13—THE EFFECT OF DAYLIGHT ON THE PERIODATE OXIDATION OF β–METHYL GLUCOSIDE, β–METHYL CELLOBIOSIDE, AND CELLULOSE

Abstract

Light accelerates the periodate oxidation of β-methyl glucoside, β-methyl cellobioside, and cellulose. It is doubtful whether the initial (Malaprade) stage of the oxidation is affected, but the rates of the subsequent “over–oxidation” reactions are greatly increased. In the dark the oxidation becomes very slow at the end of the Malaprade stage, but in daylight there is no detectable discontinuity in the rate curves at this point. Over–oxidation proceeds slowly even in the dark, however, and ultimately the same results are obtained as in the light–accelerated reactions. When sufficient periodate is used, the oxidation continues until the organic matter has been oxidised to carbon dioxide and water; with insufficient oxidant, complete reduction of periodate to iodate occurs, followed by reduction of iodate and liberation of iodine. With a moderate excess of periodate over the amount required for the Malaprade reaction, cotton cellulose suffers a progressive loss of weight when oxidised in daylight, but in the dark the loss does not become considerable until the Malaprade stage is passed. Oxidation beyond this stage leads to the formation of an increasing proportion of soluble products, and ultimately a homogeneous, non–viscous solution is obtained. Formaldehyde and formic acid are formed in greater proportions than would be expected from oxidation of the terminal glucose units. The yield of acid is higher in the light than in the dark. For a given degree of oxidation, periodate oxycelluloses prepared in daylight have lower copper numbers than those made in the dark. These results suggest that, for a given set of conditions and a fixed degree of oxidation, the ratio of Malaprade to other kinds of oxidation is higher in the dark than in daylight. The mechanism of the over–oxidation of cellulose is discussed.