35400-55-6

?1-Aminonaphthalene-6,8-disulfonic acid gives 5-amino-4-hydroxynaphthalene-2-sulphonic acid on fusion with 50 % potassium hydroxide at 200℃, but because the former is not readily available, a more convenient process is the desulfonation of K acid by boiling with zinc dust in aqueous sodium hydroxide solution.