Synonyms: 2-Pyrazolin-5-one,4-(2-chloro-4-nitrophenylazo)-3-methyl-1-(tetrahydro-3-thienyl)-, S,S-dioxide(6CI); 3H-Pyrazol-3-one,4-[(2-chloro-4-nitrophenyl)azo]-2,4-dihydro-5-methyl-2-(tetrahydro-1,1-dioxido-3-thienyl)-(9CI); 3H-Pyrazol-3-one, 4-[(2-chloro-4-nitrophenyl)azo]-2,4-dihydro-5-methyl-2-(tetrahydro-3-thienyl)-,S,S-dioxide