Fundamental study of relative delignification efficiencies .3. Organosolv pulping systems

Reactions of 1-(4-guaiacyl)-2-(O-guaiacyl)-1,5-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 beta-aryl 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.