P-31 NMR-SPECTROSCOPY IN WOOD CHEMISTRY .3. SOLID-STATE P-31 NMR OF TRIMETHYL PHOSPHITE DERIVATIVES OF CHROMOPHORES IN MECHANICAL PULP

High yield pulps were treated with potassium nitrosodisulphonate (Fremy's salt) to produce orthoquinone groups, sodium hydrosulphite to reduce quinone groups, and alkaline hydrogen peroxide to oxidize quinone groups. These pulps and selected model compounds were then reacted under ambient conditions with trimethyl phosphite and the solid state P-31 CP/MAS NMR spectra of the resulting adducts were obtained. The information derived from the P-31 NMR spectra of the model compounds coupled with FTIR and UV/Visible spectra of the treated pulps allowed for assignments to be made for the chemical shifts observed in the P-31 solid state NMR spectra. Freshly oxyphosphorylated pulp samples exhibited P-31 NMR signals in two regions. A strong signal centred around 10 ppm and a broader set of signals ranging between 20 and 40 ppm. Thc upfield signal at around 10 ppm was assigned to ortho-quinones present within the lignin in high yield pulps. The model compound work, however, supplied some evidence that there may be a contribution to the intensity of this signal from carboxylic acids present in pulps. The downfield signals ranging between 20 and 40 ppm have been assigned to alpha,beta-unsaturated aldehydes and ketones present in the lignin within high yield pulps. Sample aging was found to seriously affect the line-shapes of these P-31 NMR spectra. This was attributed to an oxyphosphorane ring opening reaction induced by the highly protonated environment present within a high yield pulp sample.