Microwave-assisted acylation of aromatic compounds using carboxylic acids and zeolite catalysts

Abstract

Acylation of aromatic compounds with carboxylic acids smoothly proceeded at 190–230 °C in the presence of zeolite catalysts under microwave irradiation to give aromatic ketones efficiently. H–Y (SiO 2/Al 2O 3 = 30–80) and H–beta (25) zeolites were active for the acylation reaction, giving the aromatic ketones in good yields. Carboxylic acids such as hexanoic and butyric acid smoothly underwent the acylation, while propionic acid showed somewhat lower reactivity. Anisole gave the para-acylation products nearly selectively. Anisole, 2,3-dihydrobenzofuran, and thiophene were reactive aromatic compounds. 2,3-Dihydrobenzofuran also reacted at the para position to the oxygen atom predominantly to give the corresponding ketones as the major products. The microwave reactions were generally faster than the conventional oil bath reactions and gave higher yields of the acylation products. Activation energies for the reaction of anisole with butyric acid by microwave and by oil bath heating were also estimated on the basis of the Arrhenius plots.