Preparation
2,4-Diaminobenzenesulfonic acid and 2,4,6-Trichloro-1,3,5-triazine condensation, and again 3-Aminobenzenesulfonic acid condensation, and then diazo, and 2,5-Bichloro-4-(3-methyl-5-oxo-4,5-dihydropyrazol-1-yl)benzenesulfonic acid coupling, and finally hydrolysis.