[NH2:1][C:2]1[CH:14]=[CH:13][C:5]([CH2:6][C@H:7]2[CH2:11][O:10][C:9](=[O:12])[NH:8]2)=[CH:4][CH:3]=1.[N:15]([O-])=O.[Na+].[OH-].[Na+]>O.Cl>[NH:1]([C:2]1[CH:14]=[CH:13][C:5]([CH2:6][C@H:7]2[CH2:11][O:10][C:9](=[O:12])[NH:8]2)=[CH:4][CH:3]=1)[NH2:15]A mixture of (S)-4-(4-aminobenzyl)-1,3-oxazolidin-2-one (100 gms) and concentrated hydrochloric acid (250 ml) in water (500 ml) was treated with an 50% aqueous solution of sodium nitrite (46 gms) at −5 to 10° C. Upon completion of the reaction, as monitored by TLC, the reaction mass was further treated with stannous chloride dihydrate (420 gms) dissolved in concentrated hydrochloric acid (500 ml) and water (544 ml) at −15 to 10° C. When the reaction was complete, as monitored by HPLC, the pH of the reaction mass was adjusted in the range of 2.0 to 6.0 by adding aqueous sodium hydroxide solution. The reaction mass was cooled and filtered to separate the solid. The aqueous layer was extracted with dichloromethane and further made alkaline in the pH range of 6.0 to 10.0 with aqueous sodium hydroxide. The mixture was cooled and filtered to give solid (S)-4-(4-hydrazinobenzyl)-1,3-oxazolidin-2-one (III), which was then suspended in isopropanol (420 ml) and converted to the hydrochloride salt by treatment with hydrogen chloride at reflux temperature to yield the hydrochloride salt of (S)-4-(4-hydrazinobenzyl)-1,3-oxazolidin-2-one (IIIa).
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