1,3-Dihydro-1,3-dioxoisobenzofuran-4-sulphonic acid 28181-92-2 3-Sulfophthalic anhydride 4-Isobenzofuransulfonic acid, 1,3-dihydro-1,3-dioxo- EINECS 248-888-0 Phthalic anhydride, 3-sulfo-