Abstract: A process for preparing certain cephalosporin antibiotics, namely, cefotaxime, cefetemet, and ceftriaxone sodium comprising acylation of 7-amino-3-cephem-4-carboxylic acid derivatives with 2-mercapto-5-methyl-1,3,4-thiadiazolyl-(Z)-2-(2-aminothiazol-4-yl)-2-metho xyiminoacetate having the formula: ##STR1##

Abstract: A process for preparing a 2-chlorosulfinylazetidinone comprises heating in an inert organic solvent a penicillin sulfoxide ester, at a temperature between about 75.degree. C. and 140.degree. C., with an N-chlorohalogenating agent in the presence of a weakly basic N-alkali metal salt of a cyclic imide. The weakly basic N-alkali metal salt of a cyclic imide acts as an acid scavenger to bind the hydrogen chloride which is produced as a byproduct of the reaction. Preferably, the N-chlorohalogenating agent is N-chlorosuccinimide or N-chlorophthalimide, and the weakly basic N-alkali metal salt of a cyclic imide is the sodium or potassium salt of succinimide or phthalimide.