Synthesis of 2-acetyl-6-methoxynaphthalene using mesoporous SO ₄^2-/Al-MCM-41 molecular sieves

The mesoporous molecular sieves Al-MCM-41 with Si/Al ratio equal to 16, was synthesized under hydrothermal conditions using cetyltrimethylammonium bromide (CTMA⁺Br^-) as surfactant. The SO42-/Al-MCM-41(Si/Al = 16) material was synthesized using sulfuric acid under impregnation method, and the resulting material is sulfated Al-MCM-41 (SO42-/Al-MCM-41). The mesoporous materials viz. Al-MCM-41 and SO42-/Al-MCM-41 were characterized using several techniques e.g. ICP-AES, Nephelometer, XRD, FT-IR, TG/DTA, N₂- adsorption, solid-state-NMR, SEM, TEM and TPD-pyridine. By impregnating of sulfuric acid on silica surface, crystallinity, surface area, pore diameter and pore volume of SO42-/Al-MCM-41 decreased except wall thickness. While the Lewis acidity is increased because of the expelling aluminum from the Al-MCM-41 framework by impregnating sulfuric acid. The SO42-/Al-MCM-41 has been used for synthesis of 2-acetyl-6-methoxynaphthalene using 2-methoxynaphthalene with acetic anhydride as acylating agent and 1,2-dichloroethane as solvent. The catalytic results were compared with those obtained using 0.8 N sulfuric acid, amorphous silica-alumina, H-β, USY and H-ZSM-5 zeolites. From the catalytic results it was concluded that the conversion of 2-methoxynaphthalene and selectivity of 2-acetyl-6-methoxynaphthalene in the SO42-/Al-MCM-41 is higher than that in other catalysts due to higher number of Lewis acid sites. Thus the SO42-/Al-MCM-41 is found to be a highly active and recyclable heterogeneous catalyst while the catalyst is a very suitable for the synthesis of 2-acetyl-6-methoxynaphthalene.