Combustion synthesized La2O3 and La(OH)3: Recyclable catalytic activity towards Knoevenagel and Hantzsch reactions

Combustion synthesized La<inf>2</inf>O<inf>3</inf> and subsequently produced La(OH)<inf>3</inf> are characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and Brunauer-Emmitt-Teller (BET) methods. The basicity of La<inf>2</inf>O<inf>3</inf> and La(OH)<inf>3</inf> is utilized for Knoevenagel and Hantzsch reactions. Reaction of aldehydes with suitable substrates containing active methylene groups led to Knoevenagel and Hantzsch products in good to excellent yields in organic solvents, water and under dry or solvent free conditions. Catalytic activity remains unchanged even after multiple (nine) cycles. Detailed mechanistic investigation using the simple adsorption reveals the prevalence of Eley-Rideal type adsorption where only one of the reactants is adsorbed for the reaction.