A C-13 NMR-STUDY OF MILLED WOOD LIGNINS FROM HYBRID SALIX CLONES

Acetylated milled wood lignins from four 1-year old and one 14-year old hybrid Salix (willow) clones were examined by qualitative and quantitative C-13 NMR spectroscopy. Intensity variations of given signals within a clone and between clones facilitated the characterization of minor functional entities,The lignins contained 71%-8.7% pinoresinol/syringaresinol structures, 2%-4% phenylcoumaran structures, and 4.4%-6.5% p-hydroxybenzoate structures. Quantitation of these structures was based on prominent signals that were previously assigned. In addition, in the case of acetylated p-hydroxybenzoate structures, all the carbon signals were assigned by means of conventional proton decoupled spectra and DEPT spectra, and by comparison with model compounds. Examination of Salix milled wood lignins by C-13 NMR spectroscopy before and after mild hydrolysis indicated that the p-hydroxybenzoate units were attached to lignin via an ester linkage. No evidence for the existence of ether-linked benzoate subunits was found.