2-Aminonaphthalene-6-sulfonic acid [93- 00-5]. (6-aminonaphthalene-2-sulfonic acid), Bronner acid, C10H9NO3S, Mr 223.24, crystallizes from water as the monohydrate in plates although only 0.2 % soluble at 100℃. Sulfonation with 20 % oleum at 20℃ gives a mixture of 1,6- and 6,8-disulfonic acids.