To a suspension of 6.25 g of phosphorus pentachloride in 45 ml of anhydrous methylene chloride cooled at -10° C., is added 20 ml of anhydrous methylene chloride solution containing 2.4 g of pyridine and the mixed solution is stirred for 30 minutes. To the solution is dropwise added a solution of 9.3 g of 7β-(2-thienylacetamido)-3-(1-methyl-1H-tetrazol-5-ylthiomethyl)-3-cephem-4-carboxylic acid benzhydryl ester in 30 ml of anhydrous methylene chloride during 30 minutes under stirring and keeping at -20° C.--10° C. The mixture is further stirred for 2 hours at the same temperature and then cooled to -30° C.--20° C., followed by adding dropwise 56 ml of methanol. Thus obtained solution is stirred for 30 minutes, keeping the temperature of the solution between -5° C. and 5° C., and 60 ml of water is added dropwise thereto, followed by further stirring for 30 minutes. Methylene chloride layer is washed with saturated aq. NaCl solution and concentrated. To the concentrate is added a mixture of water and ethyl acetate under stirring to give 4.746 g of 7-amino-3-(1-methyl-1H-tetrazol-5-ylthiomethyl)-3-cephem-4-carboxylic acid benzhydryl ester as a crystal. Yield 64.0%.
