Effect of carbomethoxysulfanilic acid on the synthesis of certain sulfanilamide preparations

A series of sulfanilamide preparations, large-capacity preparations (etazole, sulfadimethoxine, sulfamonomethoxine, etc.) also among them, are manufactured using pyridine as the solvent at the stage of condensation of phenylurethylanesulfochloride (I) with the aminoheterocyclic component. If pure (recrystallized) (I) is used for this reaction, then the yields of carbomethoxy-substituted sulfanilamides (III) are very high and close to quantitative. If technical (dried) (I) is used, then yields of the corresponding condensation products are significantly lower and are not constant. We have established that one of the impurities in technical (I) is carbomethoxysulfanilic acid (II), which is not normalized and is not determined analytically by the existing standard for technical (I).