Process for the preparation of phenylene-bis-benzimidazole-tetrasulfonic acid disodium salt

摘要

Phenylene-bis-benzimidazole-tetrasulfonic acid disodium salt which is largely free from impurities can be prepared by reacting o-phenylenediamine with terephthalic acid and chlorosulfonic acid in the presence of strong acids with a reaction time of 10 to 15 hours.