Oxidative depolymerization of lignin

Stark K, Taccardi N, Bosmann A, Wasserscheid P (2010) Oxidative depolymerization of lignin in ionic liquids. ChemSusChem 3 719... 

The mechanism proposed in Figure 3 can easily be applied to the oxidative depolymerization of the lignin macromolecule by nitrobenzene or copper(II) in aqueous alkali. A recent model of softwood lignin (24) contains 27% free benzylic hydroxyl groups and 12% aromatic ring-conjugated double bonds (stilbene... 

This initial oxidative depolymerization of cellulose evidently opens up the wood cell wall structure so that cellulolytic and hemi-cellulolytic enzymes can reach their substrates despite the presence of lignin. Solubility of wood in 1% NaOH increases markedly on brown-rot attack IS) and reflects cellulose depolymerization and the opening up of the wood structure. 

Ad/Al ratio The ratio of concentrations of the total phenolic acids relative to the total phenolic aldehydes derived from depolymerization of lignin. Larger Ad/Al ratios are indicative of greater oxidation of the lignin fraction of organic matter in a sediment sample. 

Hasegawa I, Inoue Y, Muranaka Y, Yasukawa T, Mae K (2011) Selective production of organic acids and depolymerization of lignin by hydrothermal oxidation with diluted hydrogen peroxide. Energ Fuels 25 791... 

Alkaline hydrolysis of lignin increases the number of reactive benzylic hydroxyl groups and may also be important in further depolymerizing the lignin once the oxidative-cleavage reaction has occurred. The formation of a p-electron-withdrawing -CHO substituent on aryl lignin units should increase the rate of hydrolysis of the ether bonds (26). Hydrolysis also forms p-phenylate ions, which then protect the benzaldehyde from further reaction via the Cannizzaro reaction, as mentioned earlier. 

A number of chemical analyses require prior depolymerization of the original sample e.g. starch, lignin, chitosan, carbohydrates). This process is occasionally very slow and has scarcely been subjected to US, despite the proven accelerating effect of this form of energy on these polymers [133,134] and others such as polystyrene [135] and poly(ethylene oxide) [136], or even on pharmaceutical precursors [137]. 

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