General procedure for the synthesis of D-mandelic acid and (2S,6S)-2,6-dimethylmorpholine from the compounds (CAS: 943344-44-3): the D-mandelic acid esters (R,S,S salts, 266.5 g, 1 mol) were dissolved in 20% sodium hydroxide solution (400 ml) and stirred for 1 hr at 50 °C to obtain a clarified solution. The bath temperature was then raised to 120°C and the released S,S-dimethylmorpholine was distilled azeotropically with water (100°C) by means of a distillation apparatus. After distillation of about 300 ml of condensate, the distillation receiver was cooled to room temperature and acidified with 10% HCl. The precipitated mandelic acid was extracted and dried under reduced pressure. Optical purity analysis showed complete racemization of D-mandelic acid. Solid NaOH was added to the distilled condensate to saturation, the organic phase was separated and diluted with methyl tert-butyl ether (MTBE, 200 ml). Subsequent extraction was carried out with MTBE (2 x 100 ml), the extracts were combined, dried with anhydrous sodium sulfate (Na2SO4) and concentrated by rotary evaporation. 101 g of crude product was obtained, which was fractionated under vacuum with a water jet pump. Pure S,S-dimethylmorpholine was obtained by distillation at 37-39 °C/14 mmHg in a yield of 88 g (based on 18% of the trans-dimethylmorpholine racemate used) as a clear oil. Specific optical rotation [α]D = -6.15° (pure, d = 0.94 g-cm-3). The optical purity of the isolated S,S-dimethylmorpholine was 97.9% ee based on GC analysis.
