Fundamental study of relative delignification efficiencies .1. Conventional pulping systems

Reactions of a beta-aryl ether model 1 [1-(4-guaiacyl)-2-(O-guaiacyl)-1,5-pentanediol] provide relative rates of pulping reactions that involve quinone methides (QMs). Model 1 was reacted under soda, kraft, soda/anthraquinone (AQ), and sulfite conditions. All alkaline conditions displayed the same lignin model disappearance rate, indicating a common rate determining step - QM formation. The results indicate that reactions between pulping reagents and QM are reversible in most cases and that anthahydroquinone (AHQ) was the most effective reagent at facilitating beta-aryl ether cleavage. Alkaline sulfite cooks of 1 gave a similar product distribution as a soda cooks of 1; however, an alpha-sulfonate 11 [1-(4-guaiacyl)-2-(O-guaiacyl)-5-hydroxypentane-1-sulfonic acid] was the predominant product when 1 was reacted under neutral sulfite conditions. Model 11 reverted back to a QM at high pH values. All of the sulfite cooks of 1 showed only low levels of beta-aryl ether cleavage. This paper is the first in a three-part study designed to examine beta-aryl ether cleavage in multicomponent pulping systems (e.g., alkaline sulfite/AQ/methanol [ASAM]).