Tetrahydroxy-1,4-benzoquinone

Tetrahydroxy-1,4-benzoquinone, also called tetrahydroxy-p-benzoquinone, tetrahydroxybenzoquinone, or tetrahydroxyquinone (THBQ, THQ), is an organic compound with formula C
6O
2(OH)
4. Its molecular structure consists of a cyclohexadiene ring with four hydroxyl groups and two ketone groups in opposite (para) positions.

Tetrahydroxy-1,4-benzoquinone[1]
Names
IUPAC name
2,3,5,6-Tetrahydroxycyclohexa-2,5-diene-1,4-dione
Other names
Tetroquinone
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.005.706
UNII
Properties
C6H4O6
Molar mass 172.092 g·mol−1
Appearance Blue-black crystals
Density 2.609 g/cm3
Boiling point 370.6 °C (699.1 °F; 643.8 K) at 760 mmHg
Slightly soluble in cold water
Hazards
Flash point 192.1 °C (377.8 °F; 465.2 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

The compound gives a light red solution in water,[2] and crystallizes as the glistening bluish-black (but non-conducting) dihydrate C
6O
2(OH)
4·2H2O.[2][3]

The compound can be synthesized from glyoxal[4] or from myo-inositol, a natural compound widely present in plants.[5] THBQ forms an adduct with 4,4′-bipyridine in a 2:3 ratio.[6]

Salts of THBQ

Like most phenols, THBQ is acidic and easily loses the four hydrogen ions from the hydroxyl groups, yielding anions such as C
6H
2O2−
6 and C
6O4−
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 Ca
2C
6O
6 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 K
2C
6H
2O
6 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.[11]

The black tetrapotassium salt K
4C
6O
6 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 K
4C
6O
6 affords a green, strongly paramagnetic solid, conjectured to be 3K+
·C
6O3−
6, and complete oxidation yields potassium rhodizonate 2K+
·C
6O2−
6.[12]

The greenish-black sodium salt Na
4C
6O
6 was described by Fatiadi and Sanger in 1962.[4]

The dark-violet lithium salt Li
4C
6O
6 has been proposed as an electrode material for batteries as it can be oxidized to the rhodizonate Li
2C
6O
6 and reduced to the hexahydroxybenzene salt Li
6C
6O
6.[5] In the absence of oxygen, Li
4C
6O
6 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 Li
4C
6O
6 and cyclohexanehexone C
6O
6 that promptly decomposes into carbon monoxide, carbon dioxide, and carbon.[5] Li
4C
6O
6 forms a hydrate Li
4C
6O
6·2H2O that loses its water at about 250 °C.[5]

References
  1. "Tetroquinone". The Merck Index (11th ed.). p. 9177.
  2. Klug, H. P. (1965). "The crystal structure of tetrahydroxy-p-benzoquinone". Acta Crystallographica. 19: 983.
  3. Miller, M. W. (1961). Microbial Metabolites. McGraw-Hill.
  4. Fatiadi, A. J.; Sanger, W. F. "Tetrahydroxyquinone". Organic Syntheses. 42: 90.; Collective Volume, 5, p. 1011
  5. Chen, H.; Armand, M.; Courty, M.; Jiang, M.; Grey, C. P.; Dolhem, F.; Tarascon, J.-M.; Poizot, P. (2009). "Lithium salt of tetrahydroxybenzoquinone: toward the development of a sustainable Li-ion battery". Journal of the American Chemical Society. 131 (25): 8984–8988. doi:10.1021/ja9024897.
  6. Cowan, J. A.; Howard, J. A. K.; Leech, M. A. (2001). "Interpenetrating supramolecular lattices in 4,4′-bipyridine-2,3,5,6-tetrahydroxy-1,4-benzoquinone (3/2)". Acta Crystallographica Section C. 57 (10): 1196–1198. doi:10.1107/S0108270101011647.
  7. Hof, T. (1935). Recueil des travaux botaniques néerlandais. 32: 92. Missing or empty |title= (help)
  8. Kluyver, A. J.; Hof, T.; Boezaardt, A. G. J. (1939). "On the pigment of Pseudomonas beijerinckii Hof [Chromohalobacter beijerinckii]". Cite journal requires |journal= (help)
  9. Vitamins and Hormones: Advances in Research and Applications. 3. 1945.
  10. Underkofler, L. A.; Hickey, R. J. (1954). Industrial Fermentations.
  11. Preisler, P. W.; Berger, L. (1942). "Preparation of tetrahydroxyquinone and rhodizonic acid salts from the product of the oxidation of inositol with nitric acid". Journal of the American Chemical Society. 64 (1): 67–69. doi:10.1021/ja01253a016.
  12. West, R.; Niu, H. Y. (1962). "Symmetrical Resonance Stabilized Anions, CnO−m
    n    . II. K4C6O6 and Evidence for C6O−3
    6    ". Journal of the American Chemical Society. 84 (7): 1324–1325. doi:10.1021/ja00866a068.
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