A suitable synthesis of azlactones(4-benzylidene-2-phenyloxazolin-5-ones and 4-alkylidene-2-phenyloxazolin-5-ones)catalyzed by silica-alumina supported heteropolyacids

摘要

Eleven examples of azlactones(4-benzylidene-2-phenyloxazolin-5-ones and 4-alkylidene-2-phenylox-azolin-5-ones)were prepared via an Erlenmeyer-type synthesis from aromatic aldehydes,hippuric acid and acetic anhydride was added to the hot solution as a dehydrating agent.Molybdophosphoric or tungstophosphoric acids supported on silica-alumina,obtained by the sol-gel method,catalyze the reaction.The prepared catalysts were characterized by X-ray diffraction and diffuse reflectance spectroscopy.The specific surface area of the catalysts was determined by the nitrogen adsorption/ desorption at 196°C technique,and the catalyst acidity was measured by potentiometric titration with n-butylamine.The heteropolyacid amount removed from the catalysts during the leaching with toluene was lower than 1%.The products were obtained with high conversion and selectivity.The yields were in the 87-96% range for the majority of the selected samples,with the exception of the azlactones synthesized from 2-nitrobenzaldehyde and cyclohexanone,which gave yields in the 70-80% range.The same catalysts were used several times without appreciable loss of their catalytic activity.A rational mechanism for the azlactone formation catalyzed by the supported heteropolyacid is proposed.