Effect of basic properties of MgO on the heterogeneous synthesis of flavanone

The effect of the surface basicity of MgO on the heterogeneous synthesis of flavanone from benzaldehyde and 2′-hydroxyacetophenone was examined through a series of MgO samples modified with different anions. CO2 temperature programmed desorption (TPD) was used to characterize the basic properties of these samples. The results indicate that basic sites with different strengths exist on the MgO surface. Introduction of different anions completely eliminates the weak basic sites (i.e., those desorbing CO2 in the 300–420 K range) and reduces substantially the number of medium strength sites (i.e., those desorbing CO2 in the 420–650 K range). In contrast, no substantial effect was observed – with the exception of the chloride-treated sample – on the stronger basic sites (i.e., those desorbing CO2 above 650 K). A strong correlation was observed between the number of basic sites of “medium” strength and the catalytic activity of these samples for the heterogeneous synthesis of flavanone. These sites are most likely involved in the activation of 2′-hydroxyacetophenone for the Claisen–Schmidt condensation with benzaldehyde, which represents the first step in the synthesis of flavanone.