Benzofuran, acylation with zeolites

Y zeolites also show promising activity in the acylation of heterocyclic compounds. Acylation of benzofurans by AAN was extensively studied, and some good S mthetic results have been achieved. Benzofuran and 2-methylbenzofuran undergo acylation with AAN under mild conditions, giving 2-acetylbenzofuran 13 and 2-methyl-3-acetylbenzofuran 14 respectively, as the main products over Y(32) zeolite (Scheme 4.8). 

Acylation of heterocyclics on R-exchanged zeolites has been also reported. This is the case for the acylation of furan with acetic anhydride to form 2-acetylfuran Ce,B- and La,B-ZSM-5 catalysts (Lermer et al. 1987) or the acylation of substituted benzofuran (Amouzegh et al. 1995). 

The acylation of benzofuran by acetic anhydride was carried out in the presence of Y zeolites in the liquid phase (60°C, atmospheric pressure). It is shown that the reaction procedure has a significant influence on the activity of the catalyst. Deactivation takes place but the zeolite can be completely regenerated by reactivation in air. A reaction mechanism is proposed in which the acylium ion adsorbed on the zeolite reacts with non activated benzofuran. 

Dealuminated zeolites can be fairly active in the acylation of compounds like benzofutan although their performance depends very much on the reaction procedure. The reaction kinetics agree with a deal-type mechanism in which the adsorbed acylium ion reacts with a non activated benzofuran molecule. However, benzofuran seems to be strongly physisorbed on the zeolite as indicated by a cinetic order less than unity and a very slow reaction when it is introduced first on the catalyst. 

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