Synergism of ultrasound and solid acids in intensification of Friedel–Crafts acylation of 2-methoxynaphthalene with acetic anhydride

Abstract

The Friedel–Crafts acylation of 2-methoxynaphthol is generally carried out by using highly polluting acids such as HF, AlCl₃, BF₃ which are used in more than stoichiometric quantities and are neutralized at the end creating large quantities of waste, corrosion problems and hazard. This paper discusses the use of acid treated clays such as K-10 and Filtrol-24 and cation exchange resins such as Amberlyst-36, Amberlyst-15 and Indion-130 as catalysts at 25 °C which have different acid strengths and pore size distributions. The activities were in the following order: Amberlyst-36>Indion-130>Amberlyst-15>K-10clay>Filtrol-24. In the presence of ultrasound, the activities were found to increase by more than a factor of 3 in the case of large porous resins than the clays. The selectivity to 1-acyl-2-methoxynaphthalene was found to remain the same. Utrasonics did not promote isomerisation or direct conversion to 6-acyl-2-methoxynaphthalene.