Comparison of solid acid catalysts in the production of ethyl β-naphthyl ether (neroline) by ethoxylation of β-naphthol Original Research Article

The mesoporous molecular sieves Al-MCM-41 with Si/Al ratios equal to 21, 42 and 83 were synthesized under hydrothermal conditions using cetyltrimethylammonium (CTMA+) surfactants as template in the absence of auxiliary organics. The same ratios of Al-MCM-41 materials were impregnated using sulfuric acid; the materials are sulfated Al-MCM-41 (SO42−/Al-MCM-41). The mesoporous SO42−/Al-MCM-41 materials were characterized using several techniques, e.g. CP–AES, Nephelometer, XRD, FTIR, thermogravimetric–differential thermal analysis (TG/DTA), 27Al-MAS-NMR, nitrogen adsorption and pyridine acidity (TPD and FTIR) measurements. Crystallinity, surface area, pore diameter and pore volume of SO42−/Al-MCM-41 decreased on expelling the aluminum from the Al-MCM-41 framework and the Lewis acidity increased. The Bronsted, Lewis acidity and total acidity of the SO42−/Al-MCM-41 materials were determined by FTIR-pyridine and TPD-Pyridine acidity measurements. The catalytic results were compared with those obtained by using Al-MCM-41, sulfuric acid, amorphous silica-alumina, H-β, USY and H-ZSM-5 zeolites. The SO42−/Al-MCM-41 catalysts were found to be more effective in the ethoxylation of hydroxyl biaromatics, for example, in the production of ethyl β-naphthyl ether (neroline) from β-naphthol using ethyl acetate as the ethoxylating reagent. The SO42−/Al-MCM-41 catalyst exclusively forms the product of ethyl β-naphthyl ether and has much higher selectivity than any other catalysts except USY.