p-[4,5-dihydro-4-[(2-hydroxy-5-methyl-3-nitrophenyl)azo]-3-methyl-5-oxo-1H-pyrazol-1-yl]benzenesulphonic acid

4-[[4,5-Dihydro-4-[(2-hydroxy-5-methyl-3-nitrophenyl)azo]-3-methyl-5-oxo-1H-pyrazol]-1-yl]benzenesulfonic acid