Methylation of humic acid derived from outcrop coal by two different methods gave products with methoxyl contents which did not agree with values expected from earlier functional group analyses. The discrepancies can be explained by postulating the presence in the humic acid of activated hydroxyl groups which show some of the properties of carboxylic acids.
IN CONTINUATION of the study of the oxidative degradation of humic acid derived from coal, an examination was made of methods that might be used to methylate the carboxyl and hydroxyl groups present in humic acids and so provide modified materials for oxidation. The methoxyl contents of methylated humic acids prepared by selected methods differed substantially from those expected on the basis of carboxyl and hydroxyl equivalents determined earlie& by titration and acetylation. The present paper describes the preparation of the methylated humic acids and an investigation of these differences.
EXPERIMENTAL
Humic acid (sample reference P4) was obtained as described previously3 from Warwickshire outcrop coal C65 by alkaline extraction, and had the following analysis: C, 63.1; H, 2.8; N, 1.4; S, 0.4; 0 (diff.), 32.3 (d.a.f.); ash, 2.9 ;I methoxyl (OCHs), 0.0 %.
All samples were dried in z)acuo at room temperature over phosphorus pentoxide. Methoxyl contents were determined by the semi-micro Zeisel method4. Infra-red (i.r.) spectra were determined on samples prepared as mulls in Nujol using a Perkin-Elmer Infracord spectrophotometer.
Methylation of humic acids. Several methods of methylation were tested, using the following reagents :
(1) Methanol and concentrated sulphuric acid.
(2) Methyl iodide and silver oxide in dimethylformamide, as described by R. Kuhn5 for methylation of sugars.