Chemistry of 5,8-dihydroxy-[1,4]-naphthoquinone, a Key Chromophore in Aged Cellulosics

5,8-Dihydroxy-[1,4]-naphthoquinone (DHNQ) is one of the key chromophores found in aged cellulosics. Cellulose aging and yellowing as well as bleaching of cellulosic materials are key processes in the pulp and paper industries and have considerable economic importance: the knowledge of the general reactivity and chemistry of this compound is thus helpful for a better understanding of these phenomena and the related technologies. This paper reviews the reactions reported for 5,8-dihydroxy-[1,4]-naphthoquinone, from the viewpoints of both synthesis and general reactivity. The compound exhibits a rich chemistry due to the presence of interconvertible hydroquinone and quinone moieties, reflected in strong resonance stabilization in alkaline medium. One of the most prominent reaction pathways is cycloaddition to the 2,3-double bond with various dienes to form polycyclic quinones, mainly anthraquinones. DHNQ also undergoes nucleophilic addition of amines, alcohols, olefins, water, and sulfides mainly at the 2-position followed by re-oxidation of the quinoid moiety, eventually resulting in 2-substituted DHNQ. Derivatization of the hydroxyl groups into O-acyl, O-alkyl, O-tosyl, and O-silyl derivatives is also widely reported, as are reductive conversions.