Dihydrolipoic Acid → alpha Lipoic acid

8.0 grams (0.038 mole) of 6,8-dimercapto octanoic acid were added to 1.54 grams (0.038 mole) of sodium hydroxide in 90 ml of water and the solution formed adjusted to pH 9 with dilute aqueous sodium hydroxide. The solution was extracted twice, each time with 30 ml of methyl tertiary butyl ether, the aqueous solution separated off and the residual ether removed in a vacuum. The solution was diluted with 200 ml of water, 7 mg of iron (III) sulfate added and oxygen led in with stirring at room temperture. After 2.5 hours the reaction solution had reached a pH of 12.4, the supply of oxygen was ended and the precipitated iron salt filtered off. The clear yellow solution was acidified with 10% hydrochloric acid at 5° C., to 10° C., further stirred for 1 hour at pH 1 and the precipitated crude product filtered off. The precipitate was washed with water, dried in a vacuum and recrystallized from ethyl acetate/hexane. After drying there were obtained 5.9 grams (75% of theory) of 1,2-dithiolane-3-pentanoic acid as yellow crystals having a melting point of 61° C. to 62° C.

1. customthe solution formed
2. extractionThe solution was extracted twice
3. customeach time with 30 ml of methyl tertiary butyl ether, the aqueous solution separated off
4. customthe residual ether removed in a vacuum
5. additionThe solution was diluted with 200 ml of water, 7 mg of iron (III) sulfate
6. additionadded
7. filtrationthe precipitated iron salt filtered off
8. customwas acidified with 10% hydrochloric acid at 5° C., to 10° C.
9. stirringfurther stirred for 1 hour at pH 1
10. customthe precipitated crude product
11. filtrationfiltered off
12. washThe precipitate was washed with water
13. customdried in a vacuum
14. customrecrystallized from ethyl acetate/hexane
15. customAfter drying there

ORD record

ord-1bf2dee881c547ac8266ebe59e14e576

Source dataset

uspto-grants-1987_11

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US04705867