Studies on the bond cleavage reaction in coal molecule or coal model compounds

A cleavage reaction of chemical bonds connecting between aromatic clusters in coal was investigated. We conducted the heat-treatment of coals or coal model compounds in the presence of a hydrogen donor at 380-420 °C for 5-60 min in a sealed tube. As the hydrogen donor, 9,10-dihydroanthracene (DHA) or 9,10-dihydrophenanthrene (DHP) was used. In the reaction of coal with hydrogen donor at 420 °C for 5 min, larger amounts of hydrogen were consumed for DHP than for DHA. Bond cleavage reactions using several model compounds showed that the yields of homolytically cleaved products were higher than those of ipso position cleaved products. This is reasonable in terms of their bond dissociation energies. On the other hand, ipso position cleavage reaction was preferable in the presence of DHP. As the results, it is considered that ipso position cleavage reaction has an important contribution to the reaction of coal with DHP at relatively higher temperature. Since the model compounds having dimethylene bridge are considered to represent polymethylene bridge bonds, monomethylene is believed to be a significant bridge bond which governs the coal reactivity.