Hydroxynaphthoquinone
# Hydroxynaphthoquinone

A hydroxynaphthoquinone (formula: C $_{10}H$ $_6O$ $_3)$ 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In general, the term may mean any naphthoquinone derivative where any number n of hydrogens have been replaced by n hydroxyls, so that the formula is C $_{10}H$ $_6O$ $_{2+n}.$ In this case the number n (which is between 1 and 6) is indicated by a multiplier prefix (mono-,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.

## (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
