Ozonation lignin models ozonized

To ensure complete oxidation of aldehydes to carboxylic acids, Aulin-Erdtman and Tomita (1963) treated the ozonation products of lignin model compounds with hydrogen peroxide. Soteland (1971) applied hydrogen peroxide to a groundwood ozonation product and found that it degraded the components to unidentified volatile substances. To simplify the product mixture, reduction is sometimes used to stop further oxidation. Tanahashi et al. (1975) applied palladium-catalyzed hydrogenation, while Kondo et al. (1987) added dimethyl sulfide. 

In this section, examples of information available from ozonation of lignin model compounds, related compounds, and lignins will be presented. Table 6.7.2 lists the monomeric and dimeric lignin model compounds that have been ozonated. 

Balousek et al. (1981) used the y-deoxy /J-O-4 lignin model compound (4) (Fig. 6.7.3) and an intentionally very low ozone/substrate ratio (sS0.4 1.0). They found that, of the 30% of (4) consumed, the most abundant product identified was y-deoxyveratrylglycerol (6), which accounted for 10.8% of the starting material (4) consumed. This compound and about 3% of other ident-... 

Table 6.7.2. Lignin model compounds subjected to ozonation...

Additional evidence for the stereospecific conversion of fi-O-4 and arylglycerol lignin models to tetronic acids under conditions that selectively oxidize aryl rings also comes from acidic permanganate oxidation (Tsutsumi et al. 1990). This method gives essentially the same products as ozonation. 

Fig. 6.7.4. fl-5 and fi- lignin models, ozonation to 2-hydroxy-3-hydroxymethyl-butanedioic acid (Habu et al. 1990, Tsutsumi et al. 1990)... 

Balousek PJ, McDonough TJ, McKelvey RD, Johnson DC (1981) The effects of ozone upon a lignin model containing the /1-aryl ether linkage Sven Papperstidn 84 R49-R54 Bes RS, Gas G, Molimer J, Vidal P, Mathieu J, Mora JC (1989) Enhancement of poplar cellulose susceptibility to cellulase enzyme hydrolysis by ozonation Ozone Sci Eng 11 217-226... 

Kratzl K, Claus P, Reichel G (1976) Reactions of lignin and lignin model compounds with ozone TAPPI 59(11) 86-87... 

The choice of liquid phase can affect the course of ozonation. This has been shown with phenylindenes by Miura et al. (1985) and with lignin models by Kratzl et al. (1976), who found that 4-methylveratrole gave a higher yield of dimethyl -methyl-cis,cis-muconate in 45% aqueous acetic acid than in dichloromethane and that the yield of dimethyl oxalate from acetoveratrone was markedly dependent on the solvent. Eriksson and Gierer (1985) found that in methanol the benzene ring of vanillin is cleaved (albeit only very slowly, after acetalization has occurred), but that in nonprotic solvents, such as acetone, the initial reaction is oxidation of the aldehyde function to a carboxyl group. 

T Eriksson, J Gierer. Relative rates of ozonation of lignin model compounds. 3rd International Symposium on Wood and Pulping Chemistry, Vancouver, Canada. Proceedings, Vol. 2, pp. 29-30, 1985. 

Scheme 4 Decomposition of lignin model compound by ozonization...

Hatakeyama H, Tonooka T, Nakano J, Migita N (1967) Ozonization of lignin model compounds. Kogyo Kagaku Zasshi. 70 2348-2352... 

Letumier F, Barbe J-M, Trichet A, Grulard R (1999) Ozonation reactions of monomer and dimer lignin models influence of a catalytic amount of a manganese cyclam derivaties on the ozonation reaction. Ozone Science Engineering - The Journal of the International Ozone Association 21 53-67... 

Such processes are always accompanied by a DP loss, either by electrophilic attack of ozone, by an ozone-catalyzed cleavage of the glycosidic bond or by attack of secondary radical species [15]. Residual lignin also plays a crucial role in ozone bleaching. Model studies showed that lignin with free phenolic hydroxyl groups accelerated carbohydrate oxidation, probably by activation of oxygen via phenoxyl radicals, whereas etherified phenolic model compounds had a protective effect [16,17]. 

Perhaps the most elegant application of ozonation to studies on the side chain in lignin deals with the frequency with which the glyceraldehyde-2-aryl ether unit occurs in lignin (Matsumoto et al. 1984a). After NaBH4 reduction, ozonation, and saponification, model compound (12) gave a 95% yield of... 

Aulin-Erdtman G, Tomita Y (1963) Studies on the degradation of lignin and model compounds I The configuration of dehydrodusoeugenol Acta Chem Scand 17 535-536 Bailey PS (1978) Ozonation in organic chemistry I Olefimc compounds Academic Press, New York, 272 pp... 

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