Structure and reactivity of lignin

Adler E, Lundquist K, Miksche GE (1966) The structure and reactivity of lignin. Adv Chem Ser 59 22-35... 

Kringstad, K.P., Lin, S.Y., "Mechanism in the Yellowing of High-Yield Pulps by Light. Structure and Reactivity of Free Radical Intermediates in the Photodegradation of lignin", Tappi, 1970, 53(12), 2296. 

Pan, X., Lachenal, D., Lapierre, C. and Monties, B., "Structure and Reactivity of Spruce Mechanical Pulp Lignins. Part I. Bleaching and Photoyellowing of in situ Lignins", J. Wood Chem. Technol., 1991, 12, 135. 

Krmgstad KP, Lin SY (1970) Mechanism in the yellowing of high-yield pulps by light Structure and reactivity of free radical intermediates in the photodegradation of lignin TAPP1 53 2296-2301... 

Choice of the Lignin Modification Reaction. The phenolysis reaction was selected as a means of modifying the structure and reactivity of the ammonium lignin sulfonate for three main practical reasons. First, because this lignin derivative is soluble in (and will ultimately be used in conjunction with) liquid phenol itself second, because unreacted phenol, unlike other reaction solvents, would not have to be removed from the phenolated product after reaction and before conversion to the adhesive resin and third, because lignins and carbohydrates are known to react with phenols under acidic conditions (6,7). 

X Pan, D Lachenal, C Lapierre, B Monties. Structure and reactivity of spruce mechanical pulp lignins Part I. Bleaching and photoyellowing of in situ lignins. J Wood Chem Technol 12 135-147, 1992. 

SA Braddon, CW Dence. Structure and reactivity of chlorolignin. I. Alkaline hydrolysis of chlorine-substituted lignin model compounds. Tappi 51(6) 249-256, 1968. 

These examples thus clearly show 4-hydroxy-3-methoxyphenyl and 4-hydroxy-3,5-dimethoxyphenylalkanes (typical of the lignin structure) to be reactive at positions 2 and 6 towards electrophilic substitution reactions under acidic conditions. The subject matter of this paper deals with the development of procedures whereby the 2- and 6- (i.e., meta) positions are utilized for the polymerization and modification of lignin. 

Any treatment of wood must take account of the differing accessibilities and reactivities of the principal wood constituents. Further, any chemical or microbial method of breaking down wood has to devise conversion pathways for cellulose, the hemicelluloses and lignin, and if necessary consider ways of isolating the individual reaction products so that they can be processed separately. Hydrolysis has proved to be a most effective method of opening up the wood structure for subsequent treatments. The expression hydrolysis of wood is used rather loosely. It is not technically correct since the reactions affect primarily the carbohydrate fraction of wood. Lignin is largely unaffected. 

Source Lapierre, C., Forage Cell Wall Structure and Digestibility. Madison, Wl American Society of Agronomy Inc., 133-163, 1993 Lapierre, C., Pollet, B., and Rolando, C., Res Chem Intermed, 21, 397 12, 1995 Jacquet, G., Structure et reactivity des lignines de Gramindes et des acides phynoliques associds. PhD Thesis Aix Marseille 111 University, 301, 1997. 

For reasons apparent from the previous discussion, the nature of the chemical linkage between polysaccharidic and lignin elements in woody tissues is still not well understood. More research is clearly needed. Knowledge of the nature of the lignin carbohydrate connections is of importance for the understanding of the structure and the reactivity of lignin in situ. 

Shevchenko, S. M., T. J. Elder, S. G. Semenov, andM. Ya.Zarubin. 1995. Conformational effects on the electronic structure and chemical reactivity of lignin model p-quinone methides and benzyl cations. Res. Chem. Inter. 21(3-5) 413 23. 

C Fabbri, M Bietti, and O Lanzalunga. Generation and Reactivity of Ketyl Radicals with Lignin Related Structures. On the Importance of the Ketyl Pathway in the PhotoyeUowing of Lignin Containing Pulps and Papers. J Org Chem 70 2720-2728, 2005. 

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