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Title: Chemistry of 5,8-dihydroxy-[1,4]-naphtoquinone, a key chromophore in aged cellulosics

Author
item HOSAYA, TAKASHI - University Of Natural Resources & Applied Life Sciences - Austria
item FRENCH, ALFRED - Retired ARS Employee
item ROSENAU, THOMAS - University Of Natural Resources & Applied Life Sciences - Austria

Submitted to: Journal of Organic Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2013
Publication Date: 5/20/2013
Citation: Hosaya, T., French, A.D., Rosenau, T. 2013. Chemistry of 5,8-dihydroxy-[1,4]-naphtoquinone, a key chromophore in aged cellulosics. Journal of Organic Chemistry. 10:302-308.

Interpretive Summary: Cotton or linen fabrics and paper, as well as other items composed chiefly of cellulose, tend to change to a yellow or brown color as they age. The change in color is usually accompanied by increased brittleness and loss of strength, as well. A cause of these phenomena is thought to be the formation of chemical compounds (chromophores) that originate in the individual glucose units of the cellulose which consists of many glucose residues connected together. In the present work, many aspects of the structure and chemistry of another important chromophore, 5,8-dihydroxy-[1,4]-napthoquinone are brought together along with new results from computational quantum mechanics studies to obtain new understanding of the various reaction mechanisms and potential ways to stop, or slow, the deterioration of items made from cellulose. Current attempts to change the color are by bleaching, for example, are largely futile because the benzoquinone structure is readily re-oxidized to the dihydroxy benzoquinone, a chromophore that is visible at the parts per billion level. Other chemical remedies are discussed.

Technical Abstract: 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 moties, 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.