[O:1]=[C:2]([CH2:24][CH3:25])[CH2:3][C:4]([NH:6][C@@H:7]1[C:22](=[O:23])[N:9]2[C:10]([C:19]([OH:21])=[O:20])=[C:11]([CH2:14][O:15][C:16](=[O:18])[CH3:17])[CH2:12][S:13][C@H:8]12)=[O:5].C(O)(=O)C.[N:30]([O-])=[O:31].[Na+]>O>[OH:31][N:30]=[C:3]([C:2](=[O:1])[CH2:24][CH3:25])[C:4]([NH:6][C@@H:7]1[C:22](=[O:23])[N:9]2[C:10]([C:19]([OH:21])=[O:20])=[C:11]([CH2:14][O:15][C:16](=[O:18])[CH3:17])[CH2:12][S:13][C@H:8]12)=[O:5]To a solution of 6 g. of benzhydryl ester of 7β-(3-oxovaleramido)-3-acetoxymethylceph-3-em-4-carboxylic acid in 20 ml. of glacial acetic acid are added dropwise 1.54 g. of sodium nitrite dissolved in 15 ml. of water, and the mixture is stirred for 2 hours at ambient temperature. The mixture is then diluted with 500 ml. of ethyl acetate and washed 3 times with 100 ml. of an aqueous saturated sodium chloride solution. The organic phase is made anhydrous and evaporated to dryness and the residue is triturated with diethyl ether. 5.5 g. of benzhydryl ester of 7β-(2-hydroxyimino-3-oxovaleramido)-3-acetoxymethylceph-3-em-4-carboxylic acid melting at 56°-62° C. are obtained.
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