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

ROMANELLI G.; AUTINO J. C.; VAZQUEZ PATRICIA; PIZZIO, L.; BLANCO, M.; CÁCERES, C.

APPLIED CATALYSIS A-GENERAL

Elsevier

Lugar: Amsterdam; Año: 2009 vol. 352 p. 208 - 213

0926-860X

Eleven examples of azlactones (4-benzylidene-2-phenyloxazolin-5-ones and 4-alkylidene-2-phenyloxazolin-5-ones) were prepared via an Erlenmeyer-type synthesis from aromatic aldehydes, hippuric acidand acetic anhydride was added to the hot solution as a dehydrating agent. Molybdophosphoric ortungstophosphoric acids supported on silica?alumina, obtained by the sol?gel method, catalyze thereaction. The prepared catalysts were characterized by X-ray diffraction and diffuse reflectancespectroscopy. The specific surface area of the catalysts was determined by the nitrogen adsorption/desorption at 196 8C technique, and the catalyst acidity was measured by potentiometric titration with nbutylamine.The heteropolyacid amount removed from the catalysts during the leaching with toluenewas lower than 1%. The products were obtained with high conversion and selectivity. The yields were inthe 87?96% range for the majority of the selected samples, with the exception of the azlactonessynthesized from 2-nitrobenzaldehyde and cyclohexanone, which gave yields in the 70?80% range. Thesame catalysts were used several times without appreciable loss of their catalytic activity. A rationalmechanism for the azlactone formation catalyzed by the supported heteropolyacid is proposed.