Methoxyl content determination

Copolymerization reactions Copolymerization experiments with styrene and MMA employed molar fractions of 20, 40, 60, and 80% comonomers, which were reacted in ethanol 1,2-dichIorethane 60 40 (by volume) mixtures and benzoyl peroxide as catalyst. Polymerizations were carried out at 70°C. The reactions were quenched by the addition of methanol as non-solvent, and the copolymer was isolated by centrifugation. Copolymer analysis employed UV spectroscopy for copolymers with MMA, and methoxyl content determination according to a procedure by Hodges et al. (16) in the case of styrene copolymers. Reactivity ratios were determined in accordance with the method by Kelen-Tiidos (17) and that by Yezrielev-Brokhina-Roskin (YBR) (18). Experimental details and results are presented elsewhere (15). 

The various conflicting interpretations are attributed in part to the non-specific nature of the spectrum of lignin and more so to the fact that the. molecular weight of lignin is, as yet, unknown. Recently, Aulin-Erdtman (4) has successfully used the methoxyl content of various lignins instead of molecular weights in the determination of extinction coefficients. 

Evidence was presented that thallous ethylate did not penetrate or alter the crystalline parts of the fiber. Moreover, it was possible to conduct the thallation with different solvents for thallous ethylate. When this was done with normal ethers, the extent of methylation was observed to decrease as the molecular volume of the thallous ethylate solvent increased. These results suggested that accessibility is dependent upon the penetrating power of the ether solvent. Amorphous cellulose was, therefore, defined as the percentage of cellulose wetted by an ether of zero molecular volume and was estimated by determining methylation-molecular volume values for three or more straight-chain ethers, plotting the data and extrapolating to obtain methoxyl content for an ether of zero molecular volume. The amount of cellulose corre-... 

Methoxyl content of the different samples were determined using a modified Zeisel procedure (14). 

Reactivity ratios between acrylated lignin model compound (Fig. 2), defined as Mi, with either MM A or S, defined as M2, were determined experimentally in accordance with standard procedures (15). These involve mixing two different vinyl monomers in various molar ratios with catalyst (i.e., benzoyl peroxide) and solvent, heating the mixture to achieve polymerization, and recovering the polymer by the addition of non-solvent, and centrifugation. The respective molar monomer fractions of the copolymer were determined by UV-spectroscopy in the cases where MMA served as M2, and by methoxyl content analysis in those cases in which S was the M2-species. The results were subjected to numerical treatments according to the established relationships of Kelen-Tiidos (17) and Yezrielev-Brokhina-Roskin (YBR) (18), and this is described elsewhere (15). 

Starting Material. A drum of concentrated, mixed, southern pine kraft black liquor was kindly supplied by the Canton, N. C. mill of the Champion Paper and Fibre Co. Analytical data for the liquor indicated 49.7% total solids and a methoxyl content of the oven-dried solids of 5.54%. The pH of the liquor as received was 12.3. (All melting points are uncorrected. Infrared absorption spectra were determined by Mr. Lowell Sell of The Institute of Paper Chemistry Analytical Group.)... 

Quantitative, 3C NMR has been used to determine the methoxyl contents of lignin in many wood species (Obst and Landucci 1986). The syringyl/guaiacyl composition in aspen MWL also has been measured using routine NMR acquisition parameters, but this method is restricted to carbons having the same chemical substituents and T, values and the results should be very carefully interpreted (Lapierre et al. 1984b). Semi-quantitative analysis can also be performed (Nimz et al. 1982). 

The aliphatic hydroxyl content of a lignin expressed on a methoxyl content and G> unit basis can be obtained by subtracting the phenolic hydroxyl content reported on a methoxyl or C9 basis from the corresponding total hydroxyl value (see Chap. 7.2 for determination of phenolic hydroxyl groups). 

Chemical methods for analysis of phenolic hydroxyl groups include determination of the increase in methoxyl content resulting from diazomethane methylation (Bjorkman and Person 1957), the increase in phenolic acetyl group content after acetylation (Lenz 1968, Mansson 1983), and low-molecular weight compounds derived from the degradation of phenolic structures (Chap. 5.2). The phenolic acetyl group of acetylated lignin may also be determined by an NMR spectroscopic technique (Lenz 1968, Robert et al. 1986) or by a selective deacetylation in pyrrolidine (aminolysis) (Mansson 1983). 

Determination of Methoxyl Content by the Viebock and Schwappach Procedure (Silbernagel 1980, pers. commun.)... 

Accessibility. The extent of etherification is often determined by the accessibility of a substrate under a given environment. As Segal discussed [8], the extent of methylation with ethereal diazomethane (indicated by methoxyl contents) increased in the order hydrocellulose (5.9%) < cotton (7%) < mercerized cotton (14.9%) < cuprammonium rayon (18.6%) < ball mill-ground cotton (20.6%). Crystallinity of the cellulose was considered to be a significant factor. 

Degree of esterification is an important molecular index for pectin classification that describes the extent to which carboxyl groups in pectin molecules exist as the methyl ester. Depending on the methods used for determination, DE can be expressed either by the ratio of methylated carboxyl groups to a total of carboxyl groups or by the percentage of methoxyl content. The theoretical maximum value for each expression is 100% for the former and 16.3% for the latter (Doessburg, 1965). 

Schultz, T.H. 1965. Determination of the degree of esterification of pectin. Determination of the ester methoxyl content of pectin by saponification and titration. Determination of the anhydrouronic acid content by decarboxylation and titration of the liberated carbon dioxide, in Methods in Carbohydrate Chemistry 5, New York Academic Press, pp. 189-194. 

The purity of a lignin sample can, in many cases, be judged based on the methoxyl content. The methoxyl content is nsnally determined according to modihed Zeisel procedures [123], Alternatively the methoxyl content can be determined by NMR spectroscopy [124], The methoxyl content can also be roughly estimated based on H NMR spectral examinations [79],... 

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