The reaction of 2-iminobenzimidazoline derivatives with chlorosulfuric acid

The reaction of 2-imino-1,3-dimethylbenzimidazoline and its N-substituted derivatives with chlorosulfuric acid is examined. It is shown that the reaction leads to the formation of the sulfonic acid in those cases where the hydrogen of the NH group is unsubstituted, or where the substituent possesses an electron-donor character. Sulfonyl chlorides are obtained only when the exocyclic nitrogen atom bears an electrophilic radical, which reduces the basicity of the guanidine moiety.