Rhodizonic acid
Rhodizonic acid is a chemical compound with formula C6H2O6 or (CO)4(COH)2. It can be seen as a two-fold enol and four-fold ketone of cyclohexene, more precisely 5,6-dihydroxycyclohex-5-ene-1,2,3,4-tetrone.
Rhodizonic acid is usually obtained in the form of a colorless "dihydrate" C6H2O6·2H2O. The latter is actually 2,3,5,5,6,6-hexahydroxycyclohex-2-ene-1,4-dione, where two of the original ketone groups are replaced by two pairs of geminal diols. The orange to deep-red and highly hygroscopic anhydrous acid can be obtained by low-pressure sublimation of the dihydrate.