1. 18.1g L-proline, 10ml water was added to the reaction flask and stirred. Add 16g of sodium hydroxide configured 0.1 mol/L alkaline solution adjusted to alkaline. Then 8g of (Boc)2O was added to react for I hour,then 8g of (Boc)2O was added to react for I hour and finally 9g of (Boc)2O was added to react for 3 hours.
2. The impurities were extracted three times with petroleum ether 1 ml/time. 3 mol/L hydrochloric acid was used to adjust PH=3 and then the product was extracted three times with ethyl acetate 0.5L/time. Combine the ester layers and wash with brine to neutral. Add 15 g of anhydrous sodium sulfate to dry for 6 hours.
3. Filter, filtrate concentrated dry under reduced pressure, add 50ml petroleum ether stirring crystallization. Centrifuged out the product and dried. Get product 26.3g. yield 93.57%.
