Study On The Catalysts For Friedel-Crafts Acylation Reaction Of Fluorobenzene

The Friedel-Crafts acylation is one of the most important approaches to synthesize aromatic ketones and has been widely used in the production of fine chemicals and pharmaceutical intermediates. Fluorobenzene is a passivated benzene derivative which was inactive to Friedel-Crafts acylation. Therefore, the catalysts with very strong Lewis acid or Bronste acid are requisite for its Friedel-Crafts acylation.Anhydrous aluminium trichloride (AICl3) is a conventional catalyst to catalyze acylation and has a good performance for fluorobeneze acylation, but It has some serious disadvantages and should be replaced the solid acidic catalysts. We have prepared and used ZnO, Hβ,solid superacids (SO42-/Al2O3, SO42-/ZrO2,[P(W3O10)4]3-/Al2O3,[P(W3O10)4]3-/ZrO2), chlorids (AICl3, FeCl3, ZnCl2), supported AICl3on MCM-41and SiO2, trifluoromethanesulfonic acid (TfOH) and its rare earth(III) triflates (Re(OTf)3) as the catalysts for acylation of fluorobeneze with phenylacetyl chloride. The results show that only anhydrous AICl3exhibits the highest catalytic performance among these catalysts for this acylation, for instance, under the reaction conditions of phenylacetyl chloride100mmol, molar ratio of fluorobenzene and benzoyl chloride of1.1:1, molar ratio of catalyst and benzoyl chloride of1.1:1, this acylation occurred at20-25℃for2-2.5h, the selectivity and yield to para-product4-fluorobenzoacetophenone reached up to99%and68%, respectively.For solvent-free acylation of fluorobenzene with benzoyl chloride the catalytic performances of TfOH and Re(OTf)3catalysts were investigated. It was found that Re(OTf)3has a better promotion effect when smaller amount of TfOH is used as the main catalyst. Among10tested Re(OTf)3, La(OTf)3shows the best promoting catalytic performance. Under the reaction conditions of benzoyl chloride10mmol, molar ratio of fluorobenzene and benzoyl chloride2:1,0.30g La(OTf)3and5mol%TfOH, this acylation ocuured at140℃for4h, the selectivity and yield to para-product4-fluorobenzophenone reached up to99%and87%, respectively. After the acylation reaction was finished, La(OTf)3can be fully recovered after simple treatment and used repeatedly, and it activity is hardly decreased after reused5times.At the same time, the catalytic performance of the above composite catalyst was investigated for the acylation of benzene and its derivatives with benzoyl chloride. The results show that for the acylation of different benzene derivatives with benzoyl chloride over the TfOH and Re(OTf)3catalyst, the promoting catalysis of different elements Re(OTf)3is different, for instance, for the acylation of dimethylbenzene, Ce(OTf)3exhibits the best catalytic performance among the tested Re(OTf)3promoters.