In a reactor equipped with a stirrer, 300 parts of methanol, 56 parts of a 50% aqueous solution of dimethylamine and 56 parts of 1,3-cyclohexanedione were added and the mixture was warmed up to 30 °C. A 37% aqueous solution of formaldehyde was added dropwise over a period of 1 hour. After addition, the reaction solution was maintained at 40°C for 3 hours. The unreacted 1,3-cyclohexanedione content was monitored by HPLC to confirm the reaction endpoint. Subsequently, 10 portions of 5% palladium-carbon catalyst were added to the reaction mixture and the reaction was carried out at 30°C and atmospheric pressure with hydrogen gas passed for 15 hours. The unreacted 2-dimethylaminomethyl-1,3-cyclohexanedione content was detected by high performance liquid chromatography to confirm the completion of the reaction. At the end of the reaction, the catalyst was removed by filtration at 30 °C, 300 parts of water were added to the filtrate, methanol was removed by distillation, and the residue was adjusted with 35% hydrochloric acid to pH 6. The precipitate was collected by filtration, washed with water and dried at 70 °C to give 54.8 parts of 2-methyl-1,3-cyclohexanedione as dry cake (yield: 87.0%). HPLC analysis showed that the purity of 2-methyl-1,3-cyclohexanedione in the dry cake was 97.2%. The melting point of the dried cake was 206°-208°C (literature value: 207°-209°C). FD-MS analysis showed that the dried cake had a peak at m/z 126, which was consistent with the theoretical molecular weight.
