Mo and W heteropolyacid based catalysts applied to the preparation of flavones and substituted chromones by cyclocondensation of o-hydroxyphenyl aryl 1,3-propanediones Original Research Article

Cyclization reaction of substituted 1-(2-hydroxyphenyl)-3-aryl-1,3-propanediones to obtain flavones and 2-arylchromones was studied at 90 °C. Tungstophosphoric and molybdophosphoric acids were used as catalysts, both bulk or supported on silica by means of pore filling impregnation. These catalysts were washed with glacial acetic acid before being used. The characterization of the catalysts by FT-IR, DRS and XRD showed that the heteropolyacids present undegraded Keggin structure. Catalyst acidity was measured by means of potentiometric titration with n-butylamine. The washed catalysts present a higher number of acidic sites and a higher acidic strength than that of the support. The acidity of the supported catalysts based on molybdophosphoric acid was lower than that of those based on tungstophosphoric acid. Conversion to flavones and substituted chromones at different reaction times and molar ratios of heteropolyacid to initial ketone was evaluated. The desired products were obtained in all cases with high conversion and high selectivity, the conversion being higher for the bulk catalysts.