2-Amino-4-sulfobenzoic acid is freely soluble in hot water, less soluble in cold water. The compound is obtained at a moderate yield by treating 4-methyl-3-nitrobenzenesulfonic acid with sodium hydroxide solution. This acid is used mainly in the manufacture of diazoamino compounds of the R-N=N-NH-R' type. As mixtures with naphthols these compounds have acquired importance as printing inks (Rapidogen dyes).
