Methyl group migration during heat treatment of coal in the presence of polycyclic aromatic compounds

Migration reaction of methyl groups during heat treatment of both coal and its model compounds with aromatic compounds was studied. The reaction of coal with anthracene at 420°C for 5 min gave a mixture of methylanthracene (MA) isomers along with 9,10-dihydroanthracene (DHA) and 1,2,3,4-tetrahydroanthracene, the formation of the former compound indicating participation of methyl radicals. We found that the yield of MA could be correlated with the concentration of methyl groups in coal determined by NMR analysis. To discuss the detailed mechanism, we conducted the migration reaction of methyl group using model compounds. The results suggested that heating of 9-alkylanthracenes (methyl or ethyl) and 9-methoxyanthracene in the presence of hydrogen donating aromatics leads to release of alkyl radicals (methyl or ethyl), which can be converted to gases (methane or ethane) and alkylarenes depending on the radical accepting nature of arenes employed.