Tetrahydroxy-1,4-benzoquinone

Like most phenols, THBQ is acidic and easily loses the four hydrogen ions from the hydroxyl groups, yielding anions such as C₆H₂O2−6 and C₆O4−6. The latter is symmetric and aromatic, as the double bonds and negative charges are evenly distributed over the six CO groups.

The calcium salt Ca₂C₆O₆ is the dark purple pigment produced from inositol by Chromohalobacter beijerinckii in the fermentation of salt beans, already noted by T. Hof in 1935.[3][7][8][9][10]

The dark purple and insoluble dipotassium salt K₂C₆H₂O₆ was prepared by Preisler and Berger in 1942, by oxidizing inositol with nitric acid and reacting the result with potassium carbonate in the presence of oxygen. Reaction of this salt with hydrochloric acid produces THBQ in good yield.[11]

The black tetrapotassium salt K₄C₆O₆ was prepared by West and Niu in 1962, by reacting THBQ with potassium methoxide in methanol. The salt is diamagnetic and the infrared spectrum suggests that the C–C and C–O distances are all equal, with the ring slightly distorted in the "chair" conformation.[12] Partial oxidation of K₄C₆O₆ affords a green, strongly paramagnetic solid, conjectured to be 3K⁺·C₆O3−6, and complete oxidation yields potassium rhodizonate 2K⁺·C₆O2−6.[12]

The greenish-black sodium salt Na₄C₆O₆ was described by Fatiadi and Sanger in 1962.[4]

The dark-violet lithium salt Li₄C₆O₆ has been proposed as an electrode material for batteries as it can be oxidized to the rhodizonate Li₂C₆O₆ and reduced to the hexahydroxybenzene salt Li₆C₆O₆.[5] In the absence of oxygen, Li₄C₆O₆ is stable to about 450 °C and then decomposes leaving a residue of lithium carbonate.[5] Indeed, the rhodizonate appears to disproportionate at about 400 °C into Li₄C₆O₆ and cyclohexanehexone C₆O₆ that promptly decomposes into carbon monoxide, carbon dioxide, and carbon.[5] Li₄C₆O₆ forms a hydrate Li₄C₆O₆·2H₂O that loses its water at about 250 °C.[5]