Kuhn-Roth estimation

Reduction apparently creates fresh hydroaromatic structure (at the expense of the aromatics), and thus the methyl groups attached to the aromatic structures are likely to become amenable to quantitative estimation (by the Kuhn-Roth procedure), provided that the particular aromatic ring is reduced to hydroaromatic. Significantly, the reduced samples of the lower rank coals did not yield much higher values for methyl groups than the original samples. Thus, it would appear that Kuhn-Roth estimation does not completely measure the true C-methyl content in coals, especially in high rank coal samples. 

Figure 2. The nature of variation of alicyclic and methyl-carbon (Kuhn-Roth) contents with coal rank Kuhn-Roth estimate ...

Figure 4. Variation of the true methyl content of coal with rank and its comparison with the Kuhn-Roth estimate...

Under vigorous conditions strong oxidizing agents such as chromic acid and permanganate attack alkanes, but the reaction is of little synthetic use for usually mixtures of products are obtained in low yield. The reaction was traditionally used in the Kuhn-Roth estimation of the number of methyl groups in an unknown compound. This depends on the fact that a methyl group is rarely oxidized (the relative rates of oxidation of primary, secondary and tertiary C—H bonds are 1 110 7000) and hence the amount of ethanoic acid formed can be quantified. 

Martin B. Neuworth The Kuhn-Roth method has a number of limitations. These were discussed by Brandenberger et al. (Anal. Chem. 33, 453 (1961)). The normal method for estimating C-methyl groups is based on a determination of total acidity calculated as acetic acid. Brandenberger has shown that other acids can be produced during the oxidation—e.g., benzoic acid, and these acids steam distil with the acetic acid. Therefore, when the classical Kuhn-Roth procedure is applied to a substance like coal, it would lead to methyl group values of questionable significance. 

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