Lignin Carboxylic

There is no differentiation between lignin-carboxyl and cellulose-carboxyls... 

The method of choice for determining carboxyl groups in lignin is based on potentiometric titration in the presence of an internal standard, /)-hydroxybenzoic acid, using tetra- -butylammonium hydroxide as a titrant (42). The carboxyl contents of different lignins are shown in Table 6. In general, the carboxyl content of lignin increases upon oxidation. 

Many of the chemical reactions used to modify lignosulfonates are also used to modify kraft lignins. These include ozonation, alkaline—air oxidation, condensation with formaldehyde and carboxylation with chloroacetic acid (100), and epoxysuccinate (101). In addition, cationic kraft lignins can be prepared by reaction with glycidjiamine (102). 

Lignins are most usually employed as various types of sodium lig-nosulfonate and are products of sulfite pulping. (Kraft lignins from the Kraft pulping process are also available.) They are used as dispersants, binders, sequestrants, and emulsifiers. Sodium lignosulfonate product variables include color, MW, and the degree of carboxylation and sulfonation on the lignin backbone. 

The plant cell wall contains different types of polysaccharides, proteins (structural glycoproteins and enzymes), lignin and water, as well as some inorganic components (1, 14-16). The plant cell suspensions, however, grow as a population of cells with a primary cell wall(17). The main components of these walls are cellulose-free polysaccharides and pectic polysaccharides in particular, which constitute 1/3 of their dry weight. (18). Some fragments, e g. methanol, acetic, ferulic and p-cumaric acids, are connected with the pectic polysaccharides by ester bonds with the carboxylic and hydroxylic groups. 

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. 

Figure 3.8(a) Possible ester linkage between an a-OH of lignin and a carboxyl group of a 4-0-methyl-/3-d-glucuronic acid residue on the xylan backbone. 

The fungal enzyme from R. praticola was able to catalyze the oxidative coupling of pentachlorophenol (PCP) and syringic acid, a representative of phenol carboxylic acids from lignin occurring in HS structures. 

Lignin contains phenolic and a few carboxylic acid groups it therefore dissolves in sodium hydroxide. Soda pulping is based on this fact. Here, at the high temperatures used, ester bonds arc hydrolyzed, and some of the carbohydrate-lignin ether bonds are split. Cold caustic soda is used for semichemical processes. 

Carbohydrates Ceiiuiose Starch 1 Hemiceiiuiose Lignin J ( monosaccharides "j ( hexoses "j Cx(H20)y < oligosaccharides > pentoses > [ chitin J ( glucosamine J (C2H20)4 unsaturated aromatic alcohols —> polyhydroxy carboxylic aoids HPOy, GO2, CH4, glucose, fructose, galactose, arabinose, ribose, xylose... 

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