The general procedure for the synthesis of L-threonine from 5-(1-hydroxyethyl)urea (CAS:64420-00-4) is as follows: in a 1 L autoclave, 144 g (1 mol) of 5-(1-hydroxyethyl)urea, 68 g of 25% ammonia, 110 g of calcium hydroxide (1.5 mol), 500 g of water, and 50 mL of n-butanol were added in sequence. The mixture was heated to 160-170°C and the reaction pressure was maintained at 1.5-2.0 MPa for 4 hours. Upon completion of the reaction, the mixture was cooled to room temperature and the pH was adjusted by passing carbon dioxide to 8. The reaction mixture was filtered and the mother liquor was concentrated under reduced pressure. To the residue, 150 g of methanol was added and refluxed for 2 h. Crystals were precipitated after cooling. The crystals were collected by filtration, and the filter cake was dried under vacuum at 120°C for 4 h. 106.4 g of 2-amino-3-hydroxybutyric acid was obtained with a purity of 96% and a yield of 89.4%.
