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.[2] 1,4-naphathoquinone itself has some vitamin K activity.[3]
The industrial synthesis involves aerobic oxidation of naphthalene over a vanadium oxide catalyst:[4]
C10H8 + 3/2 O2 → C10H6O2 + H2O
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.[5]
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 (45 days) exposure of naphthoquinone in neat liquid butadiene taken in huge excess at room temperature in a thick-wall glass tube or 2) fast catalyzed cycloaddition at low temperature in the presence of 1 equivalent of tin(IV) chloride:[6]
Diels-Alder reaction of 1,4-naphthoquinone with 1,3-butadiene
Reduction of 1,4-naphthoquinone with dithionite gives 1,4-dihydroxynaphthalene. The reaction is reversible: oxidation of the diol give back the quinone.[7]
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 aminoanthroquinone that is used as a dye precursor.[4]
Naphthoquinone functions as a ligand through its electrophilic carbon-carbon double bonds.[8]
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.[9]
Natural 1,4-naphthoquinones
Chemical structure of juglone, a compound produced by black walnut trees.
Alkannin, commercial red-brown dye from Alkanna tinctoria
Dichlone, a chlorinated derivative of 1,4-naphthoquinone, a fungicide.
↑Fernholz, Erhard; Ansbacher, S.; MacPhillamy, H. B. (February 1940). "The Vitamin K Activity of Naphthoquinones". Journal of the American Chemical Society. 62 (2): 430–432. doi:10.1021/ja01859a052.
↑Kündig, E. P.; Lomberget, T.; Bragg, R.; Poulard, C.; Bernardinelli, G. (2004). "Desymmetrization of a meso-Diol Complex Derived from [Cr(CO)3(η6-5,8-Naphthoquinone)]: Use of New Diamine Acylation Catalysts". Chemical Communications. 2004 (13): 1548–1549. doi:10.1039/b404006f. PMID15216374.
↑Babula, P.; Adam, V.; Havel, L.; Kizek, R. (2007). "Naphthoquinones and their Pharmacological Properties". Ceská a Slovenská Farmacie (in Czech). 56 (3): 114–120. PMID17867522.
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