DL-Carnitine → (-)-Carnitine

Participants

Reaction Conditions

Reaction Steps

To a mixture of (S)-carnitine inner salt (100 g; 0.62 moles) in glacial CH3COOH (100 g) 100% HNO3 is added (117.2 g; 1.86 moles) keeping the temperature at 10° C. and in the space of 1 hour and 5 minutes. Then, the temperature was lowered to 0-5° C. and acetic anhydride was added (76 g; 0.744 moles) in 2 hours and 10 minutes. After keeping the reaction mixture cool (3-5° C.) for further 3 hours from the end of addition, the reaction mass was left at 5° C. overnight. The following morning, temperature was left to rise up to 19° C. and ethyl acetate was added (835 ml) to precipitate nitriloxy-carnitine nitrate. After stirring the suspension for 30′, it was filtered washing with ethyl acetate (330 ml). The wet solid on the filter (164,6 g) was dissolved in water (760 ml) and NaHCO3 (94.53 g; 1.125 moles) was added to the solution. Temperature was kept at 80° C. for 9 hours, the solution was diluted with water (760 ml) and passed through IR 120 (H+) (1320 ml) with the purpose to block carnitine. After washing with water, to completely eliminate acidity, elution was made with 1N NH3 and the ammonia solution was concentrated and eliminated with an azeotrope with isobutyl alcohol, giving (R)-carnitine inner salt, having an enantiomeric excess higher than 98% (70.8 g; yield 70.2%).

Provenance & Evidence