Process for preparing carbamoyl pyridinium compounds

摘要

A process for synthesizing carbamoyl pyridinium compounds is described, in which the pyridine ring carries a sulfoalkyl group. The process comprises reacting a pyridine sulfonic acid with a carbamoyl chloride in the presence of a tert.-amine compound in a ketone solvent. The reactants are highly soluble in the ketone solvent, while, on the contrary, the carbamoyl pyridinium compounds and the tert.-ammonium halides formed by the reaction are not soluble in the ketone solvent and can be recovered from the reaction mixture. In a subsequent washing step with a selective solvent, for example in methanol in which carbamoyl pyridinium compounds are not soluble but tert.-ammonium halides are highly soluble, substantially pure carbamoyl pyridinium compounds can be obtained in high yields.