1,4-Naphthoquinone


1,4-Naphthoquinone or para-naphthoquinone is a quinone derived from naphthalene. It forms volatile yellow triclinic crystals and has a sharp odor similar to benzoquinone. It is almost insoluble in cold water, slightly soluble in petroleum ether, and more soluble in polar organic solvents. In alkaline solutions it produces a reddish-brown color.
Natural vitamin K is a derivative of 1,4-naphthoquinone. It is a planar molecule with one aromatic ring fused to a quinone subunit. 1,4-naphathoquinone itself has some vitamin K activity.
It is an isomer of 1,2-naphthoquinone.

Preparation

The industrial synthesis involves aerobic oxidation of naphthalene over a vanadium oxide catalyst:
In the laboratory, naphthoquinone can be produced by the oxidation of a variety of naphthalene compounds. An inexpensive route involves oxidation of naphthalene with chromium trioxide.

Reactions

1,4-Naphthoquinone acts as strong dienophile in Diels-Alder reaction. Its adduct with 1,3-butadiene can be prepared by two methods: 1) long fast catalyzed cycloaddition at low temperature in the presence of 1 equivalent of tin(IV) chloride:
Reduction of 1,4-naphthoquinone with dithionite gives 1,4-dihydroxynaphthalene. The reaction is reversible: oxidation of the diol give back the quinone.

Uses

1,4-Naphthoquinone is mainly used as a precursor to anthraquinone by reaction with butadiene followed by oxidation. Nitration gives 5-nitro-1,4-naphthalenedione, precursor to an that is used as a dye precursor.
Naphthoquinone functions as a ligand through its electrophilic carbon-carbon double bonds.

Derivatives

Naphthoquinone forms the central chemical structure of many natural compounds, most notably the K vitamins. 2-Methyl-1,4-naphthoquinone, called menadione, is a more effective coagulant than vitamin K. Some naphthoquinone derivatives are cytotoxic, they have significant antibacterial, antifungal, antiviral, insecticidal, anti-inflammatory, and antipyretic properties. Plants with naphthoquinone content are widely used in China and the countries of South America, where they are used to treat malignant and parasitic diseases.

Natural 1,4-naphthoquinones

Synthetic 1,4-naphthoquinones