Solid-Sample Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Lignin and Hydroxymethylated Lignin

Abstract

Abstract Solid-sample carbon-13 NMR spectroscopy with cross polarization and magic angle spinning (CP/MAS) was employed to study the hydroxymethylation of lignin. Kraft pine and steam-exploded hardwood lignins were reacted with formaldehyde and the resultant structural changes in the lignins evaluated by comparing the spectra of the treated and untreated lignins. The results indicated that hydroxymethylation had occurred at the 5 position of phenolic guaiacyl units, in keeping with known reactions for phenol-formaldehyde resole formation. The degrees of formaldehyde substitution determined from CP/MAS NMR spectra were in excellent agreement with those determined by other methods. Intensities in the untreated kraft pine lignin spectrum implied the presence of unsaturated sidechains with some loss of γ carbons.