Acetylation of 2-methoxynaphthalene in the presence of beta zeolites: influence of reaction conditions and textural properties of the catalysts

The Friedel Crafts acetylation of 2-methoxynaphthalene (2-MN) in the liquid phase has been studied over three H-beta zeolite catalysts, featuring the same composition and acidity, but exhibiting different textural characteristics. The various catalysts led to significantly different yields of acetylated products, 1-acetyl-2-methoxynaphthalene (1-Ac-2-MN) and 2-acetyl-6-methoxynaphthalene (2-Ac-6-MN). On the basis of the relationship between the product yields and the textural characteristics of the samples, the formation of the two acetylated products has been assumed to occur at different locations: inside the micropores in the case of 2-Ac-6-MN and on the outer surface of the crystals in the case of 1-Ac-2-MN. The influences of the temperature of the reaction and of the polarity of the solvent have been also examined. Under our conditions, products were formed via parallel reactions whatever the temperature and no consecutive and secondary reactions occurred. An increase of the solvent polarity led to a decrease of both catalytic activity and 2-Ac-6-MN/1-Ac-2-MN yield ratio. Such a result has been explained by a competitive adsorption between solvent and reactants on the active sites, which is more pronounced in the micropores.