Ozonation

Abstract

Ozone has long been known to cleave carbon-carbon double and triple bonds and the products are often useful in elucidating the structure of the parent compound. The first ozonations of wood and lignins were carried out by Doree and Cunningham (1913). It was found that lignins were highly reactive toward ozone even at room temperature and became rapidly degraded to low-molecular weight compounds, while polysaccharides were much more resistant. In early work, the isolated reaction products, consisting largely of otherwise obtainable or excessively degraded acids, appeared to have little structural significance. It was not until comparatively recently, mainly thanks to Nakano and coworkers (but presaged by Aulin-Erdtman and Tomita in 1963), that it was discovered that extensive ozonation of lignin destroyed the aromatic moieties while leaving largely intact the side chains, which could be recovered in the form of identifiable mono- and dicarboxylic acids (Matsumoto et al. 1986 and earlier references therein). Thus, the side chain of the dominant structure in all native lignins, the arylglycerol-β-aryl ether moiety, can be obtained in the form of erythronic and threonic acids. Often, the only surviving aromatic carbons in the ozonation products are those directly attached to side chains. These carbons are recovered in the form of carboxylic acid groups.