PROCESS FOR THE PREPARATION OF PHENYLENE-BIS-BENZIMIDAZOLE-TETRASULPHONIC ACID DISODIUM SALT AND A MIXTURE COMPRISING TEH SAME

摘要

Process for the preparation of phenylene-bis-benzimidazole-tetrasulphonic acid disodium salt by reacting o-phenylene-diamine with terephthalic acid and chlorosulphonic acid in the presence of strong acids of the kind such as herein described, characterized in that the reaction time is 10 to 15 hours, wherein the phenylene-bis-benzimidazole-tetrasulphonic acid obtained in the reaction is, in a first step, dissolved in water and treated with activated carbon, which is then separated off, and where the phenylene-bis-benzimidazole-tetrasulphonic acid disodium salt is precipitated out by adding sodium chloride and separated off and, in a second step, is again dissolved in water and again treated with activated carbon, which is then again separated off, where pure phenylene-bis-benzimidazole-tetrasulphonic acid disodium salt precipitates out of the filtrate by acidification and is then optionally also purified.