Cupric oxide oxidation

The reaction mechanism for nitrobenzene oxidation of lignin is still not well understood Thus, although nitrobenzene m an alkaline solution has been usually regarded as two-electron-transfer oxidant (Chang and Allan 1971), recent investigations on the nitrobenzene oxidation of lignins and related compounds indicate that nitrobenzene m alkaline solution acts as an one-electron-transfer oxidant (Schultz and Templeton 1986) 

The successful conversion of lignms into vanillin (2) and its analogs by nitrobenzene oxidation stimulated a search for economically viable processes for the manufacture of vanillin (2) from technical lignms In 1942, Pearl found that vanillin (2) could be obtained in a yield of about 20% of the lignin when 

The cupric oxidation of lignins is optimally performed by heating a mixture of lignin preparation, cupric oxide, and sodium hydroxide m an approximate weight ratio of 1 6 2 9 m an autoclave at 170°C for 2-5h, the concentration of sodium hydroxide being 1 5-2 M (Pearl and Beyer 1950, Pepper et al 1967) In the laboratory, cupric oxide oxidation of lignins is usually conducted according to the procedure of Pepper and co-workers (1967) The constituents of the oxidation mixture are qualitatively and quantitatively determined as described for the compounds m nitrobenzene oxidation mixtures 

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Kogel, I. and Bochter, R. (1985). Characterization of lignin in forest humus layers by high-performance liquid chromatography of cupric oxide oxidation products. Soil Biology and Biochemistry 17 637-640. 

Alkaline Cupric Oxide Oxidation after Preliminary Etching . 

Hedges, J.I. and Ertel, J.R. (1982) Characterization of lignin by gas capillary chromatography of cupric oxide oxidation products. Anal. Chem. 54, 174—178. 

Fig. 6.2.1. Nitrobenzene and cupric oxide oxidation products of lignins...

Table 6.2.2. Yields on nitrobenzene and cupric oxide oxidation products from Norway spruce (Picea abies) and aspen (Populus tremuloides) woods...

Nitrobenzene and Cupric Oxide Oxidations of Lignins in Grass Tissues... 

Table 6.2.5. Conversion factors (C) and HPLC retention times for the major saponification, nitrobenzene, and cupric oxide oxidation products of lignins...

As mentioned previously (Chap. 2.2.2.4.1), the major purpose of the GC-MS analysis of a nitrobenzene or cupric oxide oxidation mixture is to verify the identity of the oxidation products established previously by GC or HPLC analysis, and to elucidate the structure of unknown constituents. For example, GC-MS analysis of the nitrobenzene oxidation mixture of milled bamboo lignin from Phyllostachys pubescence showed unequivocally that compounds (l)-(3) in the total ion chromatogram of the oxidation mixture (Fig. 6.2.2) are indeed p-hydroxybenzaldehyde, vanillin, and syringaldehyde, respectively (Tai et al. 1990) (see Chap. 9.1 for a discussion of the GC-MS technique). In addition, the unknown compound in the chromatogram was identified as p-hydroxyazobenzene (15) (Fig. 6.2.1), one of the phenolic reduction products of nitrobenzene. 

For the characterization of lignins, nitrobenzene oxidation has the following advantages over cupric oxide oxidation (a) the constituents of the oxida-... 

Significance of the Results from Nitrobenzene and Cupric Oxide Oxidations... 

As stated above, nitrobenzene and cupric oxide oxidations of lignins are simple but by no means perfect methods for the characterization of lignins However, the methods are effective in the characterization of lignins if they are... 

Table 6.2.10. Aromatic products from the alkaline cupric oxide oxidation of chlorinated pine kraft pulp 1...

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