Acetyl Propionyl CAS 600-14-6 | Look Chemical

Disadvantages of existing synthesis methods
The main synthesis methods of 2,3-pentanedione reported in the literature are: 1) Using hydroxyacetone and triacetaldehyde as raw materials, a heterogeneous reaction is carried out under the action of a phase transfer catalyst [1], with a mass yield of 85.0%, but the raw materials are expensive and the catalyst is difficult to recover; 2) Using 2-methylpentenone as raw material for ozonation reaction, the reaction selectivity is 96.9% and the mass yield is 66.9%, but the reaction conditions are very harsh, requiring deep cooling at -75 °C, and the product purification is difficult, causing serious environmental pollution; 3) Using 3-chloro-2-pentanone as raw material, the product is obtained through multi-step reactions. This method has a long route and a total yield of 39.1%; 4) Using acetaldehyde and propionaldehyde as raw materials, acyloin is prepared through 5-(2-hydroxyethyl)-3,4-dimethyl-1,3-thiazole salt catalyzed cross-coupling, and 2,3-pentanedione, 3,4-hexanedione and 2,3-butanedione mixture are obtained through oxidation, and then separated to obtain the product. The preparation method has a complex separation process and cumbersome operation; 5) Using lactic acid as raw material, it is prepared by base-catalyzed condensation, with a selectivity of 80.0% and a mass yield of 60.0%. This method is costly and polluting.

New synthesis method
The first step: Add 20g 60% sodium hydride and 132g methyl propionate to a 250L three-necked round-bottom flask with a magnetic stirrer, a thermometer and a reflux condenser (the upper part of the condenser is connected to a calcium chloride drying tube), stir and heat to 60℃ for 3h, change the reflux device to a distillation device, reduce the pressure to P=0.05MP and then slowly heat to 90℃ for 3h, and collect a total of 28g of fractions (gas chromatography analysis components are mainly methanol and methyl propionate). Cool to 20~25℃, slowly add 300g 10% acetic acid solution, stir for 10mi, let stand and separate, separate the organic layer, and extract the water layer with ethyl acetate (50mL×3). The organic layers were combined, washed with saturated sodium chloride solution to pH 7, dried with anhydrous sodium sulfate, the solvent and unreacted methyl propionate were recovered under normal pressure, and the 75~80℃/533.2P fraction was collected by vacuum distillation to obtain 56g of compound 2, with a purity of 98.2% and a yield of 77.8% according to gas chromatography analysis.

Step 2: Add 56g of compound 2 to a 1000L three-necked round-bottom flask with a magnetic stirrer, a thermometer and a dropping funnel, control the temperature at 0~5℃, slowly add 160g of 10% sodium hydroxide solution, control the temperature at 0~5℃ after the addition, slowly add 138g of 20% sodium nitrite solution to the solution, and continue stirring at 0~5℃ for 5 hours. Control the temperature ≤10°C, add 120g of 35% hydrochloric acid, and then quickly add 609g of 40% formaldehyde solution, slowly heat to 20°C and stir for 2 hours, let stand to separate the organic layer, and extract the water layer with ethyl acetate (50mL×2). Combine the organic layers, wash with 5% sodium bicarbonate solution until the pH is greater than 7, and wash twice with saturated brine. Recover the solvent under normal pressure, collect the 110~112°C fraction to obtain 21.8g of compound 4, i.e. 2,3-pentanedione, with a purity of 98.7% and a yield of 90.3% by gas chromatography.