The general procedure for the synthesis of (S)-2-hydroxybutyric acid from L-2-aminobutyric acid was as follows: (S)-2-aminobutyric acid (20.0 g, 194 mmol) was dissolved in 1N sulfuric acid solution (228 mL). Aqueous sodium nitrite solution (26.8 g, 338 mmol, 68 mL) was slowly added dropwise at -5 °C, and stirring of the reaction mixture was continued for 0.5 h after completion of the dropwise addition. Subsequently, the reaction mixture was warmed to room temperature and stirred continuously for 2 hours. Upon completion of the reaction, the mixture was cooled to 0 °C and sulfuric acid was added to adjust the pH to 1. After adjusting the pH, the mixture was stirred for 12 hours at room temperature. Next, sodium chloride (120 g) and methyl tert-butyl ether (MTBE, 120 mL) were added to the reaction mixture and stirred for 30 min before MTBE extraction. The organic layer was washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to afford (S)-2-hydroxybutyric acid (13.8 g, 69% yield) as a pale yellow solid. The product was characterized by 1H NMR (400 MHz, CDCl3), δ 1.00 (t, J=7.6 Hz, 3H), 1.68-1.79 (m, 1H), 1.84-1.93 (m, 1H), 4.24 (dd, J=6.8,4.4 Hz, 1H).
