F-19 nuclear magnetic resonance spectroscopy for the quantitative detection and classification of carbonyl groups in lignins

A novel method that permits the quantitative detection and classification o f various carbonyl groups in lignins has been developed. The proposed metho d was optimized with the quantitative trifluoromethylation of a series of c arbonyl-containing lignin-like model compounds. This effort was followed by F-19 NMR spectral analyses of the resulting fluorine derivatives allowing for a thorough understanding of their structure/F-19 chemical shift relatio nships. The various carbonyl groups present in Lignins were also investigat ed by trifluoromethylating them in the presence of catalytic amounts of tet ramethylammonium fluoride (TMAF), followed by hydrolysis with TMAF in tetra hydrofuran, By using a variety of selective reactions, it became possible t o assign a number of prominent F-19 NMR signals to a variety of carbonyl gr oups present in lignins These studies demonstrated that the proposed method can be applied to the quantitative determination of carbonyl groups that a re present in soluble native and technical lignins.