Carbonyl content in lignins

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

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). 

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. 

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... 

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 ... 

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