2,4′:2′,4 Dianhydride of 3-keto-glucoside, a precursor to chromophores of aged, yellow cellulose, and its weak interactions

Abstract

Studies of cellulose aging and yellowing that involved a 1,4-dimethyl 3-keto β-d-glucoside (compound 1) model of oxidized cellulose led to a hemi-hydrated crystal of title compound 2 (1,6-dihydroxy-3,8-bis-hydoxymethyl-5,10-dimethoxy-4,9-dioxa-tricyclo [5,3,1,1,2,6] dodecane-11,12-dione). The same compound 2 was isolated in low yield from “real-world” oxidized and aged cellulosic pulp. Formation of compound 2 implies cellulose chain cleavage and, unexpectedly, cross-linking during aging. X-ray diffraction revealed an encompassing 10-membered ring whose two carbonyl group bridges define two eight-membered rings and three six-membered rings. The central six-membered ring is antecedent to 2,5-dihydroxy-1,4-benzoquinone (compound 3), a potent and nearly ubiquitous chromophore in aged cellulose; the outer rings derive from the keto-glucosides and have 4C1 and 1C4 shapes with gt and rare tg O-6 positions. Weak trans-annular interactions between >C=O carbon and ring oxygen atoms were confirmed with Atoms-in-Molecules theory. That theory was also used to analyze a questionable cyclic hydrogen bond and bonds between adjacent O–H and carbonyl oxygens.