29—THE METHYLATION OF CELLULOSE WITH DIAZOMETHANE, AND SOME PROPERTIES OF THE PRODUCTS

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Abstract
Comparative methylations of cotton, mercerized cotton, cupranimonium rayon, a powdery hydrocellulose, and a product obtained by grinding cotton in a ball mill, have shown that the degree of methylation achieved with etherial diazomethane decreases with increasing crystallinity of the cellulose material. Although methylation takes place most readily in the amorphous regions, X–ray examination has shown that it is not confined to these regions. Methylation of cellulose with diazomethane greatly increases its loss of weight on heterogeneous hydrolysis with acid. This increase is attributed partly to an increase in the amorphous fraction as a result of the methylation, but mainly to the effect of methoxyl groups in preventing crystallization of initially amorphous material during the hydrolysis process. Chromatographic separation of the methylglucoses produced by hydrolysis of a cellulose methylated with diazomethane has shown that this material contained mono–, di–, and tri–substituted glucose units. In the metaperiodate oxidation of a series of methylcelluloses prepared with diazomethane, an increase in the degree of methylation has been found to result in a decrease in the rate of the Malaprade reaction but an increase in the rate of the degradative over–oxidation processes. A more highly methylated product (degree of substitution, 2·7), prepared by the action of alkali and dimethyl sulphate, has also been found to be progressively oxidized by metaperiodate; oxygen consumptions exceeding one atom per chain–unit have been observed, although the average number of α–glycol groups in this material cannot have exceeded 0·15 per chain–unit. Periodate oxidation does not provide a reliable means of determining the proportion of free α–glycol groups in the methylcelluloses studied.