1-Amino-8-hydroxynaphthalene-2,4-disulfonic acid [82-47-3]. (4-amino-5-hydroxynaphthalene-1,3-disulfonic acid), Chicago acid, 2 S acid, C10H9NO7S2, Mr 319.3, and its acid sodium salt are readily soluble in water; the latter can be salted out with sodium chloride. In alkaline solution, coupling with diazo compounds takes place ortho to the hydroxyl group. Alkaline hydrolysis at 170℃ gives 1,8-dihydroxynaphthalene-2,4-disulfonic acid. Heating with dilute sulfuric acid results in desulfonation to give 1-amino-8-hydroxynaphthalene-2-sulfonic acid.
Chicago acid is used as a coupling component for C.I. Direct Blue 1, C.I. Direct Blue 22, and C.I. Direct Blue 76 (the dicopper complex of demethylated).
A solution of the disodium salt of naphthosultam-2,4-disulfonic acid is concentrated and mixed with potassium hydroxide liquor at 130℃. The temperature is raised to 155℃ over 20 h to complete the reaction. After being cooled and diluted with water, the melt is run into excess hydrochloric acid and the monopotassium salt is collected by filtration at 30℃ and slurry washed with recycling of the wash liquors. A yield of 87 % is obtained.
