✍ Scribed by Werner Hodek; Georg Kölling
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Four bituminous coals of different rank were acylated with aliphatic acyl chlorides using Friedel-Crafts catalysts. A dry steam coal and a coking coal showed particularly good reactivity, five acyl groups being inserted per 100 carbon atoms. Compared with the initial coal, the acyfated coats were distinguished by considerably higher amounts soluble in pyridine and other solvents. 85% of the coking and dry steam coal substance became soluble when acylated with lauric acid chloride or acyl chlorides having still longer chains. The extractability of the coals after acylation depends on the chain length of the inserted acyl groups. To all appearances, the extracts are dispersed in the solution in the form of molecules. It is supposed that the good extractability of acylated coals is mainly due to depolymerization of the coal substance during acylation, disappearance of hydrogen bridges by esterification of the phenolic OH groups, and neutralization of intermolecular forces between the aromatic structures by insertion of long-chain substituents.
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