Aniline-2,5-disulfonic acid is used as pharmaceutical intermediate. 2-Amino-1,4-benzenedisulfonic acid is used as an intermediate for dyes; 2-Amino-1,4-benzenedisulfonic acid is converted to triazine derivatives, which are intermediates in the manufacture of dyes and optical brighteners.
2-Amino-1,4-benzenedisulfonic acid is obtained by sulfonating metanilic acid in 100% sulfuric acid with 50% oleum at 160 ℃ (5 – 6 h); the sulfonation mixture is diluted with water, lime is added, and the resulting calcium sulfate is removed; the product is then precipitated with excess concentrated hydrochloric acid in hot solution; yield 90 – 91%
