A facile 1,2 proton migration of chalcone epoxide using acid activated palygorskites

Different natural as well as modified palygorskite clays, Padappakkara blue (Kaolinite) and Zeolite 4A have been used to study the rearrangement of chalcone epoxide. Acid washed palygorskite clays have been identified as an excellent catalytic material for promoting a facile 1,2 proton migration of chalcone epoxide. The rearrangement of α-epoxyketone (chalcone epoxide) was found to yield E(−) enolic form of 1,3-diphenyl-1,3-propanedione indicating that the proton migration has taken place from the less favoured direction of the epoxide ring. It was observed that acid washed palygorskite gave higher yield of the compound. As the acidity and specific surface area of the clay increased, the rate of the reaction was found to increase. An attempt has been made to correlate the properties of the more active (4 M HCl activated) clay, an eco-friendly catalyst in the formation of the final product. 4 M HCl activated palygorskite clay catalysed a very high yield of 90% of E(−) enolic form of 1,3-diphenyl-1,3-propanedione. Raw palygorskite, Padappakkara blue clay as well as Zeolite 4A have no effect in the rearrangement of chalcone epoxide, even after increasing the epoxide/catalyst ratio to 1:1.