A Study on the Qxygen-Containing Groups in Pyridine Extracts from Coals

Abstract

The oxygen-containing functional groups and their contents in pyridine extracts prepared from a series of twelve Japanese coals were investigated toobtain some insight into their structures.
The estimation of the oxygen-containing functional groups (-OH, C=O, COON) in pyridine extracts was made by chemical methods which were applied previously to parent coals. The variation of thecontents of the oxygen-containing functional groups in pyridine extracts with respect to the carbon contents of parent coal was compared with those of parent coals. It was found that, in the case of relatively lower carbon content of coal, the contents of the hydroxyl and carbonyl groups in pyridine extract were lower than those of parent coals. As the coalification proceeded, the difference in thecontents between the parent coals and pyridine extracts diminished to disappear approximately at about 80% carbon or thereabouts.
It is to be mentioned that, in the proton NMR spectra of the pyridine extract of coal, the signals at c 3. 5to 5. 0 are assigned to the aliphatic hydrogens at the a position to the oxygen atom in the alkyl ethers. It may be concluded on this basis that the unreactive oxygen groups such as dialkyl and alkylaryl ethers are not important in coal andcoal derivatives with the exception of Ishikari peat pyridine extract which has the lowest carbon content. Therefore, it can be assumed that almost all unreactive oxygen functions in coal consist of heterocyclic or diphenyl ether types. By considering the results of structural analysis of aromaticity f in parent coal and their pyridine extracts, it can also be concluded that the hydroxyl groupsconsist of phenolic group.
Moreover, in the fraction isolated by various solventsfrom Sumiyoshi coal, the content of oxygen-containing groups was correlatedwith the character of these structures, especially with aromaticity. The conclusionsimilar to the one obtained above was found to hold true for the structure of the hydroxyl and unreactive oxygen functions in solvent fractionation products.