Quantification and Classification of Carbonyls in Industrial Humins and Lignins by 19F NMR

Abstract

Lignin and humins are both (by-)products of biorefining processes aimed at the valorization of lignocellulosic biomass. In order to improve the efficiency of such biorefineries and to develop new valorization pathways for these polymeric materials, detailed insight into their complex chemical structure and functional group distribution is required. Here, we report on the quantification and classification of the ketone and aldehyde carbonyl functional groups contained in these two polymers by 19F NMR. The known method of carbonyl derivatization with 4-(trifluoromethyl)phenylhydrazine to the corresponding hydrazone has been improved and simplified, allowing derivatization directly in an NMR tube, requiring no additional workup before quantification by 19F NMR. Furthermore, the scope of the method was assessed and expanded, with model compound studies, which included monomeric and dimeric compounds as well as synthetic polymers, showing that the carbonyl functions can indeed be reproducibly quantified. Using...