1,2-Benzoquinone

1,2-Benzoquinone, also called ortho-benzoquinone, is an organic compound with formula C₆H₄O₂. It is one of the two isomers of quinone, the other being 1,4-benzoquinone. It is a red volatile solid that is soluble in water and diethyl ether. It is rarely encountered because of its instability, but it is of fundamental interest as the parent compound of many derivatives which are known.^[3][4]

1,2-Benzoquinone

Names
Preferred IUPAC name Cyclohexa-3,5-diene-1,2-dione[1]
Other names ortho-Benzoquinone o-Benzoquinone o-Quinone
Identifiers
CAS Number	583-63-1 Y
3D model (JSmol)	Interactive image Interactive image
ChEBI	CHEBI:17253 Y
ChemSpider	10941 Y
ECHA InfoCard	100.243.463
KEGG	C02351 Y
PubChem CID	11421
UNII	SVD1LJ47R7 Y
CompTox Dashboard (EPA)	DTXSID60894765
InChI InChI=1S/C6H4O2/c7-5-3-1-2-4-6(5)8/h1-4H Y Key: WOAHJDHKFWSLKE-UHFFFAOYSA-N Y InChI=1/C6H4O2/c7-5-3-1-2-4-6(5)8/h1-4H Key: WOAHJDHKFWSLKE-UHFFFAOYAR
SMILES O=C1/C=C\C=C/C1=O C1=CC(=O)C(=O)C=C1
Properties
Chemical formula	C6H4O2
Molar mass	108.096 g·mol−1
Appearance	Red volatile solid
Density	1.424 g/cm3
Melting point	60–70 °C (140–158 °F; 333–343 K) decomposes[2]
Hazards
Flash point	76.4 °C (169.5 °F; 349.5 K)
Related compounds
Related compounds	1,4-benzoquinone quinone
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

Structure

The molecule has C_2v symmetry. X-ray crystallography shows that the double bonds are localized, with alternatingly long and short C-C distances within the ring. The C=O distances of 1.21 Å are characteristic of ketones.^[5]

Preparation and reactions

1,2-Benzoquinone is produced on oxidation of catechol exposed to air in aqueous solution^[6] or by ortho oxidation of a phenol.^[6]

A strain of the bacterium Pseudomonas mendocina metabolises benzoic acid, yielding 1,2-benzoquinone via catechol.^[7]

Ortho-quinones are widely used in organic synthesis.^[8]

Occurrence of ortho-quinones

The oxidation of lysyl side chains is effected in nature by the action of an orthoquinone called lysyl tyrosylquinone.

4,5-Dimethyl-1,2-benzoquinone, also a red solid, is a well behaved synthetic ortho-quinone.^[9]

The biological pigment melanin is rich in ortho-quinones.

Finally, the enzyme cofactors tryptophan tryptophylquinone (TTQ), cysteine tryptophylquinone (CTQ), lysine tyrosylquinone (LTQ) and pyrroloquinoline quinone (PQQ) contain the ortho-quinone moiety in their chemical structure.^[10]

See also

• 1,4-Benzoquinone