Zirconium potassium phosphate methyl and/or phenyl phosphonates as heterogeneous catalysts for Knoevenagel condensation under solvent free conditions

Three different basic zirconium potassium phosphate methyl and/or phenyl phosphonates of general formula Zr(PO3OK)2-(x+y)(PO3Me)x(PO3Ph)y namely ZrKP-Me, ZrKP-Ph and ZrKP-MePh have been prepared as amorphous solids. The catalytic activity of the solids was tested in the Knoevenagel condensation between several aldehydes with malononitrile and ethyl cyanoacetate in solvent free condition at room temperature and 50 °C, respectively. The hydrophobic groups on the solid catalysts surface favour reagent diffusion toward the basic sites increasing the catalytic activity of the prepared solids compared to the complete inorganic layered zirconium potassium phosphate, Zr(KPO4)2.