Zeisel method, 0-methyl determination

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. 

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). 

Methylated phenols very often form part of the molecule of natural products, in particular, of alkaloids. In the elucidation of their constitution the quantitative determination of the methoxyl groups is of great importance. This determination is carried out by the excellent method of Zeisel, in which the methyl group is removed as methyl iodide by the action of concentrated hydriodic acid. This method (directions, p. 80) should be practised with the anisole already prepared. 

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