A hydroxynaphthoquinone (formula: ) is any of several organic compounds that can be viewed as derivatives of a naphthoquinone through replacement of one hydrogen atom (H) by a hydroxyl group (-OH).
In general, the term may mean any naphthoquinone derivative where any number n of hydrogens have been replaced by n hydroxyls, so that the formula is . In this case the number n (which is between 1 and 6) is indicated by a multiplier prefix (mono-, di-, tri-, tetra-, penta-, or hexa-).
The unqualified term "hydroxynaphthoquinone" usually means a derivative of 1,4-naphthoquinone. Other hydroxy- compounds can be derived from other isomers of the latter, such as 1,2-naphthoquinone and 2,6-naphthoquinone. The IUPAC nomenclature uses dihydronaphthalenedione instead of "naphthoquinone", with the necessary prefixes to indicate the positions of the carbonyl oxygens (=O) — as in 5,8-dihydroxy-1a,8a-dihydronaphthalene-1,4-dione (= 5,8-dihydroxy-1,4-naphthoquinone).
The hydroxynaphtoquinones (in the particular or the general sense) include many biologically and industrially important compounds, and are a building-block of many medicinal drugs. Quoted by Khalafy and Bruce. Quoted by Khalafy and Bruce.
(Mono)hydroxynaphtoquinones
From 1,4-naphthoquinone Due to its symmetry there are only three isomers:
2-Hydroxy-1,4-naphthoquinone (lawsone), coloring principle of henna. 5-Hydroxy-1,4-naphthoquinone (juglone), coloring principle of black walnut. Also active antimicrobial principle in Caesalpinia sappan heartwood. 6-Hydroxy-1,4-naphthoquinone, can be prepared from 1,7-dihydroxynaphthalene. One of the main products of photochemical oxidation of 1-naphthol.
From 1,2-naphthoquinone From 1,2-naphthoquinone (ortho-naphthoquinone) there are 6 possible isomers: 3-Hydroxy-1,2-naphthoquinone 4-Hydroxy-1,2-naphthoquinone 5-Hydroxy-1,2-naphthoquinone 6-Hydroxy-1,2-naphthoquinone 7-Hydroxy-1,2-naphthoquinone 8-Hydroxy-1,2-naphthoquinone
From 2,3-naphthoquinone From 2,3-naphthoquinone, also a symmetric molecule there are only three isomers: 1-Hydroxy-2,3-naphthoquinone 5-Hydroxy-1,2-naphthoquinone 6-Hydroxy-1,2-naphthoquinone
From 2,6-naphthoquinone From the symmetrical 2,6-naphthoquinone (amphi-naphthoquinone) there are only three:
1-Hydroxy-2,6-naphthoquinone 3-Hydroxy-2,6-naphthoquinone 4-Hydroxy-2,6-naphthoquinone
(Poly)hydroxynaphthoquinones Dihydroxynaphthoquinone Trihydroxynaphthoquinone Tetrahydroxynaphthoquinone Pentahydroxynaphthoquinone Hexahydroxynaphthoquinone
See also Hydroxybenzoquinone Hydroxyanthraquinone
References