Lignin carbonyl content

Our constitutional scheme is based on different kinds of information. The first type of information comes from an analytical study of milled spruce wood lignin prepared according to Bjorkman (3). The analytical data considered comprise the elemental composition of lignin, its content of methoxyl groups and other ether bonds, the types and amount of its different hydroxyl groups, carbonyl, and lactone groups, and the kind and number of its biphenylyl linkages and other bonds in which the benzene nucleus is involved. The work that led to data of this kind has been carried out in various laboratories and has been described previously (9,11). 

The mesomeric quinonemethides and 0-quinonemethides described above are somewhat more stable than the simple p-quinonemethides whose properties are already well known even from classical studies. The o-quinonemethides XX and XVII do not add on water even in solution in aqueous organic solvents their solution in dioxane/water is stable for months. They do not add on methanol or higher alcohols and react only slowly with phenols and organic acids. The addition of water is not catalyzed by mild alkalies the red color of the phenoxide ion (XVIII) prevails for weeks in soda solution. Addition of water occurs more rapidly in strongly alkaline solution. The addition of mineral acids and reduction by sodium borohydride are instantaneous. The addition of HC1 is rapid even at pH 4.0, the conditions used for determining the carbonyl content of lignin by the hydroxylamine hydrochloride reaction 13). 

With the pulp used, a very low ozone charge did not significantly increase the carbonyl content, since preferably the residual lignin present in the material was attacked by the oxidant [16]. The progressing degradation of the polysaccharide material upon further oxidation, as reflected by the decreasing Mw, is clearly visible in Fig. 8. 

Alternatively, the total carbonyl content of a lignin preparation may be determined by reduction with either sodium or potassium borohydride. This method is based on the Lindberg-Misiorny method for the determination of carbonyl groups in carbohydrates (Lindberg and Misiorny 1952, Lindberg and Theander 1954). Both sodium and potassium borohydrides are insoluble in ether but soluble in water without decomposition. At room temperature, they effectively reduce aldehydes and ketones in aqueous and methanol solutions, in particular in weakly alkaline solutions, without simultaneously reducing olefinic double bones ... 

Determination of Total Carbonyl Content of Lignins by Reaction with Hydroxylamine Hydrochloride (Gierer and Soderberg 1959, Gierer and Lenz 1965)... 

Note 8. The value C=0/C9 is meaningful only if the lignin preparations under study are sufficiently pure and have C9 structure (some technical lignins may not have a true C9 structure). In such a case, results for the total carbonyl content of lignin should be expressed as C=0/0CH3. See Chapter 7.6.3 for the significance of the methoxyl content of lignin. 

I Tomoda, Y Matsumoto, G Meshitsuka. Semi-quantitative method to evaluate the alpha -carbonyl content in lignin. J Wood Sci 51 172-175, 2005. 

By use of a peroxide under alkaline conditions, Bailey and Dence (129) produced a sharp increase in the carbonyl content of lignin but also induced a 16 to 17 percent loss of methoxyl groups as methanol. Further, production of ethanedioic, 1,3-propanedioic, 1,4-butenedioic, and 2-methor - 1,4-butanedioic acids verified extensive degradation of the lignin. This degradation occurred at... 

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