Heterogeneous catalytic synthesis of flavanone

Flavanoids are tricyclic organic compounds that have recently attracted significant interest as fine chemical and pharmaceutical components. Flavanone is one of the basic members of the flavanoid family and is utilized in various syntheses of higher derivatized flavanoids. Currently, flavanone is produced via homogeneous catalytic routes. In our work, we have studied the heterogeneous synthesis of flavanone from benzaldehyde and 2-hydroxyacetophenone over MgO. This process takes place in two steps: the Claisen-Schmidt condensation of benzaldehyde and 2-hydroxyacetophenone to form 2′-hydroxychalcone and the subsequent isomerization of 2′-hydroxychalcone to flavanone. We have evaluated mass transfer effects in studies conducted with different catalyst particle sizes, catalyst loadings, and stirring rates and determined conditions for the operation of a batch reactor in the kinetic regime. Subsequently, kinetic measurements were made under these conditions. The results of these studies indicate that the rate of the Claisen-Schmidt reaction has a first order dependence on the concentration of both reactants. The isomerization of 2′-hydroxychalcone is also a first order reaction. Results from kinetic studies conducted using various solvents indicate a strong dependence of the rates, kinetic dependencies, and selectivities towards flavanone and 2′-hydroxychalcone on the solvent used. Among the different solvents tested, dimethyl sulfoxide (DMSO) resulted in a strong promoting effect on the synthesis of flavanone. Kinetic results obtained in the presence of DMSO indicate a fractional kinetic dependence for benzaldehyde, suggesting that significant adsorption of benzaldehyde takes place on the catalyst surface. Temperature dependent studies also show a significant decrease in the activation energy for the both reactions in the presence of DMSO. Complementary in situ FTIR studies were conducted in an effort to rationalize some of the kinetic results and elucidate elements of the surface reaction mechanism. Results from these studies suggest that the presence of DMSO results in sulfidation of the MgO surface and subsequent strengthening of the catalyst-benzaldehyde interaction.