Acylation of phenol with acetic acid. Effect of density and strength of acid sites on the properties of MFI metallosilicates

Abstract The C-acylation of phenol with acetic acid was carried out over MFI aluminosilicates and gallosilicates with different Si/Al or Si/Ga ratios. The greater strength of the acid sites of aluminosilicates is confirmed with NH 3 TPD and with metaxylene isomerization. Whatever the sample phenol undergoes two main reactions: O-acylation into phenylacetate and C-acylation selectively into ortho-hydroxyacetophenone. While the rate of metaxylene isomerization depends only on the acidity of the MFI samples (density and strength of the acid sites) the rate of ortho-hydroxyacetophenone production is also determined by the diffusion path (characterized by the para/ortho xylene ratio). This effect of the diffusion path can be related to the strong adsorption of reactants and products on the acid sites of the zeolite pores. A slow deactivation is observed which can be attributed to the trapping in the zeolite pores of relatively simple secondary reaction products.