(3R,6S)-3,6-dimethyl-1,4-dioxane-2,5-dione

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: When DL-lactic acid is used as a raw material, the crude lactide has a high meso-lactide content. When the crude lactide is gradually cooled, DL-lactide is precipitated and allowed to persist in the form of crystals in the molten meso-lactide phase and the whole crude lactide assumes a slurry state. The crude lactide in the slurry state is mixed with a substantially equal weight of water and the resultant mixture is immediately cooled to the vicinity of 30° C. for the purpose of preventing DL-lactide from undergoing hydrolysis and kept stirred at this temperature for a period in the range of 30 minutes to one hour, with the result that meso-lactide is dissolved in water and, at the same time, part of the dissolved meso-lactide undergoes hydrolysis. The crystals of DL-lactide are separated by filtration from the water phase and are dissolved in such an organic solvent as acetone or MIBK thereby recrystallizing therefrom to produce easily DL-lactide crystals of high purity. hydrolysis The crystals of DL-lactide are separated by filtration from the water phase are dissolved in such an organic solvent as acetone or MIBK thereby recrystallizing

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: Succinic anhydride is often a significant component of the intermediate-boiling impurities. Succinic anhydride can be separated from meso-lactide by washing the meso-lactide stream with a weakly basic aqueous phase. A suitable pH of the washing solution is in the range of from about 7.2 to about 11. This is believed to hydrolyze the succinic anhydride to form succinic acid. Some of the lactide may also be hydrolyzed to form mainly linear oligomers and possibly some lactic acid. The succinic acid is much more soluble in the basic aqueous phase than in the lactide phase, and will partition to the aqueous phase. The aqueous and organic phases are then separated to form a washed meso-lactide stream having a reduced level of succinic anhydride and perhaps other intermediate-boiling impurities. The washed meso-lactide stream can be recycled as described before. will partition to the aqueous phase The aqueous and organic phases are then separated