Benzazoles: IV. Reaction of 1,3-Dihydro-2H-benzimidazol-2-ones with Chlorosulfonic Acid

1,3-Dihydro-2H-benzimidazol-2-ones reacted with chlorosulfonic acid at 50–60°C to give 5-chloro­sulfonyl-1,3-dihydro-2H-benzimidazol-2-ones regardless of the reactant ratio (1:1 to 1:5). 5-Chloro-1,3-dihy­dro-2H-benzimidazol-2-ones failed to react with chlorosulfonic acid at 50–60°C, and the corresponding 5-chloro-6-chlorosulfonyl derivatives were obtained at 110–120°C.