反应详情

106 g of benzaldehyde are dissolved in 150 ml of toluene with 2 g of zinc acetate dihydrate and 1.5 ml of acetic acid in a stirred apparatus, under a nitrogen atmosphere. Ketene gas, which can easily be produced on a laboratory scale by splitting of diketene by means of heat (compare Houben-Weyl, Volume VII/4, page 80; and Org. Syntheses. Coll. Vol. V, page 679) is passed into this solution at 30° to 40° C. in the course of 3 to 4 hours. When 92 to 96% of the benzaldehyde has reacted, determined by analysis by gas chromatography, the addition of ketene is interrupted and the reaction mixture is subsequently stirred for a further brief period and transferred to a VA steel low-pressure autoclave. 4 g of 92% pure sodium hydroxide powder are added and the toluene and excess benzaldehyde are distilled off over a descending condenser into a receiver. The viscous, light-colored residue is then heated at 180° C. for 1 hour and, after cooling to about 100° C., the resulting reaction product is taken up in 700 ml of water and dissolved by adding 140 ml of 20% strength ammonia. After addition of about 20 g of active charcoal, the mixture is stirred at 60° to 70° C. for a further brief period and clarified by filtration and the filtrate is acidified with 30% strength hydrochloric acid until it gives a clearly acid reaction. Cinnamic acid thereby precipitates in white crystals, which are filtered off with suction, washed with a little acidified cold water and dried at 70° C. in a drying cabinet.