Aromatic units in coal

Abstract

THE organic matter in coal consists largely of a macromolecular material of complex and variable composition. When coal is pyrolysed, a large fraction is converted to char, and a number of complex aromatic compounds are formed. Because of the extensive chemical change which takes place during this process, however, it is not clear what relationship the products have to the original structure of coal. Many workers have used oxidation procedures to degrade coal to simpler species which are more readily interpreted in terms of coal structure. Oxidation products, however, were in general studied by limited classical organic chemistry methods for separation and identification of products^1,2. To date the only aromatic acids definitely identified have been the carboxylic acids of benzene^3,4. Commonly used oxidants have been HNO₃, HNO₃–K₂Cr₂O₇, KMnO₄, O₂ and H₂O₂–O₃ in conditions for drastic degradation of aromatic rings. On the basis of results of oxidation of coal with a selective oxidant, NaOCl, Chakrabartty and Berkowitz have suggested⁵ that coal has a largely non-aromatic “tricycloalkane or polyamantane” structure. They pointed out that no evidence for aromatic compounds other than benzene derivatives was found in their oxidation product. Our experimental data do not support this view but rather the generally accepted idea that coal is predominantly an aromatic material.