Tetrahydroxy-1,4-benzoquinone

Tetrahydroxy-1,4-benzoquinone

Names
IUPAC name 2,3,5,6-tetrahydroxycyclohexa-2,5-diene-1,4-dione
Other names Tetroquinone
Identifiers
CAS Number	319-89-1 Y
3D model (JSmol)	Interactive image
ChemSpider	5231 N
ECHA InfoCard	100.005.706
InChI InChI=1S/C6H4O6/c7-1-2(8)4(10)6(12)5(11)3(1)9/h7-8,11-12H Key: DGQOCLATAPFASR-UHFFFAOYSA-N
SMILES O=C(C(O)=C1O)C(O)=C(O)C1=O
Properties
Chemical formula	C6H4O6
Molar mass	172.09 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
Solubility in water	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  (what is YN ?)
Infobox references

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.

The compound gives a light red solution in water, and crystallizes as the glistening bluish-black (but non-conducting) dihydrate C₆O₂(OH)₄·2H₂O.

The compound can be synthesized from glyoxal or from myo-inositol (phytic acid), a natural compound widely present in plants. THBQ forms an adduct with 4,4'-bipyridine in the 2:3 ratio.

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 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.

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.