Reaction #1505

Reaction equation

trimethylene carbonate

acetic anhydride

L-Lactide

trimethylene carbonate

→

trimethylene carbonate

lactic acid

Solvents

water

Conditions

Workup

1. 1
   Otherequipped with a mechanical stirrer
2. 2
   workup.DISTILLATIONdistillation head
3. 3
   Temperaturethe temperature was raised to 140° C.
4. 4
   workup.DISTILLATIONto distill off water
5. 5
   TemperatureThe reaction was cooled to 80° C.
6. 6
   workup.STIRRINGThe solution was stirred at 80° C. overnight under a slow nitrogen
7. 7
   Otherpurge
8. 8
   OtherAfter 18 hours the remaining acetic anhydride and acetic acid were removed under vacuum
9. 9
   workup.DISTILLATIONAfter the acetic acid and acetic anhydride distillation
10. 10
    workup.ADDITION180 mL of tetrahydrofuran/water (85/15; v/v) was added
11. 11
    workup.STIRRINGwith stirring
12. 12
    Otherto drop to 60° C
13. 13
    workup.WAITAfter 15 min the reaction mixture was transferred to a round bottom flask
14. 14
    Otherthe tetrahydrofuran was removed under vacuum on a rotary evaporator
15. 15
    workup.ADDITIONChloroform (300 mL) was added
16. 16
    Extractionthe resulting solution was extracted twice with 150 mL of millipore water in a separatory funnel
17. 17
    Dryingdried with MgSO4
18. 18
    FiltrationThe mixture was filtered through a "d" fritted glass funnel
19. 19
    workup.DISTILLATIONthe solvent distilled from the oligomer by rotary evaporation
20. 20
    OtherFinal traces of solvents were removed under high vacuum (0.4 mmHg) on a Kugelrohr apparatus at 90° C.

Procedure

L-Lactide (85.07 g; 0.945 moles) and water (100 mL; millipore) were placed in a 1 L 3-neck flask equipped with a mechanical stirrer, distillation head, and a thermometer. The reaction mixture was warmed to 80° C. and stirred under nitrogen overnight. The flask was then placed under vacuum (aspirator, 7 mmHg) and the temperature was raised to 140° C. to distill off water. After 2 hrs trimethylene carbonate (8.51 g, 0.083 moles) was added. Two hours later a second portion of trimethylene carbonate (8.52 g, 0.083 moles) was added and the reaction was allowed to proceed for 3 more hours. The reaction was cooled to 80° C. and 120 mL of acetic anhydride was added. The solution was stirred at 80° C. overnight under a slow nitrogen purge. After 18 hours the remaining acetic anhydride and acetic acid were removed under vacuum. After the acetic acid and acetic anhydride distillation was complete, 180 mL of tetrahydrofuran/water (85/15; v/v) was added with stirring and the flask temperature was allowed to drop to 60° C. After 15 min the reaction mixture was transferred to a round bottom flask and the tetrahydrofuran was removed under vacuum on a rotary evaporator. Chloroform (300 mL) was added and the resulting solution was extracted twice with 150 mL of millipore water in a separatory funnel and then dried with MgSO4. The mixture was filtered through a "d" fritted glass funnel and the solvent distilled from the oligomer by rotary evaporation. Final traces of solvents were removed under high vacuum (0.4 mmHg) on a Kugelrohr apparatus at 90° C. to yield acetyl-oligo(L-lactic acid-co-trimethylene carbonate) with trimethylene carbonate n=1.6, lactic acid n=7.6, MN =974, and MW =1684.

Source