Solvent effect on coal liquefaction

Effectiveness of various hydrogen-donor solvents toward coal liquefaction has been investigated by carrying out hydrogenation or hydrogenolysis of coal-related model compounds such as benzophenone, trans-stilbene, anthracene, and 9-benzylphenanthrene. The hydrogen-donatability of the hydroaromatic hydrocarbon is governed by the lability of the benzylic CH bond. 9,10-Dihydroanthracene and 9,10-dihydrophenanthrene are good hydrogen-donors not only in hydrogenation of unsaturated structures but also in deoxygenation of benzophenone. Hydrogen-donatabilities of polar solvents highly depend on the structure of the hydrogen acceptor. The rates for reduction of polar compounds are considered to be governed by the relative rate of the initiation step where ionic interaction between solvent and hydrogen-acceptor is important. Superior hydrogen-donatabilities of 5,6,7,8-tetrahydro-2-naphthol and 1,2,3,4-tetrahydroquinoline are ascribed to their ambident character as hydroaromatic and phenol or secondary amine.