Method for the preparation of ceftiofur sodium and its intermediates

The present invention relates to preparation of Ceftiofur acid of formula (I),and its pharmaceutically acceptable salts. The process includes the steps of(i) condensing an activated derivative ofwherein the activated derivative is selected from acid halides, mixed anhydrides and active amides, and wherein X represents halogen atom selected from chlorine and bromine, with silylated derivative ofwherein R represents p-methoxybenzyl, p-nitrobenzyl or diphenylmethyl in the presence of a solvent at -40° C. to 0° C. to produce(ii) cyclising (V) with thiourea in the presence of water miscible solvent and sodium acetate at room temperature to produce cephalosporin(iii) deesterifying (VI) to produce (I) using anisole/trifluoroacetic acid, phenol/trifluoroacetic acid or formic acid at 0° C. to 10° C. and, if desired,(iv) converting (I), to its pharmaceutically acceptable salt. The invention also relates to intermediates (V) and (VI)