Synthesis
Currently, the domestic production process for (R)-(-)-2-(2,5-dihydrophenyl)glycine involves mixing 1500–1700 L of liquid ammonia with 300–400 L of water and cooling the mixture (using an ammonia compressor or vacuum pump to create a vacuum) to below -30 °C. Then, 40 kg of D(-)-phenylglycine is added, followed by 22–32 kg of metallic sodium in batches. The reaction is carried out at a temperature below -15 °C for at least 1 hour. After the reaction, the liquid ammonia is recovered, and the mixture is decolorized at 30–50 °C for at least 30 minutes. After filtration, the pH is adjusted to 6.5–6.8 with hydrochloric acid at a temperature below 35 °C. The mixture is then cooled to below 15 °C, centrifuged, washed with purified water, and dried using a wet product airflow dryer.
