13C NMR of Lignins in Aqueous Alkali. II. Ionization Effects on the Spectra of Technical Lignins

Aqueous alkali is a convenient medium for obtaining 13 C NMR spectra of lignins. The spectra of a series of model compounds were recorded in both aqueous alkali and a deuterated organic solvent that, with the data published previously, made up the basis for interpreting the spectra of lignins in aqueous alkali and changes in chemical shifts upon ionization of functional groups in the polymer. The spectra of sample lignins of distinctively different origin, i.e., ALCELL, oxygen-organosolv, and kraft lignins were recorded and interpreted. It is shown that the spectra in aqueous alkali can be used in lignin characterization exactly in the same manner as the spectra in an organic solvent. In addition, ionization chemical shifts may be used as a structural probe. This new technique brings valuable extention to 13 C NMR spectroscopy of lignins.