Cellulose Studies:XI. Acetal Type of Methoxyl Groups in Methanolyzed Celluloses
AbstractNative cotton and commercial viscose rayon were degraded by using a saturated solution of hydrogen chloride (about 43%) in methanol at 0° C. It was found that, on the average, 8.1 bonds in native cotton suffered methanolysis during the first 6 hrs. of the reaction, whereas in the ensuing period of 666 hrs. only 1.6 bonds became cleaved. The results indicate that the initial reaction comes to a practical standstill after about the same stage of degradation has been reached as in the mild hydrolytic scission of the same materials (D.P. ∼ 250 for cotton, and D.P. ∼ 60 for viscose rayon). In order to gain information as to the nature of the methoxyl groups in the methanolyzed products, a study of the rate of hydrolysis of the latter was made. Evidently, if the classical concept of cellulose structure is correct—that is, if only normal methyl. glucopyranoside end groups are present—then the rate of acid hydrolysis, as measured by the increase in the reducing power, should be of the order of magnitude shown by the normal methyl glucopyranosides. On the other hand, a very fast rate of hydrolysis, which is characteristic for the open-chain dimethyl acetals of the sugars, would constitute evidence for the presence of such types of residues; hence, it would favor the new concept of cellulose structure. The results showed that more than one-half of the material in the case of viscose rayon and about one-half in that of native cotton were hydrolyzed by 0.05N HCl at 60°C in a period of 48 hrs., which is shorter beyond all comparison than the half-life (3,450 hrs.) of methyl α-gluco pyranoside under identical conditions. These results are considered to supply the chemical proof for the presence of the acid-sensitive, open-chain glucose residues which were suggested in the new formula for cellulose.