Acetylation using reduced volume of acetic acid anhydride for synthesizing non-ionic X-ray contrast agents

This invention relates to an improved method for the synthesis of 5-acetamido-N,N'-bis(2,3-dihydroxypropyl)-2,4,6-triiodoisophthalamide ("Compound A"), an intermediate in the industrial preparation of non-ionic X-ray contrast agents. In particular, it relates to acetylation of 5-amino-N, N'-bis(2,3-dihydroxypropyl)-2,4,6-triiodo-1,3-benzenedicarboxamide ("Compound B") using a reagent and solvent mixture containing between about 1.5 and about 3.0 liter of acetic anhydride and acetic acid per kilogram of Compound B. Preferably, following the acetylation reaction, the reagent and solvent mixture is distilled for re-use.