Dimerization of 1,4-Naphthoquinone by Rhodium (III) Chloride

Abstract

When 1,4-naphthoquinone was treated with rhodium (II) chloride in a refluxed ethanol for 20 hr under nitrogen, a white product [ 1 ] was obtained along with a small amount of dark-red chlororhodium complex. The product [ 1 ] was identified as 4,4'-diethoxy-l, l'-dihydroxy-2,2'-binaphthalene on the basis of spectral data and elemental analysis. The structure of [1] was further confirmed by the fact that [1] was oxydized to well known blue dye (Russig Blue: 4,4'-diethoxy-2,2'-bi(l H-naphthylidene)-l,l'-dione) by relatively mild oxydizing agents such as lead(IV) oxide, iron (III) chloride, or oxygen. © 1977, The Chemical Society of Japan. All rights reserved.