Over HBEA, liquid phase acetylation of 2-methoxynaphthalene (2-MN) by acetic anhydride leads directly to 1-acetyl-2-methoxynaphthalene (I), to 2-acetyl-6-methoxynaphthalene (II), and to a small amount of 1-acetyl-7-methoxynaphthalene (III). At a long contact time, isomer I undergoes deacylation into 2-MN and isomerisation into II and III. Isomerisation of I is much faster in the presence of 2-MN than in its absence, which suggests that this reaction occurs through an intermolecular transacylation mechanism. The transformation of isomer I with a deuterated methoxy group (OCD3) in the presence of 2-MN shows that isomer II results only from this mechanism whereas an intramolecular mechanism participates also in the formation of isomer III. (C) 2000 Academic Press.