Lignin quinone methides

The quinone methide can also be generated in situ, at least in aqueous NaOH, directly from the peracetate, as hydrolysis of the phenolic acetate is faster than the benzylic acetate (see an example in Section 12.5.3). This method was used to demonstrate the addition of anthrahydroquinone (AHQ) and anthranol to (actual polymeric) lignin quinone methides in studies elucidating the anthraquinone (AQ)-catalyzed 8-0-4-aryl ether cleavage mechanisms in alkaline pulping.64-66... 

Quinone methides have been shown to be important intermediates in chemical synthesis,1 2 in lignin biosynthesis,3 and in the activity of antitumor and antibiotic agents.4 They react with many biologically relevant nucleophiles including alcohols,1 thiols,5-7 nucleic acids,8-10 proteins,6 11 and phosphodiesters.12 The reaction of nucleophiles with ortho- and /iara-quinone methides is pH dependent and can occur via either acid-catalyzed or uncatalyzed pathways.13-17 The electron transfer chemistry that is typical of the related quinones does not appear to play a role in the nucleophilic reactivity of QMs.18... 

Through these works, Wan has conclusively demonstrated that the photodehydration of hydroxybenzyl alcohols is a general reaction, and a wide variety of quinone methides can be photogenerated and detected using this method. Quinone methide photogeneration via this method has been shown to have importance in the photochemistry of Vitamin B641,42 and in model lignins 43... 

Quinone methides play an important role in lignification. They are produced directly, as intermediates, when lignin monomers, be they hydroxycinnamyl alcohols, hydroxy-cinnamaldehydes, or hydroxycinnamates, couple or cross-couple at their 8- positions. A variety of postcoupling quinone methide rearomatization reactions leads to an array of structures in the complex lignin polymer (Fig. 12.2). 

Ralph, J. Reactions of lignin model quinone methides and NMR studies of lignins. Ph. D. thesis, University of Wisconsin—Madison, University Microfilms DA 82-26987.1982. 

Ralph, J. Adams, B. R. Determination of the conformation and isomeric composition of lignin model quinone methides by NMR. J. Wood Chem. Technol. 1983, 3, 183-194. 

Ralph, J. Ede, R. M. Robinson, N. P. Main, L. Reactions of P-aryl lignin model quinone methides with anthrahydroquinone and anthranol. J. Wood Chem. Technol. 1987, 7, 133-160. 

Landucci, L. L. Ralph, J. Adducts of anthrahydroquinone and anthranol with lignin model quinone methides. 1. Synthesis and characterization. J. Org. Chem. 1982, 47, 3486-3495. 

Zanarotti, A. Synthesis and reactivity of lignin model quinone methides. Biomimetic synthesis of 8.0.4 neolignans. J. Chem. Res., Synop. 1983, 306-307. 

Ralph, J. Lignin model quinone methides—facts and fallacies. In Proceedings of the Third International Symposium of Wood and Pulping Chemistry, Vancouver, BC, Canada, Chemical Institute of Canada (CIC), and Canadian Pulp and Paper Association (CPPA), Canada. 1985. 

Leary, G. Miller, I. J. Thomas, W. Woolbouse, A. D. The chemistry of reactive lignin intermediates. Part 5. Rates of reactions of quinone methides with water, alcohols, and carboxylic acids. J. Chem. Soc., Perkin Trans. 1977, 2, 1737-1739. 

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