1,2-Benzenedicarbothioic acid, cyclic anhydrosulfide 5698-59-9 Benzo[c]thiophene-1,3-dione NSC89543 Phthalic acid, 1,2-dithio-, cyclic anhydrosulfide Phthalic thioanhydride Phthaloyl monosulfide Thiophthalic anhydride