Suspend 60 g of NaH (50% dispersed in mineral oil) in 200 mL of anhydrous benzene, heat to reflux and stir for 30 minutes. After cooling to 60°C, 2 mL of ethanol was slowly added dropwise. The reaction was continued for 2 hours after the dropwise addition was completed. Subsequently, a mixture of 2.5 mol of ethyl propionate and 1.0 mol of 2-butanone was added slowly dropwise to the reaction flask. After completion of the reaction, it was cooled to room temperature, 200 mL of water was added dropwise under nitrogen protection and the pH was adjusted to 7.0 with dilute hydrochloric acid. after standing and layering, the organic layer was separated and treated by adding 50 mL of acetic acid to it. The solvent was recovered by distillation under reduced pressure to obtain the crude 3,5-heptanedione. The crude product was dissolved in 200 mL of ethanol and a solution prepared from 55 g of copper chloride dissolved in 300 g of water was added to form a 3,5-heptanedione copper salt chelate. The blue chelate was collected by filtration, dissolved in 1000 mL of 20% sulfuric acid solution, and extracted three times with 500 mL of dichloromethane. The organic layers were combined, dried with anhydrous sodium sulfate, and the methylene chloride was recovered by distillation under reduced pressure to give a final 65.3 g of 3,5-heptanedione (boiling point: 174-175°C) with a purity of 97.3% (as determined by gas chromatography), and a yield of 49.6% as 2-butanedione.
