Key chromophores in celluloses: analysis by 31P NMR spectroscopy

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 P-31 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 P-31 NMR approach adds to the toolbox of methods applicable in cellulose chromophore analysis, bleaching and aging studies.

Automated summary

This paper investigates the three key chromophores in cellulosic materials, which have special structures and high resonance stabilization, making them thermodynamically stable and resistant to bleaching. The study explores the derivatization of these hydroxyl groups by a phosphitylation agent and analyzes them using P-31 NMR, a commonly used method for quantitative analysis and differentiation of OH groups in lignins and lignin derivatives. The chemical shifts and structural characteristics of the chromophore derivatives are discussed. The P-31 NMR approach contributes to the analysis, bleaching, and aging studies of cellulose chromophores.