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To a solution of 165 g of d,l-phenylalanine in 1100 ml of 1 N sodium hydroxide was added simultaneously 1000 ml of 1 N sodium hydroxide and 146 g of benzoyl chloride over a period of 1 hr with maintenance of the temperature at 2°-5° C. After 3 hr at 5°-10° C., the solution was acidified to pH4 with 5 N hydrochloric acid. The precipitate was collected, washed with water and acetone and dried to leave 234.5 g (87%) of N-benzoyl phenylalanine, mp 185°-188° C. The material was mixed with 2000 ml of acetic anhydride and heated at 95°-100° for 45 minutes. The solvent was removed in vacuo to afford 222 g (100%) of the azlactone, m.p. 60° C.

1. customThe precipitate was collected
2. washwashed with water and acetone
3. customdried