Mechanism of ozone attack on α‐methyl glucoside and cellulosic materials

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Abstract
Ozone attack on cellulose and related substances was investigated and appears to involve a twofold mechanism. One is a free‐radical chain mechanism involving oxygen in the propagating step. This slow reaction is highly indiscriminate, showing very little, if any, specificity as to the site of attack and resulting in the formation of peroxide, carbonyl, carboxyl, and presumably lactone groups. In the presence of oxygen, kinetic chain lengths of over 100 were measured, but in nitrogen atmosphere the total oxidation of substrate was equivalent to the amount of ozone consumed. The second process appears to be an electrophilic attack which liberates the anomeric carbon of glycosides via an ozone‐catalyzed hydrolysis of glycosidic linkages. This reaction, analogous to a nitronium or chloronium ion‐ or proton‐catalyzed hydrolysis, is postulated since chain degradation of polysaccharides is equally severe in the presence or absence of oxygen, and occurs in buffered solutions or suspensions even in the neutral pH range, and because the main product of ozone attack on α‐methyl glucoside is glucose. Brightness improvement in cellulose involves an electrophilic attack on double bonds and therefore is a direct function of the quantity of ozone used, like chain degradation. It is therefore not surprising that we have found no method of enhancing the specificity of ozone attack on the colored material relative to chain degradation. Because of the topochemical and diffusion‐controlled character of the reaction on cellulose, the use of a different temperature range will cause only a trivial difference in the relative rates of attack.

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