Friedel–Crafts Acylation of Anisole Catalysed by H–Zeolite Beta of Crystalline Rice Husk Ash

Abstract

Kereaktifan zeolit H-Beta yang disintesis secara terus daripada abu sekam padi berhablur dengan berbagai-bagai nisbah SiO₂/Al₂O₃ gel dikaji dalam pengasilan Friedel-Crafts anisol dengan propionik anhidrida. Tindak balas dilakukan dalam reaktor kelompok pada berbagai-bagai suhu dan masa tindak balas untuk mendapatkan keadaan optimum. Hasil tindak balas yang dianalisis menggunakan kaedah gas kromatografi menunjukkan p-metoksipropiofenon adalah hasil utama di samping asid propionik sebagai hasil sampingan. Mangkin H-Beta daripada nisbah gel SiO₂/Al₂O₃ = 27 menunjukkan keaktifan tertinggi dengan peratus pertukaran anisol 88.9% dan kepilihan terhadap p-metoksipropiofenon 75.3%. Keadaan optimun pengasilan adalah pada suhu 100°C dalam masa 4 jam. Kajian menunjukkan mekanisme pengasilan adalah penukargantian elektrofilik aromatik yang dimangkinkan oleh tapak asid Brnsted daripada zeolit H-Beta. Kata kunci: beta zeolite; abu sekam padi; penghasilan Friedel-Crafts; anisol The reactivity of H-Beta zeolite, synthesised directly from crystalline rice husk ash in various SiO₂/Al₂O₃ gel ratios, was studied in the Friedel-Crafts acylation of anisole with propionic anhydride. Reactions were carried out in a batch reactor at various times and reaction temperatures in order to obtain the optimum acylation condition. Products identified by gas chromatography showed that p-methoxypropiophenone is the main product with propionic acid as the main side product. H-Beta catalyst from the SiO₂/Al₂O₃ = 27 gel ratio gave the highest activity, with anisole conversion of 88.9% and product selectivity toward p-methoxypropiophenone of 75.3%. The optimum acylation condition was taken at 100°C reaction temperature in 4 hour reaction. Study showed that acylation reaction follows the electrophilic aromatic substitution mechanism catalysed by Brnsted acid sites of H-Beta zeolite. Key words: zeolite beta; rice husk ash; Friedel-Crafts acylation; anisole