Work-Up of Ozonation Product Mixtures

In most lignin ozonation studies, residual ozone is purged from the system by a stream of nitrogen. Ozonides and ozone-generated peroxides can survive in the crude product mixture for several days (Kolsaker and Bailey 1967, Soteland 1971). Conversion of the ozonation products to stable, more easily identifiable products can be achieved by further oxidation, reduction, acid- or base-induced decomposition, or some combination of such methods. 

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. 

Lignin ozonation products contain some diacids that occur in nonesterified, partially esterified, and fully esterified forms (typically methyl esters derived from cleavage of the methoxylated aromatic rings). Bonnet et al. (1989) chose to esterify the free carboxyl groups by use of diazomethane to simplify the 

CM Fig. 6.7.2. Effect of acidity/basicity on decomposition of a styrene-type ozonide. (Kolsaker and Bailey 1967) 

If so desired, the hydrolyzed ozonation products can first be separated on an anion exchange resin into what have been described as neutral, monocarboxylic and dicarboxylic fractions (Matsumoto et al. 1986, Taneda et al. 1989). In our experience, however, acids do not always appear in the expected fraction, and there is a complicating contamination by succinic acid, apparently originating in the resin. These difficulties together with the greatly increased resolution of capillary gas chromatography (GC) have combined to render this preliminary separation unnecessary. 

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