Determination of Methoxyl Groups

When a compound with an alkoxyl group is heated with concentrated hydriodic acid, the alkoxyl group is cleaved and converted to the corresponding alkyl iodide as follows  

When the alkyl iodide (R l) produced is volatile, as is the case with methyl or ethyl iodide, it is quantitatively stripped from the reaction mixture by purging with an inert gas such as carbon dioxide. The methyl or ethyl iodide in the 

Springer Senes in Wood Science Methods in Lignin Chemistry (Edited by S.Y. Lin and C.W. Dence) 

Finally, the iodine thus produced is titrated with a dilute standard sodium thiosulfate solution using 1% starch solution as indicator (Leipert 1929). Since six atoms of iodine are liberated for each alkoxyl group, the alkoxyl content can be quantitatively determined with very high accuracy, even on a micro scale. 

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Filippov, M.P. and Kuz minov, V.l. 1971. Photometric determination of methoxyl groups in pectic substances. J. Anal. Chem. USSR (Zhurnal Analiticheskoi Khimii). 26 143-146. 

Note 6. See Chapter 7.6.3 for determination of methoxyl groups in lignins. 

Sobue H, Hatano A, Arai T (1959) Determination of methoxyl group. Sen-i Gakkaishi (J Soc Textile Cellul Ind Jpn) 15 21-23... 

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. 

Note 6. See Chapter 7.6.3 for determination of methoxyl groups in lignins. Note 7. Although the reaction is conducted under nitrogen atmosphere by passing nitrogen gas through the reaction mixture, a small amount of... 

Kujawski, M. and Tuszynski, T. 1987. A comparison of some methods for the determination of methoxyl groups in commercial pectin preparations, Nahrung, 31(3) 233-238. 

C-L Chen. Determination of methoxyl groups. In SY Lin, CW Dence, eds. Methods in Lignin Chemistry. Berlin Springer-Verlag, 1992, pp. 465 72. 

A number of compounds of this type are in use and they consist of methyl (and in some cases ethyl or hydroxypropyl)ethers of cellulose they are characterised by their alkoxyl content. A general method for the determination of methoxyl groups is as follows ... 

The above method is applicable to the determination of methoxyl groups in methylcellulose 20, B.P.C. (which contains about 28 per cent of —OCH3), and to the determination of ethoxyl groups in ethylcelllllose, N.F. In the latter case 1 ml 0 1 N sodium thiosulphate = 0 0007510 g of ethoxyl (—OCgHg). 

In a related approach, Ni et al (1990) have developed a procedure for determining lignin in softwood kraft pulp based on the conversion of methoxyl groups in the lignin to methanol when the pulp is chlorinated under a specified... 

Interesting data have been obtained from the determination of the content of methoxyl groups in the products of the saponification of cellulose tosylate with a methanol solution of KOH (Table 3). 

The use of lead tetraacetate for adding acetoxy groups to a double bond, as here used for preparing the pentaacetate (76), has been widely applied in synthetic organic chemistry, but there have been only a few applications to carbohydrates (see Perlin s review in this Series, for other examples). The conversion of (76) to the dicarbonyl derivative (77) (in 65% yield and in the crystalline state) was made by autohydrolysis in water at room temperature for 3 hr. The structure was deduced from elemental analysis, acetyl analysis, and the absence of methoxyl groups, and from its mode of synthesis. The acetyl determination could be made by direct titration with... 

Determination of Methoxyl and Ethoxyl Groups in Acetals and Easily Volatile Alcohols, D. O. Hoffrnan and M. L. Wolfrom, Anal. Chem., 19, 225-228 (1947). 

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