Key chromophores in celluloses: analysis by 31P NMR spectroscopy

Abstract

The three cellulosic key chromophores, 2,5-dihydroxy-[1,4]-benzoquinone, 5,8-dihydroxy-[1,4]-naphthoquinone and 2,5-dihydroxy-acetophenone, are nearly ubiquitous in cellulosic materials because of their special structures and resonance stabilization with highly delocalized double bonds that renders them thermodynamically very stable and resistant towards bleaching. All of these compounds possess acidic hydroxyl groups. The current work explores the derivatization of these OH groups by a phosphitylation agent followed by 31P NMR analysis, an approach that is very frequently used for quantitative OH group analysis and differentiation in lignins and lignin derivatives. The chemical shifts are reported and structural peculiarities of the chromophore derivatives are discussed. The 31P NMR approach adds to the toolbox of methods applicable in cellulose chromophore analysis, bleaching and aging studies. Graphical abstract