Catalytic activity of Keggin heteropolycompounds in the Pechmann reaction

Different heteropolycompounds were used as catalysts in the synthesis of coumarins from phenols and ethyl acetoacetate. Keggin heteropolyacids were supported on silica and the aluminium salts of these heteropolyacids were prepared. The catalytic activity using several phenols were determined and high yield of product was obtained in the case of 4-methyl-7-hydroxycoumarin, 4-methyl-5,7-dimethoxycoumarin and 4-methyl-7,8-benzocoumarin. The use of microwave radiation increases the reaction yield and mainly decreases the reaction time. ▪ Different heteropolycompounds were used as catalysts in the synthesis of coumarins from phenols and ethyl acetoacetate. The H 3PMo 12O 40 and H 3PW 12O 40 Keggin heteropolyacids were supported on different types of silica. On the other hand, the aluminium salts of these heteropolyacids and that of the H 4SiW 12O 40 acid were prepared. The specific surface area ( S BET), and the mean pore diameter of the obtained catalysts were estimated from the adsorption isotherms of nitrogen at 77 K. Their Fourier transform infrared spectra were recorded and their acidity was determined by potentiometric titration with a solution of n-butylamine in acetonitrile. The catalytic activity using several phenols such as resorcinol, 3,5-dimethoxyphenol, α-naphtol and β-naphtol were determined. High yield of product was obtained in the case of 4-methyl-7-hydroxycoumarin (80–95%), 4-methyl-5,7-dimethoxycoumarin (60–92%) and 4-methyl-7,8-benzocoumarin (90%). However, the 4-methyl-5,6-benzocoumarin yield was low. The use of microwave radiation as power source increases the reaction yield and mainly decreases the reaction time.