Potassium exchanged zirconium hydrogen phosphate Zr(O3POK)(2): a heterogeneous basic catalyst for Knoevenagel reaction without solvent

A simple work-up to prepare crystalline potassium exchanged zirconium hydro gen phosphate Zr(O3POK)(2) is proposed. In addition the synthesis of amorph ous potassium exchanged zirconium hydrogen phosphate Zr(O3POK)(2), obtained from an amorphous sample of Zr(O3POH)(2).H2O is reported. All these exchan ged materials Zr(O3POK)(2) are powerful catalysts for the Knoevenagel react ion. Furthermore the absence of solvent increases the rate of the reaction. Products can be separated from the catalyst by sublimation thus avoiding t he use of solvent in the purification step. The catalyst, which is thus eas ily recovered, shows no appreciable loss of activity when recycled three ti mes.