Acetylation of 2-methoxynaphthalene with acetic anhydride over a HBEA zeolite

Acetylation of 2-methoxynaphthalene (2MN) with acetic anhydride (AA) was ca rried our over a HBEA 15 zeolite (framework Si/Al ratio of 15) under the fo llowing conditions: batch reactor, 500 mg of zeolite, 35 mmol of 2MN and 7 mmol of AA, 4 cm(3) of solvent, temperature of 90 degrees C, 120 degrees C or 170 degrees C (generally 120 degrees C). In addition to acetic acid, the main reaction products are 1-acetyl-2-methoxynaphthalene (I) and 2-acetyl- 6-methoxynaphtalene (LI); 1-acetyl-7methoxynaphthalene (III) is formed in l ow amounts and 2-acetyl-3-methoxynaphthalene (IV) in trace amounts. I, whic h initially is preferentially formed, undergoes isomerization into II and I II and also deacylation afterwards, However, high yields into isomer II, wh ich is a precursor of the anti-inflammatory Naproxen, can be obtained by op erating at relatively high temperatures (greater than or equal to 170 degre es C) in the presence of a solvent of intermediate polarity such as nitrobe nzene. The solvent polarity has a significant effect on the reaction rates and on the selectivity to acetylation, isomerization and deacylation. Very polar solvents such as sulfolane, which compete with the reactant molecules for diffusion inside the zeolite micropores and for adsorption on the acid sites, reduce significantly the reaction rates. Low acetylation and isomer ization rates and high deacetylation rates are found with non-polar solvent s, such as 1-methylnaphthalene which cannot solvate the acylium ion interme diates. Adsorption experiments suggests that all the acetylmethoxynaphthale ne products are mainly formed inside the zeolite micropores. (C) 2000 Elsev ier Science B.V. All rights reserved.