Lignin alkaline oxidation

Alkali lignin was oxidized with alkaline cupric oxide at atmospheric and superatmospheric pressure after first etching the lignin with alumi-... 

We found that when phenols (or lignins) are oxidized in alkaline media the initial step is a one-electron abstraction from the phenolic hydroxyl group forming a phenoxyl radical. We discovered an electrochemical method which allows us to determine roughly the free enthalpy of this particular reaction (phenol —> phenoxyl radical). This method has been... 

It is highly probable that since a similar ratio is found regarding the identifiable products (phenolic aldehydes and ketones) obtained by the alkaline oxidation of these species, that the same readily releasable fraction of the original lignin is involved in each case. 

The alkaline oxidative cleavage of softwood lignin to vanillin is an other important reaction of wood chemistry. Such typical one-electron oxidants as nitrobenzene, cupric salts, and cerium ammonium nitrate are used. The reaction includes a cation radical step and pro-... 

Another category of lignin-based chemicals is obtained when lignosulfonates are degraded to low molecular weight products. The commercially most important product is vanillin, which is obtained by alkaline oxidation... 

Wu, G. X., Heitz, M., and Chomet, E., Improved alkaline oxidation process for the production of aldehydes (vanillin and syringaldehyde) from steam-explosion Hardwood Lignin. Industrial Eng Chem Res 1994, 33 (3),... 

Tanaka J, Kondo T (1959) Degradation of lignin III Alkaline oxidation products of hardowood lignin Mokuzai Gakkaishi 5 105-108... 

Alkaline oxidation of lignin is the commercial source of vanillin. This procedure converts a significant portion of the lignin to aromatic fragments that are, for the most part, aromatic aldehydes. The mechanism probably involves two steps, hydrolysis of the aryl ether linkages followed by side chain oxidation. 

Lignin is an abundant component of vascular plants, and the phenolic units from which it is synthesized are relatively stable towards chemical alteration but exhibit some compositional variation with plant type. Lignin constituents are, therefore, potentially useful indicators of different types of vascular plant sources. Alkaline oxidation of lignins from vascular plant tissue using copper(II) oxide (e.g. Hedges Mann 1979 Hedges Ertel 1982) yields four groups of... 

Ferulic acid One of the cinnamyl degradation products released from the alkaline oxidation of lignin. 

Phenolic aldehyde One of the degradation products released from the alkaline oxidation of lignin. Aldehydes represent a level of oxidation of the building blocks of the lignin macromolecule that is intermediate to ketones and acids. 

Vanillyl phenols A group of degradation products released from the alkaline oxidation of lignin that includes vanillin, acetovanillone, and vanillic acid. The vanillyl components are diagnostic of vascular-plant organic matter. 

Many of the chemical reactions used to modify lignosulfonates are also used to modify kraft lignins. These include ozonation, alkaline—air oxidation, condensation with formaldehyde and carboxylation with chloroacetic acid (100), and epoxysuccinate (101). In addition, cationic kraft lignins can be prepared by reaction with glycidjiamine (102). 

The aromatic nature of lignin contrasts with the aliphatic stmcture of the carbohydrates and permits the selective use of electrophilic substitution reactions, eg, chlorination, sulfonation, or nitration. A portion of the phenoUc hydroxyl units, which are estimated to comprise 30 wt % of softwood lignin, are unsubstituted. In alkaline systems the ionized hydroxyl group is highly susceptible to oxidative reactions. 

Further Preparative Reactions. When pulps are to be used in the production of materials that do not retain the original fiber stmcture, such as rayon or ceUulose acetate film, the lignin, hemiceUulose, and other components must be reduced to the lowest possible concentrations. A surfactant (ionic or nonionic) is often added during a hot, weakly alkaline extraction step after chlorination. Another approach, sometimes used in addition to the surfactant step, is to treat the pulp with 6—10% NaOH after most of the oxidative bleaching is finished. This treatment removes most of the hemiceUulose. In most purification plants the final stage includes use of sulfuric acid chelators are optional. 

Sodium chlorite has also been used for treatment and removal of toxic and odorous gases such as hydrogen sulfide and mercaptans. Chlorine dioxide from chlorite is also useful for microbial and slime control in paper mills and alkaline paper machine systems (164,165). The use of sodium chlorite in textile bleaching and stripping is well known. Cotton is not degraded by sodium chlorite because the oxidation reactions are specific for the hemiceUulose and lignin components of the fibers. 

Rapid Micromethod for Alkaline Nitrobenzene Oxidation of Lignin... 

Certain derivatives of the lignin sulfonic acids can be determined directly in water. The nitroso derivatives, which are easily formed in solution, can be determined by differential pulse polarography [438]. Vanillin can be formed by alkaline hydrolysis [439] or alkaline nitrobenzene oxidation [440], extracted into an organic solvent and determined by gas chromatography. 

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