Preparation of chlorinated pyridine sulfonic acid chloride derivatives from hydroxypyridine sulfonic acids and phosphorus trichloride/chlorine gas; useful as intermediates for drugs, e.g. torasemide

摘要

Preparation of chlorinated pyridine sulfonic acid chloride derivatives (I) comprises reaction of the corresponding hydroxypyridine sulfonic acids with phosphorus trichloride/chlorine gas, followed by removal of impurities by distillation, dissolution in an organic solvent and vacuum distillation. Preparation of chlorinated pyridine sulfonic acid chloride derivatives of formula (I) comprises reaction of the corresponding hydroxypyridine sulfonic acids of formula (II) with a mixture of phosphorus trichloride and chlorine gas. Chlorine gas is passed through a mixture of (II) and phosphorus trichloride at 70-90 deg C, and the temperature is increased to 100-120 deg C. The resulting phosphoroxy chloride and any excess phosphorus trichloride is distilled off and the residue is dissolved in an organic solvent and the mixture vacuum distilled to give (I).