|Molar mass||172.09 g·mol−1|
|Boiling point||370.6 °C (699.1 °F; 643.8 K) at 760 mmHg|
|Slightly soluble in cold water|
|Flash point||192.1 °C (377.8 °F; 465.2 K)|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Tetrahydroxy-1,4-benzoquinone, also called tetrahydroxy-p-benzoquinone, tetrahydroxybenzoquinone, or tetrahydroxyquinone (THBQ, THQ), is an organic compound with formula C6O2(OH)4. Its molecular structure consists of a cyclohexadiene ring with four hydroxyl groups and two ketone groups in opposite (para) positions.
Salts of THBQ
Like most phenols, THBQ is acidic and easily loses the four H+ ions from the hydroxyl groups, yielding anions such as C6H2O62− and C6O64−. The latter is symmetric and aromatic, as the double bonds and negative charges are evenly distributed over the six CO groups.
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 affords THBQ in good yield.
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. Partial oxidation of K4C6O6 affords a green strongly paramagnetic solid, conjectured to be (K+)3 C6O63−, and complete oxidation yields potassium rhodizonate (K+)2 C6O62−.
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. In the absence of oxygen, Li4C6O6 is stable to about 450 °C and then decomposes leaving a residue of carbonate Li2CO3. Indeed, the rhodizonate appears to disproportionate at about 400 °C into Li4C6O6 and cyclohexanehexone C6O6 that promptly decomposes to carbon monoxide, carbon dioxide, and carbon. Li2C6O6 forms a hydrate Li4C6O6·2H2O that loses its water at about 250 °C.
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