A suitable synthesis of azlactones (4-benzylidene-2-phenyloxazolin-5-ones

G. ROMANELLI; J.C. AUTINO; P. VA´ZQUEZ; L. PIZZIO; M. BLANCO; C. CA´ CERES

APPLIED CATALYSIS A-GENERAL

ELSEVIER SCIENCE BV

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 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 8C technique, and the catalyst acidity was measured by potentiometric titration with nbutylamine. 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. 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. 8C technique, and the catalyst acidity was measured by potentiometric titration with nbutylamine. 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.