[CH2:1]([CH:3]1[CH:6]([CH2:7][CH2:8][OH:9])[NH:5][C:4]1=[O:10])[CH3:2].P([O-])([O-])([O-])=[O:12].[Na+].[Na+].[Na+].OP([O-])(O)=O.[Na+].[OH-].[Na+].[Mn]([O-])(=O)(=O)=O.[K+].S(=O)(=O)(O)O.S(S([O-])=O)([O-])(=O)=O.[Na+].[Na+]>O>[CH2:1]([C@@H:3]1[C:4](=[O:10])[NH:5][C@H:6]1[CH2:7][C:8]([OH:12])=[O:9])[CH3:2]A mixture of the crude 3-ethyl-4-[2(hydroxy)ethyl]-2-azetidinone (6.41 g) obtained according to step (g) above, sodium phosphate bibasic (5.5 g) and sodium phosphate monobasic (3.4 g) in water (65 ml) is stirred for 20 minutes at room temperature. The pH of the solution is brought to 6.6 by the gradual addition of 10% sodium hydroxide (4.6 ml). The temperature is lowered to 15° C. and potassium permanganate (9.92 g) is added. The reaction mixture is stirred at 15°-20° C. for 24 hours maintaining the pH in the range of 6.6-8.5 by the gradual addition of 10% sulfuric acid (4.6 ml). The mixture is cooled to 5° C. and the excess of potassium permanganate is reduced by adding dropwise a 3.3M sodium meta-bisulfite solution (about 1.5 ml). After removing manganese dioxide by vacuum filtration on Celite, the clear aqueous solution is saturated with ammonium sulfate, brought to pH 3.5 with 10% sulfuric acid, and extracted with ethyl acetate (90 ml followed by four 40-ml portions). The combined extracts are dried over magnesium sulfate and concentrated under reduced pressure at 35° C. to a small volume. Crystallization is allowed to proceed at room temperature and then for two days at 0° C. The precipitate is removed by filtration and dried under vacuum. The yield in crystalline trans-(±)-3-ethyl-4-oxo-2-azetidinacetic acid is 3.2 g (48%).
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