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A stirred solution of anhydrous methylene chloride (200 ml) containing 2-(2-tritylamino-4-thiazolyl)-2-methoxyimino acetic acid (syn-isomer) (11.35 g; 0.0256 mole) and triethylamine (3.61 ml; 0.0256 mole), was cooled at 0° C. and phosphorus pentachloride (5.6 g; 0.027 mole) was added portionwise. After 15 minutes of stirring at 0° C. and 1 hour at room temperature, the mixture was evaporated under reduced pressure, taken up with anhydrous benzene, evaporated again in order to remove any trace of phosphorus oxychloride. This treatment was repeated twice (2×50 ml). The residue was suspended in 50 ml of anhydrous acetone; triethylamine hydrochloride was then removed by filtration. The acetone solution of 2-(2-tritylamino-4-thiazolyl)-2-methoxyiminoacetyl chloride thus obtained was dropped into a vigorously stirred ice-cooled solution of 7-amino-3-[(8-carboxy-6-tetrazolo[1,5-b]pyridazinyl)-thiomethyl]-3-cephem-4-carboxylic acid (10 g; 0.0232 mole) NaHCO3 (15 g) in a mixture of water and acetone (500 ml; 250 ml). The mixture was stirred for 30 minutes at 0°-5° C. and then for 90 minutes at room temperature, the undissolved matter was filtered off, the acetone was eliminated by evaporation under vacuum. The aqueous phase was brought to pH 2 with 8% HCl and extracted with ethyl acetate (3×400 ml), washed with aqueous sodium chloride, dried (Na2SO4) and evaporated to dryness. The residue was stirred with diethyl ether; after 20 minutes of stirring the white solid was filtered, washed with ether and dried thus giving 3-[(8-carboxy-6-tetrazolo[1,5-b]pyridazinyl)-thiomethyl]-7-[2-(2-tritylamino-4-thiazolyl)-2-methoxyiminoacetamido]-3-cephem-4-carboxylic acid. The above mentioned compound was added portionwise to a stirred hot (55° C.) solution of 50% formic acid (140 ml). Stirring and heating at the same temperature was maintained for 30 minutes and then the solid was filtered from the cooled mixture. The filtrate was evaporated to dryness under vacuum, leaving a residue. After complete removal of water and formic acid, followed by trituration with water, a solid was obtained. The crude product was crystallized from 50% ethanol to give 9.1 g (60%) of the title compound, which decomposed at 255° C.

1. customthe mixture was evaporated under reduced pressure
2. customevaporated again in order
3. customto remove any trace of phosphorus oxychloride
4. customtriethylamine hydrochloride was then removed by filtration