Abstract: Cinnamic acid was prepared by Knoevenagel method with KF/K₂CO₃/γ-Al₂O₃ as catalyst and benzaldehyde and propanedioic acid as starting materials under assistance of ultrasonic irradiation.IR,¹H NMR and elemental analysis were used to characterize the product.The effects of catalyst dosage,molar ratio of benzaldehyde and propanedioic acid,ultrasonic irradiation power and irradiation time on the yield of cinnamic acid were studied.The results showed that KF/K₂CO₃/γ-Al₂O₃ catalyst displays good catalytic activity under ultrasonic irradiation.The optimal reaction conditions are as follows:for benzaldehyde 20.4 mL (21.2 g,0.2 mol),n(benzaldehyde)∶n(propanedioic acid)=1∶1.10,KF/K₂CO₃/γ-Al₂O₃ dosage 4.5 g,ultrasonic irradiation power 120 W,ultrasonic irradiation time 60 min;and the yield of cinnamic acid reaches higher than 95%.

Key words: cinnamic acid, ultrasonic irradiation, catalytic synthesis