3,3'-[3-Oxoisobenzofuran-1(3H)-ylidene]-6-sodiooxy-6'-hydroxybis(benzenesulfonic acid)disodium salt

trisodium alpha-(4-hydroxy-3-sulphonatophenyl)-alpha-(4-oxo-3-sulphonatocyclohexa-2,5-dienylidene)-alpha-toluate