Methanol was added to the 3L and 2L flasks, 257 g of sodium methanolate (1.852 mol) was dissolved in methanol and the temperature was maintained at 40 °C. A mixture of 118.1 g of acetone (2.036 mol) and 333.6 g of methyl formate (5.555 mol) was added dropwise to the reaction system at 40 °C for 4 hours. After the dropwise addition, stirring was continued for 1 h. Subsequent cooling to 20 °C gave 184 g of formalin acetone sodium salt (92% quantitative yield by HPLC using sodium methanol as standard). The resulting formalin acetone sodium salt was transferred to a necked down 3L reactor, methanol was added, and 6.2 g of sulfuric acid (0.063 mol) was added, keeping the temperature at 30 °C. The reaction solution of formylacetone was added to the reaction system simultaneously with 93.8 g of sulfuric acid (0.957 mol) dropwise at 30 °C or lower for 1 hour, during which the pH was maintained between 0-1. After completion of the dropwise addition, the mixture was continued to be stirred at the same temperature for 4 hours and subsequently cooled to 20°C. The pH was adjusted to 7-8 with 20% sodium hydroxide solution, the resulting salt was removed by filtration, and the distillate was collected by distillation to give a final 195.6 g of 4,4-dimethoxy-2-butanone (80.0% yield based on sodium methanol and 87.0% yield based on formalin acetone sodium salt).
