Sonocatalysis and alkaline-doped carbons: an efficient method for the synthesis of chalcones in heterogeneous media

The Claisen-Schmidt condensation between benzaldehyde and acetophenone has been carried out for the preparation of chalcones. Two basic activated carbons (Na- and Cs-Norit) have been used as catalysts. The order of activity is Na-Norit < Cs-Norit. Chalcones have been synthesized by sonochemical irradiation. The effect of the ultrasound activation has been studied. Cs-doped carbon is presented as the optimum catalyst, giving excellent activity for this type of condensation. A substantial enhancing effect in the yield was observed when the carbon catalyst was activated under ultrasonic waves. This "green" method (combination of alkaline-doped carbon catalyst and ultrasound waves) has been applied to the synthesis of several chalcones with antibacterial properties achieving, in all cases, excellent activities and selectivities. 4′-Hydroxy and 4′-carboxy-chalcones have been prepared under mild conditions by sono-activation of the carbon catalyst. A comparative study under non-sonic activation has showed that the yields are lower in silent conditions, indicating that the sonication exerts a positive effect on the activity of the catalyst. Cs-Norit carbon catalyst can compete with the traditional NaOH/EtOH when the reaction is carried out under ultrasounds. The role of solvent in this reaction was studied with ethanol. High conversion was obtained in absence of solvent. The carbons were characterized by thermal analysis, nitrogen adsorption and X-ray photoelectron spectroscopy.