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. Vitamin K is a derivative of 1,4-naphthoquinone. It is a planar molecule with one aromatic ring fused to a quinone subunit. It is an isomer of 1,2-naphthoquinone. Preparation The industrial synthesis involves aerobic oxidation of naphthalene over a vanadium oxide catalyst: CH + 3/2 O → CHO + HO 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 (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: Uses 1,4-Naphthoquinone is mainly used as a precursor to anthraquinone by reaction with butadiene followed by