To a 500 mL three-necked round-bottomed flask equipped with a stirrer was added 100 mL of deionized water, glyoxal (20 g, 0.345 mol, 1.00 eq., 50 mL of a 40 wt% aqueous solution) and urea (51.7 g, 0.862 mol, 2.50 eq.). The reaction mixture was heated to 90°C and stirred for 5 minutes. Concentrated sulfuric acid (4 mL) was slowly added dropwise over 5 minutes, and a white solid formed within 10 minutes after the drop was completed. Stirring of the reaction mixture was continued for 12 hours. Upon completion of the reaction, the mixture was cooled to room temperature and 50% aqueous sodium hydroxide was added dropwise until the pH was adjusted to 14. Stirring was stopped and the reaction mixture was cooled to 0°C. The suspension was separated by vacuum filtration through a Brinell's funnel and the solids were washed with cold water (2 x 500 mL). The solid was transferred to a Brinell funnel and dried under suction for 3 h. Subsequently, it was transferred to a 700 mL beaker and dried at 80°C for 16 h. Glycuronium (1) was obtained as an off-white powder in 45.0 g (0.304 mol, 92% yield). Melting point: 335.19°C; IR (cm^-1): 3182.5 (s), 1677.0 (s); 1H NMR (90 MHz, DMSO-d6): δ 7.13 (s, 4H, -NH), 5.23 (s, 2H, N-CH-N).
