Hydrochloric Acid → Dihydrolipoic Acid

Participants

Reaction Steps

α-Lipoic acid (5.15 g, 25.0 mmol) was suspended in water (125 mL), and sodium bicarbonate (2.1 g, 25.0 mmol) was added. The mixture was stirred to produce a clear solution. The resulting pale yellow solution was cooled in an ice bath, and solid sodium borohydride (1.90 g, 50.0 mmol) was added, with stirring, in small portions over 20 min. The solution was stirred in an ice bath for another 30 min and then at room temperature for 30 min. The cloudy solution was cooled in an ice bath, and the pH was adjusted to 1 by slow addition of 2M hydrochloric acid. A vigorous evolution of hydrogen occurred as the excess sodium borohydride decomposed, and an oily liquid was seen to separate. The mixture was extracted with chloroform (3×50 mL). The combined chloroform extracts were dried over magnesium sulfate, filtered and the solvent evaporated under reduced pressure at room temperature. The remaining oil was further dried under vacuum to remove traces of solvent. 6,8-Bismercaptooctanoic acid was isolated as a colorless oil: 5.2 g (100%). The product was stored at −20° C. under nitrogen. 1H-NMR (CDCl3): δ 2.89 (m, 1H, S—C—H). 2.67 (m, 2H, S—CH2), 2.34 (t, J=7.1 Hz, 2H, CH2C(O)), 1.4-1.92 (m, 8H, (CH2)2), 1.33 (t, J=8.0 Hz, 1H, S—H), 1.30 (t, J=7.6 Hz, 1H, S—H).

Provenance & Evidence