4-hydroxy-3-[(2-methoxyphenyl)diazenyl]naphthalene-1-sulfonic acid
4-hydroxy-3-[(2-methoxyphenyl)diazenyl]naphthalene-1-sulfonic acid
A naphthalenesulfonic acid that is naphthalene-1-sulfonic acid carrying additional hydroxy and (2-methoxyphenyl)diazenyl substituents at positions 4 and 3 respectively. The sodium salt is the biological stain 'acid red 4'.