22.68 g of L-pyroglutamic acid (0.176 mol) and 29.70 g of vitamin B6 base (0.176 mol) were mixed thoroughly. The mixture remained a dry powder without becoming sticky. This powder mixture was placed in a 150 ml reaction flask, and then 40 ml of isopropanol containing 1.5 ml of deionized water (the isopropanol's specific gravity was 0.7851) was added with stirring. The mixture was stirred in a 35°C water bath for 2 hours and then allowed to stand at 35°C for 15 hours. The mixture was then filtered, and the resulting white solid was vacuum dried at 35°C for 4 hours. It was then ground finely, passed through an 80-mesh sieve, and vacuum dried again at 35°C for 5 hours to obtain 45.00 g of white solid. The product was metadoxine, with a yield of 85.9%.
