Distribution Of Methoxyl Groups Research Articles

Variables affecting the methylation reactions of cellulose

AbstractSolubility of methyl cellulose (MC) depends on the degree of substitution (DS), the average degree of polymerization (DP), and the distribution of methoxyl groups. Of these, the DS appears to be the most important. The DS of the MC depends on the conditions of preparation. The conditions studied in this work revealed that the DS of the MC increased as the concentration of sodium hydroxide increased from 10 to 50%. This result is attributed to the increase in the extent of formation of alkali cellulose II as a result of the increase in the alkali concentration and hence the increase of the DS of the MC. Decreasing both the ratio of dimethyl sulfate: cellulose and the liquor ratio increased the DS. High DS was achieved within a period of 2 and 3 h. However, the DS increased as the time increased. The decrease of the DS as the liquor ratio increased may be attributed to the sol–gel transition due to the interaction of the hydrophobic methoxyl groups within the polymer chains. To reveal the effect of the thermal sol–gel transition, the reaction was carried out in nonaqueous medium and the results obtained showed an increase of the DS with the increase of the solvent ratio until a maximum. This result may be contributed to the breakdown of the hydrogen bonding in the presence of solvents that transfer the reaction medium to the sol‐form and hence more methylating reaction takes place. The degree of the solvation of the methyl groups into the solvents also plays a role. © 1994 John Wiley & Sons, Inc.

Distribution of Methoxyl Groups in the Methylation of Starch Alkoxides Obtained by Metallation with Alkali Metal Naphthalene

Abstract The distribution of the alkoxide groups obtained in the metallation of starch in dimethyl sulfoxide solution by alkali metal naphthalenes was studied. The starch alkoxide was reacted with methyl iodide, and the methylated starch was hydrolyzed and analyzed for glucose and O-methyl glucose derivatives. The metallation reaction was found to be random, as seen from the fact that at low alkoxide concentration (D.S = 0.6), 2,3,6-tri-O-methyl glucose was formed, while at relatively high alkoxide concentration (D.S. = 1.5) unreacted glucose was still present. At low alkoxide concentration (D.S. ⋍ 0.6) there was, to a certain extent, preferential metallation at the C2 hydroxyl groups, and to a lesser extent at the C6 hydroxyl groups, as seen from the relative molar ratios of about 10:4:1 of the 2-, 6-, and 3-O-methyl glucose derivatives obtained, respectively. An increase in the metallation at the C3 hydroxyl occurred with increasing alkoxide concentration. The distribution of the methoxyl groups with th...

Quantitative determination of mixtures of alkyl ethers of d-glucose : Part II. Structural studies of partially methylated cotton cellulose

The distribution of methoxyl groups in repeatedly methylated cotton cellulose is in agreement with the suggestion that the elementary fibril is the basic structural element and suggests that a simple model for these elementary fibrils would have an average cross-section of 8 × 10 cellulose chains. The dimensions of such a cross-section are approximately 40 × 50 Å and agree closely with electron-microscopical observations. This fibril has a surface in which all of the readily accessible hydroxyl groups lie. Methylation of these hydroxyl groups is quite rapid, but the methylation of hydroxyl groups below this surface takes place at a lower rate. The slower reaction proceeds with little change in methoxyl group distribution, other than the appearance of tri-substituted d-glucose units at a rate similar to that of the disappearance of d-glucose; it is suggested that this stage of the reaction occurs with an advancing zone of methylation passing through ordered material. Evidence has also been obtained for aggregation of the elementary fibrils.

Distribution of Methoxyl Groups in the Methylation of the Monosodio Derivatives of Methyl α-D-\Glucopyranoside and Cellulose1,2

Distribution of Methoxyl Groups in the Methylation of the Monosodio Derivatives of Methyl α-D-\Glucopyranoside and Cellulose^1,2

The Effect of the Distribution of Methoxyl Groups upon Some Textile Properties of Methylated Cotton Fiber

The Effect of the Distribution of Methoxyl Groups upon Some Textile Properties of Methylated Cotton Fiber