L-Phenylalanine → 3-Phenyllactic acid, (S)-

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A solution of 14 g (217 mmol) of sodium nitrite in 20 ml of water was added dropwise to a solution of 14 g (85 mmol) of L-phenylalanine in 100 ml of 1 N sulfuric acid at 0° C. over 3 hours, and the mixture was stirred overnight at room temperature. After extraction with three 100-ml portions of ethyl acetate, the organic phase was dried over sodium sulfate. The optical purity of (2S)-2-hydroxy-3-phenylpropionic acid in this extract was 93.0% ee. The solvent was distilled off under reduced pressure to give 12 g of crude (2S)-2-hydroxy-3-phenylpropionic acid. Further, this crude product was purified by recrystallization using 35 ml of ethyl acetate to give 7.5 g (yield 53%) of the desired (2S)-2-hydroxy-3-phenylpropionic acid. The proton concentration (normality) in the reaction of this comparative example was 1.0 mol/kg, the amount of the protonic acid was 1.2 equivalents (relative to L-phenylalanine), and the reaction temperature was 0° C. to room temperature.

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