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1. α-Bromophenylacetic acid (7-1) (20 g, 93 mmol) was dissolved in anhydrous ethanol (150 mL) and concentrated hydrochloric acid (5 mL) was added slowly under magnetic stirring. After addition, the reaction mixture was heated to 50°C and refluxed overnight. 2. After the reaction was completed, the reaction solution was cooled to room temperature and concentrated under reduced pressure to obtain α-bromophenylacetic acid ethyl ester as a brown-yellow oil. 3. The resulting α-bromophenylacetic acid ethyl ester was directly dissolved in anhydrous ethanol (60 mL) and slowly added dropwise to a solution of ethylenediamine (11.18 g, 186 mmol) in anhydrous ethanol (90 mL) via a constant pressure dropping funnel. 4. After completion of the dropwise addition, sodium ethoxide (185 mmol) dissolved in anhydrous ethanol (60 mL) was added to the reaction solution, heated to reflux, and reacted for 16 hours. 5. Upon completion of the reaction, the reaction mixture was cooled and concentrated under reduced pressure to remove ethanol and excess ethylenediamine. 6. The concentrate was dissolved in water and extracted three times with ethyl acetate. The organic phases were combined, washed with saturated brine, dried over anhydrous magnesium sulfate, filtered, and the filtrate was concentrated under reduced pressure. 7. The concentrate was purified by column chromatography (eluent: CH2Cl2:MeOH:NH4OH = 20:1:0.2) to give 3-phenyl-piperazin-2-one (7-2) 5.736 g as a white solid in 35% yield.

[1] Patent: CN107174584, 2017, A. Location in patent: Paragraph 0028
[2] Patent: US2005/222166, 2005, A1. Location in patent: Page/Page column 13
[3] Archiv der Pharmazie, 2011, vol. 344, # 5, p. 320 - 332