Zeisel method

Holden84 used a method of measurement in which the methanol liberated by PM in a buffered solution of pectinic acid in ten minutes has been estimated by the Zeisel method. This procedure is much more complicated than that described above and must be regarded as unreliable on account of the rapid change in the pH of such reaction mixtures, even if buffered. 

The determination of the methoxy group (OCH ) content of soils is important in studies concerned with the degree of humification of soil organic matter. Methods used to determine methoxy groups in soils have generally been based on volumetric modifications of the classical Zeisel method, which is a complicated and tedious procedure requiring specialised apparatus. 

Cumming s Modification.—(J. S. 0.1., 41, 20.)—A convenient apparatus for the estimation of methoxyl groups by the Zeisel method consists of a long-necked round-bottomed flask attached by a ground-glass joint to a bulbed U-tube. The methyl iodide generated by the interaction of hydriodic acid and the methoxyl group is absorbed in alcoholic silver nitrate. Pyridine may also be used as absorbent. (J. C. S., 117, 193.) For purification of hydriodic acid, see p. 506. 

It should be mentioned that the formation of methyl iodide by heating methyl ethers with concentrated hydriodic acid is quantitative and is the basis of the Zeisel method for the determination of methoxyl groups. 

Proof of structure of a new ether would involve cleavage by hydriodic acid and identification of the products formed. Cleavage is used quantitatively in the Zeisel method to show the number of alkoxyl groups in an alkyl aryl ether. 

The classical Zeisel method for the determination of ether (59) consists of digesting the substrate with hydrogen iodide. Analysis shows that the reaction proceeds in a favorable manner as designated by Saville. Sulfides do not interfere with the determination because the hard-soft combination is incorrect in such cases. 

Another simplified apparatus for the Zeisel method is shown in Fig. 19 and is made by the Vereinigte Fabriken fUr Laboratoriumsbedarf, Berlin, or the Kny-Scheerer... 

Methyl groups are frequently found as esters of uronic acids and sometimes as ethers of sugar residues. Ether-linked methyl groups and total methoxyl are determined by the Zeisel method 13). Methyl esters or glycosides may be differentiated from methyl ethers by the action of alkali and acid, respectively, which will saponify the ester or glycoside but have no effect on the ether. The ester or glycosidic methoxyl can be distilled as methanol and be determined colorimetrically after oxidation to formaldehyde and condensation with Schiff reagent 14). 

The Zeisel method has been used to determine ether groups in cellulose and polyvinyl ethers [58]. 

Epoxy groups have also been determined spectrophotometrically using 2,4 dinitrobenzene sulfonic acid [66] and by the Zeisel method [67-69]. 

Jaacks a.o. discovered 32 formation of the met-hoxyl end groups in poly-1,3,T trioxan, determined by the Zeisel method, and assumed, that these groups result from the H" ion shift (intramolecularly) or transfer (intermolecularly),... 

Ether Cellulose, polyvinyl ethers Zeisel method 199... 

The Zeisel method is based upon the fact that alkoxyl groups, whether in ethers or esters, are decomposed by heating with strong hydriodic acid to jneld alkyl iodides. The latter are absorbed in alcoholic AgNO.s and estimated as Agl. ... 

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