In the method of Example 1, 20 g of xylene, 62.7 g of methyl methacrylate (MMA, Aldrich), and 0.31 g of phenothiazine (PTZ) were added to a 500 mL flask equipped with a thermometer, a gas inlet, a charging port, a magnetic stirrer, and a five-plate distillation column. The mixture was purged by slowly passing dry air and heated to reflux. When the temperature of the reaction mixture reached 70°C, 2.81 g of dibutyltin oxide (Bu2SnO, Eurecat 9555, Crompton) was added. Heating was continued until the reaction mixture began to boil at 103 °C. 8.0 g of N,N-dimethyl-1,3-diaminopropane (DMAPA, BASF) was added rapidly. distillates began to be produced after 20 min, and the reaction mixture became clarified and free of insoluble catalysts within 30 min. Subsequently, 33.0 g of DMAPA was slowly added over a period of 3 h while the temperature of the reaction mixture was raised to 140 °C. The reaction mixture was then purified by a slow addition of 33.0 g of DMAPA. The distillate was collected. After the addition was completed, the reaction mixture was kept at 140-150 °C for 2 hours. A total of 20 g of methanol/methacrylate azeotrope was collected. Notably, a small amount of distillate was collected 30 min after DMAPA addition, indicating that the reaction was near completion. The remaining methyl methacrylate and xylene were removed by vacuum distillation until the temperature of the reaction mixture dropped to 135 °C at -17.5 inches Hg. A total of 29 g of distillate was collected, which could be recycled, and 74.2 g of residue remained in the reactor.HPLC analysis showed that the product contained 89.7% N-(3-dimethylaminopropyl)methacrylamide (DMAPMA) and 2.0% methacrylic acid, with 97.4% conversion of DMAPA (Example 1, Table 1). The method of Example 5 was similar to Example 1 , with the difference that more xylene was used as solvent and less dibutyltin oxide catalyst, and the addition of DMAPA was accomplished in 1.5 hours. Yields similar to Example 1 were obtained. In Example 12, 170.0 g of DMAPMA distillate from the above reaction containing a water insoluble organotin catalyst and 1300 ppm methacrylic acid (MAA) was mixed with 2 g of 25% NaOH and 0.05 g of phenothiazine. The mixture was vacuum distilled and the distillate was collected at 91-93 °C and -30.3 inches Hg. HPLC analysis yielded 105 g of pure DMAPMA (91% yield), which was free of water-insoluble material and contained MAA below the limit of detection (<10 ppm).
