the latter compound was confirmed by a single crystal X-ray analysis. Among five Brønsted acids, HOTf, HNTf 2, HCTf 3, TsOH, and Nafion ® SAC-13, HNTf 2 has proved to be the most efficient catalyst and more effective than Eu(NTf 2) 3 for the acylation of p-xylene with heptanoic acid at 220 °C or lower temperature. HNTf 2 catalyzed the acylation of anisole with carboxylic acids in high yields in refluxing toluene with azeotropic removal of water.
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