Fundamental Study of Relative Delignification Efficiencies (III): Organosolv Pulping Systems

ABTRACT

Reactions of l-(4-guaiacyl)-2-(O-guaiacyl)-l,5-pentanediol (1) provide relative rates of pulping reactions that involve quinone methides (QMs). Model 1 was reacted under soda, kraft, soda/anthrahydroquinone (AHQ), and sulfite conditions in the presence of various water/alcohol media. All alkaline reactions displayed the same lignin model disappearance rate, verifying that QM formation was the rate-determining step. Alcohol addition had the following effect on increasing the paryl ether cleavage of model 1: no increase for methanol addition to soda, kraft, and alkaline SO₃ ⁻² systems; small increase for isopropanol addition to neutral sulfite and acid bisulfite systems; large increase for methanol addition to the soda/AHQ system. In the latter case, the amount of enhancement correlated with the level of methanol present; other solvent/water media exhibited a similar response as methanol. Several hypotheses relating to electron transfer (radical) chemistry are postulated for the observed synergism between the solvent and AHQ.