Liquid-phase reaction of 2′-hydroxyacetophenone and benzaldehyde over SO3H-SBA-15 catalysts: Influence of microwave and thermal effects

The influence of both microwave and thermal effects has been investigated for sulfonic acid functionalized SBA-15 catalysts synthesized by direct, prehydrolysis and post synthetic approaches under microwave and hydrothermal conditions. The XRD patterns revealed that the catalysts synthesized under microwave offered hexagonal type where as catalysts synthesized under hydrothermal offered cubic Ia3d as well as hexagonal type mesoporous silica. FTIR spectra indicated that the thiol groups were completely converted to sulfonic acid groups. The sulfonic acid functionalized SBA-15 catalysts were applied to the liquid-phase reaction of 2′-hydroxyacetophenone and benzaldehyde in the absence of solvent under both microwave and thermal reaction. In the case of microwave catalysts, the microwave reaction gave higher conversion of 2′-hydroxyacetophenone with higher selectivity to substituted flavanone than thermal reaction due to the strong absorption of microwave. The prehydrolysis period of the catalysts increased with decreasing the conversion of 2′-hydroxyacetophenone. It was due to the non-uniform dispersion of functional groups as well as transport limitations of bulky products such as 2′-hydroxychalcone, flavanone and substituted flavanone.