Furantetracarboxylic acid

In chemistry, furantetracarboxylic acid is an organic compound with formula C8H4O9, or (C4O)(-(CO)OH)4, which can be viewed as deriving from furan C4H4O through replacement of the four hydrogen atoms by carboxyl functional groups -(CO)OH. By removal of four protons, the acid is expected to yield the anion C8O4−9, furantetracarboxylate, which is one of the oxocarbon anions (consisting solely of oxygen and carbon. By loss of 1 through 3 protons it forms the anions C8H3O−9, C8H2O2−9, and C8HO3−9, called respectively trihydrogen-, dihydrogen-, and hydrogenfurantetracarboxylate.

Source: Wikipedia — Furantetracarboxylic acid (CC BY-SA 4.0)