Degradation Phenolic unit

Irrespective of whether the starting material is a wood, plant, or pulp sample, an isolated lignin sample, or a lignin model compound, it is essential that all free phenolic hydroxyl groups be protected by alkylation prior to oxidation to prevent degradation of the phenolic units. This is usually accomplished by methylation or ethylation in an alkaline solution with dimethyl sulfate or diethyl sulfate, respectively. The reaction step should be performed in a well-ventilated hood. 

Another factor which may influence the yield of acids obtained from lignin in wood is the presence of easily hydrolyzable aryl ether linkages such as those represented by phenylpropane-a-aryl ether structures In phenolic units, such structures are easily cleaved even under very mild alkaline conditions (Adler et al 1968) Therefore, it can be assumed that, in the alkylation step of the oxidative degradation procedure, a partial hydrolysis of such structures may occur, thereby creating new phenolic end groups that may affect the analysis... 

Fundamental. Figure 14 illustrates a general scheme for the alkaline degradation of hydrolyzable ether units. The reaction of phenolic units (40) is initiated by the phenoxide ion (41) to yield a quinonemethide intermediate (42) with elimination of the a-ether unit R,. This elimination reaction occurs quite readily for an a-aryl ether unit (in 1 M NaOH at 25°C) [326], whereas the a-ether linkage of a lignin-carbohydrate model was shown to be stable under the same conditions [304]. 

Analysis of the degradation products obtained from pyrolysis and oxidative degradation studies suggests that terrestrial humic substances are highly aromatic (c.70% of total C). However, these techniques tend to overemphasize the importance of aromatic and phenolic units. Non-degradative techniques, such as 1H and 13C nuclear magnetic resonance, probably give more realistic aromatic carbon contents of 20—50% for soil humics,... 

A strain of Candida guilliermondU degraded flavanol groups rapidly without release of phenolic units. Candida tropicalis degraded leucoanthocyanin groups with the liberation of catechin. 

The generation of nitrogen containing radicals is connected with oxidative electron-transfer reactions initiated by dimers of NO in phenol units and nonphenolic structures. The subsequent radical conversions include processes of degradation and modification (i.e., nitrosation and nitration) of lignin. 

In the experiment involving oxidative enzyme HRP (EC 1.11.1.7, RZ 1.9, 240 purpuro gallin (units/mg)) [89] for the enzymatic treatment and ultrasonic waves of 423 kHz and 5.5 W, the phenol degradation rate was found to increase. The ultrasound assisted biodegradation method has been found to be more efficient method than the sonolysis and enzyme treatment when operated individually. 

TCE is the other major contaminant at the site and is a common groundwater contaminant in aquifers throughout the United States [425]. Since TCE is a suspected carcinogen, the fate and transport of TCE in the environment and its microbial degradation have been extensively studied [25,63, 95,268,426,427]. Reductive dechlorination under anaerobic conditions and aerobic co-metabolic processes are the predominant pathways for TCE transformation. In aerobic co-metabolic processes, oxidation of TCE is catalyzed by the enzymes induced and expressed for the initial oxidation of the growth substrates [25, 63, 268, 426]. Several growth substrates such as methane, propane, butane, phenol, and toluene have been shown to induce oxygenase enzymes which co-metabolize TCE [428]. 

Most of the odours coming from livestock production units are associated with the biological degradation of the animal wastes (35), the feed and the body odour of the animals (1). Volatile fatty acids and phenolic compounds were found to contribute mostly to the strong, typical odour of animal houses by the help of sensory evaluations parallel to the chemical analysis (29), (30). 

While a maximum conversion of only approximately 25% of the polymer s repeating units can be obtained in solution, prolonged exposure times also result in a significant decrease in the molecular weight of polymer VI as some degradation also occurs with the liberation of phenol. The mechanism for this degradation is likely to resemble that proposed by Hiraoka and others (25,26) for the radiolysis of PMMA. The 13C NMR spectrum of the polymeric photoproduct shows clearly that the polymer contains a majority of unreacted starting phenyl methacrylate units with also some o-hydroxy ketone units. 

Phenol is present in plant and animal organic wastes as a result of decomposition. The level of phenol present in poultry manure, for example, has been shown to increase as degradation proceeds. Phenol is an important industrial chemical and enters the environment in air emissions and wastewater connected with its use as a chemical intermediate, disinfectant and antiseptic (United States National Library of Medicine, 1997). 

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