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

Abstract

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