Hydrochloric Acid → Dihydrolipoic Acid

Participants

Reaction Steps

6,8-Bismercaptooctancoic acid: α-Lipoic acid (5.15 g, 25.0 mmol) was suspended in 125 mL of water and sodium bicarbonate (2.10 g, 25.0 mmol) added. The mixture was sonicated to generate the sodium salt. The resulting pale yellow solution was cooled in an ice bath and solid sodium borohydride (1.90 g, 50.0 mmol) added with stirring in small portions over 20 min. The solution was stirred at ice bath temperature another 30 min, and then at room temperature for 30 min. The cloudy solution was cooled in an ice bath, and the pH brought to about 1 by the slow addition of 2M hydrochloric acid. A vigorous evolution of hydrogen occurred as the excess sodium borohydride decomposed and an oily liquid separated. As much as possible the following operations were performed under nitrogen. The mixture was extracted with 3×50 mL of chloroform. The combined chloroform extracts were dried over magnesium sulfate, filtered and the solvent evaporated under reduced pressure at room temperature. The oil remaining was further dried under vacuum to remove the last traces of solvent. The 6,8-bismercaptooctanoic acid was isolated as a colorless oil weighing 5.2 g (100% yield). The product was stored at −20° under nitrogen.

Provenance & Evidence