Solid acid catalysed acylation of 2-methoxy-naphthalene: role of intraparticle diffusional resistance

Synthesis of fine chemicals and intermediates by using Friedel-Crafts acyla tions is important in organic chemical technology. In most of the cases ver y good yields and selectivity can be obtained with aluminium chloride as ca talyst in conjunction with nitrobenzene as solvent. However, with the curre nt environmental restrictions, replacement of aluminium chloride-nitrobenze ne pair with solid acid catalysts has great industrial relevance. Acylation of 2-methoxynaphthalene (2-MON), also known as yarayara, with acetic anhyd ride, was carried out using different solid acid catalysts such as zeolites , acid activated clays, ion exchange resins and sulphated zirconia. The pro ducts of the reaction are precursors for many organic and pharmaceutical pr oducts. The reaction products were isolated and confirmed by their melting points, H-1-NMR, gas chromatography, etc. A mathematical model is built to describe the kinetics of the reaction. At high molar ratios of acetic anhyd ride to 2-MON, the reaction is limited by intraparticle diffusion of the su bstrate 2-MON. However, this barrier is overcome for equimolar qualities. T he reaction proceeds through the Eley-Rideal type of mechanism, wherein the chemisorbed acetic anhydride generates a carbocation and acetic acid, and the carbocation reacts with 2-MON from the liquid phase within the pore spa ce to form 1-acetyl-2-methoxy-naphthalene. (C) 1999 Elsevier Science Ltd. A ll rights reserved.