Ruthenium tetroxide oxidation of lignite

The objective of these studies was to develop new methods for the elucidation of the organic structure of low-rank coals, especially with regard to the nature of the hydroaromatic groups, the substituent groups on aromatic moieties and bridging groups between aromatic moieties. Ruthenium tetroxide is a useful reagent for the oxidation of alcohols, ethers, aldehydes, amides, alkenes and aromatic compounds. In the case of alkylbenzenes, the benzene ring is preferentially attacked, preserving any alkyl substituents as aliphatic carboxylic acids. The oxidation of lignite (Beulah mine) with ruthenium tetroxide proceeded rapidly at room temperature. The products from the oxidation in the aqueous layer could not be analyzed directly by the HPLC method because the solution was too dilute. Diazomethane in ether was stirred with the aqueous layer for two hours to convert the acids to ether soluble esters, which were analyzed by GC. The major components were aliphatic dicarboxylic acids and benzene polycarboxylic acids. Very low concentrations of aliphatic monocarboxylic acids were formed. Since succinic acid is present in the largest concentrations of the diacids, we may infer that a major structural feature of the lignite is a dimethylene bridge occurring between aromatic moieties or present in a hydroaromatic such asmore » 4,5-dihydropyrene. The model compound studies with diphenylmethane show that this method is limited in its applicability to the determination of single methylene bridges. Since malonic acid was produced in only trace amounts from oxidation of diphenylmethane, the absence of malonic acid in the lignite oxidation products does not rule out methylene bridges between aromatics in the coal. 7 references, 1 figure, 2 tables.« less