Keto-pantoyllactone → (+-)-Pantolactone

Participants

Reaction Conditions

Reaction Steps

200 g (1.561 mol) of dihydro-4,4-dimethyl-2,3-furandione (ketopantolactone) and 600 ml of toluene were placed in a 1 liter stirring autoclave. After heating to 40° C. the air was removed from the autoclave by evacuation 5 times with a high vacuum pump (0.05-0.1 bar) and gasification with 10 bar of hydrogen each time. The temperature of the ketopantolactone solution was then adjusted to 35° C., the pressure was lowered to 0.5 bar and immediately 50 ml of the catalyst solution prepared in accordance with Example 1 were sucked in with the complete absence of O2. After pressurizing to 40 bar of hydrogen the mixture was hydrogented while stirring and at constant pressure (40 bar) at 35° C. for 1 hour and at 45° C. for 4 hours. After a total hydrogenation time of 5 hours the pale yellow hydrogenation solution was removed under pressure from the autoclave and the autoclave was subsequently rinsed 3 times with 100 ml of toluene each time. The combined toluene solutions were evaporated on a rotary evaporator at 60° C./17 mbar. The residue (210 g) was distilled at 130°-150° C. bath temperature and 12 mbar. There were obtained 201.6 g (99.3%) of R-(α-hydroxy-β,β-dimethyl-γ-butyrolactone (=R-(-)-pantolactone) with an optical purity of 90.7%. [α]D20 =-46.8° (c=3 in H2O).

Provenance & Evidence