How is 1-Ethyl-1H-benzimidazole-2-sulfonic acid (CAS: 90331-19-4) typically synthesized?

1-Ethyl-1H-benzimidazole-2-sulfonic acid is typically synthesized by the reaction of 1-ethylbenzimidazole with sulfur trioxide (SO3) in a suitable solvent. The reaction involves the generation of the corresponding sulfonic acid derivative. Common solvents include acetonitrile or methanol. The yield is generally high, and the reaction is performed under mild conditions to ensure selectivity and avoid over-acidification.