Lignin oxidative degradation

A large number of patents describe various procedures for the mainly continuous hydrolysis and oxidation processes, as weU as for the purification steps requited to obtain high grade vanillin. Lignin is degraded either with sodium hydroxide or with calcium hydroxide solution and simultaneously... 

The chemical and enzymatic oxidative degradation of lignin (and coal) is used to obtain not only vanillin and benzoic acid, but also other aromatics (Baciocchi et al. 1999, references therein). In principle, lignin could be a major nonfossil and renewable source of aromatic compounds, a feedstock for synthesis of useful products. The problem deserves finding new ion-radical routes to cleave lignin. At present, there is some shortage in oil, gas, and even coal, which had usually been well-available natural sources of aromatics. In the near future, biomass may (and must) replace fossil-originated materials in the manufacture of commercial carbon-based products. 

This heme-dependent enzyme [EC 1.11.1.13] catalyzes the reaction of two Mn + with two and hydrogen peroxide to generate two Mn + and two water. The enzyme participates in the oxidative degradation of lignin in white rot basidiomycetes. 

The chemical reactions used to degrade these aromatic compounds are numerous and complex. As was mentioned in Chapter 16, some fungi initiate the attack on lignin with peroxidases and produce soluble compounds that can be attacked by bacteria. In other cases elimination reactions may be used to initiate degradation. For example, some bacteria release phenol from tyrosine by P elimination (Fig. 14-5). However, more often hydroxylation and oxidative degradation of side chains lead to derivatives of benzoic acid or of the various hydroxybenzoic... 

Diconiferyl ether (XXV) has not yet been isolated, but its presence among the dilignols is not inconceivable 28). Undoubtedly, diaryl ether derivatives are also preferably formed by dehydrogenation of preformed oligolignols which contain saturated side chains. The occurrence of diaryl ethers in lignin has been proved by its oxidative degradation since the acid VIII is also formed. 

Our studies were concerned with the reactions occurring during mild oxidation. This paper deals with model experiments on one of the possible reaction sequences—namely, the formation of biphenyl structures and oxidative degradation. Numerous oxidation experiments with suitable lignin models were performed, and during these studies we determined the rate of oxygen consumption by the compounds dissolved in 0.27V NaOH at 70°C. A detailed description of our method is given under Experimental. 

The chemical and enzymatic oxidative degradation of lignin (and coal) is used to obtain not only vanillin but also other aromatics (Baciocchi et al. 1999 and references therein). 

Several compounds were also found to have a seasonal distribution. Kubatova et al. (2002) found that concentrations of lignin and cellulose pyrolysis products from wood burning were higher in aerosol samples collected during low-temperature conditions. On the other hand, concentrations of dicarboxylic acids and related products that are believed to be the oxidation products of hydrocarbons and fatty acids were highest in summer aerosols. PAHs, which are susceptible to atmospheric oxidation, were also more prevalent in winter than in summer. These results suggest that atmospheric oxidation of VOCs into secondary OAs and related oxidative degradation products are key factors in any OA mass closure, source identification, and source apportionment study. However, additional work is much desirable to assess the extent and seasonal variation of these processes. 

Gold MEI, Kutsuki H, Morgan MA. Oxidative degradation of lignin by photochemical and chemical radical generating systems. Photochem Photobiol 1983 38 647-651. 

Bao WL, Fukushima Y, Jensen KA et al (1994) Oxidative degradation of non-phenolic lignin during lipid peroxidation by fungal manganese peroxidase. FEBS Lett 354 297-300... 

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